Delta connected banks
This formula is for losing units between phase A-B. The "AMPS" are in the affected leg. If a
unit is removed from A-C, or B-C, the formula can be modified to address these situations.
Ground WYE connected banks
For single series group the formulas are as follows:
Neutral to ground current
Voltage on remaining units
If VT = V, %VR will always be 100%.
For multiple series groups the formulas are as follows:
Neutral to ground current
Voltage on remaining units
Ungrounded WYE connected banks (Neutral to ground voltage
detection)
For single series group the formulas are as follows:
The voltage on the remaining capacitors in the affected phase is
The voltage in the neutral is
The percentage of voltage shift in the affected leg is
For MULTIPLE series groups the formulas are as follows:
The voltage on the remaining capacitors in the affected phase is
The voltage shift due to removal of F units in one series section
The neutral shift when one complete series section is shorted
VT = Applied line to neutral voltage.
V = Rated voltage of capacitor units.
VR = Voltage on remaining units in affected group with F units removed
IN = neutral to ground current.
IU = Rated current of one unit.
S = Number of series sections per phase.
N = Number of parallel units in one series section.
F = Number of units removed from one series section.
Ungrounded double (split) WYE with neutral CT
The calculations for split applications with even number of units in each WYE sections
are as follows:
The amount of current flowing between neutrals of the two WYES sections. Current transformer is
assumed to have zero impedance.
Percent of rated total bank current
The voltage remaining on units in one series section with F units removed
Permissible number of units that can be removed from one series section to result in a given %VR
on remaining units in that section.
VT = Applied line to neutral voltage.
V = Rated voltage of capacitor units.
VR = Voltage on remaining units in affected group with F units removed
IN = Current between neutrals of two banks halves.
IU = Rated current of one unit.
S = Number of series sections per phase.
N = Number of parallel units in one series section.
F = Number of units removed from one series section.
The calculations for split applications with uneven WYE sections are as follows, one
series group:
The change in voltage in the phase with units removed
The voltage on this phase will be (assume units removed from phase "A")
The change in current in this phase will be
The new current in this leg is
(A phase KVAR will be the original KVAR)
To determine the new voltage on phases "B" and "C"
The effective KVAR for these phases will be
The current in these phase will be
The neutral current in the WYE section is
You will need to calculate the neutral current in the WYE section without any units removed.
The phase A voltage in the section is the same as above
, and
The current in this phase will be higher than the affected WYE section
The current in these phase will be
The voltage on B and C phase will be the same as the affected section and the effective KVAR will be
lower.
The new current will be
The neutral current in the WYE section is
(normal WYE section-no units removed)
The current on the neutral between the WYE sections will be
VN = Applied line to neutral voltage.
V = Rated voltage of capacitor units.
VR = Voltage on remaining units in affected group with F units removed
DV = change in phase to neutral voltage
VB’N’= New voltage on B & C phases
INC = Current between neutrals of two banks halves.
DI = Current change in affected phase (A).
IA’N’ = New current in affected phase (A)
IB’N’ = New current in phase B & C.
IN’(Unit removed) = neutral current in WYE section with unit removed.
IN’(Normal section) = neutral current in WYE section with unit removed.
KVAREFF = Effective KVAR
KVARRATED = rated KVAR
S = Number of series sections per phase.
N = Number of parallel units in one series section.
F = Number of units removed from one series section.
