Shunt capacitor bank fundamentals and the application of differential voltage protection of fuseless single star earthed shunt capacitor banks

摘要

The research investigates reactive power compensation and protection of shuntudcapacitor banks. The characteristics of capacitors including, formulae, design,udmanufacturing, and testing is presented. Capacitor units using extended foil solderudtype elements have losses as low as 0.1 watt/kVAr. Failure of capacitors generallyudoccurs due to overvoltage stress. The type and aging properties of the dielectricuddetermines the lifespan of the capacitor. Polypropylene film is commonly used as theuddielectric. Basic capacitor bank design calculations are presented. A detaileduddiscussion on the configurations and protection philosophies is described for singleudstar earthed, single star H-bridge, double star, and C-type filter H-bridge capacitorudbanks. A novel approach to unbalance voltage detection and the protection ofudfuseless single star earthed shunt capacitor banks is investigated, engineered andudtested. This methodology explores the potential evolution towards distributedudprotection. This involves two programmed multifunction protection relaysudcommunicating via the IEC 61850 Ethernet protocol. One relay receives voltageudmeasurements from the high voltage busbar. The other relay receives voltageudmeasurements from the low voltage capacitor tap point. The two relays share theirudmeasurements via the Ethernet link. The difference in measurements is used toudinitiate alarm and trip operations. The relay protection function satisfies criterion forudreset-ability, selectivity, stability, accuracy, and loss of potential blocking. Spuriousudoperation occurs when the Total Harmonic Distortion level is above 8%. The majorudshort coming is the cyclic processing of the logic function. The algorithm processingudduration is 396ms as opposed to an anticipated time of 60ms. This application has audcompetitive overall cost advantage. This is based on the number of componentsudrequired, manufacturing and testing times, and onsite installation and commissioningudworks. It is recommended to further investigate the cyclic processing of the logicudfunctions, as well as, to test the protection function on a power system simulator.udFuture prospects involve using the programmability and flexibility of the onboardudrelay PLC to count capacitor element failure, on a discrete basis, instead of detectionudand protection based on analogue threshold settings. This will mitigate ambiguousudmeasurements and spurious operation.