METHOD AND ARRANGEMENT FOR AN INTERNAL FAILURE DETECTION IN A Y-Y CONNECTED CAPACITOR BANK

摘要

The present invention relates to a method for detecting an internal failure 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 and each leg includes series and/or parallel-connected capacitor units. The internal failure 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 (100), calculating the root mean square value, denoted by RMS, of the measured phase currents (110), measuring the unbalance current between the two sections (120), calculating the RMS value of the measured unbalance currents (130), detecting the phase angle between the measured phase current and the measured unbalance current (140), calculating the per unit value of the unbalance current based on the calculated RMS value of the measured phase current and the calculated RMS value of the measured unbalance current (145), tracking and detecting a change of the unbalance current between the present calculated per unit value of the unbalance current and the previous calculated per unit value of the unbalance current (150), determining the vectorial step change of the unbalance current (160), normalizing the phase angle of the determined vectorial step change to be one of 0°, 60°, 120°, 180°, 240° and 300° (170), identifying the number of internal failures and their corresponding locations based on the determined vectorial step change of the unbalance current and the normalized phase angle (200), 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 (210).