Voltage unbalance in Australian power-quality checks
How voltage unbalance uses comparable three-phase voltage readings, average deviation and an entered threshold basis.
What Voltage Unbalance Means
Voltage unbalance describes how far comparable three-phase voltage readings differ from their average. In Australian power-quality work it is commonly reviewed around 400 V line-to-line readings or 230 V phase-to-neutral readings, but those two measurement sets should not be mixed.
The result belongs to one measurement point and one time or loading condition. It is not the same as phase balancing, motor voltage dip, cable voltage drop or harmonic THD.
Formula Fields
The average-deviation worksheet uses these relationships:
Vavg = (V1 + V2 + V3) / 3.
maximum deviation = largest absolute difference between a measured voltage and Vavg.
unbalance_% = maximum deviation / Vavg x 100.
For line-to-line mode, keep Vab, Vbc and Vca together. For phase-to-neutral mode, keep Van, Vbn and Vcn together. The threshold basis must come from the project, equipment manufacturer, DNSP requirement, power-quality report or engineering review.
| Field | Use it for | Why it matters |
|---|---|---|
| Measurement set | `Vab`, `Vbc`, `Vca` or `Van`, `Vbn`, `Vcn`. | Mixed sets make the percentage meaningless. |
| Measurement point | MSB, distribution board, motor terminals or generator output. | Unbalance is location-specific. |
| Loading condition | Time, load state and instrument or report source. | Voltage spread can change with operating condition. |
| Threshold basis | Project, DNSP, report or manufacturer criterion. | The calculator does not create a universal limit. |
Worked Measurement Example
A main switchboard record has Vab = 400 V, Vbc = 397 V and Vca = 405 V.
Vavg = (400 + 397 + 405) / 3 = 400.67 V.
The maximum deviation is 405 - 400.67 = 4.33 V, so unbalance_% = 4.33 / 400.67 x 100 = 1.08%.
| Item | Example value | Reading |
|---|---|---|
| Measurement set | Line-to-line `Vab`, `Vbc`, `Vca`. | Keep it separate from 230 V phase-to-neutral data. |
| Highest and lowest | `Vca` highest at 405 V, `Vbc` lowest at 397 V. | Voltage spread is 8 V. |
| Result | 1.08% average-deviation unbalance. | Compare only with the entered threshold basis. |
| Context | Main switchboard, loaded condition, instrument report. | The value should stay tied to the record source. |
Related Power-Quality Terms
Voltage unbalance is not a phase-balancing worksheet. Phase balancing usually looks at load distribution. Voltage unbalance looks at measured voltage spread. It is also different from motor voltage dip, which is a starting or event issue, and harmonic THD, which uses harmonic magnitudes.
Some engineering reports may use negative-sequence VUF or other methods. Keep that method label visible if the source is not the average-deviation calculator.
Next checks
- Use voltage unbalance when the three comparable voltage readings and threshold basis are ready.
- Use the formula chart when the average, maximum deviation and percentage relationship needs review.
- Use the power-quality measurement table to keep measurement point, loading condition and instrument context visible.
Boundaries
- This page does not set a universal allowable unbalance.
- It does not diagnose root cause or replace a power-quality investigation.
- DNSP requirements, equipment manufacturer data, report criteria, measurement conditions and qualified review remain controlling inputs.
Voltage unbalance in Australian power-quality checks in Australian work
Explain voltage unbalance so measured voltage set, average, deviation, threshold basis and equipment context stay together. The useful record is not just the final number or definition; it is the combination of the entered value, the supply arrangement, the equipment or circuit reference and the decision that still needs project review.
Help users understand voltage unbalance in Australian three-phase measurement work before using calculators, charts, tables and guides. Keep the wording in Australian English, use metric units, and treat 230/400 V a.c. at 50 Hz as the ordinary low-voltage context unless the project information states a different value.
Checks that belong beside this page
- Regional scopeAustralia; public power-quality terminology.
- Standards contextAustralian power-quality measurement context; current DNSP, equipment manufacturer, report and project requirements remain controlling sources.
- Review timingReview cadence: Annual voltage-unbalance wording review or sooner if calculator, chart or measurement table wording changes.. Update trigger: Update when voltage-unbalance calculator inputs, formula chart rows or measurement table fields change.
Practical use sequence
For Voltage unbalance in Australian power-quality checks, begin with the circuit, board, load, cable route, equipment item or measurement record named by this topic. Record the value basis, such as current, voltage, kW, kVA, route length, test value, product rating, tariff value or worksheet field, then note the review boundary so another person can see what this page explained and what still needs a project decision.
The strongest Voltage unbalance in Australian power-quality checks record is specific enough to be reviewed later. It names the Australian context, keeps the entered assumptions visible, separates calculation support from compliance decisions and shows where a calculator, table, chart or term definition should be opened next.
Record detail to capture
Keep the Voltage unbalance in Australian power-quality checks note attached to Australia; public power-quality terminology.. When the page is used during design, estimating, testing, review or study work, write the entered assumption, the source that supplied it, the circuit or equipment label and the person or role that must review the following action.
For Voltage unbalance in Australian power-quality checks, the review cadence is Annual voltage-unbalance wording review or sooner if calculator, chart or measurement table wording changes. and the update trigger is Update when voltage-unbalance calculator inputs, formula chart rows or measurement table fields change.. If the topic connects to Power-quality measurement record, open that page after the current definition, input basis or boundary has been recorded, so the next calculation inherits the right Australian context.
A complete Voltage unbalance in Australian power-quality checks record leaves four facts visible: why the page was opened, which Australian supply or equipment context applies, which value remains user-entered and what later change would alter the result. That makes the page useful as a working note instead of a loose reference copied away from the project evidence.
- InputsWrite down the entered values and their units before comparing results across calculators or reference pages.
- LocationKeep the value tied to the board, circuit, cable run, equipment terminal, supply point or worksheet row it describes.
- Authority checkCompare the record with current Australian requirements, DNSP or local authority conditions and product information.
- Review trailRetain the date, edition context and reason for the calculation so later changes can be traced.
Connected AUWiring pages
Use the related pages for Voltage unbalance in Australian power-quality checks when the topic needs a calculator input, lookup table, formula chart or supporting term before the project record is complete. Open Power-quality measurement record first when that page owns the next value or definition.
- Power-quality measurement recordFields used for voltage and harmonic measurement records.
- Voltage unbalance formulasFormula relationships for unbalance review.
- Voltage unbalanceCalculate unbalance from entered three-phase voltage values.
- Voltage unbalanceWorkflow guide for power-quality measurements.