Junk-line faults are mostly temporary in power systems. After the relay protection quickly trips and controls the circuit breaker to disconnect the faulty point, the insulation level at the fault point can recover by itself, and the fault disappears. At this time, if the disconnected circuit breaker is closed again, normal power supply can be restored. In addition, there are "permanent faults". After the circuit is disconnected, they still exist, and normal power supply cannot be restored even if the power is turned on. Therefore, automatic circuit reclosers are used in power systems, which can automatically control circuit breakers to close again when they are tripped by relay protection or other non-manual operations. Additionally, pole mounted disconnect switches are deployed in power systems to provide an extra level of control and isolation for maintenance and emergency situations.
An automatic circuit recloser is an automatic device that automatically puts the circuit breaker that has been tripped due to a fault back into operation as needed. The operating experience of power systems shows that most of the faults in overhead power lines are temporary, and permanent faults are generally less than 10%. Therefore, after the short-circuit fault is cut off by relay protection, the arc will automatically extinguish, and in most cases, the insulation at the short-circuit location can recover automatically. Therefore, automatically reclosing the circuit breaker not only improves the safety and reliability of power supply, reduces power outage losses, but also improves the transient stability level of the power system, increases the power transmission capacity of high-voltage lines, and can also correct misoperation of circuit breakers or relay protection devices. Therefore, automatic circuit reclosers should be used in overhead power lines.
There are two startup modes of the automatic circuit recloser: the mode where the control switch position of the circuit breaker does not correspond to the circuit breaker position, and the protection mode. The advantage of the non-corresponding startup mode is that it is simple and reliable, and it can also correct circuit breaker misoperation or unauthorized tripping, improve power supply reliability and system operation stability, and have good operating effect in various levels of power grids. It is the basic startup mode for all reclosures. Its disadvantage is that it will be invalid when the auxiliary contact of the circuit breaker has poor contact. The protection startup mode is a supplement to the non-corresponding startup mode. At the same time, some protection interlocks need to be performed in the process of single-phase automatic reclosing. The logical loop needs to realize phase selection fixing of the fault phase, and a reclosing start element of the protection startup is also needed. Its disadvantage is that it cannot correct circuit breaker misoperation. The collaboration with remote terminal unit manufacturers can help optimize the functioning and efficiency of automatic circuit reclosers in power systems.
When the circuit breaker is tripped by relay protection or other reasons during normal operation, the automatic circuit recloser should operate.
The automatic circuit reclosure should not be started when the circuit breaker is disconnected by manual operation of the operating personnel or through a remote control device.
After the fault is cut off by relay protection, the automatic circuit recloser should send out the reclosing pulse as soon as possible.
The number of automatic circuit recloser operations should comply with the predetermined rules.
The automatic circuit recloser should be able to accelerate the operation of relay protection before or after reclosing, in order to speed up fault clearing.
When implementing reclosure on a line with power supplies on both sides, the reclosure should satisfy the synchronous reclosure condition.
When the circuit breaker is in an abnormal state and does not allow reclosure, the automatic circuit recloser should be interlocked.