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Analysis of electromagnetic interference problem of permanent magnet DC motor for switchgear

Dec 08, 2018

The commutation performance of permanent magnet DC motor for switchgear is an important indicator to measure the quality of its operation. This index is closely related to the motor's speed, power, and external electromagnetic interference generated by the motor. Because of the commutation problem, an instantaneous high-frequency voltage is generated on the power supply line, causing conducted electromagnetic interference, which affects the normal operation of the surrounding equipment.

That is to say, the permanent magnet DC motor used in the switchgear often generates radiated electromagnetic interference during the commutation process. The first case is a permanent magnet DC brush motor with a brush and a commutator, and the rotor coil is connected to the power source via a brush and a commutator. When the motor is working, the direct contact between the brush and the commutator is a dynamic contact, forming a spark. The spark is actually a large current pulse that enters the wire by coupling, producing conduction and radiation.

In addition, during the operation of the permanent magnet DC motor for switchgear, since the commutator surface is not very smooth, the brush and the commutator cannot be in smooth contact, so transient voltages are generated during operation, and these transient voltages pass through the wires. Infiltrating other devices in a conductive manner, when the frequency of the transient voltage is high enough, it can also affect other devices by radiation.

In order to prevent the negative impact of such interference, it is necessary to improve the commutation performance of the permanent magnet DC motor for the switchgear and control the commutation spark to suppress the electromagnetic interference. In some places where interference requirements are relatively high, interference is suppressed by weakening the interference propagation path.