1, mechanical failure of open coil burning
1, open electromagnet of plastic case circuit breaker. when the coil is loosened, the core of the electromagnet moves when the circuit breaker is disconnected, the core is stuck and the coil burns down. it is also possible that because of the short active travel of the iron core, when the power supply of the open circuit is connected, the iron core will not open the tripping mechanism, so that the coil will be energized for a long time, resulting in combustion.
2, inappropriate dead-point adjustment, the mechanism can not release in time, resulting in coil overload, so that the opening coil burned. if the opening state of
3 and auxiliary switch is not adjusted properly and the gear auxiliary switch exceeds the range of the opening state, the auxiliary switch will not be able to switch the opening circuit normally and the opening coil will be burnt out. improper use of
4 and auxiliary switch. when the closing time of the circuit breaker is very short, far less than the opening time of the circuit breaker, and the circuit breaker is not timely, the circuit breaker is in the closing position. the delay effect of the delay contacts of the switch control circuit will disappear. on the contrary, due to the small insulation gap between the static and dynamic shocks of the auxiliary switch, the arc phenomenon often occurs, which burns the auxiliary switch contacts and causes the coil to burn out.
5, when the shunt relay in the device fails or the auxiliary switch contacts of the shunt are bigger and even, the shunt can not exit in time, and the shunt coil will be energized for a long time, resulting in burnout.

p from p from6, when the circuit insulation of the switching coil decreases, or the circuit resistance is too small, it will lead to the voltage attenuation of the switching circuit, resulting in the voltage can not reach the voltage value of the coil switch, resulting in the long charging time of the switching coil, burning the coil.
{span 0} 2. causes of burnout of closed coil of plastic case circuit breaker  
1, internal conductor pole of circuit breaker body due to mismatch of working mechanism of circuit breaker, bad blocking of transmission connecting rod, improper operation of protective locking mechanism, failure of mechanism to open circuit breaker, resulting in burnout of closed coil due to overload of closing core.
2. when the protection control device issues the opening instructions, the switching relay in the device fails or the auxiliary switch in the gate control circuit has a large operating journey, so the opening instructions can not be withdrawn in time, resulting in the switch coil being charged and burned for a long time.
3. when the circuit breaker closes, because of the large closing current, the control loop can not directly control the closing coil, and can only indirectly connect the closing coil through the closing contactor. when the closing contactor fails, it can not be timely disconnected, resulting in the opening time of the closing coil is too long and the coil is burned.
3, how to prevent coil burnout
1, correctly adjust the position of auxiliary switch.
2, fixed switch coil, check whether the core of the opening coil is clamped.
3, correctly adjust the connecting rod mechanism of circuit breaker during overhaul.
4, strengthen the inspection and maintenance of contactors.p from

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