This part of IEC 1660 describes a method for calculating short-circuit currents in d.c. auxiliary systems in power plants and substations. Such systems can be equipped with the following equipment, acting as short-circuit sources: 1) Rectifiers in three-phase a.c. bridge connection for 50 Hz. 2) Stationary lead-acid batteries. 3) Smoothing capacitors. 4) D.C. motors with independent excitation. This standard is only concerned with rectifiers in three-phase a.c. bridge connection. It is not concerned with other types of rectifiers.