hvds basic

8/10/2019 HVDS basic

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High Voltage Distribution System-A Lasting Solution For The ILLs of

the Last Mile of the Power Chain


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High Voltage Distribution System

Distribution is called the last mile in the power supply chainbeing closest to the consumer.

Its quality controls / governs the consumer satisfaction

However it is the most neglected segment of the power sector formany years due to paucity of funds

Major challenge of reforms process is the up gradation ofDistribution system

-To maintain the Standards of performance fixed by the

Regulator.

--To achieve the targets set Under National Electricity policy.

-- To meet the stipulations of various codes like Supply Codes,Grid code etc., in all its functioning


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National Electricity Policy stipulates achieving thefollowing targets, among others, by 2012

- Extension Power supply of quality , continuity and reliability

to all areas including rural areas as per the standards fixed

by the respective Commission, meeting the demand in full,all at affordable price.

- Bringing down AT&C losses to 15.5%

Both the targets are of a very tall order, requiring adoptingof every conceivable method of system improvement.


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Parameters for assessing supply quality Voltage Frequency, Harmonics

Parameters for assessing Reliability Power CutsNo Supply Periods Interruptions - Frequency & Duration

---Measured variables

Number of interruptionsDuration of interruptions


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MAX. TOLERABLE TARGET LEVEL

TRANSMISSION 4 4.00 2.00

SUB TRANSMISSION 4 4.50 2.25HIGH VOLTAGE DISTRIBUTION 6 5.00 3.00

LOW VOLTAGE DISTRIBITION 8 2.00 1.00

TOTAL 22 15.50 8.25

SYSTEM COMPONENTSEXISTING

LEVELS

INTERNATIONAL NORMS

NORMS FOR TECHNICAL LOSSES

REVIEW OF SYSTEM LOSSES

Source:World Bank Energy Department Paper No 6-July 1982 on

"Energy Efficiency:Optimization of Electrical Power Distribution System losses"


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Objectives of a power utility

Supplying of Power of quality, continuity andReliability

Extending supply network to all parts in the area

under its jurisdiction

Meeting the demand in full

Operating plants and network at Optimum

efficiency

Keeping the losses at bare minimumProviding effective consumer services

Supplying power at affordable price


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PRESENT STATUS OF DISTRIBUTION SYSTEM

Power supply for few hours on any day. Number of interruptions even during the hours of supply due to

the bad condition of net work.

Poor quality of power supply with low voltages

Growing consumer dissatisfaction. Poor revenue realization

Comparatively higher losses.

Financial status which permits only little investment in the systemimprovement.

Achieving targets set in NEP by 2012, against the above back

ground, calls for drastic changes in the set up.


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Low Voltage Distribution System

The two widely prevalent distribution practices invogue across the world are:

Low Voltage Distribution System (LVDS):

It is based on European practice. A Three phase transformer of considerable capacity,

say 63kVA and above, is installed and a large group

of loads are fed through longer LV lines .

This system is best suited to meet the concentratedloads of high load density.


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Low Voltage Distribution System

This system is widely adopted in our power sector despitethe contrasting status, particularly in rural areas, of

scattered loads with low load density.

This has resulted in system losses well beyond the tolerablelimits, poor Voltage profile and host of other ills, many a

times compounding in nature


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Problems of Existing Distribution

As Power is drawn through longer L.T. lines with higher current,

there is increased power and energy losses

Higher voltage drop in lengthy LT lines resulting in Low Voltages atconsumer end.

Frequent motor burning outs due to low voltage at consumer end andconsequent expenditure on repairsHigher rate of transformer failures due to commonly ocuring defectsin L.T. network and over loading increased expenditure on repairs-increased interruptions to the consumer.

For any transformer failure large number of consumers gettingaffected.

For any delays in replacing failed transformers , damages to standingcrops


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Problems of Existing Distribution

As more number of consumers are connected under eachtransformer , more fluctuations.

Higher possibilities for theft of energy by direct hooking to thebare L.T. lines, running in remote areas

More number of interruptions due to the defects in the lengthyL.T net work. lesser reliability

As bare L.T network has only fuse protection ,without anybreaker, Chances for accidents are more by coming in to contact

with snapped bare wires.

Poor quality of supply resulting in lesser end use efficiencyThe above drawbacks are automatically call for adopting a

different distribution system devoid of these defects


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High Voltage Distribution System (HVDS):

It is the best remedy for all the prevailing ills in the existing LowVoltage Distribution System (LVDS)

It is based on North American practice.

A Three phase or single phase HV line is taken as near to a smallgroup of loads as possible, and a distribution transformers of smaller

capacities , single phase or three phase transformer as the case may

be , are installed to feed a small group of loads through AB cables

and service wire , such that the length of the LV lines is minimum or

is eliminated altogether.

To the extent LV lines are permitted, they are with insulated ABcables only

This system is best suited to meet the scattered loads of low loaddensity.


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Different Types of High Voltage

Distribution System

There are three types of High Voltage distribution system in vogue:

Phase Neutral HVDS (PN-HVDS)

Phase Phase HVDS (PP-HVDS)

Phase-Ground HVDS (PG HVDS)


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Phase-Neutral HVDS


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Phase-Neutral HVDS

It is widely adopted in North America. Under this system:

- the main line from substation is three-phase 4 wire (3 phases +

Neutral)

-- laterals are single-phase 2 wire line or two-phase 3-wire line orthree-phase 4-wire line depending upon the loads and feeding

arrangement.

Unique feature of the system lies in providing the neutral rightthrough the system, viz from substation to all nodes on the network.

Single-phase Loads:11 KV single phase line (phase neutral) branch isextended from main line and 1 No. 6350/230-0-230 V distribution

transformer is erected to feed single phase loads as shown in Part (A)

of Fig.


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Phase-Neutral HVDS

Three-phase loads: Three alternative arrangements for feeding threephase loads are described.

11 KV two-phase 3-wire branches are extended from the main lineand 2 Nos. of single-phase 6350/230-0-230 V distribution transformer

is connected, star on HV side and open delta on LV side to feed three-

phase loads, as shown in part (B) of Fig. Effective capacity of thetransformer bank is 86.6% of the total capacity of 2 transformers. Ie.

. if 2 No.s 10 kVA, transformers are used ,maximum 3 ph. load that

Can be fed is 17.32 kVA

11 KV three-phase, 4-wire line is extended and 3 Nos. 6350/230-0-230 V single phase transformers are connected, star- delta to feedthree-phase loads as shown in Part (C)of Fig.

Existing 11 KV three-phase 4-wire line is extended and three-phaseDelta/Star distribution transformer is used as shown in art D of Fi .


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Phase - Phase HVDS


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Phase - Phase HVDS

Three-Phase loads: Three alternate arrangements for feeding three-phase loads are described.

11 KV three-phase 3-wire branches are extended from main line and 2Nos. of single phase 11000/230-0-230 V distribution transformer is

connected HV side/ LV side V-V (Open delta ) to feed three phase

loads as shown in Part (F) of Fig. Effective capacity -86.6%

11 KV three-phase 3-wire line is extended and 3 Nos. 11000/230-0-230 V single phase distribution transformer are connected delta on

HV side and delta on LV side, as shown in Part (G) of Fig.

11 KV three-phase, 3-wire line is extended and existing three-phase11000/415V delta / star distribution transformer is used as shown inPart (H) of Fig.


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Phase - Ground HVDS

It is similar to Phase- Neutral HVDS in all respects exceptthat ground is used as return path and neutral wire is notprovided all along the system.

The transformer HV neutral or star point on HV side (when

more than one transformer is used) is earthed solidly atevery location, and thereby ground is used as return path.

This system is used in certain parts of North America andAustralia.

Since ground forms return path, soil resistivity plays a keyrole.

Good quality of earthing is required for the safety of


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Phase - Ground HVDS

It is unsuitable to Indian conditions due to technical and practical reasonslike :

Since ground is used for return path of the current, the soil resistivityof the area plays a vital role. The system may be hazardous in areas

where soil resistivity is high.

Good quality Earthing is required for the safety of personnel andanimals. The code of practice stipulates that the voltage rise ie., Load

current x and resistance of HV earthing system, at the point of

Earthing shall not exceed 20 V.

Providing effective Earthing and ensuring its maintenance throughoutthe period at a number of locations in rural areas is beset with severalpractical problems.

Interference with telecommunication lines.


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Advantages under HVDS

All the ills of LVDS get eliminated under HVDS

a)Drastic Reduction in system losses, both Power and energy losses

(In S.ph.HVDS energy losses are 13% of that in LVDS)

b) Improvement in system voltage profile (In S.ph.HVDS vol.drop is

10% of that in LVDS)

c)Reduction in possibilities for theft of energy by direct hooking from

LT linesas the LV lines are virtually eliminated and even the short LV

lines required are of AB cable..

d) Reduction in transformer failures as there will be no over loading andminimum or no LT line defects.

. Lesser interruptions, lesser delays in replacement of failed transformers

and lesser damage to standing crops .Better consumer satisfaction


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e)Increase in end use efficiency causing better delivery of water,drawing lesser current.

g)Sense of ownership of the transformer develops among theconsumers as the transformer caters to only two to three consumers)

Possibilities for fluctuations get reduced due to fewer consumers.

i) 11KV lines are controlled by breakers and LT lines are of ABcables. Chances for accidents due to snapping of conductors get

reduced.

J) With increase in the reliability of supply and better end use

efficiency resulting in higher delivery of water, 2 crops are beingraised increasing productivity.

k) Improvement in voltage profile, brings down cases of consumersmotor burning out drastically.


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l) Better socio economic development in rural areas. m) In case of any failure of a transformer only 2to3 consumers

will be affected.

n) In view of reduction in losses, additional loads can be fed

with the same generation , without adding any new capacity. o) schemes covering conversion of LVDS to HVDS are eligible forSale carbon emission reductions (CMRs) under Clean Development

Mechanism (CDM) . This additional benefit to the utilities will bring

down the Pay back period to a considerably lesser time frame

p) LT line maintenance is almost absent No tree cutting is requiredfor LT lines


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Advantages of HVDS compared to LVDS

System is more reliable because:

The LV lines are short and insulated, avoiding all LV faults. The faults on HT line comes to the notice of the operator immediately

due to the tripping of substation breaker.

The failure of transformer affects only a very small number of

consumers served by it. Voltage fluctuations: The voltage drop on the LV line is negligible.

The additional drop due to extension of HV line up to consumer

premises is also negligible. Thus the voltage profile is very stable and

there is no need to use voltage stabilizer.

With least or No possibilities for theft of energy , load management iscomparatively easier

Ad t f S h HVDS d


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Advantages of S ph. HVDS compared

to LVDS

The important drawbacks of LVDS and the way in which these areautomatically solved by adopting popular PhaseNeutral HVDS are:

Line Losses:The loss in Sph.HVD system for the distribution of the

same amount of power is less than 1% as compared to that of LV line.

In fact it is lesser than the losses under 3 ph. HVD system

Voltage Drop: The voltage drop for distribution of same quantum of

power is less than 1% as against that in LVDS and this ensures proper

voltage profile at all customer points.

System Power Factor : The single phase motors can be used for all

Agricultural services. The single phase motors have built in capacitorsessentially required for starting the motors.

Thus system power factor is always maintained high with good

capacitive compensation at theload end


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Advantages of S ph.HVDS Capital cost is less as Transformer, surge arrestor requiring 1 No.

Instead of 3, protection system cost less in sph.HVDS

compared to 3 ph. system

Protection requirements are simpler

For cost effectiveness new villages with lesser load demand can beelectrified through S ph. HVDS, which can be converted in to 3

ph. HVDS once the load picks up

Thus if Existing LVD systems are converted in to HVD systemstaking due care of the System improvement aspects in respect of

33 and 11kV Systems, HVDS will prove to be a boon forotherwise tottering Distribution networks.


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CAPITAL COST

HIGHER INVESTMENT ON TRANSFORMATION EQUIPMENT

LARGER CAPACITY DUE TO LOW DICERSITY

HIGH COST/KVA DUE TO SMALL CAPACITY OF TR

LOWER INVESTMENT ON LINES

SMALL SIZE CONDUCTORS ARE ADEQUATE DUE TO

LOW CURRENTS

LESS NUMBER OF CONDUCTORS

OPERATING COST.

HIGHER TRANSFORMATION LOSSES DUE TO HIGHER NO.OF. DTrs

NO LOAD LOSSES PER KVA CAPACITY

LOWER LINE LOSSES DUE TO LOW CURRENTS HANDLED

QUALITY OF SUPPLY

BETTER VOLTAGE PROFILE

LOWER SYSTEM LOSSES

BETTER RELIABILITYPREVENTS DIRECT TAPPING OF LINES

LOAD MANAGEMENT IS EASIER


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PROBLEMS AND SOLUTIONS fOR

PROBLEM SOLUTION1 Voltage bandwidth limited

to 10 %

Bandwidth can be

extended up to 20%

with a AVB online

2 Maintenance of large

number of Transformers .

ADOPT cast resin dry

technology for maintenancefree operation and reliability

These units are 25% costlier

than oil filled units.

3 Reconfiguration of

network

HVDS requires running of

continuous neutral wire from

substation.Line strengthened with

intermediate supports and stays


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. Capacitive compensation Provide online switchedcapacitor banks with automatic

SF6/VACCUM switches for

maintenance free operation and

switching on and off capacitorwith load.

Sectionalisation of primary

distribution feeder .

Provide automatic

VACCUM/SF6 line

sectionalisation on the SPUR

lines which sense the voltage on

and off sequence generated bycircuit breaker at the substation

and isolate the faulty section

automatically.


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Sphase motors Indigenous manufacturing

capacity for high efficiency

and high power factor motors

developed.

High transformation losses No load losses constitute50% of total system losses

Use of metal AMORPHOUS

ALLOYS for TR core which

reduces losses by 80% is very

attractive in the long run as

cost of AMORPHOUS metalis expected to come down

with increased production

immediately load

management of pump sets

can be adopted by

S f i l i


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Strategy for implementation

The strategy for implementation of high voltage distribution system can

be broadly divided into two parts.First part relates to extension of HVDS to meet new loads. This

ensures that the new distribution system built is energy efficient.

Second part relates to conversion of existing LV distribution system

to HVDS.

The two parts are inter dependent and can be executed simultaneously.


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Part-I of Strategy

The important problems likely to be encountered under this part are

investigated and appropriate solutions are presented.

Manufacture of small capacity single phase transformers which arerobust and fail proof.

Integration of new HVDS with existing LVDS.

Running of continuous neutral wire.


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Part -II of Strategy

Part II relates to making the existing distribution system energy efficient

by conversion to HVDS.

The work involved in this phase is :

Conversion of existing low voltage lines to single-phase 2-wire HVline.

Replacement of existing three-phase distribution transformers ofconsiderable capacity with small capacity single-phase transformers

Replacing all LT Guy insulators of Stay sets by HT Guy insulators


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Discussion

HVDS is technically superior and provides ready solution to theproblems of distribution system.

Capital investment required for building new HVDS is 16.5% lowerthan that of LVDS. The Peak Power loss and energy losses of HVDSare 33% and 18% lower than that of LVDS respectively.

Capital investment required to restructure the existing network asHVDS is marginally cheaper than restructuring the network as LVDS. The peak power loss and energy losses of restructuring HVDS are

lower by 25% and 27% respectively compared to that of LVDS.

The peak power losses and energy losses reduction by restructuring as

HVDS are 80% and 66 % respectively. Restructuring of existing distribution network as HVDS is highly

viable as the pay back period is about 18 months.


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Conclusions

Phase neutral HVDS is identified as the best system among thedifferent HVDS schemes.

HVDS effectively tackles the problems faced by the utilities in theexisting LVDS.

The strategy proposed for implementation of HVDS and itsintegration with the existing network is found to be technicallyfeasible and financially viable.

The cluster based algorithm proposed for restructuring the existingLVDS as HVDS is an effective tool for large scale restructuring of the

existing network. The restructuring of existing LVDS as HVDS is practically feasible

and financially viable.


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Summing up, the recommendation is that the utilities should adopt

HVDS in place of the prevailing LVDS; extend it to all newextensions; also restructure the existing network as HVDS

simultaneously. This is the only technically feasible and least cost

solution approach for reduction of losses in Low Voltage network.


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CASE STUDY


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Case Study 1-HVDS 1 Ph

In order to propogate the concept and as a technology demonstration the

following Two schemes are formulated.


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g

H V D S SCHEMES

WARANGAL NALAGONDA

1.Noofpumpsets 7000 3200

2. Year of sanction 1993-94 1997-98

3. Cost of the projects Rs 8.0 cr Rs 8.4 cr

4. Pay back period 3 years 3 years

5. Achivements 2500 nos 1100 nos

6. Financed by OECF(Japan) DFID( U K )


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REASONS FOR POOR PROGRESS

1. Conversion of 3 ph motors to 1 ph motors.

2. Unauthorized pump sets

3. Higher H P

4. Industrial services above 10 HP

5. Local mechanics

EVALUATION REPORT

M/S EEEC BANGLORE

OBSERVATION AND FINDING

1. Over all losses reduced from 20% to 4%.

2. Voltage level has improved substantially

3. P.F increased to 0.91 from 0.7

4. No of pump sets increased to 36% from 25%5. Possibility of theft of energy reduced

6. Pay back periods are in line with anticipated results.


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SUGGESTIONS

To go for 3 HVDS by providing small capacity DTR ie 10 / 15 / 16 KVA

ADVANTAGE1.Loss reduction is same in both cases

2.Pay back period is faster

3.Consumer involve is avoided

4.All benefits relating to s HVDS conversion ie

Better VoltageReduction in interruptions and Break do wnsTheft of energy controlledReduction in DTR failuresLoss reduction etc

SI No. Item LVDS HVDS


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1. Distribution Transformer 1. No 100 KVA11kv/415V

11 NOS 15 kVA

11kV/415 V

distribution Trs

2. Line LT 3 phase 4 wire line(3phase one 1 neutral)

11KV line (3wires)LT

line with AB cable

having 4 core cable

3. Length of the line LT-3.6mm HT(11kv)-2.6km & LTAB cable-1km

( both are cases of

conversion from LTLine)

4. NO. of agriculture loads

(Pumpsets)

39Nos. 39Nos.

5. Connected Load 179.5 HP 179.5 HP

6. Crop pattern Rice and Sugarcane Rice and Sugarcane but

2 crops


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(a) No. of days of study 13 days 15 days

(b) Input 4290 Units 5310 Units

(c) Output 3490.4 Units 5019.8 Units

(d) Loss of units 799.06 Units 290.8 Units

(e) %Line losses 18.63% 5.47%

(f) Voltage at tail end 350V 420V


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Table C: Cost benefit Analysis

Line losses before conversion :18.63%Line losses before conversion :5.47%

Connected load :179.5HPNo. of units fed into LT network per annum

(approximately 900 units/H.P) :161550

5) (a) Line losses under LVD System (units) :30097

( b)Line losses HVD System (units) :8837

6) a) Savings in losses (units) by conversion to

HVDS (units) 21260

b) Hence with the same input energy, additional units

available for sale after meeting the load demand

of 179.5HPagl.loads :21260

HVDS t ti P ti


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HVDS construction Practices

HVDS conversion can be in two ways

A)Erecting a new HVDS network altogether, transferring theloads to the new system and dismantling the old system, as is

being adopted in Rajasthan where a large portion of LVDS is

already converted in to HVDS .

Push-fit covers for meters and armoured cabels for service wiresare used to curb thefts.

Where only 1 or 2 services are to be fed, Meters and capacitorsare located in a separate compartment on the backside of the

transformer.

This method permits free flow of work and reduces interruptionsto the consumer during conversion.

But it is costly and suffers from right of way problems.


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B) By converting LT 3ph. 4wire into 11kV line to the extentrequired.

No new lines are needed to be laid to execute this new concept.

Re- configuration and modification of the existing lines is done,using the materials that are already in use except for a few items.

ie converting existing LT lines in to 11kV (HT) lines by replacingonly insulators, suspension and tension hardware and x arms,

introducing new stay sets where required etc.

Existing poles are continued except for introducing 9.01 mt polesin the new transformer locations, for obtaining standard

clearances.

If the existing conductors are of adequate size, 3 out of 4 areused dismantling the fourth n is carriedout during the hours when

there is no su l in a ricultural feeders. .


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Using polymer insulators for 11kV line extension, for easyinstallation and puncture proof life

This method is less costlier and involves no right of wayproblems. As adopted in APSPDCL, Constructio

Specific steps needed to derive benefits in full


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Specific steps needed to derive benefits in full

The new system also requires certain steps to be taken to make itwork successfully.

With increased transformers their maintenance requiresadditional attention, particularly in remote areas. Better to use

Fail proof / Cast Resin transformers.

Perfect Earthing of transformers is essential to lessentransformer failures and accidents, as these locations cannot be

revisited frequently.

HT line shall be maintained systematically, particularly in case oftree trimming, as even a momentary fault will trip the feeder.


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Each transformer shall be provided with drop out switches tolocalize the unavoidable interruption.

Measures to prevent theft of oil or winding from transformers ortransformer itself, shall be adopted.

It is equally important to upgrade and strengthen the up stream

systems ie., 11kV and 33 kV systems adequately, to reap thebenefits of change in full.

In either case, survey of existing 3 phase or single phase motorloads has to be carried out ( using tongtester and measuring load

current of each motor

This is required to ensure that small capacity transformers beinginstalled under HVDS do not get over loaded and fail

Erecting New Line


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Erecting New Line

Route survey to be conducted ( Preliminary walk over fallowed bydetailed survey)Route shall be as close to the loads it has to feed as

Possible, as short as possible ,avoiding difficult country side,naturalhazards, higher transportation costs etc

Transportation of RCC/PCCpoles:

a) Generally heavier and stronger on the longer axis than shorter axis.This shall be considered

b)Un loading from trucks and trailers shall be by using suitable skid

boards(Not to be dropped).Preferable to use chain pulley block and a

beam arrangement.c) Shall not be dragged on rough surfaces.Use Small carts

Pole locations


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Pole locations

A) spans shall be limited by the tensile strength of the conductor,wind pressure .

In a given length span shall be uniform with horizontal grade to theextent possible

Not to be located along the edges or cuts

Cut points for a section, geneally not longer than 1,6 km (10 poles/km for HT and 15 poles/ km for LT)

Right of way shall be identified and tree and vegetation clearanceshall be carried out

HTLine Erection


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HTLine Erection

Pit marking and digging

Erection of poles and concreating

Providing of Stays with guy insulators

Mounting x arms, insulators

Paying out and Stringing the conductor

Sagging and tensioning the conductor

Providing earthing and gaurdings

Testing and commissioning

Pit- 1.2mtx o.6mt

poles to be erected with its longer axis in the direction of the line.

Planting depth for pole 1/6 th of the pole length


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Each pole shall be raised on a base plate or RCC padding for betterload distribution on the ground below

For smooth sliding an inclined trench of a length of 15.2cmWx10.2cm L is made adjacent to the pit and a piece of MS channel

is placed on the other side in an inclined position so that pole can

smoothly slipped in to the pit Using a Bipod and 3 ropes pole is erected and kept in vertical position

using manila ropes. Verticality checked with spirit level, earth filling

in the balance pit and ramming is done. In Swamp locations poles are

concreted up to pit level

Stay sets with 7/3.15 mm stay wire and turn buckle rod of 16mm diaae erected to prevent tilting of poles. Most commonly used is anchor

guy


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.

Guy is used at angle locations, Dead ends, Tee offs, steep geadientsand where wind pressure is more than 50 kg/Sq.m Guy insulator kept

at a level of 3.5mts .Stay rod shall project 2mts. above ground level

(A type for LT line and C type for 11kV line)

At 35 to 40 inclined. After concreting and backfilling the balance 7

days are allowed for settling X-arms and insulators are fixed

Conductor drum or conductor shall not get damaged while transport,paying out.

Conductor is passed through Wooden or Aluminium rollers or snatchblock

Mid point joint through compression crimping o if helical fittings areused manually


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Conductor is pulled using come along clamp, tensioned and passed onto the insulator after Sag tensioning as per the Chart

Sag d= WI/2T

I= half the Span, T= tension in the conductor

W= w+ww., w= wt. of the unit length of conductor acting

vertically

Ww= Wind pressure on the conductor

Up to 33kV sag is checked by sighting

Pin binding with tie wire

Soft annealed Aluminium wire so that may not be brittle and injurethe conductor

Length of wire 1mt to 3 mt(33kV) required for a complete

Constuction Practices


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Constuction Practices

Metal supports Facto

Lattice type& compound type- not less than 1.5

Mechanically processed concrete pole- 2.0

Hand moulded concrete pole --------------- 2.5

Lattice & compound type -- not less than 1.5( under broken wire condition)

Minimum factor of safety for Guard wire,

stay wireand bearer shall not be less than 2.5, based on

Ultimate strength of the wire

Minimum FS for a conductor shall be 2 based on its Ultimate

strength


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For calculating F.S.:

Max. wind pressure as specified by the State govt.

For cylindrical bodies, the effective area shall be taken as 2/3 of theprojected area exposed to wind pressure

For lattice or compound structures the wind pr. On the lee side shall

be taken as one half of the wind pressure on the windward side

Factor safety shall be calculated on the the crippling loads for thesupports used as struts and up on the Elastic limit of the tension

members

Max. and Minimum temperatures as specified by the State govt. Not withstanding any thing stated above, in locations susceptible forice accumulation loadings to be stated by govt.


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Conductor tension at 32degC without external load shall not exceedthe following % of the ultimate tensile strength of the conductor

Initial unloaded tension- 35%

Final unloaded condition 25%

Conductors having a cross section of a triangular shape like

conductors composed of 3 wires, final unloaded tension at 32C shallnot exceed 30% of the ultimate tensile strength of the conductor


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Rule 82: When conductors forming part of circuits of differentvoltages are to be erected on the same support, proper clearance

between circiuits of different voltages shall be ensured.

Once a line is commissioned , if any building / structure is to beerected/ extended fouling the clearances, corrective action shall be at

the cost of building / structure owner. Cost shall include a) cost of the material giving credit for depreciated

cost b) cost of retrieved material giving credit C) Cost of labour d)

supervision charges@ 15% of wages and e) any other charges

involved


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TYPE Voltage level Ground clearance in mts

Across the street Low and medium voltage lines 5.8

High voltage lines 6.1 mts

Along the street Low and medium voltage lines 5.5

High voltage lines 5.8.mts

Else WhereLow and medium voltage and highvoltage lines up to 11kV bare 4.6

Low and medium voltage and high

voltage lines up to 11kV(Insulated) 4.0

High voltage lines above 11kV 5.2

Extra high voltage linesProvided minimum clearance across or

along

5.2 + 0.3 mt for every 33 kV6.1

Min. CLEARANCES in mts AT LINE

CROSSINGS


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CROSSINGS

Line

volt.

22kV 33kV 66kV 110kV 132kV 220kV

250V 2.44 2.44 2.44 2.75 3.05 4.58

11kV 2.44 2.44 2.44 2.75 3.05 4.58

22kV 2.44 2.44 2.44 2.75 3.05 4.58

33kV 2.44 2.44 2.44 2.75 3.05 4.58

66kV 2.44 2.44 2.44 2.75 3.05 4.58

110kV 2.75 2.75 2.75 2.75 3.05 4.58

132kV 3.05 3.05 3.05 3.05 3.05 4.58

220kV 4.58 4.58 4.58 4.58 4.58 4.58


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Rule 87: When two lines cross

It shall be as nearly at right angle as possible

As near to the support as possible

Support in the lower line shall not be erected below the upper line

Rule 88:Guarding at crossings :

Every guard wire is to be connected with earth at each point at whichits electrical continuity is broken.

Every guard wire shall have an actual breaking strength of not lessthan 635.02 kgs and if made of Iron or steel it shall be galvanized

Every guard wire or cross connected system of guard wire shall haveenough current carrying capacity so that they shall not melt or fuse

before the live line wire is rendered dead or removed

CLEARANCES of OH LINE &

S i Wi AS PER RULE 77


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Service Wire AS PER RULE 77 Rule 89:No service line or tapping shall be taken of from any over

headline except from the point of support

Rule 90: Earthing

All metal supports and metallic fittings attached there to shall bepermanently & efficiently earthed.

A continuous earth wire shall be secured fastened to each pole andconnected to the earth at 4 points per every 1.609 km

Each stay wire shall be earthed efficiently or a guy insulator shall beprovided in it at a height not less than 3 mts from the ground

Spacing between the 4 points shall be equal to the extent possible Alternatively each pole and metallic fittings attached there to shall beefficiently earthed.


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Metallic bearer wires supporting insulated low/ medium voltageservice lines shall be efficiently earthed/ insulated

Each stay wire shall be earthed unless guy insulator is placed at aheight not less than 10 from the ground

Rule 91 Safety devices

Every over head line laid along/ across the street shall have aprotective device to render it harmless when it brakes,

Every over head line Shall be fitted with an anti- climbing device toprevent unauthorized persons climbing the poles/towers

Rule92: Every over head line Shall be fitted with a device toprotect the line from lightning by diverting the surge to the earth

connected to earth mat


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The earthing lead from a LA shall not pass through any metallic pipebut taken directly to an earth electrode in a separate earth pit

Guard wire shall be earthed at each point where its electricalcontinuity is broken

Guard wire minimum breaking strength-635 kgs

To be galvanized if made of iron or steel Guard shall have sufficient capacity not to melt or fuse till the live

wire in contact is removed


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1/6th of the pole height be buried in the pit.

Base plate shall be provided underneath the pole for uniformdistribution of load on a larger area.

Pole shall be earthed through earths and combined earth resistanceshall not be more than 5 ohms

Danger boards to be fixed at a conspicuous position as per IS 2551 onevery motor, generator, transformer, Electrical equipment, pole


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