Views: 12 Author: Site Editor Publish Time: 2022-10-22 Origin: zhihu
Contactor is an important low-voltage electrical appliance in power drag and automatic control systems, and it is also a typical representative of electromagnetic electrical appliances with contacts.
When the term "contactor" is prefixed with "AC" or "DC", then it can be divided into "DC contactor" and "AC contactor", which are used in AC circuit or DC circuit.
1.The main circuit of the DC contactor is generally two poles, and the DC only has positive and negative poles.
The AC contactor has 3 poles because of the opening and closing of three-phase electricity.
2.About contactor overvoltage and arc extinguishing measures:
For the AC circuit, when the contactor is disconnected, the overvoltage generated by the circuit is relatively small. At the same time, the AC arc has a zero-break moment of zero-crossing, and the arc will be extinguished and reignited after the zero-crossing, so the AC arc extinguishing measures are relatively easy.
For the DC circuit, when the contactor is disconnected, the overvoltage generated by the circuit is high, and the arc is not easy to extinguish. It can be seen that compared with the AC contactor, the DC arc extinguishing measures are relatively difficult.
3.Coordination of the contactor and the previous line protection device:
When the line is short-circuited, the protection action of the previous line protection device (fuse, circuit breaker) takes time.
During this period of time, the contactor must withstand the thermal shock of the short-circuit current. We call this phenomenon the protection coordination relationship of the contactor, which is represented by SCPD.
In the national standard GB/T14048.4 "Low-voltage switchgear and control equipment - Part 4: Contactors and motor protection devices...", SCPD is divided into two categories:
Type 1: The main circuit of the contactor will be damaged after the breaking is completed.
Type 2: The main circuit of the contactor will not be damaged after the breaking is completed.
Therefore, it is obvious that the protection coordination relationship between DC and AC SCPD is different, and the parameter table must be carefully consulted when using it.
See More: CSQ AC Contactor
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