Analysis of AC Contactor Selection Method

1. Serial and parallel use of contactors

There are many electrical devices that are single-phase loads. Therefore, several poles of multipole contactors can be used in parallel. Such as resistance furnaces, welding transformers and so on. When using several poles in parallel, smaller capacity contactors can be used. It must be noted, however, that the agreed-upon heating current of the parallel contactor is not exactly proportional to the number of poles connected in parallel. This is due to the fact that the resistance values ​​of the active and static contact circuits are not necessarily equal, so that the positive current flow is not evenly distributed. Therefore, after two parallel analysis, the current can only increase to 1.8 times. After three parallel connections, the current can only increase to 2 to 2.4 times.

In addition, it should be pointed out that since the pole contacts after parallel connection cannot be turned on and off at the same time, the ability to turn on and off can not be improved.

In some cases, several poles of the contactor can be used in series. As the number of fractures in the contact increases, the arc can be divided into many segments, the arc extinguishing ability is improved, and the extinguishment of the arc is accelerated. So after several poles in series can increase its operating voltage, but can not exceed the rated insulation voltage of the contactor. The contracted heating current and rated operating current of the series-connected contactor do not change.

2, the impact of the power frequency

For the main circuit, the change of frequency affects the skin effect. When the frequency is high, the skin effect increases, and for most products, the temperature rise of the conductive loop at 50 Hz and 60 Hz does not have a great effect. However, it is necessary to pay attention to the attraction coil. When the attraction coil of 50 Hz is used for 60 Hz, the magnetic flux of the magnet wire will be reduced and the suction force will be reduced. Whether it can be used depends on the margin of its design. Under normal circumstances, the user is best to use according to its calibration value, ordering according to the frequency of the operating power supply used for ordering.

3, the impact of operating frequency

The number of operating cycles per hour of the contactor has a great influence on the burning of the contacts. Attention should be paid when selecting them. The operating frequency of the contactor is given in the technical parameters of the contactor. When the actual operating frequency of the electrical equipment is higher than the given value, the contactor must be derated.