DIN EN 60076-3:2014-08

This International Standard applies to the power transformers specified in the scope of IEC 60076-1. It specifies the insulation requirements and the corresponding insulation tests with reference to specific windings and their terminals. It also defines external clearances in air. This part of the series IEC 60076 gives details of the applicable dielectric tests and minimum dielectric test levels. Appropriate recommended values are given in the event that the minimum external clearances in air between live parts and between live parts and earth are not specified by the purchaser. The insulation levels and dielectric tests which are specified in this standard apply to the internal insulation only. Whilst it is reasonable that the rated withstand voltage values which are specified for the internal insulation of the transformer should also be taken as a reference for its external insulation, this may not be true in all cases. A failure of the non-self-restoring internal insulation is catastrophic and normally leads to the transformer being out of service for a long period, while an external flashover may involve only a short interruption of service without causing lasting damage. Therefore, it may be that, for increased safety, higher test voltages are specified by the purchaser for the internal insulation of the transformer than for the external insulation of other components in the system. When such a distinction is made, the external clearances should be adjusted to fully cover the internal insulation test requirements. The Annex sets out some of the principles used in assigning the tests, test levels and clearances in air to the transformer according to the highest voltage for equipment U_m. For categories of power transformers and reactors which have their own IEC standards, this standard is applicable only to the extent in which it is specifically called up by cross reference in the other standard.