S&C BankGuard PLUS, Setup Instructions

Page: 8 / 50

1011-530 8
For F = 1,
For F = 2,
For F = 1, enter at 10 on the horizontal scale. Follow this up to the curve for S = 2 (2
series groups per phase). Here, V
n
= 0.018 per unit.
Similarly, for F = 2, enter the graph at 20 on the horizontal scale. Follow this up to the
curve for S = 2. Here, V
n
= 0.038 per unit.
To convert V
n
to an actual voltage, multiply by the system voltage V
L-n
:
For F = 1,
For F = 2,
To determine the lockout level, calculate the midpoint value between V
n
for F = 1 and V
n
for F
= 2 (= F
c
):
Thus, the desired lockout level for this capacitor bank is 560 volts.
Graphical Method – Example 2
An installation has the following profile:
•
Highest anticipated continuous system line-to-neutral voltage (
V
L-n
): 139.44 kV
•
Nameplate rating of the capacitor units (
V
r
): 19.92 kV
•
Number of series groups per phase (
S
): 7
•
Number of capacitor units in parallel per series group (
P
): 12
For
F
= 1, enter at 8.33 on the horizontal scale (1/12 = 8.33% of capacitor units isolated
from a series group). Follow this up to a point corresponding to 7 series groups per
phase (interpolate between the curves for
S
= 6 and
S
= 8). Here on the vertical scale,
V
o
= 1.085 per unit.
Similarly, for F = 2, enter the graph at 16.67 on the horizontal scale (2/12 = 16.67% of
capacitor units isolated from the same series group). Follow this up to a point corre-
sponding to 7 series groups per phase. Here,
V
o
= 1.18 per unit. Because we are looking
for a
V
o
of 1.1 or less per unit, our
F
c
in this example is 2.
With
V
L-n
= 139.44 kV and 7 series groups per phase, the capacitor units are normally
operated at 19.92 kV, their rated voltage. Therefore, no correction factor is needed.
For F = 1, enter at 8.33 on the horizontal scale. Follow this up to a point corresponding
V
o
1.072 10kV
×
9.96kV
---------------------------------- 1.076 per unit = =
V
o
1.16 10kV
×
9.96kV
------------------------------- 1.16 per unit = =
V
n
0.018 20000 volts
×
360 volts
= =
V
n
0.038 20000 volts
×
760 volts
= =
360 volts 760 volts +
2
--------------------------------------------------- 560 volts =