One-stop shop for testing
The core activities of our HV lab are research tests, and type and special testing of power transformers, mainly the transformers used in the distribution network. As an accredit lab, our service is very useful to transformer manufacturers who are present or wish to be present in the European market and need their products to be certified. Particularly interesting, we are also able to perform linearly rising front-chopped impulse test, 2,000 kV/µs. This is a very complex test considering the difficulty of generating an impulse of such steepness in the lab.
For the transformer to pass the linearly rising front-chopped impulse test, the manufacturer needs to be equipped with an adequate technology and the know-how. For example, it is impossible for a standard distribution transformer to pass this test due to unfavourable distribution of voltage along the windings – because the steeper the wave, the more stressed the so-called first turns. This requires special design and Končar D&ST was among the first manufacturers to be able to develop an adequate solution in 1987. The advantage of a specially designed and tested transformer for the end user – a utility – is that such unit can be integrated in the grid in a rural community with a minimum overvoltage protection using a spark gap. Following this test, the transformer is subjected to standard tests only to confirm that it has successfully passed the linearly rising front-chopped impulse test and that nothing unexpected occurred. A lot of these test have been performed for Končar D&ST on the transformers set for delivery to Finland and Cyprus, for example.
Instrument transformer testing
One particularity of instrument transformer (IT) testing at our lab is that we conduct tests for instrument transformers that are intended for use in power quality measurements. Although there are no set standards for these tests, there is a specific need for them as they can provide utilities with information on power measurement uncertainty which is caused by higher harmonics. This is why the IT manufacturers are nowadays required to develop features which can indicate how the transformer behaves at higher frequencies – specifically, how the harmonics are transmitted in terms of the ratio and phase angle errors, and how the transformer itself generates higher harmonics.