Gec-alsthom Limited

Carl Christopher Ennis

Graham Dilkes

Roy Clarke

John Stanley Stewart

A power-line trip circuit models the transient characteristic of a change in load (e.g. appearance of a fault current, or switch-on to a normal load) and compares the current actually flowing in the power lines with this modelled or simulated transient. Line currents that do have a transient component but do not exceed normal limits are not then sufficient to trip a circuit breaker associated with the power lines, whereas transient-bearing currents that do exceed such limits, i.e. fault currents, are recognized as such and the circuit breaker is tripped. This circuit allows fast, reliable tripping even in the presence of a substantial transient overshoot.

Power-line trip circuit

A vacuum recloser in which an isolator switch is incorporated in series with the vacuum interrupter and is driven by the same actuator. The isolator must only be operated when the vacuum switch is open and no arc current remains. This is ensured in one of two ways (a) by providing a significant lost motion in the isolator drive, giving, say, 20 milliseconds between opening of the vacuum contacts and opening of the isolator contacts, and (b) by latching the isolator drive against opening, compressing a spring against the latch by the actuator attempting to open the isolator, and tripping the latch by a solenoid responsive to lock-out conditions.

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Middleton, United Kingdom

Carl Christopher Ennis