Patent ID: 8912801
Filing Date: 2014-12-16
Classification: G01R,G05F,H02H,H02J

Abstract:
1. A method for detecting a number of internal failures in a capacitor bank connected to a power system, wherein the capacitor bank comprises a plurality of capacitor units that are divided into two Y sections, each phase in each of the Y sections defining a leg, each leg including series and/or parallel-connected capacitor units, and each internal failure event may occur in one or more capacitor elements or units or involve one or more legs, the method comprises: measuring the phase current in one of the phases, calculating the Root Mean Square value, denoted by RMS, of the measured phase current, measuring the unbalanced current between the two sections, calculating the RMS value of the measured unbalanced currents, and detecting the phase angle between the measured phase current and the measured unbalanced current, characterized in that the method further comprises: calculating the per unit value of the unbalanced current based on the calculated RMS value of the measured phase current and the calculated RMS value of the measured unbalanced current, recognizing each internal failure event by tracking the change in the unbalanced current, tracking and detecting a change of the unbalanced current between the present calculated per unit value of the unbalanced current and the previous calculated per unit value of the unbalanced current, determining the vectorial step change of the unbalanced current for each internal failure event, normalizing the phase angle of the determined vectorial step change of each internal failure event to be one of 0°, 60°, 120°, 180°, 240° and 300°, identifying the number of internal failures and their corresponding locations based on the determined vectorial step change of the unbalanced current and the normalized phase angle, and initiating an alarm or a trip signal when the determined total number of internal failures exceeds a first or a second threshold value respectively.