Reliability analyses and predictive modeling: Voltage regulators on electric systems

The study performed reliability analyses and predictive modeling of voltage regulators at a midwestern electric transmission utility to improve its maintenance program. It determined the reliability of equipment in service by studying the number and types of failures occurring on the different types of voltage regulators. The research questions addressed in this study were: What type of voltage regulator had the most failures, what type of failures occurred most frequently, and what are the correlations between types of voltage regulators and failures? In addition, the study determined regression equations for the failures based on the operational variables of the voltage regulators. These results were utilized to derive key recommendations for establishing preventative maintenance intervals and tasks for the improvement of the reliability of the voltage regulators of this electric transmission utility.; The study produced seven fundamental conclusions from the statistical findings. The key conclusions are that the probability of failure was related to the years of operation of the voltage regulator, the probability of a mechanical or an electrical failure was related to the number of years of operation and age of the voltage regulators, and the manufacturer or size of the voltage regulator had no significant effect on the probability or type of failure. The others conclusions are that the number of operations was directly related to the years of operation, the various types of failures were considered uniformly distributed, and an estimate of the probability of some specific failures were possible once the failure was determined to be mechanical or electrical.; From these seven fundamental conclusions, the study produced fifteen specific recommendations for improving the maintenance and operations of voltage regulators at the electric transmission utility. The first six recommendations pertained directly to establishing preventative maintenance intervals and tasks that are designed to reduce the overall system outage rate by over half for the voltage regulators in service. The remaining recommendations facilitate the accurate planning for annual repair costs, development of efficient inventory levels for spare parts, minimization of future capital costs, and reduction of recovery time for repairs of voltage regulators in service.