A convertor connection for connection to a DC circuit includes current sensing members for forming a quantity corresponding to the direct current of the convertor connection. An indicating arrangement is provided for indicating asymmetrical operating conditions, which includes a first band pass filter connecting to the current sensing members which let through frequencies in a frequency band located between zero and the fundamental frequency of the AC component during undisturbed operation. When the output signal of the first filter exceeds a predetermined value, through a second filter an asymmetry indicating signal is emitted. The release of an output signal is prevented by a delay arrangement if the duration of the asymmetrical operating condition is less than a predetermined time.