Views: 1 Author: Site Editor Publish Time: 2022-09-16 Origin: Site
Among many electrical secondary equipment, the ac contactor is only one of the devices that controls a large current through a small current. Why control a large current through a small current?
1. Written meaning
Electrical secondary equipment refers to the low-voltage electrical equipment required to monitor, control, regulate, and protect the work of primary equipment and provide operating conditions or production command signals for operation and maintenance personnel. It means that the secondary equipment is the control electrical appliance used in the power system.
2. What are the control devices?
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 life, and corresponding conversion capabilities, that is, high-current devices can be controlled by small currents.
When the switch cuts off the power supply of the heavy-load equipment, an arc will be generated. If the main line current is greater than the maximum current of the contactor, it will cause the contactor to burn, endangering personal and equipment safety.
This risk can be greatly reduced by remote small current control.
Take the AC contactor as an example, it is mainly used for frequent connection or disconnection of the main circuit with heavy load over a long distance, and we often use it to control motors, electric heating equipment and capacitor banks.
Its structure is mainly composed of electromagnetic system, contact system, arc extinguishing device, etc. The electromagnetic system is coil, iron core and armature. The AC contactor realizes the connection and disconnection of the main line through the electrification and de-energization of the electromagnetic coil, which makes the armature pull in and release.
The contactor in the control circuit above is a 380V contactor, that is, the rated voltage of the coil is 380V. Because there is no excessive load in the control circuit, the control circuit current is very small.
Some contactor coils use direct current, a small voltage direct current, which has less damage to the equipment of the control line.
The main circuit is controlled by the power-on and power-off of the AC contactor, and the phase sequence of any one of the three phases is changed, so as to achieve the effect of forward and reverse rotation of the motor.
Button switches, AC contactors, time relays, travel switches, etc. These devices are used to control large currents with small currents, that is, to protect equipment safety and personal safety, which is necessary for on-site safety.