Trip Circuit Supervision Circuit senses any fault either in the trip coil of breaker or trip circuit. On sensing a fault, Trip Circuit Supervision Relay changes its contact status to window annunciation on the panel. Here fault in the circuit means any break or open circuit. In this post we will be discussing the working principle of trip circuit supervision.
Basically, a breaker is equipped with two trip coils. Both the trip coil energizes if relay issues a tripping command. On energization of trip coil, breaker mechanism opens the circuit breaker. Therefore, it is very important to monitor the trip coil healthiness otherwise during the requirement the breaker may not open to clear the fault. Figure below, shows the simplified diagram of trip circuit supervision.
As shown in the figure, contacts A and B are breaker auxiliary contacts. Mind that theses contacts are connected to the breaker mechanism and therefore their status depends on the breaker position. If the breaker is open, contact A will be OPEN and contact B will be CLOSE. Similarly if breaker is close, contact B will be OPEN and contact A will be CLOSE. Now we will consider pre-close and post close supervision separately.
Pre-close Trip Circuit Supervision:
Now carefully observe the circuit of TCS Relay. Since RLA and RLB are close, DC supply will be extended and hence TCS relay will be energized. Therefore, its output contact 1-2 will be open and hence no window will appear. This means that trip circuit is healthy. Assume there is any open circuit, in such case as no current could flow through the coils RLA and RLB, hence relay TCS will not be energized. Because of this its output contact 1-2 will be close for window annunciation . This means to the operator that either DC supply has failed or there is some problem in the trip circuit.
Post Close Trip Circuit Supervision:
Post close means that breaker is close. Thus the status of contact A will be CLOSE and that of B will be OPEN. If you observe the circuit carefully, you will notice that, in this case current will be flowing through both the coils RLA.
Now carefully observe the circuit of TCS Relay. Since output contact of RLA is close, DC supply will be extended to TCS relay and hence TCS relay will be energized. Therefore, its output contact 1-2 will be open and hence no window will appear. This means that trip circuit is healthy. Assume there is any open circuit, in such case as no current could flow through the coils RLA, hence relay TCS will not be energized. Because of this its output contact 1-2 will be close to annunciate window. This means to the operator that either DC supply has failed or there is some problem in the trip circuit.
It shall be noticed that, as the resistance of relay coil is very less therefore a high resistance shall be connected in series so that less current flows through the circuit to operate the trip coil of the breaker. It shall also be noticed that, in case of protection trip, separately positive DC voltage is extended to the trip coil of circuit breaker so that full current flows through the trip coil to operate the breaker as clear from the figure.
24 thoughts on “How does Trip Circuit Supervision Work?”
WHAT IS THIS WINDOW AND OUTPUT CONTACT IN TRIP CIRCUIT SUPERVISION
Window annunciation is a kind of indication with preferably hooter to alert the operator. Relays are employed for trip circuit supervision, its output contact is wired to provide annunciation.
May I know what happen if there is a jumper across RLB when CB status changed from close to open ? Thanks
breaker will trip. As breaker is open, a continuous flow of high current through trip coil will damage it.
Why two coils RLA & RLB are required???
Is it possible to use only one coil(i.e.RLA or RLB) by making parallel connection between breaker auxiliary contacts??
Two coils are required for pre-close and post close supervision.
SIR, DURING FIRST AND SECOND CONDITION TRIP COIL IS GETTING THE SUPPLY THROUGH RLA AND RLB, SO THE COIL WILL ALSO TRIP RIGHT?
No actually, through trip coil negative is extending to breaker auxiliary contacts and then through that any one of the coil get energized (at pre and post close condition any one coil will be energized – (but here pre close shows both enerziged — yet to confirm) ), and by using energized coil auxilary contact TCS coil get energized. and trip coil get positive only when Trip coil contact makes.
A resistance in series to reduce a high current traversing continuously coil to avoid damaging trip coil.
At pre close how both RlA and Rlb get energized, seems only Rlb get energized. kindly help to understand whether i m right or wrong.. got confused ??
As a general concept, we use to say that when a coil gets both positive and negative, only then it is energised. Now here, see negative is extended through coil b and then and positive is fed at coil a, so both are energised actually and as in one + and -, both coils are coming and main coil is energised through b coil. i hope this helps
SIR, DURING FIRST CONDITION TRIP COIL, IS GETTING THE SUPPLY THROUGH “RLA” AND “RLB”,
AND SECOND CONDITION TRIP COIL IS GETTING THE SUPPLY THROUGH ONLY “RLA”
1.WHY WE USE PRE CLOSE SUPERVISION FOR RLA” AND “RLB” BOTH??
WHY NOT POST CLOSE??
2.WHY WE USE POST CLOSE SUPERVISION FOR ONLY “RLA”??
WHY NOT PRE CLOSE??
Sir is TCS relay healthy when any tripping command in breaker trip circuit.
Yes, it is healthy.
simple and sweet explanation
1.WHY WE USE “RLA” AND “RLB” BOTH COIL FOR PRE CLOSE SUPERVISION ??
2.WHY WE USE ONLY “RLA” COIL FOR POST CLOSE SUPERVISION ??
The reason to use RLA and RLB is to make the supervision of trip coil possible in three conditions:
1. When the CB is Closed (In this case, only RLA will be conducting)
2. When the CB is open normally by an operator (In this case, RLA and RLB will be conducting)
3. When the CB is open due to a tripping dc positive supply by a protective relay (In this case, RLA and RLB will be conducting)
A couple of points to note:
Had the RLB coil been not in its place, the Trip coil would get continuous DC supply and it will burn out, when the tripping dc positive supply from a hand reset type master trip relay’s NO element.
The reason for wiring the Post Close supervision through the RLA and RLB, is interesting. It is just to have the functionality of checking the RLA’s coil healthiness while checking for Pre Close Supervision, so that we know even before closing the CB that whether or not the Post close supervision of the TC is going to work or not. Since we’d know about this beforehand, you would not take panic measures to shutdown the sources to a CB, that has its TC Unhealthiness appearing after CB closure due to an open circuited RLA during when the CB is OFF.
Thank you for your value addition. It will help a lot.
We have 230 V ac control supply system when we made supply off (MCB) off Still there is 170V with respect to ground what is cause unable to understand some time after stop command motor is not off please guide
Check the wiring. This is wiring mixing problem.
What to do if we recevied trip circuit unhealthy alarm in 220 kV circuit breaker
Check the following:
1) 220 V DC MCB is ON which is going to Trip Circuit of breaker.
2) Check the healthiness of TCS Relay.
3) Check the healthiness of Trip Coil
Great article, please what’s the perfect replacement for a TSG 912 trip circuit supervision relay