Difference between Electromechanical Relay and Numerical Relay

In electric circuits, there is a device used to detect faulty conditions and protect the circuit from damages. It is known as relay. Thus, a relay can be defined as a device that identify faults and isolate the unhealth section of the circuit from the heathy system. In an electric circuit, a relay can provide protection against various types of faults like short-circuit, overcurrent, over-voltage, under-voltage, earth fault, and more. Overall, a relay is a protective device used to protect electric circuits from undesirable conditions, called faults.

These protective relays can be classified in several types depending on their construction and mechanism. In this article, I will explain two common types of relays namely, electromechanical relay and numerical relay. Also, I will explain the key differences between electromechanical relay and numerical relay. So, let’s start with the basic definition of electromechanical and numerical relays.

What is an Electromechanical Relay?

An electromechanical relay is a protective device used in electrical circuits to isolate the faulty part from the heathy section in an electric circuit. It is basically an electrically operated switch that disconnects two segments of an electric circuit.

Electromechanical relays are mainly used in high power transmission and distribution system. Because, electromechanical relays provide a way of controlling a high-power electric circuit using a low power electronic signal.

An electromechanical relay consists of an electromagnetic coil and a moving contact. The moving contact makes or breaks the main power circuit depending on the applied operating signal to the relay.

The main application of electromechanical relays is to control the switching operation of a high-power circuit by using a low power signal. Some common applications of electromechanical relays are in automatic appliances, automobiles, power systems, etc.

What is a Numerical Relay?

A numerical relay is an improved form of an electromechanical or static relay. A numerical relay is a type of relay that measures parameters like voltage, current, etc. in an electric circuit and then converts these measured parameters into numerical data that are then utilized to make or break the circuit.

Again, the primary purpose of a numerical relay is to protect the electric circuit from unexpected conditions that may occur.

The major advantages of using numerical relays in electric circuits are −

  • A single numerical relay can measure multiple circuit parameters such as voltage, current, frequency, etc.

  • A single numerical relay can analyze and detect multiple faults like over-current, over-voltage, and more.

A typical numerical relay consists of several digital components, such as microprocessor, A/D converter, digital communication module, I/O module, etc.

Since, the operation and functioning of numerical relays depend on data based digital instructions, hence, they are also called computer-based relays or microprocessor-type protective relays.

The numerical relays are mainly used in power generating stations, transmission and distribution substations to provided automated protection. The numerical relays are also used to protect electrical machines like transformers, electric motors, generators, etc.

This is all about basics of electromechanical and numerical relays. Let us now discuss the key differences between electromechanical and numerical relays in detail.

Difference Between Numerical Relay and Electromechanical Relay

The major differences between electromechanical relay and numerical relay are given in the following table −

Parameter Electromechanical Relay Numerical Relay
Basic Electromechanical relay is an electromagnetic induction-based relay that protect circuit against fault by opening mechanical switch. Numerical relay is a microprocessor-based relay that uses software to provide protection in electric circuits.
Major components Electromechanical relays have an electromagnetic coil and a mechanical switch. Numerical relay has I/O module, microprocessor, and communication module.
Technology Electromechanical relays use 1st generation technology standards. Numerical relays use modern technology standards.
Response speed Electromechanical relays have slow response speed. Numerical relays have very fast response speed.
Principle of operation The operation of electromechanical relays is based on the principle of electromagnetic induction. The operation of numerical relay is based on the microprocessor functioning and computer algorithms.
Size Electromechanical relays have large physical size. Numerical relays have compact size.
Multi-functioning Electromechanical relays cannot perform multiple functions. A numerical relay can perform multiple functions.
Accuracy Electromechanical relays are less accurate. Numerical relays are highly accurate.
Memory Electromechanical relays do not have memory features. Numerical relays have memory features.
Flexibility Electromechanical relays have mechanical operation. Thus, they are less flexible. Numerical relays have high flexibility due to programming capabilities.
Type of settings Electromechanical relays have some fixed settings. Numerical relays have software-based settings that can be changed easily.
Maintenance Electromechanical relays require more maintenance due to presence of moving parts. Numerical relays require less maintenance.
Self-monitoring Electromechanical relays do not have self-monitoring feature. Numerical relays have self-monitoring feature.
Compatibility with SCADA Electromechanical relays are not compatible with SCADA. Numerical relays have SCADA compatibility.
Input In electromechanical relays, inputs are provided through plug or dial settings. In numerical relays, inputs are provided through keyboards.
Output Electromechanical relays provide output as flags or targets. Numerical relays provide output through LED or LCD display.
Burden on current transformer Electromechanical relays have high burden on current transformer. Numerical relays have low burden on current transformer.
Reliability Electromechanical relays are highly reliable due to mature technology. Numerical relays are less reliable.
Sensitivity Electromechanical relays have good sensitivity. Numerical relays have excellent sensitivity.
Remote operation In electromechanical relays, the remote operation is not possible. Numerical relays can be operated remotely.
Immunity to disturbances Electromechanical relays have high immunity against disturbances. Numerical relays have very low disturbance immunity.
Applications Electromechanical relays are used in motor control circuits, automotives, power systems, etc. Numerical relays are mainly used in generating stations and substations.


In conclusion, the primary function of electromechanical and numerical relays is the same, i.e., provide protection against unexpected faults in the electrical system. However, they are completely different from each other in all aspects like technology, input-output, accuracy, reliability and more. In this comprehensive article on difference between electromechanical and numerical relays, I have explained an overview of electromechanical relay and numerical relay individually along with the key differences between them.

Updated on: 13-Nov-2023


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