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In a substation the equipment used to limit short circuit current level is
Series reactor
Coupling capacitor
Lightening switch
Isolator
Series reactor
A series reactor is an inductor placed in series with the power line to limit the magnitude of fault current during a short-circuit condition. By introducing high reactance, it limits the prospective fault current to a value that protective switchgear can safely interrupt.
A series reactor is an inductor placed in series with the power line to limit the magnitude of fault current during a short-circuit condition. By introducing high reactance, it limits the prospective fault current to a value that protective switchgear can safely interrupt.
XLтАЛ=2╧АfL тАФ Inductive reactance formula
IfaultтАЛтЙИXLтАЛVтАЛ тАФ Fault current limitation principle
During a short circuit, the impedance of the system drops significantly, causing a massive surge in current. A series reactor acts as a high-impedance element that increases the total series impedance of the circuit (Z=R+jXLтАЛ). Since the fault current is inversely proportional to impedance (IfтАЛтЙИXLтАЛVтАЛ), the reactor effectively restricts the fault current to prevent thermal and mechanical damage to station equipment.
Series reactors protect circuit breakers by keeping the fault current within their interrupting capacity.
They are usually air-cored and operate continuously at full load current.
The voltage drop across the reactor is usually small under normal load conditions but significant during faults.
Reduces mechanical stress on busbars and equipment during faults
Allows the use of lower-rated (cheaper) circuit breakers
Causes a continuous voltage drop during normal operation
Increases the total system loss (I2R)
Impacts the system power factor
Busbar sectioning
Feeder protection
Generator short-circuit protection
Coupling capacitors are used in Power Line Carrier Communication (PLCC), not for fault limitation.
Isolators are mechanical switches used for maintenance isolation, not for current interruption or limiting.
Lightning switches (or surge arresters) are used for overvoltage protection, not current limiting.
A is correct тАФ A series reactor provides additional inductive impedance to limit the magnitude of short-circuit current.
Always remember: Reactors limit current (impedance addition), whereas Capacitors allow communication/compensation and Arresters limit voltage (clamping).