I. Working Principle of Contactors
A contactor is a widely used switching device that uses electromagnetic, pneumatic, or hydraulic principles to control the switching of the main circuit. Contactors have advantages such as strong current interruption capability, rapid action, safe operation, frequent operation, and remote control. However, they cannot interrupt short-circuit currents; therefore, contactors are usually used in conjunction with fuses. The primary control object of a contactor is an electric motor, but it can also control other electrical loads, such as welding machines and electric furnaces.
There are many ways to classify contactors. They can be classified according to the power source of the driving contact system into electromagnetic contactors, pneumatic contactors, and hydraulic contactors; or according to the nature of the arc-extinguishing medium into air contactors, oil-immersed contactors, and vacuum contactors, etc.
The working principle of a contactor is as follows: When the contactor coil is energized, the coil current generates a magnetic field. This magnetic field causes the stationary iron core to exert an electromagnetic attraction, drawing in the moving iron core and causing the AC contactor contacts to actuate. The normally closed contacts open, and the normally open contacts close; these actions are linked. When the coil is de-energized, the electromagnetic attraction disappears, and the armature is released by the release spring, causing the contacts to return to their original position. The normally open contacts open, and the normally closed contacts close. The working principle of a DC contactor is somewhat similar to that of a temperature switch.
II. Contactor Wiring Method
The wiring method for contactors varies depending on the specific application and model. Here are some common wiring methods:
Wiring method for a self-locking circuit: A self-locking circuit utilizes the normally open auxiliary contact of a contactor connected in parallel with the start button. After the start button is released, the contactor remains engaged. During wiring, connect both ends of the start button to the coil of the contactor, and connect both ends of the normally open auxiliary contact to the other end of the contactor.
Wiring method for interlock circuit: An interlock circuit uses the normally closed auxiliary contacts of two contactors to control each other, thereby achieving interlocking of the forward and reverse rotation of the motor. During wiring, connect the coils of the two contactors to the normally closed auxiliary contacts of the other contactor, and simultaneously connect the normally closed auxiliary contacts of the two contactors to each other.
Wiring method for star-delta reduced voltage starting: Star-delta reduced voltage starting utilizes a contactor to switch the motor windings from a delta connection to a star connection, thereby reducing the motor starting current. During wiring, connect the normally closed contacts of the contactor to the delta connection of the motor windings, and connect the normally open contacts of the contactor to the star connection of the motor windings.
Regardless of the wiring method used, the following points should be noted:
The power supply should be disconnected before wiring to avoid electric shock.
Wiring should be done according to the circuit diagram; do not connect wires or change the wiring arbitrarily.
When wiring, ensure a good connection between the contactor coil and the load to avoid problems such as poor contact or short circuit.
After the wiring is completed, each contactor terminal should be carefully checked to ensure that it is making good contact and that there are no short circuits or poor contacts.
III. Development Direction of Contactors
1. Development towards miniaturization and lightweighting: Miniaturization and lightweighting have always been basic requirements for contactors. With the development of equipment, the requirements for miniaturization and lightweighting are becoming increasingly important, especially in aviation and unmanned equipment, where small size and light weight of contactors are the primary indicators for selection.
2. Development Towards Intelligentization: Traditional contactors only have electrical breaking functions. Load current and voltage detection, overcurrent and overvoltage protection, and short-circuit protection are all handled by the user on the device itself. With the increasing demand for equipment miniaturization, these functions must be integrated to reduce equipment size. Therefore, these protection functions are best integrated with the contactor, allowing it to perform these functions, effectively reducing the overall size and achieving equipment miniaturization. Future contactors will inevitably develop towards intelligentization, meaning that in addition to basic load breaking functions, they should also have load current and voltage detection, overcurrent and overvoltage protection, load short-circuit protection, 2t inverse time protection, and bus control functions.
3. The breaking load voltage is trending towards high-voltage DC: Traditional contactors typically break voltages and currents of 25VDC, 1200A; 115VAC, 400Hz, 422A; and 386VAC, 54Hz, 100A, falling into the low-voltage, high-current range. With the increasing application of high-voltage DC in equipment systems, new requirements are placed on contactors in power distribution systems. These contactors must be able to break 274VDC series (including 400VDC, 500VDC, and 600VDC) DC voltages, which we call "high-voltage contactors." With the development of new energy and unmanned equipment, high-voltage DC systems will be widely used. Contactors used for power distribution control must meet these requirements; therefore, breaking higher DC voltage loads is the future development direction for contactors.
Finally, I sincerely thank you all for reading. Every time you read, it's a great encouragement and inspiration to me. I hope you now have a basic understanding of contactors. Lastly, I wish you all a wonderful day.
