Knkong Electric Co.,Ltd

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What is the selection method of AC contactor

AC contactor

1. Series and parallel use of contactors There is much electrical equipment that is single-phase loads. Therefore, several poles of a multi-pole contactor can be used in parallel. Such as resistance furnace, welding transformer, etc. When several poles are used in parallel, a contactor with a smaller capacity can be selected. However, it must be noted that the conventional heating current of the contactor after the parallel connection is not completely proportional to the number of parallel poles. This is because the resistance values ​​of the active and static contact loops are not necessarily equal so that the current flowing through the active is not evenly distributed. Therefore, the current can only be increased to 1.8 times after the two parallel connections, and the current can only be increased to 2 to 2.4 times after the three poles are connected in parallel. 

In addition, it should be pointed out that since the pole contacts in parallel cannot be turned on and off at the same time, it is impossible to improve the turning on and breaking capacity.

Sometimes, several poles of the contactor can be used in series. Due to the increase of contact breaks, the arc can be divided into many segments, which improves the ability to extinguish the arc and accelerates the extinction of the arc. Therefore, the working voltage can be increased after several poles are connected in series, but it cannot exceed the rated insulation voltage of the contactor. The conventional heating current and rated working current of the contactors after series connection will not change. 

2. The influence of power supply frequency For the main circuit, the change in frequency affects the skin effect. The skin effect increases at high frequencies. For most products, the effect of 50 Hz and 60 Hz on the temperature rise of the conductive circuit is not very great. Big. But for the suction coil, it needs to be noted that the magnetic flux of the electromagnetic wire will be reduced when the 50 Hz designed suction coil is used at 60 Hz, and the suction will also be reduced. Whether it can be used depends on the design margin. Under normal circumstances, the user is best to use according to its calibration value, when ordering according to the operating power frequency used. 

3. Effect of operating frequency The number of operating cycles per hour of the contactor has a great influence on the burnout of the contacts. Care should be taken when sellecting. The applicable operating frequency 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 contractor must be derated.

Date:2019-06-21 09:35

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