Industrial Automation Magazine India

Contactors and Relays

Published on : Monday 11-12-2023

Contactors and relays are essential components in electrical systems, serving as switches for controlling power flow.

A contactor is an electromagnetic switch which is designed to make or break the connection between the electric power supply and the load. In practice, the contactors are mainly used to control the high power-consuming devices because they offer heavy-duty contacts so as to provide safe switching of power circuits.

A relay is a simple electromagnetic switch which makes or breaks the electric connection between the power supply and the load. A typical relay uses an electric signal to control an electromagnet, which operates the armature of the relay for making or breaking the connection. The main parts of a relay include an electromagnet, movable contact, switching points and a control spring.

A relay is an electromagnetic switch operated by a relatively small electric current that can turn on or off a much larger electric current. The heart of a relay is an electromagnet (a coil of wire that becomes a temporary magnet when electricity flows through it)

As contactors are used for high-current load applications they are designed to control and reduce the arc produced when the heavy motor currents are interrupted. Other than the low current contacts, they are also setup with Normally Open contacts. These are devices which handle more than 20 Amperes current and over 100 Kilo Watts power.

The contactor has an AC/DC supply driven coil input. This will depend on the requirement. This coil will mostly be controlled by a lower voltage PLC. They can also be controlled by the motor voltage. The motor may have series of coils connected to either control the acceleration or even the resistance.

When current is passed through the contactor, the electromagnet starts to build up, producing a magnetic field. Thus the core of the contactor starts to wind up. This process helps in energising the moving contact. Thus the moving and fixed contacts make a short circuit. Thus the current is passed through them to the next circuit. The armature coil brings in high current in the initial position. This reduces as soon as the metal core enters the coil. When the current is stopped, the coil gets de-energised and thus the contacts get open circuited.

Durga Mechatronics, Mumbai. Email: [email protected]