Before revision: Five European countries (Germany, Austria, Switzerland, Norway, and Sweden), where electricity is three-phase AC as 50 Hz, have standardised on single-phase AC at 15 kV Hz for railway electrification; phase converters are, therefore, used to change both phases and frequency.
After revision: Five European countries (Germany, Austria, Switzerland, Norway, and Sweden), where electricity is three-phate AC as 50 Hz, have standardised on single-phase AC at 15 kV Hz for railway electrification; phase converters are, therefore, used to change both phases and frequency.