Voltage Unbalance Calculations

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There are a few different ways to calculate voltage unbalance, and the ION meter can use any of the calculations! In general, when unbalance is low the different between the results is small but as unbalance starts to exceed 5% the difference becomes more noticeable. Where voltage unbalance is excessive and connected to customer with equipment susceptible to voltage unbalance. Any of the below equations may be incorporated into your ION meter.

The various calculations and definitions are;

Line Voltage Unbalance Rate (LVAR)

Maximum Voltage Deviation from Average Line Voltage (MVDALV)

Average Line Voltage (ALV)

Phase Voltage Unbalance Rate (PVAR)

Maximum Voltage Deviation from Average Phase Voltage (MVDAPV)

Average Phase Voltage (APV)

Voltage Unbalance Factor (VUF)

Negative Sequence Voltage (V₂)

Positive Sequence Voltage (V₁)

[1] is the NEMA definition for voltage unbalance, and it is the definition used by the Power Meter module in ION meters that are configured for DELTA measurements. [2] is a variation of the NEMA definition that uses phase voltages or line-to-neutral voltages and is the definition used by the Power Meter module when ION meters are configured for WYE measurements like the Form 9S volts mode.

[3] is considered the True Definition for voltage unbalance and is a comparison between the negative sequence voltage V₂ and positive sequence voltage V₁. The main difference between equation [3], and [1] and [2] is that it uses complex algebra and is looking at magnitude and phase angles as a part of the calculations. Were [1] and [2] only account for the magnitude of each phase and it’s deviation from the average voltage.

The power meter module already uses the LVUR and PVUR calculations, and the symmetrical components are available from the symmetrical components module in the meter! For a WYE configured meter an arithmetic module can be used to calculate LVUR as well as VUF.

Input Registers (Sources, S)	Setup Registers	Output Registers (Results, R)
Vll ab	ABS(S1–S4)	R1
Vll bc	ABS(S2–S4)	R2
Vll ca	ABS(S3–S4)	R3
Vll avg	MAX(R1,R2,R3)/S4*100	LVUR
PosSeqMag	(S6/S5)*100	VUF
NegSeqMag

For more information reach out to your Schneider Electric Utility Account Executive, Regional Manager, or local Sales Representative.