본 논문은 서지호보기용 온라인 진단장치의 설계 및 제작에 관하여 연구하였다. 전기적 특성 변화 및 건전성 기준을 제시하기 위해서 표준 뇌 충격전류(8/20μs) 10 kA를 인가하여 가속열화 실험을 수행하였다. 실험결과를 바탕으로 누설전류, 기준전압 및 제한전압을 측정할 수 있는 온라인 진단장치를 제작하였다. 누설전류 측정회로는 저잡음증폭기 및 클램프형 영상변류기로 설계하였고, 기준전압 측정회로는 선형제어부, 연산부, 누설전류 측정부 및 직류고전압 발생부로 구성하였다. 제한전압 측정회로는 서지발생부 및 커플링 회로로 제작하였다. 제안한 진단장치와 독립 실험계와의 측정값 차이는 3% 미만으로 정확한 진단이 가능하다. This thesis dealt with the deterioration and an on-line diagnosis equipment for surge protective device(SPD). An accelerated aging test was carried out using a 8/20μs standard lightning impulse current to analyze the changes of electrical characteristics and to propose the diagnostic parameters and the criterion for deterioration of metal oxide varistor(MOV) which is the core component of SPDs.
The leakage current of MOV increased whereas the reference voltage decreased with the aging process. When they changed more than 10% compared with the initial values, the deterioration was accelerated. On the other hand, since there was little change in the clamping voltage, it could not be used to evaluate the deterioration but its waveform could be applied to verify the operation of varistor. In addition, the criterion of soundness MOV was proposed.
Based on the experimental results, an on-line diagnosis equipment for SPD was fabricated, which can measure total leakage current, reference and clamping voltage. The leakage current measurement circuit is composed of a low-noise amplifier and a clamp type zero-phase current transformer(ZCT). A linear controller, a data acquisition module, and a HVDC supply were used in the measurement of reference voltage. The clamping voltage measurement circuit consists of a surge generator and a coupling circuit.
In a calibration process, measurement error of the protype equipment was less than 3%. From the experimental results, it was confirmed that the proposed equipment is avaliable to diagnose the SPD condition in operation.