Abstract: Class-10A solid-core insulators (BIL 90kV) have been used instead of class-6A pin insulators (BIL 60kV) in order to improve the insulation level of distribution lines. However, lightning protective devices attached to pole transformers may have the effect of reducing the overvoltages on phase conductors. We have investigated the lightning protection effect of devices attached to pole transformers by experiment and analysis using the EMTP (Electro-Magnetic Transients Program). The sparkover rate changes from 2.0˜3.3% to 5.5˜9.9% and increases 2.4˜2.8 times when the line insulator of the phase conductors is changed from class-10A to class-6A. It is thought that the insulation level of the line insulator can be reduced depending upon the local particularities, such as number of installed transformers, frequency of direct lightning stroke to the distribution line, and so on although the overall fault rate may increase to some extent.
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