Electric Substations are the part of the power system and used for transferring power from generating points to load centers. Some of the important components of substation are
Various incoming and outgoing circuits are connected to busbars. Busbars receive power from incoming circuits and deliver power to outgoing circuits.
Surge arrestors or Lightning arrester:
Surge Arresters or Lightning Arresters discharge the over voltage surges to earth and protect the equipment insulation from switching surges and lightning surges. Surge arresters are generally connected between phase conductor and ground. In a Substation surge arrester is located at the starting of the substation as seen from incoming transmission lines and is the first equipment of the substation. Surge arresters are also provided near the transformer terminals phase to ground. Two type of surge arresters are available 1) Gapped Arresters 2) Gapless Zinc – Oxide arresters.
Isolators or Disconnecting Switches:
Isolators are provided for isolation from live parts for the purpose of maintenance. Isolators are located at either side of the circuit breaker. Isolators are operated under no load. Isolator does not have any rating for current breaking or current making. Isolators are interlocked with circuit breakers
Types of Isolators are
- Central rotating, horizontal swing
- Vertical swing
- Pantograph type
Earth Switch is used to discharge the voltage on the circuit to the earth for safety. Earth switch is mounted on the frame of the isolators. Earth Switch is located for each incomer transmission line and each side of the busbar section
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Current transformers are used for Stepping down current for measurement, protection and control. Current transformers are of two types
- Protective CT
- Measuring CT
Voltage transformers are used to step down the voltage for measurement, protection and control. Voltage transformers are of two types.
- Electro magnetic type
- Capacitive VT located on the feeder side of the Circuit Breaker.
Circuit Breaker is used for Switching during normal and abnormal operating conditions. It is used to interrupt the short circuit currents. It is used to interrupt short circuit currents. Circuit Breaker operations include.
- Auto – reclosing
Circuit Breaker is located near every switching point and also located at the both ends of every protection zone.
Power Transformers are used to step up or step – down a.c. voltages and to transfer electrical power from one voltage level to another. Tap changers are used for voltage control.
Shunt Reactors are used for long EHV transmission lines to control voltage during low – load period. Shunt reactors is also used to compensate shunt capacitance of transmission line during low load periods. Usually Shunt reactors are unswitched.
Shunt capacitors are used for compensating reactive power of lagging power factor. Shunt Capacitors are used for improving the power factor. It is also used for voltage control during heavy lagging power factor loads. Shunt Capacitors are located at the receiving stations and distribution substations. Shunt Capacitors are switched in during heavy loads and switched – off during low loads.
Series Capacitors are used for some long EHV a.c lines to improve power transferability. Capacitors are located at the sending end / receiving end of the lines. Series Capacitors are provided with by – pass circuit breaker and protective spark – gaps.
Series reactors are used to limit short – circuit current and to limit current surges associated with fluctuating loads. Series reactors are located at the strategic locations such that the fault levels are reduced.
Lightning protection is used to protect substation equipment from direct lightning strokes. Lightning Masts are located at the outdoor yard. Overhead Shielding wires are used to cover entire outdoor yard.
Isolated Phase Bus System:
Isolated Phase Bus System provides connection between Generator and the main Transformer. It carries very high currents.
Neutral Grounding Equipment:
Neutral Grounding Equipment are Resistors and reactors. They are used to limit the short circuit current during ground fault. They are connected between neutral point and ground.
Line Trap consists of Inductive coil usually connected in the outdoor yard incoming line. Line traps are usually mounted above Capacitor Voltage Transformer (CVT) or on separate structure.
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Used for Insulation purpose. Different types of insulators are porcelain, Glass, Epoxy.
Power Cables are used to carry the power. They are single core and three core. Types of power cables are PVC insulated, XLPE insulated.
Control Cables are for protection, control and measurement etc.. They are of low voltage and PVC insulated. Control Cables are Multi core and Shielded.
Station Earthing System:
Station Earthing System includes Earth Mat and Earth electrodes placed below ground level. These Earth Mat and Earth electrode is connected to the equipment structures, neutral points for the purpose of Equipment earthing and neutral point earthing.
Function earthing system is to provide low resistance earthing for
- Discharging currents from the surge arresters, overhead shielding, earthing switches
- For equipment body earthing
- For safe touch potential and step potential in substation.
Metering, Control and Relay panels:
To house various measuring Instruments, control Instruments, Protective relays. They are located in air-conditioned building. Control Cables are laid between Switchyard equipment and these panels.
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