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IEC TS 62749
Edition 2.0 2020-02
TECHNICAL
SPECIFICATION
colour
inside
Assessment of power quality – Characteristics of electricity supplied by public
networks
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IEC TS 62749
Edition 2.0 2020-02
TECHNICAL
SPECIFICATION
colour
inside
Assessment of power quality – Characteristics of electricity supplied by public
networks
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.220.99 ISBN 978-2-8322-7849-9
– 2 – IEC TS 62749:2020 © IEC 2020
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 9
4 Recommended values for power quality indices . 17
4.1 General . 17
4.2 Frequency deviation . 19
4.3 Supply voltage deviation . 19
4.3.1 General . 19
4.3.2 Low voltage systems . 19
4.3.3 Medium voltage systems . 20
4.3.4 High voltage systems . 20
4.4 Voltage unbalance . 20
4.5 Flicker . 21
4.6 Harmonic and interharmonic voltage . 21
4.6.1 General . 21
4.6.2 Low voltage systems . 21
4.6.3 Medium voltage systems . 22
4.6.4 High voltage systems . 23
4.7 Voltage dip . 24
4.8 Voltage swell . 25
4.9 Voltage interruption . 25
4.10 Mains communicating voltage . 26
4.11 Rapid voltage change . 26
4.12 Transient overvoltage . 27
4.12.1 Low voltage systems . 27
4.12.2 Medium and high voltage systems . 27
5 Objectives and methods for power quality assessment . 27
5.1 General . 27
5.2 Site power quality assessment . 28
5.2.1 General . 28
5.2.2 Continuous phenomena . 28
5.2.3 For discontinuous phenomena (single event) . 30
5.3 System aspect power quality assessment . 31
5.3.1 General . 31
5.3.2 For continuous phenomena . 31
5.3.3 For discontinuous phenomena (events) . 31
Annex A (informative) Examples of profiles for power quality specification . 34
A.1 General . 34
A.2 LV and MV public distribution networks in European countries . 34
A.3 LV, MV and HV power supply system in China . 35
A.4 Example of a transmission system in Canada . 36
A.5 Examples of profiles in Australia . 37
Annex B (informative) Additional information on power quality assessments . 38
B.1 Weekly percentile values assessed on a daily sliding basis . 38
B.2 Example on system aspect continuous disturbance evaluation . 39
B.3 Aggregation method used for events . 39
B.3.1 General . 39
B.3.2 Time aggregation . 39
Annex C (informative) Main impact of poor power quality . 42
C.1 General . 42
C.2 Harmonic distortion . 42
C.3 Voltage unbalance . 42
C.4 Voltage deviation . 43
C.5 Frequency deviation . 43
C.6 Voltage fluctuation . 43
C.7 Flicker . 43
C.8 Voltage dip (or voltage sag) . 43
C.9 Transient overvoltages . 43
Annex D (informative) Power quality issues related to distributed generation and
micro-grids . 44
D.1 General . 44
D.2 Voltage deviation . 44
D.3 Harmonics . 44
D.4 DG magnetic bias (DC current injection) . 44
D.5 Voltage fluctuation and flicker . 45
D.6 High frequency conducted disturbances . 45
Annex E (informative) Methods to maintain and improve power quality . 46
E.1 General . 46
E.2 Voltage deviation . 46
E.3 Harmonics . 46
E.4 Flicker . 47
E.5 Voltage unbalance . 47
E.6 Voltage dip/swell/short time interruption . 48
Annex F (informative) Relation between power quality and EMC . 49
F.1 General . 49
F.2 Differences between power quality and compatibility levels . 49
F.3 Example of power quality level versus compatibility level . 50
Annex G (informative) Other phenomena . 53
G.1 General . 53
G.2 Level behaviour over time . 53
G.3 Duration . 53
G.4 Periodicity . 53
G.5 Bandwidth . 54
Annex H (informative) Role of stakeholders for power quality management –
Coordination of the parties involved . 55
H.1 General . 55
H.2 Network operator – Network user . 55
H.3 Network user – Equipment supplier . 55
H.4 Network operator – Equipment supplier . 56
Bibliography . 57
– 4 – IEC TS 62749:2020 © IEC 2020
Figure 1 – Mains communicating voltages recommended values in percent of U used
N
in public LV networks (or U in public MV networks) . 26
c
Figure 2 – Example for illustrating voltage THD assessment result trends . 30
Figure 3 – Example showing information of single event assessment . 31
th
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