www bzfxw com BRITISH STANDARD BS EN 61000 2 12 2003 Electromagnetic compatibility (EMC) — Part 2 12 Environment — Compatibility levels for low frequency conducted disturbances and signalling in publi[.]
General definitions
(electromagnetic) disturbance any electromagnetic phenomenon which, by being present in the electromagnetic environment, can cause electrical equipment to depart from its intended performance
3.1.2 disturbance level the amount or magnitude of an electromagnetic disturbance, measured and evaluated in a specified way
EMC (abbreviation) ability of an equipment or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment
Electromagnetic compatibility (EMC) refers to the state of the electromagnetic environment where disturbance emissions are minimal and immunity levels are robust This ensures that all devices, equipment, and systems function as intended without interference.
Electromagnetic compatibility (EMC) is attained when emission and immunity levels are managed to ensure that the disturbance levels from cumulative emissions do not surpass the immunity levels of devices and systems at any given location Compatibility is typically defined as a low probability of deviation from intended performance, as outlined in Clause 4 of IEC 61000-2-1.
NOTE 3 Where the context requires it, compatibility may be understood to refer to a single disturbance or class of disturbances
Electromagnetic compatibility refers to the study of how devices, equipment, and systems are affected by adverse electromagnetic effects from one another and from electromagnetic phenomena.
(electromagnetic) compatibility level specified electromagnetic disturbance level used as a reference level in a specified environment for co-ordination in the setting of emission and immunity limits
NOTE By convention, the compatibility level is chosen so that there is only a small probability that it will be exceeded by the actual disturbance level
The planning level refers to a specific disturbance level within an environment, serving as a benchmark for establishing emission limits for large loads and installations This ensures that these limits are aligned with the standards set for equipment connected to the power supply system.
The planning level is tailored to local specifics and is implemented by the authorities in charge of planning and managing the power supply network in the respective region For additional details, please refer to Annex A.
PCC point on a public power supply network, electrically nearest to a particular load, at which other loads are, or could be, connected
Phenomena related definitions
The definitions pertaining to harmonics are derived from the analysis of system voltages or currents using the Discrete Fourier Transform (DFT) method, which serves as a practical application of the Fourier transform as outlined in IEV 101-13-09 For further details, refer to Annex B.
The Fourier Transform converts a time function, whether periodic or non-periodic, into its frequency spectrum, which represents the function in the frequency domain For periodic time functions, the spectrum consists of discrete lines or components, while for non-periodic functions, the spectrum is continuous, indicating the presence of components across all frequencies.
Other definitions related to harmonics or interharmonics are given in the IEV and other standards Some of those other definitions, although not used in this standard, are discussed in
The fundamental frequency is the primary frequency in the spectrum derived from the Fourier transform of a time function, serving as a reference for all other frequencies in the spectrum According to this standard, the fundamental frequency is equivalent to the power supply frequency.
NOTE 1 In the case of a periodic function, the fundamental frequency is generally equal to the frequency of the function itself (See Annex B.1).
In situations where ambiguity persists, it is essential to consider the power supply frequency in relation to the polarity and rotational speed of the synchronous generator(s) supplying the system.
3.2.2 fundamental component component whose frequency is the fundamental frequency
3.2.3 harmonic frequency frequency which is an integer multiple of the fundamental frequency The ratio of the harmonic frequency to the fundamental frequency is the harmonic order (recommended notation: “h”)
3.2.4 harmonic component any of the components having a harmonic frequency Its value is normally expressed as an r.m.s value
For brevity, such a component may be referred to simply as an harmonic
3.2.5 interharmonic frequency any frequency which is not an integer multiple of the fundamental frequency
NOTE 1 By extension from harmonic order, the interharmonic order is the ratio of an interharmonic frequency to the fundamental frequency This ratio is not an integer (Recommended notation “m”)
NOTE 2 In the case where m< 1 the term subharmonic frequency may be used
3.2.6 interharmonic component component having an interharmonic frequency Its value is normally expressed as an r.m.s value
For brevity, such a component may be referred to simply as an “interharmonic”
According to IEC 61000-4-7, the time window for this standard is defined as 10 fundamental periods for 50 Hz systems or 12 fundamental periods for 60 Hz systems, equating to roughly 200 ms Consequently, the frequency difference between two consecutive interharmonic components is approximately 5 Hz.
THD ratio of the r.m.s value of the sum of all the harmonic components up to a specified order (recommended notation “H”) to the r.m.s value of the fundamental component
Q represents either current or voltage
Q 1 = r.m.s value of the fundamental component h = harmonic order
Q h = r.m.s value of the harmonic component of order h
H = 50 generally, but 25 when the risk of resonance at higher orders is low
NOTE THD takes account of harmonics only For the case where interharmonics are to be included, see B.1.2.1,
3.2.8 voltage unbalance (imbalance) condition in a polyphase system in which the r.m.s values of the line-to-line voltages
The phase angles between consecutive line-to-line voltages are not uniform, and the extent of this inequality is typically represented by the ratios of the negative and zero sequence components to the positive sequence component.
NOTE 1 In this standard, voltage unbalance is considered in relation to three-phase systems and negative phase sequence only
NOTE 2 Several approximations give reasonably accurate results for the levels of unbalance normally encountered
(ratio of negative to positive sequence components):
U U U where U 12 , U 23 and U 31 are the three line-to-line voltages
General comment
The compatibility levels for various disturbances are defined individually; however, the electromagnetic environment often includes multiple disturbances at once, which can negatively impact the performance of certain equipment due to specific combinations of these disturbances For further details, refer to Annex A.
At the power input terminals of equipment connected to medium-voltage distribution systems, the disturbance severity levels are generally consistent with those at the point of common coupling However, there are specific situations where this may not hold true.
• a long line dedicated to the supply of a particular installation;
• equipment being part of an extensive installation;
• a disturbance generated or amplified within the installation of which the equipment forms a part
In medium voltage networks linked to low voltage networks, disturbance levels are typically lower in the medium voltage systems, particularly regarding harmonics and interharmonics However, exceptions may occur due to factors like resonance and the accumulation of disturbances from other network areas It is crucial for compatibility levels to accurately represent the disturbance levels that are likely to be experienced in practice, even if the likelihood is relatively low.
The MV compatibility level is designed to address exceptional conditions with a significant risk of occurrence, rather than average conditions This approach ensures that it serves as a valuable reference for specifying immunity levels for equipment connected to MV networks.
• emission and immunity limits for equipment supplied from public low-voltage distribution systems are co-ordinated on the basis of low-voltage compatibility levels specified in IEC 61000-2-2;
• limits for the emissions from large loads and installations are co-ordinated on the basis of planning levels – see 3.1.6 and Annex A; see also the technical reports IEC 61000-3-6 and IEC 61000-3-7;
• emission and immunity limits for equipment supplied from non-public distribution systems are co-ordinated on the basis of compatibility levels specified in IEC 61000-2-4
Accordingly, despite the fact that there is usually a margin between the disturbance levels on
MV and LV networks, this standard specifies MV compatibility levels that are the same as those specified in IEC 61000-2-2.
Voltage fluctuations and flicker
Voltage fluctuations in medium voltage networks arise from varying loads, the operation of transformer tap changers, and other adjustments made to the supply system or connected equipment.
In normal circumstances the value of rapid voltage changes is limited to 3 % of nominal supply voltage However step voltage changes exceeding 3 % can occur infrequently on the public supply network
Voltage fluctuations beyond the normal operational tolerances (±10% of the declared supply voltage) can occur for several seconds after significant load changes or switching operations, until the on-load tap-changers on high voltage-medium voltage transformers adjust accordingly.
Voltage fluctuations in medium voltage networks, by being transferred, with or without alteration, to low voltage networks, can cause flicker See IEC 61000-2-2 for compatibility levels in low-voltage networks.
Harmonics
When determining compatibility levels for harmonics, it is essential to recognize two key factors: the rising number of harmonic sources and the declining proportion of purely resistive loads, such as heating loads, which act as damping elements Consequently, power supply systems are likely to experience increasing harmonic levels until effective limits are established for harmonic emissions.
The compatibility levels outlined in this standard pertain to quasi-stationary or steady-state harmonics, serving as reference values for both long-term and very short-term effects.
• The long-term effects relate mainly to thermal effects on cables, transformers, motors, capacitors, etc They arise from harmonic levels that are sustained for 10 min or more
• Very short-term effects relate mainly to disturbing effects on electronic devices that may be susceptible to harmonic levels sustained for 3 s or less Transients are not included
Table 1 presents the compatibility levels for individual harmonic components of the voltage, highlighting that the total harmonic distortion (THD) is at 8%.
Table 1 – Compatibility levels for individual harmonic voltages in medium voltage networks (r.m.s values as percent of r.m.s value of the fundamental component)
NOTE 1 The levels given for odd harmonics that are multiples of three apply to zero sequence harmonics
In a three-phase network lacking a neutral conductor or any load connected between the line and ground, the levels of the 3rd and 9th harmonics can be significantly lower than the compatibility standards, influenced by the system's unbalance.
NOTE 2 Lower values are often appropriate – See 4.1
The compatibility levels for individual harmonic components of the voltage, as outlined in Table 1, are determined by multiplying the specified values by a factor \( k \).
The corresponding compatibility level for the total harmonic distortion is THD = 11 %
Commutation notches impact harmonic levels in the supply voltage, as outlined by the compatibility levels mentioned earlier However, to understand their additional effects, such as their influence on the commutation of other converters and their impact on equipment related to higher-order harmonic components, a time-domain description is necessary, as specified in the relevant product standard.
Interharmonics and voltage components at frequencies above that of the
Knowledge of the electromagnetic disturbance involved in interharmonic and higher frequency voltages is still developing See Annex B for further discussion
Compatibility levels relating to the flicker effect associated with this phenomenon on low voltage networks are given in IEC 61000-2-2.
Voltage dips and short supply interruptions
For a discussion of these phenomena, see Annex B, and IEC 61000-2-8
Voltage unbalance
Voltage unbalance is primarily assessed concerning the negative phase sequence component, which is crucial for understanding potential interference with equipment linked to public medium voltage distribution systems.
NOTE For systems with the neutral point directly connected to earth, the zero-sequence unbalance ratio can be relevant
Voltage unbalance from a single-phase load connected line-to-line is practically equal to the ratio of the load power to the three-phase short circuit power of the network.
The compatibility level for unbalance is defined as a negative sequence component of 2% of the positive sequence component In certain regions, particularly where large single-phase loads are commonly connected, this value can rise to 3%.
Transient overvoltages
For a discussion of these phenomena, see Annex B
Compatibility levels are not given for transient overvoltages in this standard However, for insulation co-ordination see IEC 60071.
Temporary power frequency variation
In public power supply systems, maintaining the frequency close to the nominal value is crucial, with variations typically within 1 Hz for interconnected systems On a continental scale, synchronous interconnections result in even smaller frequency fluctuations However, island systems that are not connected to larger networks may experience greater frequency variations.
The compatibility level for the temporary variation of frequency from the nominal frequency is ±1Hz
The steady-state deviation of frequency from the nominal frequency is much less
NOTE For some equipment the rate of change of frequency is significant.
DC component
Public power supply systems typically do not exhibit a significant direct current (d.c.) component; however, this can occur when specific non-symmetrically controlled loads are connected.
The critical factor in determining d.c voltage is the level of d.c current, which is influenced by various elements, particularly the resistance of the network at the relevant point Consequently, a specific compatibility level for d.c voltage cannot be established.
Mains signalling
Public networks primarily serve to supply electric energy to customers, but suppliers also utilize them for signal transmission to control specific load categories However, these networks are not employed for communication between private users.
Mains signalling generates interharmonic voltages, as detailed in section 4.4 and Annex B In this context, the signal voltage is deliberately applied to a specific section of the supply system Both the voltage and frequency of the emitted signal are predetermined, and the transmission occurs at designated times.
For co-ordination of the immunity of equipment connected to networks on which mains signals exist, the voltage levels of these signals need to be taken into account
Design of mains signalling systems should meet three objectives:
• to assure compatibility between neighbouring installations,
• to avoid interference with the mains signalling system and its elements by equipment on or connected to the network
• to prevent the mains signalling system from disturbing equipment on or connected to the network
Four types of mains signalling systems are described in Clause 10 of IEC 61000-2-1 (the frequency ranges mentioned are nominal and are a matter of common practice)
4.10.1 Ripple control systems (110 Hz to 3 000 Hz)
Ripple control signals are sent as a series of pulses, with each pulse lasting between 0.1 seconds and 7 seconds The total duration of the sequence can vary from 6 seconds to 180 seconds, although a typical pulse duration is approximately 0.5 seconds, and the average sequence duration is around 30 seconds.
These systems typically function within a frequency range of 110 Hz to 3000 Hz, with the injected sine wave signal generally set between 2% and 5% of the nominal supply voltage, although resonance may increase this level to 9% In newer installations, the signal frequencies are commonly found between 110 Hz and 500 Hz.
In certain countries, the Meister curve, illustrated in Figure 1, is officially acknowledged In regions where the Meister curve is not utilized, the signal amplitudes within this frequency range must not surpass the levels specified in Table 1 for odd harmonics, which are non-multiples of 3.
Figure 1 – Meister curve for ripple control systems in public networks
4.10.2 Medium-frequency power-line carrier systems (3 kHz to 20 kHz)
4.10.3 Radio-frequency power-line carrier systems (20 kHz to 148,5 kHz)
Due to the unique characteristics of different systems, manufacturers must ensure compatibility between their systems and the supply network, as no universal guidance can be provided.
The function of compatibility levels and planning levels in EMC
The need for compatibility levels
Electromagnetic compatibility (EMC) addresses the potential decline in performance of electrical and electronic devices caused by disturbances in their electromagnetic environment To ensure compatibility, two key requirements must be met.
• the emission of disturbances into the electromagnetic environment must be maintained below a level that would cause an unacceptable degradation of the performance of equipment operating in that environment;
• all equipment operating in the electromagnetic environment must have sufficient immunity from all disturbances at the levels at which they exist in the environment
Emission limits and immunity requirements are interdependent; effective emission control reduces the need for strict immunity standards on equipment Conversely, highly immune equipment allows for more lenient emission limits.
There is a requirement, therefore, for close co-ordination between the limits adopted for emission and immunity That is the principal function of the compatibility levels specified in this standard
The article discusses disturbance phenomena in medium voltage networks of public AC power supply systems These systems, designed to transport electrical energy from generating stations to end-use equipment, inadvertently also transmit electromagnetic disturbances from their sources to the affected equipment.
Three considerations have been borne in mind in setting the compatibility level for each phenomenon:
The compatibility level refers to the expected disturbance in the environment, with a small probability of exceeding 5% As the severity of certain disturbance phenomena increases, a long-term perspective becomes essential.
• it is a disturbance level which can be maintained by implementing practicable limits on emissions;
• it is the level of disturbance from which, with a suitable margin, equipment operating in the relevant environment must have immunity.
Relation between compatibility level and immunity levels
Each disturbance phenomenon necessitates an understanding of the compatibility level, which indicates the severity that can occur in a specific environment All equipment designed for use in that environment must possess immunity that meets or exceeds this disturbance level Typically, a margin is established between the compatibility and immunity levels, tailored to the specific equipment involved.
Compatibility levels have been established for individual disturbance phenomena, including specific frequencies for harmonics and interharmonics It is important to note that multiple disturbance phenomena can coexist in the environment, potentially degrading the performance of certain equipment due to specific combinations of disturbances, even when each is below the compatibility level.
Harmonics and interharmonics can significantly impact the voltage peak and zero crossing points due to specific combinations of frequency, magnitude, and phasing Additionally, the presence of other disturbances can further complicate these effects.
Because the number of permutations is infinite, it is not possible to set compatibility levels for combinations of disturbances
To ensure optimal product performance, it is essential to identify any combinations of disturbances within the compatibility levels that may degrade its functionality This identification allows for the appropriate consideration of the product's immunity requirements.
Relation between compatibility level and emission limits
Some disturbances originate from atmospheric phenomena, particularly lightning, or from the natural responses of a well-designed supply system to electrical faults or load switching Key disturbances include transient overvoltages, voltage dips, and short supply interruptions Emission limits for these phenomena cannot be established due to the uncontrollable nature of their sources Instead, the compatibility level aims to indicate the expected severity of these disturbances in practical scenarios.
Disturbances in public electricity supply often originate from the equipment used to utilize this power, as well as, to a lesser extent, from components of the supply system itself These disturbances occur when equipment draws an irregular current that deviates from a consistent relationship with the supplied voltage, leading to abrupt variations or incomplete cycles of the voltage waveform Such irregular currents pass through the impedances of the supply networks, resulting in corresponding voltage irregularities.
While some network impedances may be reduced to address specific disturbances, they are typically fixed due to voltage regulation and other factors unrelated to disturbance mitigation.
Voltage irregularities can disrupt other equipment, with the severity of the disturbance influenced by the types of emission sources, their quantity and location, and the interaction of emissions from various sources It is crucial that these disturbance levels remain below the established compatibility threshold.
Emission limits have a more intricate relationship with compatibility levels compared to immunity levels The diversity of emission sources complicates this relationship, particularly for low-frequency disturbances, where each source contributes to the overall environmental disturbance level indicated by the compatibility level Additionally, while many emission limits are defined in terms of current, compatibility levels are typically expressed in voltage, necessitating the consideration of network impedances.
The goal of establishing emission limits is to guarantee that actual disturbance levels remain within acceptable compatibility thresholds, excluding low-probability events that are deemed acceptable.
Emission limits for specific equipment cannot be set in isolation; they must be coordinated with limits for all other sources of the same disturbance phenomenon This coordination ensures that when all sources adhere to their individual limits and operate together as expected in the relevant environment, the overall disturbance level remains below the compatibility level.
The sources of emission are extremely diverse, but it is useful to divide them into two broad categories:
Historically, low-frequency emissions like harmonics and voltage fluctuations were primarily sourced from specific equipment It is crucial for electricity suppliers to be informed about these emissions, allowing them to collaborate with the equipment operators or owners to establish an operational regime that keeps emissions within acceptable limits This approach also includes developing a supply method that minimizes the risk of disturbances to other equipment on the network Each solution is tailored to the specific location.
Low-power equipment commonly used in domestic, commercial, and smaller industrial settings is increasingly responsible for significant low-frequency disturbances This equipment is often purchased and operated independently of electricity suppliers, leading to a cumulative effect where the total number of devices can account for up to 50% of system demand Although emissions from individual units may be small, they are substantial relative to their rated power, making this equipment a major source of low-frequency disturbances To effectively manage these emissions, it is essential to design and manufacture equipment in accordance with established emission limits.
To ensure accurate representation of the maximum potential disturbance in the electromagnetic environment, it is essential to harmonize the emission limits for a diverse array of products This includes both large installations reported to the electricity supplier and smaller devices that users choose to install independently.
Electricity suppliers may identify installations that include numerous low-power professional equipment In such cases, emissions are evaluated based on the overall installation rather than setting limits on individual components.
Planning levels
In managing large loads and installations, those in charge of the power supply system play a crucial role They utilize the concept of planning level, as outlined in section 3.1.5, to establish suitable emission limits for these installations.
Currently, planning levels are mainly applicable to medium and high voltage networks Nonetheless, low frequency conducted disturbances can travel in both directions between low voltage and higher voltage networks Therefore, the coordination of emission limits must consider all voltage levels.
The use of planning levels is described in the technical reports IEC 61000-3-6 and IEC 61000-3-7 The important points are as follows
The planning level is a crucial metric established by the authority managing the power supply system in a specific region It plays a vital role in determining emission limits for significant loads and installations that intend to connect to the system This value assists in fairly distributing the burden of emission limitations across various entities.
The planning level must not exceed the compatibility level, typically remaining lower by a margin influenced by various factors These include the nature of the disturbance phenomenon, the design and maintenance of the supply network, background disturbance levels, resonance potential, and load profiles, making it a locally specific consideration.
Effective planning for large equipment and installations must also consider various low-power devices connected at low voltage, as they can contribute to disturbances The capacity to manage emissions from larger installations is influenced by the regulation of low-power equipment Challenges in this area signal the need for stricter emission controls on low-power devices Ultimately, the primary goal is to ensure that the anticipated disturbance levels remain within acceptable compatibility limits.
Illustration of compatibility, emission, immunity and planning levels
Figure A.1 displays the different EMC levels and limits, providing a schematic representation of their relationships While the figure is not mathematically precise, it highlights that overlap between the two curves can occur However, this overlap should not be viewed as an exact measure of its extent.
Emission limits individual sources Planning levels
IEC 1185/03 Figure A.1 – Relation between compatibility, immunity, planning and emission levels
Discussion of some disturbance phenomena
Resolution of non-sinusoidal voltages and currents
The distortion of supply voltage from its intended sinusoidal waveform occurs when additional sinusoidal voltages at unwanted frequencies are superimposed on the intended voltage This concept applies equally to both voltage and current.
Fourier series analysis (IEV 101-13-08) allows for the decomposition of any periodic quantity, regardless of its non-sinusoidal nature, into sinusoidal components at various frequencies, including a direct current (d.c.) component The fundamental component, defined as the lowest frequency in the series (IEV 101-14-49), serves as the basis for the other frequencies, which are integer multiples of this fundamental frequency and are known as harmonic frequencies The components of the periodic quantity are thus categorized as fundamental and harmonic components.
The Fourier transform (IEV 101-13-09) can be utilized for both periodic and non-periodic functions, yielding a frequency domain spectrum For non-periodic time functions, this spectrum is continuous and lacks a fundamental component In contrast, when applied to periodic functions, the Fourier transform produces a line spectrum, where the lines represent the fundamental frequency and its harmonics derived from the corresponding Fourier series.
The Discrete Fourier Transform (DFT) serves as a practical implementation of the Fourier transform, analyzing signals over a specified time window (duration \(T_w\)) with a finite number of samples (\(M\)) The outcome of the DFT is influenced by the selection of these parameters, \(T_w\) and \(M\), while the fundamental frequency of the DFT is determined by the inverse of \(T_w\), denoted as \(f_b\).
The Discrete Fourier Transform (DFT) is utilized on the signal within a defined time window, while the signal outside this window is considered a repetitive extension of the internal signal Consequently, the actual signal is represented by a virtual periodic signal, with its period corresponding to the duration of the time window.
The Fast Fourier Transform (FFT) is an efficient algorithm that significantly reduces computation time, requiring the number of samples (M) to be an integer power of 2 (M = 2^i) This means that the sampling frequency must be a fixed integer power of 2 of the fundamental frequency However, contemporary digital signal processors can handle the additional complexity of the Discrete Fourier Transform (DFT), making it a more economical and flexible option compared to the frequency-locked FFTs.
To ensure that the Discrete Fourier Transform (DFT) yields results consistent with Fourier series analysis for a periodic function, the fundamental frequency must be an integer multiple of the basic frequency, necessitating that the sampling frequency be an exact integer multiple of the basic frequency (\$f_s = M \times f_b\$) Synchronous sampling is crucial, as any loss of synchronism can alter the spectrum, introducing additional lines and modifying the amplitudes of the true lines.
The measurement techniques outlined in the upcoming edition of IEC 61000-4-7, along with the definition of fundamental frequency in section 3.2.1, are applicable to all electrotechnical and power electronics devices Additional considerations are required for other scenarios.
As an illustration, the superposition of a sinusoidal ripple control signal at 175 Hz on a sinusoidal 50 Hz supply voltage may be considered
This results in a periodic voltage having a period of 40 ms and a frequency of 25 Hz
A classical Fourier series analysis of the voltage reveals a fundamental component at 25 Hz with zero amplitude, alongside two significant components: a 2nd harmonic at 50 Hz with amplitude matching the supply voltage, and a 7th harmonic at 175 Hz with amplitude equal to the ripple control signal The definitions provided in section 3.2 clarify potential confusion and align with the standard practice of the Discrete Fourier Transform (DFT) as outlined in IEC 61000-4-7, indicating a fundamental frequency at 50 Hz and an interharmonic of order 3.5.
When analyzing the voltage of a power supply system, the fundamental frequency component exhibits the highest amplitude However, this component may not always appear as the first line in the spectrum derived from applying a Discrete Fourier Transform (DFT) to the time function.
NOTE 2 When analysing a current, the component at the fundamental frequency is not necessarily the component of the highest amplitude
The voltages and currents in a typical electricity supply system are influenced by continuous switching and fluctuations in both linear and non-linear loads For analysis, these parameters are treated as stationary within a measurement window of about 200 ms, which is an integer multiple of the power supply voltage period Harmonic analysers are engineered to offer the best technological compromise, as outlined in IEC 61000-4-7.
The following definitions are complementary to those given in 3.2, and may be of practical use
B.1.2.1 total distortion content quantity remaining when the fundamental component is subtracted from an alternating quantity, all being treated as functions of time
Q is the total r.m.s value, representing either current or voltage;
Q 1 is the r.m.s value of the fundamental component
Total distortion content includes both harmonic and interharmonic components See also
TDR ratio of the r.m.s value of the total distortion content to the r.m.s value of the fundamental component of an alternating quantity [IEV 551-20-14 modified]
= with the same notation as in B.1.2.1.
Interharmonics and voltage components at frequencies above that of the 50 th
B.2.1 Sources of unwanted currents and voltages
The public a.c distribution systems are intended to deliver voltages at the power frequencies,
The standard frequencies for electrical systems are 50 Hz or 60 Hz, and it is essential to minimize the presence of voltages at other frequencies However, advancements in electricity usage are leading to an increase in unwanted frequency superposition on the supply voltage A significant contributor to these unintended frequencies is the growing use of electronic power conditioning modules in various electrical devices.
Most electronic components need a direct current (d.c.) supply, which is often provided by electronic modules that convert alternating current (a.c.) from the supply into d.c voltage, with switched mode power supplies being the most common devices for this purpose This conversion process results in power being drawn from the a.c system in a non-linear manner, generating currents at various harmonic and interharmonic frequencies, sometimes exceeding the 50th harmonic These currents create voltages at corresponding frequencies that superimpose on the supply voltage Additionally, some applications, such as variable speed drive systems, require an a.c voltage at a frequency different from the supply frequency, achieved through electronic devices that extract energy from the incoming supply and deliver it at the desired frequency, thus acting as sources of current at multiple frequencies, including both harmonic and interharmonic frequencies.
Voltage source inverters equipped with pulse width modulated converters generate harmonics at the modulation frequency, which do not synchronize with the network frequency, primarily at higher frequencies such as the switching frequency and its harmonics High power equipment, typically exceeding 1 MW and linked to medium or high voltage power networks, may utilize cycloconverters or current source inverters that operate at any frequency independently of the network frequency These systems can also produce interharmonics due to residual coupling between the motor side and the network.
Static frequency converters can generate discrete frequencies ranging from 0 Hz to 2,500 Hz or more, as outlined in IEC 61000-2-4, Annex C Electrical arc furnaces produce significant interharmonics and frequencies exceeding the 50th harmonic, typically not connected to public low voltage networks due to their high power Arc welding machines create a continuous wideband frequency spectrum linked to intermittent welding actions, with durations varying from one to several seconds Induction motors may produce irregular magnetizing currents due to stator and rotor slots, generating interharmonics between 10 to 40 times the power frequency during normal operation, while covering the entire frequency range during startup Additionally, power supplies for traction systems can lead to interharmonics at fixed frequencies.
Sources are linked to networks of varying voltage levels, leading to emissions of interharmonic and high-frequency voltages These voltages, which can reach up to 0.5%, are influenced by network impedances and may exceed this threshold, particularly during resonant effects.
(There is a background level of interharmonics of the order of 0,02 % of the nominal supply voltage, in this case measured with a bandwidth of 10 Hz.)
Mains signalling is also a source of interharmonic voltages, but in this case the emissions are intentional and utilities and users exercise careful control to ensure compatibility – see 4.9
B.2.2 Effects of the unwanted voltages
The effects of interharmonics include the following
Interharmonic voltages can interact with the fundamental frequency or harmonics, resulting in a beat frequency characterized by amplitude modulation of the supply voltage This beat frequency arises from the frequency difference between the interharmonic voltage and the fundamental or harmonic voltage Such interactions can lead to flicker in incandescent and other types of lamps, particularly affecting equipment connected to low voltage networks Compatibility levels for these effects are outlined in IEC 61000-2-2.
• Unwanted currents flowing in the supply networks generate additional energy losses
Interharmonic voltages can disrupt the functioning of fluorescent lamps and electronic devices, including television receivers Any electrical application sensitive to crest voltage or zero crossing timing may be affected if unwanted frequencies alter these characteristics of the supply voltage.
A wider range of frequencies and higher voltage amplitudes increase the risk of unpredictable resonant effects, which can amplify voltage distortion and potentially overload or disrupt equipment in supply networks and user installations.
The production of acoustic noise is another significant effect, resulting from voltages ranging from 1 kHz to 9 kHz and higher, with amplitudes starting at 0.5% This noise generation is influenced by both the frequency value and the type of equipment affected.
B.2.3 Need for compatibility levels for the unwanted voltages
Given the possible effects of voltages at interharmonic frequencies and frequencies beyond the
Establishing reference levels for emission and immunity is crucial for electromagnetic compatibility, particularly concerning the 50th harmonic However, current knowledge of these frequencies in public power networks is insufficient to reach a consensus on compatibility levels, except for flicker issues related to beat frequencies Continuous monitoring of this situation is essential.
It is essential to prevent the unchecked growth of voltages at unwanted frequencies As these voltages become increasingly common, it is crucial for equipment connected to public networks to possess adequate immunity to function properly in their presence.
When assessing compatibility levels, it is advisable to limit them to those of adjacent harmonics For instance, in a 50 Hz system, the voltage at 95 Hz should not exceed that at 100 Hz, and similarly, in a 60 Hz system, the voltage at 115 Hz should not be higher than at 120 Hz Therefore, it is recommended that the reference level for each interharmonic frequency aligns with the compatibility level specified in Table 1 for the next higher even harmonic.
Ripple control receivers are unique devices that can respond to voltage levels as low as 0.3% of the nominal supply voltage If an unintended interharmonic voltage exceeds this threshold and matches the operational frequency of the receivers, it can lead to disturbances Consequently, the reference level at the defined frequency should be set at 0.2% of the nominal supply voltage, with the defined frequency being specific to the local context.
At frequencies above the 50th harmonic, the distinction between harmonics and interharmonics becomes less significant These voltage variations can manifest at specific frequencies or across broader frequency bands.
For discrete frequencies ranging from the 50th harmonic to 9 kHz, the recommended reference level, denoted as \( u \), is defined as the ratio of the root mean square (r.m.s.) voltage at that frequency to the r.m.s value of the fundamental component, with a suggested value of \( u = 0.2\% \).
For a band of frequencies in the range from the 50 th harmonic up to 9 kHz, the suggested reference level for any 200 Hz bandwidth centred at frequency F is as follows: u b = 0,3 %, where
V 1 =r.m.s value of the voltage (fundamental component);
F = centre frequency of the band (the band is above the 50 th harmonic)
Voltage dips and short supply interruptions
Voltage dips and short supply interruptions are unpredictable and largely random occurrences, primarily caused by electrical faults in the power supply system or significant installations These events are most effectively characterized using statistical analysis.
A voltage dip is a two-dimensional disturbance phenomenon, since the level of the disturbance increases with both the depth and duration of the dip
The severity of a voltage dip is influenced by how close the observation point is to the location of the short circuit, where the voltage can drop to nearly zero, resulting in a dip depth nearing 100% Conversely, for other events like significant load fluctuations, the depth of the dip is typically less severe.
A voltage dip can occur in the transmission system and may last for less than one tenth of a second, especially when addressed by rapid protection systems or in the case of a self-clearing fault.
Faults impacting lower voltage levels in a network can be resolved by specific protection systems, typically lasting only a few seconds Generally, voltage dips range from half a period to 1,000 milliseconds.
The significance of voltage dips arises primarily when a device's immunity is inadequate for the specific depth and duration of the dips, or when assessing whether a particular process requires a certain level of immunity.
Voltage dips on a specific line are influenced by faults from other lines within the same network, as well as from upstream networks In rural regions served by overhead lines, the frequency of these voltage dips can soar to several hundred annually, largely determined by factors such as the incidence of lightning strikes and local meteorological conditions.
Recent data reveals that residential electricity users connected at low voltage may experience voltage dips ranging from approximately ten to one hundred times annually, influenced by local conditions.
Short supply interruptions can last up to 180 s according to the type of reclosing or transfer system used in overhead networks Frequently, short supply interruptions are preceded by voltage dips
To ensure effective management of voltage dips, it is essential to coordinate immunity levels across compatibility levels This coordination should be represented in a two-dimensional format to accurately depict the disturbance levels However, there is currently insufficient data to achieve this representation.
Immunity of electrical equipment is not a suitable concept for short interruptions or severe voltage dips, as no device can function properly without its energy supply Instead, addressing these disturbances relies on quickly restoring power from an alternative source or adapting the equipment and its processes to handle brief power interruptions, prioritizing safety and damage limitation.
Transient overvoltages
Transient overvoltages in medium-voltage power supply systems can be caused by various phenomena, such as the operation of switches and fuses, as well as lightning strikes near supply networks These overvoltages can be classified as oscillatory or non-oscillatory, typically exhibiting high damping and rise times from under one microsecond to several milliseconds The levels and durations of these overvoltages can often be mitigated by implementing surge arrestors throughout the system, rather than solely at the point of common coupling.
Transient overvoltages differ in magnitude, duration, and energy content based on their source Typically, atmospheric overvoltages exhibit higher amplitudes, while switching overvoltages last longer and possess greater energy To safeguard critical equipment, it is essential to use individual surge protective devices specifically designed to handle the higher energy levels associated with switching overvoltages.
Capacitor bank switching often leads to transient overvoltages, which are usually less than twice the nominal voltage at the point of incidence However, as the transient travels along a line, wave reflections and voltage magnification can significantly increase the overvoltage experienced by connected equipment It is essential to consider these factors when assessing the immunity of specific equipment or installations.
Synchronised switching is a possible mitigation technique to minimise capacitor, reactor and transformer switching transients, more often applied at medium and higher voltages
See also IEC 60071-1 in relation to insulation coordination.
DC component
Public power supply systems typically do not exhibit a significant d.c component in their voltage However, the connection of certain non-symmetrically controlled loads can introduce this phenomenon Additionally, geomagnetic storms can occasionally cause large d.c currents and voltages in specific areas, although these effects are not considered in this standard.
A direct current (d.c.) component in the supply voltage can result in unsymmetrical magnetization in distribution transformers, which may cause overheating Additionally, when this current flows through the earth, it can accelerate the corrosion of underground metal fixtures.
The current value is variable, influenced by the direct current (d.c.) resistance of the circuit and the voltage of the d.c component Consequently, the acceptable d.c voltage must be assessed on a case-by-case basis.
Normative references to international publications with their corresponding European publications
This European Standard includes provisions from other publications, which are referenced throughout the text and listed subsequently Dated references will only apply to this Standard if amendments or revisions are incorporated, while for undated references, the latest edition of the cited publication, including any amendments, is applicable.
NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant
Publication Year Title EN/HD Year
IEC 60071 Series Insulation co-ordination EN 60071 Series
Part 1: Definitions, principles and rules
Part 2-2: Environment - Compatibility levels for low-frequency conducted disturbances and signalling in public low-voltage power supply systems
IEC 61000-2-4 - 1) Part 2-4: Environment - Compatibility levels in industrial plants for low- frequency conducted disturbances
IEC 61000-4-7 - 1) Part 4-7: Testing and measurement techniques - General guide on harmonics and interharmonics measurements and instrumentation, for power supply systems and equipment connected thereto
2) Valid edition at date of issue.
IEC 60050-101:1998, International Electrotechnical Vocabulary (IEV) – Part 101: Mathematics
IEC 60050-161:1990 International Electrotechnical Vocabulary (IEV) – Chapter 161: Electroma- gnetic compatibility
IEC 60050-551-20:2001, International Electrotechnical Vocabulary – Part 551-20: Power electronics – Harmonic analysis
IEC 60868:1986, Flickermeter – Functional and design specifications
IEC 60868-0:1991, Flickermeter – Part 0: Evaluation of flicker severity
IEC 61000-2-1:1990, Electromagnetic compatibility (EMC) – Part 2: Environment – Section 1:
Description of the environment – Electromagnetic environment for low-frequency conducted disturbances and signalling in public power supply systems
IEC 61000-2-8, Electromagnetic compatibility (EMC) –Part 2-8: Environment - Voltage dips and short interruptions on public electric power supply systems with statistical measurement results
IEC 61000-3-2:2000, Electromagnetic compatibility (EMC) – Part 3-2: Limits – Limits for harmonic current emissions (equipment input current ≤ 16 A per phase) 2)
IEC 61000-3-3:1994, Electromagnetic compatibility (EMC) – Part 3: Limits – Section 3:
Limitation of voltage fluctuations and flicker in low-voltage supply systems for equipment with rated current ≤ 16 A
IEC 61000-3-6:1996, Electromagnetic compatibility (EMC) – Part 3: Limits – Section 6: Assessment of emission limits for distorting loads in MV and HV power systems Basic EMC
IEC 61000-3-7:1996, Electromagnetic compatibility (EMC) – Part 3: Limits – Section 7: Assessment of emission limits for fluctuating loads in MV and HV power systems Basic EMC
IEC 61037:1990, Electronic ripple control receivers for tariff and load 3)
UIE:1997, Flicker measurement and evaluation
UIE:1988, Connection of fluctuating loads
1) There exists a consolidated edition 6.2 (2002) including edition 6.0 and its Amendments 1 and 2.