In power system protection, circuit breaker tripping is crucial if any fault occurs in the system. If the trip circuit is unhealthy and the fault occurs, the circuit breaker will not trip, the fault will pass through the circuit breaker into the system and equipment will get damaged or the upstream breaker would have to clear that fault causing an unwanted power outage. A trip circuit Supervision relay (TCS) is used to monitor trip circuit healthiness continuously and give an alarm if any abnormalities like loss of control supply, trip coil problem, or wiring problem.
The trip circuit supervision relay ( 95 Relay) is designed for the supervision of the trip circuit and monitoring of the healthiness of the trip coil. To avoid any unwanted tripping of the breaker, in the event of any short circuit in the lamp, a series resistor (R) is added in the circuit.
The supervision function is particularly important when there is only one tripping coil and circuit breaker tripping is vital.
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The TCS relays working is based on the low-level current injection principle of approximately 3mA. The ANSI code of the TCS relay is 95.
Working of Trip Circuit Supervision Relay (VAX 31)
Trip circuit supervision relay VAX31 wiring diagram is shown below
Under healthy conditions, the circuit breaker is in the closed position, if the trip circuit gets open or the control supply fails. Relay A will drop off and open contact A-1. this will lead to relay C’s, coil de-energization followed by relay C flag drop off and an alarm will be generated on the annunciation panel.
Under trip circuit healthy condition with Circuit breaker is in closed position Relay A and C are energized as discussed above.
When the circuit breaker gets open, to monitor the healthiness of the trip circuit, relay B is energized by NC contact of the auxiliary switch of the circuit breaker and relay C of the TCS relay is held by contact B-1 of relay B and will monitor the circuit healthiness in a similar way as the relay “A” monitor when the circuit breaker is in closed position.
Application Of TCS (95) relay
- Used to monitor tripping circuit wiring from the positive supply to the negative supply in both states of the circuit breaker.
- Used to give alarm in case of trip circuit unhealthy.
- TCS relay monitors trip coil condition.
the trip circuit supervision relay is an essential device used in electrical power systems to ensure the reliability and safety of circuit breakers. Its primary function is to monitor the trip circuitry and detect any faults or abnormalities that could compromise the breaker’s operation.
By continuously monitoring the trip circuit, the relay can detect various faults such as open circuits, short circuits, or wiring errors. It provides a crucial layer of protection by initiating an alarm or trip signal when it detects such faults. This prompt detection and response help prevent serious damage to the electrical system and ensure that the circuit breaker operates as intended during fault conditions.