Electrical supply line protection apparatus

摘要

Teed circuit protection is provided by a master unit at one terminal and slave units at the other terminals with broad band communication links between the master unit and the slave units. All units include line current transformers to the master unit signals derived from the current transformers to the master unit and circuit breakers controlled by operating signals sent from the master unit. The master unit has a logic decision-making facility which takes measurements of the amount by which a differential quantity proportional to the sum of the measurement signals exceeds a bias quantity proportional to the difference between the measurement signals proportional to the sum of the measurement signal exceeds slave units. The facility sends operating signals when that amount exceeds a threshold value. To prevent spurious operation of the circuit breakers a sequence of consecutive measurements may be taken all of which must exceed the threshold value.