1011-530
14
Field Determination of the need for Unbalance Compensation.
Close the capacitor bank switching device to energize the capacitor bank.
Verify that no capacitor units have been isolated from the capacitor bank (check for
blown fuses).
The LCD should display a voltage that is essentially zero, or at most 50% of the capaci-
tor bank neutral-to-ground voltage calculated to result from the isolation of one capaci-
tor unit. If the voltage reading exceeds the 50% guideline, it will be necessary to either
increase the alarm level setting or to utilize the optional Unbalance Compensation fea-
ture.
Coordinating Bank Lockout and Individual Capacitor Unit Fuses
It is important to coordinate capacitor bank isolation and lockout with the individual
capacitor unit fuses. The control device should not lock out before the fuse of the last-
failing capacitor unit has had sufficient time to operate. If the fuse does not operate,
there will be no indication of which capacitor unit was in the process of failing.
In general, bank lockout and the individual capacitor unit fuses will be coordinated if
all of the following are true:
The lockout and alarm levels are set as described above (graphical method or formula
method.
The lockout delay time is adequate.
The individual capacitor unit fuses use a fusing ration of 1.25 or less.
The gross overvoltage circuit time delay should be a minimum of 0.5 seconds* plus the
elapsed time between energization of the capacitor bank switching device opening cir-
cuit and closing of the switching device “b” contact (which is coincident with mechani-
cal parting of the disconnect blades, if an S&C Circuit-Switcher is furnished).
For example, if the capacitor-bank switching device is a 230-kV S&C Circuit-Switcher,
the minimum gross overvoltage circuit time delay setting should be 0.5 seconds plus 0.6
seconds, or 1.1 seconds total. The elapse time between energization of the opening cir-
cuit and mechanical parting of the disconnect blades can be approximated as 40% of
the maximum operating time of the particular S&C Circuit-Switcher used.
* Required to prevent gross overvoltage lockout due to transient system voltage.
Summary of Contents for BankGuard PLUS
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