GE Multilin C70 Capacitor Bank Protection and Control System 9-199 APPLICATION OF SETTINGS 9.4 SETTING EXAMPLE9Therefore, the alarm delay is specified as 10 seconds. The following setting values are programmed in the EnerVista URSetup software.The pickup setting for the stage 2 current unbalance trip element is specified as the unbalance current during maximumsystem conditions midway between the third and fourth capacitor element failure unbalance currents.(EQ 9.26)Therefore, the trip delay is chosen 50 ms.9.4.7 BANK PHASE OVERVOLTAGE SETTINGSTo protect the capacitor bank from overvoltage resulting from abnormal system conditions, the capability of the bank towithstand transient overvoltages must be evaluated according to the IEEE 1036-1992 standard or to manufacturer specifi-cations. For example, consider the following manufacturer overvoltage data:• 2 pu overvoltage toleration for 0.25 second.• 1.5 pu overvoltage toleration for 15 seconds.• 1.25 pu overvoltage toleration for 5 minutes.When the relay settings are calculated, the number of prospective overvoltage transients stressing the capacitor insulationduring the bank lifetime must be taken into account. As such, it is preferable to set the relay conservatively.Based on the manufacturer overvoltage data above, three overvoltage trip stages are applied using a factor of 0.9 for thestage pickup overvoltage levels and half of the allowable time indicated above.(EQ 9.27)60P trip I unbal f4_max I unbal f3_max +2------------------------------------------------------------------------ 0.0904 pu 0.0660 pu+2------------------------------------------------------------ 0.078 pu= = =59B pickup (stage 1) 0.9 1.25 1.125 pu= =59B pickup (stage 2) 0.9 1.5 1.35 pu= =59B pickup (stage 3) 0.9 2 1.80 pu= =
