

Tuesday, June 28, 2011

Power Circuit Breaker Trip Circuit Diagram (substation equipment operation)

The basic trip circuit for a power circuit breaker is illustrated below. The trip and close circuit of power circuit breakers is just a simple DC circuit. Trip circuit consists of miniature circuit breaker (CB2) that protects the trip coil from overcurrent.
Then tracing the circuit, the first node is a provision for Trip Low SF6. The normally open contact EA 63GX1 is pressure operated. If the pressure of the SF6 becomes very low, this contact will become close contact, thus supplying voltage to the trip coil and tripping the circuit breaker. However, it is not recommended to trip a power circuit breaker with low SF6 since this is dangerous. It might not have enough interrupting SF6 gas to quench the arc at the contacts of power circuit breaker and might cause explosion of the equipment. The second node is intended for local trip control. The push button will give supply to the trip coil if operated. The contacts for changeover switch L and R is important so that tripping the power circuit breaker will just be one location at a time, local (at the equipment itself) and remote (at control room or via SCADA). The normally closed contact EA 63GX1 is the monitoring of SF6 gas level of the power circuit breaker. If the SF6 pressure becomes low, the nomally closed contact will become open thus the breaker cannot be tripped. This is the recommended practice for power circuit breaker, to make the circuit breaker inoperable if the SF6 gas becomes low. Next contact is the MA1 52-1. This is a normally open contact of the power circuit breaker. This is done to monitor if the auxiliary contacts (NO and NC contacts) of the power circuit breaker are in normal position. The MD52TC1 is the tripping coil of the power circuit breaker. Once voltage is supplied to the trip coil, then it gives signal for the power circuit breaker to trip.
Usually, power circuit breakers have two trip circuits. This is done to make sure that the line can be properly isolated in case there is a fault occurence. Most substation configure trip circuit 1 for main 1 protection relay and trip circuit 2 for main 2 protection relay. This is being done so that if relay 1 fails to trip the power circuit breaker during fault (because of defective trip coil for example), then relay 2 can isolate the line by using the trip circuit 2.Another connection made to trip circuits is the trip circuit 1 is connected to station battery bank 1 and trip circuit 2 connected to station battery bank 2. The reason for this is so that if battery bank 1 fails or already discharged, then the battery bank 2 can still supply the trip coil of the trip circuit 2.


Diagram: SIEMENS Circuit Breaker


  1. sir questions po;
    1. Para saan yung floating node (TB9 in series w/+MA52-1, b contact)?
    2.Bkit po floating yung TB2(subscript 9 and 10)? ska ano po ung purpose...for adding jumper po ba?pakipaliwanag naman ung portion n to..
    3.Bakit po nglalagay ng option for tripping the PCB when SF6 is low?? usual arrangement po ba ito? at saan po ba ito nakalocate? Local cubicle po ba?

    tnx in advance...

  2. saka po sir, baka pwede po kaung mg refer ng material for studying schematic diagram ng closing operation ng PCB ska ibang equipment s substation tulad ng isolators. grounding switch atbp....mraming slamat po

  3. To anonymous:
    Sir, please see answers to your queries below:
    1. The floating node is a b-contact which is pre-wired on a siemens circuit breaker as illustrated on their diagram. Engineers could utilize this contact for other applications like alarms, annunciators and visual indicators. But it can be left as it is if the said contact is not needed.
    2. TB means terminal block, so TB2 means terminal block number 2. On the other hand, 9 and 10 means terminal number, so to locate the termination, look for terminal block number 2, terminals 9 and 10. Yes, these two terminal points have provisions for jumpers or additional wires which can be additional requirement of a certain substation. Just like answer no. 1, it can be left as it is if not needed.
    3. Option for tripping if low SF6 is the own design of Siemens breaker. circuit breakers must have enough SF6 to properly quench the arc during tripping. Since SF6 refilling is ideally done when the circuit breaker is de-energized, then Siemens included in their design a provision to trip the breaker automatically when the SF6 is low or at a certain level below its nominal value. This should be the proper wiring of circuit breakers, to trip automatically when the SF6 is low. Most of the SF6 gauges have a and b contacts that can be set to actuate at different levels of pressure.

  4. to anonymous:
    I would recommend to research on the operating manuals of different substation equipment like what you have mentioned. Better if you could visit a substation since it is where these manuals are usually available.

    Thanks for your comments.

