Research On Protection Configuration Of Parallel Capacitor And Its Reliability Analysis

Because of playing an important role in improving power quality and transmission capacity and reducing the loss of power grid, the shunt capacitor is widely applied in the low voltage bus of the main transformer in the substations. But with the scale and capacity of power grid increasing, a large number of shunt capacitors are put into operation in the power system. The fault of shunt capacitor occurs frequently, which threats the safe and stable operation of the power grid seriously. Therefore, how to improve the reliability of shunt capacitor protection has become a heated research issue. Centering around the issue, the research in this paper puts forward some effective solutions to improve the reliability of shunt capacitor protection.Firstly, this paper introduces the neutral ungrounded connection and protection of shunt capacitor detailedly through the structure of shunt capacitor, internal and external fuse protection, the broken delta voltage protection of single wye connection, the phase voltage difference protection of single wye connection, the phase current difference protection of single wye connection in H bridge, the neutral current unbalance protection of double wye connection and other protections for the system fault, which lays the foundation for the deduction of unbalance protection’s setting. Secondly, analyses the maximum number of faulty elements or units that allows resection for the shunt capacitor and the reasonable setting value of shunt capacitor protection through the setting of unbalance protection deduction that bases on internal and external fuse protection. Thirdly, studies the reliability of shunt capacitor protection bases on the above content, which researches that the initial unbalance influences the unbalance protection of shunt capacitor through unbalance capacitor, three-phase unbalance power voltage and the performance difference of transformer, which improves the traditional setting algorithm, analyzes that the connection ways of shunt capacitor protection disturbs fuse protection through the broken delta voltage protection of single wye connection, the phase voltage difference protection of single wye connection, the phase current difference protection of single wye connection in H bridge and the neutral current unbalance protection of double wye connection, which puts forward some improved suggestions for the influence, discusses that the restrike overvoltage of switching-off and lighting overvoltage affect the reliability of shunt capacitor and ponits out the best protection configuration scheme among the three connection ways of restrike overvoltage and protection measures of lighting overvoltage. Lastly, a system simulation model is built to analyze and verify the above conclusions by PSCAD/EMTDC according to the shunt capacitor banks’actual capacity in the lOkV bus of the main transformer in the substations of some power grid, which provides an important reference for improving the reliability of shunt capacitor actual protection.