Harmonics, neutral current at K-factor
THD, neutral current at k factor mula sa spectrum.
Reads AS/NZS 3000:2018, AS/NZS 3008.1.2:2017 (NZ) and AS/NZS 3008.1.1:2017 (AU). Tables checked 2 Oct 2026.
Subukan ang isang job 4
Nilalagyan ng halimbawang value ang bawat job. Palitan ang mga ito ng sarili mong value.
- Find the harmonic neutral current of an officeThe neutral current of an office floor full of computers, from its spectrum.
- Find the K-factor for a drive transformerThe K-factor of six-pulse drives, for the transformer that feeds them.
- Check an LED lighting circuit for harmonicsWhether a cable for LED drivers is picked on its neutral current.
- Neutral current with some electronic loadThe neutral of a board where electronics are 30 % of the load.
Mga input
Worked example gamit ang mga default na input.
- Hurisdiksyon
- NZ · AS/NZS 3008.1.2
- Phase current, true rms
- 100 A
- Third harmonic
- 35 %
- Fifth harmonic
- 20 %
- Seventh harmonic
- 10 %
- Ninth harmonic
- 5 %
- Eleventh harmonic
- 4 %
- Thirteenth harmonic
- 3 %
- Fifteenth harmonic
- 2 %
- Bahagi ng phase load na lumilikha ng harmonics
- 100 %
- Out-of-balance current
- 0 A
Triplen neutral
97.88A
- Total harmonic distortion ng current
- 42.18%
- K-factor
- 3.59
- Reduction factor ng Table 2
- ×0.86
- Batayan ng pagpili ng cable
- Ang phase current
- Current na batayan sa pagpili ng cable
- 116.28A
- Cl 3.5.2(b)(i) pinakamababa para sa neutral
- 38.86A
Design aid lang ang resultang ito. I-verify ito laban sa kasalukuyang standard.
Mga hakbang ng kalkulasyon
- Total harmonic distortion ng current42.18%
- Fundamental current92.14A
- Triplen harmonics, √(h3² + h9² + h15²)35.41%
- Triplen neutralResulta97.88A
- Third harmonic, porsyento ng phase current32.25%
AS/NZS 3008.1.2:2017 Table 2
- Reduction factor ng Table 2×0.86
AS/NZS 3008.1.2:2017 Table 2
- Neutral current mula sa ikatlong harmonic lamang96.75A
AS/NZS 3008.1.2:2017 Cl 3.5.9
- Current na batayan sa pagpili ng cable116.28A
AS/NZS 3008.1.2:2017 Cl 3.5.9
- Harmonic current ng isang phase, ikatlo at mas mataas38.86A
- Cl 3.5.2(b)(i) pinakamababa para sa neutral38.86A
AS/NZS 3000:2018 Cl 3.5.2(b)(i)
- K-factor3.59
Tungkol sa calculator na ito
How this is calculated
Electronic loads draw current in pulses, not as a smooth wave. A power quality analyser splits that current into the fundamental and its harmonics, each shown as a percent of the fundamental. The tool takes the true rms phase current and that spectrum, from the third to the fifteenth order.
The total harmonic distortion is the rms of all the harmonic percents. The fundamental current is the rms current divided by the square root of one plus the distortion squared.
The third, ninth and fifteenth harmonics are the triplens. In the three phases they are in step, so they add in the neutral instead of cancelling. With equal phases the neutral carries three times one phase's triplen current. That is the tool's main answer.
AS/NZS 3008.1 Table 2 bands the third harmonic as a percent of the phase current. So the tool converts the analyser's percent of the fundamental to a percent of the rms current. It reads the band through the cable size tool's own path, and gives the reduction factor, whether the cable is picked on the phase or the neutral current, and the current to carry to cable size.
AS/NZS 3000 Cl 3.5.2(b)(i) gives a minimum for the neutral of a substantial harmonic load: the out-of-balance current plus one phase's harmonic current. Size the neutral for the larger of it and the triplen figure. AmpSize reads the harmonic current as the rms of the third and higher orders. Note 1 sets what substantial means.
The K-factor weights each harmonic by its order squared, because eddy current loss in a transformer rises with frequency squared. A clean load gives 1.
| Step | Table or clause | What it decides |
|---|---|---|
| Distortion | The rms of the harmonic percents | The THD and the fundamental current |
| Triplen neutral | Three times one phase's triplens | The neutral current of three equal phases |
| Third harmonic band | Table 2 | The reduction factor and the basis the cable is picked on |
| Neutral of the third harmonic | Cl 3.5.9 | The current the cable is picked on above the middle band |
| Clause neutral | Cl 3.5.2(b)(i) | The out-of-balance current plus one phase's harmonic current |
| Substantial load | Cl 3.5.2(b)(i) Note 1 | Whether the clause figure applies |
| K-factor | Each order squared, weighted by its share | The transformer K rating to pick at or above |
Worked examples
- An office floor of 80 A with 40 % third harmonic puts 87.16 A in the neutral, more than a phase. The current has 49.34 % THD and a K-factor of 4.37.
- Six-pulse drives drawing 150 A put only 13.43 A in the neutral, as their harmonics are mostly fifth and seventh. The current has 35.14 % THD and a K-factor of 5.12.
- An LED lighting circuit of 40 A puts 64.28 A in the neutral. The current has 89.16 % THD and a K-factor of 10.01.
- A 60 A board where electronics are 30 % of the load puts 58.73 A of triplens in the neutral if every load had this spectrum. The current has 42.18 % THD and a K-factor of 3.59. Below 40 % the clause figure does not apply.
Limits
The tool assumes three equal phases with the same spectrum. A real board has a mix. Enter the worst phase's readings for a safe answer.
It does not work voltage distortion, resonance with power factor capacitors or filter design. Those need the supply's impedance and a harmonic study.
See also: Neutral current, Cable size and Transformer.
Mga tanong
Design aid ang resulta. I-verify ito laban sa kasalukuyang standard.
Paano kinakalkula ang harmonic neutral current?
Magkasabay ang ikatlo, ikasiyam at ikalabinlimang harmonic ng tatlong phase, kaya nagdaragdag sila sa neutral. Kapag pantay ang phase, ang neutral ay nagdadala ng tatlong beses sa triplen current ng isang phase. Kinakalkula ito ng tool mula sa phase current at sa spectrum.
Ano ang THD ng current?
Ang total harmonic distortion ay ang rms ng lahat ng harmonic current sa ibabaw ng fundamental, bilang porsyento. Ipinapakita ng analyser ang bawat order bilang porsyento ng fundamental. Kinukuha ng tool ang mga iyon at ibinibigay ang THD at ang fundamental current.
Ano ang k factor?
Tinitimbang nito ang bawat harmonic ayon sa order nito na naka-square, dahil tumataas ang eddy current loss sa transformer kasabay ng frequency na naka-square. Ang malinis na load ay K-1. Pumili ng transformer K rating na katumbas o higit sa figure. Wala sa standard na hawak ng AmpSize ang mga rating step.
Kailan ibinabatay ang cable size sa neutral current?
Ang AS/NZS 3008.1 Table 2 ay naglalagay ng third harmonic bilang percent ng phase current. Kapag higit sa 33 %, ang cable ay pinipili batay sa neutral current. Ibinibigay ng tool ang factor, basehan at current na dapat dalhin para sa cable size.
Ano ang hinihingi ng AS/NZS 3000 sa harmonic load?
Idinadagdag ng Cl 3.5.2(b)(i) ang third at mas mataas na harmonic current sa out-of-balance current para sa neutral, kinukuha ang 100 % ng harmonic current ng pinakamataas na phase. Tinatawag ng Note 1 na malaki ang harmonic load na 40 % o higit pa ng load ng isang phase.
Mga clause at table na binabasa ng tool na ito
- AS/NZS 3000:2018 Cl 3.5.2(b)Neutral of a multiphase circuit
- AS/NZS 3008.1.2:2017 Cl 3.5.9Third harmonic current in the neutral
- AS/NZS 3000:2018 Cl 3.5.2Neutral conductor of a circuit
- AS/NZS 3008.1.2:2017 Table 2Reduction factors for harmonic currents in 4- and 5‑core cables
- AS/NZS 3008.1.1:2017 Table 2Reduction factors for harmonic currents in 4- and 5‑core cables
Bawat clause at table, kasama kung paano ito na-verify
Huling na-check ang mga table noong 2 Oct 2026.
Mga kaugnay na tool
- Cable size calculatorFind the smallest cable size that passes each check.AS/NZS 3008.1.2AS/NZS 3008.1.1AS/NZS 3000
- Transformer calculatorCalculate transformer full load current and impedance.Walang standard
- Neutral current ng unbalanced loadThe neutral current of an unbalanced three‑phase load.AS/NZS 3000
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