Types of Relays
An 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:
- Attracted armature type
- Solenoid type
- 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:
- Induction cup relay
- Induction disc relay
Directional type relay
Directional type relays operate on the direction of current and power. They are classified into two groups:
- Reverse current
- Reverse power
The tripping instant in time-based relays can be controlled. Such relays are classified into three classes:
- Instantaneous type relays
- Definite time lag type
- Inverse time lag type
- Capacitor type
- 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:
A differential relay compares the difference of quantity entering and leaving the system. They are also classified into two groups:
- Differential current
- Differential voltage
The relay operates when the temperature rises above certain limit due to current.
The sensed quantities are first rectified and then provided to relay coil.
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.
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.
One part of such relays in electro-mechanical 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.