S&C BankGuard PLUS, Setup Instructions

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1011-530 20
Because we are looking for a V
o
of 1.1 or less per unit, our F
c
in this example is 2.
Now calculate U
tp
:
For F = 1,
For F = 2,
To determine the lockout level, calculate the midpoint value between U
tp
for F = 1 and
U
tp
for F = 2 (= F
c
):
Thus, the desired lockout level for this capacitor bank is 8.19%.
Formula Method – Example 2
An installation has the following profile:
•
Highest anticipated continuous system line-to-ground voltage ( V
L-g
): 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,
For F = 2,
Because we are looking for a V
o
of 1.1 or less per unit, our F
c
in this example is 2.
Now calculate U
tp
:
V
o
(volts)
10 20000
⋅
2 10 2 –
( )
2 +
-------------------------------- 11111 volts = =
V
o
(per unit)
11111
9960
---------------
1.1156 per unit (or 11.56% overvoltage)
= =
U
tp
100 1
⋅
2 10 1 –
( )
1 +
--------------------------------
5.26%
= =
U
tp
100 2
⋅
2 10 2
–
( )
2
+
-------------------------------- 11.11% = =
5.26% 11.11% +
2
----------------------------------------- 8.19% =
V
o
(volts)
12 139440
⋅
7 12 1 –
( )
1 +
-------------------------------- 21452 volts = =
V
o
(per unit)
21452
19920
---------------
1.0769 per unit (or 7.69% overvoltage)
= =
V
o
(volts)
12 139440
⋅
7 12 2 –
( )
2 +
-------------------------------- 23240 volts = =
V
o
(per unit)
23240
19920
---------------
1.1667 per unit (or 16.67% overvoltage)
= =