Factors of contactor controlling large current through small current

In many electrical secondary equipment, contactor is only one of the equipment that controls large current through small current. Why control a large current with a small current?

1、 Written meaning.

Because electrical secondary equipment refers to the low-voltage electrical equipment required to monitor, control, regulate and protect primary equipment and provide operation conditions or production command signals for operation and maintenance personnel.

This means that the secondary equipment is a control appliance for the power system.

2、 What controls are available?

The control equipment mainly includes contactors, starters and various control relays.

3、 Common characteristics of these devices.

Their common characteristics are high operating frequency, long service life and corresponding conversion ability, that is, large current equipment can be controlled by small current.

Reasons for small current controlling large current

When the switch cuts off the power supply of heavy load equipment, an arc will be generated. If the main line current is greater than the maximum current of the contactor, the contactor will be burned, endangering personal and equipment safety.

Remote low current control will greatly reduce this risk.

The way to control large current with small current

Taking AC contactor as an example, it is mainly used to frequently connect or disconnect the main circuit with large load from a long distance. We often use it to control motor, electric heating equipment and capacitor bank.

Its structure is mainly composed of electromagnetic system, contact system, arc extinguishing device, etc. Through the power on and power off of the electromagnetic coil, the AC contactor can pull in and release the main line to realize the disconnection of the main line.

Some contactor coils adopt DC and low voltage DC, which will cause less damage to the equipment of the control line.

Through the power on and power off of the AC contactor, the main line is controlled to change the sequence of any one of the three phases, so as to achieve the effect of forward and reverse rotation of the motor.

Button switch, AC contactor, time relay, travel switch, etc. Are used to control small current and large current, that is, to protect equipment safety and personal safety, which is necessary for site safety.