- Trip Circuit Supervision Defined: Trip circuit supervision relay is an essential system in electrical circuit breakers that monitors and ensures the readiness and health of the trip circuit.
- Components: Essential parts of a supervision circuit include NO and NC contacts, relays, lamps, and resistors, all of which contribute to maintaining circuit integrity.
- Supervision Types: Pre and post-close supervision schemes ensure the trip circuit’s functionality before and after the breaker has closed.
- Visual Indicators: The use of lamps in the supervision circuit allows easy monitoring of the system’s status, indicating circuit readiness for operation.
- Alarm and Safety Features: Dedicated alarm circuits, separate from the trip power supply, enhance safety by ensuring system alerts remain active even if the primary trip circuit fails.
The trip path of an electrical circuit breaker can include protection contacts, test links, fuses, wiring, auxiliary contacts, interlocks and the trip coil. A pressure switch on an SF6 circuit breaker or pneumatic mechanism may signal an alarm, block an operation or initiate another action. The exact response is breaker-specific and must follow the manufacturer’s control diagram; low pressure does not justify a universal rule that every fault current trip should be blocked. A 52a auxiliary contact, commonly connected in series with the trip coil, closes while the breaker is closed and opens after the breaker trips. This removes sustained coil current.
An open wire, failed fuse, poor terminal, open trip coil or lost control supply can prevent an electrical trip. Trip circuit supervision passes a small monitoring current through the required path and raises an alarm when continuity or control voltage is lost. The monitoring current must remain below the trip coil’s pickup level.
The first diagram shows a simple manual continuity check. A lamp, push button and current-limiting resistor form a supervision branch across the open protective relay trip contact. Pressing PB completes the low-current path. A lit lamp indicates continuity through the monitored circuit at that moment. It does not prove the breaker’s mechanical operation or replace a correctly commissioned continuous trip circuit supervision relay.
This arrangement checks the trip path while the circuit breaker is closed, so it provides post-close supervision. A pre- and post-close scheme uses both breaker auxiliary-contact states to supervise the trip coil when the breaker is open or closed. The exact portion of wiring monitored in each state depends on the circuit.
The pre- and post-close scheme adds the complementary 52b auxiliary contact in parallel with the 52a path. The 52a contact closes when the breaker is closed, while 52b closes when it is open. Supervision current can therefore pass through the trip coil in either stable breaker position. A series resistor limits current if the lamp or monitoring input fails short-circuit, but its value must be calculated for the control voltage, trip-coil pickup current and relay input requirements.
A dedicated supervision relay or protection-device input provides a remote alarm. Its circuit must be selected for the trip contact type because a latched trip contact can bypass some monitoring arrangements for longer than the alarm delay.
In the illustrated electromechanical scheme, relay A is energised through the healthy closed-breaker path. Its NO contact A1 keeps alarm relay C energised, so NC alarm contact C1 remains open. With the breaker open, relay B and contact B1 provide the corresponding healthy-path signal, which keeps relay C energised and contact C1 open.
If the closed-breaker trip path opens, relay A drops out and opens A1. Relay C then drops out, closing C1 to operate the alarm. With the breaker open, relay B provides equivalent trip circuit supervision through the alternate auxiliary-contact path. An alarm delay must ride through normal 52a/52b transition time and trip-contact operation without hiding a persistent fault. Resistors must be mounted and rated for their continuous dissipation, and a credible short circuit in the supervision branch must not supply enough current to trip the breaker.
Where loss of tripping DC must itself raise an alarm, power the alarm indication from an independent monitored supply. If the alarm uses the failed trip supply, it cannot report that loss. Commissioning should prove detection of an open trip coil, open wiring, failed control supply and both breaker positions without causing an unwanted trip.
