Variable toroidal transformers

General
Variable transformers are used wherever AC voltages and currents between 0 and 100% of the nominal value are required.

Our variable toroidal transformers are manufactured in accordance with EN 61558-2-14:
Special requirements and tests for variable transformers and power supply units containing variable transformers.

Installation and cooling
When installing in enclosures, care must be taken to ensure that the self-ventilation is not impeded. Otherwise, excessive heating can destroy the transformer, even during rated operation.
If the ambient temperature exceeds 40°C, the rated current must be reduced by 20% for every 10°K increase in temperature.
All relevant safety regulations (VDE, EN, IEC, equipment protection, etc.) must be observed, particularly when using built-in transformers. This is part of our warranty conditions and must be proven by the user in the event of damage.

Connection and overload protection
The star point of three-phase variable transformers in a star connection is 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. It can be 20 – 30 times the rated current in the first moment and subsides after a few milliseconds.
Variable transformers can only be adequately protected by overload protection 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 itself as the standard circuit, i.e. there is a conductive connection between the input and output circuit. Protective measures on the mains side, e.g. protective conductor system, zeroing or residual current circuit, are not affected. Device mounting frames, chassis or housings can be integrated directly into the existing protection system.

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

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

• Visual inspection of all mechanical and electrical parts
• Checking the connections for tight fit
• Remove dust deposits from the winding using a brush or compressed air
• If necessary, clean the contact track first with polishing abrasive fleece, then with a soft, lint-free cloth,
• isopropanol-soaked cloth. Do not use mechanical abrasives!
• Check the carbon rollers and bearings for ease of movement and pressure. Caution: The carbon roller bearings must not be lubricated!

Warning!
Touching live parts is life-threatening! It is essential to disconnect the power supply before starting maintenance work!