Harmonic THD in Australian power-quality checks
How total harmonic distortion uses fundamental RMS, harmonic RMS rows, dominant harmonic and an entered threshold basis.
What Harmonic THD Means
Harmonic THD means total harmonic distortion. It is a ratio between the combined harmonic RMS magnitude and the fundamental RMS magnitude from the same voltage or current measurement record.
In Australian 230/400 V a.c., 50 Hz sites, THD can appear in main switchboard analyser reports, VSD feeder records, UPS output records, generator output checks and plant-room investigations. Voltage THD and current THD are different records and should stay separate.
Formula Fields
The worksheet combines selected harmonic RMS values using a root-sum-square relationship:
H_rms = sqrt(H2^2 + H3^2 + H5^2 + H7^2 + H11^2 + H13^2 + other harmonic RMS^2).
THD_% = H_rms / H1 x 100.
H1 is the fundamental RMS value from the same analyser record. The 2nd, 3rd, 5th, 7th, 11th and 13th harmonic rows, plus any other harmonic RMS value, must come from the same measurement basis.
| Field | Use it for | Why it matters |
|---|---|---|
| Measurement type | Voltage THD or current THD. | The two records answer different questions. |
| `H1` fundamental RMS | Base value for the percentage. | THD is calculated relative to this value. |
| Harmonic RMS rows | 2nd, 3rd, 5th, 7th, 11th, 13th and other RMS. | Missing rows change the root-sum-square result. |
| Dominant harmonic | Largest entered harmonic row. | Helps focus the measurement review. |
| Threshold basis | Project, DNSP, report or equipment criterion. | The calculator does not create a universal limit. |
Worked THD Example
A switchboard voltage record has H1 = 230 V, with harmonic RMS values of 0 V, 4 V, 6 V, 2 V, 0 V, 0 V and 1 V for the selected rows.
H_rms = sqrt(0^2 + 4^2 + 6^2 + 2^2 + 0^2 + 0^2 + 1^2) = 7.55 V.
THD_% = 7.55 / 230 x 100 = 3.28%.
| Item | Example value | Reading |
|---|---|---|
| Measurement point | Main switchboard analyser record. | THD is tied to a location and time window. |
| Measurement type | Voltage THD. | Do not compare directly with current THD. |
| Dominant harmonic | 5th harmonic at 6 V. | The largest row helps guide review. |
| Result | 3.28% THD. | Compare only with the entered threshold basis. |
Related Power-Quality Terms
THD is not voltage unbalance, phase balancing, motor voltage dip, flicker, interharmonics or a neutral-current review. Those may be related in an investigation, but they use different inputs.
For VSD feeders, UPS outputs, generator outputs or plant-room records, keep the analyser setup, loading condition, threshold basis and equipment data with the THD value.
Next checks
- Use harmonic THD when the fundamental RMS value and harmonic RMS rows come from one analyser record.
- Use the harmonic THD formulas chart when the root-sum-square relationship needs review.
- Use the power-quality measurement table to keep location, loading condition, analyser setup and threshold basis visible.
Boundaries
- This page does not set harmonic limits or diagnose distortion source.
- It does not replace waveform analysis, equipment review or supply investigation.
- DNSP requirements, equipment limits, analyser settings, measurement conditions and qualified investigation remain controlling inputs.
Harmonic THD in Australian power-quality checks in Australian work
Explain harmonic THD so fundamental RMS, harmonic RMS rows, threshold basis and measurement 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 harmonic THD in Australian power-quality measurements before using THD 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 harmonic THD wording review or sooner if calculator, chart or measurement table wording changes.. Update trigger: Update when harmonic THD calculator inputs, formula chart rows or measurement table fields change.
Practical use sequence
For Harmonic THD 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 Harmonic THD 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 Harmonic THD 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 Harmonic THD in Australian power-quality checks, the review cadence is Annual harmonic THD wording review or sooner if calculator, chart or measurement table wording changes. and the update trigger is Update when harmonic THD 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 Harmonic THD 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 Harmonic THD 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 harmonic and voltage measurements.
- Harmonic THD formulasFormula relationships for THD review.
- Harmonic THDCalculate THD from entered fundamental and harmonic RMS values.
- Harmonic THDWorkflow guide for harmonic measurements.