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The coil of the dc contactor is a bit special

Dec 20, 2018

As we know, the structure of dc contactor and ac contactor is basically the same. It is composed of coil, main contact, auxiliary contact, armature and so on.

If you look careful, you'll see that there are still a lot of differences.

Direct current goes through, at the moment the contact closes and disconnects, the voltage is very high. The arc is much larger than the ac contactor. It is better to choose magnetic blowing type for arc extinguishing. That is to say, to make a short circuit of the coil, set in the arc path, due to the effect of electromagnetic induction, the current generated in the magnetic blowing coil. So the arc is short-circuited.

Since there is no eddy current in direct current, the core of the coil can be made of a whole piece of iron. It is less labor and material than using ac contactor.

The coil of the dc contactor is also different. Since there is no eddy current loss, the key heating point is the dc resistance of the coil. So make the coil long and thin. This helps dissipate heat.

For dc contactor over 200A, there are two coils, one for starting coil and the other for holding coil.

Two coils work like this: before the circuit is energized, keep the coil short-circuited by its normally closed contacts. So the starting voltage is all added to the starting coil, In order to meet the requirements of starting the required of large magnetic force. But when the suction is complete, only a small magnetic force is needed to maintain the force. Therefore, after the suction, the coil disconnected due to the series of normally closed contacts, therefore, the starting voltage is Shared by the starting coil and the holding coil.

The current in the whole coil is reduced by half. According to the power calculation, the power consumption has been reduced to a quarter of the original.

The purpose of normal operation and energy saving and consumption reduction is obtained.