Combined high frequency and high voltage insulation system investigation

Due to the increasing extension of power grids and decentralization of power generation, the need for control and compensation is more and more increasing. The intensive use of modern power electronics in FACTS elements can provide a feasible solution. Especially STATCOM and UPFC, for their versatile application can be the method of choice. Voltage sourced converters with IGBTs are used for compensation, providing both leading and lagging power. Filters need to be applied to block the high frequencies, generated by the large slew-rate of the converter pulses, from the connecting transformers. Their impact on the oil-cellulose insulation system as well as on most of the other dielectric insulation materials is unknown. This includes the breakdown voltage at higher frequencies as well as possible influences on accelerated aging. The first step in a breakdown investigation of any AC insulation system at frequencies beyond 10 kHz is the generation of a test voltage. Derived by the strength of transformerboard at 50 Hz, an amplitude of 100 kV needs to be provided to exceed its insulation capabilities. Based on investigations concerning enameled wires, where the dielectric strength dropped by factor 10, similar eventualities need to be taken into account in the design. A resonance principle was chosen to generate the test voltage of frequencies between 10 kHz and 250 kHz with an amplitude up to 100 kV. Major challenge in the design is a reduction of losses in the circuit, caused either by resistivity or by corona discharge. Insulation failure, other than at the specimen, obviously has to be excluded as well. With the resulting voltage source, miscellaneous dielectric materials will be tested for breakdown and aging, starting in this investigation with oil and its combinations with cellulose