Static trip unit comprising a circuit for detecting the residual current

Claim 1

A solid-state trip device for a multipole electrical circuit breaker protecting an A.C. electrical supply system comprising: ― a current sensor (16R, 16S, 16T, 16N) per pole, which generates a signal proportional to the current flowing through the associated conductor (R, S, T, N) of the supply system protected by the circuit breaker; ― a detection and rectification circuit (18) to which said signals are applied to supply on the one hand signals representative of the currents flowing through the conductors (R, S, T, N) to be protected and on the other hand a zero sequence signal if an insulation fault occurs, ― an electronic processing unit (20) to which the output signals from the detection and rectification circuit (18) are applied to perform delayed and/or instantaneous tripping functions and delivering, with or without a time delay, a circuit breaker tripping order when preset thresholds are exceeded by the signals representative of the currents flowing through the conductors or by the zero sequence signal, a trip device characterized by the fact that the detection and rectification circuit (18) comprises first rectification means (22, 28, J) producing a first signal representative of the sum of the positive half-waves of the output signals from the set of current sensors (16), second rectification means (26, 24, K) producing a second signal representative, in absolute value, of the sum of the negative half-waves of the output signals from the set of current sensors (16), and means effecting the difference between the first and second summed signals so as to produce said zero sequence signal.