Mardira et al.: In©estigation of Diagnostic Techniques for Metal Oxide Surge Arresters50 Investigation of Diagnostic Techniques for Metal Oxide Surge Arresters

()Gapless metal oxide surge arresters MOSA have been available in the market for many years since they were first introduced in the 1970’s. The aim of this study is to investigate some reliable diagnostic techniques to assess the condition of a metal oxide surge arrester when subjected to severe lightning strikes in the field. A num-ber of non-destructive and destructive diagnostic techniques for Metal Oxide Surge ()Arrester MOSA are discussed in this paper. The non-destructive techniques in-clude the standard 1 mA reference voltage, lightning impulse discharge residual voltage and a number of modern diagnostics based on polarization methods: Re-turn voltage and polarizationrdepolarization current measurements. In order to observe, analyze and correctly explain the degradation phenomena, a number of destructive techniques based on microstructure observation are also conducted. The techniques include optical microscopy, scanning electron microscopy, X-Ray diffraction and energy dispersive spectrometry. The single and multi-pulse cur-rents of 8r20 s wave shape were used to artificially degrade the MOSA. The be-fore and after diagnostic results of the non-destructive and destructive techniques are presented and interpreted to understand the aging mechanism in MOSA. The importance of modern non-destructive electrical diagnostics based on polarization methods is validated by test results and is highlighted in detail in this paper. Fi-nally the correlation of the results of different diagnostic techniques with each other and with the results of standard techniques is discussed. Index Terms — Metal oxide surge arrester, aging by lightning impulse cur-rents, degradation mechanism, polarizationrdepolarization current, return volt-age, optical microscopy, scanning electron microscopy, X-Ray diffraction, energy dispersive spectrometry.