IEC TS 62749:2015

IEC TS 62749


®


Edition 1.0 2015-04



TECHNICAL



SPECIFICATION




colour
inside


Assessment of power quality – Characteristics of electricity supplied by public
networks

IEC TS 62749:2015-04(en)

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IEC TS 62749



®



Edition 1.0 2015-04







TECHNICAL





SPECIFICATION











colour

inside










Assessment of power quality – Characteristics of electricity supplied by public

networks




























INTERNATIONAL

ELECTROTECHNICAL


COMMISSION





ICS 17.220.99 ISBN 978-2-8322-2547-9



  Warning! Make sure that you obtained this publication from an authorized distributor.


® Registered trademark of the International Electrotechnical Commission

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– 2 – IEC TS 62749:2015 © IEC 2015


CONTENTS



FOREWORD . 4

INTRODUCTION . 6

1 Scope . 7


2 Normative references . 8

3 Terms and definitions . 9

4 Recommended values for power quality indices . 16


4.1 General . 16
4.2 Frequency deviation . 16
4.3 Supply voltage deviation . 16
4.3.1 General . 16
4.3.2 Low voltage systems . 16
4.3.3 Medium voltage systems. 17
4.3.4 High voltage systems . 17
4.4 Voltage unbalance . 18
4.5 Flicker. 18
4.6 Harmonic and interharmonic voltage . 18
4.6.1 General . 18
4.6.2 Low voltage systems . 18
4.6.3 Medium voltage systems. 19
4.6.4 High voltage systems . 20
4.7 Voltage dip . 21
4.8 Voltage swell . 22
4.9 Voltage interruption. 22
4.10 Mains signalling voltage . 22
4.11 Rapid voltage change . 23
4.12 Transient overvoltage . 23
4.12.1 Low voltage systems . 23
4.12.2 Medium and High voltage systems . 24
5 Objectives and methods for power quality assessment . 24
5.1 General . 24
5.2 Site power quality assessment . 24
5.2.1 General . 24

5.2.2 For continuous phenomena. 25
5.2.3 For discontinuous phenomena (single event) . 26
5.3 System aspect power quality assessment . 27
5.3.1 General . 27
5.3.2 For continuous phenomena. 27
5.3.3 For discontinuous phenomena (events) . 27
Annex A (informative) Examples of PROFILES for Power Quality Specification . 30
A.1 LV public distribution in European countries . 30
A.2 LV, MV and HV power supply system in China . 31
A.3 Example of a transmission system in Canada . 32
A.4 Examples of Profiles in Australia . 33
Annex B (informative) Example on System Aspect Continuous Disturbance Evaluation . 34
Annex C (informative） Main Impact of Poor Power Quality. 35

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IEC TS 62749:2015 © IEC 2015 – 3 –


C.1 Harmonic distortion . 35

C.2 Voltage unbalance . 35

C.3 Voltage deviation . 36

C.4 Frequency deviation . 36

C.5 Voltage fluctuation . 36

C.6 Flicker. 36

C.7 Voltage dip (or Voltage sag) . 36

C.8 Transient overvoltages . 36

Annex D (informative) Power Quality Issues Related to Distributed Generation and

Micro-grids. 37

D.1 Voltage deviation . 37
D.2 Harmonics . 37
D.3 DG magnetic bias (DC current injection) . 37
D.4 Voltage fluctuation and flicker . 37
D.5 High frequency conducted disturbances . 38
Annex E (informative) Methods to Maintain and Improve Power Quality . 39
E.1 Voltage deviation . 39
E.2 Harmonics . 39
E.3 Flicker. 40
E.4 Unbalance . 40
E.5 Voltage dip/swell/short time interruption . 40
Annex F (informative) Relation between Power quality and EMC . 41
Bibliography . 43

Figure 1 – Signal voltages recommended values in percent of U used in public LV
N
networks (or U in public MV networks) . 23
c
Figure 2 – An example for illustrating voltage THD assessment result trends . 26
Figure 3 – An example showing information of single event assessment . 27
Figure F.1 – Application points in a LV system (example) . 42
Figure F.2 – Relation between disturbance levels (Schematic significance only) . 42

Table 1 – Classification of electromagnetic phenomena addressed by power quality
indices . 8
Table 2 – Flicker severity P recommended values . 18

lt
Table 3 – Recommended values of individual harmonic voltages at the low voltage
supply terminals for orders up to 50 given in percent of the fundamental voltage U . 19
1
Table 4 – Recommended values of individual harmonic voltages at the medium voltage
supply terminals for orders up to 50 given in percent of the fundamental voltage U . 20
1
Table 5 – Indicative values of individual harmonic voltages at the high voltage supply
terminals given in percent of the fundamental voltage U . 21
1
Table 6 – Site power quality assessment methods . 25
Table 7 – Example of single event assessment . 27
Table 8 – List of individual events measured at a single monitoring site . 28
Table 9 – SARFI-X indices coming out of Table 8 . 28
Table 10 – Magnitude – duration table format . 29
Table B.1 – Listing of System Power Quality Evaluation . 34

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– 4 – IEC TS 62749:2015 © IEC 2015


INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________


ASSESSMENT OF POWER QUALITY – CHARACTERISTICS OF

ELECTRICITY SUPPLIED BY PUBLIC NETWORKS



FOREWORD


1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC TS 62749, which is a technical specification, has been prepared by IEC technical
committee 8: System aspects of electrical energy supply.

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IEC TS 62749:2015 © IEC 2015 – 5 –


The text of this technical specification is based on the following documents:


DTS Report on voting


8/1363/DTS 8/1381/RVC



Full information on the voting for the approval of this technical specification can be found in

the report on voting indicated in the above table.


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• transformed into an International standard,
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– 6 – IEC TS 62749:2015 © IEC 2015


INTRODUCTION


The description of ELECTRICITY is of fundamental importance within electricity supply

systems. In general, its characteristics depend less on its generation than on the way in which

it is transported by networks and being used by the equipment of the multiple users. Faults or

other events such as short-circuit and lightning strikes occurring within users' installations or

public networks also disturb or degrade it.

There is a need for a common set of power quality indices and measurement methods in order

to allow different system operators to measure and report power quality in a consistent

manner.


Regarding the limits or levels of power quality, the situation differs. Historically, the electrical
systems in different countries/regions have been designed in different ways to cater for
national/regional variations like different geographic, climatic or commercial conditions, etc. It
is thus essential that any set of internationally agreed power quality limits or levels also
recognize these differences which depends namely on the system configuration, the transfer
characteristics between the different voltage levels (attenuation or amplification), the actual
disturbance levels on the system, etc.
Also, the level of power quality is not absolute rather it depends on the price that clients are
willing to pay for it. Optimizing power quality should be carried out in a cost-effective manner
in that if NETWORK USERs expect power quality to be an intrinsic characteristic of the
product they also want it at the lowest price.
This is why some of the objectives recommended hereafter allow for a range of values, or
options, while still ensuring the coordination of disturbance levels between different parts of
the system or voltage levels.
Then, the requirements to be applied can be expressed by the association of the IEC Power
Quality framework from the normative part of this Technical Specification and PROFILES.
Examples of profiles are given in Annex A.
Nowadays, Smart Grid construction and massive deployment of renewable energy sources
increase the complexity of power quality management.

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IEC TS 62749:2015 © IEC 2015 – 7 –


ASSESSMENT OF POWER QUALITY – CHARACTERISTICS OF

ELECTRICITY SUPPLIED BY PUBLIC NETWORKS







1 Scope


This Technical Specification specifies the expected characteristics of electricity at the

SUPPLY TERMINALS of public low, medium and high voltage, 50 Hz or 60 Hz, networks.


NOTE 1 The boundaries between the various voltage levels may be different for different countries/regions. In the
context of this TS, the following terms for system voltage are used:
• low voltage (LV) refers to U ≤ 1 kV;
N
• medium voltage (MV) refers to 1 kV < U ≤ 35 kV;
N
• high voltage (HV) refers to 35 kV < U ≤ 230 kV;
N
NOTE 2 Because of existing network structures, in some countries/regions, the boundary between medium and
high voltage can be different.
Most of the recommendations for power quality at the SUPPLY TERMINALS are expressed as
POWER QUALITY INDICES that describe the manner in which the characteristics of
electricity vary. Such variations may appear random in time, with reference to any specific
supply terminal, and random in location, with reference to any given instant of time. As such,
the POWER QUALITY INDICES are based on the occurrence of the applicable
electromagnetic phenomena:
• continuous phenomena, i.e. deviations from the nominal value that occur continuously
over time. Such phenomena occur mainly due to load pattern, changes of load, non-linear
loads or distributed generation, and
• discontinuous phenomena or events, i.e. sudden and significant deviations from normal or
desired wave shape which typically occur due to unpredictable events (e.g. faults) or
external causes (e.g. weather conditions).
The power quality indices and the recommended values are intended to be used as technical
reference for regulatory purposes (e.g. in NETWORK CODES) or for contracts between
network operator and network user (e.g. part of a CONNECTION AGREEMENT).
Power quality requirements combine the obligations of NETWORK OPERATORS with the
requirements of equipment or installations on the electromagnetic environment. It is worth
noting however, that the requirements of equipment or installations on the electromagnetic
environment also include emission aspects that are addressed in other IEC standards (see
Clause 2 and Annex F).

NOTE 3 Network operators are in charge of developing and operating the electricity supply system taking into
account at the same time:
• provision of adequate conditions for equipment, installations or other networks connected to their network;
• avoidance of unnecessary costs.
NOTE 4 In many countries/regions, requirements concerning the essential characteristics of electricity at supply
terminals of public networks are set, or controlled, by National/Regional Regulatory Authorities.
In some cases, additional requirements or differences in requirements can be agreed by
terms of a contract (usually a CONNECTION AGREEMENT) between an individual NETWORK
USER and the network operator. Such a contract is most likely to arise for network users with
relatively large electricity demand, supplied from the MV or HV network, or having power
quality sensitive load. It may also arise in sparsely populated or difficult terrain, such as
mountain regions, where distribution costs are high. In such an area a network user may be
willing to accept a connection, at lower cost, which does not entirely comply with the power
quality standards.
NOTE 5 The quality indices and the recommended values appropriately cover the vast majority of locations under
acceptable economic conditions, despite the differences in situations, provided that:

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– 8 – IEC TS 62749:2015 © IEC 2015


• for mass-market products, emission requirements in standards such as IEC 61000-3-2, 3-3, 3-11and/or 3-12

are regularly and appropriately updated to take into account the development of markets and changes in
technologies;

• for large installations, emission levels are effectively controlled, e.g. through connection agreement (Annex E
lists some methods to improve power quality);


• network operators make use of appropriate methodologies and engineering practices, e.g. based on
PLANNING LEVELS and IEC TR 61000-3-6, 3-7, 3-13 and/or 3-14.

This Technical Specification applies to the phenomena listed in Table 1.

Table 1 – Classification of electromagnetic phenomena

addressed by power quality indices


Continuous phenomena Discontinuous phenomena – Events
FREQUENCY DEVIATION SUPPLY INTERRUPTION
SUPPLY VOLTAGE DEVIATION VOLTAGE DIP
VOLTAGE UNBALANCE VOLTAGE SWELL
HARMONIC VOLTAGE TRANSIENT OVERVOLTAGE
INTERHARMONIC VOLTAGE RAPID VOLTAGE CHANGE

FLICKER （VOLTAGE FLUCTUATION）
MAINS SIGNALLING VOLTAGES

NOTE 6 Specification of related measurement methods can be found in IEC 61000-4-30, EMC – Testing and
measurement techniques – Power Quality measurement methods.
NOTE 7 Specification of the performance of related measuring instruments can be found in IEC 62586, Power
quality measurement in power supply systems.
While power quality is related to EMC in a number of ways, especially because compliance
with power quality requirements depends on the control of cumulative effect of
electromagnetic emission from all/multiple equipment and/or installations, this Technical
Specification is not an EMC publication (see also Annex F).
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60038, IEC standard voltages
IEC 60364-4-44, Low-voltage electrical installations – Part 4-44: Protection for safety –

Protection against voltage disturbances and electromagnetic disturbances
IEC 60364-5-53, Electrical installations of buildings – Part 5-53: Selection and erection of
electrical equipment – Isolation, switching and control
IEC 61000-2-2, Electromagnetic compatibility (EMC) – Part 2-2: Environment – Compatibility
levels for low-frequency conducted disturbances and signalling in public low-voltage power
supply systems
IEC TR 61000-2-8, Electromagnetic compatibility (EMC) – Part 1-8: Environment – Voltage
dips and short interruptions on public electric power supply systems with statistical
measurement results
IEC 61000-2-12, Electromagnetic compatibility (EMC) – Part 2-12: Environment –
Compatibility levels for low-frequency conducted disturbances and signalling in public
medium-voltage power supply systems
IEC TR 61000-2-14, Electromagnetic compatibility (EMC) – Part 2-14: Environment –
Overvoltages on public electricity distribution networks

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IEC TS 62749:2015 © IEC 2015 – 9 –


IEC 61000-3-2, Electromagnetic compatibility (EMC) – Part 3-2: Limits – Limits for harmonic

current emissions (equipment input current ≤ 16 A per phase)


IEC 61000-3-3, Electromagnetic compatibility (EMC) – Part 3-3: Limits – Limitation of voltage

changes, voltage fluctuations and flicker in public low-voltage supply systems, for equipment

with rated current ≤ 16 A per phase and not subject to conditional connection

IEC TR 61000-3-6, Electromagnetic compatibility (EMC) – Part 3-6: Limits – Assessment of

emission limits for the connection of distorting installations to MV, HV and EHV power

systems


IEC TR 61000-3-7, Electromagnetic compatibility (EMC) – Part 3-7: Limits – Assessment of

emission limits for the connection of fluctuating load installations to MV, HV and EHV power
systems
IEC 61000-3-11,
...