Energy-based discrimination for low-voltage protective devices

The purpose of this "Cahier Technique" publication is to present the new energy-based discrimination techniques that ensures tripping discrimination between protective devices during a short-circuit. Both simpler and more effective than standard discrimination techniques, it has been implemented on the Compact NS range of circuit-breakers used in low-voltage power distribution networks. Discrimination is ensured for all prospective fault currents on the condition that upstream and downstream circuit-breakers have different current ratings (ratio greater or equal than 2.5) with a trip-unitrating ratio greater or equal than 1.6.
Following a brief review of standard discrimination techniques, the authors examine the behaviour of circuit-breakers and various trip units from the energy standpoint.