Applies to self-commutated semiconductor power convertors intended for service on single-phase rolling stock supplied with current of rated frequency between 15 Hz and 60 Hz. Covers the following types of convertors: rectifier, a.c. direct convertor (cycloconvertor) and a.c. indirect convertor (inverter with rectifier) when intended for supplying traction vehicle circuits). Also applies to convertors for supplying auxiliary services on traction vehicles.