Power System Protection: 20 Different Types of Relays

The electrical relay is a switch that is used for controlling circuits. Today you’ll learn about different types of electrical relays.

Electromagnetic attraction type

The magnetic force produced by undesired current attracts the armature of the relay. Electromagnetic attraction type relays can operate on either a.c or d.c quantities. They are further divided into three types:

1. Attracted armature type
2. Solenoid type
3. Balance beam type

Induction type relay

The working of Induction type relays relies on the electromagnetic induction phenomenon. They are only used for a.c quantities. They are further classified into two groups:

1. Induction cup relay
2. Induction disc relay

Directional type relay

Directional type relays operate on the direction of current and power. They are classified into two groups:

1. Reverse current
2. Reverse power

Time relays

The tripping instant in time-based relays can be controlled. Such relays are classified into three classes:

1. Instantaneous type relays
2. Definite time lag type
3. Inverse time lag type
4. Capacitor type
5. Electronic type

Distance type relay

Distance type relays contain two coils. One of which is energized using current and another one with voltage. The voltage to current ratio is measured and working of distance relays is based on this voltage to current ratio. They are further classified into three distinctive groups:

1. Admittance
2. Impedance
3. Reactance

Differential relay

A differential relay compares the difference of quantity entering and leaving the system. They are also classified into two groups:

1. Differential current
2. Differential voltage

Thermal Relay

The relay operates when the temperature rises above certain limit due to current.

Rectifier relay

The sensed quantities are first rectified and then provided to relay coil.

PMMC Relay

It is a permanent magnet d.c relay in which he coil is free to rotate.

Gas actuated relay

In such relays, the gas pressure is adjusted in a manner so as to trip the relay coils.

Numerical/Microprocessor based relay

Microprocessor based relays are the most advanced type of programmable relays.

Reed switch relays

These are simple and compact relays. The basic reed relay is simple reed switch which has a winding wrapped around the relay. They are manufactured in many DIP and SIP packages as well as winding free reeds are also available.

Static relays – Solid State Relays

Static relays are composed of electronic components. Such relays are composed of transistors, diodes, integrated circuits, resistors and other electronic components. An essential part of such relays is a comparator which takes two or more current/voltages as input and provides an output.

Frequency Monitoring relays

The frequency of voltage plays key role in electrical power networks. The working of various electrical machines, generators, and mechanisms heavily relies on frequency. Frequency relays continuously monitor the operating frequency of system and trip on the variations.

Thermal relays

As the name indicates, the working of thermal relays depends on the temperature of the equipment. They can either directly detect the temperature or can detect the current overloading conditions.

Motor load monitoring relays

Such relays monitor the load condition and operate under specified conditions. These relays can be based on current measurement or on cosφ based.

Insulation monitoring relays

Insulation monitoring relays continuously monitor the insulator. Whenever insulation fault occurs it immediately trips when the voltage drops behind specified threshold value.

Liquid monitoring relays

They are used to monitor regulator and control of liquid fluids.

Hybrid Relays

One part of such relays in electromechanical while another part is solid state electronics.

General purpose relays

These are different types of relays whose working principle is based on either of above types.