Abstract: A method and apparatus for determining the quenching angle in inverter valves, in which the pulse-shaped deviations, which occur in the valve voltages due to the current commutations as compared to the corresponding fundamental waveforms, are blanked out in the form of voltage blocks. For the duration of the quenching angle, a binary measuring signal is generated which is triggered by an end-of-conduction pulse and is terminated by a zero voltage crossing pulse. The end-of-conduction pulse indicating the completion of the commutation is formed by the flank at the end of the voltage shift caused by the preceeding commutation in the valve voltage as compared to the fundamental waveforms.