HomeElectricalRelayWhat is The Distance Protection Relay?

What is The Distance Protection Relay?

We can easily guess that the distance protection relay has a relation with distance by its name. Let us discuss what is the distance protection relay?

This distance is the substations feeder line’s distance. This relay reacts according to the feeders’ certain distance. 

And the time of reaction depends on the impedance ratio of voltage and current. And the impedance of relay and fault point depends on their distance. Today we will have a detailed discussion on what is the distance protection relay?

What is the distance protection relay

Distance Protection Relay

Distance relay is of two types.

  1. Impedance Relay.
  2. Reactance Relay.

Work Principles of Distance Protection Relay

  • Different types of relay have different work principles.
  • Because its work principle depends on the ratio of voltage and current. 
  • It’s one coil get energized by voltage and the other coil get energized by the current.
  • The current element can make positive/pickup torque and the voltage element can make negative/reset torque.
  • This relay will be activated when the ratio of the voltage and current will be below a set value.
  • If there is any fault in the power system, the current will increase and voltage will decrease in the fault point.
  • At that moment we can measure the ratio of voltage and current, by the current and potential transformer. The amount of voltage in the potential transformer depends on the distance of the potential transformer and fault point.
  • If the fault point is far then the voltage will be high, and if the point is near there will be less voltage drop of the potential transformer. 
  • By measuring the ratio of impedance and voltage current, we can measure the distance between feeder point and fault.
  • This type of relay is used for detecting faults in the transmission line. This relay can maintain high-speed switching and small fault clearing time.
Work Principle of Distance Protection Relay

What is Fault Clearing Time?

Fault clearing time is the total time of sensing, relay activation, and arching of fault in a circuit breaker or any type of protective system. This means the time needed for clearing the fault.

This relay is used for both phase fault and ground fault in the transmission lines. Over Current relay was used before for this. But It’s fault clearing time is more than the distance relay.

This relay works as a guard when a short circuit current occurs in the generation, transmission system.

Advantages of Distance Protection Relay

  • The settings are permanent. No need to adjust.
  • Fault clearing time, overcurrent is less than overcurrent relay.
  • It keeps the system secured by switching in-phase and ground fault conditions in no time. 
  • It can measure the distance of feeder point and fault by calculating the ratio of impedance and voltage current.

That’s all for today’s article ‘what is distance protection relay?’

Hope this article was helpful for you to understand what is the distance protection relay? If you have any questions you can ask in the comment section.

You can also read: What is The Function of a Buchholz Relay?

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Md. Nazmul Islam
Md. Nazmul Islam
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