How does Trip Circuit Supervision Work?

Updated: Mar 2


A breaker is used to switch on and switch off the circuit. The breaker must trip in case of fault in the electrical network. In order to perform the closing,opening,and tripping operation, a breaker has two coils namely closing coil and tripping coil. The tripping of the breaker in the event of the fault is must to safeguard the electrical network and the equipment connected to breaker.


The healthiness of the tripping circuit should be always intact to get the tripping of the breaker without fail. The trip circuit supervision of the breaker always check the healthiness of the breaker tripping circuit. The tripping circuit of the breaker has mainly a 110 volts DC tripping coil,110 VDC source, and the 110 VDC to tripping coil connecting wires. If the tripping circuit is healthy the breaker will definitely trips in the case of the fault.


The breaker gets closed if the trip circuit supervision relay outputs its contact. The breaker will not close if there is fault in trip circuit.When breaker is closed and if fault is sensed in running condition, the protection relay senses the fault and issues trip command to tripping circuit.


The some breakers have two tripping coil one is operated with 110 VDC and other is operated with 220 VAC. This is done to ensure tripping of the breaker in the case of failure one of the supply system. Two separate trip circuit supervision circuit is used in this case.


The basic circuit diagram of the trip circuit supervision is as given below.

Circuit Diagram of Trip Circuit Supervision

The trip supervision relay has three coils KM1, KM2 and TCS. To limit the current through KM1 and KM2 relay coils,resistance R is added. The relay needs to monitor the healthiness of the trip circuit in breaker closed and open condition. According to this, the trip circuit supervision function can be divided into two categories.


  1. Pre-Circuit Trip Circuit Supervision

  2. Post Close Circuit Supervision


Pre-Close Trip Circuit Supervision:


Pre-close means breaker status before closing. The breaker is open in pre-close condition.Thus, the status of breaker contact 52a is open and contact 52b is close. In this condition, current through the trip circuit supervision is as given below.


Pre-Close Trip Circuit Supervision

When breaker is in open condition, the current does not flow through 52a contact. Current finds its path through breaker auxiliary NC contact, KM2 and KM1. Thus current flowing through KM1 and KM2 energizes both the relay. The positive supply routes through the contact of KM1 and KM2 and energizes trip coil supervision relay(TCS). The NC contact of TCS gets NO and no annunciation window glow in this case.This shows that trip circuit supervision circuit is healthy.


If both KM1 and KM2 relay do not operate, the TCS relay will not operate, and the contact of TCS will remain in NC state. The window annunciation will glow in this case and, it shows that either supply is missing or Trip coil is open or there is defect in the wiring of trip circuit supervision circuit.


Post Close Trip Circuit Supervision:


Post close means that breaker is close. The current through the contact 52a and 52b and trip coil is as given below.


Post Close Supervision Circuit

Current will flow through the breaker auxiliary contact 52a and trip coil, and the relay KM1 will energize.The NO contact of KM1 will become NC and it will energize the TCS relay. The contact of TCS will get open and the annunciation window show no fault.


In case of the fault in the supply system, KM1, TRIP COIL and wiring, the contact of KM1 will remain in open state and thus the TCS will be inoperative. The NC contact of TCS output the contact to annunciation window which shows trip circuit supervision circuit faulty.


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