Gross Overvoltage - S&C BankGuard PLUS Setup Instructions

Gross
Overvoltage
For F = 1,
⋅
100 1
U = ------------------------------- -
tp
( )
7 12 1 – +
For F = 2,
⋅
100 2
= ------------------------------- -
U tp
( )
7 12 2 – +
Because the number of series groups per phase in this example is odd, you must com-
pute alternate values of U
in a series group between the tap point and ground. In this example, the adjustment
factor is (7 + 1)/(7 - 1) = 1.33.
For F = 1,
×
U tp = 1.28% 1.33
For F = 2,
×
U tp = 2.78% 1.33
In this example, the desired tap-point voltage imbalance lockout level is the midpoint
between the higher value of U
1.70% + 2.78%
------------------------------------- - =
2
Thus, the desired lockout level for this capacitor bank is 2.24%.
You can calculate the tap-point voltage percent imbalance (U
within the capacitor bank that would short out an entire series group:
100
U = ----------- -
tp
–
S 1
The desired gross overvoltage lockout level is the midpoint between the V
ical step and the V resulting from shorting out a series group.
n
NOTE: If the calculated gross overvoltage lockout level is more than 65,536 volts, set
the setpoint value to its maximum level.
For Example 1 above, the U
from shorting out a series group is:
100
= ----------- - =
U 100%
tp
2 1 –
Therefore, the desired gross overvoltage lockout level is:
11.11% + 100%
-------------------------------------- - = 55.56%
2
For Example 2 above, the U
= 1.28%
1
=
2.78%
2
using the adjustment factor for isolation of capacitor units
tp
= 1.70%
= 3.70%
for F = 1 and the lower value of U
tp
2.24%
for the critical step (F
tp
for the critical step (F
tp
21
for F = 2 (= F
tp
) resulting from a fault
tp
for the crit-
n
= 2) was 11.11%. The U
c tp
= 2) was 3.70%. The U
c tp
):
c
resulting
resulting
1011-530