New method of capacitors failure detection and location in shunt capacitor banks

Abstract

To achieve more reliable grid it is crucial for utilities to expedite the repair process of critical assets, including Shunt Capacitor Banks (SCBs). Exposure to sharp temperature variations, transient over voltages, aging and manufacturing defects can cause internal failures of capacitor elements. A new method using indicating quantity Superimposed Reactance (SR), is presented in this paper to locate capacitor elements failures in Shunt Capacitor Banks. The proposed quantity is estimated using available measurements to the unbalance protection function of SCBs numerical protective relays. The proposed SR adopts calibrating factors for fault location and can provide live report of the number of failed capacitor elements. The proposed method benefits are: Rapid identification of the SCBs failed elements for fuseless and internally fused designs, Determining failure and faulted phase of single-wye connected banks, Ability to detect consecutive failures, even in the same or different phases due to self-tuning, Online reporting of elements failure for proactive maintenance planning. The developed method supports three different grounding arrangements, wye-ungrounded, wye-grounded via a low ratio current transformer, and wye-grounded via a grounding capacitor at the SCB neutral point. Comprehensive simulation and fault-location analysis using PSCAD and MATLAB have verified the proposed algorithm performance. Advantages of the proposed method reports over conventional unbalance relaying alarms are also demonstrated using a relay test results comparison.