TECHNICAL REPORT IEC TR 61000 1 4 First edition 2005 05 Electromagnetic compatibility (EMC) – Part 1 4 General – Historical rationale for the limitation of power frequency conducted harmonic current e[.]
Before 1960
The most numerous non-linear loads were television receivers with half-wave rectifiers
The reversible polarity of the mains connectors led to the approximate cancellation of d.c components Although the number of installed receivers was not enough to cause significant system issues from harmonic current emissions, some countries experienced enough random polarity imbalances to result in corrosion problems in underground cables.
Phase-controlled dimmers for home lighting have been introduced to the market, leading to concerns over high-frequency conducted emissions that caught the attention of radio-spectrum protection authorities While mandatory measures to limit these emissions could be implemented, it was observed that these dimmers also generate harmonic currents, and there is currently no feasible method to reduce the ratio of harmonic to fundamental current.
A European system survey established the 90th percentile supply impedance value for residential customers, primarily served by overhead low-voltage distribution, as \$(0.4 + j0.25) \, \text{ohms}\$, where \$h\$ represents the harmonic order This value is documented in IEC 60725 Furthermore, it was found that without regulating emissions from dimmers, voltage distortion could rise beyond acceptable 'compatibility levels'.
NOTE There is no direct relationship between compatibility levels and emission limits generally Further information on this subject can be found in Annex A
The European standard EN 50006, established in 1975, was the first of its kind and was not based on any prior standards It was adopted into various national standards, including BS 5406:1976 This standard addressed burst-firing techniques and also included provisions for voltage fluctuations, which are now governed by IEC 61000-3-3 and IEC 61000-3-11.
Limitation of harmonic current emissions was achieved by:
• prohibiting the use of phase control for heating loads over 200 W;
• applying limits for odd-harmonic emissions;
• applying limits for even-harmonic emissions to both symmetrical and asymmetrical control techniques
The voltage-harmonic percentage limits were based on a supply system with an impedance of (0.4 + j0.25) ohms for single-phase loads The testing procedure involved measuring harmonic currents to calculate voltage distortions Notably, the standard lacks an explanation for how these limits were derived, which are maintained as Class A limits in the IEC 61000-3-2 standard up to the 2000 edition The numerical values were likely established through negotiations between experts from the supply industry and equipment manufacturers, rather than through a strict mathematical framework.
A study developed an approximate algorithm to assess the cumulative impact of multiple dimmers, each set at varying firing angles, on the net voltage distortion level at the terminals of the low-voltage transformer supplying the final distribution.
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During this period, a more comprehensive standard, IEC (60)555-2:1982, was developed Still effectively restricted to 220(380) V-240(415) V 50 Hz European systems, it was adopted by
In 1987, CENELEC established the EN (60)555-2 standard, which introduced three sets of current limits These included the original limits from EN 50006, increased limits 1.5 times higher for short-duration use products like portable tools, and specific limits for television receivers However, an exemption for receivers with input power below 165 W meant that these limits affected only a small percentage of manufactured receivers, with the limits expressed directly as currents, even for televisions.
All IEC standards were renumbered in the 60000 series starting from January 1, 1998 References to standards that were withdrawn prior to this date or not reprinted afterward are indicated with the '6xxx' prefix enclosed in parentheses.
The standard featured an Annex intended to clarify the derivation of the original current limits; however, it fell short by only referencing the voltage distortion limits from EN 50006 without providing any explanation.
During this period, three significant changes emerged: the widespread adoption of switch-mode power supplies in both commercial and residential settings, the indication that Europe would implement mandatory regulations for the electromagnetic compatibility (EMC) of electronic products, and the suggestion that the European public electricity supply would need to meet specific 'product quality' standards.
The early standards, EN 50006 and IEC (60)555-2, did not specifically address professional equipment, leading to ambiguity regarding their applicability to desktop computers, which were classified as 'household appliances' in Europe Consequently, the original current limits were enforced, although CISPR 14/EN 55014 was not applied for high-frequency emissions The rapid growth of single-phase consumer electronics, particularly those utilizing direct on-line switch mode DC power units like television receivers and desktop computers, resulted in significant peak flattening of supply voltage waveforms due to the coinciding large current pulses drawn by these devices.
Direct-on-line switch mode DC power units offer benefits such as higher efficiency, reduced weight, and compact size However, the simultaneous large current pulses can cause considerable distortion in the supply voltage waveform In contrast, transformer-fed non-switching supplies produce lower emissions due to the transformer’s series impedance, which leads to a larger conduction angle for the rectifiers.
As a result, the development of the successor to IEC (60)555-2 was extremely controversial
The electricity supply industry has made significant progress in developing IEC 61000-3-2, while the equipment manufacturing sector has shown less structured involvement This disparity can be attributed to the diverse nature of the equipment manufacturing industry, where various sub-sectors prioritize harmonic current emissions differently In contrast, the supply industry maintains a more uniform focus on priorities, largely influenced by the varying infrastructure configurations across different countries.
IEC 61000-3-2:1995 introduced significant features, particularly applying to all electrical and electronic equipment with an input current of up to 16 A per phase, intended for connection to public low-voltage distribution systems Notably, 'professional equipment' as defined in the standard is exempt from certain requirements.
The standard outlines specific requirements and limits for various product types, categorized into four classes It is primarily applicable to European systems, consistent with previous standards.
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The 'Millennium Amendment'
CENELEC initiated a reappraisal of the standard, leading to extensive discussions within a working group The resulting document was submitted to IEC SC 77A, prompting further in-depth discussions that included economic considerations as a key topic By the end of 1999, a reluctant consensus was reached, based on the belief that additional discussions would yield minimal improvements It was agreed to commence work on a comprehensive revision of the standard, ensuring that all provisions would be supported by documented rationales.
The resulting amendment became known as the 'Millennium Amendment', because it was substantially finalized at the beginning of 2000
Unfortunately, Amendment 3 was also in process in IEC during 1998-99, and the IEC procedures resulted in a divergence of the editions of the IEC standard from those of
CENELEC, which implemented the Millennium Amendment, but not the 3rd IEC amendment, in a consolidated edition, creating confusion that might have been avoided
The Millennium Amendment clarified the ambiguities of the 1995 edition, making it more user-friendly for regulatory purposes It removed the complex criteria for Class D membership, recognizing the challenges in categorizing certain products Instead, it introduced a concise list of high-volume products that, without built-in mitigation measures, generate odd harmonic currents with minimal phase diversity This list includes personal computers, personal computer monitors, and television receivers.
The amendment also included a clarification of the requirements for lighting equipment.
Future development of IEC 61000-3-2
A detailed consideration of this subject is a matter for IEC 61000-1-X (to be published) Initial considerations are described in Annex F
7 History of IEC 61000-3-12 and its predecessor
IEC 61000-3-2 deals with equipment rated at up to 16 A/phase A complementary document, dealing with equipment rated at over 16A/phase, was prepared as IEC 61000-3-4, a Technical
Report type 2 ('prospective standard for provisional application'), by a team comprising experts from ES, FR, DE, IE, IT, UK and US Some conclusions of the team were recorded:
• an arithmetic superposition law was used for harmonics up to the fifth and a geometric law for higher orders;
• approximately 75 % of the compatibility level (for the fifth harmonic, for example) is transmitted from the MV level and is present as a background disturbance throughout the
LV network Hence only 25 % of the compatibility level is left for the admissible additional voltage distortion due to non-linear loads connected to a specific LV supply See Annex A
Rough calculations, depending on different assumptions on the partition of distorting loads, yielded:
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The limits will be determined by the short-circuit ratio \( R_{sce} \), with higher limits corresponding to higher values of \( R_{sce} \), while still adhering to the general range established by preliminary calculations.
Further studies were made to find a justified relation between the R sce values and the limits
The detailed calculations are lost An attempt to 'recover' the basis of these studies, and relate it to the limits in IEC 61000-3-12, is presented in Annex G
This rationale does not consider the provisions of IEC 61000-3-4 in detail, since all but one
(relating to equipment rated at over 75 A/phase) will have been superseded by provisions of
IEC 61000-3-12 by the time that the rationale is published
The report was published in October 1998
NOTE Technical reports type 2 are no longer produced by IEC
Such reports were required to be reviewed within three years of publication, and IEC decided to convert the report into a standard, IEC 61000-3-12, which might also be adopted by
CENELEC and could then be used to demonstrate compliance with the European EMC
NOTE This was seen to be helpful for manufacturers intending to export to Europe, as well as for manufacturers within Europe.
After 1998
The insights gained from implementing IEC 61000-3-4 prompted proposals for revisions to IEC 61000-3-12 Following extensive discussions, the initial voting document was distributed in 2003.
8 Economic considerations taken into account in setting limits in
IEC 61000-3-2 before publication in 1995, and before the finalization of the text of the Millennium Amendment
At that time, IEC deemed only passive mitigation economically feasible, specifically for single-phase equipment This approach would increase the production cost of a TV set by about €1 or $1, representing roughly 1 to 2% for high-volume products, unlike low-price items such as self-ballasted lamps.
The cost-sharing idea was implemented by the lower power bound of 75 W:
• no harmonics limits up to this power value; costs only to the supply system;
• existing harmonics limits beyond this power value; costs to both, the product and the supply system (because the harmonic currents are not zero!)
This was considered in setting the limits in Table 3
The limits of Tables 1 and 2 were taken from an older European standard (EN 50006) into
IEC (60)555-2 No definite information on economics is available for the limits in these tables
The European Standard focused specifically on household appliances, with active participation from industry experts Consequently, it can be inferred that the economic impact of implementing these limits was deemed acceptable by the stakeholders involved at that time.
During the preparation of the Millennium Amendment, consideration of economic aspects was intensified As a result, many products were re-allocated from Class D to Class A (see 6.6)
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Compatibility level and compensation factor
A.1 Explanation of the allocation of only part of the total compatibility level to the low-voltage network
Harmonic distortion in low voltage (LV), medium voltage (MV), and high voltage (HV) networks primarily arises from the harmonic currents generated by non-linear loads in the LV network This distortion is the geometric sum of harmonic voltage drops across the LV network and the superimposed MV and HV systems As per IEC standards, specifically IEC 61000-2-2, the harmonic distortion in the LV network must not exceed the established compatibility levels.
Harmonic currents from non-linear loads in low voltage (LV), medium voltage (MV), and high voltage (HV) networks lead to harmonic voltage drops across the harmonic impedances of the respective transformers and the HV network, including generators The percentage of these harmonic voltage drops is roughly equivalent to the percentage of transformer impedances, which are determined by the percentage short circuit voltage of each transformer involved.
The typical percentage impedances in European networks are illustrated in Figure A.1, which shows how the total compatibility level is divided among different voltage levels, reflecting the relationship of these impedances To account for the geometric summation of voltage drops, the value for the low-voltage (LV) network is adjusted to 25%, exceeding the value derived from the impedance ratio This 25% of the total compatibility level is utilized in IEC 61000-3-2 and IEC 61000-3-12 to assess the maximum harmonic currents from non-linear loads in the LV network.
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Generator (Short-circuit at harmonic frequencies)
Maximum permissible harmonic voltage drop as % of compatibility level
Figure A.1 – Allocation of harmonic voltage drops over the transformer impedances in a typical system
A.2.1 Derivation from the model in Figure A.1
From the model, the maximum permissible current emission from equipment at each harmonic frequency can be shown to be:
The equation \( h = h_{eq} \) defines the relationship between harmonic order and the maximum permissible current emission from equipment at that harmonic The compatibility level for voltage distortion at harmonic \( h \) is represented by \( u_{h,CL} \), while \( k_{N,LV} \) denotes the sharing factor for the low voltage (LV) network.
Z LV,h is the network impedance at harmonic h; k p,h is the compensation factor for harmonic h
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The factor \( k_{p,h} \) is influenced by various sub-factors, and there is no universally applicable analytical method to determine its values The initial values used in the first edition of IEC 61000-3-2 are presented in Table A.1 The likelihood of compensation among different harmonic currents increases when the power consumed by the equipment generating these currents is relatively small compared to the short circuit power \( R_{sc} \) Consequently, \( k_{p,h} \) is dependent on the factor \( R_{sce} \), which is the ratio of \( R_{sc} \) to the rated apparent power of the equipment, as detailed in Table A.1.
The values referenced are derived from Table 3 of IEC 61000-3-6 and are generally applicable, based on published research For equipment that generates harmonic currents with minimal phase differences, such as uncontrolled rectifiers with capacitive smoothing, values of \$k_{p,h}\$ closer to 1.0 are relevant for low-order harmonics, as indicated in Table 4 of IEC 61000-3-6 Ongoing investigations aim to verify and enhance these values.
When accounting for actual system impedances, the term \( k_{p,h} \) becomes the sole focus for estimation, isolating any discrepancies between modeling and survey results to this term Table A.2, based on [14], presents a comprehensive set of sub-factors, with additional suggestions possible It also outlines plausible value ranges for these sub-factors and the composite compensation factor \( k_{p,h} \), which is derived from the combination of individual sub-factors For initial calculations, the sub-factors in Table A.2 are multiplied together to determine the composite factor.
It is important to recognize that certain equipment and configurations may have interdependent factors The method of multiplying sub-factors to determine the composite factor remains applicable, provided that all but one factor in a non-independent set is assigned a value of 1.
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Estimated values for fifth harmonic factors Sub-factor
Low estimate Typical value High estimate
Non-linear load penetration factor a 0,1 0,14 1
The composite factor \( k_{p} \) is influenced by various parameters, including linear and non-linear loads, which are not considered in the calculation of \( k_{p,h} \) Triplen cancellation in delta-connected transformers is relevant only for medium-voltage networks This factor can lead to significant cancellation effects for the 5th and 7th harmonics, potentially reaching values as high as 3.0 for triplen harmonics, particularly when all loads are connected line-to-neutral Additionally, it accounts for the distribution of harmonic currents between the mains system impedance and the total impedance of connected linear loads, including capacitor banks.
Table A.2 reveals significant insights, particularly regarding the variability of the value of \$k_{p,h}\$ based on selected sub-factors The analysis shows that using justifiable values for \$k_{p,h}\$ can lead to estimates of permissible 5th harmonic emissions that range dramatically—from over 400% of the fundamental current at one end to under 0.7% at the other Such extremes highlight the absurdity of these results.
Ignoring a specific sub-factor by setting it to 1.0 can greatly affect the calculated value of \$k_{p,h}\$ While simple multiplication of various sub-factors may suggest that only a limited subset is relevant, this perspective is misleading and can lead to significant inaccuracies in the overall assessment.
Work is on-going to develop formally-defined sub-factors (which may or may not be those in
Table A.2) The results of this work are intended to be reported in IEC 61000-1-X (to be published)
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Comparison of Class A limits and the harmonic spectra of phase- controlled dimmers of incandescent lamps at 90° firing angle
The harmonic spectra of phase-controlled dimmers of incandescent lamps at 90° firing angle
Harmonic current emissions exhibit minimal variation across different products, with Class A limits defined in terms of currents Consequently, it is feasible to derive the fundamental current value corresponding to each limit.