Development of a test bench to investigate the breakdown voltage of insulation oil in a frequency range between 1 kHz and 10 kHz

The increased power and voltage capability of semi conductive devices enable the usage of Medium Voltage Direct Current (MVDC) grids. One component of the MVDC system is the transformer inside the DC/DC converter. A reduced size and increased efficiency of the converter is expected, when the switching frequency is in the range between 1 and 10 kHz [1, 2]. The Medium voltage transformers of the converter may be insulated with insulation oil, which has better thermal properties in contrast to solid insulation materials. Compared to 50 Hz, the insulation capability of the oil might change between 1 and 10 kHz because of changing dielectric losses. Due to the unknown insulation capability at frequencies between 1 and 10 kHz, the insulation oil of the transformer has to be examined with respect to the changes of the breakdown voltage compared to 50 Hz. Therefore, a test bench is developed to investigate the breakdown voltage. The rms output voltage of the test bench should be higher than 50 kV at frequencies between 1 and 10 kHz. Breakdown investigations have proved the test bench as a possible principle for the tests. The breakdown voltage is not frequency dependent for low water content in the examined frequency range compared to 50 Hz.