Auxiliaries in trains are all electrical consumers, with the exception of the main drive of the train. Auxiliaries are, for example: lighting, battery charging, three-phase power supply for compressed air compressors for brakes, doors, air conditioning systems, radio and telemetry systems. These systems expect a constant input voltage regardless of the potentially fluctuating catenary or locomotive voltage and protected from possible lightning strikes on the contact wire. For this purpose, inverters are used that compensate for all fluctuations and are often isolated and short-circuit protected to supply the consumers with 3-phase AC voltage and / or DC voltage, where required. In order to keep the size and weight of the inverter small, the voltage conversion and transmission takes place with frequencies of 10 - 50 kHz, making the inductive components such as chokes and transformers are very compact and lightweight and thus the devices much smaller than when operating with the usual mains frequency 50 Hz.