What are the common types of relays?

Relay (English name: relay) is an electrical control device, when the input (excitation) changes to meet the requirements, in the electrical output circuit to make the controlled amount of a predetermined step change. It has an interactive relationship between the control system (also known as the input loop) and the control system (also known as the output loop). Usually used in automatic control circuits, it is actually a small current to control the operation of large current "automatic switch". Therefore, it plays the role of automatic regulation, safety protection and conversion circuit in the circuit.

Common types:

1. Over current relay

Over-current relay, referred to as CO, is a relay that operates from the current exceeds its set value. It can be used as the protection of system circuit and overload. The most commonly used is induction type over-current relay, which uses electromagnets to oppose aluminum or copper rotating discs and relies on electromagnetic induction principle to rotate the rotating discs to achieve protection.

Action principle:

Induction type overcurrent relay uses the secondary current of current transformer to produce magnetic field in the relay to impel the disk to rotate, but the current flowing through the relay must be greater than the current value of the current plate to rotate.

2. Over voltage relay

Overvoltage relay, referred to as OV, is mainly used to protect power equipment from damage when the abnormal voltage of the system rises to above 120% rating. The structure and operation principle of inductive overvoltage relay is similar to that of overcurrent relay, only the main coil is different.

3. Undervoltage relay

Undervoltage relays, or UVs for short, are constructed in the same way as overvoltage relays, except that the internal contacts and the turntable turn immediately when applied voltage.

4. Grounding overvoltage relay

Grounded overvoltage relay, called OVG, or grounding alarm relay, called GR, its structure is the same as overvoltage relay, using three-phase three-wire non-grounding system, connected to open triangular grounding transformer to detect zero-phase voltage.

5. Grounding overcurrent relay

Earthing over current relay, or GCR, is a high voltage line ground protection relay.