SUBSTATION EQUIPMENTS-INTRODUCTION

 

SUBSTATION EQUIPMENTS.

INTRODUCTION:

              A substation is an assemblage of electrical apparatus. It receives electrical power from

generating station via incoming transmission lines and delivers electrical power via the outgoing transmission lines. Substations are integral parts of a power system and form important links between the generating stations, transmission systems, distribution system and the load points.

              In every electrical substation, there are various indoor and outdoor equipment's. Each

equipment has certain functional requirements. The choice of equipment depends on technical considerations, rated voltage, rated MVA, and the type of substation.

Function of substation equipment:

Outdoor Equipment's

The following are the various EHV outdoor equipment's and their functions are here

under.

Power Transformer: It is used to step-up or step-down a.c voltages and to transfer electrical power from one voltage level to another. The choice of KVA rating of transformers in a particular installation depends upon the KVA load.

Power Transformers

Shunt Reactor: It is used for long EHV transmission lines to control voltage during lowland period. 

To compensate shunt capacitance of transmission line during low load periods.

Shunt Reactor

Circuit-breaker: A device capable of making and breaking an electrical circuit under normal and abnormal conditions such as short circuits. It can operate automatically/ manually and clear fault currents safely and quickly.

Circuit breaker

Isolator (Disconnecting switch): A switching device which can be opened or closed only under no current conditions. It provides isolation of a circuit for the purpose of maintenance.

Isolator (Disconnecting switch)

Earthing switch: It is a switch which connects a conductor to the earth so as to discharge the charges on the conductor to earth. Earthing switches are generally installed on frames of the isolators.

Earthing switch

Current transformer (CT): The Current ratio of current transformer is generally high and volt ampere capacity is relatively low as compared with that of the power transformers. It step downs the current for measurement, protection and control.

Current transformer

Voltage transformer (VT): The volt ampere capacity is relatively low and the voltage ratio is high. The protective relays are connected in secondary circuits of CTs and VTs. It step downs the voltage for measurement, protection and control.

Voltage transformer

Lightning arrester (surge arrester): It discharges the over-voltage surges to earth and protect the equipment insulation from switching surges and lightning surges. The equipment connected between the conductor and ground, to discharge the excess voltages to earth.

Lightning arrester 

Capacitor Voltage Transformers (CVT): Capacitor potential transformer, in which the primary voltage is applied to a series capacitor group. The voltage across one of the capacitor is taken to auxiliary voltage transformer. The secondary of auxiliary voltage  transformer is taken for measurement of protection.

Shunt Capacitor: It is used for compensating reactive power of lagging power factor. To improve power factor and voltage control during heavy lagging power factor loads.

Series Capacitor: It is used for some long EHV a.c lines to improve power transferability.

Carrier Equipment: It consists of line trap unit, coupling capacitor, electronic equipment and it is used for protection and communication signaling, voice communication, protection signaling, telex channel, control and monitoring signals.

Marshalling Kiosks: It is used to mount monitoring instruments, control equipment and to provide access to various transducers. Control and protective cables are laid between Marshalling Kiosks located in switchyard and corresponding indoor control panels.

Marshalling Kiosk

Insulators: - It provides mechanical support to the conductor and subject to the normal operating voltage and transient over voltages. It should have sufficient mechanical strength to withstand the maximum wind-loading, ice-loading, dead load, etc., and should not flash over under any conditions of humidity, dirt, salt contaminates, etc. The materials used in the manufacturing of insulators are porcelain, glass and Epoxy type.

Indoor Equipment's:

The following are the various indoor equipment's and their functions are here under.

These are installed inside a separate building near the switchyard. Protective Relay: An electrical relay is a device designed to produce sudden, predetermined changes in one or more electrical output circuits, when certain conditions are 5 fulfilled in the electrical input circuits controlling the device.” The function of any faulty section of the power system from service.

Medium and low voltage A.C. Switchgear (In-door): It is used to provide a.c. power to auxiliaries, station lightning system, etc. at respective voltage levels. Control and Protection Panels: Control and protection panels have a functionally important role. They perform the following functions:

1.  They provide facility for centralized control.
2.  They provide a point for centralized supervision at which all vital information relating to             controlled  equipment is received and assimilated.
3.  They provide for necessary protection and isolation facility of all power circuits like generators,    feeders, transformers, bus-coupler, reactors, etc. 
4.   The control and protection panels provide alarm and trip commands under abnormal conditions and hence function like a watchdog for the system.

Switchgear

Metering Panels: Electrical parameters like current, voltage, active power, reactive power, frequency, etc. are monitored for the convenience of the operator. For transmission lines, energy is monitored at high accuracy of the order of class 0.2 for the purpose of tariff metering. Load profile data is also recorded for the purpose of analysis of energy flowing through the line of protective relay is to affect disconnection .