This thesis deals with an effect of a single and a quadruple lightning impulse currents on electrical characteristics of ZnO blocks, and an expert system to diagnose deterioration of arresters.
Lightning arresters are the best protective device on electric power systems to transient overvoltages caused by lightning discharge and switching operation. Though there have been accomplished technical and economical renovations by the development of a ZnO block having excellent nonlinear I-V resistive characteristics, substantial parts of the power system failures are still occupied by deterioration of lightning arresters.
Electrical characteristics of ZnO blocks are deteriorated by repeated impulse current, and the deteriorated ZnO block is brought to a thermal runaway and finally destroyed. It is therefore important to estimate the change of electrical characteristics of ZnO blocks.
In this study, an accelerated deterioration test is carried out to deduce the parameters needed for diagnosing arrester deterioration, and leakage current components are measured. Also, wave height distribution of the leakage current with the progress of arrester deterioration is analyzed.
From the experimental results, the wave height distribution of the leakage current showed a conspicuous difference even in an immaterial leakage current increase. The use of wave height distribution of the leakage current in deterioration diagnostic technique makes more accurate diagnosis than the conventional method using only a leakage current value. Finally, the expert system based on the experimental results is developed, and the effectiveness of the system is estimated in a 18[kV] lightning arrester, a 72[kV] and a 170[kV] gas insulated switchgear system.