GE C70 Instruction Manual page 602

OVERVIEW
9.1.6.2 Balanced case
The currents in the neutral current unbalance protection are driven by the individual admittances in each string:
In these equations, I
same per-unit base used by the relay. Voltages are in primary volts, capacitances in Farads, and frequency in radians per
second.
The two neutral currents can be derived from these equations, as follows:
The differential current is the vector difference between the two currents. By subtracting I
At the same time the total currents in each phase are driven by the total admittance of the two banks in each phase:
Inserting the equations above into equation 9.58 so as to eliminate the voltages:
Label k , k , and k
A B
9
9-16
represents the differential CT primary current rating, inserted here to put the string currents on the
base
as follows:
C
C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL
CHAPTER 9: THEORY OF OPERATION
Eq. 9-56
Eq. 9-57
from I , one obtains:
N2 N1
Eq. 9-58
Eq. 9-59
Eq. 9-60
Eq. 9-61