ceb report
TRANSCRIPT
NATIONAL DIPLOMA IN ENGINEERING SCIENCES
TRAINING REPORTGENARAL INDUSTRIAL TRAINING
AT
CEYLON ELECTRICITY BOARD
SUBMITED BY : P.A.U.A.BANDARA
ADD. NO : EP\01\4701
FIELD : ELECTRICAL ENGINEERING (POWER) DURATION : 06 / 10/ 2003 TO 31/ 08/ 2004
TECHNICIAN TRAINING INSTITUTE KATUNAYAKE.
CONTENTS
Acknowledgement Chapter 1 Introduction
1.1 Introduction1.2 Vision1.3 Mission1.4 The board’s statuary obligation1.5 Environment policy statement1.6 Power stations operated by CEB
Chapter 2 Government Installation2.1 Introduction2.2 Cinnamon Garden Depot2.3 Wiring Installation & testing2.4 Trip switch
Chapter 3 High Tension Maintenance3.1 Introduction3.2 Main element connected in Ring system3.3 Underground Cables3.4 Construction of cables3.5 Cables for three-phase service3.6 Types of cable faults3.7 Fault location3.8 Cable fault Locating Methods
Chapter 4 Sub Stations (Kolonnawa & Biyagama Grid Sub Station)4.1 Introduction4.2 Types of Sub Stations according to the service4.3 Types of Sub Stations according to the construction4.4 Switch yard Equipment4.5 Oil breakers 4.6 Circuit breaker testing4.7 Interlocking System4.8 Transformer protection4.9 Operation of transformers4.10 Transformer testing
4.11 Laying underground cablesChapter 5Generation (Victoriya power station)
5.1 Introduction5.2 Water ways5.3 Underground Power station5.4 Generators5.5 Protection of generators5.6 Excitation5.7 Control room
5.8 Switch yardChapter 6 Medium voltage maintenance
6.1 Introduction6.2 Equipment applied in overhead distribution lines6.3 Hot line Maintenance
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6.4 sub Station Maintenance6.5 Line Maintenance
Acknowledgement
It is indeed a great pleasure to present the training report in the
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completion of the second practical training 6 months of general industrial training at
Ceylon electricity board which were very satisfactory places to cover most of the
modules that gave me technical and management knowledge.
It is pleasure to thank the chairmen and all the managers and engineers
at C.E.B for contributing the optimum support and guidance to receive a standard
training in electrical field. Further I’m very much thankful to other engineers,
electrical superintendents, foremen, supervisors in various technical work shops &
fields in addition I received the fullest cooperation from all segments of general
workforce.
I would also like to thank the TTI management Including all the IT & Academic staff
for providing necessary instructions, guidance, and giving me the fullest cooperation.
Finally I thank all my colleagues for been with me exchanging views, sharing
experiences, etc during this period.
Thank You,
P. A.U.A.Bandara
EP / 01/4701
TRAINING SCHEDULE OF CEB
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Period Work site
From To
Government installation (Cineman garden)High Tension Maintenance (Maligawatta)Grid substation (Biyagama)Grid substation (Kolonnawa)
Mahaweli complex (Victoriya power station)Medium Voltage Maintenance (Piliyandala)
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1.1 INTRODUCTION
CEB is a leading government institute. It has the responsibility of handling almost all the
control of electricity sector in Sri Lanka.
Namely,
Generation
Transmission
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Distribution (major part)
Ceylon Electricity Board has the monopoly of electrical power sector in Sri
Lanka. C.E.B. constituted under the Ceylon Electricity Board Act No 17 of 1969, which
had been subsequently amended by Act No 31 of 1969 and Act No 29 of 1979. Now
CEB is under ministry of energy and power and the ministry of energy and power is Mr.
Susil Premjayantha
1.2 Vision
Be an internationally recognized efficient utility providing high quality service to
all its stakeholders.
1.3 Mission
To provide reliable quality electricity to the entire nation at internationally competitive
prices effectively and efficiently through a meaningful partnership with skilled and
motivated employees using appropriate state-of-the-art technology for the socio economic
development of the country in an economically sustainable manner while meeting
acceptable environment standards.
1.4 The board’s statutory obligation
“The Board is under a statutory duty to develop and maintain an efficient,
coordinated and economical system of Electricity Supply. It is also the duty of the Board
to generate or acquire supplies of electricity; to construct, maintain and operate the
necessary works for the generation of electricity by all means, to construct, maintain and
operate the necessary works for the inter-connection of Generating Stations and Sub-
stations and for the transmission of electricity in bulk from
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Chairman, Vice ChairmanAnd
Board of Directors
General Manager
A.G.M.Transmission
A.G.M. Distribution Operation
A.G.M.Commercial
Manager Investigation
D.G.M.Engineering Audit
FinanceManager
A.G.M.Human Resources
A.G.M. DistributionDevelopment and Services
A.G.M.Generation
Chief Internal Auditor
Secretary To The Board
Pension and Provident Fund
Generating Stations and Sub-stations to such places as may be necessary from time to
time; to distribute and sell electricity in bulk or otherwise”.
“It is the duty of the Board to exercise its powers and perform its functions so as
to secure that the revenue of the Board are sufficient to meet its total outgoing properly
Chargeable to revenue account including depreciation and interest on capital, and to meet
a reasonable proportion of the cost of the development of the services of Board”.
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1.5 Environment policy statement
Ceylon Electricity Board will manage all its business activities in a manner,
which cares for the natural and manmade environment and contribute to sustainable
development. By means of openness in dealing with environmental issues, CEB intends
to create confidence in their activities on the part of the public, customers, authorities,
employees, and owners. CEB will actively pursue a policy of incorporating and
integrating environmental considerations into CEB activities.
CEB policy is elaborated below in more concrete terms
a. CEB will lead the development of environmentally compatible and efficient
energy solutions.
b. CEB will, by means of quantifiable environmental targets, endeavor to cause
minimum impact on the environment.
c. CEB will, in all our operations, economize on natural resources and energy.
d. CEB will attach key importance to human health and safety.
e. CEB will analyze in advance the environmental impact of all new activities.
f. CEB will improve the environmental awareness of their staff by training and
motivating them to take responsibility for the environmental consequences of
their activities.
g. CEB will place the same high environmental demands on our suppliers,
contractors and business partners as CEB place on their own operations.
h. CEB will be able to discuss environmental issues with their customers from an
overall perspective and promote electricity's environmental benefits.
i. CEB will openly report on our environmental work and their impact on the
environment, and conduct a close dialogue with various interested parties on
environmental issues important to our activities.
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1.6 Power station operated by CEB
The details of power stations operated by CEB are given in Table.1.1and Table. 1.2
PlantInstalled Capacity
MWGeneration (million
units/yr)Commissioning
Laxapana Complex
Canyon 2 * 30 60 137.3Unit 1 March 1983Unit 2 1988
Wimalasurendra 2 * 25 50 122.1 Jan 1965
Old Laxapana3 * 8.33 502 *12.5
260.8Dec 1950Dec 1958
New Laxapana 2*50 100 465.8Unit 1 Feb 1974Unit 2 Mar 1974
Polpitiya 2*37.5 75 396.8 April 1969
Laxapana Total 335 1382.8
Mahawelli Complex
Victoria 3* 70 210 663.7 Unit 1 Jan 1985Unit 2 Oct 1985Unit 3 Feb 1986
Kotmale 3*67 201 445.13 Unit 1 April 1985Unit 2 Feb 1988Unit 3 Feb 1988
Randenigala 2*61 122 326.4 July 1986
Ukuwela 2*19 38 164.4 Unit 1 July 1976Unit 2 Aug 1976
Bowatenna 1*40 40 48.8 Jan 1981
Rantambe 2*24.5 49 189.1 Jan 1990
Mahawelli total 660 1837.53
Samanalawewa 2*60 120277.3 Oct 1992
Small hydro Plants
Inginiyagala2*2.475 112*3.15
26.8June 1963
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Uda walawe 3*2 6 7.6 April 1969
Nilambe 2*1.6 3 11.6 July 1988
Small hydro Total 20
Under construction
Kukule 2*35 70 306 Jan 2002
Total hydro 1205 3803.63Table1.1Hydro Power plants of Sri Lanka
Thermal Plant Installed Capacity (MW)
Commissioning
Kelanitissa Gas Turbines
6 * 20 1201* 115 115
Nov 1980-Mar 1982August 1997
Kelanitissa Steam 2*22 44
June 1962 & Sep 1963
Sapugaskanda Diesel 4*18 72
May 1984- Oct 1984
Sapugaskanda Diesel Extension (ADB)
4*10 40
Sep 1997
Lakdanawi Diesel (BOO)
22.5
Late 1997
Asia power diesel (BOO)
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Mid 1998
Under construction
Kelanitissa combined Cycle
1*150 150
Late 1999 - 2000
Sapugaskanda Diesel Extension
4*10 40
Early 1999
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2.1 INTRODUCTION
The government installation branch of CEB has established to under take the
installation and maintenance of electricity supply in government organizations. All the
materials used by government installation branch are satisfied with British Standard and
all the wiring is carried out according to the IEE regulations. After the installation they
check whole wiring to make sure that all the wirings have done properly.
They check – Earthling are proper
- Correct wires have used for correct place
2.2 Cinnamon Gardens depot
At Cinnamon Gardens depot we studied the following things,
Brief idea about the motor windings of fans
Direct online starter
Operation of MCB and trip switches
Domestic consumer box
Electric wiring planning of a house
2.3 WIRING INSTALLATIONS AND TESTING
Main elements of a wiring installation are
- Main switch
- Distribution Board
- RCD (Trip switch)
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- MCB’s
- Electrical equipments
- Earthings
Testing
Check live, neutral and earth are properly connected
Check earthings are properly connected
Live and neutral and live and earth are properly insulated
L N
Coil
Test Live
Button Neutral
E Second Main earth wire Earth
Earth wire
Fig 2.1
Voltage Control Trip Switch
N L
Test
Resister
L
Test button N
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E
Fig 2.2
Current Control Trip Switch
INSULATION TESTInsulation test for wiring is usually carried out with a 500v megger and tests
should be made.
Insulation Test Between Live and Neutral ConductorsBefore carryout this test, Circuit breakers must be closed, Switches must be on
and lamps out. Then megger is connected between live and neutral. The reading should
not be less than 1Ω.
INSULATION TESTS BETWEEN LIVE AND EARTH
Live and neutral must be connected together. Circuit breakers must be closed. All
switches must be on and lamps must be in. The megger is connected between conductor
and earth. The reading should not be less than 1 Ω.
Trip switch
There are mainly two types of trip switches and they are
Voltage control trip switch
Current control trip switch (Rcd)
The function of operation of Voltage control trip switch is based on the leakage current in
the earth wire. Hence these types of trip switches prevent the electric hazards, which
could arise from any electric appliances and protect the human body.
Current control trip switch operation is based on current different between live and
neutral conductor. Hence prevents having electric shocks from live conductor.
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2.4 OPERATION OF MCB
Miniature circuit breaker (MCB) is a device which act as switch and it can be
operated either manually or automatically.
The tripping action may be either magnetic or thermal. Both these actions have applied in
the MCBs, which is observed in the G.I. branch. Protection against current slightly higher
than the rated current is given by the bending of a bimetal strip, while high-speed
protection against a short circuit is given by magnetic operation.
3.1 INTRODUCTION
High-tension maintenance can be divided into 6 parts.
Routine maintenance
Seasonal maintenance
Breakdowns
Shifting
Augmentation
Civil and other minor works
Routine maintenance is done without interrupting the supply .eg: cleaning, visual
inspection. Seasonal maintenance are done without supply.(Oil circuit breakers –
3yrs,Vacuum circuit breakers/ Air circuit breakers-1yr.,Ring main unit-3yrs.)
Breakdowns are done as they incur.
Other three are very rare situations.
Colombo City
Colombo city electricity distribution is carried out order of area office namely
South, East, West and North. An Area Engineer leads each area.
Area staff does commercial functions, LT breakdown and LT maintenance work.
A control center is opened over 24 hrs a day at Maligawatta to accommodate
consumer complaints, coordinating breakdown staff, HT operation and maintenance.
HT operation, HT maintenance, primary substations maintenance and fault
location staff and rehabilitation staff are located at Maligawatta.
Colombo city demand is supplied by approximately 1020 substations (11kV/HT)
as shown in figure 7.1, which are having ring connections to enable alternative
feeding.
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There are 8 primary substations (33kV/11kV)namely A, B, C, D, E, F, G and H
Substations are connected to primary substation in ring, radial and satellite
Primary substations A, B, C, D, E, F, G and H are fed from Kolonnawa receiving
station, Kelanitissa power station, etc. (at 33kV or 132kV levels)
11kV/LT substations: There are few types,
Ring substation
Radial substation
Satellite substation
Test terminal Test terminal
To Ring To Ring
Fuse
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Power taking off
To the sub T/F
Fig 6.3Internal wiring of ring main unit
3.2 MAIN ELEMENT CONNECTED IN RING SYSTEM
Ring main unit
This is very important device is connected to ring in 11KV underground
system 11KV supply will be feed through the RMU for each transformers. To protect
transformers against over current RMU contains three 50A fuses are available in each
phase. In the RMU fuses will immerse in oil because to get a high insulation between
each phase reduces heat build up in each phase.
Transformers
In underground system used step down transformers (132KV/33KV),
(132KV/11KV ), (33KV/11KV), (11KV/415V). Mostly used 11KV/415V transformers
because out put is directly connected to the consumers. Where transformers KVA rating
is depend on the consumers requirement. Generally following ratings are commonly used
800 KVA, 500 KVA and 1000 KVA.
Bus-bar panel
This is a metal box, which is consisting of Cu bars that are isolated from fiber
plates. The current rating of the bus bar depending upon the consumer capacity and the
requirement. In general 1600A, 800A, 400A rating bus bars panels are placed in Colombo
city.
Feeder piller panels
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This is a low voltage panel same as bus bar panels. But this panel has neutral
bus bar, which is connected to transformer neutral point. To protect the human life to the
electric shock metal panel casing should be grounded properly.
Circuit brakers
Circuit breakers are placed low voltage side for purpose of protect the
transformer where overload the consumer side.
3.3 UNDERGROUND CABLES
Electric power can be transmitted or distributed either by overhead system or
by underground cables. I n modern cities and towns, the distribution of power by bare
over head conductors is avoided for reasons of safety and cables laid in air are not
pleasing to the eye. Therefore we use underground cable system. An under ground cable
essentially consists of one or more conductor covered with suitable insulation and
surrounded by a protecting cover.
ADVANTAGES OF UNDERGROUND SYSTEM
In the under ground system, the cable is not effected by weather condition, such
as rain, storm, snow, etc. On the other hand, overhead lines are exposed to
weather conditions with consequent chances of interruption of power.
Under ground cables do not suffer from such fault as birdcage, breaking of
conductors owing to falling objects, flash over fault because of lightening.
In densely populated areas, overhead line is unsafe and can lead to accidents.
Since the chances of faults on underground cable are low, the maintenance cost of
the under ground system is low.
The underground system does not disturb the environmental because of its
location. Therefore, it is increasingly preferred in modern town and cities.
Because of the metallic sheath covering g on the underground cables, the system
concerned does not interfere with telecommunication cables.
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The inductive reactance of cables is less compared to that case of overhead
conductors. This is because the spacing between the cables is less. Therefore the
voltage drop on the under ground system is less compared to the overhead system.
DISADVANTAGES OF UNDERGROUND SYSTEM
The capital cost of laying under ground cable is high
The incidence of fault in under ground system rare. However, once a fault occurs
it is difficult to locate and repair it.
The current carrying capacity of the cable is reduced due to the close grouping of
cables and unfavorable conditions for distribution of heat.
3.4 CONSTRUCTION OF CABLE
Core or conductor
A cable may have one or more than one core (conductor) depending upon the type
of service for which if is intended. For instance, the three-conductor cable as shown
above used for phase service. The conductors are made of tinned copper or aluminum and
are usually stranded in order to provide flexibility to the cable.
Insulation
Each core or conductor is provided with a suitable thickness of layer depending
upon the voltage to be with stood by the cable. The commonly used material for
insulation ate impregnated paper, varnished cambric or rubber mineral compound.
Metallic sheath
In order to protect the cable from moisture, gases or other damaging liquids (acids
or alkalies ) in the soil and atmosphere, a metallic sheath of lead or aluminium is
provided over the insulation as shown in figure.
Bedding
Over the metallic sheath is applied a layer of bedding, which consists of a fibrous
material. The purpose of bedding is to protect the metallic sheath against corrosion and
from mechanical injury due to armoring.
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Armouring
Over the bedding armoring is provided which consists of one or two layers of
galvanized steel wire or steel tape. Its purpose protects the cable from mechanical injury
while laying and during the course of handling. Armoring may not be done the case of
some cables.
Serving
In order to protect armoring from atmospheric condition, a layer of fibrous
material (like jute) similar to deeding is providing over the armoring. This is known as
serving.
3.5 CABLES FOR THREE PHASE SERVICE
Belted cables
These cables are used for voltages up to 11kv but in extraordinary cases, their use
may be extend up to 22kv. The cores are insulated from each other by layers of
impregnated paper. Another layer of impregnated paper tape, called paper belt is wound
round the grouped insulated cores. The gap between the insulated cores is filled with
fibrous insulating material to give circular cross section to the cable. The belt is covered
with lead sheath to protect the cable against moisture and mechanical injury. The lead
sheath is covered with one or more layers of armouring with an outer serving.
Screened cables
These cable are used for voltage up to 33KV but in particular cases their use may
be extended to operating voltage up to 66KV.There are two types of screened cable.
H type cable
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In this layer of impregnated paper insulates each core. The insulation in each core
is covered with a metallic screen, which usually consist of perforated aluminum and oil.
The cores are laid in such a way that metallic screens make contact with one another.
An additional conducting belt (copper woven fable tape) is wrapped round the
three cores. The cable has no insulating belt but lead sheath, bedding, armoring and
serving as usual.
SL type cable
It is basically H type cable but the screen around each insulation is covered by its
own lead sheath. There is no overall lead sheath but only armoring and serving is
provided.
There are two main advantages than H type. Frost the separate sheaths minimizes
the possibility of core-to-core breakdown. Secondary, bending of cables because easy due
to the elimination to overall lead sheath.
Pressure cable
For voltage beyond 66KV,solid cable is unreliable because there is a danger
of breakdown of insulation due to the presence of voids. When
the operation voltages are greater of than 66KV, pressure cables are used. There are two
types of pressure cable.
Oil filled cable
Gas pressure cable
Oil filled cable
In such type of cables, channels of duets in the cable for oil circulation. The
oil under pressure is kept constantly supplied to the channel by means of external
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reservoirs placed at suitable distance along the tout of the cable oil filled cables are of
three types, viz. single core conductor channel, single core sheath channel and there core
filler space channel.
Gas pressure cable
The voltage required setting up ionization inside void increases as the
pressure is increased. Therefore, if ordinary cable is subjected to another eliminated
3.6 TYPES OF CABLE FAULTS
Cables are generally laid directly in the underground distribution system. For this reason,
there are little chances of faults in under ground cables. However, if a fault does occur, it
is difficult to locate and repair the fault because conductor is not visible. Nevertheless,
the following are the faults most likely to occur in underground cables.
Open circuit fault
When there is a break in the conductor of a cable, it is called open circuit fault.
The open circuit fault can be checked by a megger. For this purpose, the three conductors
of the 3-corecable at the far end are shorted and earthed. Then resistance between each
conductor and earth is measured by a megger. The megger will indicate zero resistance in
the circuit of the conductor that is not broken. How ever if the conductor is broken, the
megger will indicate infinite resistance in its circuit.
Short circuit fault
When two conductors of a multi-core cable come in electrical contact with each
other due to insulation failure, it is called a short circuit fault. We can seek the help of
megger to check this fault. For this purpose, the two terminals of the megger are
connected two any two conductors. If the megger gives zero reading, it indicates short
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circuit fault between these two conductors. The same step is repeated for other conductors
taking two at a time.
Earth fault
When the conductor of a cable comes in contact with earth, it is called earth fault
or ground fault. To identify this fault, one terminal of the megger is connected to the
conductor and the other terminal connected to earth. If the megger indicates zero reading,
it means the conductor is earthed. The same procedure is repeated for other conductors of
the cable.
3.7 Fault Location In a good power system stability and continuity are very important.. When a fault
occurs on the network and power is lost, the company’s priority is to reconnect as many
customers as quickly as possible. ‘Switching’ customers to alternative supplies wherever
possible does this. The fault location and maintenance is done by operation control center
and HTM complex to Maligawatta. The maintenance and repairing of high-tension line of
11KV and 33KV and low tension of Colombo city is done by above branch. All of the
high-tension lines are installed in an underground ring system. Therefore special kinds of
underground cables, special type of joints and special kind of insulation are used to
maintain that system.
Test-Vans
The branch has three state-of-the-art test vans equipped with the latest fault finding
technology. This equipment on board enables faults to be detected by sending a signal
down the cable to highlight any inaccuracies, which are shown on a computer screen. A
trace is put on the signal to pick up any mismatch to determine how far down the cable
the problem is. The exact fault is found by using a surge generator to pinpoint the area of
irregularity. The equipment is used mainly on the 11,000-volt and 33,000 volt
underground cable network
Rezaps
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Low voltage cables are designed to be very resilient and when a fault does occur, they
have a tendency to rectify them, which can make fault location and repair extremely
difficult. This ability to self-repair means that low voltage faults can often be intermittent.
To help engineers locate them, the branch uses devices called ‘Rezaps’. Connected at a
local substation, this device automatically switches the power back on after a fuse has
blown, restoring customer supplies in seconds if the fault has cleared. Once the fault
develops permanently, engineers are dispatched to locate and repair it. Although
customers will experience short interruptions to their supply during this period, it does
reduce the time off supply from several hours to a minute or so.
Transient interruptions
Brief supply interruptions with duration of less than one minute are called transient
interruptions. There are many causes, such as lightning strikes, contact by animals and
birds, and high winds blowing tree branches onto overhead lines. By using sensitive
electrical equipment to disconnect the supply for a few seconds and then restoring it, the
cause of the fault is given the chance to clear.
This ensures customers’ supplies are restored quickly and prolonged interruptions are
often avoided. The HTM knows that transient interruptions are inconvenient to customers
and continues to work towards reducing the causes. This work involves extensive tree
cutting near overhead lines and installing modern, automatic switches, which can be set to
operate more sensitively without causing transient interruptions. These measures will
reduce the number of transients.
3.8 CABLE FAULT LOCATING METHODS
Echo Meter (Tele Fault)
Battery operated and portable, the instrument is microprocessor based and
utilizes the well-established pulse echo technique of fault location but with an entirely
new level of simplicity of operation and accuracy. The unique combination of hardware
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and software filtering in the echo meter allows it to continue operating normally, without
distortion or instability of the displayed fraces, even when connected to energize low
voltage power cables. Echo meter can therefore be used locate many types of faults on
low voltage on low voltage power cables, e.g. open circuit s, phase to phase etc. Without
the need to disconnect supplies to consumers. In addition if echo meter is triggered from
an external fault-detecting device such as a ct or voltage dip detector transitory faults may
also be located.
The LCD graphics panel displays the reflected pulse signals and calibrated
cursors are used to measure the distance to the fault. In addition the LCD panel displays
alphanumeric message giving the instrument status and measured fault distance. We can
be measured approximately 3.2 km distance. According to the waveform we can identify
the types of the fault.
Cable Finder (CAT)
Complicated cities electrical network go through as underground network.
The under ground cables lay different different directions in consumers requested. After
few years any one don’t know underground cable layouts and the further extension are
also carried out. At this times electrical company face to more problems find out the
cables for maintenance work. In this time electrical company is used handiness,
ruggedness and reliability in and interesting design equipment as called cable finder
(CAT), the cable finder consists of two parts. Those are one hand locater and signal
transmitter.
First we select cable end and the signal transmitter is connected the cable end. The signal
transmitter consist two terminals. One terminal is connected to the “good” earth and there
other terminal is connected to the one of conductor of the cable.
We can find the cable layout by using one hand locator. The track of the
line is determined by swiveling the CAT from one side of the line to the other, where by
the instrument is carried crosswise to the track of the line. Both visual and acoustic
indications reach a maximum directly over the line. In this way the track can be selected
continuously.
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Surge (Thumber) Method
This method consists if using a charge capacitor to transmit high-energy pulse
between the conductor and ground. The pulses creates an arc at the fault, which in turn
heats the surrounding air, and the energy is released as an audible thump. The fault
location can be found by listening to the acoustical thump or by tracing the magnetic field
generated by the air. The surge source is a capacitate discharge circuit consisting of
power supply, capacitor bank and high voltage switch. The surge signal can be detected
by means of a magnetic loop antenna, a microphone, an earth gradient detector, or a
seismic transducer.
3.9 LAYING OF UNDERGROUD CABLES
The reliability of underground cable network depends to a considerable extent
upon the proper laying and attachment of fittings. There are three main methods of laying
underground cables.
Direct laying
Draw in system
Solid system
Direct laying
This method of laying underground cables is simple and cheap and is much
favored in modern practice. In this method, a trench of about 1.5 m deep and 45 cm wide
is dug. The trench is covered with a layer of fine sand bed. The sand prevents the enter of
moisture from the ground and thus protects the cable from decay. After the cable has been
laid in the trench, it is covered with another layer of sand of about 10 cm thickness. The
trench is then covered with bricks and other materials in order to protect the cable from
mechanical injury. When more than one cable is to be laid in the same trench, A
horizontal or vertical inter axis spacing of at least 30 cm is provided in order to reduce the
effect of mutual heating and also to ensure that a fault occurring on one cable does not
damage the adjacent cable.
This method of laying cables is used in open areas where excavation can be done
conveniently and at low cost.
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Draw-in system
In this method, conduit or duct of glazed stone or cast iron or concrete are laid in
the ground with manholes at suitable positions along the cable route. The cables are then
pulled into position from manholes. Figure shows section through four way underground
duct line. Three of the ducts carry transmission cables and the fourth duct carries relay
protection connection, pilot wires. The distance between the manholes should not be too
long so as to simplify the pulling in of the cables.
This method of cable laying is suitable for congested areas where excavation is
expensive and inconvenient, for once the conduits have been laid, repairs or alterations
can be made without opening the ground. This method is generally used for short length
cable routes such as in workshops, road crossing where frequent digging is costlier or
impossible.
Solid system
In this method of laying, the cable is laid in open pipes or through dug out in earth
along the cable route. The troughing is of cast iron, stoneware, asphaltic compound and
covered over. Cables laid in this method are usually plain lead covered because troughing
affords good mechanical protection.
This method of laying underground cables is rarely used now a days. Because it is
more expensive than direct laying system & due to poor heat dissipation facilities, the
current carrying capacity of the cable is reduced.
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4.1 INTRODUCTION
The Present day Electrical power system is Generated, transmitted and
distributed in the form of alternating current. The electric power is produced at the power
stations which are located quite away from the consumers. It is delivered to the
consumers through a large network of transmission and distribution. Substation is the
assembly of apparatus with use to transform the electrical characteristic from one form to
another. Near the consumer localities, the voltage may have to be stepped down to
utilization level. This job is done by sub stations.
Kolonnawa Stanley substation had four switchyards. There are 33kv, 66kv, 132kv
and 11kv. 11kvswitchyard is indoor switchyard and other three are out door switchyards.
But these outdoor switchyards converted to the indoor substation and gas insulation
substation (GIS). It has two switchyards. Those are 33kv and 132kv.
4.2 TYPES OF SUBSTATIONS ACCORDING TO SERVICE
REQUIREMENT.
Transformer sub-stations
Switching sub-stations
Power factor correction sub-stations
Frequency changer sub-stations
Converting sub stations
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Industrial sub-stations
Transformer substations
Those sub stations which change the voltage level of electric supply are called as
transformer substations. These substations receive power at some voltage and deliver it at
some other voltage. Transformer is the main component in such substations.
Switching substations
These substations do not change the voltage level. There for incoming and
outgoing lines have the same voltage. They simply perform the switching operations of
power lines.
Power factor correction substations
Those sub stations which improve the power factor of the system are called power
factor correction substations. Such substations are generally located at the receiving end
of transmission lines.
Frequency changer substations
Those substations which change the supply frequency are known as frequency
changer substation. Such a frequency change may be required for industrial utilization.
Converting substations
These substations which change a.c power into d.c power are called converting
sub stations. These substations recive a.c power and convert it into d.c power with
suitable apparatus to supply for such purpose as electroplating, electric welding etc.
Industrial sub stations.
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Those substations which supply power to individual industrial concern are known
as industrial sub stations.
4.3 TYPES OF SUBSTATIONS ACCORDING TO
CONSTRUCTIONAL FEATURES.
Pole mounted substation
Out door substation
Indoor substation
Underground substation
4.4 SWITCHYARD EQUIPMENT
Isolators
Isolators are the disconnectors. There are two types according to operating
mechanism.
Manual (spring loaded)
Motor controlled
After closing the isolator physically checking is required. (If possible). Also
isolators can categorized in two parts there are single operated and ganged operated (3
phase together)
Circuit breakers
Mainly circuit breakers are used for protection of equipment in a grid substation.
Also it is avoided over current faults and earth faults. Circuit breaker should be defiantly
placed in between two isolators. When close the circuit breaker first the isolators must be
disconnected.
Operating principle
A circuit breaker essentially consists of fixed and moving contacts, called
electrodes. Under normal operating conditions, these contacts remain closed and will not
open automatically until and unless the system becomes faulty. The contacts can be
opened manually or by remote control whenever desired, When a fault occurs on any part
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of the system, the trip coils of the circuit breaker get energized and the moving contacts
are pulled apart by some mechanism, thus opening the circuit.
When the contacts of a circuit breaker are separated under fault conditions, an arc
is struck between them. Therefore, the main problem in a circuit breaker is to extinguish
the arc within the shortest possible time so that heat generated by it may not reach a
dangerous value.
Methods of arc extinction
There are two methods of extinguishing the arc in circuit breakers.
High resistance method
Low resistance or current zero method
High resistance method
The resistance of the arc may be increased by,
(i) Lengthening the arc
The resistance of the arc is directly proportional to its length. The length of the
arc can be increased by increasing the gap between contacts.
(ii) Cooling the arc
Cooling helps in the deionisation of the medium between contacts. This increase
the arc resistance. Efficient cooling may be obtained by a gas blasted direct along the arc.
(iv)Splitting the arc
The resistance of the arc can be increased by splitting the arc into a number of
smaller arcs in series. Each one of these arc experiences the effect of lengthen and
cooling. The arc may be split by introducing some conducting plates between
the contacts.
Low resistance method
This method is employed for arc extinction in a.c circuits only. In this method, arc
resistance is kept low until current is zero where the arc extinguishes naturally and is
prevented from restriking in spite of the rising voltage across the contacts. There are
several ways of classifying the circuit breakers.
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Circuit breakers are divided in to three types according to operating mechanism.
There are;
Mechanical (spring chargeable)
This is two types. Spring is charge manually and spring is charge by using motor.
Pneumatic
Hydraulic
Also circuit breakers are classified in to parts according to arc extinguishing
medium. There are; oil circuit breakers, SF6 gas breakers, air breakers.
4.5 OIL CIRCUIT BREAKERS
In such circuit breakers, some insulating oil is used as an arc quenching medium.
The contacts are opened under oil and an arc is struck between them. The heat of the
evaporates the surrounding oil and dissociates it in to a substantial volume of gaseous
hydrogen at high pressure. The hydrogen gas occupies a volume about one thousand
times that of the oil decomposed. The oil is there for pushed away from the arc and an
expanding hydrogen gas bubble surrounding the arc region and adjacent portions of the
contacts as shown in the figure.
The advantages of oil as an arc quenching medium are;
It absorbs the arc energy to decompose the oil into gases which have excellent
cooling properties.
It acts as an insulator and permits smaller clearance between live conductors and
earthed components.
The surrounding oil presents cooling surface in close proximity to the arc.
The disadvantages of oil as an arc quenching medium are;
It is inflammable and there is a risk of a fire
It may form an explosive mixture with air
The arcing products remain in the oil and its quality deteriorates with successive
operations. This necessitates periodic checking and replacement of oil.
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The breaking unit consists of braking chamber, top cap and mechanism housing. The
unit is hermetically sealed, filled with oil and nitrogen. The breaker chamber contains an
inner support cylinder, manufactured of glass fiber reinforced epoxy resin and
constituting a consolidating and pressure absorbing element. The cylinder is housed in an
outer porcelain insulator. The active elements are the upper terminal, the fixed contact,
the extinguishing chamber, the moving contact, the rolling contacts and lower terminal.
The contact unit consists of the fixed sleeve contact and the moving plug
contact/The contact material is silver plated copper. Those parts of the contacts, which are
exposed to arcs during the breaking, which reduces, contact bum to a minimum.
The top cap is made of welded steel and constitution the expansion chamber
for the gases, which develop when high current are interrupted. It also houses the gas
cushion providing the permanent overpressure, which ensures restrike free interruption of
capacitive current. A magnetic oil level indicator and a pressure gauge shown oil level
and internal readings are clearly visible from ground level. A control valve maintains the
overpressure within the permissible limits.
The mechanism housing is a light alloy casting and contains the actuating
mechanism for the moving contact. It is furnished with an oil drain cock. The operating
force is transmitted via the link gear and operating insulator to the rectilinear motion
mechanism and further to the contact unit.
SF6 CIRCUIT BREAKERS
The most used gas circuit breakers are SF 6 gas circuit breaker. In such
breakers, sulphur hexafluoride (SF6) gas is used as the arc-quenching medium. The SF6 is
an electro negative gas and has a strong tendency to absorb free electron. The contacts of
the breaker are opened in a high-pressure flow of sf6 gas and an arc is stuck between
them. The sf6 circuit breakers have been found to be very effective for high power and
high voltage service.
4.6 CIRCUIT BREAKER TESTING
Gas leakage test
This instrument is used for find gas leakages but this instrument is sensed
only SF6gas .If gas leakage is in any where of pole, instrument detect it and came sound.
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Dew point test
Temperature of SF6 vapor is measured by dew point instrument. According
to this temperature, moisture amount of SF6 vapor is conformed by a chart. Moisture
particles per mass should be less than 150.
Resistance test
Micrometers are used to measure contact resistance in high voltage breakers,
disconnecting switches (isolators), bus joints, line joints etc. Resistance should be less
than 50 micro ohms.
4.7 INTERLOCKING SYSTEM
First off the isolators between circuit breakers and then can off circuit breaker.
First off the line isolator then can on earth isolator.
This is used castle key system.
Busbar
Bus bars are the hollow circular Cu bars. Basically this bus bar arrangement
is classified in to five parts. There are;
Single
Double
One and half
Ring
Mesh (complicated ring system)
Bus section
Bus section is a breaker which it can connect and disconnect both side of bus bar.
Bus coupler
Bus coupler is the circuit breaker which it can connect and disconnect two bus
bars.
Current transformer
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An instrument current transformer also called a CT is used to step down a
relatively high current to some lower value for the operation of instruments and isolate
current measuring instruments and relay s from the high voltage line. The primary of the
CT is connected in series with the load circuit and the secondary is connected to the
instruments or relays.
The CT is filled with oil and fine grain quartz sand for mechanical stabilization
and reduction of the oil quantity .The CT is completely sealed and expansion space is
filled with dry nitrogen gas.
Voltage transformer
It is essentially a step down transformer and step down the voltage to a
known ratio. The primary of this transformer consists of a large number of turns of fine
wire connected across the line. The secondary winding consists of a few turns and
provides for measuring instruments and relays a voltage which is known fraction of the
line voltage.
PARTS OF A TRANSFORMER
Conservator
Conservator is a sort of drum, mounted on the top of the transformer. A
level indicator is fixed to it. Conservator is connected through a pipe to the transformer
tank containing oil. This oil expands and contracts’ depending upon the heat produced
and sob the oil level in the conservator rises and falls. Pipes connected to the conservator
is left open to the atmosphere through a breather so that the extra air may go out or come
in.
Breather
Breather is mounted on the top of the conservator tank & it is a small cylindrical
unit containing silica gel to absorb moisture of air entering the conservator tank.
Radiator
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These are fitted for cooling the transformer oil. The hot oil circulate through these
unit where it becomes cool due to the air touching.
windings
Transformer windings are wound with rectangular, cable paper insulated copper
wires. There are two windings HV side and LV side.
Tap changer
Tap changer is used for on load changing of the voltage ratio. It is a three-
phase unit located in one container, which is placed in the transformer tank.
Each phase regulating winding is located at the star point of HV side of transformer. Tap
changer is controlled from a motor drive unit, fixed to the transformer tank.
Transformer voltage may have to be constantly regulated and it is often very
inconvenient to cut off the power supply each time. On load tap changer solve
such problems, and are being used increasingly as a means of offering better power
supply service as well as for general power receiving purposes.
Tap changer may be classified in to three groups; there are D type, V type
and MS type.
4.8 TRANSFORMER PROTECTION
Buchholz relay
This relay is situated in the pipe connected between the transformer and the
conservator. Relay is a gas actuated relay which is meant for the protection of oil
immersed transformer from insulation failure, core heating or any type of internal fault
which may cause the heating of coil beyond the specified temperature due to this faults
either alarm circuit or the trip circuit operate.
Pressure & relief valve
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If is the fault condition in transformer a signal is came to relief valve and it
is operated. There fore circuit breaker is tripped.
Temperature meters
Those meters measure oil temperature and winding temperature and meters
are set to fixed temperature when temperature is rise over that settings circuit breakers
tripped.
Arching horns
Arching horns are situated top of the transformer it is protected transformer by
lightings.
Differential
When two or three transformers are parallel, if the tap or impedance differs
from each other, this tripped without alarm.
4.9 OPERATIONS OF TRANSFORMERS
Master follower method
This method is used in substations. One transformer act as a master and
other transformers are followed it. In this case master transformer keep to operate
manually and other one or two transformers act auto mode. If master transformer had a
fault another transformer will be master or transformers will be run individual.
4.10 TRANSFORMER TESTING
Transformer oil testing
The oil is to be tested is poured in to the glass container supply with the
tester. This should be done in a dry day. Because humidity can change the actual reading
that the oil test shows. Oil samples should be taken carefully without opening to the
atmosphere. Applying a voltage across terminals is increased slowly until the sparking
occurred. Now the reading of the indicator is the break down voltage of the insulating oil.
This is done several times to obtain average breaking voltage of oil.
We have use two different kinds of oil testers. In one tester we have to
manually increase the voltage apply to it and the final value that the dial shows is the test
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reading. And the other tester voltage is automatically increased by it self and it shows the
voltage that the sparking occurs.
Meter reading > 30Kv -it is good for breakers
Meter reading > 45Kv -it is good for transformers
After this test, if transformer oil is bad oil refilling or oil filtering.
Vector group test
Normally transformer vector group is represented by this format; DY1 or
DY11. It means;
DY1
delta star angle between primary and secondary=300
Always vector group is in transformer nameplate. Sometimes if vector group is
not showing clearly or nameplate missing we can use this method to check vector group.
Firstly R and r terminals are shorted. Then these voltages are taken.
Rr-0V Yr-409V Br-410V RY-409V
Ry-138V Yy-298V By-298V YB-409V
Rb-138V Yb-430V Bb-299V RB-409V
RN-80V YN-375V BN-315V
Diagram (vector group) was plotted by using those readings.
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6.1 INTRODUCTION
Medium Voltage maintenance (MVM) branch is responsible for maintaining
33KV distribution system of entire Island. [i.e. both routine maintenance and restoration
of supply after major break down in 33KV lines or primary substations] There are four
sections.
Substation maintenance
Distribution line maintenance
Hot line maintenance
Service primary substations
6.2 EQUIPMENT APPLIED IN OVER HEAD DISTRIBUTION LINE
Overhead distribution lines are generally to faults due to high winds,
lighting, falling tree, bird’s etc. Most faults are transient in nature and the system would
be ready for operation again as soon as the fault has been interrupted by the system
protection. The fault current might have been caused by a falling tree, which falls across
the high voltage line .In many tree will fall off the line again after a circuit breaker has
de-energized line. Alighting stroke will cause the same transient fault; a flash over will
cause a short circuit current to flow, but as soon as this current is interrupted, the system
is back to normal again.
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Usually majority of the faults recoded in an overhead line system is of a
transient in nature. This is in contrast to a cable network distribution system where most
faults are of a permanent nature.
Expulsion Fuse
A non-current-limiting device interruption the current by the melting of a
fuse element and an arc is drawn inside a gas evolving type. These may be recharged with
limited cost. Interruption principal similar to load –break switch.
Drop Down Lift Over (DDLO)
An expulsion fuses in a holder, arranged in such a way that the expulsion
fuse tube drops out of the electrical circuit when the fuse has operated. These are
commonly used in the CEB distribution network mainly for the protection of distribution
transformers and some cases for sectionalizing spur MV lines.
Air break Switch
A switch device, which is normally, only used as a disconnection, i.e. only
operated in a de energized system. However a very limiting making and breaking and
breaking performance. Contact velocity at making is operator dependent; an arcing horn
may give a high arcing contact velocities at oppugn sufficient for the interruption of load
transformers.
The switch can in most cases be equipped with a load current interrupting
device. Still, the switch has only very limited making performance .In the CEB, the ABS
were installed in area boundaries, interconnection points and on long spur line etc. to
facilitate isolation of section for fault location, maintenance and repair works.
Load Break Switch
The so-called “general purpose” switch is according to standards defined as
follows; mechanical switching device capable of making, carrying the breaking currents
40
under normal. A circuit condition, which may include specified operating overload
conditions, such as those of a short circuit .It may also be capable of as those of a short
circuit. It may be capable to making but not breaking of short circuit current. The load
break switch contains some special arts .One of the interrupter head. It reduces there
formed. When the switch is operate.
Aout Recloser
Auto reclosers are self contaminated devises that make and break the
distribution system under normal at and fault conditions. A basic feature of a recloser is to
reclose immediately once the circuit under which it served breaks due to temporary fault.
Recloser will lock out its operation whenever it senses a permanent fault clears before
lock out, recloser will reset for another cycle of operation.
Before CEB has introduced auto reclosers to the distribution system, only
DDLO’s are provided as the protective devices.
But this needs some one to operate the DDLO in order to isolate the line
from the power supply. Therefore by introducing auto reclosers to distribution system, the
speed of fault clearing has improved and hence which promotes the stability of the power
system. Because of these reasons the concepts of auto reclosers entered as a time and
money saving method [the interruption period becomes less].
The minimum requirement for installing an auto recloser is 100 km 1 MVA.
The reclosers are sensitive for over current, and in modern types sensitive earth faults too.
There are three types of auto reclosers available in medium voltage system in
CEB.
SF6 gas auto recloser
Oil auto recloser
Vacuum auto recloser
McGraw Edison type
These type reclosers are insulated with oil. This is the earliest type of auto
reclosers installed in distribution system by CEB. The major disadvantage of this type is
that its tripping times are fixed and cannot be adjusted at the site. The set time is 2
seconds. And also after some operations the oil contained in the recloser should change.
The faulty level is about 14.1Ka.
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PMR Dynatrip type
These type reclosers are mainly installed in DERP gantries. Only 33KV
dynatrip model is available in CEB system. They are filled with SF6 gas at normal
pressure.
These reclosers are equipped with following devices;
A closing coil protection system
A control battery supply 12V and 24V battery pack for control circuit and
energized auxiliary closing coil and main trip coil.
Electronic control unit; the settings can be change within a range at 25% to 225%
with 25 % intervals.
Dynatrip reclosers having CT ratio of200/1 is available in CEB .The
advantage of this type is that the recloser s are independent of thee total no of trips can be
set as dead time, reclosing time, auto/non auto switch and earth protection enable /disable.
The major disadvantage of this type is that the possibility to leak SF6 gas if the bushings
are damaged.
PMR Micro type
The following types are available in CEB 33KV CT ratio 300/100/1, 11KV
CT ratio 300/100/1.
The main advantage of this type is;
Micro trip type is programmable and therefore different settings can be given
Availability of memory facility, data for later viewing can be stored. This will
includes the no of tripping occurred, the no of occurred as over current and earth
fault or sensitive earth fault and the percentage of these failures .The only thing is
to maintain the pressure of the gas in side at specified region given in the name
plate.
The tripping period (dead time) for this type when connecting in the
distribution system are selected as follows;
1st tripping operation 0.25 sec.
2nd tripping operation 0.50 sec
3rd tripping operation 1.00 sec
4th tripping operation trip /lockout
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This type of reclosers is guarantied for 2500 tripping operations without
maintenance. Not like in previous type there is no any possibility to leakage of SF6 gas
under a damage of bushings.
6.3 HOT LINE MAINTANANCE
Hot Line Maintenance includes routine inspection and maintenance in
33kV tower lines all over the country. The purpose of the hot line maintenance is to carry
out the operations without the power being cutoff. This promotes the reliability and the
stability of the system. The main functions of the hot line maintenance are
Inspection and replacement of suspension and pin insulators of the 33kV towers
Replacement of cross arms on poles
To do above functions specially trained sets of people (Gangs) are needed.
There are three gangs and each gang has eight workers. The workers are working with the
live 33KV wires. If there is a small mistake, it will cause damages to their lives. So the
safety precautions shown below are extremely needed.
Always use safety belts and helmets.
Use the appropriate tools
Do maintenance in suitable weather conditions
Always keep the required clearance with the live wire.
6.4 SUBSTATION MAINTANANCE
Substation maintenance is the major functions of this branch are;
Maintaining existing primary substations
43
Building and commissioning new primary substations.
Primary substation is always converted 33KV to 11 KV. Always 33KV side
is in out door and 11 KV side is indoor. There is the normal diagram of primary
substation.
6.5 LINE MAINTANANCE
This section involves in maintenance of 33KV tower lines, routine
maintenance, installation and restoration of air break switch [ABS], load break switch
[LBS] and DDLO, identification of breakdowns, and preventive maintenance of 33KV
network.
5.1 INTRODUCTIOn
The Victoriya Project is one of five major hard works projects being under taken the
accelerated Mahaweliganga Scheme. It is the most upstream of these projects and
develops the hydro potential of a major right bank tributary of the MahaweliGanga,at
Hakuruthale. The Victoriya is SriLanka largest power station. The primary functions of
the project is the generation of electric power but additional irrigation and power benefits
will arise from the improved regulation of river flows at the Randenigala &Rantabe
division Woter way tunnel is 5.8 km ,before the power generating water way has many
main point.
There are 3 machines 71 MW each,(Type vertical axis medium head Francis)
On the first day we reported at the Mahawelli complex office at Ampitiya, and the next
day visited the power station. We were given the training schedule and an explanation
about the power station.
5.2 WATER WAYS
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We studied about the waterways. It includes Reservoir, Tunnel intake, Tunnel,
Surge shaft, Penstock, Spiral casing, Draft tube and Tailrace.
Dam and reservoir
The dam is constructed as 438 m high with concrete membrane dam across
the reservoir.
Top water level 438 m - MSL
Maximum operation level 370 m - MSL
Tunnel and Penstock
Penstocks is begin in 516 m down from the surge shaft and 60^ angled to the horizontal
axis. The penstock is steel lined.
Length of tunnel 5.8 km
Type linier concrete lined (Steel line at base)
Diameter of penstock 3 m
Surge shaft
The surge tank is a concrete lined, 145 This is situated in 5 km from the
beginning of the tunnel. These are some of the functions of a surge chamber.
When the load on the turbine decreases, the governor closes the gates of turbine,
reducing water supply to the turbine. The excess water at the lower end of the
conduit rushes back to the surge tank and increases its water level.
When load on the turbine increases, additional water is drawn from the surge tank
to meet the increased load requirement. Hence the surge tank acts as a reservoir
during increase of load on the turbine.
The gat in the surge chamber is use to separate low-pressure tunnel and high-
pressure tunnel.
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Draft Tube
This is the end of the water way . Draft tube divide to 2 part four end s at tail raise with
rectangular opening. The two gates per machine availability insulated draft tube from tail
raise.
Tail Race
The water after having done its usual work in the turbine is discharged to the
tailrace, which may lead it to the same stream or to another one.
5.3 POWER STATION
Main Inlet Valve
Each turbine is protected on the upstream side by a 2.7 m inlet valve of the lattice
blade butterfly type, constructed in cast steel and operated by two double acting oil
operated servo motors is supplied from an air/oil 60 bar hydraulic accumulator which is
charged by an oil pumping set. In the event of power failure, the valve can be closed
using the residual oil pressure in the accumulator. So that the inlet valve does not have to
open against full different at head, an oil operated needed valve is provided as a bypass to
balance the penstock the pressure between the penstock and the spiral casing of the
turbine prior to opening.
spiral casing and guide vanes
Water flows through the spiral casing and is guided 18 guide vanes on to
the 2.25m stainless steel one-piece runner. Each guide vane is connected by links and
levers to a regulating ring which is moved by two hydraulic servo motors .The oil to
move the servomotors is provided by an air/oil receiver and pumping set similar to that
provided for the main inlet valve.
Governor
Each turbine is controlled by an electronic governor taking its speed and
power signals from the generator terminals, with the toothed wheel mounted on the shaft
46
providing signals for the speed relays. The electronic governor cubicle is located on the
turbine floor and transmits instructions electrically to and electro hydraulic actuator
which converts them to oil hydraulic signals to the guide vane servomotors.
Turbine
Water turbines are divided in to two main categories. The impulse type and
reaction type. In the impulse type, water flows out of a nozzle in the form of a jet such
that all the pressure energy is converted in to kinetic energy. This jet hits one of a series
buckets mounted on a runner. Because of the impact, the runner is rotated about the axis.
There for the turbine is called the impulse turbine.
The reaction type turbines works on the principle of reaction. Water enters the turbine at
high pressure and low velocity in the guide passage. Some pressure energy is converted in
to kinetic energy and water then enters the runner and pressure energy is converted in to
kinetic energy. As the water flowing through the runner is accelerated, it creates a
reaction on the runner vane and the runner is rotated.
According to the type of flow of water, the water turbines used as prime
movers in hydroelectric power stations are of four types.
Pelton weel type
This is suitable for high head and low flow plants. Pelton type used above 300m
to 1800 m head.
47
48
Francis type
This is suitable for low to medium head and water flow plants. These type
turbines can be constructed in vertical and horizontal forms. In Kotmale the three
vertical shaft turbines are designed to operate at 375rev/min, and to deliver 90 MW
under a net head of 201.5m.
Spiral case
This is an angular spiral-shaped casing forming the circumference
of the turbine. One end of it is connected to the penstock to receive the
water under pressure from it, and this water is admitted uniformly all over
the circumference of the runner. The cross sectional area of the casing
decreases progressively, as more and more water is diverted on the runner
so that the velocity of the flow is constant. The inner shape of the casing
is cylindrical, Where the stay vanes ring is attached.
The Stay vanes ring
This is a ring with a number of fin-shaped stay vanes welded
between two angular rings. The functions of the stay vanes are,
(i) To guide the water received from the Spiral case at a proper angle
on the movable guide vanes for which their shape is carefully
designed.
(ii) To strengthen the spiral case against the high pressure of the water
passing through it. There for it is rigidly welded to the spiral case.
Guide Vanes
The guide vanes are located between the stay vanes and the
runner.This serves three functions
(i) To receive water from the stay vanes and direct it at proper angles on
the runner vanes
Kaplan type
Low loads due to rotary motion of water in Francis turbine is overcome.
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5.4 GENERATORS
The three generators are of the vertical shaft, salient rotor type of
construction and are designed for counter clockwise rotation as viewed from above the
unit. Each generator has a rated output of 95MVA at 0.85 power factor with a stator
winding temperature rise of 600c and a maximum continuous output of 95,000 kVA with
a rise of 40c. The generated voltage is 1250 V at 50 Hz and the normal running speed is
333.3 rev/min.
It will be noted that a semi umbrella arrangement has been adopted in which
a combined thrust and guide bearing is mounted below the rotor and a second guide
bearing is located above the rotor. The thrust bearing is designed for a maintain the
maximum load.
The generator stator is enclosed above the machine floor level by a D shaped
sheet steel casing, which completes the air circuit and also forms an integrated design
with the line and neutral terminal cubicles. The ventilating air is circulated by axial fan
mounted at each end of the rotor. These fans are assisted by the natural fan action on the
rotating salient pole s.
Cool air is drawn in at each end of the machine and forced between the poles,
where it flows across the machine air gap into radial ducts formed in the stator core. After
passing through these ducts and cooling the stator winding and core, the hot air passes
through to water cooled air cooler units mounted on the back of the stator frame. The
cooled air is then re circulated to the top and bottom of the machine. The generator slip
ring s and brush gear, together with creep detector unit and a speed signal toothed wheel
are mounted in a separate enclosure located above the casing floor panels for ease of
access and maintenance.
Six combined braking and jacking units are mounted on the bottom
bracket .W hen used as breaks the units are operate by compressed air from the unit break
air compressor and when used as jacks by oil from a portable high pressure pump.
Installed capacity 80.75 MW
Turbine - Type Vertical Francis
Rating 71 MW
Speed 333.3 R.P.M.
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5.5 PROTECTION OF GENERATORS
The generating units, especially the large ones, are relatively few in number and
higher in individual cost than most other equipments. Therefore it is desirable and
necessary to provide protection to cover the wide range of faults which may occur in the
modern generating plant.
Some of the important faults which may occur on a generator are;
(i) Over voltage
(ii) Over speed
(iii) Stator winding faults
(iv) Unbalanced loading
(v) Stator over voltage
(vi) Loss of excitation
(vii) External faults
5.6 EXITATION
D.C current should be fed to the poles to excite them. Standby battery bank use
for first excitation. Now a days static excitation system is used in which a transformer
brings down the generator voltage to 230 V and thyristors convert it to D.C and feed it to
the rotor .
In Victoriya, excitation system is as follows. When the r.p.m is increased up to
300 the battery supply disconnects and the need voltage is taken from the generator out
put. From the excitation transformer the 415 v out put is step down into 230v and then the
thyristors convert this A.C supply in to D.C. Then it is given to the stator winding through
the field breaker.
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5.7 CONTROL ROOM
The special room called, control room where all controlling of the plant and
system being done. In controlling room, the main task is to control the system frequency
and it is tried to maintain within the range of (49-51) Hz. The rated frequency is 50 Hz. In
there, all equipments including the protective devices, auxiliary devices being controlled
and inspections are done. There is a computer which being used to locate the faults,
which happened in the past and analyze them. There are so many panel boards, which are
used to indicate the controlling position of the all the equipments. For example if we want
to maintain particular generator first we should indicate it in the board so that it may
make the controller clear idea about the generators, which are in operation. Then it will
help to get idea about total load, which can be handled and the total generating capacity.
2.8 SWITCH YARD
Net work of all controlling backing & distribution equipments are situated at
switch yard. Mainly it consists of transformers, Isolators, Lighting arrestors, CTs, VTs &
several busbars.
Victoriya power Station
On the first day we had to go to the Mahawelli complex office at Ampitiya. On
the second day we went to the power station. We were given a training schedule and we
were to follow that schedule. Studied about the general layout of the power station. We
had the opportunity to attend to a routine maintenance of the generator number 3. For a
routine maintenance they were cleaned and a visual inspection is done. We studied about
the 220KV switchyard and their operations. In the switchyard there were two outgoing
feeders. One feeder is to Randenigala and others are to the . We were able to do Circuit
Breaker MeggerTest& Contact resistance test. There is a Diesel Generator for
Emergency auxiliary supply .
Normally auxiliary supply is taken as follow.33kv Generating voltage is step
down to 415v by using earthing transformer
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Indoor sub stations
Generally, local substations, which control a large no: of LT feeders are of
indoor type. In these substations usually the primary voltage is 11kV and the secondary is
400/440 volts. Gas insulation substation is the indoor substation. All apparatus are inside
therefore cannot see close or open condition.
There are only two Gas Insulated Sub stations in Sri Lanka. One is in
Kolonnawa And the other is in Kelanitissa. In these sub stations all the apparatus are
computerized and all the readings for voltages and current can be read from the
computers.
Outdoor sub stations
Generally, main substations for primary and secondary transmission are outdoor
type substations for which control 11kV to 132 kV. It is because for such voltages the
clearance between conductors and the space required for switches, circuit breakers and
other equipment become so great that it is not economical to install the equipment indoor.
Pole mounted sub stations
This type of substation is suitable for low rating say ,up to about 100kVA . It
does not require much attention for its operation. It is cheaper in first cost and
maintenance cost is also low. For village electrification work, distributions to small
residential colonies, and medium consumers pole mounted type of substations are most
common.
It consists of H type of structure for the poles at the end of the line. At a
suitable height, a platform of roll steel joint is created for placing transformer. Other
accessories are:
HRC fuse on primary side
Gang operating switch on HT side
Lighting arresters
Switch and fuses for secondary distribution
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Underground sub stations
In thickly populated areas, the space available for equipment and building
is limited and the cost of land is high. Under such situations, the sub station is created
underground.
generating station to the substations and from substations to the consumer’s premises. So
conductors are made of that material which has;
High electrical conductivity
High tensile strength in order to withstand mechanical stresses
Low cost so that it can be used for long distance
Low specific gravity so that weight per unit volume is small
Following conductors are used for overhead line:
Copper
Aluminium
ACSR (Aluminium Conductor Steel Reinforced)
AAC (All Aluminium Conductor)
ABC ( Arial Bundle conductors)
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55
4.1 INTRODUCTION
Electric power can be transmitted or distributed either by means of under ground
cables or by overhead lines. The underground cables are rarely used for power
transmission due to two main reasons. Firstly, power is generally transmitted over long
distances to load centers. Obviously, the installation costs for under ground transmission
will be very heavy. Secondly, electric power has to be transmitted at high voltages for
economic reasons. It is very difficult to provide proper insulation to the cables to
withstand such higher pressures. Therefore as a rule, power transmission over long
distances is carried out by using overhead lines. With the growth in power demand and
consequent rise in voltage levels, power transmission by overhead lines has assumed
considerable importance.
An overhead line is subjected to uncertain weather conditions and other
external interferences. This calls for the use of proper mechanical factors of safety in
order to ensure the continuity of operation in the line.
4.2 CONDUCTORS AND THEIR MATERIALS
The purposes of the conductors are to carry the load current from the
CU
From the point of view of conduct and tensile strength copper conductor is used,
but being very costly and requiring to be imported, nowadays, it is not used as conductor
material for overhead lines in our country.
ACSR
Due to low tensile strength, aluminium conductors produce greater sag. This
prohibits their use for larger spans and makes them unsuitable for long distance
56
transmission. In order to increase the tensile strength, the aluminium conductor is rain
forced with a core of galvanized steel wires. In CEB the mostly used conductor is ACSR.
AAC
These are stranded conductors made of aluminium wires. Stranded aluminium
conductors are durable and flexible. Stranded Aluminium conductors are durable and
light. Mainly used of this conductor on low voltage distribution system.
Aluminium has conductivity of 60% that of copper and therefore, for the same
resistance and voltage drop in carrying same current, aluminium conductor has 1.6 times
the cross sectional area of copper. The density of aluminium is 2.7 gm/cc as against that
of 8.89 gm/cc for copper. Taking combined effect of low conductivity and low density of
aluminium into account, the weight of aluminium required for the same resistance of the
line, is nearly half that of copper. This is big advantage in favor of aluminium.
Moreover, the aluminium is cheep and easily available, main drawback of
aluminium is that its ultimate tensile strength is about half that of copper and therefore, it
cannot be used as such for long spans.
ABC
A bundled conductor is made up of two or more stranded ACSR sub conductors
per phase. Bundle conductors are called duplex, triplex etc. With the higher effective
diameter of the bundle conductor the corona inception increases. Bundle conductors are
used for 400 kv lines. The sub conductors are held apart by means of spacers at regular
intervals along the length of line.
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4.3 MAIN COMPONENTS OF OVERHEAD LINES
An overhead line maybe used to transmit or distribute electric power. The
successful operation of an overhead line depends to a great extent upon the mechanical
design of the line. While constructing an overhead line, it should be ensured that
mechanical strength of the line is such so as to provide against most probable weather
conditions.
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INSULATORS
The successful operation of an overhead line depends of a considerable
extent upon the proper selection of an insulator. There are several types of insulators but
the most commonly used are pin type, suspension type, strain insulator and shackle
insulator.
Pin insulators
The part section of a pin type insulator is shown in figure 5.1. As the name
suggests the pin type is secured to the cross arm on the pole. There is a groove on the
upper end of the insulator for housing the conductor. The conductor passes through this
groove and is bound by the annealed wire of the same material.
Pin type insulators are used for transmission and distribution of electric
power at voltages up to 33KV.Beyond operating voltage of 33KV, the pin type insulators
become too bulky, and hence uneconomical.
Suspension insulators
The cost of pin type insulator increases rapidly as the working voltage is
increased. Therefore, this type of insulator is not economical beyond 33KV. For high
voltage (>33KV), it is a usual practice to use suspension type insulators shown in figure
5.2. They consist of a number of porcelain discs connected in series by metal link in the
form of a string. The conductor is suspended at the bottom end of this string while the
other end of the string is secured to the cross arm of the tower. Each unit or disc is
designed for low voltage, say 11KV .
The number of discs in series would obviously depend upon the working voltage .For
instance, if the working voltage is 66KV, than six discs in series will be provided on the
string.
Strain insulators
When there is a dead end of the line or there is corner or sharp curve, the line is
subjected to greater tension .In order to relive the line of excessive tension, strain
59
insulators are used for low voltage lines (<11KV), shackle insulators are used as strain
insulators. However, for high voltages transmission lines, strain insulators shown in
figure 5.3. The discs of strain insulators are used in the vertical plane. When the tension
in the lines is exceedingly high, as at long river spans, two or more strings are used in
parallel.
Shackle insulators
Now a days shackle insulators are frequently used for low voltage distribution
lines. Such insulators can be used either in horizontal position or in a vertical position.
They can be directly fixed to the pole with a bolt or to the cross arm. Figure shows a
shackle insulator fixed to the pole. The conductor in the groove is fixed with a soft
binding wire.
LINE SUPPORTS
The supporting structures for overhead line conductors are various types of
poles and towers called “line supports”. In general the line supports should have the
following properties.
High mechanical strength to withstand the weight of conductors and wind loads
etc.
Light in weight without the loss of mechanical strength.
Cheap in cost and economical to maintain
Long life
Easy accessibility of conductors for maintenance
The line supports used for transmission and distribution of electric power are of
various types including wooden poles, RCC poles, steel poles and lattice steel towers .The
choice of supporting structure for a particular case depends upon the line span, cross
sectional area, line voltage, cost and local conditions.
Towers
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For every great heights and extra high voltage, transmission towers are used.
Various angle iron sections are used to form a close cage to form tower.
Wooden poles
These are light in weight and cheap in comparison with all other types of
poles, made up of modern beam. These are easily affected and spoiled by atmosphere,
rain water, white ant soil, moisture, etc. These are used for temporary works and with
special chemical coating for works of permanent nature.
R.C.C poles
These are made by reinforcing steel rods in concrete slabs of pole shape .The
usual ratio of mixture is 1:1:5:3 for cement, sand, stone rubbles and steel rods
respectively. These poles are of permanent nature, long life, unaffected by rain sunlight
etc. So are usually used nowadays. Ducts are provided inside the poles section along its
length for,
Drawing cables/wires
To keep its weight less
Steel poles
Steel poles are of L shape, rail type and tubular in shape. These poles are
heavy in weight and cheaper than R.C.C poles. Atmospheric moisture, rain etc., affect
these poles hence while using, these poles are always painted or coated with chemicals to
avoid rusting.
4.4 LINE CONSTRUCTION
Selection of route
Following factors should be considered when selecting a line route.
One side of the road is used as far as possible.
Amount of way leave to be cleared shall be minimized.
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Inconvenience caused to the other services shall be minimized.
Swampy ground and areas liable to flood shall be avoided.
Routes which would involve excavation in rock shall be avoided
The use of taller poles at uplifts shall be avoided and construction of tension
points at uplifts also be avoided.
As far as possible route shall be least expensive to board.
Selection of poles
All poles used in the LV lines should be concrete poles. However wooden
poles may be used in difficult terrain with the recommendation of the chief engineer
(construction) of the province.
8.3 m 100 kg RC poles shall be used for LV lines. However 9m 115 kg poles may be used
to maintain the ground clearances where necessary. 8.3 m 100 kg pre stressed poles also
may use in difficult terrain.
Erection of self-supported 8.3 m 500 kg RC pole may be recommended
where erection of stays and struts is not possible due to ground conditions.
Handling and transportation of concrete pole
Concrete poles for electrical distribution networks are designed to have a
strength in the down line direction at least ¼ the strength in the transverse direction. The
shape of a section through a typical concrete pole easily demonstrates this difference in
strength.
Therefore a pole must be stored, transported, and handled at all times with
its longer axis in the vertical plane to ensure that the resulting forces are always resisted
by the poles stronger direction.
Poles must not be dropped off a truck but lifted by means of crane. Poles should
not be jarred by twisting the cross arm.
During erection the pole should not be allowed to bend on the flat or wide sides,
or to lurch against the side of the hole when it is dropped into place.
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The poles should be transported on a suitable vehicle supported full length or
with a limited amount of overhang. The poles should be lifted by crane from the
transporter and placed on the ground. They must not be dropped.
Hole digging
The position of the hole is usually indicated by a peg. The hole must be dug
so that as nearly as possible the pole is erected in its correct position. If the peg indicates
the center of the hole it is a good idea to place a temporary peg at a definite distance away
so that it is not disturbed during digging operations .The hole can be excavated either by
hand, or by truck mounted augers.
The depth of the hole is usually made equal to one sixth the length of the pole.
Precautions should be taken to prevent soil subsidence in loose ground or in
close proximity to roadways or buildings. One method taken to prevent soil subsidence is
to support the hole by wood planks and struts similar to cable trench work, but the struts
should be arranged such that they can be removed easily during pole erection.
When it is required to excavate a hole adjacent to an existing pole, temporary
stays should be added on the existing pole prior to excavating.
Foundation design
For the purpose of support foundation design it is convenient to consider
three categories of soil, good, poor and water logged. The allowable ultimate vertical
bearing pressure for each category of soil has a fixed value but lateral soil resistance is
assumed to increase with depth and to be inversely proportional to the width of
bearing surface of the foundation. The inverse relationship has been introduced to take
account of the dimensioning contribution of the boundary effect as the foundation, which
increases.
Foundation types
Where poles have to be erected in wet or swampy locations, special
foundations are required to prevent the pole sinking. Where the conditions are very wet
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and soft additional outrigger supports must be added bellow the ground surface to prevent
sideways movement of the pole.
A 100 mm layer of concrete is poured in the bottom before erection of pole
and allowed to harden. The cuission is backfilled with concrete. Temporary stays can be
used to support the pole until the concrete has hardened.
Erecting of poles
The preferred method of erection is by cranes of adequate size for the weight
of pole being handled. Traffic wardens should be posted when the crane obstructs the
road and interference with normal traffic flow must be kept to an absolute minimum.
Manual methods of inaccessible to cranes.
Poles should be erected vertically
The face of the narrow side must be aligned with the LV line in straight sections
of the line. This method is applicable to both tension and terminal poles.
Pole should be erected to be bisect the angle at angle points
D brackets, stay clamps and earth damps shall be fixed end to the pole using nut
and bolts at the ground level before erection of the pole.
Facing poles
The fact of a pole is defined as the side of the pole on which the D brackets
are mounted the narrow side of the pole.
In straight sections of the line, the face must be line with the distribution line
Poles should be erected vertical
Back filling of pole pits
The back filling of pole pits and stay pits shall be done with earth or gravel
and well rammed. The filling shall be up to a height not less than 25 cm above ground
level.
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4.5 installation of stays and struts
When a line changes direction, an additional force is introduced at the angle
pole. This force is the resultant of line tensions acting at the pole .The resultant force tries
to move the top of the pole in the direction that bisect the angle between the wires. These
forces, due to angles, can be considerable. The stays, struts and flying stays shall be fixed
to neutralize the resultant force on the poles.
Number of stays to be used at any particular pole location is designed on the
overturning force acting on the pole. The force acting on the pole depends on the
following factors;
Number of conductors and size of the conductor along with conductor tension.
Length of adjacent spans.
Angle of deviation of the line.
Equipment mounted on the pole.
Geographical position of the pole.
Stay insulators, thimbles and brackets shall be used in all stays. Following
shall be noted in fixing stays and struts.
The angle between pole and the stay wire or strut pole shall not be less than 300
Stay, strut and flying stays should be erected so as to avoid disturbances to
pedestrians or vehicular traffic.
If shall be ensured that the correct side of the ratchet nut faces the ratchet force of
the cross head of the buckle before tighting the stay buckle.
Stay and flying stay wire over a street must not be less than 5.5m from the
ground.
Stay shall be installed conforming to drawing.
In flat terrain poles used for struts and flying stays shall be of the same size as line
poles.
Stay insulator shall be positioned below the level of the lowest current carrying
conductor and not less than 3.7 m above the ground.
Splicing of stay wire shall be done according to drawing. Depth of the pole pit of
the strut pole shall not be less than 800mm.
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String of conductors
During running out, the cable drum should be securely supported on drum
jacks, with and the axle should be level.
The work areas should have sufficient employees on site to ensure that the
conductors are not damaged by contact with the ground or pole equipment during running
out. Care should be taken to avoid kinking, twisting or abrading the conductor in any
manner. Conductor should not be trampled on, run over by vehicles or dragged over the
ground. Vehicles should not be used to run out conductors.
Special care must be taken when running out conductors near other existing
electrical systems, whether they are alive or not.
4.6 TENSIONING AND BINDING (BARE CONDUCTORS)
All aluminium 7/3.40 mm (fly) and all aluminium 7/4.39mm (wasp)
conductors shall be used for LV lines.
Earth wire no: 8 shall be strung on the top of the pole before stringing the
bare conductors. Conductors shall be strung in vertical formation as per drawings. After
final tension of the conductor LV shackle insulator shall be fixed to the D brackets of the
intermediate poles. Conductors shall be bound to the insulator at each
support using aluminium-binding wire no: 11. Only one mid span joint per conductor
shall be allowed for a shackle point span .All mid span joints shall be compression type.
During stringing of conductors maximum precautions shall be taken to
prevent excessive strain and damage to the conductor. Standard sag and tensions
applicable ton the particular size of conductor shall be maintained.
The conductors shall be tensioned using ratchet pullers and wire grips (come
along clamps) designed to prevent damage to the conductor using tensioning.
4.7 EARTHING ARRENGMENT
Bottom part of the down run of the shackle point and the terminal point shall
be covered using 2m length of 12mm PVC conduit pipe. No: 8 GS wire shall be
connected to the copper clad earth rod using a crimp type tinned copper adaptor at the
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ground level to ensure a proper connection of the GS wire and the earth rod. Down run
shall be clamped along the pole by stainless steel at three positions.
The earthing rod shall be grounded approximately 500mm away from the base
of pole. The top of the earthing rod shall be approximately 300 mm below finished
ground after installation is completed.
All hardware parts of the pole shall be bridged together and connected to the
earth clamp on the pole top-using no: 8 GS wire.
8.2 TYPES OF ELECTRIC ENERGY METERS
Single phase watt-hour meter
Three phase watt-hour meter
kVA meter
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kVAr meter
Maximum demand meter
Two rate meter (peak-normal)
Poly phase meter
NAME PLATE OF A SIGLE PHASE METER
10A – base current
40A – the maximum load current
Class 2- accuracy class is 2. i.e. error can be varied +2% to –2%
240 v- rated voltage
50 Hz – frequency
2002- manufactured year
- Some adjustment are there
- Indicate disk rotation
8.3 ELECTRIC ENERGY
The Electric Power Company (PC) supplies electric energy (W) to its
consumers. Although these customers are considered as consumers, the electric energy
delivered to them is only converted into mechanical work, heat or light. The electrical
devices (appliances, machines, motors etc.), which transform electric energy into some
other form to satisfy the needs of the consumers, have, in modern times, become legion.
The consumer turns them on and off at will. Those, which are switched on at
any given moment, constitute the consumer load, as they load the power company’s
supply and distribution network. Although the expression “power” belongs to the power
company’s domain and the expression “load” to that of the consumer, “power” and “load”
are generally interchangeable In order to bill the consumer for the exact amount of energy
supplied to him, the power company measures this energy with an electricity meter.
The magnitude of the load is generally measured in kilowatts (KW). The power
company uses the kilowatt hour (KWh) as the units of measurement for the energy it
supplies to its customers.
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8.4 MECHANICAL PRINCIPLE
The electricity meter uses on aluminium disc as a rotor. Electromagnetic
forces are produced in this disc. In order to obtain rotation, a torque must drive the disc
the driving torque.
The operating principle of the meter requires that the driving torque be
proportional to the consumer load. As the load becomes larger, the driving torque
constant determines the rate at which driving torque is increased as a function
of the load.
A breaking torque opposes the driving torque. The breaking torque must be
proportional to the meter disc speed. As the disc rotates more rapidly, the breaking torque
is linearly increased. Disc speed is measured in revolution per minute (r/min).
For steady-state equilibrium, i.e. when no other force (no friction) is present,
driving torque is equal and opposed to the braking torque.
Thus, disc speed is proportional to consumer load. As the load becomes
larger, the disc speed is linearly increased. The meter constant (k) determines the ratio:
Disc speed /consumer load = Meter constant (revolutions per kwh = r/kwh)
The meter constant is an important parameter, which is always a shown on the
meter dial plate. Disc revolutions are proportional to the energy. Therefore
Meter constant = disc revolutions /energy
KWh-Display on Register
A register is used to count the disc revolutions. However, the register
should display “KWh” and not disc revolutions.
The register has 6 figure rollers. The figures: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
(evenly spaced over the roller circumference) are printed on each roller. Only that figure
is displayed, which appears in a small opening of the dial plate.
It is, therefore, possible to count from “000000” to “999999” with this
register. In order to display the measured energy (KWh), and not the disc revolutions, the
disc speed must be geared down according to the meter constant.
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8.5 MEASUREMENT OF ACTIVE ENERGY
Today, single-phase and three-phase AC distribution networks are
universally used by the power companies to supply electric energy to their consumers.
For the large majority of consumer only the active energy (kilowatt-hours) is measured
and billed.
We shall, therefore, deal only with the active energy meter, and
concentrates on the task it must be perform.
P P
supply Load
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KWH METER
1 2 3 4
N N
Figure 8.1
Wiring diagram of a single phase meter
8.6 SINGLE-PHASE METER APPLICATION
The description of electrical meter operation is restricted to the measurement of
active energy [KWH] in single-phase network.
However, active energy meters in other networks [e.g. three phase network] are
similar to the single-phase meter in design and operation.
Basically, to measure the active load, the meter must perform the
multiplication operation, voltage X current. As a measure of the quantities to be
multiplied, two magnetic fluxes, voltage flux and current flux, are produced in the
meter .In preparation for the multiplication operation, eddy current s are induced by these
fluxes in the meter disc.
To measure the load, the line voltage and the consumer load current must
be introduced into the meter. The current phase displacement (cos Φ) must also be
measured, in order to produce a driving torque, which is proportional to the active load.
The current is measured by driving it through a coil (the current coil) in
the meter current coil is in series with the consumer load, always in the phase wire.
To measure the voltage a second coil (the voltage coil) in the meter is
connected to the line voltage between the phase wire and the neutral wire.
The ends of the both coils are connected to the terminal block inside the
meter. The cable from the power company and the consumer wiring are connected to the
outside of the terminal box.
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The phase wire current enters and leaves the meter via the two terminals
[1 and 4]. Two terminals [2 and 3] serve to connect the neutral wire and the voltage coil.
The other end of the voltage coil is connected internally [2] to the current input terminal
[1], which carries phase potential.
A link [called calibration link] serves to separate the voltage circuit from the
Current when the meter is beginning tested and calibrated. The consumer load, i.e. the
power at the metering location, is measured by individual measurement of the voltage (U)
and the current (I).
The consumer load, i.e. the power at the metering location, is measured by
individual measurement of the voltage and the current.
The magnitude of current and voltage and their phase position, i.e. the lag angle of the
current with respect to the voltage, are measured.
8.7 METERING ELEMENT DESIGN
The metering element produces two torques, the driving torque [MD] and
the barking torque [MB], required to measure the electric energy. The metering element
comprises, primarily;
The voltage element
With voltage coil, voltage core and counter -pole
The current element
With current coil and current core
The brake magnet
The meter disc [as rotor]
The voltage element produces a magnetic field, the voltage flux, which
traverses the meter disc [From voltage core to counter-pole].
The current element produces a magnetic field, the current flux that
traverses the meter disc.
The brake magnet produces a magnetic field, the braking flux that
traverses the meter disc.
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The magnetic fluxes are utilized to produce a driving torque [MD] and a
barking torque [MB] in the meter disc.
Together, the voltage fluxes, representing the voltage and the current
flux, representing the current, act to produce a driving torque (MD) proportional to
consumer load.
The breaking flux is issued to produce a breaking torque (MB) proportional
to the speed of the meter disc.
Induced disk current
Voltages and Currents are induced in all conductors, which move through
a magnetic field. No currents are produced in a stationary meter disc. Only a magnetic
flux, whose magnitude varies, would induce currents in the disc.
As soon as the disc begins to rotate, however eddy currents are induced in
the area, where the braking flux traverses the disc.
The eddy currents flow in closed loops, to both sides of the magnetic flux,
whereby the sense of rotation on one side is opposed to that on the other side.
8.8 TESTING PROCEDURE OF SINGLE PHASE METERS
wiring
- Remove the cover and disconnect the inner voltage link between the current and
voltage terminal.
- Place the meter onto the test bench and connect the wires.
- Check the tightness of accessible screws.
Heating
Pre heat the meters by applying the rated voltage and basic current at 1.0
power factor for approximate 30 minutes.
Quality test
Check the meters by applying the maximum current (40 A ) for approximate 5
minutes.
Full load check
Set the power source to the base current (IB) at 1.0 power factor (unity).
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Power factor test
Set the power source to the base current (IB) at 0.5 power factor.
Low load test
Set the power source to the rated voltage 0.5% of basic current at 1.0 power factor.
Starting current test
Check that the rotor of the meter rotates and continues to run at the rated voltage,
frequency, 1.0 power factor and 0.5% of the rated current.
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75
Creep test
With no current in the current circuit, check that the rotor of the meter does not make one
complete revolution when a voltage between 80% and 110% of the rated voltage is
applied.
Dial test
Set the meter to rotate rated speed (420rev/kwh) and check the unit consumption.
Shown in fig: 6.testing report of single-phase meters.
8.9 WIRING OF ENERGY METERS
There are several types of L.T. single phase, three phase (Direct) and
three phase (CT operated) meters in CEB. Hence the wiring methods are also different
from type to type of the meter, especially in CT operated meters.
Wrong wiring of a meter would result a high magnitude error. Therefore it
is very essential to wire the meters correctly. Following steps should be taken when
meters are wired.
Direct Meters
1. Meter should be selected according to the consumer load
2. Meter should be installed vertically
3. Load wire should be connected properly.
CT Operated Meters
1. Meter should be selected according to the consumer load
2. Meter should be installed vertically.
3. CT’s should be inserted correctly (correct direction)
4. CT connection to the meter should be correct.
5. Voltage connection to the meter should be correct.
6. Do not use single strand wire for meter wiring. Always use multi strand wires.
7. Check phase sequence.
8. Terminal cover should be sealed properly after meter connection.
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Connect to 11th
Terminal
P N
Connect to 11th
terminal
P N
Supply
Wiring Diagram of 3 phase two rate kWh meter GEC with timer(English type)
Figure 8.3
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P
N
1 2 3 4 5 6 7 8 9 10 11 1212
Timer(English Type)
1 2 3 E 4 56 6
8.9 TIMERS
1.correct wiring of the timer.
2.proper wind up by using the key (when the timer is mechanical one)
3.To set the time turn the dial in direction of arrow until pointer indicates the time of
day at the moment of setting.
4.turn dial one round to the correct side and check whether the solenoid in the timer
operates in set time.
5.Timer also should be sealed properly.
8.10 ELECTRICITY METERING ERROR
The electric meter serves the CEB to measure and bill electrical energy
consumption. It is essential that the meter reading represent, with the smallest possible
deviation, the true value of the energy supplied to the consumer. All disturbance factors,
which can cause metering errors, must be recognized and attended to.
Metering error=actual value-nominal value
nominal value
where,
Actual value=the result of the measurement as indicated by the measuring device
Nominal value=the true value of the measured
On the first day we had the chance to dismantle a kWh meter and to identify various parts
and to reconnect. Then an idea about the basic procedure of a meter testing was taken.
Also we had the chance to study about the causes and methods of meter repairing.
CT testing procedure was observed.
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9.1 INTRODUCTION
Lift has been an essential component in modern multi storied buildings.
It makes easy for passengers and it is economically worth and it save most of the time
that takes to travel up and down of a building.
All the Lifts in the Government Buildings are maintain by the lift branch.
9.2 MAIN PARTS OF A LIFT
Lift well
In most buildings lift well is situated near the main entrance. Lift well is created
to cover machinery and open space to present a smooth finished surface for passenger
protection. The area of the well depend on the size and number of the cars, and by the
disposition of the car and landing entrance. The necessary clearance for the car and
counter weight is also determine when creating the lift well.
Car and the two door system
There is a door provided for the car extending the full height and width of the car
opening and Another door is provided at all landing openings. When the lift reaches to a
floor these two doors open together. These are provided for the protection of the
passengers.
Counter weight
The object of the counter weight is to provide traction and to balance the weight
of the car. Incidentally the counter weight provides a certain measure of safety when
landing on its buffer and removing traction from the car. This is made up of cast iron
sections firmly secured against movement by at least two steel tie rod having lock nuts or
split pins at each end and passing through each section.
Car traveling cable
This is made by means of multi core hanging flexible cable, one end is connected
to a terminal box fitted under the car floor. The other to a terminal box fitted in the well at
approximately the mid position to remove any twist in the cable.
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Machine room
This is at the top of the well and it consists of driving motor, break, gearing and
the control panel.
9.3 THE OPERATING MECHANISM OF LIFTS
There are mainly two types of roping system in lifts. Those are
(i) 2 x 2 system
(ii) 2 x 1 system
In first type there are four or six ropes as sown in the figure. There is a spring connected
to one end of the cable. So that if there is a break in any rope the spring get release and it
operate a switch for emergency stop. In the Second type The one end of the rope is
connected to the car and the other to the counter weight.
Over load alarm
Modern lifts are made to give maximum protection to the passengers. There are
four springs which acts as resistors and those are connected according to the principle of
vinston bridge.
If R1 R3
R2 R4
The voltage between Point A & B is zero.
If the lift is over load the ratio get unbalance & there will be a voltage difference at point
a& B. This makes an alarm to operate.
Read contactor
This is use to stop the lift at a floor. Normally it is in close position because of the
Magnetic field of the magnet in the floor level. When The lift reaches in between of the
read contactor and the magnet The magnetic field breaks and the contactor open and the
lift stop at the floor.
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10.1 INTRODUCTION
In Western Province There are five area offices as follows. Kelaniya, Ja-Ela,
Gampha, Negambo and Veyangoda. Under Kelaniya area office there are three Consumer
Service Centers. Those are Delgoda, Mavaramandiya andKirillawala.
We were at the Kelaniya area office for three week. During that period, we were
asked to go to the Mawaramandiya depot for One week, to Area Maintenance Branch
Kiribathgoda for One week and one week at the area office.
Kelaniya depot is responsible for billing, new connections, disconnections
Maintain the low voltage lines and Take actions for consumer complains.
The main function of an area office is making bills. There are meter readers and they
take the reading and the billing part is done by the area office. Electricity bill chargings
are different from each other according to the purpose of the building. Tariff is the rate at
which electrical energy is supplied to a consumer. There are five main types.
1. Domestic tariff
2. Tariff applicable to religious premises and charitable institutions
3. Tariff applicable for bulk sales to Lanka Electricity Company (pvt)Limited.
4. General purpose Tariff
5. Industrial Tariff.
10.2 MAVARAMANDIYA CONSUMER SERVICE CENTER
At mavaramandiya depot we identified some equipments and units used in power
distribution. Main activities of the Consumer Service Center are
1. Give new service connections
2. Service maintenance of H.T Lines & L.T Lines
3. 24 hours breakdown service
10.3 TYPES OF SERVICE CONNECTIONS1. Single phase - 30 A only
2. Three phase - 30 A & 60 A
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1. Giving new connections
There are four steps to follow when giving new connection
1. Receiving an application
2. Estimation
3. Payment
4. Giving connection
Connections are giving according to the regulations.
2.Service maintenance
Replacement of Service wires, meters, Meter boxes
3.Bulk supply connections
There are two types of bulk consumers.
1. L.T Bulk consumers
2. H.T Bulk consumers
L.T bulk supply is given using a L.T transformer. Consumption is measured
through KWH meters and KVh meters, using CTs .
H.T bulk connection is given through a CT/PT transformer. Consumption is
measured by using CT/PT. H.T bulk supply is given in 11 KV or 33KV.
4. Maintenance of H.T & L.T lines
The depot with the assistance of Area Maintenance Unit does both H.T & L.T
Line Maintenance.
5. Break down service
Break downs occur at both H.T & L.T lines and bulk supply connection are
reported to the depot break down section. There is a 24 hour break down service to attend
to the service.
10.4 AREA MAINTENANCE UNIT
We were able to study about cable Joints, Sub stations, Auto reclosers,
Breakers, Insulators,……….etc. The duties of this unit is to maintain the overhead
lines in Kelaniya area, take actions for customer complains and requests……etc.
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10.5 CLEARANCES
When laying a voltage line we must keep particular distance between conductors, and
high enough from ground. It is always pre calculated value, mainly depend on line
voltage.
Clearances between low voltage bear/aerial bundled conductor
Across the road or street 5.5 m
In any other plane 4.9 m
Clearances above
Voltage exceeding 650 V & below 11 KV
Across the road street 6.1 m
In any other plane 5.2 m
Place in accessible to vehicular traffic 4.6 m
Voltage exceeding 11 KV & below 33 KV
Across the road street 6.1 m
In any other plane 5.2 m
Place in accessible to vehicular traffic 4.6 m
Clearances between other conductors
Conductors of same circuit
Over head line conductors must have following clearances from other
conductors of same circuit.
low voltage 0.2 m 0.3 m
11 kV 7.0 m 0.6 m
33 kV 6.7 m 0.9 m
circuit voltage clearance
low voltage & 11 kV 0.2 m
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low voltage & 33 kV 0.5 m
33 kV & 11 kV 0.9 m
11 kV & 11kV 0.9 m
33 kV & 33 kV 0.2 m
Bare conductors of different circuit on the same supports.
The medium voltage circuits & the vertical clearances between conductors of the
different circuits at any point of the support under normal working conditions
shall not be less then specified below;
Horizontal spacing between different circuit.
The horizontal spacing between different shall not be less than specified
below.
circuit voltage clearance
low voltage & 11 kV 1.2 m
low voltage & 33 kV 1.5 m
33 kV & 11 kV 1.2 m
11 kV & 11kV 0.9 m
33 kV & 33 kV 1.2 m
Safety clearances
To ensure personnel safety, the following maximum safety clearances shall be
maintained.
Medium voltage bare conductors
Any part of human body 0.8 m
Any construction building 5.0 m
Low voltage bare conductors
Any part of human body 0.15
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Location of poles
Poles are located so as to provide a easy access for maintenance works. some compromise
may also be needed to ensure that poles located on corners and drive way will not unduly
obstruct vehicular traffic maximum pole spacing are :
Pole height Along the road Across the road
MV on 11m pole 70m 35m
MV on 30m pole 70m 35m
10m pole only be used with maximum span of 80m, when runs across country.
The distance between shackle poles are not exceed either of following.
Pole height Distance between two
adjacent poles
Maximum number of poles
MV 12m 560m 07
MV 11m 490m 07
MV 11m 490m 07
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11.1 INTRODUCTION
Demand side management activities are those involve action on the demand
side of the electric meter either directly caused or indirectly simulated by the utility.
DSM branch of CEB provides a range of services to industrial and
commercial electricity consumers. Features of some DSM services are described below.
Energy audit : an analysis of energy consumption patterns and measures available
to reduce monthly energy cost.
Pre construction consultancy services :an overview of technical drawings and
recommendations based on energy efficiency.
Power quality analyzing :an analysis of voltage, power, harmonic variations and
measures available to suppress harmonic and improve voltage quality.
Lighting design :professional lighting design for buildings
Implementation monitoring and testing :monitoring and testing of implementation
of DSM recommendations based on energy audits to verify the saving potential
and testing on customers request.
Customer education programs
11.2 MODERN EQUIPMENT AND SOFTWARE
It is necessary to use various types of modern equipment and software in the
Demand Side Management branch when giving the several services specially to their
industrial and commercial customers. Those are;
1. Power analyzer
2. Recording poly phase power meter (Data logger) with software
3. Flue gas analyzer
4. Light meter
5. Infra Red thermometer
6. Digital thermometer / humidity meter
7. Energy balance software
8. Photo/ Contact tacho meter
9. Power quality analyzer
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1. Power analyzer
Power analyzer is mainly used for getting any reading of consumed electricity.
According to the customer’s required, when gives the service like energy audit we
must used the power analyzer. By using current transformers and other component it
must be connected to the supply and can get readings.
2. Data Logger
Also data logger is act as the power analyzer. By using data logger we can
record the data of the supply within number of days as required. After setting the data
logger to the supply, it can be recorded any data and after required days, it must be
down loaded and disconnect from the electricity supply.
The comparison between power analyzer and data logger
Power analyzer Data logger
Can record the harmonics Can’t recorded harmonics, only can seen
Need external power supply Not need external power supply
Memory capacity is less Memory capacity is high
All data were recorded Recorded only the selected data
3. Flue gas analyzer
Mainly it is used for measuring the combustion efficiency of the boilers.
Inserting the flue gas analyzer in to the chimney and can get the measurement of
content of gases like CO2, CO in air as a percentage.
4. Light meter
By using this we can measure the amount of light rays in unit of “ Lux “ in
any required area.
5. Infra red thermometer
In the places or equipment that we can’t reach like boilers, used this for
measuring the temperature. By using the beam of red light rays, it can be detected the
temperature of element.
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6. Digital thermometer
By using this can be measure the temperature of any thing like water, ice…
7. Photo/ contact tachometer
For measuring the RPM value of any rotating device like motor shaft the
tachometer is used. If the meter cannot touch that surface can use the photo sensor
method.
8. Power quality analyzer
Its action is same as the action of power analyzer. But it can’t save data and
we can see the data at the required time.
11.2 DSM OBJECTIVES
DSM activities are broadly categorized under the headings such as
load management
strategic conservation
electrification ,
strategic growth.
Those objectives are intended to achieve by,
Peak clipping generally involves reduction of load during peak hours(for Srilanka
system peak is experienced from 6.00 to 9.00 p.m.) to defer the need to install new
capacity by reducing the peak demand. Peak clipping will also reduce the energy
requirement, thus saving on expensive fuels.
Peak reduction can be achieved through the use of more efficient end-use equipment or
direct utility control of end-use equipment as well as time-of-use and interruptible tariffs
For example effective use of efficient lights such as compact fluorescent lamps can
substantially reduce the peak load.
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Peak Clipping Valley Filling
figure 11.1 figurer 11.2
LOAD SHIFTING STRATEGIC CONSERVATION
figure 11.3 figure 11.4
FLEXIBLE LOAD SHAPE
figure 11.5
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Valley Filling
Valley filling essentially includes building off-peak loads resulting in an increase in the
total energy consumption with no increase in the peak load. This is applicable for utilities
with low cost plants running on low load factors.
In the case of Srilanka, for example railway electrification can successfully achieve high
utilization of inexpensive plants in the system during off-peak hours.
Load Shifting
Load shifting can be viewed as a combination of peak clipping and valley filling.
Consumers are encouraged to reduce consumption during the peak hours by shifting their
consumption from peak to off-peak hours.
Some industrial consumers whose consumption can be shifted to off-peak hours with
minimum disturbance can take advantage of load shifting .
This is achieved mostly through introduction of two-part (time-of-use) tariffs. Other
methods such as direct load control and thermal energy storage can also be used .
Strategic Conservation
Strategic conservation targets selected applications for energy conservation .Reduction of
electricity consumption mostly through efficient use of end-use equipment, will generally
cause a downward shift in the load curve. The reduction in the peak demand will be
determined by the coincidence factor.
Flexible Load Shape
Some customers may be willing to trade reliability for some incentive such as reduced
rates. Utilities are then able to make some adjustments to the load shape according to their
operating needs. Utilities (by offering a choice of reliability) can effectively reduce the
necessity for adding peaking plants.
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11.3 Activities of DSM
Customer education
Energy survey/ audits
Seminars
Workshops
Promotional programs
Publicity programs
Introduce DSM programs
Provide direct incentives and other financial options for customer to adopt DSM
measures
Low interest loans
Cash grants
Subsidised installation
Rebates
Promote the manufacture of energy efficient appliances and equipment.
Set efficiency standards for electrical machinery /equipment /appliances(co-
ordinate with SLS)
Proposals to GOSL on taxes /tariffs to promote the use of energy efficient
appliances.
BENEFITS FROM DSM PROGRAMS
Customer
Reduced electricity bills.
Utility incentives.
Utility
Avoided supply cost.
Reduced demand.
The DSM branch identifies the customer segments as follows;
Retail sector (Domestic customers, Small Industry, Small commercial buildings)
Industry sector
Hotel and large commercial buildings sector
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From the figure we can see that that the most electricity consumption is taken by the
industrial sector and the retail sector is the least contributor to the electric power
consumption.
11.5 ENERGY EFFICIENCY
Energy efficiency measures available for domestic customers
Efficiency lighting.
Efficient refrigerators
Good house keeping.
ENERGY EFFICIENCY MEASURES AVAILABLE FOR INDUSTRIES
Energy audits/surveys
Efficient motors
Power factor correction
Efficient lighting.
Load management.
Fuel switching.
Captive generation.
Efficiency A/C and ventilation system.
Efficient boilers and steam distribution system.
ENERGY EFFICIENCY MEASURES AVAILABLE FOR HOTELS/ BUILDINGS.
Energy audits/surveys
Power factor correction
Efficient lighting.
Load management.
Fuel switching.
Captive generation.
Efficiency A/C and ventilation system.
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Energy Audit
The main service provided by DSM to industrial and commercial customers is
conducting “Energy Audit” programs.
Energy audit is an analysis of your energy consumption pattern. In addition it,
provides an array of recommendations on the measures available to reduce the
monthly energy costs. The fees on energy audit based on the contract demand.
The energy audit involves the following major functions
Power quality analysis
The voltage, power ,harmonic variations are analysed, and measures are
recommended to suppress undesirable harmonics and to improve the voltage.
Energy management programs
Conduction of employee education programs
Load research services
Pre construction consultancy services
Make recommendations for energy efficiency improvements.
System monitoring
Lighting designs
Energy efficiency building code
Applicable for new commercial buildings of more than 4 storied
Covers lighting ,ventilation and air conditioning ,building envelope ,electrical power and
distribution, and service water heating.
11.6 ENERGY EFFICIENCY BUILDING CODE (EEBC)
Purpose
Reduce energy consumption of new buildings by 40%.
Reduce energy consumption of existing building by 20%.
This is used for commercial buildings only. Initial requirements of this;
Four stories or higher
Floor area of 2000m2 or greater
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Energy efficiency lighting
Maximum allowable power
Power credit for lighting controls
Recommended light levels
Equipment efficiency levels
Energy efficiency ventilation and airconditing
Efficient A/C system design
Equipment efficiency levels
Commissioning and testing
Maintenance
Water treatment
Building structure
Building orientation
Wall construction to reduce heat gain
Window design and selection of glass to reduce heat gain
Air leakages
Electrical power and distribution
Equipment efficiency
Internal distribution requirements
Motor rewinding
11.7 ENERGY LABELING
CEB in association with the SLSI & ECF has decided to implement energy labeling
program on a voluntary basis.
Main Objectives of the program is to promote use of energy efficient electrical items to
save energy.
The purpose of energy labels
- To provide information to consumers regarding the energy efficiency of products
- To encourage consumers to buy the most energy-efficient appliances
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Main components of energy labelingFigure 11.6
Figure 11.7
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Standards Labeling
Testing Facilities
Testing Procedures
Evaluation
Monitoring & Enforcement
How does energy labels work?
- Influences consumer purchase decisions
- Influences manufacturer production and marketing
(More stars means more energy efficient)
Watt loss Star rating
loss <4 W * * * * *
4 W < loss < 6 W * * * *
6 W < loss < 8 W * * *
8 W < loss < 10 W * *
10 W < loss < 12 W *
loss > 12 W no stars
11.8 ENERGY AUDIT
An energy audit is a systematic gathering and evaluation of energy data about
a plant/process, for the purpose of promoting energy efficiency.
COMPONENTS OF AN ENERGY AUDIT
Pre audit consultation
Site analysis and data logging including metering
Preparation of report
AUDIT PROCEDURE
Customer request
Information to customer
Analysis of historical data
Customer interview/ incoming electricity supply logging
Sub section data logging
Data collection
Analysis of data
Preparation of energy balance
Identification of energy efficiency measures
Preparation Of costs/benefits
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Formulate recommendations
Preparation of audit report
Prepare monitoring schedules
Presentation of report
11.9 POWER FACTOR CORRECTION
Power factor (PF) is given by the ratio of useful current to the total current; it
is also the ratio of useful power expressed in kW to total power expressed in kilowatt
amperes (kVA). Power factor is usually expressed as a decimal number or a percentage.
PF = Useful power (kW)/Total power (kVA)
11.10 FUNCTION OF CAPACITORS
Electrical used by industrial plants consists of two major components:
Real power (generally expressed in kilowatt) that produces useful work ranging
from providing motive power to industrial machinery to lighting a single bulb in
one’s home.
Reactive power (generally expressed in kilovar), necessary to generate magnetic
fields to operate electrical machinery.
Inductive electrical equipment such as motors and transformers draw their
reactive power requirements from the electricity distribution system to which they are
connected.
The ratio of useful power to total power is called the power factor. When
equipment has a low power factor, it will require a relatively large amount of reactive
power. The power factor correction capacitors essentially provide the necessary reactive
power requirements from the electricity distribution system
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11.12 TYPES AND SELECTION OF CAPACITORS
The load in typical industrial installation changes virtually every instance. As a
result, the amount of kVAr to be provided externally to maintain a desired power factor
also changes with the changing kW demand. Although it may be technically possible to
provide the correct amount of kVAr in other words, to follow the load curve so as to
maintain a fixed power factor, it is generally uneconomical to do so.
Fixed capacitors: Power factor correction capacitors are commercially
manufactured to provide a fixed quantity of reactive power (5kVAr, 10kVAr, 50kVAr,
etc). In some situations, installing a fixed capacitor may suffice to improve the power
factor to an adequate level. For example, fixed capacitors are often recommended for
individual machines such as motors or installations exhibiting relatively steady demands.
One should, however, exercise caution in selecting the correct rating of fixed capacitors
as a higher rating than necessary (over compensation0 could lead to problems.
Automatic capacitor banks: In some situations, fixed capacitors may not provide
the necessary correction. A bank of capacitors with the facility to “sense” the reactive
power demand and provide the right amount of reactive power demand and provide the
right amount of reactive power (by connecting the required number of capacitors) is more
appropriate in such situations. This method, obviously, is more expensive than installing
fixed capacitors as additional switching circuits are involved. Switched capacitor banks,
however, are superior in performance as they could “follow” the load curve closely
(provided capacitor selection is done carefully).
FACTORS THAT AFFECT THE ELECTRICITY BILL
The energy charge number of units used during the billing period in kilowatt
hours (kWh);
Demand charge this charge compensates the utility for the capital investment
required to serve the plant’s peak load. Demand charge can be a large portion of
the total electricity bill. Demand charge can be reducing by smoothing out the
peaks. This charge usually involved power factor or kVAr.
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11.13 LOAD RESEARCH PROJECT
Load research is primarily aimed at analyzing and understanding the utility’s
system load profile. This entails breakdown of the system load profile into various sub
components. Therefore, the main objectives of the load research can be identified as
follows:
To develop shapes at the system, regional, and customer sector level
To develop shapes database by major end uses within customer sectors.
It will be evident that these objectives are quite flexible to accommodate any
sub system of the main network and to analyse any sub categories of end uses.
Load research may either be conducted by starting from customer end use to
build and develop the total system load shape or by starting form the total system load
shape and breaking it down to customer end use .it may well be a combination of the
two.
Both approach require primary and secondary data collection and are
generally accomplish through a combination of the following data collection methods:
Metering
Market survey
Statical methods
Using engineering models
By analyzing other data
Substation log book data
System control data
Sales and billing data
Fig: 11.8 Shows the conceptual approach that was used in the load research
of the CEB system. It has used the bottom-up approach, with a combination of data
collection by metering, customer surveys and using other recorded load data.
RESULTS
Final results of the load research project consisted of the following load
profiles and the associated data for the CEB network.
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1. CEB system
2. Provincial load profiles
3. System load profiles by sectors
4. Domestic sector by segments
5. End use load profiles
Domestic
Domestic (by lighting technology)
Small commercial and industrial
Industrial and commercial (bulk) customers
11.14 LOAD SHAPE OBJECTIVES
DSM activities in Sri Lanka cannot considered to be an alternative to supply
side options available for power system capacity expansion. But some load shape
objectives of demand side management could effectively complement the supply side
options.
The knowledge available from load research regarding the composition of the
load shape is of valuable to design any of these DSM activities and to forecast their
impacts. Through subsequent load research, i.e. after implementing the DSM measures,
the utility would also be able to evaluate and monitor the impacts of such measures.
11.15 AIR CONDITIONING
INTRODUCTION
Air conditioning is the control the temperature and moisture content of the
occupied space.
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Figure 11.9
104
Evaporator
Compressor
Discharge lineHot vaporHigh pressure
Suction lineCold vaporLow pressure
Filter
Expansion valve
Liquid line
Evaporation
Liquid Vapor
Condensation
Most air conditioners have their capacity rated in British Thermal Units
(BTU). Generally speaking a BTU is the amount of heat required to raise the temperature
of one found (0.45 kg) of water 1 degree Fahrenheit (0.560C).
11.16 REFRIGERATION CYCLE
An air conditioner is basically a refrigerator without the insulated box. It
uses the evaporation of a refrigerant, like Freon, to provide cooling. The mechanics of the
Freon evaporation cycle are the same in a refrigerator as in an air conditioner.
This is how the evaporation cycle in an air conditioner works.The
compressor compresses cool Freon gas, causing it to become hot, high-pressure Freon
gas. This hot gas runs through a set of coils so it can dissipate its heat, and it condenses
into a liquid. The Freon liquid runs through an expansion valve, and in the process it
evaporates to become cold, low-pressure Freon gas. This cold gas runs through a set of
coils that allow the gas to absorb heat and cool down the air inside the building.
11.17 AIR CONDITIONING SYSTEMS
NON DUCTABLE SYSTEM
This system is categorized in two types. There are window type and split
type.
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Window type
Normal small size air conditioning plants are available in this form. We can
identify the following parts and assures in this plant, there are compressor, condenser,
evaporator, blower, fan expansion valve and controlling arrangement etc.
Window type plants are available in as a compact set including all
mentioned above. But the unit can be filter, exporter, motor drives fan remote bulb and
refrigerant control. The out side part consists of compressor condenser and motor driven
fan. The two fan driven by the same motor. The condenser cooling system is air-cooling.
Split type
This type air-conditioning plants are available in small and medium size,
which differ from the other parts. This type has several advantages than window type or
package type, which is not noise. Evaporator can be installed very suitable place etc. This
plant consists of air-cooling and water-cooling system.
DUCTABLE SYSTEM
This system is categorized in two types. There are package type and chill
water type.
Package type
This type air conditioning plants available in large sizes , which are better to
use corridors and large halls. Where condensing unit and evaporator are separate one and
the duct line are used to distribute cooled air into rooms or anything. This is two types
fresh air type and return air type .In fresh air type we supply atmospheric gas into room
through the evaporator and the return air type cooled air release to evaporator from the
room and then re cooled the gas.
Central type
Large size air conditioning system are commonly used this system. Which
has as advantage of comparatively low refrigerant volume is used for
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Figure 11.10
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Condenser Water (95°)
Outdoor Air
Outdoor Air
Condenser Water (85°)
refrigerant cycle. According to condenser cooling system the chill water plants are two
types.
Chill water plants with condenser water cooling system
Chill water plants with condenser air cooling system
Generally chill water plant is consists of high power compressor (normally use
centrifugal or reciprocating type), water cooled or air cooled condenser, filter, cooling
tower, duct line, evaporator with large chill water system expansion valve and various
types of controlling and protection device.
Compressor
Compressors may be classified as either open or hermetic.
Open compressor: A compressor unit consisting of a compressor, motor, and
safety controls mounted as a unit.(see fig:8. )
Hermetic: A condensing unit consisting of a compressor unit plus an
interconnected water cooled or air cooled condenser mounted as a unit.
Cooling tower
The cooling tower is used in a conjunction with the water-cooled condenser
(see fig:11.). Water in passing through the condenser water tubes only gets warmed up
but does not get contained. It can therefore be used again, after cooling. The cooling
tower cools the warm water for re circulating it in the condenser. It is thus a water
conservation equipment .The heat removed by the refrigeration system from the space or
product to be cooled is ultimately thrown to the atmosphere through the cooling tower in
a water-cooled condenser system. Thus cooling tower should function efficiently for the
refrigeration system to perform well.
The warm water from the condenser is pumped to the top of the cooling
tower. From there it is allowed to fall down a substantial height to the cooling tank or
through at the bottom. The falling water droplets are cooled by the air circulating through
the tower. The cooling is brought about both by sensible heat transfer and by the
evaporation of the water.
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