Rotary converter

A rotary converter is a type of electrical machine which acts as a mechanical rectifier, inverter or frequency converter. Rotary converters were used to convert alternating current (AC) to direct current (DC), or DC to AC power, before the advent of chemical or solid state power rectification and inverting. They were commonly used to provide DC power for commercial, industrial and railway electrification from an AC power source.

A rotary converter plant is a facility at which rotary converters are used. With appropriate equipment, such facilities may also allow the setting of voltages and frequencies. Rotary converter plants were commonplace in railway electrification before the invention of mercury arc rectifiers in the 1920s. At each facility, power from an AC power grid was converted to DC to feed into an overhead line or a third rail of a railway. Rotary converter plants were also used for coupling power grids of different frequencies and operation modes. The former Neuhof Substation was an example of the latter. Former machinery transmitters like the Alexanderson alternator were, strictly speaking, rotary converter plants. In spite of modern power semiconductor technology, rotary converters are still common for feeding railway systems with AC of a different frequency from that of the main electricity grid. In Europe, this would typically be for 15 kV AC railway electrification.