Cause analysis and treatment of trip rejection of MCCB

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Due to the frequent operation of molded case circuit breaker, the phenomenon of refusing to jump often occurs due to the influence of mechanical and electrical factors. For the circuit breaker that has been put into operation, when the fault reappears at the load side of the circuit breaker, once the failure occurs, it will inevitably cause override trip, expand the scope of accident and power failure, so it should be eliminated as soon as possible. The intelligent console has the function of insulation impedance test, which directly reflects the insulation strength of the tested object


1. Reasons for refusing to jump


There are two reasons for the failure of MCCB: one is the mechanical failure of the operating mechanism, the other is the electrical failure of the operating circuit.


When the circuit breaker refuses to trip, the personnel on duty shall first judge whether the trip circuit is in good condition according to the light indication. If the red light is not on, it means that the trip circuit is not working. At this time, it is necessary to check whether the operation fuse is fused or poorly contacted, whether the contact of the universal transfer switch and the auxiliary contact of the circuit breaker are poorly contacted, whether the coil of the anti jump relay is broken, whether the operation circuit is broken, and whether the bulbs and lamps are in good condition.


If the operation power supply is good and the trip iron core is weak, it means that the trip coil action voltage is too high, or the operation voltage is too low, the trip iron core is jammed, separated, or the trip coil itself is faulty. If the trip iron core ejector is transported well and the circuit breaker refuses to trip, it may be that the mechanism is jammed or the drive link pin is detached.


2. Treatment


After finding out the cause of the failure, the personnel on duty should be calm and take different treatment schemes according to the nature of the failure. If the red signal lamp does not light up during normal opening operation, replace the operation fuse immediately after confirming that the lamp is in good condition, and then open. At this time, it should be carried out by two people, one is to operate the transfer switch remotely, the other is to observe the opening iron core action locally, and at the same time, pay attention to keep a safe distance. If the action of the iron core is weak, it means that the iron core is blocked; if the action of the opening iron core is normal, but the circuit breaker can not be tripped, it means that the mechanical anti blocking. At this time, the mechanical opening device should be used locally to block the circuit breaker. For air circuit breaker and SF6 circuit breaker, the air pressure must be normal before the mechanism can be blocked.


When it is necessary to open in emergency, such as relay protection device action or manual remote switch refusing to open, which may cause damage to the main equipment, the personnel on duty shall immediately manually open the upper level circuit breaker, and then use mechanical opening device to block the circuit breaker at the fault circuit breaker; If the mechanical opening device can not disconnect the circuit breaker, the isolating switches on both sides of the fault circuit breaker shall be quickly disconnected, and then the upper level power supply shall be restored, and the cause shall be found out before treatment; if time permits under the accident condition, the personnel on duty shall quickly run to the fault circuit breaker and disconnect the circuit breaker with the mechanical opening device; If the mechanical opening device cannot be disconnected, the operation mode shall be changed immediately, or the bus tie circuit breaker and the upper circuit breaker shall be used to disconnect, and then the isolating switch shall be used to isolate the fault circuit breaker and restore the operation mode.


However, it should be noted that the circuit breaker itself is limited by the interrupting capacity. When one of the following faults occurs, it is forbidden to disconnect it to avoid explosion accident.


(1) The oil circuit breaker has no oil or is seriously short of oil or the oil quality is seriously carbonized.


(2) When the two-phase insulation pull rod of oil less circuit breaker breaks.


(3) The gas circuit breaker pressure is too low and cannot be maintained.


(4) The circuit breaker with hydraulic mechanism is used when the hydraulic system drops to zero.


Once the above phenomenon occurs, the operator on duty shall immediately remove the operating fuse of the circuit breaker, so that the circuit breaker can not be disconnected in the distance, and even if the circuit breaker is in fault, the protection device will not make it open. At the same time, the personnel on duty shall hang the warning board of "no operation" on the operating handle and the operating machinery of the circuit breaker, and then deal with it according to the following principles.


(1) If a load of the station (substation) breaks down, it is necessary to transfer the load according to the command of the director or dispatcher, and then cut off the bus connected to the fault circuit breaker, open the circuit breaker and resume the operation of the upper circuit breaker.


(2) If it is the fault of the circuit breaker of the working power supply of a power plant (substation), the standby power circuit breaker should be put into operation, the superior circuit breaker of the working power supply should be cut off, and then the fault circuit breaker should be opened.


(3) If the circuit breaker fails, it is necessary to switch the bus. When the bus circuit breaker or bypass circuit breaker is used, the special person in charge of relay protection shall be informed to adjust its setting value, and then the relevant units shall be informed to cut off the power for maintenance.


When on duty personnel inspect and find the following abnormal phenomena, they should take decisive measures. First, they should take measures to make the circuit breaker unable to switch on automatically or remotely, and then they should take remote operation to quickly open the circuit breaker and cut it off


(1) The bushing of the circuit breaker cracked.


(2) MCCB on fire.


  1. In case of personal accident, the circuit breaker should be opened immediately.


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