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
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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

– 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

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
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
Table 5 – Indicative values of individual harmonic voltages at the high voltage supply
terminals given in percent of the fundamental voltage U . 21
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

– 4 – IEC TS 62749:2015 © IEC 2015

INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
ASSESSMENT OF POWER QUALITY – CHARACTERISTICS OF

ELECTRICITY SUPPLIED BY PUBLIC NETWORKS

FOREWORD
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all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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The main task of IEC technical committees is to prepare International Standards. In
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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.

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.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

The committee has decided that the contents of this publication will remain unchanged until

the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 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.

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:

– 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

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, Electromagnetic compatibility (EMC) – Part 3-11: Limits – Limitation of
voltage changes, voltage fluctuations and flicker in public low-voltage supply systems –
Equipment with rated current ≤ 75 A and subject to conditional connection
IEC 61000-3-12, 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
IEC TR 61000-3-13, Electromagnetic compatibility (EMC) – Part 3-13: Limits – Assessment of
emission limits for the connection of unbalanced installations to MV, HV and EHV power
systems
IEC TR 61000-3-14, Electromagnetic compatibility (EMC) – Part 3-14: Limits – Assessment of
emission limits for the connection of disturbing installations to LV power systems
IEC 61000-4-7:2009, 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
IEC 61000-4-15, Electromagnetic compatibility (EMC) – Part 4-15: Testing and measurement
techniques – Flickermeter – Functional and design specifications
IEC 61000-4-30:2008, Electromagnetic compatibility (EMC) – Part 4-30: Testing and
measurement techniques – Power quality measurement methods
IEC 62586-1, Power quality measurement in power supply systems – Part 1: Power quality
instruments (PQI)
IEC 62586-2, Power quality measurement in power supply systems – Part 2: Functional tests
and uncertainty requirements
3 Terms and definitions
For the purpose of this Technical Specification, the following terms and definitions apply.
NOTE Terms are listed in alphabetical order.
3.1
code (in electric power system)
collection of rules concerning rights and duties of the parties involved in a certain part of the
electric power system
Note 1 to entry: For example: grid code, distribution code.
[SOURCE: IEC 60050-617:2009, 617-03-03]

– 10 – IEC TS 62749:2015 © IEC 2015

3.2
connection agreement
agreement entered between the system operator and a system user which governs the

procedure and conditions for connection

[SOURCE: IEC 60050-617:2009, 617-04-03]

3.3
declared supply voltage
U (abbreviation)
c
supply voltage U agreed by the network operator and the network user
c
Note 1 to entry: Generally declared supply voltage U is the nominal voltage U but it may be different according
c N
to the agreement between the network operator and the network user.
3.4
electricity
set of the phenomena associated with electric charges and electric currents
[SOURCE: IEC 60050-121:1998, 121-11-76]
Note 1 to entry: In the context of electric power systems, electricity is often described as a product with particular
characteristics.
3.5
electromagnetic compatibility
ability of an equipment or system to function satisfactorily in its electromagnetic environment
without introducing intolerable electromagnetic disturbances to anything in that environment
[SOURCE: IEC 60050-161:1990, 161-01-07]
3.6
(electromagnetic) compatibility level
specified electromagnetic disturbance level used as a reference level for coordination in the
setting of emission and immunity limits
Note 1 to entry: By convention, the compatibility level is chosen so that there is only a small probability that it will
be exceeded by the actual disturbance level.
3.7
flicker
impression of unsteadiness of visual sensation induced by a light stimulus whose luminance
or spectral distribution fluctuates with time
Note 1 to entry: Voltage fluctuation cause changes of the luminance of lamps which can create the visual
phenomenon called flicker. Above a certain threshold, flicker becomes annoying. The annoyance grows very
rapidly with the amplitude of the fluctuation. At certain repetition rates, even very small amplitudes can be
annoying.
Note 2 to entry: For the time being, flicker is qualified based on incandescent lamp’s behavior.
[SOURCE: IEC 60050-161:1990, 161-08-13, modified (addition of Notes to entry)]
3.8
flicker severity
intensity of flicker annoyance evaluated by the following quantities:
• short term severity (P ) measured over a period of ten minutes;
st
) calculated from a sequence of 12 Pst-values over a two hour
• long term severity (P
lt
interval, according to the following expression:
12 3
P
sti
P = 3
lt ∑
i =1
Note 1 to entry: For details of Pst and Plt, see IEC 61000-4-15.

3.9
frequency deviation
difference between power supply frequency (f ) and nominal frequency (f )
H,1 N
3.10
group total harmonic distortion

THDG (abbreviation)
(symbol)
THDG
Y
ratio of the r.m.s. value of the harmonic groups (Y ) to the r.m.s. value of the group
g,h
associated with the fundamental (Y ):
g,1
h
max
 
Y
g,h
 
THDG =
Y
∑
 
Y
g,1
h=2  
Note 1 to entry: The symbol Y is replaced, as required, by the symbol I for currents or by the symbol U for
voltages.
[SOURCE: IEC 61000-4-7:2009, 3.3]
3.11
harmonic frequency
f (abbreviation)
H,h
frequency which is an integer multiple of the power supply (fundamental) frequency
[SOURCE: IEC 61000-4-7:2009, 3.2.1, modified (removal of formula and Note to entry)]
3.12
harmonic order
h (abbreviation)
(integer) ratio of a harmonic frequency (f ) to the power supply frequency (f )
H,h H,1
3.13
harmonic ratio
HR (abbreviation)
ratio of individual harmonic order component (U or I ) to the fundamental component
h h
(U or I )
1 1
3.14
mains signalling voltage
signal superimposed on the supply voltage for the purpose of transmission of information in
the public supply network and to network users' premises

Note 1 to entry: Three types of signals in the public supply network can be classified:
• ripple control signals: superimposed sinusoidal voltage signals in the frequency range 110 Hz to 3 000 Hz;
• power-line-carrier signals: superimposed sinusoidal voltage signals in the frequency range 3 kHz to 148,5 kHz;
• mains marking signals: superimposed short time alterations (transients) at selected points of the voltage
waveform.
3.15
network operator
system operator
party responsible for safe and reliable operation of a part of the electric power system in a
certain area and for connection to other parts of the electric power system
[SOURCE: IEC 60050-617:2009, 617-02-09]
3.16
nominal frequency
f (abbreviation)
N
value of frequency used to designate or identify a system

– 12 – IEC TS 62749:2015 © IEC 2015

3.17
nominal system voltage
U (abbreviation)
N
value of voltage used to designate or identify a system

[SOURCE: IEC 60050-601:1985, 601-01-21, modified (addition of abbreviation, removal of

"suitable approximate" from beginning of definition)]

3.18
normal operating conditions (of a public electricity supply system)

operating conditions of a public electricity supply system typically including all generation

variations, load variations and reactive compensation or filter states (e.g. shunt capacitor

states), planned outages and planned arrangements during maintenance and construction
work, non-ideal operating conditions and normal contingencies under which the considered
system has been designed to operate
Note 1 to entry: Normal system operating conditions typically exclude exceptional situations such as: conditions
arising as a result of a fault or a combination of faults beyond that planned for under the system security standard,
unavoidable circumstances (for example: force majeure, exceptional weather conditions and other natural disasters,
acts by public authorities, industrial actions), cases where NETWORK USERs significantly exceed their emission
limits or do not comply with the connection requirements, and temporary generation or supply arrangements
adopted to maintain supply to NETWORK USERs during maintenance or construction work, where otherwise supply
would be interrupted.
[SOURCE: IEC TR 61000-3-6:2008, 3.14, modified ("of a public electricity supply system"
added to term and definition)]
3.19
percentile value
U (symbol)
x%
value such that × percent (x %) of measurements are smaller than or equal to that value, over
a given period
3.20
planning level
level of a particular disturbance in a particular environment, adopted as a reference value for
the limits to be set for the emissions from the installations in a particular system, in order to
co-ordinate those limits with all the limits adopted for equipment and installations intended to
be connected to the power supply system
Note 1 to entry: Planning levels are considered internal quality objectives to be specified at a local level by those
responsible for planning and operating the power supply system in the relevant area.
[SOURCE: IEC TR 61000-3-6:2008, 3.16]
3.21
point of common coupling
PCC (abbreviation)
point in a public power supply network, electrically nearest to a particular load, at which other
loads are or may be connected
Note 1 to entry: These loads can be either devices, equipment or systems, or distinct network user’s installations.
[SOURCE: IEC 60050-161:1990, 161-07-15, modified ("consumer's installation" replaced by
"load")]
3.22
supply terminals
point in a distribution network designated as such and contractually fixed, at which electric
energy is exchanged between contractual partners
Note 1 to entry: Supply terminals may be different from the boundary between the electricity supply system and
the user’s own installation or from the metering point.
[SOURCE: IEC 60050-617:2009, 617-04-02, modified Note 1 to entry]

3.23
(power) network user
party supplying electric power and energy to, or being supplied with electric power and energy

from, a transmission system or a distribution system

[SOURCE: IEC 60050-617:2009, 617-02-07]

3.24
power quality
characteristics of the electricity at a given point on an electrical system, evaluated against a

set of reference technical parameters

Note 1 to entry: These parameters might, in some cases, relate to the compatibility between electricity supplied
on a network and the loads connected to that network.
Note 2 to entry: In the context of this Technical Specification, power quality refers to supply terminals and
focuses on defining the characteristics of the voltage and frequency.
[SOURCE: IEC 60050-617:2009, 617-01-05, modified ("electric current, voltage and
frequencies" replaced by "electricity" and Note 2 to entry added)]
3.25
power quality indices
technical parameters characterizing the quality of electricity, measured at a given point,
relevant for the assessment of the quality of the electricity delivered by a network operator
3.26
profile
specification that supplement a standard by limiting options, in order to serve the needs of
users in a geographic area or in an application domain
3.27
r.m.s. value of a harmonic component
Y (abbreviation)
H,h
r.m.s. value of one of the components having a harmonic frequency in the analysis of a non-
sinusoidal waveform. For brevity, such a component may be referred to simply as a 'harmonic'
Note 1 to entry: The symbol Y is replaced, as required by the symbol I for currents, by the symbol U for voltages.
Note 2 to entry: For more details, see IEC 61000-4-7:2009.
[SOURCE: IEC 61000-4-7:2009, 3.2.3]
3.28
r.m.s. value of a harmonic group
Y (abbreviation)
g,h
square root of the sum of the squares of the r.m.s. value of a harmonic and the spectral
components adjacent to it within the time window, thus summing the energy contents of the

neighboring components with that of the harmonic proper
Note 1 to entry: The symbol Y is replaced, as required by the symbol I for currents, by the symbol U for voltages.
Note 2 to entry: For more details, see IEC 61000-4-7:2009.
[SOURCE: IEC 61000-4-7:2009, 3.2.4]
3.29
r.m.s. value of an interharmonic centred subgroup
Y (abbreviation)
isg,h
r.m.s. value of all interharmonic components in the interval between two consecutive
harmonic frequencies, excluding frequency components directly adjacent to the harmonic
frequencies
Note 1 to entry: The r.m.s. value of the centred subgroup between the harmonic orders h and h + 1 is designated
as Y ; for example, the centred subgroup between h = 5 and h = 6 is designated as Y
isg,h isg,5.
Note 2 to entry: For more details, see IEC 61000-4-7:2009.

– 14 – IEC TS 62749:2015 © IEC 2015

[SOURCE: IEC 61000-4-7:2009, 3.4.4]

3.30
r.m.s. value of an interharmonic component

Y (abbreviation)
C,i
r.m.s. value of a spectral component of an electrical signal with a frequency between two

consecutive harmonic frequencies

For brevity, such a component may be referred to simply as an ‘interharmonic’.

Note 1 to entry: For more details, see IEC 61000-4-7:2009, 3.4.2.

3.31
rapid voltage change
RVC (abbreviation)
quick transition (that may last more than several cycles) in r.m.s. voltage between two steady-
state conditions while the voltage stays in-between the thresholds defined for voltage swells
and dips (otherwise, it would be considered as a swell or a dip)
RVC is expressed by the relative steady-state voltage change and/or by a maximum relative
r.m.s. voltage change aggregated over several cycles.
Note 1 to entry: For more information, see IEC 61000-4-30.
3.32
recommended values
value under which, or values within which, the voltage characteristics should remain in view of
providing an acceptable quality of the electricity supply
Note 1 to entry: The characteristics of electricity agreed between network operator and a network user or set by
national/regional regulatory authority can be locally optimized.
3.33
reference voltage (for interruptions, voltage dips and voltage swells measurement and
evaluation)
value specified as the base on which residual voltage, thresholds and other values are
expressed in per unit or percentage terms
3.34
supply voltage
r.m.s. value of the line-to-line or line-to-neutral voltage at a given time at the supply terminal,
measured over a given interval
3.35
time aggregation
combination of several sequential values of a given parameter (each determined over
identical time intervals) to provide a value for a longer time interval

Note 1 to entry: In this Technical Specification, 3 s value refers to IEC 61000-4-30 150/180-cycle interval
aggregation value (150 cycles for 50 Hz nominal or 18
...