Low-
voltage circuit breaker (LS) for a low-
voltage AC circuit, comprising: - a
voltage sensor (SS) for determining the level of voltage between conductors of the low-voltage
AC circuit, - a
Rogowski coil (RS1, RS2, RS3, RSN) for determining the magnitude of the
electric current of a conductor (L1, L2, L3, N) of the low-voltage
alternating current circuit, which outputs an analog voltage (A1, A2, A3, AN) equivalent to the magnitude of the
electric current of the conductor, - an interruption unit (UE) with contacts (K) for interrupting the low-voltage
alternating current circuit, - a
control unit (ETU) connected to the
voltage sensor (SS), the
Rogowski coil (RS1, RS2, RS3, RSN) and the interruption unit (UE), with a
microprocessor (MP), wherein the low-voltage
circuit breaker is designed in such a way that if the current and / or current-
time limit values of a conductor are exceeded, an interruption of the low-voltage
alternating current circuit is initiated, and: - that the
Rogowski coil (RS1, RS2, RS3, RSN) is connected to an analog
integrator (INT), followed by a first analog-to-
digital converter (ADU1) which converts the integrated analog voltage (uc(t)) into a
digital signal (P1, P2, P3, PN) so that a sample value of the current is available every X degrees, related to the period of the alternating current, - that the
voltage sensor (SS) is connected to a second analog-to-
digital converter (ADU2) so that every Y degrees, based on the period of the alternating voltage, a sample value of the voltage (PU) is available which corresponds to the level of the voltage or an equivalent of the level of the voltage at the respective time, - that a power value is calculated from a sampled value of the current (P1, P2, P3, PN) and an interpolated voltage value, wherein the interpolated voltage value is determined from two successive sampled values of the voltage (PU) in such a way that a
phase error generated by the Rogowski coil and / or the
integrator, related to the
electrical current in the conductor, is compensated, so that a power value which is at least approximately free of phase errors is determined.