Variable toroidal transformers

General information
Variable transformers are used where AC voltages and currents between 0 and 100% of the nominal value are required and can be controlled.

Our variable toroidal transformers are manufactured in accordance with EN61558-2-14:
Particular requirements and tests for variable transformers and power supplies containing variable toroidal transformers.

Installation and Cooling
When installing in housings, it must be ensured that self-ventilation is not impeded. Even at rated operation, excessive heating can otherwise destroy the transformer. If the ambient temperature of 40°C is exceeded, the rated current must be reduced by 20% for each 10°K temperature increase. Especially when used as built-in transformers, all relevant safety regulations (VDE, EN, IEC, equipment protection, etc.) must be observed. This is part of our warranty conditions and must be proven by the user in case of damage.

Connection and overload protection
In three-phase variable toroidal transformers in star connection, the star point is brought out isolated. This must not be used to form an artificial star point. Input-side overload protection devices cannot adequately protect a variable transformer due to the variable transformation ratio. In addition, the inrush current of the transformer must also be taken into account when using them. In the first moment it can be 20-30 times the rated current and decays after a few milliseconds.
Variable transformers can only be adequately protected by an overload protection device arranged in the output circuit and matched to the rated current of the transformer. The tripping characteristic of the protective device must also be taken into account.

Circuits
The economy circuit has proven to be the standard circuit, i.e. there is a conductive connection between input and output circuit. Protective measures existing on the mains side, such as protective line system, zeroing or residual current protection circuit are not affected. Device mounting frames, chassis or housing can be directly integrated into the existing protection system.

Special versions are available on request for networks without neutral conductor. Variable transformers with galvanic isolation are also available.

Maintenance
Maintenance must be carried out at regular intervals depending on the load, but at the latest after each 12 months as follows:

  • Visual inspection of all mechanical and electrical parts

  • Check the connections for tightness

  • Remove dust depositis from the winding with a brush or compressed air

  • If necessary, clean the contact path beforehand with polishing abrasive fleece, then with a soft, lint-free cloth,

  • isopropanol-soaked cloth. Do not use mechanical abrasives!

  • Check coal rollers and bearings for smooth running and pressure. Attention: The bearings of the coal rollers must not be lubricated!



Warning!
Touching voltage parts is life-threatening! Before starting maintenance work, it is essential to disconnect the unit from the mains!