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:

        1.  Lockout Relays/ Latched Relays: When this Relay is Operated, it latches its output contact and locks out the Circuit, and hence it is called as Lockout Type Relay as Circuit cannot be Normalised, untill and unless this Relay is Reset. To Reset, we have to Manually Reset the Relay by Hand (Hand Reset Type) or Energise the Reset Coil Electrically through  Push Button or SCADA (Electrically Reset Type).
        2. Self Reset Type Relay: Once the Coil of this Relay is Energised, it Contacts are operated and it immediately Resets it Self. This Type of Relays are used for Single Phase Tripping.


          What is the Working Principle?

          1. DC Postive is given to one end of the Parallely connected  NO Output Contacts of the different Protection Relays. The other end of the Parallely connected output contacts of different Protection Relays, is connected to the Operating Coil of the 86 Relay.
          2. When any of the Concerned protection Operates, the DC Positive is extended to the Operating Coil of 86. Negative DC being continously given to the other end of the Operating Coil, the 86 relay Operates.
          3. As 86 relay Operates, its Contacts Changes its Status.
          4. Its NO Contact is used for Tripping the Breaker, giving indication etc. as it Closes when the 86 Relay is operated.
          5.  Its NC Contact is used in Closing Circuit of the Breaker. When 86 is operated, its NC Contact used in the Closing Circuit of the Breaker opes up and so the Breaker cannot be closed unless the 86 Relay is Reset.
          6. It NO contact is used for LBB Initiation.

            Thank You so Much. See you in some other Post.