IEEE Transactions on Dielectrics and Electrical Insulation Vol. 14, No. 6; December 2007 1070-9878/07/$25.00 © 2007 IEEE 1381 Temporal and Frequency Analysis of the Leakage Current of a Station Post Insulator during Ice Accretion F. Meghnefi, C. Volat and M. Farzaneh NSERC/Hydro-Quebec/UQAC Industrial Chair on Atmospheric Icing of Power Network Equipment (CIGELE), and Canada Research Chair on Atmospheric Icing Engineering of Power Networks (INGIVRE), Université du Québec à Chicoutimi, Chicoutimi, Quebec, G7H2B1, Canada ABSTRACT This research is concerned with the analysis of leakage current, LC, of a porcelain standard station insulator during a glaze ice accretion. The results obtained show that the leakage current during ice accumulation goes through two distinct periods characterized by specific LC waveforms and frequency harmonics. Laboratory tests demonstrated that the duration of the first period is directly dependent on the icing rate. Hence, measuring the duration of the first period is equivalent to measuring the icing rate. However, this requires the determination of either the transition between the two periods or the detection of the onset of the ice accumulation. The results show that icing rate measurement can be achieved by using results of leakage current analysis, like the time evolution of the third and fifth harmonic, as well as the phase angle difference between leakage current and applied voltage. This analysis makes it possible to characterize the severity of an ice accumulation on a porcelain station insulator. Index Terms — EHV outdoor insulator, signal analysis, ice accumulation, monitoring. 1 INTRODUCTION IN cold climate regions, flashover of insulators under severe icing conditions still constitutes a challenging problem for overhead electrical power transmission systems. Reports from a number of utilities support the fact that flashovers can occur on both line and post insulators either during an ice accretion event, or after it, under warming conditions [1-3]. In Canada, practical experience [3] suggests that station post insulators are more susceptible to flashover than suspension line insulators, especially during melting periods. A large number of investigations revealed that flashover of an ice- covered insulator is a complex phenomenon resulting from the interaction of several parameters such as the type, density, thickness, and distribution of the accumulated ice layer, the conductivity of the water forming the ice as well as the insulator parameters and the dynamic behavior of the leakage current (LC) flowing at the ice surface [1-3]. Laboratory studies and industrial experience have shown that measurement and analysis of leakage current provide a good tool for condition-based monitoring of polluted insulators [4-12]. Some attempts have been made to apply LC measurement, for example, to evaluating the insulator performance under pollution conditions [4-6], and determining the pollution severity [7-9] or state of an insulator surface due to aging and dry-band arcing [10-12]. However, similar studies on ice-covered insulators, which can be considered as a severe type of pollution [1], have not been investigated until recently. A few investigations reported in [13-14] have been done on the behavior of LC during icing and melting periods for suspended line insulators. In particular, these studies have shown that LC depends on environmental parameters such as ambient temperature, ice type and thickness. Also, the results obtained showed that LC is made of four components as well as a critical value leading to the appearance of a white arc [13]. But these results mainly focused on the melting period and were obtained under freezing water conductivity as high as 275 μS/cm at 8°C, which is not representative of naturally occurring conductivities of freezing rain. Moreover, these studies were limited to the behavior of the LC current envelope. However, as demonstrated in more recent studies [15-17], time and frequency analyses of LC can provide additional information on the behavior of the ice-covered insulators, something which requires additional specific attention. Leakage current behavior of an ice-covered insulator would be of great interest to utilities since it could be used to predict ice build-up severity as well as the time of the flashover imminence. With such information, a maintenance program based on the diagnostic criteria of a monitoring system could be developed in order to avoid flashovers and related power outages. This could be carried out by triggering maintenance activities such as steam de-icing using a specific remote vehicle [18], or reduction in operating voltage to ensure stable operation after faults. Obviously, an accurate diagnostic Manuscript received on 12 December 2006, in final form 2 April 2007.