This Part 1-3 of the International Standard relates, in general, to those characteristics wherein convertor transformers differ from ordinary power transformers. In all other respects, the rules specified in IEC 76 shall apply to convertor transformers also, as far as they are not in contradiction with this standard. It should be borne in mind that a rectifier transformer operates with non-sinusoidal current waveshape. In single-way connection, the current in each cell winding contains a d.c. component which calls for special a ttention in design and testing. In some cases, a special design is necessary when external short-circuits and cell failures would cause abnormal stress. For certain types of transformers, the waveshape of the normal operating voltage is non-sinusoidal. The core loss of such equipment is to be determined by applying a sinusoidal voltage having the same half-cycle arithmetic mean value and the same fundamental frequency as the voltage applied in service.