Overcurrent protection circuit for three=phase HV network - avoids amplification by using release coil and diode short circuited by switch opening in half wave preceding circuit breaker operation

摘要

The overcurrent protection circuit, for a 3-phse h.v. network, e.g. 10 kV local distribution network, has a transformer in each phase line. The secondary (6) of each transformer excites the shared release coil (2) belonging to the h.v. circuit breaker (1) in the phase lines. The release coil is connected via each of three diodes to the three secondaries. The release coil and diode are short circuited by a motor protection switch (8) which opens in the half wave immediately preceding the actuation of the circuit breaker.