Influence of Dry-type Air-core reactor Turn-to-turn Overvoltage Waveform Parameters on the Deterioration Law of Insulating Materials

The validity of the inter-turn insulation overvoltage test in the insulation tests of 35 kV and below dry-type air-core reactors have been fully verified. However, the relevant standards for the inter-turn overvoltage insulation test of 66 kV and above dry-type reactors have not yet been formulated, and the design and development of test equipment for dry-type air-core reactors of higher voltage levels are more difficult. The national standards for 35 kV and below emphasize that the voltage amplitude and the steepness of the waveform need to meet the requirements. In this paper, referring to the test method and platform for the inter-turn overvoltage test of dry-type reactors, the electrode system and samples were designed. The overvoltage cumulative effect tests with different voltage amplitudes and different steepnesses were carried out to obtain the influence rules of the degradation of the model samples under the exponentially decaying oscillating voltage. The electrical aging lifetime is characterized by the cumulative number of pulses, yielding a lifetime curve. The voltage amplitude and rise time serve as influencing factors, with their respective equations obtained as follows: N = 3.9×10 6 U −1.26 & N = 0.2 t 2 – 40.34 t + 4.96×10 5 The degradation Law of the Polyethylene terephthalate (PET) film sheet samples under electrical aging was studied by scanning electron microscopy and FT-IR spectroscopy, and the corresponding electrical aging life curve was obtained. Based on the life curve, an adjustment scheme for the waveform parameters of the exponentially decaying oscillating wave used in the tests of 66 kV and above dry-type air-core reactors is provided, offering a theoretical basis for parameter selection during the development process of equipment at higher voltage levels.