Application of three-phase AC power supply: Measuring 100th order harmonics
Keywords: Harmonics, inter-harmonics, UK ENA
Engineering Recommendation G5 Issue 5 published by the UK Energy Network Association (UK ENA) in 2020 referred to as ER G5/5 harmonic voltage distortion and the connection of harmonic sources and/or resonant equipment to the UK power transmission system and distribution networks, requiring measurement of harmonics to the 100th order. The IEC 60034-1 rating and performance standard for rotating motors also requires the measurement of harmonics to the 100th order.
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ENA ER G5/4 |
ENA ER G5/5 |
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Voltage range |
Voltage total harmonic distortion rate (THDV %) |
Voltage range |
Voltage total harmonic distortion rate (THDV %) |
|
Up to 400V |
5% |
<400V |
5% |
|
6.6kV、11k and 20kV |
4% |
400V<V<25kV |
4.5% |
|
From 22kV to 400kV |
3% |
25kV<V<66kV |
3.7% |
|
Greater than 66kV |
3% |
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|
Total harmonic distortion formula |
 |
Total harmonic distortion formula |
 |
Table 1: Differences between the old and new British regulations
(The voltage range in Table 1 refers to the voltage of PCC, PCC=Point of Common Coupling)
Causes and harms of harmonics
Cause of voltage harmonics: Harmonic currents of nonlinear loads cause voltage waveform distortion (as shown in Figure 1); Conducted electromagnetic interference (Conduction EMI); Resonance between capacitors (or capacitor banks) that correct virtual power and inductive loads.
Cause of current harmonics: Non-linear loads.
The main hazards of harmonics: Cable loss, equipment overload and resonance.
Figure 1: Voltage waveform distortion caused by harmonic currents of nonlinear loads
In addition to providing test functions, modern AC power supplies also have greatly improved measurement and test capabilities
Harmonics come from every single load. When many single loads are aggregated into the power grid, they have a huge impact on the overall power system. Therefore, it is the rightful approach if each electrical appliance can strictly follow the regulations before being designed and shipped from the factory, and the impact on the power system can be reduced as much as possible.
Hence, it is necessary to use AC power supply to test the relevant power quality tolerance (sag, swell, instantaneous interruption, long-term voltage changes, etc.). Furthermore, the new generation of AC power supply also provides rich test and measurement capabilities. Test and measurement data can be obtained while testing the product. Taking ASR-6000 as an example, the test and measurement parameters provided are as shown in Table 2.
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T&M item |
Output mode |
|||
|
AC+DC-INT |
AC-INT |
DC-INT |
AC+DC Sync |
|
|
Vrms / Vavg / Vmax / Vmin / |
✔ |
✔ |
✔ |
✔ |
|
Irms / Iavg / Imax / Imin |
✔ |
✔ |
✔ |
✔ |
|
VpkH / IpkH |
✔ |
✔ |
✔ |
✔ |
|
P |
✔ |
✔ |
✔ |
✔ |
|
S/Q |
✔ |
✔ |
X |
✔ |
|
PF / CF |
✔ |
✔ |
X |
✔ |
|
Freq |
X |
X |
X |
✔ |
|
THDv / THDi |
X |
✔ |
X |
X |
Table 2: Correspondence table between ASR-6000 output modes and test and measurement items
| Test and measurement parameter description | |
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Another meaning of voltage total harmonic distortion
It is mentioned in the article that the current of non-linear loads will cause voltage waveform distortion and cause voltage harmonics. When the voltage total harmonic distortion is too large, it may also mean that the capacity of the AC power supply is insufficient. At this time, users need to choose a larger capacity AC power supply.
Figure 3: Important features of the ASR-6000 series
Annotation:
1： UK ENA: UK ENERGY NETWORKS ASSOCIATION
References:
1：Engineering Recommendation G5 Issue 5 2020 https://www.energynetworks.org/
2： Fluke, Modern Power Quality Measurement Technology Written by He, Xuenong
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