GE C70 Instruction Manual page 592

OVERVIEW
In this case, we have:
The derivative is thus:
Substituting equation 9-17 into equation 9-13, we have:
Therefore:
Substituting this value into equation 9-19, we get:
Or alternately,
The value can be expressed as:
In this equation, ΔC
ground voltage, and V
per-unit of nominal bus phase-to-ground voltage, so V
however that under external fault conditions sensitivity can be much different from the non-fault sensitivity.
9
In practice, k is no less than 2.0 as the tap is no more than half way up the phase string. Comparing equation 9-16 with
A
equation 9-24, it can be seen that V
a operating signal no smaller than the same failure in the upper sub-string. Thus V
sensitivity. A failure resulting in a 0.01 pu capacitance change in the leg capacitance results in an operating signal of at
least 0.01 pu of bus phase-to-ground voltage.
9-6
(pu) is the capacitance change as a per-unit of the leg capacitance, V
A
(pu) is the operating signal resulting from the failure in the lower sub-string. Both voltages are in
OP(2A)
(pu) ≥ V
OP(2A) OP(1A)
can be taken as 1 when the system is normal (not faulted). Note
Spg
(pu), and thus that an element failure in the lower substring produces
C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL
CHAPTER 9: THEORY OF OPERATION
is the system phase-to-
Spg
(pu) represents the worse case
OP(1A)
Eq. 9-18
Eq. 9-19
Eq. 9-20
Eq. 9-21
Eq. 9-22
Eq. 9-23
Eq. 9-24