AC contactors utilize main contacts to control the power circuit and auxiliary contacts to energize the control circuit.
The main contacts are typically normally open (NO), while the auxiliary contacts often consist of pairs of both normally open and normally closed (NC) contacts; smaller contactors are also frequently employed as intermediate relays in conjunction with the main circuit.
The contacts of an AC contactor are fabricated from a silver-tungsten alloy, a material chosen for its excellent electrical conductivity and high resistance to thermal erosion.
The actuating force of an AC contactor is derived from the magnetic field generated when alternating current flows through a coil fitted with an iron core. This electromagnetic core is constructed from a stack of thin, silicon-steel laminations shaped like the Chinese character "Shan" . One half serves as the stationary core, around which the coil is wound; these coils are available in a variety of operating voltage options. To ensure magnetic stability and prevent chatter, a short-circuit ring is embedded within the contact surface of the core. Upon loss of power, the AC contactor returns to its original state via spring-loaded reset.
The other half of the assembly consists of the movable core, which mirrors the structural design of the stationary core and serves to actuate the opening and closing of both the main and auxiliary contacts.
Contactors rated at 20 amperes or higher are equipped with arc chutes; these devices harness the electromagnetic forces generated during circuit interruption to rapidly extinguish the electric arc, thereby protecting the contacts from damage.
Contactors are capable of high-frequency operation; when utilized for the switching and control of power supplies, they can achieve a maximum operating frequency of up to 1,200 switching cycles per hour.
Contactors boast an exceptionally long service life: their mechanical lifespan typically ranges from several million to ten million cycles, while their electrical lifespan generally spans from several hundred thousand to several million cycles.
Technological Evolution
AC contactors are now manufactured as integrated, self-contained units, and while their physical form and performance characteristics have undergone continuous improvement, their fundamental functional principles remain unchanged. Regardless of the extent of technological advancement, the standard AC contactor continues to occupy a vital and indispensable position within electrical systems.
Air-Break Electromagnetic Contactors (English: Magnetic Contactor): These devices primarily consist of a contact system, an electromagnetic actuation system, a support frame, auxiliary contacts, and an outer housing (or baseplate).
Since the coils of AC electromagnetic contactors are typically powered by an AC supply, the energization of the contactor is often accompanied by a distinct, high-decibel "clack" or clicking sound; this characteristic audible signature is a hallmark feature of electromagnetic-type contactors. Since the 1980s, researchers worldwide have focused on developing AC contactors that are both silent and energy-efficient. One fundamental and viable approach involves stepping down the AC power supply via a transformer, rectifying it through an internal circuit to convert it into DC power, and then using this DC power to energize the contactor. However, this complex control method is not widely adopted.
Vacuum Contactor: A vacuum contactor is a type of contactor in which the contact system utilizes a vacuum arc-extinguishing chamber.
Semiconductor Contactor: A semiconductor contactor is a type of contactor that performs current switching operations by altering the conduction and interruption states of the electrical circuit.
Permanent Magnet Contactor: A permanent magnet AC contactor is a low-power-consumption contactor designed by replacing the traditional electromagnetic driving mechanism with a permanent magnet driving mechanism; it operates based on the principles that like magnetic poles repel each other, while unlike poles attract.
