Master Trip Relay

Master Trip Relay, you may have herd this term , quite a lot of times, now we are going to understand, what it exatly is, in the following post.

What is a Master Trip Relay?

  1. Defination: Master trip relay is a contact multiplication or an Auxillary  relay, which operates on the command from Multiple protection relays and gives a Single Commmand to the Breaker Trip Coil.
  2. ANSI Code: Its ANSI Code is 86.
  3. Remarks: Master Trip Relay (86) cannot Sense Faults.

What is its Significance?

  1. Creates an Isolation between Protection Relay and the Breaker Tripping Coil. If there is some problem in the Tripping Circuit, if 86 Relay is not used, the Protection Relay Contacts will get burned. Protection Relays being expensive, we cannot afford that and so we use Master Trip Relay. So that, if there is any problem, Master Trip relay contacts will get burned and not Protection Relays.
  2. If Master Trip Relay is not used, then we need to wire up all the Protection Relays to the Tripping Coil of the Breaker, which will result in lot of wiring on the Breaker Tripping Circuit, leading to DC Leakage and also increase in the Cost of Wiring. On the other, if Master Trip Relay is used, there will be only one wire from Master Trip Relay Contact to the Tripping Circuit.
  3. Master Trip Relay has higher Contact Capacity and so if there is any fault in the Tripping Circuit, the contacts of the 86 relay can withstand the Fault Current. If Tripping is given directly from the Protection relay, the contacts of the Protection relay may get damaged , we cannot afford that , as Protection relays are costly.
  4. High Speed Operation.
  5. The Additional Contacts of the Master Trip Relay can be used for Tripping Multiple Circuit Breakers, Annunciations, Interlocking and LBB Initiation

How is it Constructed?

  1. Operating Coil: It is given a continous Negative DC Voltage to one end. The other end receives the DC Positive Voltage, when any of the Protection relay Contacts wired to it, operates. An NC Contact is placed in series, which opens up, when 86 Relay is operated, therby protecting the Operating Coil of the 86 Relay from Continous DC Voltage.
  2. Resetting Coil: To Reset the Relay, Resetting Coil needs to be Energised.
  3. The Additional Contacts of the Master Trip Relay can be used for Tripping Multiple Circuit Breakers, Annunciations and Interlocking.

What are the Types of Master Trip Relays?

Based on how they reset, Master Trip Relays are classified into following two types:

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