As the regulating winding rotates inside the transformer and the current is running through copper brushes there is some copper dust in this kind of transformers. Mohaupt regulating transformers type STO are especially designed to minimize this effect. However in order to ensure reliable operation throughout decades, periodic maintenance is recommended, which is provided by Mohaupt High Voltage. As a further measure to ensure reliable operation, the input voltage of the regulator is limited to 10kV maximum. In case of necessity for higher input voltages, the use of a step down transformer (can be build optionally into the same tank) is recommended. This can be provided as a complete set together with the regulating transformer.