If you are selling electrical or electronic products that draw less than 16 A in the European Union, then you must meet the requirements of EN 61000-3-2 and EN 61000-3-3 by Jan. 1, 2001. These two standards to control harmonic emissions and voltage fluctuations from electrical and electronic apparatus are the current product of a Darwinian progression—IEC 555, EN 60555, IEC 1000-3, EN 1000-3, and EN 61000-3.
While related in purpose, the two standards address different areas:
- EN 61000-3-2—EMC limits for harmonic current emissions (equipment input current of 16 A per phase).
- EN 61000-3-3—limitation of voltage fluctuation and flicker in low-voltage supply systems for equipment with rated current of 16 A.
Evolution of the Standards
In 1899, the Lighting Clauses Act was introduced in the United Kingdom to prevent arc-lamps from causing incandescent lamps to flicker. To correct the problem and enforce the concept that one customer on the public electrical supply system shall not interfere with the supply of another customer, changes were made to the arc lamps. That concept still exists today.
In recent years, the proliferation of electrical and electronic products has increased dramatically. The problems caused by so much equipment connected to the public power grid resulted in the publication of IEC 555-2 and IEC 555-3, but these only applied to residential apparatus.
Since then, revisions and legislation have taken us to the now current EN 61000-3-2 and EN 61000-3-3. These standards are still being scrutinized, criticized, and revised.
Definitions
Let’s begin with some basic definitions found in the standards and revisions:
- Harmonics or, more correctly, total harmonic distortion (TDH)—The ratio of the rms value of the supplied voltage to the rms sum of all spectral components other than the fundamental, including distortion components.
- Voltage fluctuation—A series of voltage changes or a continuous variation of the rms voltage.
- Flicker—Impression of unsteadiness of visual sensation induced by light stimulus whose luminance or spectral distribution fluctuates with time.
Why do we care? Harmonic voltage distortion that lasts more than 10 minutes is considered long-term and of great concern to the power-generation industry. It can cause an increase in the operating temperature of the generation facility, which reduces the life of equipment including rotating machines, cables, transformers, capacitors, fuses, switching contacts, and surge suppressors.
Problems are caused by the harmonics creating additional losses and dielectric stresses in capacitors and cables, increasing currents in windings of rotating machinery and transformers and noise emissions in many products, and bringing about early failure of fuses and other safety components. They also can cause skin effect, which creates problems in cables, transformers, and rotating machinery.
Electricity meters can be affected. We may or may not like that depending upon which way the error goes. In any case, this is unacceptable to the electricity suppliers, and products in your home or workplace may be adversely impaired.
Power-generation companies are concerned that the growth in products such as switched-mode power supplies, electronic voltage regulators, and converters will cause THD levels to increase to unacceptable levels. In fact, these products could exceed the levels called out in IEC 61000-2-2 for low-voltage networks. If this happens, widespread failures of consumer equipment are likely.
Flicker can be a bit more ambiguous but still presents some major problems, especially for the consumer. By definition, voltage dips to less than 90% of the nominal supply voltage can cause problems with and damage to consumer equipment. The voltage in the specification for equipment operation at 16 A or less is set at a minimum of 93%.
Considering an incandescent lamp, the human eye can detect changes that are equal to or greater than 3%. Infrequent changes are not of much concern since they typically do not affect humans. Regular changes, however, can cause behavioral problems with the most disturbing frequency being at about 11 Hz. A voltage change of only about 0.5% at that frequency will cause discomfort to humans.
Consumer usage of appliances likely to cause flicker, such as air conditioners, dehumidifiers, and large refrigerators, is increasing. This could cause an increase in the levels of flicker experienced on the low-voltage networks.
EN 61000-3-2
Various manufacturing groups have called for a delay of this document until a full revision is complete; however, the delay probably will not happen.
EN 61000-3-2: April 1998 is the current standard for harmonics in conjunction with amendments A1 and A2. It covers all equipment connected to the power lines, not just appliances as before.
EN 61000-3-2 is described by the IEC as one that “specifies limits for harmonic current emissions applicable to electrical and electronic equipment having an input current up to and including 16 A per phase and intended to be connected to public low-voltage distribution systems.” The tests according to this standard are type tests. Test conditions for particular equipment are given in annex C. For systems with nominal voltages less than 220 V (line to neutral), the limits have not yet been considered.
Work on the latest revision to the document still is unfinished. Document Provisional A14 will contain the latest revisions and recommendations to the standard. This document is out for vote and should be ready for use by September 2000.
When it is adopted, there will likely be a three-year transition in which you can use EN 61000-3-2 alone or in conjunction with A14. After that, use of A14 will be mandatory. Following are some changes that will be introduced by A14:
- No limits for equipment using 75 W or less.
- No limits for professional equipment over 1,000 W.
- New class D for PCs, monitors, and TVs.
- Test confirmation mode with expected maximum THD (no worst-case search).
- Limits applying only to the power lines, not to the neutral.
- IEC 61000-4-7 Guide replacing Annex B.
- New measurement method for fluctuating loads.
The A14 amendment provides a temporary solution to many of the problems with the standard. It gives legislation the means to apply the standard in conjunction with the amendments after Jan. 1, 2001. However, there still is a major hurdle to overcome. The IEC has not agreed to the content of A14, so the EN A14 document may cause problems for manufacturers that sell their products internationally.
EN 61000-3-3
EN 61000-3-3: 1994 is the current document for flicker, and of course, there is a revision in process as well. In the words of the IEC: “This section of IEC 61000-3 is concerned with the limitation of voltage fluctuations and flicker impressed on the public low-voltage system. It specifies limits of voltage changes that may be produced by equipment tested under specified conditions and gives guidance on methods of assessment. This section is applicable to electrical and electronic equipment having an input current up to and including 16 A per phase and intended to be connected to public low-voltage distribution systems of between 220 V and 250 V at a 50-Hz line to neutral.”
Although this document is somewhat less controversial than EN 61000-3-2, the limits are unnecessarily stringent for commercial and industrial environments. IEC 61000-3-11 provides some relief by assessing lower Zref values. Also, many people think that the inrush requirements and test methods are unstable and unjustified.
There are some very interesting—and even confusing—statements. For example, Section 5 states, “If voltage changes are caused by manual switching or occur less frequently than once per hour, the observation-period Pst and Plt requirements shall not be applicable. The long-term observation period, Plt, is flicker severity evaluated over a long period (a few hours) using successive short-term observation-period, Pst, values. Pst is flicker severity evaluated over a short term (in minutes). The three requirements related to voltage changes shall be applicable with the previously mentioned voltage values, multiplied by a factor of 1.33.”
Further, the specification requires the user to make subjective decisions because of imprecise wording such as that found in Sections 6.1 and 6.5. In any case, this document must be used until a replacement is finished and becomes the standard.
Conclusion
The requirements of EN 61000-3-2 and EN 61000-3-3 must be met as of Jan. 1, 2001. To ensure you will be ready, obtain the most current documents. Many good websites can update you on the current standards. Just type the document numbers into your search engine, and you will be led to many of them.
If you do not want or need to purchase the documents, be sure the test laboratory you choose is up-to-date on the standards. The lab also must have the latest test equipment or the latest revisions of test equipment and software.
Although the current standards have many problems, you are stuck with them for now, so make the best of it. There is much work going on to correct the problems, and things should get a bit better as time goes on and the revisions take effect.
About the Author
Gary Fenical is the EMC technical support engineer at Instrument Specialties and has been with the company for 18 years. He is the only American invited to sit on the European EMCIT and has been a member of the Association of Competent Bodies Committees. The NARTE-certified EMC engineer is chairman of the SAE AE-4 Executive Committee on EMC and holds membership in the IEEE-EMC Society and SMRI. Instrument Specialties, Delaware Water Gap, PA 18327, 570-424-8510.
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September 2000