ENGINEERING RECOMMENDATION G5/5

Transcription

1 ENGINEERING RECOMMENDATION G5/5 EMISSION LIMITS FOR HARMONIC VOLTAGE DISTORTION AND THE CONNECTION OF NON-LINEAR AND RESONANT EQUIPMENT TO TRANSMISSION SYSTEMS AND DISTRIBUTION NETWORKS IN THE UNITED KINGDOM FOREWORD...2 ACKNOWLEDGEMENT...2 Comment [DMJ1]: Te Title as Canged to Include te term Resonant Equipment since tis is as applicable for te connection of HV Cables et. al. as it is for te connection of Non-Linear Load. 1 INTRODUCTION Scope Exclusions Normative References Terms and Definitions PRINCIPLES OF HARMONIC VOLTAGE DISTORTION Roles and Responsibilities Distinction between Planning, Compatibility and Immunity Levels HARMONIC VOLTAGE DISTORTION LEVELS Planning Levels Compatibility Levels ASSESSMENT OF NON-LINEAR AND RESONANT CONNECTIONS Guidelines Point of Evaluation System Impedance Aggregation and Diversity Uncertainty Measurement Non-Continuous Distortion Limits Stage A Stage B Estimation of te Connection Headroom Calculation of Connection Limits Stage C CONCLUSION...23 REFERENCES...24 APPENDIX A: EXAMPLE OF A STAGE A ASSESSMENT...25 APPENDIX B: EXAMPLE OF A STAGE B ASSESSMENT...25 APPENDIX C: EXAMPLE OF A STAGE C ASSESSMENT...25 Page 1 of 25

2 Foreword Engineering Recommendation G5/5 supersedes Engineering Recommendation G5/4-1 on 1 st MONTH YEAR. Engineering Recommendation G5/4-1 will be witdrawn on tat date. For practical reasons, connections subject to contract specifications based on Engineering Recommendation G5/4-1 entered into before te effective date above may be connected in accordance wit tat recommendation. Interim Foreword to te Working Group Members Tis document as been drafted from first principles were necessary and as taken te best input from existing documents, namely: ER G5/4-1 and ETR 122 IEEE 519; and Te IEC series. Comment [DMJ2]: Obviously tis date is presently undefined. Comment [DMJ3]: To be removed after te next meeting. Primarily te intentions of te document, as directed during our previous meeting, are to improve on te structure and readability of te engineering recommendation, and to combine te guidance of ETR122 (were applicable) into a singular and coerent ER G5/5 draft. As suc, member will notice a distinct different in te structure of te document. Additionally, due consideration as been given to members concerns of te lack of guidance for circumstances were planning levels are already exceeded and tis as been improved in tis draft. Distinction as been made between Levels, wic are overarcing, and Limits wic are connection related. Additionally, intense work in te area of resonant plant as been included wic allows Stage A and B assessment to provide an indication of te affect of resonant plant witout aving to proceed to a Stage C assessment unnecessarily. It is recommended tat tis not be read alongside ER G5/4-1 at first as tey are structurally dissimilar. Furtermore, some concepts presented in tis draft are not present in ER G5/4-1 and mark a step toward improving on te applicability and practicality of te Engineering Recommendation. Te Appendices will be developed in due course and on acceptance of te metodologies presented in te recommendation. We accept tat prior publication of tese appendices migt aid in te group s reading of te new draft, but time did not permit teir development. Please also note tat te increase scope to te 100 t order does not jeopardise te requirements of tose for wom iger order armonics are not relevant, but does provide guidance for tose for wom tey are. At tis point, we would consider tis a first Beta release. Te derivations of te various tables and equations from te prior recommendation will be made to te group on request by Danson Micael Josep and Josep McCullag. Acknowledgement Acknowledgements to be developed. Page 2 of 25

3 1 Introduction Te Electromagnetic Compatibility Regulations 2006 [1], wic implements into UK law te Electromagnetic Compatibility Directive 2004/108/EC of te European Parliament [2], defines te interaction of Equipment and Fixed Installations suc tat: Regulation 4: Equipment sall be designed and manufactured, aving regard to te state of te art, so as to ensure tat it as a level of immunity to te electromagnetic disturbance to be expected in its intended use wic allows it to operate witout unacceptable degradation of its intended use, and Regulation 5: A Fixed Installation sall be installed applying good engineering practices; and respecting te information on te intended use of its components, wit a view to meeting te essential requirements set out in regulation 4. Tis Recommendation defines te good engineering practices applicable to armonic voltage distortion on transmission and distributions systems in te UK, being Fixed Installations by definition, so as to limit te disturbance levels tereon to below te immunity levels of Equipment connected tereto. Disturbance levels on supply systems are defined in terms of armonic voltage distortion and are affected by emissions of non-linear loads and generating plant as well as te connection of resonant plant wic modifies already existing disturbance levels. Tis recommendation provides planning and compatibility disturbance levels on UK transmission and distribution networks as well as a staged assessment plan for te connection of non-linear and resonant plant and equipment. Section 2 defines te guiding principles of armonic voltage distortion along wit te roles and responsibilities of te various parties involved in te electricity market. Specifically, it covers te distinction between Planning, Compatibility and Immunity levels. Section 3 defines te Planning and Compatibility limits applicable to te UK transmission and distribution systems. Section 4 describes a tree-staged approac of assessing te connection of non-linear and resonant plant to supply systems. Tis staged approac limits te assessment detail to an approximate level to matc te context of te connection being assessed, tus enabling a pragmatic connection of plant and equipment. An assessment sall result in armonic voltage distortion and/or emission limits wic sall inform te design of any necessary mitigation measures, as required under te relevant transmission, distribution or generation licence or indeed te customer connection agreement as applicable. Tere may be exceptional circumstances tat can enable a Network Owner to permit a connection of non-linear or resonant plant wic is likely to cause levels of system voltage distortion to exceed planning levels. However, te final decision as to weter or not particular equipment can be connected to a supply system rests wit te Network Operating Company responsible for te connection. Appendix A: Appendix B: and Appendix C: provide application guidance for Stage A, B and C assessments respectively. Page 3 of 25

4 1.1 Scope Tis Recommendation provides te individual and total armonic voltage distortion Planning and Compatibility limits wic are applicable on te UK transmission and distribution networks. Te general principles of Electromagnetic Compatibility, as applied to armonic voltage distortion, are presented along wit guidance as to te development of emission limits troug a tree-staged assessment procedure. Tis recommendation is focussed on conducted penomena resulting in te development of armonic voltages on te system, troug te emission of armonic currents, in te form of: Continuous armonic, sub-armonic, inter-armonic voltage distortion witin te range of 0 to 5 khz, Sort bursts of armonic voltage distortion, and Voltage notcing. Parts of tis guidance are based on simplification wic migt not provide te optimal solution under all operating conditions. Te onus is on te responsible party to apply sound engineering judgement were suc circumstances arise and to adequately document te justifications for applying alternative approaces and tecniques. Bot te connection of non-linear load or generating plant and of resonant plant, namely cables and sunt and series capacitive elements, fall under te requirements of te connection assessment. Te levels and limits presented in tis Recommendation are statistical in nature and are applicable to te normal temporal variations wic are caracteristic of a power system and to te credible outage scenarios wic migt prevail on te system. Tis Recommendation applies te voltage level definitions of BS EN [3] wit te extension of HV to 230 kv and te addition of EHV covering all voltages above 230 kv as per te Terms and Definitions in Section 1.4. Comment [DMJ4]: Tis is te scope of te recommendation. Tis caters for bot tose wo need to consider iger orders and tose wo don t: if tere are not effects at iger orders on any particular system, ten tere is no cause for concern. 1.2 Exclusions Tis Recommendation does not cover te design of mitigation measures to ensure compliance wit any armonic voltage distortion or emission limits wic result from te application of te assessment procedure. Tis Recommendation does not replace nor negate te relevant armonised equipment standards wic are applicable to particular Equipment, and are a pre-requisite for Electromagnetic Compatibility of te Equipment under te terms of te UK Regulations [1]. Radiated interference wic migt affect communications systems is not considered in tis recommendation. voltage distortion arising from switcing transients is not considered in tis Recommendation. 1.3 Normative References Te following referenced documents are indispensable for te application of tis document. For dated references, only te edition cited applies; for undated references, te latest edition of te referenced document (including any amendments) applies. IEC 60050(161) International Electrotecnical Vocabulary Capter 161: Electromagnetic Compatibility Page 4 of 25

5 1.4 Terms and Definitions Furter to te definitions in Capter 161 of IEC 60050, te following terms and definition apply trougout tis Recommendation. Aggregate Connected Capacity A term denoting tat items of non-linear load and generation connected to a Customer s installation are being considered as an item of equipment wit a rating equal to te sum of te individual non-linear equipment ratings wic te customer and te network owning company agree. Connection Agreement A contractual agreement between te Network Operator and Customer wic defines te conditions, specified by a Network Owner, by wic a connection is permissible. Convertor Equipment (Convertor) An operating unit in te connection between te supply system and a load or generator for te conversion of power from one frequency to anoter, including AC/DC and DC/AC conversion. It usually comprises one or more diode or tyristor assemblies, togeter wit convertor transformers, essential switcing devices, and oter auxiliaries. Customer A person, company, or organisation connected to, or entitled to be connected to, a Supply System by a Network Owner. Distribution Code Te code produced by eac older of a Public Electricity Supply Licence. Distribution Network All te lines, switcgear, and transformer windings connected togeter and energised at or over a range of voltages, oter tan a Transmission System. Distribution Network Operator, DNO Te Company responsible for making tecnical connection agreements wit Customers wo are seeking connection of load or generation to a Distribution Network. Electromagnetic Compatibility Level Te specified disturbance level in a system wic is expected to be exceeded only wit small probability, tis level being suc tat electromagnetic compatibility sould exist for most equipment witin te system. Emission Level (of a disturbing source) Te level of a given electromagnetic disturbance emitted from a particular device, equipment or system, measured in a specified manner. Emission Limit (of a disturbing source) Te specified maximum emission level of a source of electromagnetic disturbance. Extra Hig Voltage (EHV) Nominal voltage greater tan 230kV Comment [jmc5]: Added to provide clarity around voltage levels. Page 5 of 25

6 Fault Level A fictive or notional value expressed in MVA of te initial symmetrical sort-circuit power at a point on te Supply System. It is defined as te product of te initial symmetrical sort-circuit current, te nominal system voltage and te factor 3 wit te aperiodic component (DC) being neglected. Generating Plant Any equipment tat produces electricity togeter wit any directly connected or associated equipment suc as a unit transformer or convertor. Grid Code Te code required under te terms of a Transmission Licence to be produced and maintained by eac Grid Operating Company. Current, I Te RMS amplitude of a armonic current, of order, expressed in Amperes. Distortion Te cyclic departure of a waveform from te sinusoidal sape. Tis can be described by te addition of one or more armonics to te fundamental. Voltage, V Te RMS amplitude of a armonic voltage, of order, expressed as a percentage of te RMS amplitude of te fundamental voltage. An additional suffix p denotes tat it is a predicted value; c tat it is a calculated value, and m tat it is a measured value. Hig Voltage (HV) Nominal voltage greater tan 36kV up to but not equal to 230kV Immunity Level Te maximum level of a given electromagnetic disturbance on a particular device, equipment or system for wic it remains capable of operating wit a declared degree of performance. Comment [jmc6]: Added to provide clarity around voltage levels. Immunity (from disturbance) Te ability of a device, equipment or system to perform witout degradation in te presence of an electromagnetic disturbance. Inter-armonic Voltage, V µ A periodic voltage disturbance aving a frequency wic is a non-integer multiple, µ, of te fundamental 50 Hz system frequency. If µ is less tan 1, ten te term sub-armonic voltage disturbance is used. Load Te active, reactive or apparent power taken from a Supply System by eiter a Customer or by all te Customers connected to a Supply System according to te context. Low Voltage (LV) Nominal voltage less tan or equal to 1kV Comment [jmc7]: Added to provide clarity around voltage levels. Page 6 of 25

7 Medium Voltage (MV) Nominal voltage greater tan 1kV up to but not equal to 36kV Network Owner Te owner of te network, eiter transmission or distribution, wit wom a customer is seeking connection of load or generation to. Non-Linear or Resonant Equipment A load or equipment tat draws a non-sinusoidal current wen energised by a sinusoidal voltage or alters te self and/or transfer impedances of te supply system. For te purpose of tis Recommendation, all references to non-linear load also includes Generating Plant, and any source of non-sinusoidal current emissions suc as regenerative braking systems. Partial weigted armonic distortion (PWHD) Ratio of te r.m.s. value of a selected group of iger order armonics (in tis Engineering Recommendation te PWHD spectrum covers te range 23 rd 100 t armonic inclusive), weigted wit te armonic order, to te r.m.s. value of te sort circuit current ISsc: I PWHD = V (1) = 23 ISsc Comment [jmc8]: Added to provide clarity around voltage levels. Comment [jmc9]: To prevent confusion around network owners and operators. Comment [DMJ10]: Increase d to accommodate te increased scope of ER G5/5. Were: Note: V represents te line voltage, represents te armonic order I is te armonic emission current, and I Ssc represents te sort-circuit current. Te partial weigted armonic distortion (PWHD) is employed to provide a margin for some ig order armonics to exceed specified limits wilst still ensuring tat te overall eating effect of ig order armonics does not exceed acceptable limits. Te PWHD used in ER G5/% is based on te equation used in IEC [4]. Point of Common Coupling, PCC Te point in te public Supply System, electrically nearest to a Customer s installation, at wic oter Customers loads are, or may be, connected. Supply System All te lines, switcgear and transformers operating at various voltages wic make up te transmission systems and distribution systems to wic Customers installations are connected. Switc Mode Power Supply, SMPS A simple single pase AC/DC power supply used in most small electronic equipment and wic is designed to operate over a wide input voltage range. An SMPS device is composed basically of a full wave rectifier wit a capacitor connected across te output. Te current taken from te AC system is very spiky and is a significant source of fift order armonic distortion in Supply Systems and also of tird armonic distortion in low-voltage Supply Systems. Page 7 of 25

8 Total Voltage Distortion, THD Te RMS value of individual armonic voltages expressed as a percentage of te fundamental RMS voltage, and calculated using te following expression: THD = N 2 V = 2 (2) Were: V represents te individual armonic distortion, and represents te armonic order Te parameter N represents te igest armonic order under consideration. Te increasing number of power-electronic interfaces wit supply systems as made it necessary to consider integer values of up to and including N = 100. Tyristor AC Power Controller, AC Regulator An item of power electronic equipment for te control or switcing of AC power using circuits witout forced commutation and were switcing, multicycle control or pase control are included. Transmission Licensee Te older of a Transmission Licence granted under section 6(1)(b) of te Electricity Act 1989 or article 10(i) b of te Electricity (Nortern Ireland) Order Transmission System Te system of 132, 275 and 400 kv lines and plant owned by a Transmission Licensee. Comment [jmc11]: Added to provide clarity around onsore and offsore transmission companies. OFTO olds a transmission licence and are tus bound by te STC. Voltage Notcing A severe voltage cange, generally of very sort duration, caused by te commutating action of a rectifier. Page 8 of 25

9 2 Principles of Voltage Distortion Voltage distortion as long been recognised as being able to interfere wit telecommunications systems, to increase losses in circuits and equipment, and to cause overeating of rotating plant and capacitors, te latter being particularly susceptible to damage. Section 2.1 defines te roles and responsibilities eld by te relevant parties in ensuring tat te permissible levels of armonic distortion are not exceeded. Section 2.2 details te distinction between te planning, compatibility and immunity levels of armonic distortion, to wic te parties are required to comply. 2.1 Roles and Responsibilities Te connection of Non-linear or Resonant Plant will eiter be part of a Network Owner s investment strategy or be te result of a Customer connection to te Network Owner s system. Te Network Operator is ultimately responsible for compliance under operational timescales; under planning timescales, responsibility is delegated to te Network Owner (were different). In planning for armonic compliance wen considering Customer connections, a Network Owner may place additional responsibilities upon a Customer troug te terms of a Connection Agreement between te Customer and Network Operator. Te Network Operator is responsible for te overall co-ordination of disturbance levels under normal operating conditions in accordance wit national requirements and sall refer to te compatibility levels erein. Te Network Owner is responsible for assessing te impact of any connection of Non-linear or Resonant Plant to teir network. Tis assessment must cover all affected networks, including Distribution and Onsore and Offsore Transmission Networks and sall refer to te planning levels erein. Te Network Owners and Network Operator sall provide, were necessary and practicable, any Network Data, suc as armonic impedance data, necessary to enable te Network Owner osting te connection to fully assess te impact on armonic levels on all affected networks to ensure tat te overall Supply System armonic voltage levels will not exceed planning and compatibility levels. Tis armonic assessment is to consider te effect of emissions as well as modification to existing armonic levels due to resonance effects. 2.2 Distinction between Planning, Compatibility and Immunity Levels Te basic concepts of Planning, Compatibility and Immunity Levels are illustrated in Figure 1 and Figure 2. Figure 1 - Illustration of statistical power quality concept applied at a single site Figure 1 illustrates te relationsip between Disturbance Level and Immunity Level for an exemplary site. Te Immunity Level is specified by relevant standards or agreed upon between manufacturers and customers. Page 9 of 25

10 It is clear ere tat one would not expect overlap of Disturbance Level and Immunity Level and so interference would be of little concern for tis site. Figure 2 - Illustration of statistical power quality concept applied to te wole Supply System Figure 2 illustrates ow, wen one takes a system wide view, te distributions are wider, and overlap between Disturbance Level and Immunity Level will occur in some instances. Tis risk is managed by te setting of Compatibility Levels and Planning Levels for eac armonic order. Te Compatibility Level sown is te decreed limit of acceptability for probability of interference and is set for eac armonic order. Te Planning Levels are set equal to or lower tan te Compatibility Levels. Page 10 of 25

11 3 Voltage Distortion Levels Planning and compatibility levels for all voltage levels are given in Table 1 troug Table 10. Tis Engineering Recommendation does not contain provisions for DC current emissions because of teir deleterious effects on te supply system. All DC emissions are deprecated. 3.1 Planning Levels Table 1 provides te THD planning Levels for LV, MV, HV and EHV systems. Table 2 troug to Table 5 provides te planning levels for Voltage Distortion in LV, MV, HV and EHV systems respectively. Table 1: THD Planning Levels Nominal Voltage THD [%V 1] LV 5% MV 4% HV 3% EHV 3% Comment [DMJ12]: Te voltage levels ave been redefined from previous Recommendation G5/4 to include all possible system operating voltages. Te voltage levels for LV, HV and EHV are in line wit IEC Te upper range limit for MV is 36kV to account for a 10% operational level for 33kV. Comment [jmc13]: Do we want to keep tis in? Sould we give guidance as to were one can limit DC emissions? Comment [DMJ14]: Subject to Revision based on Work Package 3. Table 2: Planning Levels for Voltages in LV Systems Odd armonics Odd armonics (non-multiple of 3) (multiple of 3) Even armonics > > > (25/) Table 3: Planning Levels for Voltages in MV Systems Odd armonics Odd armonics (non-multiple of 3) (multiple of 3) Even armonics > > > (25/) Table 4: Planning Levels for Voltages in HV Systems Odd armonics Odd armonics (non-multiple of 3) (multiple of 3) Even armonics > > > (25/) Comment [jmc15]: Tese were used for 6.6, 11 and 20kV in G5/4. We ave used tem MV. Comment [jmc16]: Tese values were used for >20kV and <145kV in G5/4. We ave used tem HV. Page 11 of 25

12 Table 5: : Planning Levels for Voltages in EHV Systems Odd armonics Odd armonics (non-multiple of 3) (multiple of 3) Even armonics > > > (25/) Comment [jmc17]: Tese were used for just 275kV and 400kV in G5/4. We ave used tem for EHV in G5/ Compatibility Levels Table 6 provides te THD compatibility Levels for LV, MV, HV and EHV systems. Table 7 troug Table 10 provides te compatibility levels for Voltage Distortion in LV, MV, HV and EHV systems respectively. Table 6: THD Compatibility Levels Nominal Voltage THD Limit [%V 1] LV 8% MV 8% HV 5% EHV 3.5% Table 7: Voltage Compatibility Levels for LV Systems - from IEC Odd armonics Odd armonics (non-multiple of 3) (multiple of 3) Even armonics < < (10/) < (17/)-0.27 Table 8: Voltage Compatibility Levels for MV Systems - from IEC Odd armonics Odd armonics (non-multiple of 3) (multiple of 3) Even armonics < < (10/) < (17/)-0.27 Comment [DMJ18]: Subject to Revision based on Work Package 3. Comment [DMJ19]: I tink we sould remove reference to IEC Comment [jmc20]: Tis as been recalculated from 1.76 to 1.50 as G5/4 at 19 t armonic is above EN Comment [jmc21]: Tese values were defined up to 36.5kV by IEC. We ave defined tem up to 36kV. Comment [DMJ22]: I tink we sould remove reference to te IEC Comment [jmc23]: Tis as been recalculated from 1.76 to 1.50 as G5/4 at 19 t armonic is above EN Page 12 of 25

13 Table 9: Voltage Compatibility Levels for HV Systems Odd armonics Odd armonics (non-multiple of 3) (multiple of 3) Even armonics > > > (25/) Table 10: Voltage Compatibility Levels for EHV Systems Odd armonics Odd armonics (non-multiple of 3) (multiple of 3) Even armonics > > > (25/) Comment [jmc24]: Tese values were just defined for 66 and 132kV only. We ave defined tem for HV. Comment [jmc25]: Tese values were just defined for 275 and 400kV only. We ave defined tem for EHV. Comment [EP26]: Upper DC injected limit of 0.25% of total rated output AC current of SSEG system as been concluded. Tis limit was 5mA DC per SSEG in G77/1 wic was ten superseded by G83/1 and it seems tat safety factor of 1/2 as been applied. Comment [jmc27]: SS of WPD For te basis of te DC current emission limits see te ENA DC Injection Working Group report; refer to David ENA. Considerations include transformer noise. See also DCODE G Final (2).pdf. Comment [DMJ28]: Te Section on DC Emissions as been removed because of insufficient information; Tis Recommendation already declares DC emissions as problematic. Deleted: <#>DC Current Emissions Te effects of, and terefore limits for, DC currents injected in te DNO s Distribution System is an area under current investigation by DNO s. Until tese investigations are concluded te upper limit for DC injection is 0.25% of AC current rating per pase. Page 13 of 25

14 4 Assessment of Non-Linear and Resonant Connections Te assessment procedure for te connection of non-linear and resonant equipment follows tree stages. Te objective of tis tree-stage approac is to balance te degree of detail required by te assessment process wit te degree of risk tat te connection of te particular installation will result in unacceptable armonic voltage distortion levels occurring on te network if it is connected witout any mitigation measures. Section 0 provides general guidance on te application of te assessment and associated tecniques and metods. Sections 4.1.6, 4.3 and 4.4 present te process for Stage A, B and C assessments respectively. Figure 3 illustrates te tree-stage process wit te relevant decisions wic affect progress troug te tree stages. Comment [jmc29]: In response to SS comment below, if connection does not meet stage B, ten it is ten assessed in accordance wit stage C. Comment [jmc30]: SS of WPD Low Voltage equipment does not reac Stage C. For suc equipment no connection is possible witout mitigation. Figure 3: Tree-Stage Assessment Process Page 14 of 25

15 4.1 Guidelines Point of Evaluation Te Point of Evaluation (POE) is te point on te NOC s network were te impact of te nonlinear or resonant equipment upon armonic distortion is to be assessed against te planning levels of section 3.1. In most cases te POE will also be also be te PCC. If te assessment results in limits being issued to te customer, te POE is te point were te limits apply. For bot Stage A and B te POE is always te PCC. For a Stage A assessment, no limits are issued to te customer and permission to connect is eiter granted or denied. Te current emissions limits resulting from a Stage B assessment are issued at te PCC. For a Stage C assessment, more tan one POE migt exist. Te PCC will be te first POE at te commencement of te assessment but trougout it may become apparent tat oter nodes of te NOC s network require evaluation. Tis could be due to sifts in resonances modifying existing levels of armonic distortion or ow injected armonic currents propagate troug te network. Tese remote nodes ten become a POE as well as te PCC. Comment [DMJ31]: A scematic sowing te difference between te POE and PCC will be inserted System Impedance Assessment connections under Stages A, B and C require te armonic system impedance at te PCC to be taken into consideration troug calculation of te system fault level. Te system impedance at a particular frequency is needed in order to calculate te resulting armonic voltage distortion developed at a given node due to te connection of non-linear or resonant equipment. For bot Stage A and B assessments, te sort circuit power at te PCC is required. In order to calculate te maximum armonic voltage distortion, te minimum sort circuit power sall be used as tis corresponds to te maximum system impedance. For Stage C assessments, detailed armonic impedance models are required and sall be represented wit minimal simplification. For all stages of assessment, te calculation of te system armonic impedances sall consider relevant planned outages and various generation and demand backgrounds Aggregation and Diversity Wen assessing a connection of multiple non-linear equipments, it is sensible to aggregate te armonic current emissions. If linear addition of te armonic current emissions from te non-linear equipment results in te criteria of Stage A or B not being met, it is prudent to consider te diversity of operation of te non-linear equipment wit te use summation exponents in Table 11 and Equation (3). Exponent α Table 11: Summation Exponents Order 1.0 < >10 α U i i U = α ( ) (3) Te exponent α is cosen on te basis of te expected average pase angle between te armonic sources. An exponent of 1 implies tey are in pase (angle 0 ), wilst an exponent of 2 implies tey are at 90. An exponent of 1.4 implies an angle in te region of 70. Tese are to be adopted wen knowledge of te operation of te various equipments is known and realistic assumptions can be made about te addition of te armonic emissions. Page 15 of 25

16 4.1.4 Uncertainty Eac assessment will ave inerent uncertainty associated wit it wic can affect te outcome and any limits imposed on a connection. Due diligence is required to ensure suc uncertainties are acknowledged and minimised trougout te assessment. Suc uncertainties exist witin te: Modelling of te NOC s network and te non-linear and resonant connection, wic will affect te calculated resonances in te model; Absence of data; and Te measurement of background armonic distortion. Were necessary, derived values or data may be used in lieu of actual data so as to better inform te assessment and limit te uncertainty. Suc approaces are particularly useful for deriving values of background armonic voltage distortion at sites from wic measurements are unavailable using data obtained from adjacent sites and system impedance modelling Measurement General measurements of te existing levels of distortion on te network form part of bot Stage B and Stage C assessments in order to calculate te available eadroom for new connections. Stage B measurements are required to be made at te PCC, wilst under Stage C, measurements are required to be made at te PCC and at nodes deeper witin te network. Tese nodes could be at any voltage level and on networks not owned by te NOC. Te selection of tese remote nodes will be dependent upon te outcome of system studies identifying problematic transfer gains. It is recommended tat armonic measurements be carried out prior to and post energisation of te connection of te non-linear or resonant plant. Tis will aid compliance monitoring and ensure armonic emission limits imposed on te connection are met. It is beyond te scope of tis recommendation to give procedural details on performing measurements. Guidance on making armonic measurements is given in International Standard IEC [5]. Since te defined accuracy of a Class A power quality monitor according to IEC is limited to 0.1%, no measured value can be presented as lower tan 0.1%. Terefore, were measured values are eiter negligible or beyond te scope of te monitor, te values sall be rounded up to 0.1% across all armonic orders, sub- and inter-armonics. Transducers Voltage and current transducers are necessary wen performing armonic measurements at voltages above LV; for LV it is possible to connect measuring devices directly. Voltage transducers are typically voltage transformers wic form part of protective relay circuits or meter circuits. Suc VTs available are of te electromagnetic (wound) type, capacitive divider type and resistive voltage divider type. All transformers ave teir limitations in terms of frequency response and careful consideration needs to be given to te selection of VT. It is generally accepted tat electromagnetic VTs ave a frequency response up to one kiloertz and resistive voltage dividers up to undreds of kiloertz. Te lower capacitor unit of te capacitor divider type generally comprises a parallel inductance, wic overall gives an arrangement tuned to 50Hz. Tis arrangement is not suitable for armonic measurements. However, capacitor divider types can be modified wit CTs in suc a way as to extend te armonic frequency response up to tens of kiloertz wen necessary. It sould be noted tat te burden placed on te transformer secondary will affect te overall VT accuracy. Comment [jmc32]: Need a paragrap on CTs after tis one. Page 16 of 25

17 Instrumentation Instruments for armonic measuring are usually power quality monitors. For armonic measurements IEC [5], wic makes reference to te algoritm described in IEC [6], details two classes of accuracy for instrumentation measuring armonic components; tese are Class A and B. For te purpose of connection assessment and compliance monitoring it is recommended for te NOC to adopt a Class A device for armonic measuring and post-commissioning monitoring. Based on IEC , a 3 second and 10 minute caracteristic sould be measured, depending on te continuity of te connection s emissions. Tese values can ten be used as appropriate wen assessing te potential impact of any new item of non-linear equipment to be connected. Te 95% value from te cumulative probability function sould be used in te assessment process. Temporal and Seasonal Variation Levels of armonic distortion on transmission and distribution networks vary over a 24 our period, and between weekdays and weekends. It is important tat measurements be taken over a contiguous period of at least seven days, and in multiples of seven days i.e. 14, 21, etc. Were possible and practicable, winter peak and summer minimum demand periods sould be evaluated to cater for seasonal variation Non-Continuous Distortion Limits Sort-Duration Bursts and Fluctuating Distortion Non-continuous loads wic ave eiter sort-duration bursts or fluctuations sall be considered by selecting a more appropriate averaging period. Suitable averaging periods wic migt be selected include tree seconds, one minute and ten minutes. Wit respect to te affect of sort duration effects on armonic voltage distortion, compliance sall be assessed wit reference to te compatibility levels for individual armonic orders presented in Section 3.2, adjusted according to Equation (4), and wit a corresponding increase in te THD compatibility level of 11%. k = ( 5) / 45 (4) Comment [DMJ33]: Tis corresponds to te guidance in IEC Sub- and Inter-armonic Distortion Contingent upon te connection being compliant wit ER P28 for flicker [7], if te predicted sub-armonic and inter-armonic voltage emissions from an item of equipment or aggregate load are less tan 0.1% of te fundamental voltage, connections may be made witout any furter assessment. In te United Kingdom, it is assumed tat ripple control systems are not being used and terefore a customer s load, aving individual sub- or inter-armonic emissions less tan te following Table 12 limit values, may be connected witout assessment. Table 12: Sub- and Inter- Emission Limits Frequency [Hz] IHD [%V 1] Limits for particular inter-armonic frequencies between 80 and 90 Hz may be interpolated linearly from te limits given in Table 12. Page 17 of 25

18 Notcing Voltage notcing occurs during rectifier commutation wen two pases of te supply are effectively sort-circuited. Figure 4 illustrates a typical voltage caracteristic exibiting commutation notcing. Figure 4: An Explanation of Voltage Notcing Equipment tat results in voltage notcing can only be connected if te level of armonic distortion present at te PCC on te supply system is less tan te appropriate planning level. Te additional requirements at te PCC sall be: Te notc dept, d, sall not exceed 15% of te nominal fundamental peak voltage; Te notc duration, in seconds, sall not exceed: t = V nom (5) d Te peak amplitude of oscillations, due to commutation at te start and at te end of te notc, sall not exceed 10% of te nominal fundamental peak voltage. As a sort duration effect, te affect of notcing on armonic voltage distortion sall follow te same guideline as presented in Equation (4) above. Comment [DMJ34]: Tis as been derived using ER G5/4 Limits and te Guidance of IEEE519 on notc area using curve fitting. Page 18 of 25

19 4.2 Stage A Te Stage A assessment applies to all installations, including individual items of plant and equipment and groups of plant and equipment defined by teir aggregated effect. Stage A applies to installations to be connected to a PCC were te following condition would remain valid after said connection: Were: S S sc plant 0.8% S W nlrplant or 0.8% S plant represents te capacity of eac connection to te PCC, S nlrplant represents te capacity of eac non-linear or resonant plant or equipment connected to te PCC as eiter an individual item or as part of a group, W represents a weigting factor for eac type of equipment defined in Table 13, and S sc represents te sort-circuit power at te Point of Common Coupling Table 13: Weigting Factors for Various Types of Plant and Equipment [9] Equipment Type Single Pase Power Supply (Rectifier and Smooting Capacitor) Typical Current Waveform S sc Typical Current THD 80% wit ig 3 rd 2.5 Weigting Factor (6) Comment [DMJ35]: Te value of 08% is indicative and is based on te individual connection limit in IEC and IEC of 0.2% and its original basis of four connection per PCC. Tis metod, as opposed to just te IEC metod, prevents successive connections from leading to planning level breaces because te amount of non-linear and resonant capacity becomes a defining factor not just te singular connection under question. Semi-Converter Hig 2 nd, 3 rd and 4 t at partial loads Pulse Converter, Capacitive Smooting, No Series Inductance 80% Pulse Converter, Capacitive Smooting, Series Inductance > 3%; DC Drive 6-Pulse Converter, Large Inductor 40% % 0.8 AC Voltage Regulator Varies wit firing angle Pulse Converter 15% 0.5 Large Capacitive N/A 2.0 Element: HV/EHV Cable, PFC, Filter Oter N/A 2.5 Comment [DMJ36]: IEC references a resonance multiplier of 2 (Section Page 26), wic is te basis of tis indicative value. Page 19 of 25

20 All equipment and plant sall be permitted connection witout furter consideration contingent upon te condition presented in Equation (6) being met and te relevant condition below being met: Were: For LV installations wit aggregate ratings of less tan 16 A, te installation sall be compliant wit IEC [8]; For LV installations wit aggregate ratings of between 16 A and 75 A, te installation sall be compliant wit IEC [4]; For oter installations, and for LV installations wit aggregate ratings above 75 A, te armonic current emissions sall be below tose calculated using Equation (7); or For resonant plant at all voltage levels witout armonic current emissions, no furter criterion is applicable. I = V pl K K I represents te armonic current per pase in Amperes for te armonic order, Kr represents te resonant factor equal to: LV: for 7, K r = 1. 0 MV: for 8, K r = 2. 0 for > 7, K r = 0. 5 for > 8, K r = 1. 0 Kl represents a limit factor according to Table 14, V pl represents te planning level for te armonic order, and I sc represents te sort-circuit current at te PCC derived as l r I sc I sc = S sc 3 V nom (7) Comment [DMJ37]: Stage A as been made applicable to oter voltage levels as well because Section of ER G5/4-1 is essentially te same as a Stage A wit te exception tat it refers to Table 12 of ER G5/4-1 as opposed to an IEC standard. Tus tey were conceptually te same, and sould be grouped togeter by concept as opposed to voltage level. Futermore, IEC also allows for HV and EHV connections to be assessed simply. Comment [DMJ38]: Tis formula, along wit te associated Table 12, as been developed from first principles and provides a more appropriate format applicable to more scenarios. Table 14: Limit Factors for Equation (7) Order Factor Order Factor Order Factor Order Factor Comment [DMJ39]: Te same principle as for ER G5/4-1 is followed insofar as linear addition is used for 5 and triplens; and quadrature addition is used for all oter armonic orders. Page 20 of 25

21 4.3 Stage B A stage B assessment is indicated for LV and MV connections wen te criteria of a Stage A assessment are not met and te background armonic voltage distortion levels are likely to be considerable. Stage B follows a simple calculation wic involves: Determining te modified background armonics and apportioning te available eadroom according to te capacity of te connection under question, and Calculating te effect of te connection based on te equipment caracteristics, as declared by te equipment manufacturer, and using a linearised impedance model as used in Stage A Estimation of te Connection Headroom Wit consideration to te guidelines on measurement provided in Section 4.1.5, te Network Owner sall obtain measurements of armonic voltage distortion at te PCC from wic te total remaining eadroom for eac armonic order sall be calculated according to: V = V V r total pl bg for armonic orders subject to linear addition, and (8) Were: V = ( ) 2 V ( V ) 2 r total pl bg for armonic orders subject to quadratic addition Vr total represents te eadroom (remaining) armonic voltage distortion for armonic, Vpl is te armonic voltage distortion planning level for armonic, defined in Section 11, and Vbg is te measured background armonic voltage distortion for armonic. (9) Linear addition in accordance wit Equation (8) is applicable to: All orders less tan or equal to five, All triplens, and Oter site-specific problematic armonic orders. Te quadratic addition of Equation (9) is applicable to all oter orders. Once te total remaining eadroom as been determined, te eadroom available to te connection sall be calculated according to Equation (10). V S W nlrplant r = Vr total (10) Scapacity Were: Scapacity represents te connection capacity at te PCC. Tis provides a connection-related eadroom profile wic prejudices neiter te present, nor te possible future connections at te PCC, wilst considering te effects of te existing connections. Tis profile sall be considered as a guideline to te Network Owner; te ultimate decision as to te suitability of a connection rests wit te Network Owner. Te Network Owner may adjust tis profile, subject to te following limitations: Were background levels are below planning levels, te eadroom profile sall not lead to a breac of te planning levels, Were background levels are above planning levels, te profile sall be limited to 0.1%, and Were te calculated value falls below 0.1%, te value sall be raised to 0.1%. Page 21 of 25

22 4.3.2 Calculation of Connection Limits Having determined te armonic voltage distortion wic may be associated wit te new connection, a two-step calculation is necessary in order to: Determine te effect of te connection on te existing armonic distortion (wic is of particular importance for Resonant Plant), and Determine te current emission limits wit wic te connection must comply in order for te connection to qualify under a Stage B assessment. Te connection of Resonant Plant can magnify existing background armonic beyond te available connection eadroom. Equation (11) provides a simple means of approximating tis magnification. Were: S P Q sc c r V r bg < Vr by at least 0.1% (11) PCC Qc is te reactive power of te resonant plant, r is te resonant order, equal to S sc Qc P PCC is te active power delivered at te PCC, excluding tat from te present connection, V r bg if te background measurement for te resonant order r, and V r r is te connection eadroom calculated for te resonant order r according to Equation (10). Comment [DMJ40]: Tis equation as been developed from first-principles as an approximation to te modification and includes te effect of load (PCC) load wic provides damping. A caracteristic of tis equation is tat lower order resonances are more likely to not satisfy tis equation wilst iger order resonances are. Terefore, te connection of small or lower voltage resonant plant will qualify under tis Stage B criterion. Were a connection contains bot Resonant and Non-Linear Plant, Equation (11) sall be used to reduce te available eadroom at te resonant armonic order for use in te following determination of current emissions limits. Te available eadroom at te resonant armonic order is equal to te amount by wic te left-and side of Equation (11) is less tan te rigtand side, and sall not be less tan 0.1%, as indicated above. Te available connection eadroom is now used in combination wit a linear armonic impedance approximation according to Equation (12) to determine te current emission limits according to Om s law in Equation (13). Z 2 Vnom = K r (12) S sc Were: V Z r I = (13) Qc is te reactive power of te resonant plant, r is te resonant order, equal to S sc Qc P PCC is te active power delivered at te PCC, excluding tat from te present connection, V r bg if te background measurement for te resonant order r, and V r r is te connection eadroom calculated for te resonant order r according to Equation (10). A connection sall be permitted, witout furter consideration, if te conditions in Equations (11) and (13) are satisfied for Resonant and Non-Linear Plant Equipment respectively. Page 22 of 25

23 4.4 Stage C Engineering Recommendation G5/5 Tis final stage of assessment is applicable wen te calculations of a Stage B assessment indicate tat eiter a resonant condition exists wic jeopardises compliance or te emissions of te connection installation exceed tose calculated using a simplistic model of te system and plant caracteristics. Stage C requires detailed modelling of bot te system and te connected installation in an effort to more accurately predict te affect of te connected installation on te system. Te assessment of te connection under Stage C involves: 1. Identifying remote electrical nodes wic migt be affected by te connection of te installation, eiter by te propagation of armonic emissions or by te modification of te system armonic impedances; 2. Measurement of te background armonic voltage distortion at te PoE (and PCC were different) and at tese remote nodes as appropriate and practicable; 3. Calculation of te eadroom available to te connection according to Section 4.3.1; 4. Calculation of te modification to te background armonic voltage distortion resulting from te expected cange in system armonic impedances wit te new connection energised and operating; 5. Calculation of te incremental (additional) armonic voltage distortion impressed on te system by te armonic emissions of te connection; and 6. Prediction of te resultant armonic voltage distortion troug te system by an addition of te modified background armonic voltage distortion levels and te incremental armonic voltage distortion levels in te preceding calculations 4 and 5 respectively. For te purposes of addition, te criteria for te use of linear and quadratic addition sall follow te same principle defined in Section Te connection of te installation is acceptable if te result of te predicted resultant armonic voltage distortion levels is below te connection eadroom calculated according to Section Conclusion In support of te Electromagnetic Compatibility Regulations 2006 [1], tis Recommendation sets out te good practice for te limitation of armonic voltage disturbance on te public supply systems in te United Kingdom. Tis is acieved troug te definition of Planning and Compatibility limits for all power system voltage levels and a suitable tree-staged procedure for te assessment of te impact of equipment connections to te supply system. Bot non-linear and resonant plant connections are considered: non-linear plant because of teir associated armonic emissions and resonant plant because of te sift in network resonances wic migt result in non-compliance if not assessed. Page 23 of 25