Protection Relays

What is a Relay & How it Works

What is a relay?

A relay is an electrically operated switch. Most relays use an electromagnetic to operate the switch. An electromagnet is a device that creates a magnetic field by passing an electrical current through a coil of wire. The magnetic field is then turned off when the current is removed. 

Why use relays?

Relays are commonly used when there is a need to control a switch with high voltage or circuits with large amounts of current passing through them. Operating these types of switches manually can be dangerous, inefficient and impractical. By using relays, operational safety is increased while also providing the ability to use smaller, safer and less expensive electrical equipment to control devices. Using relays allow for control of several devices on a single switch, as opposed to using several switches for each device. Relays can be combined with timers and logic circuits to assist in electrical automation. 

How do relays work? 

A relay consists of two separate circuits that work together to open or close a switch (or contacts). The first circuit drives the coil (or electromagnet). The electricity passes through the coil, creating a magnetic field. The second circuit contains a set contacts and a separate power source. This circuit is what provides power to the electrical load.   

When electricity passes through the coil, it creates a magnetic field. This magnetic field pulls the contact from the other circuit closed (or against the stationary contact) which will allow current to pass through the contacts, therefore allowing the load to become energized. When the coil is de-energized, the magnetic field is gone which allows the contact to be pushed back into its original state, de-energizing the load side of the circuit.