T HARMONIC VOLTAGE DISTORTION AND THE...Resonant Plant to supply systems. This staged approach...

DRAFT

ENGINEERING RECOMMENDATION G5/5

HARMONIC VOLTAGE DISTORTION AND THE

CONNECTION OF NON-LINEAR AND RESONANT

PLANT AND EQUIPMENT TO TRANSMISSION

SYSTEMS AND DISTRIBUTION NETWORKS IN THE

UNITED KINGDOM Comment [DMJ1]: The Titlehas Changed to Include theterm ’Resonant Equipment’since this is as applicable forthe connection of HV Cableset. al. as it is for the con-nection of Non-Linear Load.

Comment [DMJ1]: The Titlehas Changed to Include theterm ’Resonant Equipment’since this is as applicable forthe connection of HV Cableset. al. as it is for the con-nection of Non-Linear Load.

Energy Networks Association

January 2015

1

DRAFT

ER G5/5, January 2015

Foreword

Engineering Recommendation G5/5 supersedes Engineering Recommendation G5/4-1 on

1st MONTH YEAR . Engineering Recommendation G5/4-1 will be withdrawn on that date. Comment [DMJ2]: Obvi-ously this date is presentlyundefined.

Comment [DMJ2]: Obvi-ously this date is presentlyundefined.For practical reasons, connections subject to contract specifications based on Engineering

Recommendation G5/4-1 entered into before the effective date above may, at the discre-

tion of the Network Operator, be connected in accordance with that recommendation.

Acknowledgement

Acknowledgements to be developed.

©ENA January 2, 2015

DRAFT

CONTENTS ER G5/5, January 2015

Contents

1 Introduction 5

1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.2 Exclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.3 Normative References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.4 Terms and Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2 Principles of Harmonic Voltage Distortion 11

2.1 Roles and Responsibilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.2 The Distinction between Planning and Compatibility Levels . . . . . . . . . . . . . . 12

3 Harmonic Voltage Distortion Levels 13

3.1 Planning Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.2 Compatibility Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4 Assessment of Non-Linear and Resonant Connections 18

4.1 Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4.1.1 Point of Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4.1.2 System Impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.1.3 Aggregation and Diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.1.4 Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.1.5 Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.1.6 Sub-Harmonic and Inter-harmonic Distortion . . . . . . . . . . . . . . . . . . . 23

4.1.7 Short-Duration Bursts and Fluctuating Harmonic Distortion . . . . . . . . . 23

4.1.8 Notching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

4.1.9 Marginal Results under Stage A and Stage B . . . . . . . . . . . . . . . . . . . 25

4.2 Stage A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

4.3 Stage B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.3.1 Calculation of the Connection Headroom . . . . . . . . . . . . . . . . . . . . . 28

4.3.2 Assessment of Resonant Conditions . . . . . . . . . . . . . . . . . . . . . . . . . 29

4.3.3 Assessment of Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

4.4 Stage C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

4.4.1 Identification of Remote Electrical Nodes . . . . . . . . . . . . . . . . . . . . . 32

4.4.2 Harmonic Impedance Representation of the Network . . . . . . . . . . . . . 32

4.4.3 Harmonic Design Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

4.4.4 Harmonic Performance Specification . . . . . . . . . . . . . . . . . . . . . . . . 35

4.4.5 Dealing with Concurrent Connections . . . . . . . . . . . . . . . . . . . . . . . . 36


DRAFT

CONTENTS ER G5/5, January 2015

5 Conclusion 39

References 40

Appendices 42

A Stage A Assessment Examples 42

A.1 Application of Equation 8 as the Stage A Qualifying Criterion . . . . . . . . . . . . 42

A.1.1 Connection of a Water Treatment Facility to an Existing Substation . . . . 42

A.1.2 Variation of Equation 8 With the Number of PCC Connections . . . . . . . . 43

A.1.3 Assessment Based on Non-Linear and Resonant Plant Capacity . . . . . . . 44

A.2 Calculation of Harmonic Current Limits Using Equation 9 . . . . . . . . . . . . . . . 45

A.3 Application of PWHD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

A.4 Low Voltage Assessments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

A.4.1 Connection of a 50 kVA Three-Phase Low Voltage Heat Pump . . . . . . . . 47

A.4.2 Connection of a 50 kVA Three-Phase Electric Vehicle Charger . . . . . . . . 48

A.4.3 Connection of a 10.35 kVA Single Phase Heat Pump . . . . . . . . . . . . . . 49

B Stage B Assessment Examples 51

B.1 Headroom Calculations Using Equations 10, 11 and 12 . . . . . . . . . . . . . . . . 51

B.2 Ensuring Resonance Compliance Using Equation 13 . . . . . . . . . . . . . . . . . . 52

B.3 Calculation of Harmonic Impedances and Current Limits Using Equations 14

and 15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

C Intermediary Voltage Distortion Levels 58


DRAFT

1 INTRODUCTION ER G5/5, January 2015

1 Introduction

The Electromagnetic Compatibility Regulations 2006[1], which implements into UK law the

Electromagnetic Compatibility Directive 2004/108/EC of the European Parliament[2], de-

fines the interaction of Equipment and Fixed Installations such that:

Regulation 4: “Equipment shall be designed and manufactured, having regard

to the state of the art, so as to ensure that it has a level of immunity to the

electromagnetic disturbance to be expected in its intended use which allows it to

operate without unacceptable degradation of its intended use”, and

Regulation 5: “A Fixed Installation shall be installed applying good engineering

practices; and respecting the information on the intended use of its components,

with a view to meeting the essential requirements set out in regulation 4.”

This Recommendation defines the good engineering practices applicable to harmonic volt-

age distortion on transmission and distributions systems in the UK, being Fixed Installations

by definition, so as to limit the disturbance levels thereon to below the immunity levels of

Equipment connected thereto.

Disturbance levels on supply systems are defined in terms of harmonic voltage distortion

and are affected by emissions of Non-Linear loads and generating plant as well as the con-

nection of Resonant Plant which modifies already existing disturbance levels. This recom-

mendation provides Planning and Compatibility disturbance levels on UK transmission and

distribution networks as well as a staged assessment plan for the connection of Non-Linear

and Resonant Plant and Equipment.

Section 2 defines the guiding principles of harmonic voltage distortion along with the roles

and responsibilities of the various parties involved in the electricity market. Specifically, it

covers the distinction between Planning, Compatibility and Immunity levels.

Section 3 defines the Planning and Compatibility limits applicable to the UK transmission

and distribution systems.

Section 4 describes a three-staged approach of assessing the connection of Non-Linear and

Resonant Plant to supply systems. This staged approach limits the assessment detail to an

approximate level to match the context of the connection being assessed, thus enabling

a pragmatic connection of plant and equipment. An assessment shall result in harmonic

voltage distortion and/or emission limits which shall inform the design of any necessary

mitigation measures, as required under the relevant transmission, distribution or genera-

tion licence or indeed the customer connection agreement as applicable.


DRAFT


There may be exceptional circumstances that can enable a Network Owner to permit a con-

nection of Non-Linear or Resonant Plant which is likely to cause levels of system voltage

distortion to exceed Planning Levels. However, the final decision as to whether or not par-

ticular equipment can be connected to a supply system rests with the Network Operating

Company responsible for the connection.

Appendix A and Appendix B provide application guidance for Stage A and B assessments

respectively. Appendix C demonstrates the graduation of distortion levels discussed in

Section 3.

1.1 Scope

This Recommendation provides the individual and total harmonic voltage distortion Plan-

ning and Compatibility limits which are applicable on the UK transmission and distribution

networks.

The general principles of Electromagnetic Compatibility, as applied to harmonic voltage

distortion, are presented along with guidance as to the development of emission limits

through a three-staged assessment procedure.

This recommendation is focussed on conducted phenomena resulting in the development

of harmonic voltages on the system, through the emission of harmonic currents, in the form

of:

• Continuous harmonic, sub-harmonic, inter-harmonic voltage distortion within the range

of 0 to 5 kHz, Comment [DMJ3]: This isthe scope of the recommen-dation. This caters for boththose who need to considerhigher orders and those whodon’t: if there are not effectsat higher orders on any par-ticular system, then there isno cause for concern.

Comment [DMJ3]: This isthe scope of the recommen-dation. This caters for boththose who need to considerhigher orders and those whodon’t: if there are not effectsat higher orders on any par-ticular system, then there isno cause for concern.

• Short bursts of harmonic voltage distortion, and

• Voltage notching.

Parts of this guidance are based on simplification which might not provide the optimal

solution under all operating conditions. The onus is on the responsible party to apply sound

engineering judgement where such circumstances arise and to adequately document the

justifications for applying alternative approaches and techniques.

Both the connection of Non-Linear load or generating plant and of Resonant Plant, namely

cables and shunt and series capacitive elements, fall under the requirements of the con-

nection assessment.


DRAFT


The levels and limits presented in this Recommendation are statistical in nature and are

applicable to the normal temporal variations which are characteristic of a power system

and to the credible outage scenarios which might prevail on the system.

This Recommendation applies the voltage level definitions of BS EN 60050[3] with the

extension of HV to 230 kV and the addition of EHV covering all voltages above 230 kV as

per the Terms and Definitions in Section 1.4.

1.2 Exclusions

This Recommendation does not cover the design of mitigation measures to ensure compli-

ance with any harmonic voltage distortion or emission limits which result from the applica-

tion of the assessment procedure.

This Recommendation does not replace nor negate the relevant harmonised equipment

standards which are applicable to particular equipment, and are a pre-requisite for Elec-

tromagnetic Compatibility of the equipment under the terms of the UK Regulations[1]. Ra-

diated interference which might affect communications systems is not considered in this

recommendation.

Harmonic voltage distortion arising from switching transients is not considered in this Rec-

ommendation.

This Engineering Recommendation does not contain provisions for DC current emissions

because of their deleterious effects on the supply system. Therefore, all DC emissions are

deprecated. However the final decision regarding the connection of any DC-emitting plant

and equipment is at the discretion of the Network Owner.

1.3 Normative References

The following referenced documents are indispensable for the application of this document.

For dated references, only the edition cited applies; for undated references, the latest

edition of the referenced document (including any amendments) applies.

• IEC 60050(161) – International Electrotechnical Vocabulary – Chapter 161: Electro-

magnetic Compatibility


DRAFT


1.4 Terms and Definitions

Further to the definitions in Chapter 161 of IEC 60050, the following terms and definition

apply throughout this Recommendation.

Background Harmonic Distortion Level The level of harmonic distortion, defined in terms

of the Individual and Total Harmonic Distortion levels, which exists without the connec-

tion of the Non-Linear or Resonant Plant under assessment. This typically represents

the pre-existing state of the network, but might also include predicted levels resulting

from the effects of nearby contemporary connections.

Compatibility Level The level of harmonic distortion, defined in terms of the Individual

and Total Harmonic Distortion levels, within which the network should be operated.

Extra High Voltage Voltage with a nominal RMS value of greater than 230 kV.

Fault Level A fictive or notional value expressed in MVA of the initial symmetrical short-

circuit power at a point on the Supply System. It is defined as the product of the initial

symmetrical short-circuit current, the nominal system voltage and, for three-phase

systems, the factor with the aperiodic component (DC) being neglected.

High Voltage Voltage with a nominal RMS value of greater than 36 kV and less than or

equal to 230 kV.

Individual Harmonic Distortion (IHD) The RMS value of an individual harmonic voltage

or current expressed as a percentage of the fundamental RMS voltage or current.

Low Voltage Voltage with a nominal RMS value of less than or equal to 1 kV.

Medium Voltage Voltage with a nominal RMS value of greater than 1 kV and less than or

equal to 36 kV.

Normal Operating Conditions Normal Operating Conditions include the variation of gen-

eration, demand and plant and equipment energisation as a consequence of temporal,

seasonal and operational variability, including credible planned outages, under which

the system is expected to operate.


DRAFT


Partial Weighted Harmonic Distortion (PWHD) Ratio of the RMS value of higher order

harmonic current emissions between h = 23 and h = 100 weighted with the harmonic

order h, to the RMS value of the short-circuit current:

PWHD =

√

√

√

√

h=100∑

h=23

h

�

h

sc

�2

(1)

Where:

h represents the Individual Harmonic Distortion in Amperes, and

sc represents the Fault Level in Amperes.

Note: The Partial Weighted Harmonic Distortion (PWHD) is employed to provide a

margin for some high order harmonics to exceed specified limits whilst still ensuring

that the overall heating effect of high order harmonics does not exceed acceptable

limits. The PWHD used in ER G5/5 is based on the equation used in Section 3.2 of

BS EN 61000-3-12[5].

Planning Level The level of harmonic distortion, defined in terms of the Individual and To-

tal Harmonic Distortion levels, against which the connection of Non-Linear or Resonant

plant is assessed.

Point of Common Coupling (PCC) The point in the public Supply System, electrically

nearest to a Customer’s installation, at which other Customers’ loads are, or may be,

connected.

Point of Evaluation (PoE) A point in the public Supply System where the effect of the

connection is assessed.

Root Mean Square The square root of the average of the squared values.

Short Burst A burst in power system harmonics occurring in a time interval that is short

when compared to the time-scale of interest such that its effect during the time-scale

of interest is unnoticeable.

Supply System All the lines, switchgear and transformers operating at various voltages

which make up the transmission systems and distribution systems to which Cus-

tomers’ installations are connected.


DRAFT


Total Harmonic Current (THC) The RMS value of individual harmonic currents in Am-

peres calculated using the following expression:

THC =

√

√

√

√

h=100∑

h=2

�

h�2

(2)

Where:

h represents the Individual Harmonic Distortion in Amperes, and

h represents the harmonic order

Total Harmonic Distortion (THD) The RMS value of individual harmonic voltages ex-

pressed as a percentage of the fundamental RMS voltage, and calculated using the

following expression:

THD =

√

√

√

√

h=100∑

h=2

�

Vh�2

(3)

Where:

Vh represents the Individual Harmonic Distortion in percent, and

h represents the harmonic order

The parameter h = 100 represents the highest harmonic order under consideration.

The increasing number of power-electronic interfaces with supply systems has made

it necessary to consider integer values of h up to and including 100.


DRAFT

2 PRINCIPLES OF HARMONIC VOLTAGE DISTORTION ER G5/5, January 2015

2 Principles of Harmonic Voltage Distortion

Voltage distortion has long been recognised as being able to interfere with telecommuni-

cations systems, to increase losses in circuits and equipment, and to cause overheating of

rotating plant and capacitors, the latter being particularly susceptible to damage.

Section 2.1 defines the roles and responsibilities held by the relevant parties in ensuring

that the permissible levels of harmonic distortion are not exceeded.

Section 2.2 details the distinction between the planning, compatibility and immunity levels

of harmonic distortion, to which the parties are required to comply.

2.1 Roles and Responsibilities

The connection of Non-Linear or Resonant Plant will either be part of a Network Owner’s

investment strategy or be the result of a Customer connection to the Network Owner’s

system. The Network Operator is ultimately responsible for compliance under operational

timescales; under planning timescales, responsibility is delegated to the Network Owner

(where different). In planning for harmonic compliance when considering Customer con-

nections, a Network Owner may place additional responsibilities upon a Customer through

the terms of a Connection Agreement between the Customer and Network Operator.

The Network Operator is responsible for the overall co-ordination of disturbance levels

under normal operating conditions in accordance with national requirements and shall refer

to the Compatibility Levels herein.

The Network Owner is responsible for assessing the impact of any connection of Non-Linear

or Resonant Plant to their network. This assessment must cover all affected networks,

including Distribution and Onshore and Offshore Transmission Networks and shall refer to

the Planning Levels herein.

The Network Owners and Network Operator shall provide, where necessary and practicable,

any Network Data, such as harmonic impedance data, necessary to enable the Network

Owner hosting the connection to fully assess the impact on harmonic levels on all affected

networks to ensure that the overall Supply System harmonic voltage levels will not exceed

Planning and Compatibility Levels. This harmonic assessment is to consider the effect of

emissions as well as modification to existing harmonic levels due to resonance effects.


DRAFT

2 PRINCIPLES OF HARMONIC VOLTAGE DISTORTION ER G5/5, January 2015

2.2 The Distinction between Planning and Compatibility Levels

The basic concepts of the Planning Level, the Compatibility Level and Equipment Immunity

are illustrated in Figure 1.

System-WideDisturbance

(Location & Time)

SiteDisturbance

(Time)

System-WideEquipmentImmunity

(Location & Time)

SiteEquipmentImmunity

(Time)

CompatibilityLevel

PlanningLevel

Disturbance Level

Pro

bab

ility

Densi

ty

Figure 1: Illustration of Statistical Power Quality Concepts

Figure 1 illustrates the relationship between the time-based distribution of an individual

site’s disturbance and equipment immunity. Equipment Immunity Levels are specified by

relevant standards or agreed upon between manufacturers and customers.

The system-wide distributions of disturbance and equipment immunity are over both loca-

tion and time and are therefore wider than those of a specific site.

The Compatibility Level is set at the 95th percentile of the system-wide disturbance; the

Planning Level is lower than this by the lesser of either 0.1% absolute or 10% of the Compat-

ibility Level. This differential ensures that there is enough margin to account for planning

uncertainty and operational variability.


DRAFT

3 HARMONIC VOLTAGE DISTORTION LEVELS ER G5/5, January 2015

3 Harmonic Voltage Distortion Levels

Planning and Compatibility Levels for all voltage levels are given in Tables 1 to 10. Comment [DMJ4]: The volt-age levels have been rede-fined from previous Recom-mendation G5/4-1 to includeall possible system operatingvoltages. The voltage lev-els for LV, HV and EHV are inline with IEC 61000-3-6. Theupper range limit for MV is36 kV to account for a 10%operational level for 33 kV.

Comment [DMJ4]: The volt-age levels have been rede-fined from previous Recom-mendation G5/4-1 to includeall possible system operatingvoltages. The voltage lev-els for LV, HV and EHV are inline with IEC 61000-3-6. Theupper range limit for MV is36 kV to account for a 10%operational level for 33 kV.

Where an Intermediary Voltage (IV) level, being either LV, MV or HV, is present between

two successive voltage bands (LV, MV, HV and EHV ), as part of a series of transforma-

Comment [DMJ5]: The IVconcepts works on the upperof the two voltages within aband e.g. 33 kV is the IV ifthe MV is 11 kV. Therefore,275 kV cannot be graduated,and 400 kV is not betweentwo other voltages. There-fore, this will typically applyto:- 132kV in 132/66/33kV;- 33kV in 132/33/11kV;- 22kV in 132/22/11kV; or- 11kV in 132/11/6.6kV.If we adjusted the lower oftwo voltage levels within aband, then the downstreamvoltage level e.g. 400Vwould not be protected.The general concept is grad-uate upwards. There seemsno way to make this conceptmore generic without usingMV as an example.

Comment [DMJ5]: The IVconcepts works on the upperof the two voltages within aband e.g. 33 kV is the IV ifthe MV is 11 kV. Therefore,275 kV cannot be graduated,and 400 kV is not betweentwo other voltages. There-fore, this will typically applyto:- 132kV in 132/66/33kV;- 33kV in 132/33/11kV;- 22kV in 132/22/11kV; or- 11kV in 132/11/6.6kV.If we adjusted the lower oftwo voltage levels within aband, then the downstreamvoltage level e.g. 400Vwould not be protected.The general concept is grad-uate upwards. There seemsno way to make this conceptmore generic without usingMV as an example.

tion stages, the Planning and Compatibility levels for THD and IHD shall be adjusted for

that particular IV level according to Equation 4, which demonstrates the scaling applica-

ble between MV and HV. This equation is graphically represented in Figure 2 and provides

sufficient graduation through the successive voltage transformation stages.

VDLV = VDLMV − (VDLMV − VDLHV) ×

√

√

√

Vnom−V − Vnom−MVVnom−HV − Vnom−MV

(4)

Where:

VDLn represents the nominal voltage, in kilo-Volts, at the voltage level n.

Vnom represents the nominal voltage, in kilo-Volts, at the voltage level n.

HV

IV

MV

Volta

geD

isto

rtio

nLe

vel[

%]

MV IV HVNominal Voltage [kV]

Figure 2: Adjustment of Voltage Distortion Levels for an Intermediary Voltage Level Withina Series of Transformation Stages Between Two Voltage Bands

The quadratic relationship ensures a greater graduation effect in the lower region of the

voltage range. For example, an IV between 11 kV (MV) and 132 kV (HV) is likely to be 20,

22 or 33 kV which are sufficiently separated from 132 kV such that a linear relationship

would not prove useful.


DRAFT


Using a MV busbar for the IV, if this IV busbar is connected to both an MV and LV busbar,

as shown in Figure 3, the IV busbar shall be assigned the Voltage Distortion Levels as

calculated using Equation 4 and not the MV Voltage Distortion Levels. This protects the LV

busbars.

HV IV MV

LV

Figure 3: Parallel Connections from HV through to LV

3.1 Planning Levels

Table 1 provides the THD planning Levels for LV, MV, HV and EHV systems. Tables 2 to

Table 5 provide the Planning Levels for Harmonic Voltage Distortion in LV, MV, HV and EHV

systems respectively.

Table 1: THD Planning Levels

Nominal Voltage THD [%V1]

LV 5MV 4HV 3EHV 3

Table 2: Planning Levels for Harmonic Voltages in LV Systems

Odd harmonics Odd harmonics Even harmonics(non-multiple of 3) (multiple of 3)

Order h Vhp [%] Order h Vhp [%] Order h Vhp [%]

5 4.00 3 4.00 2 1.607 4.00 9 1.20 4 0.90

11 3.00 15 0.30 6 0.4513 2.50 21 0.20 8 0.4017 1.60 ≥27 0.18 10 0.4019 1.20 ≥12 0.2023 1.20

≥25 0.5025h + 0.20


DRAFT


Table 3: Planning Levels for Harmonic Voltages in MV Systems



5 3.00 3 3.00 2 1.507 3.00 9 1.20 4 0.90

11 2.00 15 0.30 6 0.4513 2.00 21 0.20 8 0.4017 1.60 ≥27 0.18 10 0.4019 1.20 ≥12 0.2023 1.20

≥25 0.5025h + 0.20

Table 4: Planning Levels for Harmonic Voltages in HV Systems



5 2.00 3 2.00 2 1.007 2.00 9 1.00 4 0.80

11 1.50 15 0.30 6 0.4513 1.50 21 0.20 8 0.4017 1.00 ≥27 0.18 10 0.4019 1.00 ≥12 0.2023 0.70

≥25 0.5025h + 0.20

Table 5: Planning Levels for Harmonic Voltages in EHV Systems



5 2.00 3 1.50 2 1.007 1.50 9 0.50 4 0.80

11 1.00 15 0.30 6 0.4513 1.00 21 0.20 8 0.4017 0.50 ≥27 0.18 10 0.4019 0.50 ≥12 0.2023 0.50

≥25 0.3025h + 0.20


DRAFT


3.2 Compatibility Levels

Table 6 provides the THD compatibility Levels for LV, MV, HV and EHV systems. Tables 7

to Table 10 provide the Compatibility Levels for Harmonic Voltage Distortion in LV, MV, HV

and EHV systems respectively.

Table 6: THD Compatibility Levels

Nominal Voltage THD [%V1]

LV 8MV 8HV 5EHV 3.5

Table 7: Compatibility Levels for Harmonic Voltages in LV Systems



5 6.00 3 5.00 2 2.007 5.00 9 1.50 4 1.00

11 3.50 15 0.33 6 0.5013 3.00 21 0.30 8 0.50

17 2.00 ≥27 0.20 ≥10 0.2510h + 0.25

19 1.50

≥23 1.6823h − 0.27

≥53 0.2653h + 0.22

Table 8: Compatibility Levels for Harmonic Voltages in MV Systems



5 6.00 3 5.00 2 2.007 5.00 9 1.50 4 1.00

11 3.50 15 0.40 6 0.5013 3.00 21 0.30 8 0.50

17 2.00 ≥27 0.20 ≥10 0.2510h + 0.25

19 1.50

≥23 1.6823h − 0.27

≥53 0.2653h + 0.22


DRAFT


Table 9: Compatibility Levels for Harmonic Voltages in HV Systems



5 4.00 3 2.10 2 1.107 2.10 9 1.10 4 0.88

11 1.60 15 0.33 6 0.5013 1.60 21 0.22 8 0.4417 1.10 ≥27 0.20 10 0.4419 1.10 ≥12 0.2223 0.77

≥25 0.5525h + 0.22

Table 10: Compatibility Levels for Harmonic Voltages in EHV Systems



5 3.00 3 1.70 2 1.107 1.60 9 0.55 4 0.88

11 1.10 15 0.33 6 0.5013 1.10 21 0.22 8 0.4417 0.55 ≥27 0.20 10 0.4419 0.55 ≥12 0.2223 0.55

≥25 0.22 + 0.3325h

Comment [DMJ6]: The Sec-tion on DC Emissions hasbeen removed because ofinsufficient information; ThisRecommendation alreadydeclares DC emissions asproblematic.

Comment [DMJ6]: The Sec-tion on DC Emissions hasbeen removed because ofinsufficient information; ThisRecommendation alreadydeclares DC emissions asproblematic.


DRAFT

4 ASSESSMENT OF NON-LINEAR AND RESONANT CONNECTIONS ER G5/5, January 2015

4 Assessment of Non-Linear and Resonant Connections

The assessment procedure for the connection of Non-Linear and Resonant Plant and Equip-

ment follows three stages. The objective of this three-stage approach is to balance the

degree of detail required by the assessment process with the degree of risk that the con-

nection of the particular installation will result in unacceptable harmonic voltage distortion

levels occurring on the network if it is connected without any mitigation measures.

Section 4.1 provides general guidance on the application of the assessment and associated

techniques and methods.

Sections 4.2, 4.3 and 4.4 present the process for Stage A, B and C assessments respec-

tively. Figure 4 illustrates the three-stage process with the relevant decisions which affect

progress through the three stages. It is recommended that LV connections are not pro-

gressed through to a Stage C assessment because of the relative time- and cost-efficiencies

of providing mitigation when compared to those of a Stage C assessment.

4.1 Guidelines

4.1.1 Point of Evaluation

The Point of Evaluation (PoE) is the point on the Network Owner’s network where the im-

pact of the Non-Linear or Resonant Plant and Equipment upon harmonic distortion is to be

assessed against the Planning Levels of Section 3.1.

In most cases the PoE will also be the Point of Common Coupling (PCC). For both Stage A

and B the PoE is always the PCC. For a Stage C assessment, more than one PoE might

exist as a result of either shifts in resonances at or the propagation of harmonics through

to remote nodes in the network.

If the assessment results in limits being issued for the connection, the PCC is the point

where the limits apply. For Stage A and Stage B assessments, the Network Operator may

limit the customer’s current emissions according to the calculations in Section 4.2 and 4.3

respectively. For Stage C assessments, the Network Operator may limit the voltage emis-

sions which must be accompanied by a harmonic impedance representation of the network

according to the calculations in Section 4.4.


DRAFT


Start

∑

Snrpnt×WSsc

Individual LV

Equipment?

≤ 16A and

BS EN 61000-3-2

Compliant?

≤ 75A and

BS EN 61000-3-12

Compliant?

Minimum

Fault Level

Achievable?

h below

Equation 9

Limit Values?

Section 4.1.9

Marginal

Conditions

Met?

Measure PCC

Background

Distortion

Calculate Total

Headroom

Equation 10

Calculate Resonance

Headroom

Equation 11

Risk of

Resonance?

Equation 13

Calculate Emission

Headroom

Equation 12

h below

Equation 15

Limit Values?

Section 4.1.9

Marginal

Conditions

Met?

Identify Affected

Remote Nodes

Measure Remote

Background

Distortion

Calculate Re-

mote Total

Headroom Equa-

tions 10 and 12

Generate

Impedance Loci

Section 4.4.2

Calculate Design

Limits Section 4.4.3

Harmonic Design

Specification

Design & Assess

Performance

Complies

with Design

Specification?

Calculate

Performance Limits

Section 4.4.4

Harmonic Performance

Specification

Permit

Connection

≤ β

Y

N

N

N

Y Y

Y

N

N Y

Y

> β N

N

Y

N Y

NY

N Y

Sta

ge

ASta

ge

BSta

ge

C

Figure 4: Three-Stage Assessment Process


DRAFT


4.1.2 System Impedance

Connection assessments under Stages A, B and C require the harmonic system impedance

at the PCC to be taken into consideration, either directly or through calculation of the

system fault level. The system impedance at a particular frequency is needed in order to

calculate the resulting harmonic voltage distortion developed at a given node due to the

connection of Non-Linear or Resonant Plant and Equipment.

For both Stage A and B assessments, the short circuit power at the PCC is required. In order

to calculate the maximum harmonic voltage distortion, the minimum short circuit power

expected for planned system conditions shall be used, taking into account maintenance

and operational variations. For Stage C assessments, detailed harmonic impedance models

are required and shall be represented with minimal simplification.

For all stages of assessment, the calculation of the system harmonic impedances shall

consider relevant planned outages and various generation and demand backgrounds as

defined by the Normal Operating Conditions. Comment [DMJ7]: Thisclarifies that multiple net-work configurations must beconsidered. The definitionof Normal Operating Condi-tions has been added to theDefinitions list.

Comment [DMJ7]: Thisclarifies that multiple net-work configurations must beconsidered. The definitionof Normal Operating Condi-tions has been added to theDefinitions list.

4.1.3 Aggregation and Diversity

Equation 5 provides a means of aggregating multiple values for each harmonic order based

on the summation exponents in Table 11. This accounts for the operation of multiple Non-

Linear Equipment through the aggregation of their individual harmonic emissions. This

form of aggregation is only valid based on a realistic appreciation of the equipments’ oper-

ational diversity, without which linear addition shall be employed.

Vh = α

√

√

√

∑

�

Vh�α

(5)

Table 11: Summation Exponents

Exponent α Harmonic Order

1.0 h ≤ 51.4 5 < h ≤ 102.0 h > 10

Comment [DMJ8]: Noticethat this is different from IECaggregation insofar as the5th is linear. This aligns withER G5/4-1

Comment [DMJ8]: Noticethat this is different from IECaggregation insofar as the5th is linear. This aligns withER G5/4-1

The exponent α is chosen on the basis of the expected average phase angle between

the harmonic sources. An exponent of 1.0 implies they are in phase (angle 0◦), whilst an

exponent of 2.0 implies they are at 90◦. An exponent of 1.4 implies an angle in the region

of 70◦.


DRAFT


4.1.4 Uncertainty

Each assessment will have inherent uncertainty associated with it which can affect the

outcome and any limits imposed on a connection. Due diligence is required to ensure

such uncertainties are acknowledged and minimised throughout the assessment. Such

uncertainties exist within the:

• Modelling of the Network Owner’s network and the Non-Linear and Resonant connec-

tion, which will affect the calculated resonances in the model;

• Absence of data;

• Relevant future network variations which will not be subject to their own assessment

according to this Recommendation; and

• The measurement of background harmonic distortion.

Where necessary, derived values or data may be used in lieu of actual data so as to better

inform the assessment and limit the uncertainty. Such approaches are particularly useful

for deriving values of background harmonic voltage distortion at sites from which mea-

surements are unavailable using data obtained from adjacent sites and system impedance

modelling.

4.1.5 Measurement

Harmonic measurements of the existing levels of distortion on the network form part of

both Stage B and Stage C assessments in order to calculate the available headroom for

new connections.

Stage B measurements are required to be made at the PCC, whilst under Stage C, mea-

surements are required to be made at the PCC and at nodes elsewhere within the network.

These nodes could be at any voltage level and on networks not owned by the host Network

Owner. The selection of these remote nodes will be dependent upon the outcome of system

studies identifying problematic transfer gains. It is recommended that harmonic measure-

ments be carried out prior to and post energisation of the connection of the Non-Linear or

Resonant Plant. This will aid compliance monitoring and ensure harmonic emission limits

imposed on the connection are met.


DRAFT


Instrumentation: Instruments for harmonic measuring are usually power quality mon-

itors. For harmonic measurements BS EN 61000-4-30[7], which makes reference to the

algorithm described in BS EN 61000-4-7[6], details two classes of accuracy for instrumen-

tation measuring harmonic components; these are Class A and B. For the purpose of con-

nection assessment and compliance monitoring it is recommended for the Network Owner

to adopt a Class A device for harmonic measuring and post-commissioning monitoring.

The minimum defined accuracy of a Class A power quality monitor according to BS EN 61000-

4-30 is 0.1%. This factor should only be incorporated into the final results of an assessment

so as to prevent double-accounting, especially in the calculation of background modifica-

tion. Comment [DMJ9]: Prevents0.1% for noise being ficti-tiously amplified beyondPlanning Levels.

Comment [DMJ9]: Prevents0.1% for noise being ficti-tiously amplified beyondPlanning Levels.Based on BS EN 61000-4-30, a ten minute characteristic should be measured and the 95th

percentile value from the cumulative probability function should be used in the assessment

process. Section 4.1.7 considers the use of alternative aggregation periods depending on

the continuity of the connection’s emissions.

Temporal and Seasonal Variation: Levels of harmonic distortion on transmission and

distribution networks vary over a 24 hour period, and between weekdays and weekends. It

is important that measurements be taken over a contiguous period of at least seven days,

and in multiples of seven days i.e. 7,14, 21, etc. Where possible and practicable, winter

peak and summer minimum demand periods should be evaluated to cater for seasonal

variation.

For the purpose of planning studies, the 95th percentile value should be applied to mea-

surements over the longest possible integer number of weeks and assessed against the

Planning Levels. For the purpose of compliance assurance, the 95th percentile value should

be applied to each week of measurement and assessed against Compatibility Levels on a

week-by-week basis.

Transducers: Voltage transducers are necessary when performing harmonic measure-

ments at voltages above LV; for LV it is possible to connect measuring devices directly.

Voltage transducers are typically voltage transformers which form part of protective relay

circuits or meter circuits. Such VTs available are typically of the electromagnetic (wound)

type, capacitive divider type and resistive-capacitive voltage divider type. All transformers

have their limitations in terms of frequency response and careful consideration needs to be

given to their selection.


DRAFT


Electromagnetic VTs have a useful frequency response up to approximately one kilo-Hertz

and resistive-capacitive voltage dividers up to hundreds of kilo-Hertz. The lower section of a

capacitor divider type generally comprises a capacitor in parallel with an electromagnetic

VT. This arrangement is tuned to 50 Hz and is not suitable for harmonic measurements

because the higher frequencies pass through the capacitor and not the electromagnetic

VT. However, capacitor divider types can be modified with ring-CTs on the earth links of the

lower capacitor and electromagnetic VT in such a way as to extend the harmonic frequency

response up to tens of kilo-Hertz when necessary.

4.1.6 Sub-Harmonic and Inter-harmonic Distortion

Contingent upon the connection being compliant with ER P28 for flicker[8], if the predicted

sub-harmonic and inter-harmonic voltage emissions from an item of equipment or aggre-

gate load are less than 0.1% of the fundamental voltage, connections may be made without

any further assessment.

In the United Kingdom, it is assumed that ripple control systems are not being used and

therefore a customer’s load, having individual sub- or inter-harmonic emissions less than

the following Table 12 limit values, may be connected without assessment.

Table 12: Sub- and Inter-Harmonic Emission LimitsFrequency [Hz] IHD [%V1]

≤ 80 0.2≥ 90 0.5

Limits for particular inter-harmonic frequencies between 80 and 90 Hz may be interpolated

linearly from the limits given in Table 12.

4.1.7 Short-Duration Bursts and Fluctuating Harmonic Distortion

Non-continuous loads which have either short-duration bursts or fluctuations shall be con-

sidered by selecting a more appropriate aggregation period of either one minute or three

seconds. The 99th percentile value of these measurements is to be used for the purposes

of planning and compliance.

With respect to the effect of short duration effects on harmonic voltage distortion, compli-

ance shall be assessed with reference to the Compatibility Levels for individual harmonic


DRAFT


orders presented in Section 3.2, multiplied by a factor k as defined in Equation 6, and with

a corresponding increase in the THD Compatibility Level by a factor ofp2. Comment [DMJ10]: This

corresponds to the guidancein IEC 61000-2-12. The guid-ance in IEC 61000-2-12 isbased on an MV THD Com-patibility Level of 8% forlong-term effects and 11%for short-duration effects.This increase is approxi-mately

p2 (11/8=1.375;p

2=1.42).

Comment [DMJ10]: Thiscorresponds to the guidancein IEC 61000-2-12. The guid-ance in IEC 61000-2-12 isbased on an MV THD Com-patibility Level of 8% forlong-term effects and 11%for short-duration effects.This increase is approxi-mately

p2 (11/8=1.375;p

2=1.42).

k = 1.3 + 0.7 ×�

h − 5

45

�

(6)

4.1.8 Notching

Voltage notching occurs during rectifier commutation when two phases of the supply are

effectively short-circuited, being connected to each other through only their commutating

impedances. Figure 5 illustrates a typical voltage characteristic exhibiting commutation

notching.

t [s]

d [p..]

Figure 5: A Depiction of Voltage Notching

Equipment that results in voltage notching can only be connected if the level of harmonic

distortion present at the PCC on the supply system is less than the appropriate Planning

Level. The additional requirements at the PCC shall be: Comment [DMJ11]: Thishas been derived usingER G5/4-1 Limits and theGuidance of IEEE519 onnotch area using curve fit-ting.

Comment [DMJ11]: Thishas been derived usingER G5/4-1 Limits and theGuidance of IEEE519 onnotch area using curve fit-ting.

• The notch depth, d, shall not exceed 15% of the nominal fundamental peak voltage;

• The notch duration, in seconds, shall not exceed:

t =2.23 × 10−7

pd

Vnom (7)

Where:

Vnom represents the nominal system voltage in kV.

• The peak amplitude of oscillations, due to commutation at the start and at the end of

the notch, shall not exceed 10% of the nominal fundamental peak voltage.

As a short duration effect, the effect of notching on harmonic voltage distortion shall follow

the same guideline as presented in Equation 6.


DRAFT


4.1.9 Marginal Results under Stage A and Stage B

With the exception of the triplen and fifth harmonic orders, any two emission currents up

to the nineteenth and any four emission currents above the nineteenth may exceed the

calculated limit by up to 10% in both Stage A and B assessments without progression onto

the next stage of assessment.

For connections where multiple harmonic current emissions of orders 23 ≤ h ≤ 100 marginally

exceed the calculated limits, the connection could still be acceptable without progression

onto the next stage of assessment if the PWHD value does not exceed the relevant value

of Table 13. The use of the PWHD method does not remove the requirement to comply with

the applicable THD Planning Levels defined in Section 3.1.

Table 13: PWHD LimitsNominal Voltage PWHD Limit [%V1]

LV 0.92MV 0.46HV 0.43EHV 0.36

4.2 Stage A

The Stage A assessment applies to all installations, including individual items of plant and

equipment and groups of plant and equipment defined by their aggregated effect, where:

• The existing distortion is sufficiently below the Planning Level, i.e. less than 75%

thereof, such that there is little risk of exceeding the Planning Levels;

• Any amplification resulting from system resonances is not expected to exceed a factor

of two; and where

• There is no risk of interference with other customers or system plant and equipment.

Stage A applies to installations to be connected to a PCC where the condition of Equation 8

would remain valid after the connection. The summation represents the total capacity of

all connections to a PCC and not that of an individual connection.

∑

Snrpnt ×W

Ssc≤ β (8)


DRAFT


Where:

Snrpnt represents the MVA capacity of each connection’s Non-Linear or Resonant

Plant or Equipment connected to the PCC;

W represents a weighting factor, defined as:

THD100 for Non-Linear plant; and

1.0 for Resonant Plant.

THD represents the Total Harmonic Current Distortion, in percent;

Ssc represents the Fault Level in MVA at the Point of Common Coupling; and

β is defined according to the voltage level as:

1.44% for LV;

0.57% for MV;

0.41% for HV; and

0.32% for EHV;

If the knowledge of existing Non-Linear Plant is not be readily available, each feeder’s term

of Snrpnt×THD/100 in the summation may be replaced by the aggregated Total Harmonic

Current (THC) in kilo-Amperes at the feeder, multiplied byp3Vnom.

All equipment and plant shall be permitted connection without further consideration con-

tingent upon the condition presented in Equation 8 being met and the relevant condition

below being met:

• Individual LV equipment with ratings of less than or equal to 16 A shall comply with

BS EN 61000-3-2[4];

• Individual LV equipment with ratings of more than 16 A and less than or equal to

75 A shall comply with BS EN 61000-3-12[5]. In association with a manufacturer’s

statement of compliance with BS EN 61000-3-12, it is necessary to meet the associ-

ated minimum fault level requirements to ensure voltage distortion is controlled as

intended. Appendix A provides examples of the relevant calculations;

• For other installations, and for individual LV equipment with ratings above 75 A or

where the minimum fault level requirements defined in the manufacturer’s statement

of compliance cannot be met, the declared harmonic current emissions shall be below

the limit values calculated using Equation 9; or


DRAFT


• For Resonant Plant at all voltage levels without harmonic current emissions, no further

criterion is applicable.

h = VpK

Krαph

sc (9)

Where:

h represents the harmonic current limit per phase in Amperes for the harmonic

order,

Vp represents the Planning Level in percent for the harmonic order h,

K represents a limit factor according to Table 14,

Kr represents the resonant factor which for LV equals 1.0 and for MV, HV and

EHV equals 2.0.

α is the alpha factor defined in Section 4.1.3,

sc represents the short-circuit current at the PCC derived as sc =Sscp

3×Vnomin kA,

and

Vnom represents the nominal system voltage in kV.

Table 14: Limit Factors for Equation 9

Order K Factor

h ≤ 5 2.505< h ≤10 2.90h >10 3.16

If the connection does not comply with the limits calculated according to Equation 9, it

might still be acceptable under Stage A if the marginal conditions of Section 4.1.9 are

satisfied.

4.3 Stage B

A Stage B assessment is indicated for connections where the criteria of a Stage A assess-

ment are not met and the background harmonic voltage distortion levels are likely to be

considerable. Stage B follows a simple calculation which involves:

• Apportioning the available headroom into components of Resonance Headroom and

Emission Headroom according to the capacity of the connection under question,

• Assessing the effect of the resonant plant in relation to the Resonance Headroom, and

• Calculating the effect of the connection’s emissions based on the equipment charac-

teristics, as declared by the equipment manufacturer, using a simplified impedance

model of the system.


DRAFT


4.3.1 Calculation of the Connection Headroom

With consideration to the guidelines on measurement provided in Section 4.1.5, the Net-

work Operator shall obtain measurements of harmonic voltage distortion at the PCC from

which the total remaining headroom for each harmonic order shall be calculated according

to the aggregation principles of Section 4.1.3 such that:

Vhhr−tot =αs

�

Vhp�α−�

Vhbg�α

(10)

Where:

Vhhr−tot represents the headroom (remaining) harmonic voltage distortion for har-

monic h,

Vhp is the harmonic voltage distortion Planning Level for harmonic h, defined in

Section 3.1, and

Vhbg is the measured background harmonic voltage distortion for harmonic h.

Once the total remaining headroom has been determined, the Resonance Headroom and

Emission Headroom available to the connection, Vhhr−resonnce and Vhhr−emsson, shall be

calculated according to Equations 11 and 12 respectively.

Vhhr−resonnce = Vhhr−tot α

√

√

√

√

√

Sresonnt−pnt

2β�

1 −VTHDbg

VTHDp

�

× Ssc(11)

Vhhr−emsson = Vhhr−tot α

√

√

√

√

√

√

Semttng−pnt × THD100

2β�

1 −VTHDbg

VTHDp

�

× Ssc(12)

Where:

Sresonnt−pnt is the resonant component of the connection in MVA,

Semttng−pnt is the emitting component of the connection in MVA,

VTHDbg is the measured background THD, and

VTHDp is the THD Planning Level, defined in Section 3.1.

This provides connection-related headroom profiles which distinguish between the differ-

ing effects of the connection’s Resonant and Non-Linear plant respectively and prejudice

neither the present, nor the possible future connections at the PCC.

These profiles shall be considered as a guideline to the Network Operator; the ultimate

decision as to the suitability of a connection rests with the Network Operator. The Network

Operator may adjust these profiles, subject to the following limitations:


DRAFT


• Where background levels are below Planning Levels, the headroom profile shall not

lead to a breach of the Planning Levels, and

• Where background levels are above Planning Levels, the profile shall be limited to

either a value which will not lead to a breach of 110% of the respective Planning Level

or 0.1% above the respective Planning Level (whichever is the lesser of the two, and

subject to the Compatibility Levels not being breached).

Where multiple concurrent, nearby connections are being assessed based on one set of

background measurements and system parameters, the successive adjustment of the VTHDbg

according to the results of the preceding connection’s assessment shall ensure that a fair

allocation of the headroom is achieved.

Having determined the harmonic voltage distortion profiles which may be associated with

the new connection, a two-step calculation is necessary in order to:

• Evaluate the resonant effect of the connection on the existing harmonic distortion,

and to

• Determine the current emission limits with which the connection must comply in order

for the connection to qualify under a Stage B assessment.

4.3.2 Assessment of Resonant Conditions

The connection of Resonant Plant can magnify existing background harmonics beyond the

available Resonance Headroom. Equation 13 provides a simple means of approximating

this magnification.p

SscQc

PPCC× Vhrreƒ < Vhrhr−resonnce (13)

Where:

Qc is the reactive power of the Resonant Plant in MVAr,

hr is the resonant order, equal top

Ssc/Qc,

PPCC is the active power delivered at the PCC in MW, excluding that from

the connection under assessment,

Vhrreƒ is the greater of either the measured background distortion, Vhrbg, or

0.1%, and

Vhrhr−resonnce is the Resonance Headroom calculated for the resonant order accord-

ing to Equation 11.


DRAFT


It is unlikely that hr will be calculated as an integer. Therefore, both of the orders on either

side of the calculated value shall be evaluated.

A characteristic of this equation is that lower order resonances are more likely to not satisfy

this equation whilst higher order resonances are. Therefore, the connection of small or

lower voltage Resonant Plant is more likely to qualify under this Stage B criterion.

4.3.3 Assessment of Emissions

The available Emission Headroom is now used in combination with a simple harmonic

impedance approximation according to Equation 14 to determine the current emission lim-

its according to Ohm’s law in Equation 15.

Zh = Krαp

hV2nom

Ssc(14)

h =Vhhr−emsson

Zh(15)

Where:

Zh is the system harmonic impedance at harmonic order h in Ohms,

Vhrhr−emsson is the Emission Headroom calculated for the harmonic order according

to Equation 12 for Non-Linear Plant and Equipment

A connection shall be permitted, without further consideration, if the conditions in Equa-

tions 13 and 15 are satisfied for Resonant and Non-Linear Plant and Equipment respectively.

If the connection does not comply with the limits calculated according to Equation 15, it

might still be acceptable under Stage B if the marginal conditions of Section 4.1.9 are

satisfied.


DRAFT


4.4 Stage C

This final stage of assessment is applicable when the calculations of a Stage B assess-

ment indicate that either a resonant condition exists which jeopardises compliance or the

emissions of the connection installation exceed those calculated using a simplistic model

of the system and plant characteristics. Stage C requires detailed modelling of both the

system and the connected installation in an effort to more accurately predict the effect of

the connected installation on the system.

Stage C is typically required for large connection projects for which detailed design data

is unlikely to be available at the beginning of the assessment. To assist in the delivery of

a project whilst still protecting the Network Operator’s mandate to assure compliance, the

concepts of Design and Performance Limits are introduced as follows:

Design Limits are a representation of the headroom profiles developed in Section 4.3.1

which are independent of the detailed connection data. They represent the upper

limits to which the design team may design the connecting assets.

Performance Limits are a representation of the modelled plant performance based on

the detailed design. Should a contract exist for the connection, then it is these limits

which shall be included in the contract.

Both sets of Limits are accompanied by a Harmonic Impedance representation of the net-

work in the form of Harmonic Impedance Loci.

By distinguishing between the Design and Performance Limits, the project is able to progress

based on maximum design criteria, and the Network Operator is able to recycle headroom

that is not needed, thereby facilitating further Grid access.

The issuing of the Design and Performance Limits is the responsibility of the Network Op-

erator. This responsibility is typically delegated to the responsible host Network Owner in

the event that they are different entities.

The critical steps involved in performing a Stage C assessment are:

1. Identifying remote electrical nodes which might be affected by the connection of the

installation, either by the propagation of harmonic emissions or by the modification of

the system harmonic impedances, according to Section 4.4.1;

2. Measurement of the background harmonic voltage distortion at the PoE (and PCC

where different) and at the remote nodes as appropriate and practicable;


DRAFT


3. Development of the Harmonic Impedance Loci according to Section 4.4.2;

4. Development of the Harmonic Design Specification according to Section 4.4.3;

5. Assessment of the detailed design; and

6. Development and issuing of the Harmonic Performance Specification according to Sec-

tion 4.4.4.

It is possible that a single set of background measurments and system conditions might be

used to assess multiple connections which are due to connect in short succession of one an-

other. Section 4.4.5 provides guidance on how to utilise the Harmonic Design Specification

of one connection to inform the Harmonic Design Specification of another.

4.4.1 Identification of Remote Electrical Nodes

The purpose of identifying remote nodes which might be affected by the connection of the

Non-Linear or Resonant Plant is to develop a representative set of nodes as opposed to a

comprehensive set. The responsible party might choose to include nodes which are:

• Within a set number of substations from the PCC on the same voltage level;

• On the opposite side of a transformation between two voltage levels;

• Already subject to contractual harmonic limits with other Customers; or are

• Host to sensitive or strategic connections.

It is important to realise that some affected nodes might be in adjacent networks and shall

be considered in the assessment.

4.4.2 Harmonic Impedance Representation of the Network

The impedance data at the PCC shall be collated into Harmonic Impedance Loci which shall

be developed as follows:

• A set of resistance and reactance values shall be calculated for each operating sce-

nario considered to be Normal Operating Conditions. The values shall be presented in

Per-Unit notation on an Apparent Power base of 100 MVA.


DRAFT


• The impedance values shall be calculated in steps of at least a quarter of a harmonic

order, with at least one quarter on either side of the first and last integer harmonic

orders.

• The spectrum shall be broken up into several bands overlapping by at least one quar-

ter of a harmonic order. The bands should be narrower at the lower end of the spec-

trum than at the upper end and should focus on problematic or characteristic harmonic

orders. As far as is practicable, the boundaries of the bands shall not be located on or

near any parallel or series resonance, or any resistive minima.

• For each band, the harmonic resistances and reactances for all studied network con-

ditions shall be plotted on a Cartesian scatter chart, with the abscissa representing

resistance and the ordinate representing the reactance.

• A margin of at least δ = 1%× αph shall be applied to each datum point (Rh, Xh) thereby

generating a set of four additional points in the form (Rh ± δ, Xh ± δ).

• For each band, a Locus shall be drawn to encompass all of the (Rh ± δ, Xh ± δ) points

using straight lines and arcs where appropriate.

• The Cartesian coordinates of each vertex and of the centre and radius of any arcs shall

be depicted on the plot to at least six decimal places.

• For each Locus, the minimum resistance shall be defined along with the maximum

and minimum Impedance Angles which represent the angles of the upper and lower

tangents to the Locus, as drawn from the origin.

Figure 6 presents an example of a Harmonic Impedance Locus which illustrates the resulting

structure of the above steps.

4.4.3 Harmonic Design Specification

The Harmonic Design Specification combines the Harmonic Impedance Loci with the Design

Limits and is used in the Front-End Engineering and Design of a project. The Design Limits

comprise two sets of metrics namely the emission limits and the background gain limits.

The emission headroom developed as part of the Stage B assessment does not take into

consideration the effect on remote nodes of the network. For each remote node n, a

headroom profile, Vhhr−n, is developed using the same Equations 10 and 12 as were used

for the PCC in the Stage B assessment, based on the measurements and Planning Levels


DRAFT


Centre: (0.193683,0.024941), Radius: 0.192123

(0.005669,0.064450) (0.018880,0.064450)

(0.018880,-0.012610)(0.007534,-0.012610)(0.002291,0.008196)

Minimum Resistance: 0.001560 p.u.Maximum Impedance Angle: 87.017586◦Minimum Impedance Angle: -59.143273◦

-0.02

0.00

0.02

0.04

0.06

0.08

Har

mon

icR

eact

ance

[p.u

.]

0.000 0.005 0.010 0.015 0.020

Harmonic Resistance [p.u.]

Figure 6: An Example of a Harmonic Impedance Locus

applicable to each remote node. Therefter, a limiting source emission for each remote node

is derived according to Equation 16.

Vhpcc−n =ZhpccZhpcc−n

Vhhr−n (16)

Where:

Zhpcc−n represents the harmonic transfer impedance between the PCC and the nth

remote node; and

Zhpcc represents the harmonic self impedance at the PCC.

The resulting design limit for each harmonic order, Vhdesgn, is the lesser of either:

• The lowest value of all limiting source emissions Vhpcc−n, or

• The calculated emission headroom at the PCC, Vhhr−emsson.

The second element of the design specification is the background gain limit which shall be

calculated according to Equation 17.

Ghdesgn =

Vhhr−resonnceVhreƒ

(17)


DRAFT


Where:

Vhreƒ is the greater of either the measured background distortion Vhbg or 0.1%. This

prevents erroneous gain values from extremely low measured backgrounds.

In the event that the above ratio is less then one, the gain values shall be rounded up to

one, thereby representing no change to the background harmonic voltage distortion. The

resulting Design Limits shall be presented in a tabular form, similar to that of Table 15.

Table 15: An Example of the Design Limits

HarmonicOrder

BackgroundDistortion

Level [%V1]

IncrementalEmission

Limit [%V1]

BackgroundGain Limit

2 0.09 0.03 1.333 0.76 0.05 2.264 0.03 0.02 1.695 1.21 0.13 1.15... ... ... ...98 0.01 0.02 1.0899 0.01 0.02 1.04

100 0.01 0.02 1.09

THD 0.84 0.23

The background distortion levels presented in Table 15 are present for the purpose of de-

sign and are not rounded up to 0.1%. The consideration of the 0.1% rounding has already

been given in the determination of the Gain limits in Equation 17.

4.4.4 Harmonic Performance Specification

A Harmonic Performance Specification complements a connection agreement between a

Customer and the relevant Network Operator. It is a mutually beneficial instrument which

defines the operational criteria for each party’s Plant, Equipment or Network.

The Harmonic Performance Specification is structurally similar to the Design Specification.

The Harmonic Impedance Loci shall be identical to those defined in the Design Specifi-

cation. The emission and background gain limits are to be derived from the calculated

performance of the detailed plant design.

The emission limit at the PCC, Vhperƒormnce, shall be calculated using a comprehensive set

of impedances defined along the entire perimeter of the relevant Harmonic Impedance

Locus and must be less than or equal to the Design Limit, Vhdesgn, so as not to adversely

affect remote nodes.


DRAFT


The background gain limit shall be calculate according to Equation 18 and must be less

than the Design Limit, Ghdesgn.

Ghperƒormnce =

ZhconnectedZhdsconnected

(18)

Where:

Zhconnected represents the harmonic self impedance at the PCC with the Non-Linear

or Resonant Plant connected to the system; and

Zhdsconnected represents the harmonic self impedance at the PCC with the Non-Linear

or Resonant Plant isolated from the system.

These two sets of values shall be presented in the Harmonic Performance Specification in

the format of Table 16.

Table 16: An Example of the Performance Limits

HarmonicOrder

IncrementalEmission

Limit [%V1]

BackgroundGain Limit

2 0.03 1.333 0.04 2.134 0.02 1.345 0.11 1.15... ... ...98 0.02 1.0899 0.02 1.04

100 0.02 1.09

THD 0.21

It should be noted that for the purpose of the Harmonic Performance Specification, the

measured background distortion is excluded. This is because it represents a specific point

in time and therefore cannot remain valid for the duration of the connection contract with

which the Harmonic Performance Specification is associated.

4.4.5 Dealing with Concurrent Connections

Where multiple connections are expected to connect within similar timescales, it is unlikely

that the detailed design data of one connection will be available to incorporate into the

Harmonic Design Specification of another connection. This section describes a method

for producing successive Harmonic Design Specifications based on one set of background

harmonic measurements and one set of system parameters.


DRAFT


In Section 4.4.3 the emission limits for a connection are derived so as not to adversely

affect remote nodes. The same calculation shall be used for each connection based on the

singular set of network impedances and background measurements.

The Harmonic Impedance Locus of the subsequent connection may be derived by taking

each point of the original locus and generating six additional points as depicted in Figure 7.

The derivation of these points relies on the previous connection’s Background Gain Limit,

Gh, three constant impedance arcs about the origin (the radii of which are denoted in the

figure) and a constant impedance angle line from the origin. The new points represent:

1. The intersection of the constant impedance angle line with the minimum constant

impedance arc;

2. The extrapolation of point 1 to the constant impedance arc of the original point;

3. The point on minimum constant impedance arc which is purely resistive;

4. The intersection of the constant impedance angle line with the maximum constant

impedance arc;

5. The extrapolation of the original point to the maximum constant impedance arc; and

6. The point on maximum constant impedance arc which is purely resistive;

– Original Point, Zh

– New Point

|Zh |

|Zh | × Gh

|Zh | ÷ Gh

4

1

2

5

3 60.000

0.004

0.008

0.012

0.016

0.020

Har

mon

icR

eact

ance

[p.u

.]

0.000 0.005 0.010 0.015 0.020

Harmonic Resistance [p.u.]

Figure 7: The Adjustment of a Harmonic Impedance to Cater for a Concurrent Connection


DRAFT


Once the detailed design data of a the first connection is known, the Harmonic Impedance

Loci which shall form a part of the Harmonic Performance Specification of the subsequent

connection may be adjusted subject to the Network Operator’s approval and based on the

following guiding constraints:

• The maximum and minimum Impedance Angles of a new locus shall not exceed those

of the original locus; and

• The left-most section of a new locus shall be completely within or on the old locus.

The left-most region is defined between the point of intersection of the new locus with

the new maximum Impedance Angle tangent, through the point of minimum resis-

tance and ending at the point of intersection of the new locus with the new minimum

Impedance Angle tangent.


DRAFT

5 CONCLUSION ER G5/5, January 2015

5 Conclusion

In support of the Electromagnetic Compatibility Regulations 2006[1], this Recommendation

sets out the good practice for the limitation of harmonic voltage disturbance on the public

supply systems in the United Kingdom.

This is achieved through the definition of Planning and Compatibility levels for all power

system voltage levels and a suitable three-staged procedure for the assessment of the

impact of equipment connections to the supply system.

Both Non-Linear and Resonant Plant connections are considered: Non-Linear plant because

of their associated harmonic emissions and Resonant Plant because of the shift in network

resonances which might result in non-compliance if not assessed.


DRAFT

REFERENCES ER G5/5, January 2015

References

Precedence

This Recommendation makes reference to, and is based on, the contemporary versions of

the following documents. However, the current versions shall always take precedence over

withdrawn versions. Any conflicts between the documents shall be resolved through the

following technical precedence:

1. Directives and Regulations

2. Codes

3. This Recommendation

4. Harmonised Standards

Directives and Regulations

[1] Electromagnetic Compatibility Regulations. (Statutory Instrument 2006 No. 3418),

2006.

[2] DIRECTIVE 2004/108/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 15

December 2004 on the Approximation of the Laws of the Member States Relating to

Electromagnetic Compatibility and Repealing Directive 89/336/EEC. December 2004.

OJ L390/24.

Standards

[3] Voltage Characteristics of Electricity Supplied by Public Distribution Networks. Number

BS EN 50160:2010. British Standards Institution, 389 Chiswick High Road, London W4

4AL, United Kingdom, August 2010. ISBN 978-0-58074103-6.

[4] ElectroMagnetic Compatibility (EMC) – Part 3-2: Limits – Limits for Harmonic Current

Emissions (Equipment Input Current ≤ 16 A Per Phase). Number BS EN 61000-3-

2:2006+A2:2009. British Standards Institution, 389 Chiswick High Road, London W4

4AL, United Kingdom, May 2006. ISBN 978-0-580-67372-6.


DRAFT

REFERENCES ER G5/5, January 2015

[5] ElectroMagnetic Compatibility (EMC) – Part 3-12: Limits – Limits for Harmonic Currents

Produced by Equipment Connected to Public Low-Voltage Systems with Input Current

> 16 A and ≤ 75 A Per Phase. Number BS EN 61000-3-12:2011. British Standards

Institution, 389 Chiswick High Road, London W4 4AL, United Kingdom, second edition,

February 2012. ISBN 978-0-580-84608-3.

[6] ElectroMagnetic Compatibility (EMC) – Part 4-7: Testing and Measurement Techniques

– General Guide on Harmonics and Interharmonics Measurements and Instrumentation,

for Power Supply Systems and Equipment Connected Thereto. Number BS EN 61000-

4-7:2002+A1:2009. British Standards Institution, 389 Chiswick High Road, London W4

4AL, United Kingdom, January 2003. ISBN 978-0-580-77234-4.

[7] ElectroMagnetic Compatibility (EMC) – Part 4-30: Testing and Measurement Techniques

– Power Quality Measurement Methods. Number BS EN 61000-4-30:2003. British Stan-

dards Institution, 389 Chiswick High Road, London W4 4AL, United Kingdom, April 2009.

ISBN 978-0-580-57045-2.

[8] Planning Limits for Voltage Fluctuations Caused by Industrial, Commercial and Domes-

tic Equipment in the United Kingdom. Number Engineering Recommendation P28:1989.

Energy Networks Association, 18 Stanhope Place, Marble Arch, London W2 2HH, United

Kingdom, September 1989. ISBN 978-0-580-57045-2.


DRAFT

A STAGE A ASSESSMENT EXAMPLES ER G5/5, January 2015

A Stage A Assessment Examples

A.1 Application of Equation 8 as the Stage A Qualifying Criterion

Equation 8 represents a qualifying criterion for the continuation of the assessment under

Stage A and is repeated below for reference.

∑

Snrpnt ×W

Ssc≤ β

A notable feature of this equation is that it does not solely relate to the connection be-

ing considered; rather, it evaluates the total connection capacity at the PCC. Therefore∑

Snrpnt relates to all connections to the PCC, each identified by their respective Snrpnt.

Three examples are considered to demonstrate the use of Equation 8.

A.1.1 Connection of a Water Treatment Facility to an Existing Substation

A water treatment plant wishes to connect to an existing 33 kV substation with a fault level

of 17.5 kA (1000 MVA). The plant is planned to have 3 MVA of Twelve-Pulse drives. There

are already two load customers and one generation customer connected to the substation

according to Figure 8.

33 kV, 17.5 kA

GRID

~Generator Process Plant

6-Pulse: 0.7 MVA

PFC: 1 MVAr

THDi: 80%

Warehouses

6-Pulse: 0.6 MVA

PFC: 0.5 MVAr

THDi: 70%

Water TreatmentPlant

12-Pulse: 8.9 MVA

THDi: 14%

Figure 8: Single-Line Diagram for Water Treatment Plant Connection


DRAFT


The generator itself has no Non-Linear or Resonant Plant and so is not considered in the

equation. The existing process plant and warehouses have both Power Factor Correction

(PFC) and Six-Pulse drives without series inductors. Based on this information, Equation 8

becomes:

(0.7 × 0.80 + 1.0 × 1.0) + (0.6 × 0.70 + 0.5 × 1.0) + (8.9 × 0.14)

1000= 0.37%

This is below the 0.57% required for MV and the connection may continue to be assessed

under Stage A.

A.1.2 Variation of Equation 8 With the Number of PCC Connections

The benefit of Equation 8 is that it considers that state of the network and does not prej-

udice existing connections. Consider Figure 9 which is used to demonstrate the effect of

existing connections on the application of Equation 8.

33 kV, 17.5 kA

GRID

Esiting Load A

6-Pulse: 4.0 MVA

THDi: 75%

Existing Load B

6-Pulse: 1.5 MVA

THDi: 70%

New Warehouse

6-Pulse: 3.0 MVA

THDi: 85%

Figure 9: Variation of Equation 8 With the Number of PCC Connections

If Existing Loads A and B are both in place, Equation 8 becomes:

(4.0 × 0.75) + (1.5 × 0.7) + (3.0 × 0.85)

1000= 0.66%

This is above the 0.57% limit, and would not qualify to be assessed under Stage A; it would

require the assessment to proceed to Stage B. This is to be expected because the two


DRAFT


existing loads are producing harmonic emissions and so there is likelihood that additional

Non-Linear load will require mitigation.

However, should the New Warehouse be connecting to a substation which only has Existing

Load B, then Equation 8 becomes 0.36% which is below the 0.57% limit. Therefore the

connection may continue to be assessed under Stage A.

A.1.3 Assessment Based on Non-Linear and Resonant Plant Capacity

Figure 10 illustrates the proposed connection of 33 kV cable to an existing substation which

hosts 4.5 MVA of Six-Pulse drives without smoothing inductors.

33 kV, 17.5 kA

GRID

Existing Load

6-Pulse: 4.5 MVA

THDi: 80%

33 kV Cable

3×1c800 mm2

0.39μF/km = 0.133 MVAr/km

Figure 10: Connection of Resonant Plant

It is possible to rearrange Equation 8 to establish what length of cable would necessitate a

Stage B connection. For the Six-Pulse drives:

4.5 × 0.80

1000= 0.36%

Therefore, for the cable, 0.21% remains available from the 0.57% limit, which means that:

ength × 0.133

1000≤ 0.21%

∴ ength ≤0.0021 × 1000

0.133 × 1.0= 15.79 km


DRAFT


Thus, if this cable is shorter than 15.79 km, it may be assessed under Stage A which, given

that there are no harmonic current emissions from the cable, indicates that the cable may

be connected without further assessment i.e. Equation 9 is inherently satisfied.

If, however, this cable is used over distances greater than 15.79 km, there might be res-

onant conditions which affect the background harmonic levels. Therefore the assessment

must proceed to Stage B.

Referring to Section A.1.2, it should be apparent that if there is more Non-Linear Plant or

Equipment, the prospective length of cable which may be assessed under Stage A will be

reduced because the risk of the cable resonances being excited by the current emissions

is more pronounced. Therefore Equation 8 inherently balances the risk of connection with

the simplicity of assessment under Stage A.

A.2 Calculation of Harmonic Current Limits Using Equation 9

Having established that a connection may be assessed under Stage A, the harmonic cur-

rent limits which are applicable to the substation characteristics must be calculated using

Equation 9.

Consider the connection of the water treatment plant of Figure 8. The 33 kV system has

a fault current sc = 17.5 kA and Planning Levels as defined in Table 3. The resulting

values of h in Amperes are provided in Table 17. If the aggregate individual harmonic

current emissions from the water treatment plant are below these limit values, or within

the marginal considerations of Section 4.1.9, then the plant may be connected without

further assessment. Otherwise, the assessment must proceed to Stage B.

It is worth noting that if the 33 kV system in Figure 8 were to be connected to another MV

system in a transformation series, then the applicable Planning Levels would be those of

an Intermediary Voltage Level, as discussed in Section 3.

A.3 Application of PWHD

Where more than four higher order harmonics exceed the limit values calculated in Table 17

the PWHD method may be used to assess whether or not the connection may still be

permitted without progression on to Stage B.


DRAFT


Table 17: Harmonic Current Limits [A] from Equation 9 for Figure 8

Order h Order h Order h Order h

26 1.08 51 0.70 76 0.632 16.41 27 0.96 52 0.77 77 1.143 21.88 28 1.05 53 1.66 78 0.634 4.92 29 3.24 54 0.75 79 1.115 13.13 30 1.01 55 1.59 80 0.626 3.18 31 3.00 56 0.74 81 0.557 18.96 32 0.98 57 0.66 82 0.618 2.30 33 0.87 58 0.73 83 1.069 6.34 34 0.95 59 1.48 84 0.60

10 1.96 35 2.60 60 0.71 85 1.0411 16.67 36 0.92 61 1.43 86 0.6012 1.60 37 2.44 62 0.70 87 0.5313 15.34 38 0.90 63 0.63 88 0.5914 1.48 39 0.80 64 0.69 89 1.0015 2.14 40 0.87 65 1.35 90 0.5816 1.38 41 2.18 66 0.68 91 0.9817 10.73 42 0.85 67 1.31 92 0.5818 1.30 43 2.07 68 0.67 93 0.5219 7.61 44 0.83 69 0.60 94 0.5720 1.24 45 0.74 70 0.66 95 0.9421 1.21 46 0.82 71 1.23 96 0.5622 1.18 47 1.88 72 0.65 97 0.9223 6.92 48 0.80 73 1.20 98 0.5624 1.13 49 1.80 74 0.64 99 0.5025 3.87 50 0.78 75 0.57 100 0.55

Table 18 presents the actual aggregate individual harmonic current emissions for the sys-

tem depicted in Figure 8. Harmonic orders 23, 25, 35, 37, 47 and 49, which are in bold, all

exceed the harmonic current limits calculated in Table 17, each by less than 10%.

Equation 1 for the PWHD may now be calculated as:

PWHD =

√

√

√

√

100∑

h=23

�

h

Ssc

�2

× 100%

=1

17500

√

√

√

√

√

23 × 7.262 + 25 × 4.142 + 35 × 2.792+

37 × 2.682 + 47 × 1.992 + 49 × 1.942× 100%

= 0.31%

which is below the 0.46% required as per Table 13. Therefore, although numerous individual

higher order harmonic current emissions exceed the calculated limits according to Equa-

tion 9, the connection may be connected without further assessment because the PWHD is

below the required level, thus ensuring that their effect on the system is controlled.


DRAFT


Table 18: Individual Harmonic Emissions [A] for Figure 8

Order Current Order Current Order Current Order Current

26 51 762 27 52 773 28 53 784 29 54 795 30 55 806 31 56 817 32 57 828 33 58 83 0.939 34 59 1.42 84

10 35 2.79 60 85 0.6811 15.01 36 61 1.09 8612 37 2.68 62 8713 12.27 38 63 8814 39 64 8915 40 65 9016 41 66 9117 42 67 9218 43 68 9319 44 69 9420 45 70 95 0.4221 46 71 1.06 9622 47 1.99 72 97 0.2123 7.26 48 73 0.80 9824 49 1.94 74 9925 4.14 50 75 100

A.4 Low Voltage Assessments

Low Voltage connections are catered for through the compliance with BS EN 61000-3-2[4],

BS EN 61000-3-12[5] and Equation 9. The application of Equation 9 has already been

demonstrated. The following three examples demonstrate the nuances of the application

of the British Standards cited in this Recommendation.

A.4.1 Connection of a 50 kVA Three-Phase Low Voltage Heat Pump

Consider the connection of a 50 kVA, three phase Heat Pump to the secondary terminals of

a 500 kVA 11 kV / 415 V distribution transformer which presents a three phase short-circuit

Fault Level of 8.7 MVA. There is no other known non-linear equipment on network and the

Heat Pump has a THD = 13%. The manufacturer states that the Heat Pump complies with

IEC 61000-3-12 in accordance with BS EN 61000-3-12 which states that:

For equipment complying with the harmonic current emission limits correspond-

ing to Rsce = 33, the manufacturer shall state in the instruction manual supplied

with the equipment: “Equipment complying with IEC 61000-3-12”


DRAFT


The term Rsce is defined in BS EN 61000-3-12 for three phase equipment as the ratio of

Ssc to Seq where Seq is the apparent rated power of the equipment and is equivalent to

Snrpnt in this Recommendation.

Based on the information provided, Equation 8 simplifies to:

∑

Snrpnt ×W

Ssc=0.05 × 0.13

8.7

= 0.08%

This is below the 1.44% required for LV and the connection may continue to be assessed

under Stage A.

To ensure the connection matches the BS EN 61000-3-12 assumption of Rsce ≥ 33, the

actual Rsce is determined as follows:

Ssc

Snrpnt=

8.7

0.05

= 174

This is higher than the required 33 and so the connection may proceed without further

assessment.

A.4.2 Connection of a 50 kVA Three-Phase Electric Vehicle Charger

Consider the connection of a 50kVA, three phase Electric Vehicle Charger to the secondary

terminals of a 500 kVA 11 kV / 415 V distribution transformer which presents a three phase

short-circuit Fault Level of 8.7 MVA. There is no other known non-linear equipment on net-

work and the Electric Vehicle Charger has a THD = 37%. In accordance with BS EN 61000-

3-12, the manufacturer states that:

This equipment complies with IEC 61000-3-12 provided that the short-circuit

power Ssc is greater than or equal to 12.5 MVA at the interface point between

the user’s supply and the public system. It is the responsibility of the installer

or user of the equipment to ensure, by consultation with the distribution network

operator if necessary, that the equipment is connected only to a supply with a

short-circuit power Ssc greater than or equal to 12.5 MVA.


DRAFT



∑

Snrpnt ×W

Ssc=0.05 × 0.37

8.7

= 0.21%


under Stage A. However, the three phase short-circuit fault level is 8.7 MVA which does not

meet the stated requirement of Ssc ≥ 12.5 MVA. Therefore, the network would need to be

reinforced. For example, an 800 kVA transformer calculated to give Ssc = 12.6 MVA would

suffice.

The example manufacturer’s minimum requirement of 12.5 MVA fault level for equipment

rated at only 50 kVA implies Rsce = 250 which is very onerous and hence the onerous

network implication of having to use an 800 kVA transformer for a disturbing load of only

50 kVA.

A.4.3 Connection of a 10.35 kVA Single Phase Heat Pump

Consider the connection of a 10.35 kVA, single phase Heat Pump to an LV network which

presents a single phase short-circuit Fault Level of 749.8 kVA at 230 V. There is no other

known non-linear equipment on network and the Heat Pump has a THD = 23%. The

manufacturer states that the Heat Pump complies with BS EN 61000-3-12.


∑

Snrpnt ×W

Ssc=0.01035 × 0.23

0.7498

= 0.32%


under Stage A. The term Rsce is defined in BS EN 61000-3-12 for single phase equipment

as the ratio of Ssc to 3× Seq where Seq is the apparent rated power of the equipment and

equivalent to Snrpnt in this recommendation.

However, Ssc is the three phase fault level and may not be applicable to a single phase net-

work. This problem is overcome by dealing in single phase quantities thereby ensuring the


DRAFT


condition of Rsce ≥ 33 is met. The actual single-phase Rsce may therefore be determined

using the single phase quantities provided:

Ssc

Snrpnt=

0.7498

0.01035

= 72.44

This is higher than the required 33 and so the connection may proceed without further

assessment.


DRAFT

B STAGE B ASSESSMENT EXAMPLES ER G5/5, January 2015

B Stage B Assessment Examples

Consider the example of the Figure 11 relating to the connection of a 20 MW (25MVA) wind

farm to a 33 kV PCC.

33 kV, 17.5 kA, 50 MVA Capacity

33 kV, 17.5 kA

GRID

Existing Customers

Ppcc: 25 MW

12-Pulse: 19 MVA

THDi: 15%

PFC: 0.3 MVAr

W W

10×2 MW

Wind Turbines

THDi: 11%

cosθ: 0.8

33 kV Cable

500m×3×1c800 mm2

0.19μF/km → 0.0325 MVAr

Figure 11: Connection of Onshore Wind Turbines

The scale of the installation, and the existence of other customers with Non-Linear Plant

and Equipment means that Equation 8 results in a value of:

∑

Snrpnt ×W

Ssc=19 × 0.15 + 0.3 × 1.0 + 25 × 0.11 + 0.325 × 1.0

1000

=6.225

1000= 0.62% (19)

which is above the 0.57% required to continue assessment under Stage A. Therefore a

Stage B assessment must be undertaken.

B.1 Headroom Calculations Using Equations 10, 11 and 12

Table 19 presents the measured background harmonic voltage distortion levels at the 33 kV

PCC.


DRAFT


Table 19: Background Harmonic Voltage Distortion [%V1] for Figure 11

Order Vh Order Vh Order Vh Order Vh

26 0.0024 51 0.0016 76 0.00082 0.0160 27 0.0081 52 0.0054 77 0.00273 0.2232 28 0.0031 53 0.0021 78 0.00104 0.0249 29 0.0269 54 0.0179 79 0.00905 1.5087 30 0.0024 55 0.0016 80 0.00086 0.0095 31 0.0110 56 0.0073 81 0.00377 0.7607 32 0.0022 57 0.0015 82 0.00078 0.0040 33 0.0050 58 0.0033 83 0.00179 0.0279 34 0.0025 59 0.0017 84 0.0008

10 0.0036 35 0.0422 60 0.0281 85 0.014111 0.2039 36 0.0022 61 0.0015 86 0.000712 0.0025 37 0.0084 62 0.0056 87 0.002813 0.1901 38 0.0022 63 0.0015 88 0.000714 0.0024 39 0.0035 64 0.0023 89 0.001215 0.0170 40 0.0022 65 0.0015 90 0.000716 0.0030 41 0.0071 66 0.0047 91 0.002417 0.0813 42 0.0027 67 0.0018 92 0.000918 0.0029 43 0.0048 68 0.0032 93 0.001619 0.0434 44 0.0024 69 0.0016 94 0.000820 0.0022 45 0.0041 70 0.0027 95 0.001421 0.0076 46 0.0023 71 0.0015 96 0.000822 0.0022 47 0.0067 72 0.0045 97 0.002223 0.0158 48 0.0023 73 0.0015 98 0.000824 0.0022 49 0.0048 74 0.0032 99 0.001625 0.0210 50 0.0025 75 0.0017 100 0.0008

The total available headroom is calculated using Equation 10 based on these measured

values and the Planning Levels for MV shown in Table 3. Equations 11 and 12 are then

used develop the resonance- and emission-headroom profiles which are specific to the

connection under assessment. The resulting profiles are provided in Tables 20 and 21

respectively.

It is worth noting that if the 33 kV system in Figure 11 were to be connected to another MV

system in a transformation series, then the applicable Planning Levels would be those of

an Intermediary Voltage Level, as discussed in Section 3.

B.2 Ensuring Resonance Compliance Using Equation 13

Given that the wind farm includes a component of Resonant plant in the form of 33 kV

cables, Equation 13 shall be used to establish whether or not there is a risk of resonance.

The resonant frequency is calculated as hr =p

Ssc/Q = 55.47. Therefore this evaluation

will be performed for both orders 55 and 56. The measured background for both orders


DRAFT


Table 20: Harmonic Voltage Distortion Resonance Headroom Profile [%V1] for Figure 11based on Equation 11


26 0.0448 51 0.0403 76 0.04482 0.0745 27 0.0403 52 0.0448 77 0.08123 0.1395 28 0.0448 53 0.0977 78 0.04484 0.0440 29 0.1413 54 0.0446 79 0.08035 0.0749 30 0.0448 55 0.0958 80 0.04486 0.0530 31 0.1352 56 0.0448 81 0.04037 0.3163 32 0.0448 57 0.0403 82 0.04488 0.0472 33 0.0403 58 0.0448 83 0.07869 0.1412 34 0.0448 59 0.0923 84 0.0448

10 0.0472 35 0.1245 60 0.0444 85 0.077711 0.4459 36 0.0448 61 0.0908 86 0.044812 0.0448 37 0.1205 62 0.0448 87 0.040313 0.4462 38 0.0448 63 0.0403 88 0.044814 0.0448 39 0.0403 64 0.0448 89 0.076315 0.0671 40 0.0448 65 0.0879 90 0.044816 0.0448 41 0.1131 66 0.0448 91 0.075617 0.3581 42 0.0448 67 0.0866 92 0.044818 0.0448 43 0.1100 68 0.0448 93 0.040319 0.2688 44 0.0448 69 0.0403 94 0.044820 0.0448 45 0.0403 70 0.0448 95 0.074321 0.0448 46 0.0448 71 0.0843 96 0.044822 0.0448 47 0.1044 72 0.0448 97 0.073723 0.2689 48 0.0448 73 0.0832 98 0.044824 0.0448 49 0.1020 74 0.0448 99 0.040325 0.1568 50 0.0448 75 0.0403 100 0.0448

is below 0.1% and so Vhrreƒ is set to 0.1%. Equation 13 may now be used to check for a

prospective resonance problem:

p

SscQc

PPCC× Vhrreƒ < Vhrhr−resonnce

p1000 × 0.325

25× 0.1% = 0.0721

This value is below the resonance headroom values from Table 20 which are 0.2786% and

0.1303% for the 55th and 56th orders respectively.

Therefore, the connection does not pose a significant risk of non-compliance from resonant

amplification of the background levels. Were this not the case, the assessment would

need to proceed to a Stage C evaluation because the risk of resonance needs to be more

thoroughly investigated.


DRAFT


Table 21: Harmonic Voltage Distortion Emission Headroom Profile [%V1] for Figure 11 basedon Equation 12


26 0.1304 51 0.1174 76 0.13042 0.6310 27 0.1173 52 0.1304 77 0.23633 1.1808 28 0.1304 53 0.2842 78 0.13044 0.3721 29 0.4111 54 0.1299 79 0.23355 0.6341 30 0.1304 55 0.2786 80 0.13046 0.2435 31 0.3933 56 0.1303 81 0.11747 1.4545 32 0.1304 57 0.1174 82 0.13048 0.2169 33 0.1173 58 0.1304 83 0.22869 0.6491 34 0.1304 59 0.2686 84 0.1304

10 0.2170 35 0.3623 60 0.1291 85 0.226111 1.2974 36 0.1304 61 0.2640 86 0.130412 0.1304 37 0.3507 62 0.1304 87 0.117413 1.2983 38 0.1304 63 0.1174 88 0.130414 0.1304 39 0.1174 64 0.1304 89 0.222015 0.1953 40 0.1304 65 0.2558 90 0.130416 0.1304 41 0.3292 66 0.1304 91 0.220017 1.0420 42 0.1304 67 0.2521 92 0.130418 0.1304 43 0.3200 68 0.1304 93 0.117419 0.7820 44 0.1304 69 0.1174 94 0.130420 0.1304 45 0.1173 70 0.1304 95 0.216221 0.1303 46 0.1304 71 0.2452 96 0.130422 0.1304 47 0.3038 72 0.1304 97 0.214423 0.7824 48 0.1304 73 0.2421 98 0.130424 0.1304 49 0.2968 74 0.1304 99 0.117425 0.4563 50 0.1304 75 0.1174 100 0.1304

B.3 Calculation of Harmonic Impedances and Current Limits Using

Equations 14 and 15

Having satisfied the conditions for resonance and calculated the emission headroom which

is available to the connection, the harmonic impedance and harmonic current limits may

now be calculated according to Equations 14 and 15 respectively. The results of these cal-

culations are shown in Tables 22 and Table 23. The actual harmonic current emissions are

presented in Table 24 from which it becomes evident that the limits are not breached, and

the connection may be permitted without further assessment. Were this not the case, and

the marginal conditions of Section 4.1.9 were equally not met, then the connection would

need to proceed onto a Stage C assessment where the harmonic impedance modelling is

more accurate.


DRAFT


Table 22: Calculated Harmonic Impedance [Ohms] for Figure 11 based on Equation 14

Order Zh Order Zh Order Zh Order Zh

26 11.11 51 15.55 76 18.992 4.36 27 11.32 52 15.71 77 19.113 6.53 28 11.52 53 15.86 78 19.244 8.71 29 11.73 54 16.00 79 19.365 10.89 30 11.93 55 16.15 80 19.486 7.83 31 12.13 56 16.30 81 19.607 8.74 32 12.32 57 16.44 82 19.728 9.62 33 12.51 58 16.59 83 19.849 10.46 34 12.70 59 16.73 84 19.96

10 11.28 35 12.89 60 16.87 85 20.0811 7.22 36 13.07 61 17.01 86 20.2012 7.54 37 13.25 62 17.15 87 20.3213 7.85 38 13.43 63 17.29 88 20.4314 8.15 39 13.60 64 17.42 89 20.5515 8.44 40 13.77 65 17.56 90 20.6616 8.71 41 13.95 66 17.69 91 20.7817 8.98 42 14.12 67 17.83 92 20.8918 9.24 43 14.28 68 17.96 93 21.0019 9.49 44 14.45 69 18.09 94 21.1220 9.74 45 14.61 70 18.22 95 21.2321 9.98 46 14.77 71 18.35 96 21.3422 10.22 47 14.93 72 18.48 97 21.4523 10.45 48 15.09 73 18.61 98 21.5624 10.67 49 15.25 74 18.74 99 21.6725 10.89 50 15.40 75 18.86 100 21.78


DRAFT


Table 23: Calculated Harmonic Current Limits [A] for Figure 11 based on Equation 15


26 2.24 51 1.44 76 1.312 27.60 27 1.97 52 1.58 77 2.363 34.43 28 2.16 53 3.42 78 1.294 8.14 29 6.68 54 1.55 79 2.305 11.09 30 2.08 55 3.29 80 1.286 5.92 31 6.18 56 1.52 81 1.147 31.69 32 2.02 57 1.36 82 1.268 4.30 33 1.79 58 1.50 83 2.209 11.82 34 1.96 59 3.06 84 1.24

10 3.66 35 5.36 60 1.46 85 2.1511 34.22 36 1.90 61 2.96 86 1.2312 3.29 37 5.04 62 1.45 87 1.1013 31.50 38 1.85 63 1.29 88 1.2214 3.05 39 1.64 64 1.43 89 2.0615 4.41 40 1.80 65 2.78 90 1.2016 2.85 41 4.50 66 1.40 91 2.0217 22.11 42 1.76 67 2.69 92 1.1918 2.69 43 4.27 68 1.38 93 1.0619 15.69 44 1.72 69 1.24 94 1.1820 2.55 45 1.53 70 1.36 95 1.9421 2.49 46 1.68 71 2.55 96 1.1622 2.43 47 3.88 72 1.34 97 1.9023 14.27 48 1.65 73 2.48 98 1.1524 2.33 49 3.71 74 1.33 99 1.0325 7.98 50 1.61 75 1.19 100 1.14


DRAFT


Table 24: Actual Harmonic Current Emissions [A] for Figure 11


26 0.81 51 0.28 76 0.092 26.37 27 0.78 52 0.27 77 0.093 33.17 28 0.75 53 0.27 78 0.094 7.91 29 0.73 54 0.26 79 0.095 10.55 30 0.35 55 0.13 80 0.046 3.75 31 0.68 56 0.25 81 0.097 14.84 32 0.33 57 0.12 82 0.048 2.25 33 0.32 58 0.12 83 0.049 4.69 34 0.31 59 0.12 84 0.04

10 3.16 35 0.30 60 0.12 85 0.0411 3.84 36 0.29 61 0.12 86 0.0412 1.88 37 0.29 62 0.11 87 0.0413 4.06 38 0.28 63 0.11 88 0.0414 1.61 39 0.54 64 0.22 89 0.0815 2.30 40 0.53 65 0.22 90 0.0816 1.41 41 0.51 66 0.21 91 0.0817 2.48 42 0.50 67 0.21 92 0.0818 1.25 43 0.49 68 0.21 93 0.0819 2.22 44 0.48 69 0.20 94 0.0720 1.13 45 0.47 70 0.20 95 0.0721 1.07 46 0.49 71 0.21 96 0.0822 0.96 47 0.45 72 0.20 97 0.0723 2.29 48 0.44 73 0.19 98 0.0724 0.88 49 0.43 74 0.19 99 0.0725 1.27 50 0.42 75 0.19 100 0.07


DRAFT

C INTERMEDIARY VOLTAGE DISTORTION LEVELS ER G5/5, January 2015

C Intermediary Voltage Distortion Levels

A typical power system would comprise transformation stages from LV to MV, MV to HV and

HV to EHV. Under certain circumstances, and particularly within the MV band of voltages,

an Intermediary Voltage (IV) level is introduced within an isolated series of transformation

stages between the MV and HV voltage levels. This scenario is depicted in Figure 12.

Bus A400 V

Bus B33 kV

Bus C132 kV

Bus F33 kV

Bus E11 kV

Bus D400 V

Figure 12: An Example of a Transformation Sequence to Which Voltage Distortion LevelAdjustment is Applicable

It should be evident that only the 33 kV Bus F is subject to Voltage Distortion Level ad-

justment because it exists as an Intermediary Voltage level between the 11 kV Medium

Voltage and the 132 kV High Voltage levels. Therefore, in order to ensure sufficient gradu-

ation across the transformation stages, an adjustment must be made for its Planning and

Compatibility levels.

Although Bus B is also at a 33 kV voltage level, it is the MV level between LV and HV

levels and is therefore already covered by the inherent graduation of the Planning and

Compatibility levels in this Recommendation.

As an example of the application of Equation 4, consider the IHD Planning Level for the 7th

harmonic order of 3% for MV and 2% for HV. Therefore for the IV level of 33 kV between

11 kV and 132 kV, we derive a Planning Level at Bus F of:


DRAFT


VDLV = VDLMV − (VDLMV − VDLHV) ×

√

√

√

Vnom−V − Vnom−MVVnom−HV − Vnom−MV

VDLBsF = 3.00% − (3.00% − 2.00%) ×

√

√

√33 − 11

132 − 11

= 2.57% (20)

Figure 13 provides a visual representation of the equation and the resulting solution. This

same philosophy may be applied to all Planning and Compatibility levels for both Indi-

vidual and Total Harmonic Distortion levels. Tables 25 and 26 document the Graduated

IHD Planning and Compatibility Levels respectively for this example. These correspond to

Graduated THD Planning and Compatibility Levels of 3.57% and 6.72% respectively for the

Intermediary Voltage of 33 kV.

2.00

2.57

3.00

Volta

geD

isto

rtio

nLe

vel[

%]

11 33 132Nominal Voltage [kV]

Figure 13: Planning Level Adjustment of the 7th Harmonic Order IHD for Figure 12

Another common transformation series 132/66/11 kV for which the IV THD Planning and

Compatibility Levels are 3.33% and 5.98% respectively. Tables 27 and 28 provide the IHD

Planning and Compatibility Levels respectively.


DRAFT


Table 25: Planning Levels for the Intermediary Voltage 33kV in a 132/33/11kV Transforma-tion Series



5 2.57 3 2.57 2 1.297 2.57 9 1.11 4 0.86

11 1.79 15 0.30 6 0.4513 1.79 21 0.20 8 0.4017 1.34 ≥27 0.18 10 0.4019 1.11 ≥12 0.2023 0.99

≥25 0.5025h + 0.20

Table 26: Compatibility Levels for the Intermediary Voltage 33kV in a 132/33/11kV Trans-formation Series



5 2.33 3 2.33 2 1.167 2.33 9 1.07 4 0.83

11 1.66 15 0.30 6 0.4513 1.66 21 0.20 8 0.4017 1.20 ≥27 0.18 10 0.4019 1.07 ≥12 0.2023 0.86

≥25 0.5025h + 0.20

Table 27: Planning Levels for the Intermediary Voltage 66kV in a 132/66/11kV Transforma-tion Series



5 5.15 3 3.76 2 1.627 3.76 9 1.33 4 0.95

11 2.69 15 0.37 6 0.5013 2.40 21 0.27 8 0.4717 1.62 ≥27 0.20 10 0.47

19 1.33 ≥12 0.1212h + 0.23

23 1.14

≥25 1.1225h − 0.25

≥53 0.2653h + 0.22


DRAFT


Table 28: Compatibility Levels for the Intermediary Voltage 66kV in a 132/66/11kV Trans-formation Series



5 4.65 3 3.04 2 1.397 3.04 9 1.23 4 0.92

11 2.22 15 0.35 6 0.5013 2.06 21 0.25 8 0.4617 1.39 ≥27 0.20 10 0.46

19 1.23 ≥12 0.0712h + 0.23

23 1.15

≥25 0.8725h − 0.24

≥53 0.2653h + 0.22


T HARMONIC VOLTAGE DISTORTION AND THE...Resonant Plant to supply systems. This staged approach...

Documents

Transcript of T HARMONIC VOLTAGE DISTORTION AND THE...Resonant Plant to supply systems. This staged approach...