project report on electricity transmission and distribution

8/2/2019 Project Report on Electricity Transmission and Distribution

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Eletricity Transmission and Distributionc

Electric power transmission is the process in the transfer of electrical powerto consumers and refers to the 'bulk' transfer of electrical power from one

location to another. Transfer of electrical power from Generating Stations tothe industrial, commercial or residential consumers is as important aspower generation. Typically power transmission is between the power plantand a substation in the vicinity of a populated area. To satisfy variousinstantaneous demands from consumers requires an uninterrupted flow ofelectricity. In the energy delivery industry, the transmission systemfunctions in much the same way as the interstate highway system, servingas its major transport arteries. A power transmission system is sometimesreferred to as a "grid", which is a fully connected network of transmission

lines. The Regional Power Grids are established for optimal utilization ofthe power generated from the unevenly distributed power generatingstations, by having intra-regional and inter-regional power exchangesdepending upon day-to-day power availability and load conditions. Thesurplus power is transferred to the power deficit regions. Due to the largeamount of electric power involved, transmission normally takes place athigh voltage (110 kV or above). Electric power is usually sent over longdistances through overhead power transmission lines. Power is transmittedunderground in densely populated areas, such as large cities, but istypically avoided due to the high capacitive and resistive losses incurred.Redundant paths and lines are provided so that power can be routed fromany power plant to any load center, through a variety of routes, based onthe economics of the transmission path and the cost of power. The gridconsists of two infrastructures: the high-voltage transmission systems,which carry electricity from the power plants and transmit it hundreds ofmiles away, and the lower-voltage distribution systems, which drawelectricity from the transmission lines and distribute it to individualcustomers. High voltage is used for transmission lines to minimize electricallosses; however, high voltage is impractical for distribution lines. Electricity

distribution is the penultimate process in the delivery of electric power, i.e.the part between transmission and user purchase from an electricityretailer. It is generally considered to include medium-voltage (less than50kV) power lines, low-voltage electrical substations and pole-mountedtransformers, low-voltage (less than 1000V) distribution wiring andsometimes electricity meters. This interface features transformers that "stepdown" the transmission voltages to lower voltages for the distribution


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systems. Transformers located along the distribution lines further stepdown the voltage for household use. Substations also include electricalswitchgear and circuit breakers to protect the transformers and thetransmission system from electrical failures on the distribution lines. Circuitbreakers are also located along the distribution lines to locally isolateelectrical problems (such as short circuits caused by downed power lines).

Captive Power Generation

Captive Power refers to generation from a unit set up by industry for itsexclusive consumption. The estimates on captive power capacity in thecountry vary with the Central Electricity Authority putting the figure at about11600 MW while industry experts feel that it is much higher, close to 20000MW.

The industrial sector is the largest consumer of electricity. Besidespurchasing power from the utilities, a number of industries, viz. aluminum,cement, fertilizer, iron, steel, paper, sugar etc. have their own captivepower plants either to supplement the electricity supply from the utilities orfor generating electricity as a by-product through co-generation. Captivepower plants can be set up by industries to meet their own powerrequirements to enable them to tide over problems due to power shortagesand poor quality of supply. They can use any easily available fuel - coal,gas, diesel, fuel oil - or any other conventional or non-conventional so longas they are able to generate stable power for their requirements all throughthe year without any interruption.

Electrical Substation

A substation is a part of an electrical generation, transmission,

and distribution system. Substations transform voltage from high to low, or

the reverse, or perform any of several other important functions. Electric

power may flow through several substations between generating plant and

consumer, and its voltage may change in several steps.

A substation that has a step-up transformer increases the voltage while

decreasing the current, while a step-down transformer decreases the

voltage while increasing the current for domestic and commercial

distribution. The word substationcomes from the days before the

distribution system became a grid. The first substations were connected to
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only one station, where the generators were housed, and were subsidiaries

of that power station.

Elements Of Substation

Substations generally have switching, protection and control equipment,and transformers. In a large substation, circuit breakers are used to

interrupt any short circuits or overload currents that may occur on the

network. Smaller distribution stations may use recloser circuit

breakers or fuses for protection of distribution circuits. Substations

themselves do not usually have generators, although a power plant may

have a substation nearby. Other devices such as capacitors and voltage

regulators may also be located at a substation.

Substations may be on the surface in fenced enclosures, underground, orlocated in special-purpose buildings. High-rise buildings may have several

indoor substations. Indoor substations are usually found in urban areas to

reduce the noise from the transformers, for reasons of appearance, or to

protect switchgear from extreme climate or pollution conditions.

Where a substation has a metallic fence, it must be properly grounded (UK:

earthed) to protect people from high voltages that may occur during a fault

in the network. Earth faults at a substation can cause a ground potential

rise. Currents flowing in the Earth's surface during a fault can cause metal

objects to have a significantly different voltage than the ground under a

person's feet; this touch potentialpresents a hazard of electrocution.

1. Circuit Breaker:A circuit breaker is an automaticallyoperated electrical switch designed to protect an electrical circuit from

damage caused by overload or short circuit. Its basic function is to

detect a fault condition and, by interrupting continuity, to immediately

discontinue electrical flow. Unlike a fuse, which operates once and

then has to be replaced, a circuit breaker can be reset (either manually

or automatically) to resume normal operation. Circuit breakers are

made in varying sizes, from small devices that protect an individual

household appliance up to large switchgear designed to protect high

voltage circuits feeding an entire city.
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All circuit breakers have common features in their operation, although

details vary substantially depending on the voltage class, current

rating and type of the circuit breaker.

The circuit breaker must detect a fault condition; in low-voltage circuit

breakers this is usually done within the breaker enclosure. Circuit

breakers for large currents or high voltages are usually arranged

with pilot devices to sense a fault current and to operate the trip

opening mechanism. The trip solenoid that releases the latch is

usually energized by a separate battery, although some high-voltage

circuit breakers are self-contained with current transformers,

protection relays, and an internal control power source.

Once a fault is detected, contacts within the circuit breaker must open

to interrupt the circuit; some mechanically-stored energy (usingsomething such as springs or compressed air) contained within the

breaker is used to separate the contacts, although some of the

energy required may be obtained from the fault current itself. Small

circuit breakers may be manually operated; larger units

have solenoids to trip the mechanism, and electric motors to restore

energy to the springs.

2. Voltage Regulator:

A voltage regulator is an electrical regulator designed to automatically

maintain a constant voltage level. A voltage regulator may be a simple

"feed-forward" design or may include negative feedback control loops. It

may use an electromechanical mechanism, or electronic components.

Depending on the design, it may be used to regulate one or

more AC or DC voltages.

Electronic voltage regulators are found in devices such as computer power

supplies where they stabilize the DC voltages used by the processor and

other elements. In automobile alternators and central powerstation generator plants, voltage regulators control the output of the plant.

In an electric power distribution system, voltage regulators may be installed

at a substation or along distribution lines so that all customers receive

steady voltage independent of how much power is drawn from the line.
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3. Busbar:

In electrical power distribution, a busbar is a stripof copper or aluminum that conducts electricity within

a switchboard, distribution board, substation or other electrical apparatus.

The size of the busbar determines the maximum amount of current that can

be safely carried. Busbars can have a cross-sectional area of as little as

10 mm but electrical substations may use metal tubes of 50 mm in

diameter (1,963 mm) or more as busbars, and an aluminum smelter will

have very large busbars used to carry tens of thousands of amperes to

the electrochemical cells that produce aluminum from molten salts.

Busbars are typically either flat strips or hollow tubes as these shapes

allow heat to dissipate more efficiently due to their high surface

area to cross-sectional area ratio. The skin effect makes 5060

Hz AC busbars more than about 8 mm (1/3 in) thick inefficient, so hollow or

flat shapes are prevalent in higher current applications. A hollow section

has higher stiffness than a solid rod of equivalent current-carrying capacity,

which allows a greater span between busbar supports in outdoor

switchyards.A busbar may either be supported on insulators, or else insulation may

completely surround it. Busbars are protected from accidental contact

either by a metal earthed enclosure or by elevation out of normal

reach. Neutral busbars may also be insulated. Earth busbars are typically

bolted directly onto any metal chassis of their enclosure. Busbars may be

enclosed in a metal housing, in the form of bus duct or busway,

segregated-phase bus, or isolated-phase bus.

Busbars may be connected to each other and to electrical apparatus bybolted or clamp connections. Often joints between high-current bus

sections have matching surfaces that are silver-plated to reduce the

contact resistance. At extra-high voltages (more than 300 kV) in outdoor

buses, corona around the connections becomes a source of radio-
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frequency interference and power loss, so connection fittings designed for

these voltages are used.

Busbars are typically contained inside of either a distribution board or

busway.

4. Relays:

In electrical engineering, a protective relay is a complex

electromechanical apparatus, often with more than one coil, designed to

calculate operating conditions on an electrical circuit and trip circuit

breakers when a fault is detected. Unlike switching type relays with fixed

and usually ill-defined operating voltage thresholds and operating times,

protective relays have well-established, selectable, time/current (or otheroperating parameter) curves. Such relays may be elaborate, using arrays

of induction disks, shaded-pole magnets, operating and restraint coils,

solenoid-type operators, telephone-relay contacts, and phase-shifting

networks. Protection relays respond to such conditions as over-current,

over-voltage, reverse power flow, over- and under- frequency. Distance

relays trip for faults up to a certain distance away from a substation but not

beyond that point. An important transmission line or generator unit will have

cubicles dedicated to protection, with many individual electromechanical

devices. The various protective functions available on a given relay are

denoted by standard ANSI Device Numbers. For example, a relay including

function 51 would be a timed overcurrent protective relay.

Design and theory of these protective devices is an important part of the

education of an electrical engineer who specializes in power systems.

Today these devices are nearly entirely replaced with microprocessor-

based digital protective relays (numerical relays) that emulate their

electromechanical ancestors with great precision and convenience in

application. By combining several functions in one case, numerical relays

also save capital cost and maintenance cost over electromechanical relays.

However, due to their very long life span, tens of thousands of these "silent

sentinels" are still protecting transmission lines and electrical apparatus all

over the world.
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5. Ground Wire:

In electrical engineering,ground or earth may be the reference point inan electrical circuit from which other voltages are measured, or a common

return path for electric current, or a direct physical connection to the Earth.

Electrical circuits may be connected to ground (earth) for several reasons.

In mains powered equipment, exposed metal parts are connected to

ground to prevent contact with a dangerous voltage if electrical

insulation fails. Connections to ground limit the build-up of staticelectricity

when handling flammable products or when repairing electronic devices. In

some telegraph and power transmission circuits, the earth itself can beused as one conductor of the circuit, saving the cost of installing a separate

return conductor.

For measurement purposes, the Earth serves as a (reasonably) constant

potential reference against which other potentials can be measured. An

electrical ground system should have an appropriate current-carrying

capability in order to serve as an adequate zero-voltage reference level.

In electronic circuit theory, a "ground" is usually idealized as an

infinite source or sinks for charge, which can absorb an unlimited amount ofcurrent without changing its potential. Where a real ground connection has

a significant resistance, the approximation of zero potential is no longer

valid. Stray voltages or earth potential rise effects will occur, which may

create noise in signals or if large enough will produce an electric shock

hazard.

The use of the term ground (or earth) is so common in electrical and

electronics applications that circuits in portable electronic devices such

as cell phones and media players as well as circuits in vehicles such asships, aircraft, and spacecraft may be spoken of as having a "ground"

connection without any actual connection to the Earth. This is usually a

large conductor attached to one side of the power supply (such as the

"ground plane" on a printed circuit board) which serves as the common

return path for current from many different components in the circuit.
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6. Overhead powerlines:

An overhead power line is an electric power transmission line suspended

by towers or utility poles. Since most of the insulation is provided by air,overhead power lines are generally the lowest-cost method

of transmission for large quantities of electric energy. Towers for support of

the lines are made of wood (as-grown or laminated), steel (either lattice

structures or tubular poles), concrete, aluminum, and occasionally

reinforced plastics. The bare wire conductors on the line are generally

made of aluminum (either plain or reinforced with steel, or sometimes

composite materials), though some copper wires are used in medium-

voltage distribution and low-voltage connections to customer premises. A

major goal of overhead power line design is to maintain adequate

clearance between energized conductors and the ground so as to prevent

dangerous contact with the line.[1]Today overhead lines are routinely

operated at voltages exceeding 765,000 volts between conductors, with

even higher voltages possible in some cases.

Overhead power transmission lines are classified in the electrical power

industry by the range of voltages:

Low voltage less than 1000 volts, used for connection between aresidential or small commercial customer and the utility.

Medium Voltage (Distribution) between 1000 volts (1 kV) and to about

33 kV, used for distribution in urban and rural areas.

High Voltage (subtransmission less than 100 kV; subtransmission or

transmission at voltage such as 115 kV and 138 kV), used for sub-

transmission and transmission of bulk quantities of electric power and

connection to very large consumers.

Extra High Voltage (transmission) over 230 kV, up to about 800 kV,used for long distance, very high power transmission.

Ultra High Voltage higher than 800 kV.

7. Lighting Arrester:
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A lightning arrester is a device used on electrical power systems to

protect the insulation on the system from the damaging effect of

lightning. Metal oxide varistors (MOVs) have been used for power system

protection since the mid 1970s. The typical lightning arrester also known

as surge arrester has a high voltage terminal and a ground terminal. Whena lightning surge or switching surge travels down the power system to the

arrester, the current from the surge is diverted around the protected

insulation in most cases to earth.

8. Current Transformers (CTs):These can be used for monitoring

current or for transforming primary current into reduced secondary current

used for meters, relays, control equipment and other instruments. CTs that

transform current isolate the high voltage primary, permit grounding of the

secondary, and step-down the magnitude of the measured current to a

standard value that can be safely handled by the instrument. To determine

which CT is appropriate for a particular application, it is important to

understand the following characteristics that are used to classify current

transformers.

Ratio

The CT ratio is the ratio of primary current input to secondary current

output at full load. For example, a CT with a ratio of 300:5 is rated for 300

primary amps at full load and will produce 5 amps of secondary current

when 300 amps flow through the primary. If the primary current changes

the secondary current output will change accordingly. For example, if 150

amps flow through the 300 amp rated primary the secondary current output

will be 2.5 amps (150:300 = 2.5:5).

Polarity

The Polarity of a CT is determined by the direction the coils are wound

around the core for the CT (clockwise or counterclockwise) and by the way

the leads are brought out of the transformer case. All current transformers

are subtractive polarity and will have the following designations to guide
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proper installation: ((H1) Primary current, line facing direction; (H2) Primary

current, load facing direction; and (X1) Secondary current. Taking care to

observe proper polarity is important when installing and connecting current

transformers to power metering and protective relays.

Accuracy Class

Accuracy Class describes the performance characteristics of a CT and the

maximum burden allowable on the CTs secondary.

Depending on their Accuracy Class, CTs are divided into Metering

Accuracy CTs or Relaying Accuracy CTs (Protection CTs). A CT can have

ratings for both groups. Metering Accuracy CTs are rated for specified

standard burdens and designed to be highly accurate from very low currentto the maximum current rating of the CT. Because of their high degree of

accuracy, these CTs are typically used by utility companies for measuring

usage for billing purposes. Relaying Accuracy CTs are not as accurate as

Metering Accuracy CTs. They are designed to perform with a reasonable

degree of accuracy over a wider range of current. These CTs are typically

used for supplying current to protective relays. The wider range of current

allows the protective relay to operate at different fault levels. The CT

Accuracy Class is listed on the label or the nameplate of the CT and is

comprised of three parts: rated ratio accuracy rating, class rating, and

maximum burden (Figure 3). Rated Ratio Accuracy RatingThe first part of

the CT Accuracy Class is a number which is the rated ratio expressed as a

percent. For example, a CT with an accuracy class of 0.3 is certified by the

manufacturer to be accurate to within 0.3 percent of its rated ratio value for

a primary current of 100 percent of rated ratio. CT Class RatingThe

second part of the CT Accuracy Class is a letter that designates the

application for which the CT is rated. Metering CTs are designated with the

letter B. Relaying CTs have several different letter designations:

C The CT has low leakage flux. (Accuracy can be calculated before

manufacturing.)

T The CT can have significant leakage flux. (Accuracy must be

determined by testing at the factory.)


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HThe CT accuracy is applicable within the entire range of secondary

currents from 5 to 20 times the nominal CT rating. (Typically wound CTs.)

L The CT accuracy applies at the maximum rated secondary burden at

20 time rated only. The ratio accuracy can be up to four times greater thanthe listed value, depending on connected burden and fault current.

(Typically window, busing, or bar-type CTs.)

Burden

The third part of the CT Accuracy Class is the maximum burden allowed forthe CT. This is the load that may be imposed on a transformer secondary

without causing an error greater than the stated accuracy classification. For

Metering Class CTs burden is expressed as ohms impedance. For

Protection-class CTs burden is express as volt-amperes (VA). Protection-

class CT burdens are displayed as the maximum secondary volts allowable

if 20 times the CT rating were to flow through the secondary circuit (100

amperes with a five ampere nominal CT secondary).

CT Shorting

CTs should remain shorted during installation until secondary wiring is

complete. A shorting screw inserted through the shorting bar ties isolated

terminal strip points together. Any shorting winding effectively shorts the

entire CT.

Potential Transformer:

The potential transformer works along the same principle of other

transformers. It converts voltages from high to low. It will take the

thousands of volts behind power transmission systems and step the

voltage down to something that meters can handle. These transformers


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work for single and three phase systems, and are attached at a point where

it is convenient to measure the voltage.The biggest feature that a potential transformer has over regular

transformers is that the voltage conversion is constant and linear. That is tosay, if the first day of operation 50,000 volts is stepped to 50 volts, then on

the last day of operation 50,000 steps to 50 volts. Linearity states that when

the voltage drops in a linear fashion, then the stepped down voltage drops

accordingly. This feature ensures that the meter will scale accordingly. The

potential transformer makes the measure of very high voltages much

easier.Potential Transformer is designed for monitoring single-phase and three-phase power line voltages in power metering applications.

The ratio and phase-angle inaccuracies of any standard ASA accuracy

class of potential transformer are so small that they may be neglected for

protective-relaying purposes if the burden is within the "thermal" volt-

ampere rating of the transformer. This thermal volt-ampere rating

corresponds to the full-load rating of a power transformer. It is higher than

the volt-ampere rating used to classify potential transformers as to

accuracy for metering purposes. Based on the thermal volt-ampere rating,the equivalent-circuit impedances of potential transformers are comparable

to those of distribution transformers.

The "burden" is the total external volt-ampere load on the secondary at

rated secondary voltage. Where several loads are connected in parallel, it

is usually sufficiently accurate to add their individual volt-amperes

arithmetically to determine the total volt-ampere burden. If a potential

transformer has acceptable accuracy at its rated voltage, it is suitable over

the range from zero to 110% of rated less voltage. Operation in excess of

10% overvoltage may cause increased errors and excessive heating.

Where precise accuracy data are required, they can be obtained from ratio-

correction-factor curves and phase-angle-correction curves supplied by the

manufacturer.


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The primary terminals can be connected either in line-to-line or in line-to-neutral configuration. Fused transformer models are designated by a suffixof "F" for one fuse or "FF" for two fuses.

A Potential Transformer is a special type of transformer that allows metersto take readings from electrical service connections with higher voltage(potential) than the meter is normally capable of handling without atpotential transformer

9.Electricity Pylon:

A transmission tower (colloquially termed an electricity pylon) is a

tall structure, usually a steel lattice tower, used to support an overhead

power line. They are used in high-voltage AC and DC systems, and come

in a wide variety of shapes and sizes. Typical height ranges from 15 to 55meters (49 to 180 ft), although heights in excess of 300 meters (980 ft)

exist. In addition to steel, other materials may be used, including concrete

and wood.

Four major functions of transmission towers are in use: suspension towers,

terminal towers, tension towers, and transposition towers. Some

transmission towers combine these basic functions. Transmission towers

and their overhead power lines are often considered to be a form of visual

pollution. Methods to reduce the visual impact include undergrounding.
http://en.wikipedia.org/wiki/Structurehttp://en.wikipedia.org/wiki/Lattice_towerhttp://en.wikipedia.org/wiki/Overhead_power_linehttp://en.wikipedia.org/wiki/Overhead_power_linehttp://en.wikipedia.org/wiki/Overhead_power_linehttp://en.wikipedia.org/wiki/Dead-end_towerhttp://en.wikipedia.org/wiki/Transposing_pylonhttp://en.wikipedia.org/wiki/Visual_pollutionhttp://en.wikipedia.org/wiki/Visual_pollutionhttp://en.wikipedia.org/wiki/Visual_pollutionhttp://en.wikipedia.org/wiki/Undergroundinghttp://en.wikipedia.org/wiki/Undergroundinghttp://en.wikipedia.org/wiki/Visual_pollutionhttp://en.wikipedia.org/wiki/Visual_pollutionhttp://en.wikipedia.org/wiki/Transposing_pylonhttp://en.wikipedia.org/wiki/Dead-end_towerhttp://en.wikipedia.org/wiki/Overhead_power_linehttp://en.wikipedia.org/wiki/Overhead_power_linehttp://en.wikipedia.org/wiki/Lattice_towerhttp://en.wikipedia.org/wiki/Structure


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Transmission substation:A transmission substation connectstwo or more transmission lines. The simplest case is where all transmission

lines have the same voltage. In such cases, the substation contains high-

voltage switches that allow lines to be connected or isolated for fault

clearance or maintenance. A transmission station may have

transformers to convert between two transmission voltages, voltage

control/power factor correction devices such as capacitors, reactors

or static VAR compensators and equipment such as phase shifting

transformers to control power flow between two adjacent power systems.

Transmission substations can range from simple to complex. A small

"switching station" may be little more than a bus plus some circuit breakers.

The largest transmission substations can cover a large area (several

acres/hectares) with multiple voltage levels, many circuit breakers and alarge amount of protection and control equipment (voltage and

current transformers, relays and SCADA systems). Modern substations

may be implemented using International Standards such as IEC61850.

Distribution Substation:

A distribution substation transfers power from the transmission system to

the distribution system of an area. It is uneconomical to directly connectelectricity consumers to the main transmission network, unless they use

large amounts of power, so the distribution station reduces voltage to a

value suitable for local distribution.

The input for a distribution substation is typically at least two transmission

or sub transmission lines. Input voltage may be, for example, 115 kV, or

whatever is common in the area. The output is a number of feeders.

Distribution voltages are typically medium voltage, between 2.4 and 33 kV

depending on the size of the area served and the practices of the localutility.

The feeders run along streets overhead (or underground, in some cases)

and power the distribution transformers at or near the customer premises.

In addition to transforming voltage, distribution substations also isolate

faults in either the transmission or distribution systems. Distribution
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substations are typically the points of voltage regulation, although on long

distribution circuits (of several miles/kilometers), voltage regulation

equipment may also be installed along the line.

The downtown areas of large cities feature complicated distribution

substations, with high-voltage switching, and switching and backup

systems on the low-voltage side. More typical distribution substations have

a switch, one transformer, and minimal facilities on the low-voltage side.

Collector Substation:

In distributed generation projects such as a wind farm, a collector

substation may be required. It somewhat resembles a distribution

substation although power flow is in the opposite direction, from many wind

turbines up into the transmission grid. Usually for economy of constructionthe collector system operates around 35 kV and the collector substation

steps up voltage to a transmission voltage for the grid. The collector

substation can also provide power factor correction if it is needed, metering

and control of the wind farm. In some special cases a collector substation

can also contain an HVDC static inverter plant.

Collector substations also exist where multiple thermal or hydroelectric

power plants of comparable output power are in proximity. Examples for

such substations are Brauweiler in Germany and Hradec in the CzechRepublic, where power is collected from nearby lignite-fired power plants. If

no transformers are installed for increase of voltage to transmission level,

the substation is a switching station.
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project report on electricity transmission and distribution

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