A kind of unbalance protection method for asynchronous motor running in forward and reverse switching mode

Abstract

The invention relates to a protection method for an asynchronous motor running in forward and reverse switching. An unbalance protection method for an asynchronous motor with forward and reverse switching operation, which includes a microcomputer integrated protection device, which includes: sending the auxiliary contact of the motor forward running control switch to a DI port of the microcomputer integrated protection device; motor reverse running control The switch auxiliary contact is sent to another DI port of the microcomputer integrated protection device; the microcomputer integrated protection device judges whether the motor is in the forward running state or the reverse running state through the input contact state; if it is judged to be in the forward running state, directly use the formula formula ( 3-3) Calculate the positive sequence and negative sequence currents; if it is judged to be in the reverse running state, use the following formula (5-1) to calculate the positive sequence and negative sequence currents. The present invention can complete the comprehensive unbalance protection for the forward and reverse switching operation motor by means of a microcomputer comprehensive protection device.

Description

technical field [0001] The invention relates to a protection method for an asynchronous motor, in particular to a protection method for an asynchronous motor with forward and reverse switching operation. Background technique [0002] Asynchronous motors are key components of industrial power systems, which directly affect the normal operation of production. In practical applications, when asymmetric faults such as unbalanced three-phase load of the motor, unbalanced three-phase supply voltage, open phase of the power supply circuit, two-phase short circuit inside the winding, and inter-turn short circuit occur, the three-phase current in the stator winding of the motor will no longer be In balance, the current can be decomposed into positive sequence current and negative sequence current. They generate positive-sequence and negative-sequence rotating magnetic fields respectively in the air gap between the stator and rotor of the motor. The negative-sequence rotating magnet...

AI Technical Summary

Problems solved by technology

[0029] Problem: This type of protection phase loss protection is generally about 40% of the rated ampere-turn of the rated relay

[0038] There is a problem: when the motor is lightly loaded, the denominator I in the formula (3-2) av Relatively small, the molecule changes slightly, it may reach the set value of negative sequence protection, and it is easy to generate unnecessary negative sequence malfunction. Therefore, when the load current of the motor is less than 30% of the full load current, the general design of the protection allows the unbalance protection to automatically exit the operation

[0058] There is a problem: the unbalance protection of this principle is configured for the motor that needs to be switched from forward to reverse, and the motor unbalance protection will operate after the motor is switched from forward to reverse.

[0062] The unbalance protection of the comprehensive protection device must act, causing shutdown

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