In the case of several points of connection, a different value may be defined for each connection point 3.2 customer a person, company or organization that operates an installation con
Compatibility levels
Reference values for coordinating the emission and immunity of equipment within a supply system are essential for ensuring electromagnetic compatibility (EMC) across the entire system, including all connected devices These compatibility levels are typically determined based on a 95% probability threshold, utilizing statistical distributions that account for both temporal and spatial variations in disturbances It is important to recognize that system operators or owners cannot oversee every point in the system at all times Consequently, evaluations regarding compatibility levels should be conducted on a system-wide basis, as no specific assessment method is available for localized evaluations.
The compatibility levels for flicker in LV systems are reproduced in Table 1 from
IEC 61000-2-2 indicates that higher values have been observed without corresponding complaints, potentially due to measurements taken at EHV/HV levels, during daylight hours, or other factors For more details, please refer to reference [3].
Compatibility levels are not defined by IEC for MV, HV and EHV systems
Table 1 – Compatibility levels for flicker in low voltage systems reproduced from IEC 61000-2-2
Planning levels
Indicative values of planning levels
Voltage flicker levels are essential for establishing emission limits, accounting for all fluctuating installations The system operator or owner specifies planning levels for all voltage levels, which can be regarded as internal standards.
The quality objectives set by the system operator or owner can be accessed by individual customers upon request Effective planning should facilitate the coordination of voltage fluctuations across various voltage levels Notably, at high voltage (HV) and extra high voltage (EHV) levels, it is possible to manage flicker levels while taking into account the attenuation effects caused by motor loads and generators downstream, which help stabilize voltages and diminish flicker perception.
Planning levels for flicker can only be provided as indicative values, as they vary based on the specific system structure and circumstances Refer to Table 2 for the indicative values of these planning levels.
Table 2 – Indicative values of planning levels for flicker in MV, HV and EHV power systems
NOTE 1 These values were chosen on the assumption that the transfer coefficient between MV or HV systems and LV systems is unity
NOTE 2 In practice, the transfer coefficients between different voltage levels are less than 1,0 This can be taken into account when establishing new planning levels For example, a typical value for the transfer coefficient between HV and LV is T PstHL = 0,8 In such a case, the indicative planning level for HV becomes
NOTE 3 In some countries, planning levels are defined in national standards or guidelines
NOTE 4 Voltage characteristics that are quasi-guaranteed levels exist in some countries for MV and HV systems
Theses should be coordinated with the planning levels [3]
To establish emission limits, it is essential to weight the planning levels at MV and HV-EHV by considering the flicker transfer coefficient from the emission source to the point of entry (POE) at various voltage levels Coordination between different voltage levels is crucial, necessitating that the system operator or owner assess the flicker transfer coefficients under various operating conditions For a detailed discussion on assessing these coefficients, refer to Annex B, while Annex C provides examples of reallocating planning levels.
In certain national contexts, it may be necessary to establish intermediate planning levels between Medium Voltage (MV) and High Voltage (HV) or Extra High Voltage (EHV) due to the diverse voltage levels present in HV-EHV systems (greater than 35 kV) Furthermore, it is essential to allocate planning levels between HV and EHV to address the effects of disruptive installations connected at the EHV level on HV systems.
The remainder of this report outlines procedures for using these planning levels to establish the emission limits for individual fluctuating installations.
Assessment procedure for evaluation against planning levels
The measurement methods to be used for flicker is the class A method specified in
IEC 61000-4-30 [4] and the related IEC 61000-4-15 [1] The data flagged in accordance with
IEC 61000-4-30 should be removed from the assessment For clarity, where data is flagged, the percentile used in calculating the indices defined below is calculated using only the valid
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The minimum measurement period is one week with normal business activity The monitoring period should include some part of the period of expected maximum flicker levels
To effectively compare actual flicker levels with planning levels, one or more indices may be utilized It is often necessary to employ multiple indices to evaluate the effects of increased emission levels permitted for brief durations, particularly during bursts or start-up conditions.
– The 95 % probability weekly value of P st
– The 99 % probability weekly value of P st
– The 95 % probability weekly value of P lt
To ensure accurate P lt calculations, it is advisable to update each new P st value using a sliding window method, where the oldest P st measurement is replaced by the latest value every 10 minutes This approach yields 144 P lt values daily and may necessitate post-processing of P st outputs from a flickermeter in certain situations.
The 95 % probability value should not exceed the planning level The 99 % probability value may exceed the planning level by a factor (for example: 1 to 1,5) to be specified by the system operator or owner, depending on the system and load characteristics
When comparing the 99% and 95% percentiles, a ratio exceeding 1.3—common in single arc furnace installations—warrants further investigation into the cause of the discrepancy It is essential to identify and eliminate any abnormal results, such as those caused by voltage dips or other transients.
Illustration of EMC concepts
The basic concepts of planning and compatibility levels are illustrated in Figure 1 and
Figure 2 They are intended to emphasize the most important relationships between the basic variables
In a power system, interference is unavoidable, leading to potential overlaps between disturbance and immunity levels Planning levels, determined by the system operator or owner, are typically set at or below the compatibility level Notably, for flicker, the transfer characteristics between various voltage levels may permit higher planning levels at high voltage (HV) and extra high voltage (EHV) while maintaining coordination with the compatibility levels applicable at low voltage (LV).
Immunity test levels are specified by relevant standards or agreed upon between manufacturers and customers
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Immunity test levels Compatibility level
Figure 1 – Illustration of basic voltage quality concepts with time/ location statistics covering the whole system
Figure 2 – Illustration of basic voltage quality concepts with time statistics relevant to one site within the whole system
Figure 2 demonstrates that the probability distributions of disturbance and immunity levels at individual sites are generally narrower compared to those across the entire power system, resulting in minimal or no overlap between the distributions of disturbance and immunity levels at most locations.
Interference is therefore not generally a major concern, and equipment is anticipated to function satisfactorily Electromagnetic compatibility is therefore more probable than Figure 1 appears to suggest.
Emission levels
This report advocates a coordination approach that derives individual emission levels from planning levels Consequently, the same indices are utilized to assess actual measurements in relation to both emission limits and planning levels, as detailed in the subsequent sections.
To evaluate the actual emission levels against the customer's emission limits, one or more indices can be utilized In cases where higher emission levels are permitted for brief durations, such as during bursts or start-up conditions, multiple indices may be necessary to accurately assess the impact.
– The 95 % probability weekly value of P sti should not exceed the emission limit E Psti
– The 99 % probability weekly value of P sti may exceed the emission limit E Psti by a factor
(for example: 1 to 1,5) to be specified by the system operator or owner, depending on the system and load characteristics
– The 95 % probability weekly value of P lti should not exceed the emission limit E Plti
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To effectively compare flicker emissions from a customer's installation with established emission limits, a minimum measurement period of one week is recommended Nevertheless, shorter measurement durations may be necessary to evaluate emissions under particular conditions.
Shorter measurement periods should reflect the expected operation over a longer assessment period, typically a week It is crucial that the duration is long enough to capture peak flicker emissions If a single large piece of equipment dominates the flicker level, the measurement should encompass at least two complete operating cycles of that equipment Conversely, if multiple items contribute to the flicker, the measurement period should cover at least one full operating shift.
Where significant the following factors should also be taken into account:
• capacitor banks within the installation with possible amplification of low order interharmonics that can cause flicker
The measurement methods to be used are IEC 61000-4-15 [1] and the Class A measurement method defined in IEC 61000-4-30 [4] for flicker (for rapid voltage changes see Clause 10)
Data flagged under the specified standard must be excluded from the assessment To clarify, the percentiles used for calculating the indices in this report are derived solely from valid (unflagged) data.
The emission level from a fluctuating installation is the flicker level assessed according to the subclauses of Clause 6
The proposed method for establishing emission limits for fluctuating installations is based on the customer's agreed power, the power of the flicker-generating equipment, and the system characteristics The goal is to restrict flicker injection from all fluctuating installations to ensure that flicker levels remain within acceptable planning limits, considering the transfer coefficient when relevant This evaluation process consists of three defined stages, which can be applied sequentially or independently.
Stage 1: simplified evaluation of disturbance emission
Customers are typically allowed to install small appliances without requiring a detailed assessment of flicker emissions by the system operator or owner The responsibility for limiting these emissions generally falls on the manufacturers of the appliances, as outlined in standards such as IEC 61000-3-3.
IEC 61000-3-5 and 61000-3-11 establish flicker emission limits for devices linked to public low voltage (LV) systems However, there are no existing emission standards for medium voltage (MV) equipment due to various reasons.
• medium voltage varies between 1 kV and 35 kV;
• no reference impedance has been internationally defined for medium-voltage systems
It is feasible to establish criteria for the quasi-automatic acceptance of customers in both the MV and HV systems, even in the absence of a reference impedance When the total fluctuating power of an installation or the customer's agreed power is minimal compared to the short-circuit power at the evaluation point, a detailed assessment of flicker emission levels may not be required.
In 8.1 and 9.1, specific criteria are developed for applying stage 1 evaluation.
Stage 2: emission limits relative to actual system characteristics
If an installation fails to meet stage 1 criteria, it is essential to assess the characteristics of the flicker-generating equipment alongside the system's absorption capacity, which is determined by the overall system design.
MECON Limited, based in Ranchi and Bangalore, has licensed materials for internal use at this location, provided by the Book Supply Bureau Planning levels are allocated to individual customers based on their demand relative to the overall system supply capacity Additionally, it is essential to consider the disturbance levels from upstream voltage systems when distributing these planning levels to customers.
This approach operates on the principle that when a system is utilized to its full designed capacity and all customers are operating at their individual limits, the overall disturbance levels will match the planned levels, considering the transfer factors across different voltage levels and the cumulative impact of various flicker-producing equipment The method for distributing the planning levels to individual customers is detailed in sections 8.2 and 9.2.
As the system's capacity expands in the future, individual customer emission levels are expected to decrease Therefore, it is crucial to take potential future system expansions into account whenever possible.
Stage 3: acceptance of higher emission levels on a conditional basis
In certain situations, customers may need permission to exceed the standard disturbance limits set in stage 2 In these cases, the customer and the system operator or owner can negotiate specific conditions to enable the connection of the variable installation A thorough analysis of both current and future system characteristics is essential to establish these special conditions.
Emission limits derived from the methods outlined in Clauses 8 and 9 aim to maintain flicker levels below the established planning thresholds Additionally, the implementation of alternative methods suggested in Clause 9 is also considered.
10 is intended to limit the magnitude of rapid voltage changes.
Responsibilities
In the context of this report from the EMC point of view, the following responsibilities are defined
– The customer is responsible for maintaining his emissions at the specified point of evaluation below the limits specified by the system operator or owner
The system operator or owner is tasked with coordinating emission levels in line with regional or national standards during normal operations For evaluation, they must provide essential system data, including short-circuit power, impedance, and current flicker levels The evaluation process aims to ensure that flicker emissions from fluctuating installations remain within acceptable planning and compatibility levels However, due to local conditions and necessary assumptions in the evaluation, there is no assurance that this approach will consistently prevent exceeding these levels.
To effectively reduce emissions, collaboration between the system operator or owner and customers is essential Customers hold the responsibility for selecting and designing the most effective methods for emission reduction.
6 General guidelines for the assessment of emission levels
Point of evaluation
The point of evaluation (POE) is crucial for assessing a customer's installation emission levels against compliance limits It serves as a defined location within the power system where planning levels are established, which may include the point of connection (POC) or the point of common coupling (PCC) Additionally, multiple points of evaluation can be designated based on the installation's characteristics and system structure, requiring evaluations to consider the specific system attributes and agreed power levels for each point.
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When determining emission limits and evaluating emission levels, it is essential to consider system parameters that extend beyond the evaluation point.
The flicker level may be elevated at the point of connection of the fluctuating installation, depending on its location relative to the point of common coupling.
NOTE 3 It should be remembered that as voltage characteristics or contracted limits generally apply at the point of connection, these should be taken into account in discussions between parties.
Definition of flicker emission level
The emission level from an installation into the power system refers to the flicker magnitude generated at the point of evaluation (POE) It is essential that this emission level remains below the specified limits outlined in the relevant clauses of this document.
Assessment of flicker emission levels
Emission levels should be evaluated under standard operating conditions unless stated otherwise When assessing flicker emissions from variable installations, it is essential to account for the worst-case normal operating conditions, including contingencies for which the system or customer installation is designed, particularly those that may occur for more than 5% of the time based on statistical averages.
For large installations where the system size ratio (e.g., S sc /S i