Medium voltage circuit breakers tripfree definition in the standard are:
If a closing operation is in progress, and a tripping signal (either mechanical or electrical) is received, the circuit breaker shall react as follows:
- If the closing signal and the tripping signal are initiated
simultaneously, the circuitbreaker contacts are permitted to close or touch momentarily before opening.
- If the trip circuit uses circuit breaker auxiliary switch contacts or other equivalent contacts, the trip coil of
the circuitbreaker cannot be energized until these contacts in the trip circuit are made.
- If the tripping command is initiated mechanically (manually) and held in the actuated position before a closing signal is applied, the circuit breaker main contacts are not permitted to close, even momentarily.
- If the closing signal is initiated before the tripping signal is initiated, the circuit breaker contacts are permitted to close or touch momentarily before opening.
Figure show Eaton trip free MV circuit breaker operation table