When the coil is energized, the static iron core generates electromagnetic attraction to attract the moving iron core. Because the contact system is linked with the moving iron core, the moving iron core drives the three moving contacts to act at the same time, the main contact is closed, the auxiliary normally closed contact mechanically connected with the main contact is disconnected, and the auxiliary normally open contact is closed, thus turning on the power supply. When the coil is powered off, the suction disappears, and the linkage part of the moving iron core is separated by the reaction force of the spring, so that the main contact is disconnected, the auxiliary normally closed contact mechanically connected with the main contact is closed, and the auxiliary normally open contact is disconnected, thereby cutting off the power supply.

How to use:

One: Generally, a three-phase contactor has eight points, three inputs, three outputs and two control points. Output and input correspond, so it is easy to see. If you want to add self-locking, you need to connect the wire from one terminal of the output point to the control point.

Two: First of all, we should know the principle of AC contactor. He added an external power supply to the coil to generate an electromagnetic field. When the power is on, the contacts are disconnected after the power is off. After knowing the principle, you should find out the contacts of the external power supply, that is, the two contacts of the coil, which are generally at the lower part and both sides of the contactor. Other inputs and outputs are generally in the upper part, which is clear at a glance. Also pay attention to the voltage of the external power supply (220V or 380V), which is generally marked. And pay attention to whether the contact is normally closed or normally open. If there is self-locking control, just arrange the circuit according to the principle.

Precautions:

The selection of AC contactor should be based on the load type and working parameters. It is specifically divided into the following steps:

1. Select the type of contactor.

Ac contactors are generally divided into class I, class II, class III and class IV according to load types, which are named AC 1, AC2, AC3 and AC4 respectively. The control object of an AC contactor is non-inductive or micro-inductive load, such as incandescent lamp, resistance furnace, etc. The second kind of AC contactor is used to start and stop the wound asynchronous motor; The typical application of three kinds of AC contactors is the operation and breaking of squirrel-cage asynchronous motor; Four types of AC contactors are used for starting, reverse braking, reverse rotation and inching of cage asynchronous motors.

2. Select the rated parameters of the contactor.

According to the controlled object and working parameters such as voltage, current, power, frequency and working system, the rated parameters of contactor are determined.

1) The coil voltage of the contactor is generally lower, which can reduce the insulation requirements of the contactor and make it safer to use. However, in order to facilitate and reduce equipment, it is often selected according to the actual grid voltage.

2) The motor running frequency is not high, such as compressor, water pump, fan, air conditioner, punch, etc. , and the rated current of contactor is greater than the rated current of load. Contactor types can be CJl0, CJ20, etc.

3) The average running frequency of heavy-duty motors such as the main motors of machine tools, lifting equipment, winches and crushers exceeds 100 times /min. When running under the conditions of starting, inching, positive and negative braking and reverse braking, CJl0Z and CJl2 contactors can be selected. In order to ensure electrical life, contactors can be used with reduced capacity. When selected, the rated current of contactor is greater than the rated current of motor.

4) For heavy-duty motors, such as printing presses and boring machines, the running frequency is very high, reaching 600 ~ 12000 times /h, and they often run under the conditions of starting, reverse braking and reverse rotation. Contactors can be selected according to electrical life and starting current, and the contactor models are CJl0Z, CJl2, etc.

5) When the capacitor in the AC circuit is put into or out of the power grid, the closing impulse current of the capacitor should be considered in the contactor selection. The rated current of general contactors can be selected according to 1.5 times the rated current of capacitors, and the models are CJ 10, CJ20, etc.

6) When the contactor is used to control the transformer, the magnitude of surge current should be considered. Such as AC arc welder, resistance welder, etc. Generally, contactors can be selected according to twice the rated current of the transformer, and the models are CJl0 and CJ20.

7) For electric heating equipment, such as resistance furnace and electric heater, the cold resistance of the load is small, so the starting current is correspondingly large. Contactor can be directly selected according to rated load current, regardless of starting current. Model can choose CJl0, CJ20, etc.

8) Due to the large starting current and long starting time of gas discharge lamps, AC contactors can be selected according to the rated current 1. 1 ~ 1.4 times, and the models can be CJl0 and CJ20.

9) Rated current of contactor refers to the maximum allowable current of contactor during long-term operation, with a duration of ≤8h, which is installed on the open control panel. If the cooling conditions are poor, the rated current of the contactor should be 1 10% ~ 120% of the rated load current when selecting the contactor. For the motor working for a long time, because the oxide film has no chance to be removed, the contact resistance increases, resulting in contact heating exceeding the allowable temperature rise. In practical selection, the rated current of contactor can be reduced by 30%.