Study on the Characteristics of Electrical Tree Partial Discharge According to the Variation of Artificial Void Gap Length in Epoxy Resin

Epoxy resin used in high-voltage power equipment such as molded power transformers and OF power cable joint-boxs is widely used because it has advantages in electrical insulation and stability of mechanical properties. However, when manufacturing power devices, nano and micro void defects occur, and cracks and interfacial defects occur due to thermal expansion coefficient at the interface between the conductor and epoxy microcomposite for a long period of time. In this way, the partial discharge is converted into an electrical tree and the tree is initiated. And it progresses further, ultimately resulting in insulation breakdown. Three types of insulation defects were simulated in epoxy resin: No Void, Void Gap_0.5mm samples. The applied voltage was 13kV/60Hz, and the discharge signal was measured from the voltage application through a microscope and the AE Signal measurement system when Tree-Partial Discharge occurred. To diagnose the deterioration state of Tree-Partial Discharge, the axial tree progression length was measured and evaluated throughout the entire process from the Tree Incubation Period to tree initiation, progression, and destruction. In order to evaluate the characteristics of Tree-Partial Discharge, the waveform of the AE Waveform and the result of FFT (Fast Fourier Transform) execution were converted from time-voltage (amplitude) to frequency-voltage (amplitude) function. In addition, the frequency characteristics of the waveform against the tree-deterioration time were evaluated, and the mechanisms of No Void and void discharge characteristics were analyzed.