S&C BankGuard PLUS, Setup Instructions

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19 1011-530
between the higher value of U
tp
for F = 1 and the lower value of U
tp
for F = 2 (= F
c
):
Thus, the desired lockout level for this capacitor bank is 2.25%.
Formula Method
To calculate the lockout level for the capacitor bank:
A. Calculate V
o
for a series of steps corresponding to increasing values of F (up to and
including F
c
) using the following formulas:
B. For each value of F used in Step A, calculate U
tp
:
C. Determine the desired lockout level: the midpoint between the U
tp
for the critical step F
c
and the U
tp
for F
c-1
. (For capacitor banks with an odd number of series groups per phase,
compute alternate values of U
tp
using the adjustment factor, then choose a lockout level
that provides the best overall response.)
Formula Method – Example 1
An installation has the following profile:
•
Highest anticipated continuous system line-to-ground voltage (
V
L-g
): 20 kV
•
Nameplate rating of the capacitor units (
V
r
): 9.96 kV
•
Number of series groups per phase (
S
): 2
•
Number of capacitor units in parallel per series group (
P
): 10
For
F
= 1,
For F = 2,
1.7% 2.8% +
2
-------------------------------- 2.25% =
V
o
(volts)
P V
L g –
( )
S P F –
( )
F +
------------------------------- =
V
o
(per unit)
V
o
(volts)
V
r
------------------------ =
U
tp
(volts)
100 F
S P F –
( )
F +
------------------------------- =
V
o
(volts)
10 20000
⋅
2 10 1
–
( )
1
+
-------------------------------- 10526 volts = =
V
o
(per unit)
10526
9960
--------------- 1.0568 per unit (or 5.68% overvoltage) = =