What protection measures must be taken in the control circuit of electric chain hoist?

The control circuit of electric chain hoist is composed of circuit breaker, contactor, transformer, terminal block, control handle button, thermal relay, wire, slide wire and other electrical components. The following protection measures must be taken in the control circuit:

  1. Undervoltage protection

  When the line voltage drops, the motor torque will decrease, and the speed will decrease, which will affect the normal operation of the motor. When the voltage drops seriously, the motor will also be damaged. In the control circuit with self-locking, when the motor is running, the power supply voltage drops to It has been set, generally lower than 85% of the working voltage, the magnetic flux of the contactor coil is weakened, the electromagnetic baptism is insufficient, the moving iron core is released, the normally open auxiliary contact is disconnected, the self-locking is lost, and the main contact is also disconnected. The motor stops rotating and is effectively protected.

  2. Contactor loss-of-voltage protection

  For the self-locking control circuit in the control circuit, when the power supply is temporarily cut off and the power supply is restored, the control circuit will not be turned on because the self-locking contact at the initial stage has been disconnected, the contact coil will not pass current, and the normally open contact will not. Closed, so the motor will not start running on its own, and accidents can be avoided. This protection is called power loss protection.

  3. Overload protection

  During the operation of the electric chain hoist, if the long-term load is too large, the operation is frequent or the short-phase operation, etc., the current of the motor may exceed its rated value. Sometimes the leakage short-circuit switch will not trip in this case, which will cause the motor winding to overheat, the temperature will exceed the allowable temperature rise, the insulation will be damaged, and the service life of the electric hoist will be affected. Overload protection. The most commonly used method is to use a thermal relay. The heating element of the thermal relay is connected in series in the two-phase main circuit of the control circuit, and the normally closed contact is installed in the control circuit. Due to overload or other reasons, when the current exceeds the rated value, it will generate heat after a period of time. When the element is heated and bent, the normally closed contact connected in series in the control circuit is disconnected, the control circuit is cut off, the coil of the contactor is powered off, the main contact is disconnected, and the motor is disconnected from the power supply and stops, which plays the role of overload protection. .

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