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Conclusion for Unbalance Formulas

Delta connected banks

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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:

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Voltage on Remaining Units:

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If VT = V, %VR will always be 100%.

For Multiple Series Groups the Formulas are as Follows

Neutral to Ground Current:

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Voltage on Remaining Units:

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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 are:

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The Voltage in the Neutral are:

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The Percentage of Voltage Shift in the Affected Leg are:

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For MULTIPLE Series Groups the Formulas are as Follows:

The voltage on the remaining capacitors in the affected phase is:

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The Voltage Shift Due to Removal of F Units in One Series Section:

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The Neutral Shift When One Complete Series Section is Shorted:

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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.

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Percent of rated total bank current

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The Voltage Remaining on Units in One Series Section with F Units Removed:

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Permissible number of units that can be removed from one series section to result in a given %VR on remaining units in that section.

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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:

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The Voltage on this Phase Will Be (Assume Units Removed From Phase "A"):

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The Change in Current in this Phase Will Be

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The New Current in this Leg is:

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To Determine the New Voltage on Phases "B" and "C":

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The Effective KVAR for These Phases Will Be

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The Current in These Phase Will Be

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The Neutral Current in the WYE Section is

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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:

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The Current in this Phase Will Be Higher than the Affected WYE Section:

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The Current in These Phase Will Be

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The voltage on B and C phase will be the same as the affected section and the effective KVAR will be lower.
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The New Current Will Be


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The Neutral Current in the WYE Section is

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The Current on the Neutral Between the WYE Sections Will Be

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LEGEND
Vt Applied line to neutral voltage.
V Rated voltage of the capacitor unit
VR Voltage on remaining units in affected group with F units removed.
△V change in phase to neutral voltage
VB’N’ New voltage on B & C phases
INC Current between neutrals of two banks halves.
△I 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.
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