IEEE C37.99-1990 pdf free.IEEE Guide for the Protection of Shunt Capacitor Banks.
IEEE C37.99 A capacitor bankof a given size and voltage rating may be made upof a number of series groups of capacitors,asindicated in Table 1, and a number of parallelcapacitors per series group.
Use of capacitors with the highest possible volt-age rating will result in a capacitor bank with thefewest number of series groups. This generallyprovides the simplest and most economical rackstructure and the greatest sensitivity for unbalance detection schemes.The available unbalancesignal level decreases significantly as the numberof series groups of capacitors is increased, or asthe number of capacitor units in parallel perseries group is increased.
The number of capacitor units in parallel perseries group is governed by both a minimum anda maximum limitation. The minimum number ofcapacitor units per group is determined by over-voltage considerations upon isolation of onecapacitor unit in the group. The general rule is that isolation of one capacitor unit in a groupshould not cause voltage unbalance sufficient toplace more than 110% of rated voltage on theremaining capacitors in the group. The value of110% is the maximum continuous overvoltage rating of capacitor units per IEEE Std 18-1980[2].The minimum recommended number of capac-itor units in parallel per series group，listed inTable 2, may lint the maximum capacitor unit kvar rating that can be used for relatively smallbanks. Moreover, it emphasizes the desirability ofusing capacitor units with the highest possiblebvoltage rating and minimum number of seriesgroups in order to obtain an adequate number ineach group.
The maximum number of capacitor units that may be placed in a parallel per series Woupagoverned by a different consideration.When a capacitor unit fails, other capacitors in the sameparallel group will contain some amount ofcharge. This charge will then drain off as a highfrequency transient current that flows throughthe faulted unit and its fuse. The fuse holder andthe failed capacitor unit should withstand thisdischarge transient.IEEE C37.99 pdf download.