This EN 50152 3 3 is applicable to new voltage transformers which are: - intended for use in indoor or outdoor fixed installations in tractions systems, and - operated with an a.c. line voltage and frequency as specified in EN 50163. NOTE 1 – EN 50163 specifies the a.c. traction systems 15 kV 16,7 Hz and 25 kV 50 Hz. NOTE 2 – As rails of a.c. traction systems are typically connected to earth and included in the return current path, all phase to earth voltages are subject to the limits as given in EN 50163. Nevertheless conductor to conductor voltages are some times higher e.g. in autotransformer systems. Voltage transformers are mainly used with: - measuring instruments, - protective devices. This EN 50152 3 3 also applies to voltage transformers other than inductive types as far as reasonably possible. Requirements of this EN 50152 3 3 have priority. NOTE 3 – Combined current and voltage transformers also capacitive voltage transformers are typically not used in fixed installations in traction systems.