Abstract: A self-commutating inverter having at least two main thyristors connected to a d-c source, a commutating arrangement consisting of an energy storage device and auxiliary thyristors connected anti-parallel to each other, a load and a firing control arrangement with outputs which are associated with the main and the auxiliary thyristors and can be impressed with firing pulses at presettable times, wherein the auxiliary thyristor associated as the commutation valve with the main thyristor to be relieved is triggered prior to the firing of the relieving main thyristor by a presettable time interval, and means to monitor the system.