Difference between Static Relays and Electromagnetic Relays

Differences Digital Electronics Electronics & Electrical

In electrical and electronics engineering, a Relay is an electrically operated switch which is used to connect or disconnect two circuits. Since the operation of a Relay is governed by an electric control signal, hence it can be operated automatically. Basically, the relays are designed for switching of high power circuits by using low power electric signals.

Depending on the technology used, the relays can be broadly classified into two types namely

Electromagnetic Relays
Static or Solid-State Relays

In this article, we will highlight all the key differences between an electromagnetic relay and a solid state relay by considering different parameters. But before getting into the differences, let's start with some basics of electromagnetic relay and solid state relay so that it becomes easier to understand the differences between them.

What is an Electromagnetic Relay?

A type of relay that uses an electromagnet to perform the switching function is known as electromagnetic relay. The working of an electromagnetic relay is based on the principle of electromagnetic induction.

A typical electromagnetic relay consists of the following main parts

Electromagnet
Movable contact, called armature
Set of input terminals
Set of contact terminals or switching points
Control spring

The electromagnet of the Relay is made by wounding a copper wire on a soft iron core. The two terminals of the electromagnetic coil are used as the input terminals to provide the control signal to the relay. The magnetic field produced by the electromagnet is used to open and close the switching terminal of the relay. The electromagnetic relays are widely used in several applications such as lighting control system, industrial processes, power generation, transmission and distribution, power system protection, automotive, etc.

What is a Static Relay?

A solid state relay or static relay is the one which uses electrical and optical properties of semiconductor materials to perform the switching functions. Therefore, a solid state relay does not contain any moving part.

The solid state relays provide a complete electrical isolation and connection between two circuits. It is because, in the off state, it offers an infinite resistance between the two circuits and when it is in on state, it offers almost zero resistance.

The main switching components of the solid state relays are transistor, SCRs, TRIAC, etc. The main advantage of the solid state relays over the electromagnetic relays is that the solid state relays do not have moving parts, hence there operation is faster than electromagnetic relays. Also, the solid state relays are comparatively smaller in size, hence these are widely in a number of electronic circuits like computer, UPS, robotics, control systems, etc.

Difference between Static Relay and Electromagnetic Relay

Both static and electromagnetic relays are used for automatic switching of electrical and electronic circuits. However, there are several differences between static and electromagnetic relays that are listed in the following table

Basis of Difference	Electromagnetic Relay	Static Relay
Definition	An electromagnetic relay is the one which uses an electromagnet to perform the switching function.	A static relay is the one that uses solid state semiconductor devices like transistor, MOSFET, SCR, etc. to perform the switching function.
Abbreviation	EMR is the abbreviation used for electromagnetic relay.	SSR is the abbreviation used for solid state or static relay.
Alternate name	Electromagnetic relay is also called as electromechanical relay	Static relay is also called as solidstate relay.
Main components	The main components of an electromagnetic relay are- Electromagnet Moving armature Set of input and switching terminals	The main components of a static relay are − Semiconductor switching device Set of input and switching terminals Opto-coupler
Working principle	Electromagnetic relays work on the principle of electromagnetic induction.	Static relays operate on the electrical and optical properties of semiconductors.
Moving parts	Electromagnetic relays consists of moving parts such as armature.	Static relays do not consist any moving part.
Switching noise	Electromagnetic relays produce switching noise.	Static relays do not produce switching noise.
Power consumption	Electromagnetic relays consume high power.	Static relays consume very less power, usually of the order of mW.
Problem of arcing	Due to presence of moving contacts, there is a problem of arcing at contact terminals in the electromagnetic relays.	As a static relay does not have any moving contact, hence there is no problem of arcing at switching terminals.
Replacement of contact	In an electromagnetic relay, the replacement of contact terminals is necessary.	Static relays do not require the replacement of contact terminals.
Position & location of relay	Electromagnetic relay is always installed in straight position and at the location away from the magnetic fields.	Static relay can be installed in any position and at any location.
Functions	A single electromagnetic relay can perform only a single function. For example, if one electromagnetic relay is used for over-voltage protection, then another EM relay has to be used for over-current protection.	A single static relay can perform multiple functions. For example, one SSR can be used for both overcurrent and over-voltage protection.
Effect of gravity on operation	The gravity can influence the operation of electromagnetic relays.	The operation of static relays is independent of the gravitation force.
Effect of shocks & vibrations	The operation of electromagnetic relays get affected by the shocks and vibrations.	There is no effect of shocks and vibrations on the operation of static relays.
Effect of temperature	In the electromagnetic relays, there is no significant effect of change in temperature.	Solid state relays may get damaged due to high temperature.
Size	Electromagnetic relays are comparatively large in size.	Static relays have compact size.
Accuracy	Electromagnetic relays are less accurate.	The accuracy of static relays is high.
Speed	Electromagnetic relays are slow.	Static relays are fast.
Cost	Electromagnetic relays are less expensive.	Static relays are comparatively costlier.

Conclusion

The most significant difference between the two is that an Electromagnetic Relay has mechanically moving parts, while a Static Relay does not have any moving parts. However, both EMR and SSR are widely used in several applications like lighting control systems, automotive, robotics, instrumentation and automation, etc.