substation equipment and its function 2

Khairpur Mir`s

Assignment of Power Distribution & Utilizations System

Submitted To: Sir Irfan Ahmed

Submitted By: Zulfiqar Mangrio (K-13EL-79)

Topic:Substation equipment’s and its Function

Department: Electrical Engineering

Date: 28-Jan-2016

Substation equipment’s and its Function

Distribution SystemThe major function of distribution system is to provide power to individual consumer requirement. Supply of electric power to different consumers is done at low voltage level.

Any Distribution of electric power is done by distribution networks. Distribution Substations distribute the power. As many equipment`s are used in substation which can lower the voltage level Control the whole system. Which are given below;

Substation equipment’s1. Power Transformer

2. Circuit Breaker

3. Disconnecting Switches & Isolator

4. Bus Bar

5. Current Transformer

6. Potential Transformer

7. Current Limiting Reactor

8. Shunt Reactor

9. Series Capacitor

10. Capacitor Voltage Transformer (CVT)

11. Coupling Capacitor Voltage Transformer (CCVT)

12. Shunt Capacitor

13. Grounding System

14. Lightning Arrester

15. Line Trap

16. Protective Relays

17. Station Batteries

1. Power Transformer

A transformer is an electric static machine used to change the voltage and current without changing the frequency and power. The power transformer is different

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from the distribution transformer because due to its high rating or it depends on the ratings. In case of a 220 KV or above KV level auto transformers are used.

As in case the of lower KV line such as less than 132KV line double winding transformers are used

2. Circuit Breaker

The circuit breakers are used to control (Break) the circuit if any fault occurs in any of the Substation system. These circuit breaker breaks for a fault which can damage other equipment in the station. For any fault over the substation station we need to break the circuit it means that line current. This is done by automatically Circuit breaker by the help of relay.

Some of the type of Circuit Breaker Oil circuit breaker. Air circuit breaker. SF6 circuit breaker. Vacuum circuit breaker

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3. Disconnecting Switches & Isolator

Isolator is a mechanical switch which can separate the part from circuit in the system when it is required. Electrical isolators separate a part of the system from rest for safe maintenance works. This isolator is to protect the transformer and the other equipment in the system. The isolator isolates or cut the circuit from the high voltage to the ground. It is protecting device.

4. Bus Bar

A bus bars in electrical power distribution are the conductors which are made up of thick strips of copper or aluminum that conduct electricity within a switchboard, distribution board, substation, or other electrical apparatus. The bus is a line in which the incoming feeders come into and get into the instruments for further step up or step down. There may be double line in the bus so that if any fault occurs in the one the other can still have the current and the supply will not stop.

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5. Current Transformer

A current transformer is defined as an instrument transformer in which the secondary current is substantially proportional to the primary current.Current transformers are used when the magnitude of AC currents exceeds the safe value of current of measuring instruments. Current transformers are basically used to take the readings of the currents entering the substation. This transformer steps down the current from 800 amps to 1 amp. This is done because we have no instrument for measuring of such a large current. The main use of this transformer is

a. Distance Protection

b. Backup Protection

c. Measurement

6. Potential transformerThe potential transformer usages a bus isolator care for itself. The main use of this transformer is to measure the voltage through the bus. This is done so as to get the detail information of the voltage passing through the bus to the apparatus. There are two main parts in it

a. Measurementb. Protection

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7. Current Limiting Reactor

The Current limiting reactor is an electrical inductance made up of a number of turns of wire of low ohmic resistance and inserted in series with a line to limit the current that can flow under short circuit.

8. Shunt Reactor

Shunt reactor is the absorption of reactive power in the case of Ferranti effect, and thus assembling the energy efficiency of the system. It is the most compact device normally used to compensate for reactive power transmission lines in high-voltage long and cable systems. Shunt reactor can be connected directly to the power line or to higher power transformer. It is used to improve and adjust the reactive power consumed reactor can also be a variable rating.

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9. Series Capacitor

• Increase power

• Transmission capability

• Improve system stability

• Reduce system losses

• Improve voltage profile

• Optimize power flow between

Parallel lines

10. Shunt Capacitor

A capacitor bank is very essential equipment of an electrical power system. The energy required to run all the electrical devices are useful load power is the active power. It is expressed in active power KW or MW. The maximum load connected to the electric power system is essentially inductive in nature such as electric transformers, induction motors, synchronous motor, electric ovens, and fluorescent lighting are all inductive in nature. The current causes the capacitor to lead the effort; the capacitive reactance can be used to cancel the inductive reactance of the system.

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11. Capacitor Voltage Transformer

A capacitor voltage transformer (CVT) is a transformer used in power systems to stepping down high-voltage signals and providing additional low voltage signals either to measure or for the operation of the protective relay. In its simplest form, the device consists of three parts: two capacitors across the divided voltage signal, which is used to adjust the inductive device on the pace of supply and transformers, used to isolate and further stepped down the voltage of the devices or relay protective element. The voltage level of this transformer is measure voltage 200KV same as potential transformer.

12. Capacitance Coupled Voltage Transformer (CCVT)

A capacitance Coupled voltage transformer (CCVT) is a same like CVT , which is used in power systems to step-down extra high voltage signals and provide low voltage signals either for measurement or to operate a protective relay. Mostly it is use EXTRA high voltage 500kv to sample the voltage for measurement purpose.

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13. Grounding System

To provide an earth mat for connecting neutral points, equipment body, support structures to the ground. For the safety of staff and to enable ground fault protection to provide a path to empty the land of neutral currents, errors, surge arresters, overhead shielding wire etc. with a safe step and touch potential possibilities.

14. Lightning Arrester

Lightening arrestors are the instrument that are used in the incoming feeders so that to prevent the high voltage entering the main station. This high voltage is very unsafe from the equipment`s used in the substation. Even equipment are very expensive, so as to prevent any damage using lightning arresters. The lightning arresters do not let the lightning to fall on the substation. In the case of some lightning and lightning arresters

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drag and ground it to the ground.

15. Line Trap

A line trap also called wave trap free parallel resonant circuit, connected series with high voltage transmission power lines to provide high frequency (40 kHz to 1000 kHz) carrier signals of power line communication purpose.

16. Protective Relays

Protection relays used to detect defective or device lines and to isolate the defective equipment. Relays are also used to detect abnormal operating conditions or undesirable from those caused by damaged equipment and either a warning or isolate the equipment. Protection relays are used in electrical system protection by causing defective device or lines to be separate or disconnect the equipment and to maintain continuity of service to the rest of the system.

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18. Station Batteries Batteries are supply the direct current to the relays for control purpose, as well as store the energy so use for the when there is no power in the substation it means that all the system is open or any fault condition. These are connected in series to increase the voltage level.

Another Apparatus Protection system

To provide alarm or automatic tripping of faulty part from healthy part and also to minimize damage to faulty equipment and associated system

Control cableIt provide supply to various auxiliary equipment’s and machines.

Auxiliary standby power system

For supplying starting power, standby power for auxiliaries.

Firefighting system

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To sense the occurrence of fire by sensors and to initiate water spray, to disconnect power supply to affected region to pin point location of fire by indication in control room.

How to Determine the Primary current and secondary current in transformer? As the input voltage is 11kv, output phase voltage is 220v and rated as;

1. Transformer Rated At 50 KVA

(a) Primary Current: As we know that Power transformer’s Primary winding connected in Delta Connection,So,IL =√3x Ip

VL = Vp

Now,Apparent power is;S = V.I => I = S/V

IPrimary = 500011000

IPrimary =4.545 A

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(b) Secondary Current: The Secondary of the Power transformer winding are connected in Delta or Wye.So,IL = IP

VL =√3x Vp

As Output Voltages are 220 VS = V.I => I = S/V

ISec = 5000220

ISec = 227.27 A

2. Transformer rated At 100KVA

(a) .Primary Current:As we know that Power transformer’s Primary winding connected in Delta Connection,So,By Using Apparent power Formula, we get;S = V.I => I = S/V

IPrimary = 100,00011000

IPrimary =9.090 A

(b) Secondary Current: So,

Using apparent power formula, we get;

IL = IP

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VL =√3x Vp


ISec = 100,000

220

ISec = 454.54 A


(a) Primary Current:

As we know that Power transformer’s Primary winding connected in Delta Connection,So,By Using Apparent power Formula, we get;S = V.I => I = S/V

IPrimary = 200,00011000

IPrimary = 18.181 A

(b) Secondary Current: So,Using apparent power formula, we get;IL = IP

VL =√3x Vp

As Output Voltages are 220 VS = V.I=> I = S/V

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ISec = 200,000

220

ISec = 909.09 A




IPrimary = 400,00011000

IPrimary = 36.36 A


VL =√3x Vp


ISec = 400,000

220

ISec =1818.18 A


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IPrimary = 630,00011000

IPrimary = 57.27 A


VL =√3x Vp

As Output Voltages are 220 VS = V.I=> I = S/V

ISec = 630,000

220

ISec = 2863.63 A

Bus Scheme`s Used in Pakistan

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I) breaker and Half scheme:

II) Siemens GIS substation with Main & Transfer bus scheme (2 BB)

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