Fault and abnormal condition
During a fault, the fault impedance is low and accordingly, the fault currents are relatively high. Since the fault currents being excessive, they damage the faulty equipment and the supply installation. During the faults, the power flow is diverted towards the fault; and the supply to the neighboring zones is affected
Faults can be classified as :
- single line to ground fault
- lint to line fault
- double line to ground fault
- simulation fault
- three phase fault
- - open circuit, etc.
The other abnormal condition
- - Voltage and current unbalance
- Undr frequency
- Over voltages
Temperature rise-
- Reverse of power
Power swing-
- Instability, etc
Fault clearing process
1- the protective relay are connected in the secondary circuit of current and voltage transformer.
2- the relays the abnormal condition and close the trip circuit of the associated circuit breaker.
3- the circuit breaker opens its contact.
4- arc is drawn between the contacts as they separate.
5- the arc is extinguished by suitable medium and technique.
6- after final arc extinction, ahigh voltage wave appears across the circuit breaker tending to re-establish the arc.
7- the transient voltage wave is called " transient recovery voltage" ( TRV ).
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