Static trip device comprising an earth protection desensitization system

Claim 1

A static trip device of a protective circuit breaker of an A.C. electrical power system made up of at least two conductors, trip device comprising detection means of the phase currents flowing in the power system conductors, detection means of the earth fault current flowing in the power system, an electronic processing unit to which the output signals from the detection means are applied and which performs an earth fault protection function by generating, with or without a time delay, a circuit breaker tripping order in the event of a preset differential tripping threshold being exceeded by the earth fault current, trip device wherein the differential tripping threshold Is, is a polynomial function, of an order greater than or equal to two, of the highest phase current Ip, flowing in the power system, i.e. a function of the type Is=a+bIp+cIp 2 +dIp 3 . . . , in which the coefficients a, b, c, d are constants.