DC contactor can be used for starting, switching, inching, reverse braking emergency stop of DC series motor. The main additive of silver base contact material used in contactor is oxidation amplitude nickel. It is necessary to analyze the DC contact characteristics due to the type of DC contact break due to the corrosion state of the DC contact.

Arc characteristics of DC contactor:

1. Switch on operation

When the contact is connected, it will be affected by the short arc produced by each bounce. However, the time constant of current growth is much longer than the duration of each bounce, so the arc energy absorbed by the contact is quite low.

2. Breaking operation

When breaking DC current, arc is the main factor to be considered. Most of the magnetic energy stored in the circuit is converted into heat energy generates a sufficiently high arc voltage. Therefore, the main circuit parameters affecting the breaking characteristics are as follows:

Line: induced voltage;

Load: the number of revolutions per minute of the motor that determines the electric driving force current;

Switch apparatus: contact material, arc length, arc blowing device.

The operation principle of DC contactor is similar to that of AC contactor, but the magnetic field energy stored by inductive load is released instantaneously during DC breaking, high-energy arc is generated at breakpoint, so DC contactor is required to have certain arc extinguishing function. Medium / large capacity DC contactors usually adopt the overall structure of single break point plane layout, which is characterized by long arc distance during breaking arc extinguishing enclosure containing arc extinguishing grid. Small capacity DC contactor adopts double break point three-dimensional layout structure.