Shunt Capacitor Bank Fundamentals and Protection

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2003 Conference for Protective Relay Engineers - Texas A&M University April 8-10, 2003, College Station (TX) Shunt Capacitor Bank Fundamentals and Protection Gustavo Brunello, M.Eng, P.Eng Dr. Bogdan Kasztenny Craig Wester GE Multilin, Canada GE Multilin, Canada GE Multilin, USA ABSTRACT Shunt capacitor banks are used to improve the quality of the electrical supply and the efficient operation of the power system. Studies show that a flat voltage profile on the system can significantly reduce line losses. Shunt capacitor banks are relatively inexpensive and can be easily installed anywhere on the network. This paper reviews…show more content…
The remaining capacitor elements in the unit remain in service with a higher voltage across them than before the failure and an increased in capacitor unit current. If a second element fails the process repeats itself resulting in an even higher voltage for the remaining elements. Successive failures within the same unit will make the fuse to operate, disconnecting the capacitor unit and indicating the failed one. Externally fused SCBs are configured using one or more series groups of parallel-connected capacitor units per phase (Fig. 2). The available unbalance signal level decreases as the number of series groups of capacitors is increased or as the number of capacitor units in parallel per series group is increased. However, the kiloVar rating of the individual capacitor unit may need to be smaller because a minimum number of parallel units are required to allow the bank to remain in service with one fuse or unit out. phase A phase B phase C Fig. 2 – Externally fused shunt capacitor bank and capacitor unit b) Internally Fused Each capacitor element is fused inside the capacitor unit. The fuse is a simple piece of wire enough to limit the current and encapsulated in a wrapper able to withstand the heat produced by the arc. Upon a capacitor element failure, the fuse removes the affected element only. The other elements, connected in parallel in the same group, remain in service but with a slightly higher voltage across them. Fig. 3

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