Grounded Wye Banks - S&C BankGuard PLUS Setup Instructions

You must establish the settings for each control device installation, using either graphs
or formulas. Both methods are described in this section for grounded wye-connected
shunt capacitor banks only. It also describes how to calculate the gross overvoltage
and alarm levels, and how to coordinate capacitor bank isolation with the individual
capacitor unit fuses.
Both the graphical and formula methods assume that the intermediate tap point for
each phase of the bank is located as follows:
•
For capacitor banks with an even number of series groups per phase, the number
of series groups between the tap point and ground should equal the number of
series groups between the tap point and the line.
•
For capacitor banks with an odd number of series groups per phase, the number
of series groups between the tap point and ground should be one less than the
number of series groups between the tap point and the line.
Before you begin, you will need on the following information:
•
The number of series groups per phase
•
The number of capacitor units in parallel per series group
•
The highest anticipated continuous system line-to-neutral voltage (in kV)
•
The nameplate rating of the capacitor units (in kV)
This section uses the following variable names:
S = Number of series groups per phase
P = Number of capacitor units in parallel per series group
V = Highest anticipated continuous system line-to-neutral voltage
L-n
V = Highest anticipated continuous system line-to-ground voltage
L-g
V = Nameplate rating of the capacitor units
r
V = Voltage applied to surviving capacitor units, per unit of capacitor-unit normal voltage
o
U = Tap-point voltage percent imbalance
tp
F = Number of isolated capacitor units
F = The "critical step" – the number of isolated capacitor units at which V
c
capacitor manufacturer's recommended maximum working voltage (which is
generally 1.1 per unit)
NOTE: The values of U that you find in this section (whether using the graphs or the
tp
formulas) are valid for the isolation of capacitor units in any series group of a capacitor
bank with an even number of series groups per phase. When the total number of series
groups per phase is odd, the values of U
units in any series located between the tap point and the line.
When the total number of series groups per phase is odd, and the capacitor unit is
located between the tap point and ground, you must multiply U
adjustment factor:
S +
Adjustment factor = ----------- -
S 1 –

Grounded Wye Banks

are also valid for the isolation of capacitor
tp
1
15
exceeds the
o
by the following
tp
1011-530