GE C70 Instruction Manual page 539

CHAPTER 9: THEORY OF OPERATION
• The phase voltages in equations 9.54 through 9.59 must have the neutral voltage V
voltages are eventually eliminated from the calculations, the outcome is unaffected.
• A low ratio CT can be used for ungrounded-wye configurations in place of a window type CT as there is no
requirement to form the difference of the primary neutral currents
• Whereas with the grounded configuration I
results in the –C , –C , and –C
A2 B2
changes.
Equation 9.64 becomes:
Equation 9.65 becomes:
Equation 9.67 becomes:
Equation 9.68 becomes:
Note that in the ungrounded case, the operating signal is half of that for the grounded case.
• With the grounded configuration, the two banks must be nominally identical. With the ungrounded configuration the
two banks need not be the identical though each ideally are balanced. In this situation, the base for ΔC(pu) is the
capacitance of the string that has the element failure, so the larger bank has a lower sensitivity than the smaller bank.
C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL
= I – I , with the ungrounded configuration I
DIF N1 N2
terms disappearing from equations 9.58 through 9.65. This results in the following
C2
OVERVIEW
subtracted. However, as these
X
= I = –I . This
DIF N1 N2
Eq. 9-69
Eq. 9-70
Eq. 9-71
Eq. 9-72
9
9-19