Voltage Transformers - General Information

Earthed voltage transformers can be equipped with an additional winding for earth-fault monitoring.

Voltage transformers for two rated primary voltages will be delivered with a secondary change over. Only this construction guarantees a high reliability in insulation and operation.

All instruments transformers contained on this website are cast-resin transformers with the following characteristics:

  • free of maintenance
  • dry-type
  • installation in any position possible

The features of the cast resin material used for construction guarantee

  • best insulation
  • great mechanical strength
  • high arc and temperature stability.

All instrument transformers are subject to a routine test according to the respective standards (e.g. DIN VDE, IEC).


Limiting Thermal Output

The apparent power which the voltage transformer can supply to the secondary circuit without exceeding the stipulated temperature limits at rated voltage.

Rated Secondary Limiting Thermal Output

The output of the winding for earth-fault monitoring at rated voltage and a time of 8h. As the windings for the earth-fault monitoring are connected in open delta they will be permanently charged only in case of an earth-fault.

Rated Voltage Factor

Earthed voltage transformers can be operated with 1,9 x rated primary voltage for a time of 8h without exceeding the stipulated temperature limits. This does only happen in case of an earth-fault.


The secondary circuits of a voltage transformer may not be short-circuited during operation as the voltage transformers will be thermally destroyed within seconds.