S&C BankGuard PLUS Setup Instructions page 20

1011-530
= ------------------------------- -
V (volts)
o
2 10 2
V o (per unit) =
Because we are looking for a V
Now calculate U :
tp
For F = 1,
⋅
100 1
U = ------------------------------- -
tp
( )
2 10 1 – +
For F = 2,
⋅
100 2
U = ------------------------------- -
tp
( )
– +
2 10 2
To determine the lockout level, calculate the midpoint value between U
U for F = 2 (= F ):
tp c
5.26% + 11.11%
---------------------------------------- - =
2
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
•
Nameplate rating of the capacitor units (V
•
Number of series groups per phase (S): 7
•
Number of capacitor units in parallel per series group (P): 12
For F = 1,
12
= ------------------------------- -
V (volts)
o
7 12 1
V o (per unit) =
For F = 2,
V (volts) = ------------------------------- -
o
7 12 2
V o (per unit) =
Because we are looking for a V
Now calculate U :
tp
⋅
10 20000
=
11111 volts
( )
– + 2
11111
-------------- - = 1.1156 per unit (or 11.56% overvoltage)
9960
of 1.1 or less per unit, our F
o
= 5.26%
1
= 11.11%
2
8.19%
): 19.92 kV
r
⋅
139440
=
21452 volts
( )
– + 1
21452
-------------- - = 1.0769 per unit (or 7.69% overvoltage)
19920
⋅
12 139440
= 23240 volts
( )
– + 2
23240
-------------- - = 1.1667 per unit (or 16.67% overvoltage)
19920
of 1.1 or less per unit, our F
o
20
in this example is 2.
c
for F = 1 and
tp
): 139.44 kV
L-g
in this example is 2.
c