GE C70 Instruction Manual page 535

CHAPTER 9: THEORY OF OPERATION
The neutral current unbalance protection uses the following operate signal:
The neutral current unbalance protection uses the following restraint signal:
where k represents the vector capacitor bank positive sequence inherent unbalance factor setting, and k
1
complex conjugate of k . The currents are as defined in the figure and are in per-unit values of the nominal current of the
1
bank source ground current channel.
These equations involve phasors, not magnitudes; that is, the vector sum of the currents is created by the protection
function implementing the method. The protection operates when the operate signal is greater than the set pickup level
for the set pickup delay.
Sensitivity is the key performance parameter. The applied comparator uses a simple integration method in addition to the
standard hysteresis approach, to deal with chattering of the operating signal at the boundary of operation.
C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL
Figure 9-6: Neutral current unbalance application
OVERVIEW
Eq. 9-54
Eq. 9-55
* represents the
1
9
9-15