Professional Interpretation | This is enough for the problem of harmonic current.

   

Recently, customers often ask questions about harmonic currents. Today, CTC's technical engineers conduct professional interpretation of harmonic current testing.

 1. what is harmonic current

Electronic, electrical equipment or systems in the design process if the use of nonlinear load, then when the current flows through the nonlinear load, and the applied voltage is not linear relationship, it will form a non-sinusoidal current, harmonic current is the non-sinusoidal periodic current function.fourier seriesWhen unfolded, its frequency is a collective term for each sinusoidal component that is an integer multiple of the original periodic current frequency. Harmonic currents with a frequency equal to k times the frequency of the original periodic current are called k-th harmonic currents, and harmonic currents with k greater than 1 are also collectively referred tohigher harmonicCurrent.

   Harm of 2. harmonic current

Harmonics reduce the efficiency of the production, transmission and utilization of electric energy, overheat the electrical equipment, produce vibration and noise, and make the insulation aging, shorten the service life, and even malfunction or burn. Harmonics can cause local parallel resonance or series resonance in the power system, which amplifies the harmonic content and causes the burning of capacitors and other equipment. Harmonics can also causerelay protectionAnd automatic device misoperation, so that the electric energy metering confusion. Harmonics can cause serious interference to communication equipment and electronic equipment.

   3. the following introduction under the most commonly used harmonic current test standards

EN IEC61000-3-2:2019 A1:2021;

    GB 17625.1-2012；

The version of the harmonic standard implemented by each country is very different, but the content is similar, mainly in the IEC and EN versions.

At present, CE and CCC have requirements for harmonics, while North America, Japan and South Korea have no mandatory requirements for harmonics.

Classification of equipment in the standard

Class A: Balanced three-phase equipment;
Household appliances, excluding equipment listed in categories B,C and D;
Tools, excluding portable tools;

Vacuum cleaner;
dimmer for incandescent lamp;
Audio equipment;

Professional stage lighting fixtures;

Equipment not specified as Class B,C,D is considered Class A equipment.

Class B: Portable tools; Arc welding equipment not classified as special equipment
CLASS C: LIGHTING EQUIPMENT
Class D: Active power not greater than 600W The following equipment: personal computers and personal computer monitors; television receivers; refrigerators and freezers have one or more variable speed drives to control the compressor motor.

 4. harmonic current exemption requirements

1) Electrical and electronic equipment not connected to the public low-voltage distribution system;

2) Electrical and electronic equipment with nominal voltage of DC power supply;

3) Lighting equipment with rated power less than 5w;

4) Electrical and electronic equipment with rated power not greater than 75W;

5) Professional equipment with total fixed power greater than 1kw.

The manufacturer can consider whether the harmonic current test is required according to this restriction.

 Limits for 5. harmonic currents

Class A requirements are as follows

 

Each harmonic of the input current of Class B equipment shall not exceed 1.5 times the value given in the Class A table.

    Class C 类

1. Class C ＞25W

2. 25w ≥ class c ≥ 5W

Lighting equipment with rated power greater than or equal to 5w and less than or equal to 25w must meet one of the following three sets of requirements:

1: Harmonic currents shall not exceed the power-related limits in column 2 of Table 3;

2: The third harmonic current, expressed as a percentage of the fundamental current, should not exceed 86%, and the fifth harmonic current should not exceed 61%. In addition, the waveform of the input current should reach the current threshold of 5% before or at 60 degrees, and the peak value should appear before 65 degrees, and cannot be reduced below the current threshold before 90 degrees. The current threshold is equal to the peak value appearing in the measurement period. 5%;

3: THD must not exceed 70%. Expressed as a percentage of the fundamental current, the third harmonic current should not exceed 35%, the fifth current should not exceed 25%, the seventh current should not exceed 30%, the ninth and eleventh currents should not exceed 20%, and the second current should not exceed 5%

    Class D类

For Class D equipment, the harmonic currents shall not exceed the limits derived from Table 3.

It can be seen from the limit value that the limit value of Class B equipment is 1.5 times that of Class A equipment, Class C equipment has stricter requirements, followed by Class D, which is also because these two types of equipment are most widely used in life. During the test, the corresponding limit value can be selected according to the product category.