Contactor: Description and Application
A contactor (also known as a modular starter or power relay) is a remotely controlled switching device capable of switching powerful, including inductive, alternating and direct current loads. Unlike electromagnetic relays, contactors have the unique ability to break the current circuit at multiple points simultaneously — in two, three, or more.
Field of Application
Contactors are generally used to control powerful electric motors or to switch circuits with large reactive powers. They find their application where frequent switching on and off of electrical devices operating with maximum load currents is required.
Main Elements of Contacts
Contactors consist of the following key elements:
- Contact system
- Arc extinguishing chamber
- Electrical magnetic mechanism
- System with block contacts
In starters with electromagnetic drives, the electromagnet armature is connected to the main and auxiliary contacts. The magnet controls the start (on) coil.
Classification of Modular Electromagnetic Starters
There are three main groups of modular electromagnetic starters:
- Alternating current contactors
- Direct current contactors
- Constantly alternating current contactors
The first type of starters is predominantly used for regulating asynchronous three-phase motors with short-circuited rotors, as well as for joint operation with electromagnetic drives of high-voltage circuit breakers and automated restart systems.
Rated Voltage of Contacts
Contactors can also be classified by the rated voltage of the main circuit:
- Voltage 220 and 440 Volts
- Voltage 380 and 660 Volts
Operating Principle of Contacts
A contactor may have from one to five main poles. The principle of operation of electromagnetic starters is that a voltage is applied to the control coil, causing the core to attract the armature. This leads to the closing or opening of the contact group depending on their initial state. The arc extinguishing system extinguishes the electric arc that occurs during the opening of the main contacts.
Additional Modules and Features
Additional modules can be connected to starters, such as a contactor attachment, timer, thermal relay, or blocking device. When connected to two starters, mechanical locking can create a reversible contactor. Connecting contacts with an overload relay transforms the device into a magnetic starter. Additional modules are used to expand the functional capabilities of the starter in automated systems, improve the operation of electrical installations, and simplify installation.