Pyrotechnique Circuit Interrupter for the Protection of Electrical Systems

The theory of operation and performance of the Ferraz current limiting pyrotechnique circuit interrupter for the protection of low and medium voltage electrical systems is described. This protective system consists of three major parts, a sensor, a control circuit and a pyrobreaker. The desired quantity, current, dl/dt, temperature, light etc., is monitored using the sensing circuit. The signal generated by the sensor is compared against a preset reference in the control circuit. When a fault occurs in the protected electrical system, an error signal is produced in the control circuit which results in the triggering of the pyrobreaker that finally interrupts the circuit. The pyrobreaker consists of two main components, a specially designed copper conductor that can carry large continuous currents and that can be sheared at high speed by pyro- breaking technique, and a current limiting fuse mounted in parallel with this conductor. When a fault is detected, the conductor is opened at high speed (the shearing of the conductor occurs in 100 Ls to 150 ¿s;, and the current is commutated to the parallel fuse which then interrupts the circuit providing current limiting protection. This system offers the advantage of carrying high continuous currents up to 10 KA at low and medium voltages, while providing current limiting protection in electrical systems where short circuit currents can be in excess of 50 KA to 75 KA.