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Analysis of Low Frequency Immunity Test of AC Power Port Harmonics, Interharmonics and Grid Signals
Release time:
2022-07-22 00:00
Source:
1 What are harmonics, interharmonics and grid signals
In layman's terms, in the power system, the voltage or current wave of 50Hz is called the fundamental wave. If it is not the voltage or current of 50Hz, it is the harmonic wave. There are some special electrical equipment in the power grid, such as high-power rectifiers, intermediate frequency furnaces, frequency converters, low-quality energy-saving lamps, etc. The operating current of such equipment is not proportional to the voltage, which we call nonlinear loads. The electric energy generated by the motor is originally a relatively regular 50Hz frequency, but if there are nonlinear devices in the power grid, when these devices work, harmonics will be generated. For example, a single-phase rectifier "rectifies" the 50Hz fundamental wave into a signal with components of 100Hz, 150Hz, 200Hz... and so on, and harmonics appear. This kind of equipment that generates harmonics is often called "harmonic source".
Usually, the frequency of the harmonic is an integer multiple of 50Hz, and the harmonic is represented by a multiple of the fundamental wave. For example, a sine wave with a frequency of 150Hz is called the 3rd harmonic, a sine wave with a frequency of 250Hz is called the 5th harmonic, a sine wave with a frequency of 350Hz is called the 7th harmonic, and so on.
Between the harmonic voltage and harmonic current of the power frequency, there are some frequencies that are not integer multiples of the fundamental frequency, and they appear in discrete frequencies or in a broadband spectrum, which are interharmonic waves.
The grid signal refers to the signal generated by the transmitter in the grid so that the power supply company can control the equipment (public lighting, meter, etc.) in the power supply network. Usually the transmitter only works for a short time with intermittent signals, and the frequency used is between harmonics, that is, the frequency range is 100Hz-3kHz.
2 Harmonic Harmonic
Hazards of Harmonics: Motors
Harmonic voltage and harmonic current produce additional iron loss and copper loss, resulting in additional heating of the motor, reducing the efficiency of the motor and generating pulsating torque, which intensifies the vibration of the motor and affects the life of the motor and the stability of the output torque.
Harmonic voltage reduces the dielectric strength of the insulation, accelerates the aging of the coil insulation, and reduces the service life of the motor.
Hazards of Harmonics: Cables
Harmonic currents can overload cables, cause overheating, and cause insulation damage and burnout.
For high-frequency harmonic current, the cable presents a skin effect, which reduces the rated carrying capacity, increases the leakage current, causes single-phase breakdown, and causes a three-phase short circuit.
Zero-sequence (multiples of 3) harmonic current will cause overload and damage to the neutral wire of the three-phase four-wire system.
Hazards of Harmonics: System Resonance
Harmonic current can increase the dielectric loss of the capacitor, heat and shorten the life; a large amount of harmonic absorption will cause the capacitor to over-current and cause the fuse to blow.
The capacitor and the grid inductance form a series resonant circuit, which can cause harmonic amplification and capacitor burnout.
Caused by system resonance, the capacitor bank, reactor bank and related electrical equipment are damaged or cannot be put into operation due to overcurrent or overvoltage.
Hazards of Harmonics: Communications Networks
Interfering with information, data, and communication systems, causing system crashes or abnormal control, downtime, serious loss of real-time data, and immeasurable losses.
For the networked operation of the communication system, if the central data processing center fails, it will cause the paralysis of the entire networked system, and high-order harmonics can cause misoperation and crash of the mainframe of the data processing center.
Harmonics will also cause misoperation and crash of communication equipment, which will bring troubles to the communication industry and users, and cause disputes between the communication industry and users.
The Harmonic Harm: Hospitals
Data errors occur; images are blurred; information is lost; some advanced medical equipment has highly sensitive microelectronic devices, and harmonic interference can easily make the equipment unable to work normally.
Harmonic Harm: Other
Changing the operating characteristics of the protective relay can cause malfunctions and cause disorder in the operation of automatic devices such as relay protection.
Harmonics delay arc extinguishing and affect the breaking capacity of circuit breakers.
Metering instruments, especially inductive watt-hour meters, produce measurement errors.
Interfere with adjacent power electronic equipment and industrial control equipment, affecting the normal operation of the equipment.
3 Introduction to harmonics, interharmonics and grid signal immunity measurement waveforms
The low-frequency immunity test of harmonics, inter-harmonics and grid signals, according to the standard GB17626.13 (IEC 61000-4-13), has four types of test methods (waveforms): harmonic combination test (flat top wave and sharp top wave), Sweep frequency tests, individual harmonic and interharmonic tests, and Meister curve tests.
3.1 Harmonic combination test (flat top wave and peak top wave)
The harmonic combination test includes two tests of flat top wave and peak wave. Each combined wave of EUT shall be tested.
flat top wave
Flat top wave voltage changes with time, each half wave consists of three parts, the waveform is as follows:
Part 1: Starting from zero, varying as a purely sinusoidal function up to 90% of the peak for level 2 and 80% of the peak for level 3.
Part 2: is a constant voltage.
Part 3: Corresponding to Part 1.
flat top wave waveform
Spire wave
Spike waves are produced by the superposition of discrete 3rd and 5th harmonics with corresponding phase relationships. The waveform is as follows:
Peak Wave Waveform Chart
3.2 Frequency sweep test
An example of frequency sweep measurement waveform is shown in the figure below:
Frequency sweep measurement waveform diagram
3.3 Single harmonic and inter-harmonic test
A single harmonic refers to a harmonic within the frequency range of 2f1~40f1. These harmonics apply a single sine wave voltage to the fundamental voltage according to the test level.
Interharmonic waves are harmonics in the frequency range of 16Hz~2000Hz. Interharmonics apply a single sine wave voltage of the test level to the fundamental voltage in certain steps.
The measurement waveform is as follows:
Schematic diagram of multiple harmonic test sequence
3.4 Meister curve test
The equipment used in the grid with grid signal and/or ripple control needs to apply the Meister curve test, the waveform is as follows:
Meister curve waveform (100Hz-3kHz)
4 Harmonic, inter-harmonic and grid signal immunity test levels and test requirements
4.1 Harmonic combination test level and requirements
1) flat top wave
See the table below for flat-top wave test grades:
|
grade |
Functions |
Voltage ratio Ky |
Voltage |
Functions |
Voltage |
|
1 |
0 ≤ |sin(ωt)| ≤ 0.95 |
1.0133 |
u = U1 × K1 × √2 × sin(ωt) |
0.95 ≤ |sin(ωt)| ≤ 1 |
u = ±0.95 × U1 × K1 × √2 |
|
2 |
0 ≤ |sin(ωt)| ≤ 0.9 |
1.0379 |
u = U1 × K2 × √2 × sin(ωt) |
0.9 ≤ |sin(ωt)| ≤ 1 |
u = ±0.9 × U1 × K2 × √2 |
|
3 |
0 ≤ |sin(ωt)| ≤ 0.8 |
1.1117 |
u = U1 × K3 × √2 × sin(ωt) |
0.8 ≤ |sin(ωt)| ≤ 1 |
u = ±0.8 × U1 × K3 × √2 |
|
x |
0 ≤ |sin(ωt)| ≤ x |
x |
u = U1 × Kx × √2 × sin(ωt) |
x ≤ |sin(ωt)| ≤ 1 |
u = ±x × U1 × Kx × √2 |
|
Note: |
|||||
The flat-top wave test time (Duration) is required to be 2 minutes, and the schematic diagram of the test waveform is as follows:
2) Peaked waves
See the table below for peak wave test grades:
|
grade |
h |
3 |
5 |
|
1 |
U1% |
4% / 180° |
3 % / 0° |
|
2 |
U1% |
6% / 180° |
4 % / 0° |
|
3 |
U1% |
8 % / 180° |
5% / 0° |
|
x |
U1% |
x / 180° |
x / 0° |
|
Note: |
|||
The peak wave test time (Duration) is required to be 2 minutes, and the schematic diagram of the test waveform is as follows:
4.2 Frequency sweep test level and requirements
The frequency level of the frequency sweep test is as follows:
|
frequency range f |
Frequency step size Δf |
Grade 1 |
Level 2 |
Level 3 |
grade x |
|
Test level U1% |
Test level U1% |
Test level U1% |
Test level U1% |
||
|
0.33f1~2f1 |
0.1f1 |
2 |
3 |
4.5 |
Open |
|
2f1 ~ 10f1 |
0.2f1 |
5 |
9 |
14 |
Open |
|
10f1 ~ 20f1 |
0.2f1 |
4 |
4.5 |
9 |
Open |
|
20f1 ~ 30f1 |
0.5f1 |
2 |
2 |
6 |
Open |
|
30f1 ~ 40f1 |
0.5f1 |
2 |
2 |
4 |
Open |
|
Note: |
|||||
See the table above for the frequency sweep amplitude of each frequency range, and the frequency sweep rate is not less than 5 minutes per decade. During the frequency sweep, the frequency point where the EUT performance is abnormal and the resulting resonance point should be dwelled at each frequency point for at least 120s. The measurement waveform is as follows:
4.3 Single harmonic and inter-harmonic test levels and requirements
1) Single harmonic
The test level of a single harmonic is as follows:
|
Odd harmonic test level that is not a multiple of 3 |
||||
|
h |
Grade 1 |
Level 2 |
Level 3 |
Grade X |
|
Test level U1% |
Test level U1% |
Test level U1% |
Test level U1% |
|
|
5 |
4.5 |
9 |
12 |
open |
|
7 |
4.5 |
7.5 |
10 |
open |
|
11 |
4.5 |
5 |
7 |
open |
|
13 |
4 |
4.5 |
7 |
open |
|
17 |
3 |
3 |
6 |
open |
|
19 |
2 |
2 |
6 |
open |
|
twenty three |
2 |
2 |
6 |
open |
|
25 |
2 |
2 |
6 |
open |
|
29 |
1.5 |
1.5 |
5 |
open |
|
31 |
1.5 |
1.5 |
3 |
open |
|
35 |
1.5 |
1.5 |
3 |
open |
|
37 |
1.5 |
1.5 |
3 |
open |
|
Note: |
||||
|
Odd harmonic test levels for multiples of 3 |
||||
|
h |
Grade 1 |
Level 2 |
Level 3 |
Grade X |
|
Test level U1% |
Test level U1% |
Test level U1% |
Test level U1% |
|
|
3 |
4.5 |
8 |
9 |
open |
|
9 |
2 |
2.5 |
4 |
open |
|
15 |
no test |
no test |
3 |
open |
|
twenty one |
no test |
no test |
2 |
open |
|
37 |
no test |
no test |
2 |
open |
|
33 |
no test |
no test |
2 |
open |
|
39 |
no test |
no test |
2 |
open |
|
Note: |
||||
|
Even harmonic test level |
||||
|
h |
Grade 1 |
Level 2 |
Level 3 |
Grade X |
|
Test level U1% |
Test level U1% |
Test level U1% |
Test level U1% |
|
|
2 |
3 |
3 |
3 |
open |
|
4 |
1.5 |
1.5 |
2 |
open |
|
6 |
no test |
no test |
1.5 |
open |
|
8 |
no test |
no test |
1.5 |
open |
|
10 |
no test |
no test |
1.5 |
open |
|
12~40 |
no test |
no test |
1.5 |
open |
|
Note: |
||||
In the frequency range of 2f1~40f1, apply a single sine wave voltage with the amplitude in the above table to the fundamental voltage U1. The application time of each frequency (Dwell Time) is 5s, and the interval (Pause Time) is 1s before applying the next frequency.
When the harmonic voltage is greater than or equal to the 3% level (up to the 9th harmonic), the test level should be applied to the fundamental wave 0 and 180 phases respectively, and the harmonic voltage of the test level less than 3% has no phase requirements.
The test waveform is as follows:
2) Interharmonic waves
See the table below for the test levels of interharmonic waves:
|
Frequency test level between harmonic frequencies (50Hz) |
||||
|
Frequency Range |
Grade 1 |
Level 2 |
Level 3 |
Grade X |
|
Hz |
Test level U1% |
Test level U1% |
Test level U1% |
Test level U1% |
|
16~100 |
no test |
2.5 |
4 |
open |
|
100~500 |
no test |
5 |
9 |
open |
|
500~750 |
no test |
3.5 |
5 |
open |
|
750~1000 |
no test |
2 |
3 |
open |
|
1000~2000 |
no test |
1.5 |
2 |
open |
|
Note: x is an open grade, which is determined by the relevant professional standard technical committee. |
||||
|
Frequency test level between harmonic frequencies (60Hz) |
||||
|
Frequency Range |
Grade 1 |
Level 2 |
Level 3 |
Grade X |
|
Hz |
Test level U1% |
Test level U1% |
Test level U1% |
Test level U1% |
|
20~120 |
no test |
2.5 |
4 |
open |
|
120~600 |
no test |
5 |
7.5 |
open |
|
600~900 |
no test |
3.5 |
5 |
open |
|
900~1200 |
no test |
2 |
3 |
open |
|
1200~2400 |
no test |
1.5 |
2 |
open |
|
Note: x is an open grade, which is determined by the relevant professional standard technical committee. |
||||
In the interharmonic wave test, the application time (Dwell Time) of each frequency step is 5s, and the interval (Pause Time) is 1s before applying the next frequency.
The frequency step size of the interharmonic wave is shown in the table below:
|
frequency range f |
Frequency step size Δf |
|
0.33f1~2f1 |
0.1f1 |
|
2f1 ~ 10f1 |
0.2f1 |
|
10f1 ~ 20f1 |
0.2f1 |
|
20f1 ~ 40f1 |
0.5f1 |
The interharmonic wave measurement waveform is as follows:
4.4Meister curve test level and requirements
The Meister curve test grades are as follows:
|
Frequency range f |
Frequency step size Δf |
Grade 1 |
Level 2 |
Level 3 |
grade x |
|
Test level U1% |
Test level U1% |
Test level U1% |
Test level U1% |
||
|
16.5 ~ 100 |
5 |
no test |
3 |
4 |
Open |
|
100 ~ 500 |
10 |
no test |
9 |
10 |
Open |
|
500 ~ 1000 |
10 |
no test |
4500/f |
4500/f |
Open |
|
1000 ~ 2400 |
25 |
no test |
4500/f |
4500/f |
Open |
|
Note: 2400Hz is the highest frequency of 60Hz system, and the highest frequency of 50Hz system is 2000Hz. |
|||||
The Meister curve test is suitable for class 2 products. During the test, the frequency scan rate is not less than 5 minutes per decade.
The Meister curve waveform is as follows:
5 Harmonics, interharmonics and power grid signal immunity test process
In order to simplify the test, according to the test level, the harmonic, interharmonic and grid signal immunity test can be divided into two test flow charts: Class 1/Class 2 test flow chart, Class 3 test flow chart.
Class 1 and Class 2 test flow chart
Class 3 test flow chart
6 Test layout
Schematic diagram of single-phase EUT test arrangement:
Three-phase EUT test layout diagram:
