유입식 변압기의 부분방전 진단에 관한 연구

Abstract

This thesis deals with the radiated electromagnetic wave detection of partial discharge(PD) in oil for insulation diagnostics of oil-immersed transformers.

Partial discharge by insulation deterioration of power facilities can lead to failure if not detected earlier. So far, the two main insulation diagnostic techniques of the oil-immersed transformer were the dissolved gas analysis(DGA) method in insulation oil and the acoustic method. These two methods, however, accompany some problems in installment and sensitivity. Therefore, research on the detection methods of radiated electromagnetic waves caused by partial discharges in insulation oil is now being actively conducted. From these backgrounds this thesis suggests the optimal detection method, analyzing frequency spectrum of radiated electromagnetic wave by partial discharge(PD) in oil. Electrode systems were fabricated to simulate the defects that might occur in oil-immersed transformers. Frequency spectrum of radiated electromagnetic wave in oil was analyzed by broad-band bi-conical antennas(300MHz～2GHz) and a spectrum analyzer(9kHz～3GHz). Frequency components for most defects showed high distribution at 500MHz. From the result, a narrow-band monopole antenna with the center frequency at 500MHz was made. The length of the antenna was 150mm. The propagation characteristic of the monopole antenna was evaluated by the network analyzer(40MHz～40GHz). It was suitable to detect the signal of partial discharge in oil. The measurement system which consists of the prototype monopole antenna, LNA(Low Noise Amplifier), oscilloscope and spectrum analyzer was evaluated from the partial discharge in insulation oil. It could detect all defects used in the experiment.