Starting transformer
A starting transformer is a transformer and is used to temporarily step down the voltage when switching on large electric motors and thus to reduce the starting current.
The starting current on the mains voltage side is reduced proportionally to the square of the transmission or voltage ratio.
Starting transformers are mostly used in motors with high output to ensure a smooth start. For cost reasons, autotransformers are mostly used. Starting from the lowest voltage, the motor voltage is gradually increased as the starting process progresses. The magnetically induced inrush currents are not eliminated, they occur again when each stage is switched. However, the longer-lasting starting currents caused by the inertia of the rotor and the load are reduced.
In order to also eliminate the magnetic inrush currents, the motor must be continuously fed without switching pauses. This is achieved through more complex circuits that overcome the switching stages by means of an auxiliary variable transformer. Such devices were used, for example, in older electric locomotives .
Starting transformers have now been almost completely replaced by frequency converters .
literature
- Günter Springer: Expertise in electrical engineering. 18th edition, Verlag - Europa - Lehrmittel, 1989, ISBN 3-8085-3018-9