Muhammad Waqas 09-EE-119 UET, Taxila

Internship report of 132 kv

Grid station

Submitted By:

Muhammad Waqas

09-EE-119

UET Taxila

Muhammad Waqas 09-EE-119 UET, Taxila

Contents ACKNOWLEDGEMENTS ............................................................................................................................. 3

Dedication ................................................................................................................................................. 4

EXECUTIVE SUMMARY .............................................................................................................................. 5

Grid and the Sub Station: .......................................................................................................................... 6

Functions of a Grid Station: ...................................................................................................................... 8

Advantages of the Grid System: ................................................................................................................ 9

Disadvantages of the Grid System ............................................................................................................ 9

Equipment Used in a Sub-Station: .......................................................................................................... 10

Bus Bars: .................................................................................................................................................. 10

Relays: ..................................................................................................................................................... 13

Function of Relay: ............................................................................................................................... 13

Qualities of a Good Relay: ....................................................................................................................... 13

Isolator Switch: ....................................................................................................................................... 14

Circuit Breaker: ....................................................................................................................................... 17

Operation: ............................................................................................................................................... 19

Switch board and Control Room: ............................................................................................................ 19

Refrences: ............................................................................................................................................... 22

Muhammad Waqas 09-EE-119 UET, Taxila

ACKNOWLEDGEMENTS

First of all I will like to thank Allah, who blessed us with ability and

wisdom to complete this project. especially thanks to IESCO who

provided us an opportunity of enhancing our professional experience and

her members and especially workers so that they have cooperated with

us. I wish to express our love and gratitude to our family and friends; for

their understanding & endless love, and help they provide while

preparing this report. My report will remain incomplete if I

don’tmention the sincere efforts of those gentlemen who helped and

guided me in completionof my internship and this report. First of all I

want to thanks to ALLAH Almighty; I also want to thanks to my worthy

teachers the main source of enlightenment of our minds and the

development of natural potentials, then I m thankful to the staff

who cooperated with me and I become able to do this work.

Muhammad Waqas

09-EE-119

UET Taxila

Muhammad Waqas 09-EE-119 UET, Taxila

Dedication

“I dedicate my work firstly to Hazrat Muhammad (s.a.w.w) and

also my respected parents and teachers whom prayers able me

to do such a work and able me to face the world.”

Muhammad Waqas 09-EE-119 UET, Taxila

EXECUTIVE SUMMARY

An electrical grid station is an interconnection point between two

transmission ring circuits, often between two geographic regions. They

might have a transformer, depending on the possibly different voltages,

so that the voltage levels can be adjusted as needed.

Grid station regulates and controls the power between interconnected

transmission lines to increase the reliability of the power system. It

receive power from the power station at extremely high voltage and then

convert these voltage to some low levels and supplied electric power to

the sub stations or to other grid stations at the same voltage level

according to the requirements.

National grid system of Pakistan contains an interconnected group of

transmission lines in a ring system. It covers most of the power stations

of the country in this single ring and supplied electric power to the

different areas of the country. Main function of the grid station is

switching between the connected line stations and the load centers. The

electric power is produce at the power station,which are located at

favorable places, generally quite away from theconsumers. It is

delivered to the consumer through a large network of transmission and

distribution. At many place in the line of powersystem, it may be

desirable and necessary to change somecharacteristic ( e.g. Voltage, ac

to de, frequency p.f. etc.) of electricsupply. This is accomplished by

suitable apparatus called sub-stationfor example, generation voltage

(11kv or 6.6kv) at the power station isstepped up to high voltage (Say

220kv to 132kv) for transmission of electric power. Similarly near the

consumer’s localities, the voltage mayhave to be stepped down to

utilization level. This job is againaccomplished by suitable apparatus

called sub-station.

Muhammad Waqas 09-EE-119 UET, Taxila

Grid and the Sub Station: An electrical power substation is a conversion point between

transmission level voltages (such as 138Kv) and distribution level

voltages (such as 11Kv). A substation has one or more step-down

transformers and serves a regional area such as part of a city or

neighborhood. Substations are connected to each other by the

transmission ring circuit system by equipments.

An electrical grid station is an interconnection point between two

transmission ring circuits, often between two geographic regions. They

might have a transformer, depending on the possibly different voltages,

so that the voltage levels can be adjusted as needed.

The interconnected network of sub stations is called the grid, and may

ultimately represent an entire multi-state region. In this configuration,

loss of a small section, such as loss of a power station, does not impact

the grid as a whole, nor does it impact the more localized

neighborhoods, as the grid simply shifts its power flow to compensate,

giving the power station operator the opportunity to effect repairs

without having a blackout.

Definition of sub-station :

The assembly of apparatus used to change some characteristics (e.g.

Voltage level, freq, p.f. etc) of electric supply is called sub-station”.

Classification of sub-station:

There are several ways of classifying sub-station. However the two most

important way of classifying them are:-

I) According to service requirement

According to service requirement sub-station may be classified into:

1) Transformer sub-station :

Muhammad Waqas 09-EE-119 UET, Taxila

Those sub-station which change the voltage level of electrical supply

are called TIF s/s.

2) Switching sub-station :-

These sub-station simply perform the switching operation of power line

3) Power factor correction S/S :-

These sub-station which improve the p.f. of the system are called p.f.

correction s/s. these are generally located at receiving end s/s.

4) Frequency changer S/S :-

Those sub-stations, which change the supply frequency, are known as

frequency changer s/s. Such s/s may be required for industrial

utilization.

4) Converting sub-station :-

That sub-station which change a.c. power into d.c. power are called

converting s/s ignition is used to convert AC to dc power for traction,

electroplating, electrical welding etc.

5) Industrial sub-station :

Those sub-stations, which supply power to individual industrial

concerns, are known as industrial sub-station.

II) According to constructional features :

According to constructional features, the sub-station are classified as

1) Outdoor Sub-Station :

For voltage beyond 66KV, equipment is invariably installed outdoor. It

is because for such Voltage the clearances between conductor and the

Muhammad Waqas 09-EE-119 UET, Taxila

space required for switches, C.B. and other equipment becomes so great

that it is not economical to install the equipment indoor.

2) Indoor Sub-station :

For voltage up to 11KV, the equipment of the s/s is installed indoor

because of economic consideration. However, when the atmosphere is

contaminated with impurities, these sub-stations can be erected for

voltage up to 66KV.

3) Underground sub-station :

In thickly populated areas, the space available for equipment and

building is limited and the cost of the land is high.Under such situations,

the sub-station is created underground.

Functions of a Grid Station:

A Grid Station has the following functions…

1 - Supply of required electrical power.

2 - Maximum possible coverage of the supply network.

3 - Maximum security of supply.

4 - Shortest possible fault-duration.

5 - Optimum efficiency of plants and the network.

6 - Supply of electrical power within targeted frequency limits, (49.5 Hz

and

50.5 Hz).

7 - Supply of electrical power within specified voltage limits.

8 - Supply of electrical energy to the consumers at the lowest cost.

An important function performed by a grid station is switching, which is

the connecting and disconnecting of transmission lines or other

Muhammad Waqas 09-EE-119 UET, Taxila

components to and from the system. Switching events may be "planned"

or "unplanned".

A transmission line or other component may need to be de energized for

maintenance or for new construction; for example, adding or removing a

transmission line or a transformer.

To maintain reliability of supply, no company ever brings down its

whole system for maintenance. All work to be performed, from routine

testing to adding entirely new substations, must be done while keeping

the whole system running.

Perhaps more importantly, a fault may develop in a transmission line or

any other component. Some examples of this: a line is hit by lightning

and develops an arc, or a tower is blown down by a high wind. The

function of the grid station is to isolate the faulted portion of the system

in the shortest possible time.

Advantages of the Grid System:

Any time electricity is available for the consumers at lower cost.

Flow of electrical energy is continuous and sure.

It is possible to fulfill the emergency demand of power.

Better regulation of the voltages.

Improved power factor

It is possible to govern the generator according to the load.

Safe transmission system.

Reduced fault timings.

Controlled frequency range.

Disadvantages of the Grid System:

Cost of the control system is increased and their maintenance is

complicated.

Power system is affected from the environmental factors.

This system is unsafe during the war.

Muhammad Waqas 09-EE-119 UET, Taxila

Extended system is going to complexity.

Due to the expensive equipments, additional load occurred on the

consumers.

During short circuit condition it is impossible to maintain the

continuity of power.

High initial and maintenance cost.

During load shedding, capacity of industries connected with the

grid is reduced which cause to industrial development problem.

For maintenance, qualified staff is required and for that reason our

country has to spend more money to call expert engineers from

other countries.

Equipment Used in a Sub-Station:

The equipment required for a transformer Sub-Station depends upon the

type of Sub-Station, Service requirement and the degree of protection

desired. TIF Sub-Station has the following major equipments.

Bus Bars:

When a no. of lines operating at the same voltage have to be directly

connected electrically, bus-bar are used, it is made up of copper or

aluminum bars (generally of rectangular X-Section) and operate at

constant voltage. Duplicate bus-bar, generally it consists of two bus-bars

a “main” bus-bar and spare bus-bar. The incoming and outgoing lines

can be connected to either b/b. With the help of a bus-bar coupler, which

consist of a circuit breaker and isolators. However, in case of repair of

main bus-bar or fault accusing on it, the continuity of supply to the

circuit can be maintain by transforming it to the spare bus-bar for

voltage exceeding 33KV,Duplicate bus-bar is frequently used.

Following bus bar schemes are used in the field of electrical power

system

Muhammad Waqas 09-EE-119 UET, Taxila

Single bus bar scheme

Sectionalizing bus bar scheme

Double bus bar scheme

Terminal section scheme

Main and transfer bus scheme

Ring bus scheme

Transformer:

A transformer is a device that transfers electrical energy from

one circuit to another circuit through inductively conductors—the

transformer's coils. A varying current in the first or primary winding

creates a varying magnetic flux in the transformer's core and thus a

varying field through the secondary winding. This varying magnetic

field induces a varying electromotive force (EMF) or "voltage" in the

secondary winding. This effect is called mutual induction.

If a load is connected to the secondary, an electric current will flow in

the secondary winding and electrical energy will be transferred from the

primary circuit through the transformer to the load. In an ideal

transformer, the induced voltage in the secondary winding (Vs) is in

proportion to the primary voltage (Vp), and is given by the ratio of the

number of turns in the secondary (Ns) to the number of turns in the

primary (Np) as follows:

By appropriate selection of the ratio of turns, a transformer thus allows

an alternating current (AC)voltage to be "stepped up" by

making Ns greater than Np, or "stepped down" by making Ns less

than Np.

Muhammad Waqas 09-EE-119 UET, Taxila

In the vast majority of transformers, the windings are coils wound

around a ferromagnetic core, air-core transformers being a notable

exception.

Transformers range in size from a thumbnail-sized coupling transformer

hidden inside a stage microphone to huge units weighing hundreds of

tons used to interconnect portions of power grids. All operate with the

same basic principles, although the range of designs is wide. While new

technologies have eliminated the need for transformers in some

electronic circuits, transformers are still found in nearly all electronic

devices designed for household ("mains") voltage. Transformers are

essential for high voltage power transmission, which makes long

distance transmission economically practical. .

Muhammad Waqas 09-EE-119 UET, Taxila

Relays:

A relay is a device that “detects” the fault and “directs” the circuit

breaker to isolate the faulty part/equipment from the system.

Function of Relay:

A relay performs three functions.

Sensing.

Comparing.

Tripping.

It senses the “fault”. This is done by the relay to “respond” to the

change if any, in the currents passing through it.It compares the current

through it with the designed value of current. It responds only if the

current through it is different from its designed current rating.If the

current through it is different from its designed current rating, it sends

information to the circuit breaker for tripping.

Qualities of a Good Relay:

In order to perform its function successfully, a relay should have the

following qualities.

Selectivity.

Speed.

Sensitivity

Reliability

Simplicity.

Economical.

Muhammad Waqas 09-EE-119 UET, Taxila

Materials that do not have any free electrons. Because of this fact, they

do not tend to share their electrons very easily and do not make good

conductors of electrical currents.

Electrical insulation is the absence of electrical conduction.

Electronic band theory (a branch of physics) says that a charge will flow

if states are available into which electrons can be excited. This allows

electrons to gain energy and thereby move through a conductor such as

a metal. If no such states are available, the material is an insulator.

Most insulators have a large band gap. This occurs because the

"valence" band containing the highest energy electrons is full, and a

large energy gap separates this band from the next band above it. There

is always some voltage (called the breakdown voltage) that will give the

electrons enough energy to be excited into this band. Once this voltage is

exceeded, the material ceases being an insulator, and charge will begin

to pass through it. However, it is usually accompanied by physical or

chemical changes that permanently degrade the material's insulating

properties.

Isolator Switch:

In electrical engineering, isolator switch is used to make sure that an

electrical circuit can be completely de-energized for service or

maintenance. Such switches are often found in electrical

distribution and industrial applications where machinery must have its

source of driving power removed for adjustment or repair. High-voltage

isolation switches are used in electrical substations to allow isolation of

apparatus such as circuit breakers and transformers, and transmission

lines, for maintenance. Often the isolation switch is not intended for

normal control of the circuit and is only used for isolation.

Muhammad Waqas 09-EE-119 UET, Taxila

Isolator switches have provisions for a padlock so that inadvertent

operation is not possible (see: Lock and tag). In high voltage or complex

systems, these padlocks may be part of a trapped-key interlock system to

ensure proper sequence of operation. In some designs the isolator switch

has the additional ability to earth the isolated circuit thereby providing

additional safety. Such an arrangement would apply to circuits which

inter-connect power distribution systems where both end of the circuit

need to be isolated.

The major difference between an isolator and a circuit breaker is that an

isolator is an off-load device intended to be opened only after current

has been interrupted by some other control device. Safety regulations of

the utility must prevent any attempt to open the disconnect or while it

supplies a circuit.

Standards in some countries for safety may require either local motor

isolators or lockable overloads (which can be padlocked).

Current Transformer:

In electrical engineering, a current transformer (CT) is used for

measurement of electric currents. Current transformers, together

with voltage transformers (VT) (potential transformers (PT)), are known

as instrument transformers. When current in a circuit is too high to

directly apply to measuring instruments, a current transformer produces

a reduced current accurately proportional to the current in the circuit,

which can be conveniently connected to measuring and recording

instruments. A current transformer also isolates the measuring

instruments from what may be very high voltage in the monitored

circuit. Current transformers are commonly used in metering

and protective relays in the electrical power industry.

Usage:

Muhammad Waqas 09-EE-119 UET, Taxila

Current transformers are used extensively for measuring current and

monitoring the operation of the power grid. Along with voltage leads,

revenue-grade CTs drive the electrical utility's watt-hour meter on

virtually every building with three-phase service and single-phase

services greater than 200 amp.

The CT is typically described by its current ratio from primary to

secondary. Often, multiple CTs are installed as a "stack" for various

uses. For example, protection devices and revenue metering may use

separate CTs to provide isolation between metering and protection

circuits, and allows current transformers with different characteristics

(accuracy, overload performance) to be used for the different purposes.

Potential Transformers:

Voltage transformers (VT) or potential transformers (PT) are another

type of instrument transformer, used for metering and protection in high-

voltage circuits. They are designed to present negligible load to the

supply being measured and to have a precise voltage ratio to accurately

step down high voltages so that metering and protective relay equipment

can be operated at a lower potential. Typically the secondary of a

voltage transformer is rated for 69 V or 120 V at rated primary voltage,

to match the input ratings of protective relays.

The transformer winding high-voltage connection points are typically

labeled as H1, H2 (sometimes H0 if it is internally grounded) and X1, X2

and sometimes an X3 tap may be present. Sometimes a second isolated

winding (Y1, Y2, Y3) may also be available on the same voltage

transformer. The high side (primary) may be connected phase to ground

or phase to phase. The low side (secondary) is usually phase to ground.

Muhammad Waqas 09-EE-119 UET, Taxila

The terminal identifications (H1, X1, Y1, etc.) are often referred to as

polarity. This applies to current transformers as well. At any instant

terminals with the same suffix numeral have the same polarity and

phase. Correct identification of terminals and wiring is essential for

proper operation of metering and protective relays.

Some meters operate directly on the secondary service voltages at or

below 600 V. VTs are typically used for higher voltages (for example,

765 kV for power transmission), or where isolation is desired between

the meter and the measured circuit.

There are primarily three types of voltage transformers(VT):

electromagnetic, capacitor, and optical. The electromagnetic voltage

transformer is a wire-wound transformer. The capacitor voltage

transformer uses a capacitance potential divider and is primarily used at

higher voltages due to a lower cost than a electromagnetic VT. An

optical voltage transformer exploits the electrical properties of optical

materials.

Circuit Breaker:

A circuit breaker is automatic operated 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.

Muhammad Waqas 09-EE-119 UET, Taxila

Muhammad Waqas 09-EE-119 UET, Taxila

Operation:

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.

Switch board and Control Room:

An electric switchboard is a device that directs electricity from one

source to another. It is an assembly of panels, each of which

contains switches that allow electricity to be redirected. The operator is

protected from electrocution by safety switches and fuses.

There can also be controls for the supply of electricity to the

switchboard, coming from a generator or bank of electrical generators,

especially frequency control of AC power and load sharing controls,

plus gauges showing frequency and perhaps a synchroscope. The

amount of power going into a switchboard must always equal to the

power going out to the loads. Inside the switchboard there is a bank

of bus bars - generally wide strips of copper to which the switchgear is

Muhammad Waqas 09-EE-119 UET, Taxila

connected. These act to allow the flow of large currents through the

switchboard, and are generally bare and supported by insulators.

A control room is a room serving as an operations centre where a facility

or service can be monitored and controlled.

A control room can, at times, be designated as an area of refuge,

particularly in high risk facilities, such as a nuclear power station or a

petrochemical facility, as an accidental fire can have severe

repercussions to the surrounding environment. As is typical for all areas

of refuge, occupants must be provided with guaranteed life support and

guarantee of functionality of the items they are intended to control for

the anticipated design-basis fire event.

It is not unusual to provide control rooms with gaseous fire suppression

systems to safeguard its contents and occupants.

The primary equipment in control rooms is housed in multi-function

cabinets. Since the control equipment is intended to control other items

in the surrounding facility, it follows that these (often fire-resistance

rated) service rooms require many penetrations. Due to routine

equipment updates, penetrates, such as cables are subject to frequent

changes. It follows that an operating control room maintenance program

must include vigilant fire stop maintenance for code compliance and for

gaseous fire suppression systems to work as well. Due to the nature of

the sensitive equipment inside control room cabinets, it is useful to

ensure the use of "T-rated" fire stops, that are massive and thick enough

to absorb penetrate heat in an effort to reduce heat transmission to the

inside of the control room. It is also not uncommon to place control

rooms under positive air pressure to prevent smoke from entering. To

put into nutshell, function of the control room is to monitor, control,

switching of the electrical power and to protect the whole system from

Muhammad Waqas 09-EE-119 UET, Taxila

any harmful problem with the help of the associated electrical

equipments inside the control room.

Components of the Control Room:

Protection Relays

Auto Transformer Bank (ATB) Panel

Bus Bar Panel

Shunt Reactor Panel

Rectifier’s

Fire Extinguisher

Battery Room

Isolator control panel

Circuit breaker control panel

Tape changer control panel

Lay out drawings

Earthing System:

In electrical engineering, ground or earth may be the reference point in

an 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 static electricity when handling flammable products or when repairing

electronic devices. In some telegraph and power transmission circuits,

the earth itself can be used as one conductor of the circuit, saving the

cost of installing a separate return conductor.

Muhammad Waqas 09-EE-119 UET, Taxila

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 sink for charge, which can absorb an unlimited amount

of current 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 as

ships, 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

Refrences:

www.google.com

www.wikipedia.org

www.scribed.com

www.engineerguarge.com

www.howstuffwork.com

Muhammad Waqas 09-EE-119 UET, Taxila

Principles of Electrical Power System

V.K MEHTA

ROHIT MEHTA

Transmission and Distribution of Electrical Power System

GULAM MUHUDDIN