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The motor-protected circuit breaker is one of the indispensable protective devices for squirrel-cage induction motor in starting, running and breaking. For motor protection, rated current 630A and below (i. e. Protected Motor 315KW and below) is used to start and break the motor infrequently during operation, when the motor short circuit, under-voltage and other faults, can be protected (automatic cut-off circuit) .

According to the use of the situation, circuit breakers used as motor protection there are three types: first, motor start, operation of the use of AC contactors, the overload protection uses thermal relay (thermal relay not only for overload protection, but also for the return of the starting current of the motor, which also belongs to the overload range) , and the open circuit protection is used for short circuit protection, because the contactor is used to divide and close the circuit, it can be operated more frequently, the over-load, short-circuit and under-voltage faults of the motor are borne by the Open Circuit III. The motor breaks off during starting and running, and the over-load, short-circuit and under-voltage are all operated and protected by a circuit breaker, but it can not be used frequently.

The motor protection circuit breaker can be divided into two types: the one with short-circuit protection and the other with overload and short-circuit protection. The common point of motor protection circuit breaker and distribution circuit breaker is that they all comply with GB14048.2 low voltage circuit breaker standard, the difference is that the overload protection characteristics of the motor protection circuit breaker must meet the requirements of the overload relay trip level in the GB14048.4 standard for contactors and motor starters, and the overload protection characteristics are consistent with those of thermal relays. Due to its transient tripping current threshold can avoid starting current peak value of motor, Type D miniature circuit breaker is often used in motor short circuit protection, but it can not provide proper overload protection, so it is necessary to configure thermal relay. The return time of the Motor Protection Circuit Breaker under 7.2 times current should be greater than the motor starting time to avoid the long time delay protection action during the starting process, and the setting value of the instantaneous protection should be greater than the peak value of the motor connecting current, in order to avoid starting the process of short-circuit instantaneous protection misoperation.

The circuit breaker should be installed vertically, and before installation should check whether the technical parameters listed on the Circuit Breaker nameplate meet the use requirements.

Before electrifying, the circuit breaker should be operated manually for several times, and its mechanism action should be flexible, reliable and non-blocking phenomenon. When pressing the close button (black) , the circuit is in the on state; when pressing the disconnect button (Red) , the circuit is in the off state. ?

During use, the circuit breaker should be checked regularly (usually for one month) , that is, when the circuit breaker is switched on and on, the Test button (the Test button is indicated by the symbol“Test”) should be pushed, and the circuit breaker should be reliably disconnected.