15 kV AC at 16.7 Hz is a railway electrification system chosen by Germany, Austria, Switzerland, Sweden, and Norway in 1912. The high voltage enables high power, while the lower frequency reflects technical limitations at the turn on the 20th century. In particular, the lower frequency reduced flashover problems in the motors, albeit at the cost of a non-standard line frequency requiring frequency conversion, and separate supplies.
In Sweden it is officially 16 kV AC, 16 2/3 Hz.
This voltage has been superseded by 25 kV AC at 50 Hz or 60 Hz since the 1950s. 25kVAC is one of the most common voltages used for railway electrification, usually at 50 Hz or 60 Hz depending on that countrys normal mains frequency. ... // Events and No. ...
Oddly, when Denmark decided to electrify in the 1970s they chose not to use 15 kV AC, which would have linked compatible systems in Germany and Sweden, but rather 25 kV AC. The 1970s decade refers to the years from 1970 to 1979, inclusive. ... 25kVAC is one of the most common voltages used for railway electrification, usually at 50 Hz or 60 Hz depending on that countrys normal mains frequency. ...