Failure analysis of medium voltage capacitor banks: the Egyptian experience

Abstract

This paper describes the failure modes in the capacitor banks installed in the Egyptian Network over the past years. The study has focused on the capacitor banks installed at the MV side of the HV substations in the Egyptian Transmission Network. Failures of capacitor units/banks in substations can be detrimental to the supply of reliable power to consumers. Failure analysis, failure mechanism, failure origin and physical damage causes were studied, not only from the manufacturing point of view, but also from the utility prospective in order to enhance the utility reliability. The results of the study on 457 capacitor banks of about 2383 MVARs capacity revealed the main causes of capacitor accidents, and sum up experiences in the Egyptian Electricity Utility.

A High Voltage Capacitor Element Model

“…'Self-healing' designs are robust, but unsuitable for high-power applications due to overheating and thermal gradients [5]. Instead, high-power applications more commonly employ internally fused designs [6], [7]. Where fuses isolate part of a module, a terminal voltage is then shared among remaining elements, and in turn, increased voltage stresses can provoke further breakdown and encourage cascading effects [4].…”

Thermal Profiles of High-voltage Capacitor Units

“…Power electronic conversion allows a modern alternative to conventional power system reinforcement: network capacity can be increased through power factor correction, high voltage direct current links, series compensation, and connection of renewable sources dispersed across a network in terms of both connection voltage and location. As such technologies bear responsibility for greater network capacities, they become more critical to network operation and as a constituent component of power electronic interfaces and standalone power factor correction, shunt capacitor banks correspondingly become "increasingly important" for reliable power systems [1], across voltage levels.…”

“…Capacitor units are generally considered a relatively reliable part of the wider system, and that banks comprise modular units aids partial replacement. However, even modest failure rates could become cumbersome when scaled to match the number of components employed for high-capacity network applications, and as units are unrepairable [1], early detection and tracking for developing faults and asset degradation is preferable. Accordingly, this paper explores how the location of a point heat source influences heat profiles of a module's external housing, by employing a simulated model of a high voltage capacitor unit as illustrated by Figure 1, which highlights internal elements.…”