Selection of dc contactor
The operating principle of direct contactor is basically the same as that of ac contactor, however, the magnetic field energy stored by inductive load is released instantaneously when dc is broken, and high-energy arc is generated at the break point, therefore, the arc extinguishing function of dc contactor is required to be higher than that of ac contactor. The large-capacity dc contactor usually adopts the single breakpoint plane layout of the overall structure, which is characterized by the arc extinguishing shield with the arc extinguishing gate, the arc distance is long when breaking. The small capacity dc contactor adopts the double breakpoint three-dimensional arrangement structure.
The following points should be noted when selecting dc contactor:
1. The rated current of the main contact is more than 1.3 times the rated load current.
2. The rated voltage of the main contact is greater than or equal to the rated voltage of the load.
3. The number and type of contacts should meet the requirements of control circuit.
4. 220V or 380V can be used when the circuit is simple and fewer electrical appliances are used.
When the circuit is complex and electrical appliances are used for a long time, 36V, 110V or 127V can be selected.
5. When the on-off current is large and the on-off frequency exceeds the specified value, the contactor type with a higher rated current shall be selected. Otherwise, the contact will be seriously heated, which will lead to melting together, resulting in the motor load phase loss operation.