Abstract: A method and apparatus for commutating a load-independent current between the valve arms of a static converter device. Each valve arm has a valve device with blocking capability in the reverse direction, and a valve damping circuit. The valve device of a current-assuming valve arm is actuated at the time of commutation, and the valve device of the current-delivering valve arm reaches a zero current level upon commutation. In order to prevent a dangerous overvoltage via the inductance of the valve damping circuit, actuation of the valve device in the current-assuming valve arm is delayed until the valve device in the current-delivering valve arm substantially attains a zero current level after being turned off. During this delay, the current can commutate to the valve damping circuit of the current-delivering valve arm and generate a positive voltage there, thus expediently avoiding a reverse current and its dangerous consequences.

Abstract: The invention concerns a monitoring circuit for a number of simultaneously current-carrying valves. In order to obtain an alarm signal in the event of trouble in a valve, provision is made that the primary winding of a current transformer is arranged in series with each of the valves; that the secondary windings of the current transformers are connected in a ring via intermediate taps; and that each intermediate tap is connected to a center tap of a bridge circuit constructed from auxiliary valves, whose output current can be taken off as the alarm signal.