Transmission line faults can be divided into instantaneous faults and permanent faults. The experience of power system operation shows that more than 80% to 90% of the faults are instantaneous faults. For this type of fault, after the replay protection action is disconnected from the power supply, the arc at the fault point is automatically extinguished, and the insulation strength is restored before the fault is eliminated automatically. At this time, if the outdoor vcb breaker is closed again, the normal power supply can be restored. For permanent faults, such as pole collapse, wire breakage, insulator breakdown or damage, the insulation strength of the fault point cannot be restored after the power supply of the fault line is disconnected, and the fault will still exist. Even if the circuit breaker is closed again, it will be disconnected again by the relay protection device.
Most of the faults of transmission lines are instantaneous faults. Therefore, if the line is disconnected due to a fault and then reclosed, the possibility of the success of the restoration of the power supply is quite high. The automatic circuit recloser is an automatic device that makes the tripped circuit breaker automatically and quickly re-insert when the transmission line fails.
The interruption of the power supply during the process of the automatic powerline recloser is very short. The reason is that it only takes a few seconds for the circuit breaker to trip and reclose after an accident on the transmission line. The voltage will restore before the motor is fully braked. At this time, the self-starting current of the motor is much smaller than that of the direct starting current, which is beneficial to the recovery of the system voltage.
In general, 10kV transmission lines are not equipped with lightning arresters in the power system. And 35kV lines are generally only installed lightning protection lines within 1km of the incoming line section, and the lightning resistance level of the line is low. AAR devices should be adopted as much as possible for transmission lines of various voltage levels to reduce the number of power outages caused by lightning and overvoltage on overhead transmission lines. Check 11 kv load break switch, 24kv vacuum circuit breaker, and 33kv VCB breaker.
After an accident trip occurs on the connecting line between systems, each system may have a power imbalance and insufficient power, and the system frequency and voltage will be severely reduced. For systems with excess power, the frequency and voltage will rise sharply. The pole mounted recloser can successfully reclose the line if the rotor position angle is not too large, and the whole system will quickly restore synchronization and maintain stable operation.
For circuit breaker trips caused by the bad operation mechanism of the circuit recloser or the relay protection malfunction, the automatic circuit recloser enables the circuit breaker to quickly re-enter, which can correct the trip caused by this misoperation. The AAR device brings considerable benefits, and the device has a simple structure and reliable operation. Therefore, it has been widely used in power systems.
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