Significance of Trip Circuit Supervision relay

            We all know basic relay operation that when fault came first main relay operate(Overcurrent or Earthfault) which trip master trip relay (86) and then it trip our circuit breaker. So you might think that master trip is very important to trip the breaker but wait, what happen if your trip coil of circuit breaker is open(faulty)..., What happen if your DC supply is fail...in this type of case neither your master trip operate nor your breaker trip so to indicate this type of condition Trip Circuit Supervision relay is used.

           Trip Circuit Supervision relay could not trip breaker but it check continuously that if fault came then circuit breaker will operate or not. It supervise trip circuit in both condition of breaker 

1. Preclose Condition:- When your breaker is open.

2. Postclose Condition:- When your breaker is close.

    

So How it supervise trip circuit?

                 Here i take reference of ALSTOM Make VAX31 relay which has 3 coil all are rated at 110V DC(Means that A coil energize only when it get voltage in the range of 70V to 110V.) which is shown in below drawing which is of course made by me.

                      In normal condition when breaker is ON and your trip coil of breaker is ok then, A and C coil will energize. HOW? A coil get positive voltage (+55V) directly but negative voltage(-55V) come through trip coil of breaker and one NO contact (which is close when breaker is close). When A coil energize it's all contact will changeover so C coil also energize at the same time. Inshort in close condition of breaker, A and C coil is energize. TAKE A LOOK IN BELOW FIGURE.

                  Now suppose fault came, so master trip operate which trip the breaker you are not reset the master trip so it's contact will remain close. In this condition your B and C coil will energize. HOW? B coil get positive voltage (+55V) from master trip close contact and negative voltage (-55V) from trip coil of breaker and NC contact of breaker. When B coil energize it's all contact will changeover so C coil also energize at the same time. Inshort in open condition of breaker (Master trip relay is tripped), B and C coil is energize. TAKE A LOOK IN BELOW FIGURE.

                  In running condition, if trip coil of circuit breaker will burned (damge) then this relay give alarm, indication for that so you can replace that faulty trip coil. If your Trip circuit is not healthy then your breaker neither will close nor will trip electrically.