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본 논문에서는 가스절연개폐장치 절연진단 알고리즘 개발을 위해 SF₆ 중 결함별 부분방전 패턴을 분석하였다. 결함을 모의하기 위하여 Protrusion on the conductor (POC), Enclo sure (POE) 및 Free particle (FP)의 전극계를 설계하고, 각 결함별 부분방전의 위상분포(φ), 크기(q) 및 펄스 수(n)를 비교하였다. POC와 POE의 경우 부분방전 펄스가 각각 40°~130°와 230°~310°에서 분포하였으며, FP는 전대역에 걸쳐 나타났다. POC는 정극성에서 98.6%, POE는 부극성에서 98.3%의 부분방전 펄스가 검출되었으나, FP는 양극성에서 비슷한 분포를 나타내었다. 또한, 최대방전량은 POC와 POE에서 12.5pC, FP에서 62.5pC이었다. 측정결과로부터 절연 결함별 부분방전의 특성을 확인할 수 있었다. This paper described the analysis of partial discharge (PD) pattern on insulation defects in SF₆ gas to develop an insulation diagnosis algorithm for Gas Insulated Switchgear (GIS). Protrusion on the conductor (POC), enclosure (POE) and free particle (FP) were fabricated to simulate insulation defects. Phase (φ) distribution, magnitude (q) and pulse counts (n) of PD pulse were compared on each defect. PD pulses on POC and POE were distributed in ranges of 40°~130° and 230°~310°, respectively. However, the distribution on FP was in all phase. The positive polarity of PD pulses detected was 98.6% on the POC and the negative one of them was 98.3% at on the POE. The polarity ratio of them on FP was about one. In addition, the peak charge was 12.5pC on POC and POE, 62.5pC on FP. From the experimental results, we could derive a feature of PD pulse on each insulation defects.
This paper dealt with the frequency component analysis of acoustic signals produced by corona and series-arc discharges as a diagnostic technique for closed-switchboards. Corona and series-arc discharge were simulated by a needle-plane electrode and an arc generator specified in UL1699, respectively. Acoustic signal was detected by a wideband acoustic sensor with a frequency bandwidth of 4 Hz~100 kHz (-3 dB). We analyzed frequency spectrums of the acoustic signals detected in various discharge conditions. The results showed that acoustic signals mainly exist in ranges from 30 kHz to 60 kHz. From the experimental results, an acoustic detection system which consists of a constant current power supply (CCP), a low noise amplifier (LNA) and a band pass filter was designed and fabricated. The CCP separates the signal component from the DC source of acoustic sensor, and the LNA has a gain of 40 dB in ranges of 280 Hz~320 kHz. The high and the low cut-off frequency are 30 kHz and 60 kHz, respectively. We could detect corona and series-arc discharges without any interference by the acoustic detection system, and the best frequency is considered in ranges of 30 kHz~60 kHz.
본 논문에서는 수배전반 내 코로나 및 직렬아크 발생 시 나타나는 초음파 신호의 측정 및 분석에 대해 기술하였다. 침-평판 전극으로 코로나 방전을, UL 1699에 규정된 아크발생장치를 이용하여 직렬아크를 모의하였으며, 최적의 검출대역은 30 kHz~60 kHz임을 알 수 있었다. 초음파 검출시스템은 전원으로부터 센서의 신호를 분리하기 위한 역결합 회로, 저잡음 증폭기 및 대역통과필터로 구성된다. 실험결과, 초음파검출시스템을 사용하여 외부 잡음에 의한 영항을 받지 않고 수배전반내에서 발생하는 코로나와 직렬아크방전을 검출할 수 있었다. This paper dealt with the frequency spectrum of ultrasonic produced by series arc and/or corona discharges inside switchboards. Corona and series arc discharge were simulated by a needle-toplane electrode system and an arc generator specified in UL1699, respectively. The measurement data showed that common frequency bandwidth is in ranges of 30 kHz~60 kHz. Ultrasonic detection system consists of a decoupler to separates ultrasonic from DC source, a low-noise amplifier (LNA) and a band-pass filter (BPF). From the experimental results, we could detect corona and series-arc discharges without any interference by the ultrasonic detection system.
This paper dealt with a defect identification algorithm which is based on single partial discharge (PD) pulse analysis in gas insulated structure. Four types of electrode systems such as a needle-plane, a plane-needle, a free particle and a crack inside spacer were fabricated to simulate defects in gas insulated switchgear (GIS). We measured single PD pulse by an oscilloscope with a sampling rate of 5 GS/s and a frequency bandwidth of 1 GHz. Data aquisition and signal processing were controlled by a LabVIEW program. Physical shapes of PD pulses were compared with kurtosis, skewness and time-based parameters as rising time, falling time and pulse-width. These parameters were analysed by an algorithm with a back propagation algorithm (BPA). By applying the algorithm, the identification rate was 97% for the needle-plane electrode, 96% for the plane-needle electrode, 91% for the free particle and 93% for the crack inside spacer. The results verified that the algorithm could identify the type of defects in GIS.
Studies on a $SF_6$-mixture and -alternative gas has been in progress to reduce the use of $SF_6$ gas as an insulation material of GIS (gas insulated switchgears). In this paper, we dealt with PD (partial discharge) characteristics in pure $SF_6$ and $N_2$, and their mixtures on aspects of insulation design and risk assessment for GIS. A POC (protrusion on conductor) and a POE (protrusion on enclosure) as the major defects were fabricated to simulate PD. We analyzed the DIV (discharge inception voltage), DEV (discharge extinction voltage), pulse magnitude, counts and phase distribution of PD pulse in $SF_6-N_2$ mixtures ($SF_6$ 100%, $SF_6$ 80%-$N_2$ 20%, $SF_6$ 50%-$N_2$ 50%, $SF_6$ 20%-$N_2$ 80%, and $N_2$ 100%) according to the IEC60270. The DIV, DEV as well as magnitude of PD pulse decreased on the POC as increase of $N_2$ ratio. For the POE, the DIV and DEV in $N_2$ ratio below 50% were the same voltages as those in $SF_6$ 100%. In this experiment, $SF_6$ 80%-$N_2$ 20% mixture could be considered with the equivalent insulation performance to a GIS.
This paper dealt with the radiated electromagnetic wave detection of partial discharge (PD) in oil for insulation diagnostics of oil-immersed transformers. Three types of electrode system were fabricated to simulate the insulation defects that could occur in oil-immersed transformers. Frequency components of radiated electromagnetic wave in oil was measured by broadband bi-conical antennas of 300 MHz~2 GHz and a spectrum analyzer of 9 kHz~3 GHz. Frequency component of electromagnetic waves from PD in oil were highly distributed at 500 MHz. From the result, a narrow-band monopole antenna with the center frequency of 500 MHz was fabricated. We could detect PD signal in insulation oil without an influence of external noise by a measurement system which consists of the prototype monopole antenna, a LNA (Low Noise Amplifier), an oscilloscope and a spectrum analyzer.