The protection of the three-phase asynchronous motor often has a certain relationship with its control method, that is, there is control in the protection, and protection in the control. Today, the editor of Dalan Motor and everyone share the relationship between the motor and the protection device.
1. Coordination of overload protection device and motor
(1) The operating time of the overload protection device should be slightly longer than the starting time of the motor. The characteristics of the motor overload protection device can only ensure its normal operation by avoiding the characteristics of the motor starting current; but its action time cannot be too long, and its characteristics can only play the role of overload protection under the thermal characteristics of the motor.
(2) The instantaneous operating current of the overload protection device should be
There is a misunderstanding in motor protection. Use circuit breakers and fuses to protect the motor. Effective and simple is the thermal relay + contactor (or other device that can cut off the power supply) for overload and phase loss protection. The action characteristic of the thermal relay bimetallic plate is matched with the heating of the motor, and there is a function with phase failure protection. Choosing a good quality thermal relay should be effective for motor protection.
The setting of the thermal relay: It is 1.05-1.1 times of the rated current learned from the books. This is no problem. However, in actual application, in order to protect more effectively, it should be set according to the maximum current in operation.
The setting method of the thermal relay is also: adjust the setting current to be small, let the motor run for a few minutes, and it can be increased to 1.1-1.2 times according to the current setting value. This can avoid failure due to inaccurate thermal relay current scale.
Second, the motor protection circuit roughly has the following four
(1) It consists of thermal relay FR, contactor kM and circuit breaker QF with instantaneous protection only, as shown in Figure 4. The contactor is used to start and stop the motor, the thermal relay is used to protect the motor from overload, and the circuit breaker with only instantaneous protection is to protect the motor from short circuit.
(2) Consists of thermal relay FR, contactor kM and fuse FS. The thermal relay protects the motor from overload, the contactor starts and stops the motor, and the fuse protects the motor against short-circuit faults.
(3) It is composed of a contactor kM and a motor protection type circuit breaker QF. The contactor is used to start and stop the motor, and the motor protection type circuit breaker is used to protect the motor from overload and short circuit faults.
(4) It is composed of a motor-protected circuit breaker. The motor-protected circuit breaker not only protects the motor from starting and stopping, but also protects the motor from overload and short circuit faults. Among the above four types, two types 1 and 2 are suitable for relatively frequent starting-stopping the motor, the third type is suitable for general frequent starting, and the fourth type is only suitable for infrequent starting and stopping.
----- Responsible Editor: Dalan Oil Pump Motor 02-Procurement Consultant
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