Relay Protection Control: Different Types of Protective Relays

Protective relays are instrumental in monitoring and detecting problems in an electrical circuit. Based on their design, dimensions and local operating range, relays can be classified into different types for use in different areas.

Understanding Protective Relays and their Types

A relay protection control device plays an important role in monitoring and detecting problems in the current, voltage and power flow in an electrical circuit. In the event of a fault, the device triggers the circuit breaker to detect and isolate the bad circuit from the rest of the power system. In doing so, protective relays help isolate/remove bad/abnormal and/or short-circuiting elements from the power system.

A protective relay can be classified based on three basic parameters – design, dimensions and operating range. Accordingly, based on these parameters, they can be differentiated into the following sub-categories:


  • Sealed
  • Open
  • Hermetic


  • Miniature
  • Micro Miniature
  • Sub Miniature

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Operating Range:

  • Micro Power
  • Low Power
  • High Power
  • Intermediate Power

Keeping these classifications in mind, relay protection control devices can be classified into the following types.

Solid State Relays

Solid-state components switch operations without moving any parts. These relays offer high power gains compared to other relay types owing to the less energy required for the switching operation. Examples include photo-coupled SSR and transformed coupled SSR.

Electromagnetic Relays

These relays use electrical, magnetic, and mechanical elements to perform the switching operation. They also use mechanical contacts and operating coils, with mechanical contacts opening or closing when the coil gets activated. Examples of electromagnetic relays include AC/DC relays, induction relays and electromagnetic attraction relays.

Hybrid Relays

These protective relays combine the use of electronic and electromagnetic elements to perform the switching operation. The electronic component rectifies the fault and the electromagnetic component relays the output. A good example would be a reed relay.

Thermal Relays

These relay protection control devices rely on temperature sensors to perform the switching operation. They detect an increase in temperature and switch the positions, isolating the faulty component. Thermal relays usually find their use in motor protection.

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To conclude, remember that it is important to choose a relay protection control based on the industry, equipment and power consumption.