On-Site Dry-type Power Transformer Condition Assessment based on Partial Discharge Activity

As part of the energy transition and the associated development of renewable energies, the number of installed dry-type transformers is increasing on the medium-voltage power grid. Therefore, the paper at hand focuses on onsite condition assessment of dry-type power transformers which are often installed in wind turbine nacelles, industrial sites as well as in marine and civil applications. The assessment of the insulation condition is based on an induced voltage test in combination with a partial discharge measurement. In contrast to laboratory tests under controlled conditions, an increased level of interference from rotating machinery, power electronics and other consumers is to be expected on site. The approach of energizing transformers of power ratings up to 15 - 20 MVA with a portable, scalable single-phase voltage source is presented. Due to the single-phase injection the power intake is reduced, and an individual evaluation of each coil becomes possible. Practical examples show how partial discharge signals can be separated from these interferences using a synchronous multi-frequency PD measurement.