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Foreword

This European Standard was prepared by the Working Group 1, Physical characteristics of electrical energy of the Technical Committee CENELEC TC 8X, System aspects of electricalenergy supply. It is submitted to the formal vote.

This European Standard will supersede EN 50160:2006.

The following dates are proposed:

latest date by which the existence of the ENhas to be announced at national level (doa) dor + 6 months

latest date by which the EN has to be implementedat national level by publication of an identicalnational standard or by endorsement (dop) dor + 12 months

latest date by which the national standards conflictingwith the EN have to be withdrawn (dow) dor + 36 months

(to be confirmed or modified when voting)

__________

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Contents

1 Scope and object .......................................................................................................................... 4 1.1 Scope ................................................................................................................................... 4 1.2 Object................................................................................................................................... 4

2 Normative references ................................................................................................................... 5 3 Definitions ...................................................................................................................................... 6

4

Low-voltage supply characteristics ............................................................................................ 11

4.1 General .............................................................................................................................. 11 4.2 Continuous phenomena ................................................................................................... 11

4.2.1 Power frequency ..................................................................................................... 11 4.2.2 Supply voltage variations ........................................................................................ 11 4.2.2.1 Requirements........................................................................................................ 11 4.2.3 Rapid voltage changes ........................................................................................... 12 4.2.4 Supply voltage unbalance ...................................................................................... 12 4.2.5 Harmonic voltage .................................................................................................... 12 4.2.6 Interharmonic voltage ............................................................................................. 13 4.2.7 Mains signalling voltage on the supply voltage .................................................... 13

4.3 Voltage events ................................................................................................................... 14 4.3.1 Interruptions of the supply voltage ......................................................................... 14 4.3.2 Supply voltage dips/swells ..................................................................................... 14 4.3.3 Transient overvoltages between live conductors and earth ................................16

5 Medium-voltage supply characteristics ..................................................................................... 17 5.1 General .............................................................................................................................. 17 5.2 Continuous phenomena ................................................................................................... 17

5.2.1 Power frequency ..................................................................................................... 17 5.2.2 Supply voltage variations ........................................................................................ 17 5.2.2.1 Requirements........................................................................................................ 17 5.2.3 Rapid voltage changes ........................................................................................... 18 5.2.4 Supply voltage unbalance ...................................................................................... 18 5.2.5 Harmonic voltage .................................................................................................... 18 5.2.6 Interharmonic voltage ............................................................................................. 19 5.2.7 Mains signalling voltage on the supply voltage .................................................... 19

5.3 Voltage events ................................................................................................................... 20 5.3.1 Interruptions of the supply voltage ......................................................................... 20 5.3.2 Supply voltage dips/swells ..................................................................................... 20 5.3.3 Transient overvoltages between live conductors and earth ................................22

6 High-voltage supply characteristics........................................................................................... 23 6.1 General .............................................................................................................................. 23 6.2 Continuous phenomena ................................................................................................... 23

6.2.1 Power frequency ..................................................................................................... 23 6.2.2 Supply voltage variations........................................................................................ 23 6.2.3 Rapid voltage changes ........................................................................................... 23 6.2.4 Supply voltage unbalance ...................................................................................... 24 6.2.5 Harmonic voltage .................................................................................................... 24 6.2.6 Interharmonic voltage ............................................................................................. 25 6.2.7 Mains signall ing voltage on the supply voltage .................................................... 25

6.3 Voltage events................................................................................................................... 25 6.3.1 Interruptions of the supply voltage......................................................................... 25 6.3.2 Supply voltage dips/swells ..................................................................................... 25 6.3.3 Transient overvoltages between live conductors and earth ................................ 27

Annex A (informative) Special nature of electricity ........................................................................ 28 Annex B (informative) Indicative values for voltage events and single rapid voltagechanges ............................................................................................................................................... 30 Bibliography ........................................................................................................................................ 33

Formattato: Evidenziato

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1 Scope and object

1.1 Scope

This European Standard defines, describes and specifies the main characteristics of the voltageat a network user's supply terminals in public low voltage, medium and high voltage electricitydistribution networks under normal operating conditions. This standard describes the limits or

values within which the voltage characteristics can be expected to remain over the whole of thepublic distribution network and does not describe the average situation usually experienced byan individual network user.

NOTE For the definitions of low, medium and high voltage see 3.1 to 3.3.

The European Standard does not apply under abnormal operating conditions including thefollowing:

a temporary supply arrangement to keep the network users supplied during condition arisingas a result of a fault, maintenance and construction work or to minimize the extent andduration of a loss of supply;

in case of non-compliance of a network user's installation or equipment with the relevantstandards or with the technical requirements for connection, established either by the public

authorities or the network operator including the limits for the emission of conducteddisturbances;

NOTE A network users installation may include load as well as generation.

in exceptional situations, in particular, exceptional weather conditions and other natural disasters, third party interference, acts by public authorities, industrial actions (subject to legal requirements), force majeure, power shortages resulting from external events.

The voltage characteristics given in this standard are not intended to be used aselectromagnetic compatibility (EMC) levels or user emission limits for conducted disturbances in

public distribution networks.

The voltage characteristics given in this standard are not intended to be used to specifyrequirements in equipment product standards and in installation standards.

NOTE The performance of equipment might be impaired if it is subjected to supply conditions which are notspecified in the equipment product standard.

This standard may be superseded in total or in part by the terms of a contract between theindividual network user and the network operator.

Measurement methods to be applied in this standard are described in EN 61000-4-30.

1.2 Object

The object of this European Standard is to define and describe the characteristics of the supplyvoltage concerning

frequency, magnitude, wave form,

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symmetry of the line voltages.

These characteristics are subject to variations during the normal operation of a supply systemdue to changes of load, disturbances generated by certain equipment and the occurrence of faults which are mainly caused by external events.

The characteristics vary in a manner which is random in time, with reference to any specific

supply terminal, and random in location, with reference to any given instant of time. Because of these variations, the levels of the characteristics can be expected to be exceeded on a smallnumber of occasions.

Some of the phenomena affecting the voltage are particularly unpredictable, which make it verydifficult to give useful definite values for the corresponding characteristics. The values given inthis standard for such phenomena, e.g. voltage dips and voltage interruptions, shall beinterpreted accordingly.

2 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 thereferenced document (including any amendments) applies.

IEC 60038+ A1+ A2

198319941997

IEC standard voltages

IEC 60050-161 International Electrotechnical Vocabulary - Chapter 161:Electromagnetic compatibility

IEC/TR 61000-2-8 2002 Electromagnetic compatibility (EMC) Part 2-8: Environment Voltage dips and short interruptions on public electric power supply systems with statistical measurement results

IEC 60364-4-44+ A1

20012003

Electrical installations of buildings Part 4-44: Protection for safety - Protection against voltage disturbances andelectromagnetic disturbances

IEC 60364-5-53

+ A1

2001

2002

Electrical installations of buildings Part 5-53: Selection and

erection of electrical equipment - Isolation, switching andcontrol

IEC 61000-3-7 1996 Electromagnetic compatibility (EMC) Part 3-7: Limits Assessment of emission limits for HV and MV fluctuating loads

EN 60664-1 2003 Insulation coordination for equipment within low-voltagesystems Part 1: Principles, requirements and tests(IEC 60664-1:1992 + A1:2000 + A2:2002)

EN 61000-3-3 1995 Electromagnetic compatibility (EMC) Part 3-3: Limits -Limitation of voltage changes, voltage fluctuations and flicker in public low-voltage supply systems, for equipment with ratedcurrent

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3 Definitions

For the purposes of this document, the following terms and definitions apply.

NOTE References and compliance with IEV as far as possible - will be checked.

3.1low voltage (LV)

voltage whose nominal r.m.s. value is U n 1 kV.

3.2medium voltage (MV)

voltage whose declared r.m.s. value is 1 kV < U C 35 kV.

NOTE According to the existing network structures, in some countries the boundary between MV and HV can bedifferent.

3.3high voltage (HV)

voltage whose declared r.m.s. value is 35 kV < U C 150 kV.

NOTE According to the existing network structures, in some countries the boundary between MV and HV can bedifferent.

3.4network user

party being supplied by or supplying to an electricity supply network.

NOTE In several countries, the term network user includes network operators connected to a supply network withthe same or higher voltage level.

3.5

network operator party responsible for operating, ensuring the maintenance of and, if necessary, developing thesupply network in a given area and, for ensuring the long term ability of the network to meetreasonable demands for the electricity supply.

3.6normal operating conditionfor a supply network, condition of meeting load and generation demands, system switching and clearing faults by automatic system protection excluding the abnormal operating conditionslisted in 1.1.

3.7supply terminal

point in a public supply network designated as such and contractually fixed, at which electricalenergy is exchanged between contractual partners.NOTE This point can differ from, for example, the electricity metering point or the point of common coupling.

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3.8supply voltage

r.m.s. value of the voltage at a given time at the supply terminal, measured over a giveninterval.

3.9

nominal voltage ( U n)voltage by which a supply network is designated or identified and to which certainoperating characteristics are referred.

3.10declared supply voltage ( U c )

the declared supply voltage U c is normally the nominal voltage U n of the supply network. If byagreement between the network operator and the network user a voltage different from thenominal voltage is applied to the terminal, then this voltage is the declared supply voltage U c.

3.11frequency of the supply voltage

repetition rate of the fundamental wave of the supply voltage measured over a given interval of time.

3.12conducted disturbance

electromagnetic phenomenon propagated along the line conductors of a supply network. Insome cases an electromagnetic phenomenon is propagated across transformer windings andhence between networks of different voltage levels. These disturbances may degrade theperformance of a device, equipment or system or they may cause damage.

3.13voltage variation

increase or decrease of voltage normally due to load variations.

3.14rapid voltage change

a single rapid variation of the r.m.s. value of a voltage between two consecutive levels whichare sustained for definite but unspecified durations (for more information see EN 61000-3-3).

3.15voltage fluctuation

series of voltage changes or a cyclic variation of the voltage envelope.

[IEV 161-08-05]

3.16

flicker impression of unsteadiness of visual sensation induced by a light stimulus whose luminance or spectral distribution fluctuates with time.

[IEV 161-08-13]

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NOTE Voltage fluctuation cause changes of the luminance of lamps which can create the visual phenomenon calledflicker. 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.

3.17flicker severity

intensity of flicker annoyance defined by the UIE-IEC flicker measuring method and evaluated

by the following quantities: short term severity (P st ) measured over a period of ten minutes;

long term severity (P lt) calculated from a sequence of 12 P st -values over a two hour interval, according to the following expression:

3

12

112

3

=

=i

P stilt P

3.18supply interruption

condition in which the voltage at the supply terminals is lower than 5 % of the reference voltage. A supply interruption can be classified as

prearranged , when network users are informed in advance, to allow the execution of scheduled works on the distribution network, or

accidental , caused by permanent or transient faults, mostly related to external events,equipment failures or interference. An accidental interruption is classified as:

a long interruption (longer than three minutes);

a short interruption (up to and including three minutes).NOTE 1 Normally, interruptions are being caused by the operation of switches or protecting devices.NOTE 2 The effect of a prearranged interruption can be minimized by the network users by taking appropriatemeasures.NOTE 3 Accidental supply interruptions are unpredictable, largely random eventsNOTE 4 For polyphase systems, an interruption happens when the voltage falls below 5 % of the reference voltageon all phases (otherwise, it is a dip).NOTE 5 In some countries, the term Very Short Interruptions (VSI) or transitory interruptions are used to classifyinterruptions with duration shorter than 1 to 5 seconds. Such interruptions are related to automatic reclosing device

operation..

3.19voltage dipa temporary reduction of the voltage at a point in the electrical supply system below a specifiedstart threshold. For the purpose of this standard, the dip start threshold is equal to 90 % of thereference voltage).

NOTE 1 Typically, a dip is associated with the occurrence and termination of a short circuit or other extreme currentincrease on the system or installations connected to it.NOTE 2 For the purpose of this standard, a voltage dip is a two dimensional electromagnetic disturbance, the levelof which is determined by both voltage and time (duration).

3.20reference voltage (for voltage dips and swells evaluation)

a value specified as the base on which residual voltage, thresholds and other values areexpressed in per unit or percentage termsNOTE For the purpose of this standard, the reference voltage is the nominal or declared voltage of the supplysystem.

3.21

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voltage dip start thresholdan r.m.s. value of the voltage on an electricity supply system specified for the purpose of defining the start of a voltage dip.

3.22voltage dip end threshold

an r.m.s. value of the voltage on an electricity supply system specified for the purpose of defining the end of a voltage dip.

3.23voltage dip duration

the time between the instant at which the voltage at a particular point of an electricity supplysystem falls below the start threshold and the instant at which it rises to the end threshold. For the purpose of the standard, the duration of a voltage dip is from 20 ms up to and including 1min.NOTE For polyphase events a dip begins when the voltage of at least one phase falls below the dip start thresholdand ends when the voltage on all phases is equal to or above the dip end threshold.

3.24voltage dip residual voltage

the minimum value of r.m.s. voltage recorded during a voltage dip.NOTE For the purpose of this standard, the residual voltage is expressed as a percentage of the reference voltage.

3.25voltage swell (temporary power frequency overvoltage)

a temporary increase of the voltage at a point in the electrical supply system above a specifiedstart threshold. For the purpose of this standard, the swell start threshold is equal to the 110 %of the reference voltage (see CLC/TR 50422, Clause 3 for more information).NOTE 1 For the purpose of this standard, a voltage swell is a two dimensional electromagnetic disturbance, thelevel of which is determined by both voltage and time (duration).NOTE 2 Voltage swells may appear between live conductors or between live conductors and earth. Depending onthe neutral arrangement, faults to ground may also give rise to overvoltages between healthy phases and neutral.

3.26voltage swell start threshold

an r.m.s. value of the voltage on an electricity supply system specified for the purpose of defining the start of a voltage swell.

3.27voltage swell end threshold

an r.m.s. value of the voltage on an electricity supply system specified for the purpose of defining the end of a voltage swell.

3.28

voltage swell duration

the time between the instant at which the voltage at a particular point of an electricity supplysystem exceeds the start threshold and the instant at which it falls below the end threshold.

For the purpose of this standard, the duration of a voltage swell is from 20 ms up to and

including 1 min.3.29

transient overvoltage

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short duration oscillatory or non-oscillatory overvoltage usually highly damped and with aduration of a few milliseconds or less.

[IEV 604-03-13 modified]NOTE: Transient overvoltages are usually caused by lightning, switching or operation of fuses. The rise time of atransient overvoltage can vary from less than a microsecond up to a few milliseconds.

3.30harmonic voltagesinusoidal voltage with a frequency equal to an integer multiple of the fundamental frequency of the supply voltage. Harmonic voltages can be evaluated

individually by their relative amplitude ( U h) related to the fundamental voltage U 1, where h isthe order of the harmonic,

globally, for example by the total harmonic distortion factor THD, calculated using thefollowing expression:

=

=40

2

2)(h

huTHD

NOTE: Harmonics of the supply voltage are caused mainly by network users' non-linear loads connected to allvoltage levels of the supply network. Harmonic currents flowing through the network impedance give rise to harmonicvoltages. Harmonic currents and network impedances and thus the harmonic voltages at the supply terminals vary intime.

3.31interharmonic voltage

sinusoidal voltage with a frequency between the harmonics, i.e. the frequency is not an integer multiple of the fundamental.NOTE Interharmonic voltages at closely adjacent frequencies can appear at the same time forming a wide bandspectrum.

3.32voltage unbalance

condition in a polyphase system in which the r.m.s. values of the line-to-line voltages(fundamental component), or the phase angles between consecutive line voltages, are not allequal. The degree of the inequality is usually expressed as the ratios of the negative and zerosequence components to the positive sequence component.

[IEV 161-08-09 modified]NOTE In this European Standard, voltage unbalance is considered in relation to three-phase systems andnegative phase sequence only.

3.33mains signalling voltage

signal superimposed on the supply voltage for the purpose of transmission of information in thepublic supply network and to network users' premises. Three types of signals in the publicsupply network can be classified:

ripple control signals: superimposed sinusoidal voltage signals in the range of 110 Hz to3 000 Hz;

power-line-carrier signals: superimposed sinusoidal voltage signals in the range between3 kHz to 148,5 kHz;

mains marking signals: superimposed short time alterations (transients) at selected pointsof the voltage waveform.

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4 Low-voltage supply characteristics

4.1 General

The present paragraph describes the voltage characteristics of electricity supplied by lowvoltage public networks. In the following, a distinction is made between:

continuous phenomena, i.e . small deviations from the nominal value that occur continuouslyover time. Such phenomena are mainly due to load pattern, changes of load or nonlinear loads.

voltage events, sudden and significant deviations from normal or desired wave shape.Voltage events are typically due to unpredictable events (e.g., faults) or to external causes(e.g., weather, third party actions).

For continuous phenomena, limits are specified 1 2; on the other side, for voltage events, onlyindicative values can be given (see annex B).

The standard nominal voltage U n for public low voltage is U n = 230 V, either between phase andneutral, or between phases.

for four-wire three phase systems:U n = 230 V between phase and neutral;

for three-wire three phase systems:U n = 230 V between phases.

NOTE In low voltage systems declared and nominal voltage are equal.

4.2 Continuous phenomena

4.2.1 Power frequency

The nominal frequency of the supply voltage shall be 50 Hz. Under normal operating conditionsthe mean value of the fundamental frequency measured over 10 s shall be within a range of:

for systems with synchronous connection to an interconnected system:50 Hz 1 % (i.e. 49,5 Hz... 50,5 Hz) during 99,5 % of a year;50 Hz + 4 % / - 6 % (i.e. 47 Hz... 52 Hz) during 100 % of the time;

for systems with no synchronous connection to an interconnected system

(e.g. supply systems on certain islands):50 Hz 2 % (i.e. 49 Hz... 51 Hz) during 95 % of a week;50 Hz 15 % (i.e. 42,5 Hz... 57,5 Hz) during 100 % of the time.

4.2.2 Supply voltage variations

4.2.2.1 RequirementsUnder normal operating conditions, voltage variations should not exceed 10 % of the nominalvoltage U n.

In cases of electricity supplies in networks not interconnected to transmission systems or for special remote customers, voltage variations should not exceed +10% / -15% of U n. Networkusers should be informed of the conditions.

NOTE 1. The actual power consumption required by individual network users is not fully predictable, in terms of amount and of contemporary demand. As a consequence, networks are generally designed on a probabilistic basis.

1 For single rapid voltage changes, only indicative values are given for the time being.2 For some specific parameters, in some national regulations stricter limits may exist.

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If, following a complaint, measurements carried out by the network operator according to 4.2.2.2 indicate that themagnitude of the supply voltage departs beyond Un+/-10% causing negative consequences for the network user, thenetwork operator should take remedial action in collaboration with the network user(s) depending on a riskassessment. The sharing of complaint management and problem mitigation costs between the involved parties isoutside the scope of EN 50160. Temporarily, for the time needed to solve the problem, voltage variations should bewithin the range +10% / -15% of Un , unless otherwise agreed with the network users.NOTE 2 In accordance with relevant product and installation standards and application of IEC 60038, network usersappliances are typically designed to tolerate supply voltages of 10 % around the nominal system voltage, which issufficient to cover an overwhelming majority of supply conditions. It is generally not technically nor economically

viable to give all appliances the ability to handle wider voltage variations at supply terminals.NOTE 3 Identification of what is a special remote customer can vary between countries, taking into account differentcharacteristics of national electric systems as, for instance, limitation of power on the supply terminal and/or power factor limits.

4.2.2.2 Test methodWhen voltage measurements are required, they will be done in accordance with 5.2 of EN61000-4-30 with a measurement period of at least one week.Under normal operating conditions excluding the periods with interruptions the following limitsapply:

100% of all 10 min mean r.m.s. values of the supply voltage shall be below the upper limit of + 10% given in 4.2.2.1 and

At least 99% of the 10 min mean r.m.s. values of the supply voltage shall be above thelower limit of -10% given in 4.2.2.1 and with not more than two consecutive 10 min mean

r.m.s. values below the lower limit of 10%.

4.2.3 Rapid voltage changes

4.2.3.1 Single rapid voltage change

Rapid voltage changes of the supply voltage are mainly caused either by load changes in thenetwork users' installations or by switching in the system.The voltage during a rapid voltage change must not exceed the voltage dip and/or the voltageswell threshold, as it would otherwise be considered as a voltage dip or swell.Some indicative values can be found in Annex B.

4.2.3.2 Flicker severity

Under normal operating conditions, in any period of one week the long term flicker severitycaused by voltage fluctuation should be P lt 1 for 95 % of the time.

NOTE Reaction to flicker is subjective and can vary depending on the perceived cause of the flicker and the periodover which it persists. In some cases P lt = 1 gives rise to annoyance, whereas in other cases higher levels of P lt arefound without annoyance.

4.2.4 Supply voltage unbalance

Under normal operating conditions, during each period of one week, 95 % of the 10 min meanr.m.s. values of the negative phase sequence component (fundamental) of the supply voltageshall be within the range 0 % to 2 % of the positive phase sequence component (fundamental).In some areas with partly single phase or two phase connected network users' installations,unbalances up to about 3 % at three-phase supply terminals occur.

NOTE In this European Standard only values for the negative sequence component are given because thiscomponent is the relevant one for the possible interference of appliances connected to the system.

4.2.5 Harmonic voltage

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Under normal operating conditions, during each period of one week, 95 % of the 10 min meanr.m.s. values of each individual harmonic voltage shall be less than or equal to the value givenin Table 1. Resonances may cause higher voltages for an individual harmonic.

Moreover, the THD of the supply voltage (including all harmonics up to the order 40) shall beless than or equal to 8 %.

NOTE The limitation to order 40 is conventional.

Table 1 - Values of individual harmonic voltages at the supply terminalsfor orders up to 25 given in percent of the fundamental voltage U 1

Odd harmonics

Not multiples of 3 Multiples of 3Even harmonics

Order h

Relativevoltage (U n)

Order h


Order h


5 6,0 % 3 5,0 % 2 2,0 %

7 5,0 % 9 1,5 % 4 1,0 %

11 3,5 % 15 0,5 % 6 24 0,5 %

13 3,0 % 21 0,5 %

17 2,0 %

19 1,5 %

23 1,5 %

25 1,5 %NOTE No values are given for harmonics of order higher than 25, as they are usually small, but largely unpredictable due toresonance effects.

4.2.6 Interharmonic voltage

The level of interharmonics is increasing due to the development of frequency converters andsimilar control equipment. Levels are under consideration, pending more experience.

In certain cases interharmonics, even at low levels, give rise to flicker (see 4.2.3.2), or causeinterference in ripple control systems.

4.2.7 Mains signalling voltage on the supply voltage

In some countries the public distribution networks may be used by the public supplier for thetransmission of signals. Over 99 % of a day the 3 s mean of signal voltages shall be less than or equal to the values given in Figure 1.

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Frequency in kHz

Voltage level in percent

Figure 1 - Voltage levels of signal frequencies in percent of U n usedin public LV distribution networks

NOTE Power line carrier signalling with frequencies in the range from 95 kHz to 148,5 kHz may be used in networkusers' installations. Though the use of the public system for the transmission of signals between network users is notallowed, voltages of these frequencies up to 1,4 V r.m.s. in the public LV distribution network have to be taken intoaccount. Because of the possibility of mutual influences of neighbouring signalling installations the network user mayneed to apply protection or appropriate immunity for his signalling installation against this influence.

4.3 Voltage events

4.3.1 Interruptions of the supply voltage

Interruptions are, by their nature, very unpredictable and variable from place to place and fromtime to time. For the time being, it is not possible to give fully representative statistical results of measurements of interruptions frequency covering the whole of European networks. Areference for actual values recorded in the European networks concerning interruptions is givenin Annex B.

4.3.2 Supply voltage dips/swells

Voltage dips are typically originated by faults occurring in the public network or in the network

users installations.Voltage swells are typically originated by switching operations, load disconnections etc.Both phenomena are unpredictable and largely random. The annual frequency varies greatlydepending on the type of supply system and on the point of observation. Moreover, thedistribution over the year can be very irregular.

4.3.2.1 Voltage dip/swell measurement and detection

Voltage dips/swells shall be measured and detected according to EN 61000-4-30, using asreference the nominal supply voltage for LV networks. The voltage dips/swells characteristics of interest for this standard are residual voltage (maximum r.m.s. voltage for swells) and duration 1.On LV networks, for four-wire three phase systems, the line to neutral voltages shall beconsidered; for three-wire three phase systems the line to line voltages shall be considered; incase of a single phase connection, the supply voltage (line to line or line to neutral, according tothe customer connection) shall be considered.

1 In this standard, values are expressed in percentage terms of the reference voltage.

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Conventionally, the dip threshold is equal to 90 % of the nominal voltage; the threshold for swells is equal to the 110 % of the nominal voltage. The hysteresis is typically 2 %; referencerules for hysteresis are given in clause 5.4.2.1 of EN 61000-4-30.

Note: For polyphase measurements, it is recommended that the number of phases affected by each event aredetected and stored.

4.3.2.2 Voltage dips evaluation

Voltage dips shall be evaluated according to EN 61000-4-30. Post treatment aimed at dipsevaluation depends on the intended purpose.Typically, on LV networks:

if a three-phase system is considered, polyphase aggregation shall be applied;polyphase aggregation consists in defining an equivalent event characterized by asingle duration and a single residual voltage;

time aggregation shall be applied; time aggregation consists in defining anequivalent event in case of multiple successive events; the method used for multipleevents aggregation can be set according to the final use of data; some referencerules are given in IEC TR 61000-2-8.

4.3.2.3 Voltage dips classification

For statistical purposes dips shall be classified according to the following table. The figures tobe put in the cells refer to the number of equivalent events (as defined in the previousparagraph) 1.

Ta b le 2: c l a s s i f i c at ion o f d ips a c c o rd ing to re s idua l vo l t a ge a nd du ra t ion Residual voltage

u [%]Duration t [ms]

20 t 200 200 < t 500 500 < t 1000 1000 < t 5000 5000 < t 60000

90>u>=80 CELL A1 CELL A2 CELL A3 CELL A4 CELL A580>u>=70 CELL B1 CELL B2 CELL B3 CELL B4 CELL B570>u>=40 CELL C1 CELL C2 CELL C3 CELL C4 CELL C540>u>=5 CELL D1 CELL D2 CELL D3 CELL D4 CELL D55 >u CELL X1 CELL X2 CELL X3 CELL X4 CELL X5

Voltage dips are, by their nature, very unpredictable and variable from place to place and fromtime to time. For the time being, it is not possible to give fully representative statistical results of measurements of voltage dips frequency covering the whole of European networks. A referencefor actual values recorded in the European networks concerning dips is given in Annex B.It should be noted that, due to the measurement method adopted, measurement uncertaintyaffecting the results has to be taken into account: this is particularly relevant for shorter events.Measurement uncertainty is addressed in EN 61000-4-30.Dips duration depends generally on the protection strategy adopted on the network, that maydiffer from network to network, depending on network structure and on neutral grounding. As aconsequence, typical durations are not necessarily matching the boundaries of columns of table2.

4.3.2.4 Voltage swells evaluation

1 This table reflects the polyphase network performance. Further information is needed to consider events affectingan individual single-phase voltage in three-phase systems. To calculate the latter, a different evaluation method hasto be applied.

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Voltage swells shall be evaluated according to EN 61000-4-30. Post treatment aimed at swellsevaluation depends on the intended purpose.Typically, on LV networks:

if a three phase system is considered, polyphase aggregation shall be applied;polyphase aggregation consists in defining an equivalent event characterized by asingle duration and a single maximum r.m.s. voltage;

time aggregation shall be applied; time aggregation consists in defining an

equivalent event in case of multiple successive events; the method used for multipleevents aggregation can be set according to the final use of data; some referencerules are given in IEC TR 61000-2-8.

4.3.2.5 Voltage swells classification

Swells shall be classified according to the following table. The figures to be put in the cells refer to the number of equivalent events (as defined in the previous paragraph) 1.

Ta b le 3 : c l a s s i f ic a t ion o f s w e l ls a c c o rd ing to m a x imum v o l t a ge a nd du ra t ion Swell voltage u [%] Duration t [ms]

20 t 500 500 < t 5000 5000 < t 60000u>=120 CELL S1 CELL S2 CELL S3

120>u>=110 CELL T1 CELL T2 CELL T3

A voltage swell generally happens in case of switching operations and load disconnections.

Note 1 Faults in the public distribution network, or in a network user's installation, typically give rise to temporarypower frequency overvoltages between live conductors and earth; such overvoltages disappear when the fault iscleared. Some indicative values are given in Annex B.Note 2 For the classification of swells between live conductors and earth, reference can be made to EN 60364-4-442.

4.3.3 Transient overvoltages between live conductors and earth

Transient overvoltages at the supply terminals are generally caused by lightning (inducedovervoltage) or by switching in the system.

NOTE 1 The rise time can cover a wide range from milliseconds down to much less than a microsecond. However,for physical reasons transients of longer durations usually have much lower amplitudes. Therefore, the coincidence of high amplitudes and a long rise time is extremely unlikely.NOTE 2 The energy content of a transient overvoltage varies considerably according to the origin. An inducedovervoltage due to lightning generally has a higher amplitude but lower energy content than an overvoltage causedby switching, because of the generally longer duration of such switching overvoltages.NOTE 3 LV Installations and end users appliances are designed in accordance with standard EN 60664-1, towithstand transient overvoltages in an overwhelming majority of situations. Where necessary, according toIEC 60364-4-44, surge protective devices should be selected, according to IEC 60364-5-53, to take account of theactual situations. This is assumed to cover the induced over-voltages due to both lightning and switching.

1 This table reflects the polyphase network performance. Further information is needed toconsider events affecting an individual single phase voltage in three-phase systems. Tocalculate the latter, a different evaluation method has to be applied.

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5 Medium-voltage supply characteristics

5.1 General

Network users with demands exceeding the capacity of the low voltage network are generallysupplied at declared voltages above 1 kV. This standard applies to such electricity supplies atdeclared voltages up to and included 35 kV.

NOTE Network users may be supplied at such voltages also to satisfy special requirements or to mitigate conducteddisturbances emitted by their equipment.

The present paragraph describes the voltage characteristics of electricity supplied by mediumvoltage public networks. In the following, a distinction is made between:

voltage variations, i.e. small deviations from the nominal value that occur continuously over time. Voltage variations are mainly due to load pattern, changes of load or nonlinear loads.


For voltage variations, definite limits are given 1, 2; on the other side, for voltage events, onlyindicative values can be given (see annex B).

The magnitude of voltage is given by the declared voltage U c.




for systems with synchronous connection to an interconnected system:50 Hz 1 % (i.e. 49,5 Hz... 50,5 Hz) during 99,5 % of a year;50 Hz + 4 % / - 6 % (i.e. 47 Hz... 52 Hz) during 100 % of the time,

for systems with no synchronous connection to an interconnected system(e.g. supply systems on certain islands):50 Hz 2 % (i.e. 49 Hz... 51 Hz) during 95 % of a week;50 Hz 15 % (i.e. 42,5 Hz... 57,5 Hz) during 100 % of the time.


5.2.2.1 RequirementsUnder normal operating conditions, voltage variations should not exceed 10 % of the declaredvoltage U c .

In cases of electricity supplies in networks not interconnected to transmission systems or for special remote customers, voltage variations should not exceed +10% / -15% of U c. Networkusers should be informed of the conditions.

NOTE 1. The actual power consumption required by individual network users is not fully predictable, in terms of amount and of contemporary demand. As a consequence, networks are generally designed on a probabilistic basis.If, following a complaint, measurements carried out by the network operator according to 5.2.2.2 indicate that themagnitude of the supply voltage departs beyond Uc+/-10%, causing negative consequences for the network user, theNetwork operators should take remedial action in collaboration with the network user(s) depending on a risk

1 For single rapid voltage changes, only indicative values are given.2 For some specific parameter, in single countries stricter limits can be found.

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assessment. The sharing of complaint management and problem mitigation costs between the involved parties isoutside the scope of EN 50160. Temporarily, for the time needed to solve the problem, voltage variations should bewithin the range +10% / -15% of Uc , unless otherwise agreed with the network users.NOTE 2 Identification of what is a special remote customer can vary between countries, taking into account differentcharacteristics of national electric systems as, for instance, limitation of power on the supply terminal and/or power factor limits.

5.2.2.2 Test methodWhen voltage measurements are required, they will be done in accordance with 5.2 of EN61000-4-30 with a measurement period of at least one weekUnder normal operating conditions excluding the periods with interruptions the following limitsapply:

100% of all 10 min mean r.m.s. values of the supply voltage shall be below the upper limit of + 10% given in 5.2.2.1 and

At least 99% of the 10 min mean r.m.s. values of the supply voltage shall be above thelower limit of -10% given in 5.2.2.1 and with not more than two consecutive 10 min meanr.m.s. values below the lower limit of 10%.



Rapid voltage changes of the supply voltage are mainly caused either by load changes in thenetwork users' installations or by switching in the system.The voltage during a rapid voltage change must not exceed the voltage dip and/or the voltageswell threshold, as it would otherwise be considered as a voltage dip or swell.Some indicative values can be found in Annex B.


Under normal operating conditions, in any period of one week the long term flicker severitycaused by voltage fluctuation should be P lt 1 for 95 % of the time.This value was chosen on the assumption that the transfer coefficient between MV and LVsystem is unity. In practice the transfer coefficients between MV levels and LV levels can be

less than 1.In case of complaints, MV limit shall be chosen in such a way that in LV the Plt values do notexceed 1, according to the stages described in IEC 61000-3-7.


Under normal operating conditions, during each period of one week, 95 % of the 10 min meanr.m.s. values of the negative phase sequence component of the supply voltage shall be withinthe range 0 % to 2 % of the positive phase sequence component. In some areas unbalances upto 3 % occur.



Under normal operating conditions, during each period of one week, 95 % of 10 min meanr.m.s. values of each individual harmonic voltage shall be less than or equal to the value givenin Table 4. Resonances may cause higher voltages for an individual harmonic.

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Moreover, the THD of the supply voltage (including all harmonics up to the order 40) shall beless than or equal to 8 %.

NOTE The limitation to order 40 is conventional.


Odd harmonics

Not multiples of 3 Multiples of 3

Even harmonics

Order h

Relativevoltage ( U c )

Order h

Relativevoltage ( U c)

Order h

Relativevoltage ( U c)

5 6,0 % 3 5,0 % a 2 2,0 %

7 5,0 % 9 1,5 % 4 1,0 %

11 3,5 % 15 0,5 % 6 24 0,5 %

13 3,0 % 21 0,5 %

17 2,0 %

19 1,5 %

23 1,5 %

25 1,5 %a Depending on the network design the value for the third harmonic order can be substantially lower. NOTE No values are given for harmonics of order higher than 25, as they are usually small, but largely unpredictable due toresonance effects.


The level of interharmonics is increasing due to the development of frequency converters andsimilar control equipment. Levels are under consideration, pending more experience.

In certain cases interharmonics, even at low levels, give rise to flicker (see 5.4.2), or causeinterference in ripple control system.


In some countries the public distribution networks may be used by the public supplier for thetransmission of signals. Over 99 % of a day the 3 s mean of the signal voltages shall be less or equal to the values given in Figure 2.

NOTE It is assumed that network users do not use the public MV network for signalling purposes.

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Frequency in kHz

Voltage level in percent

Figure 2 - Voltage levels of signal frequencies in percent of U c used in public MV distribution networks

5.3 Voltage events



5.3.2 Supply voltage dips/swells

Voltage dips are typically originated by faults occurring in the public network or in the networkusers installations.Voltage swells are typically originated by switching operations, load disconnections etc.Both phenomena are unpredictable and largely random. The annual frequency varies greatlydepending on the type of supply system and on the point of observation. Moreover, thedistribution over the year can be very irregular.

5.3.2.1 Voltage dip/swell measurement and detection

Voltage dips/swells shall be measured and detected according to EN 61000-4-30, using asreference the declared supply voltage for MV networks. The voltage dips/swells characteristicsof interest for this standard are residual voltage (maximum r.m.s. voltage for swells) andduration 1.Typically, on MV networks, the line to line voltages shall be considered.Conventionally, the dip threshold is equal to 90 % of the nominal voltage; the threshold for swells is equal to the 110 % of the nominal voltage. The hysteresis is typically 2 %; referencerules for hysteresis are given in clause 5.4.2.1 of EN 61000-4-30.

Note: For polyphase measurements, it is recommended that the number of phases affected byeach event are detected and stored.1 In this standard, values are expressed in percentage terms of the reference voltage.

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Voltage dips shall be evaluated according to EN 61000-4-30. Post treatment aimed at dipsevaluation depends on the intended purpose.Typically, on MV networks:

polyphase aggregation is applied; polyphase aggregation consists in defining anequivalent event characterized by a single duration and a single residual voltage;

time aggregation consists in defining an equivalent event in case of multiplesuccessive events; the method used for multiple events aggregation can be setaccording to the final use of data; some reference rules are given in IEC TR 61000-2-8.





20 t 200 200 < t 500 500 < t 1000 1000 < t 5000 5000 < t 60000

90>u>=80 CELL A1 CELL A2 CELL A3 CELL A4 CELL A580>u>=70 CELL B1 CELL B2 CELL B3 CELL B4 CELL B570>u>=40 CELL C1 CELL C2 CELL C3 CELL C4 CELL C540>u>=5 CELL D1 CELL D2 CELL D3 CELL D4 CELL D55 >u CELL X1 CELL X2 CELL X3 CELL X4 CELL X5

Voltage dips are, by their nature, very unpredictable and variable from place to place and fromtime to time. For the time being, it is not possible to give fully representative statistical results of measurements of voltage dips frequency covering the whole of European networks. A referencefor actual values recorded in the European networks concerning dips is given in Annex B.It should be noted that, due to the measurement method adopted, measurement uncertaintyaffecting the results has to be taken into account: this is particularly relevant for shorter events.Measurement uncertainty is addressed in EN 61000-4-30.Dips duration depends generally on the protection strategy adopted on the network, that maydiffer from network to network, depending on network structure and on neutral grounding. As aconsequence, typical durations are not necessarily matching the boundaries of columns of table5.


Voltage swells shall be evaluated according to EN 61000-4-30. Post treatment aimed at swellsevaluation depends on the intended purpose.Typically, on MV networks:

polyphase aggregation shall be applied; polyphase aggregation consists in definingan equivalent event characterized by a single duration and a single maximum r.m.s.voltage;



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Ta b le 6 : c l a s s i f ic a t ion o f s w e l l s a c c o rd ing to ma x imum vo l t a ge a nd du ra t ion Swell voltage u [%] Duration t [ms] 20 t 500 500 < t 5000 5000 < t 60000

u>120 CELL S1 CELL S2 CELL S3120>u>=110 CELL T1 CELL T2 CELL T3

A voltage swell generally happens in case of switching operations and load disconnections.Faults in the public distribution network, or in a network user's installation, give rise to temporarypower frequency overvoltages between live conductors and earth; such overvoltages disappear when the fault is cleared. Some indicative values are given in Annex B.


Transient overvoltages in MV supply systems are caused by switching or, directly or byinduction, by lightning. Switching overvoltages generally are lower in amplitude than lightning

overvoltages, but they can have a shorter rise time and/or longer duration.

NOTE The network users' insulation coordination scheme should be compatible with that adopted by the supplier.

1 This table reflects the polyphase network performance. Further information is needed toconsider events affecting an individual single phase voltage in three-phase systems. Tocalculate the latter, a different evaluation method has to be applied.

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6 High-voltage supply characteristics

6.1 General

Network users with demands exceeding the capacity of the medium voltage network aregenerally supplied at declared voltages above 35 kV. This standard applies to such electricitysupplies at declared voltages up to and included 150 kV.

NOTE Network users may be supplied at such voltages also to satisfy special requirements or to mitigate conducteddisturbances emitted by their equipment.

The present paragraph describes the voltage characteristics of electricity supplied by mediumvoltage public networks. In the following, a distinction is made between:

voltage variations, i.e. small deviations from the nominal value that occur continuously over time. Voltage variations are mainly due to load pattern, changes of load or nonlinear loads.


For voltage variations, definite limits are given 1,2; on the other side, for voltage events, onlyindicative values can be given (see annex B).

The magnitude of voltage is given by the declared voltage U c.




for systems with synchronous connection to an interconnected system:50 Hz 1 % (i.e. 49,5 Hz... 50,5 Hz) during 99,5 % of a year;50 Hz + 4 % / - 6 % (i.e. 47 Hz... 52 Hz) during 100 % of the time,

for systems with no synchronous connection to an interconnected system(e.g. supply systems on certain islands):50 Hz 2 % (i.e. 49 Hz... 51 Hz) during 95 % of a week;50 Hz 15 % (i.e. 42,5 Hz... 57,5 Hz) during 100 % of the time.


As the number of customers supplied directly from HV networks are limited and normallysubject to individual contracts, no limits for supply voltage variations are given in this standard.Existing product standards for HV equipment should be considered.



1 For single rapid voltage changes, only indicative values are given.2 For some specific parameter, in single countries stricter limits can be found.

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Rapid voltage changes of the supply voltage are mainly caused either by load changes in thenetwork users' installations or by switching in the system.The voltage during a rapid voltage change must not exceed the voltage dip and/or the voltageswell threshold, as it would otherwise be considered as a voltage dip or swell.


Under normal operating conditions, in any period of one week the long term flicker severitycaused by voltage fluctuation should be P lt 1 for 95 % of the time.This value was chosen on the assumption that the transfer coefficient between HV and LVsystem is unity. In practice the transfer coefficients between HV levels and LV levels can beless than 1.In case of complaints, HV limit shall be chosen in such a way that in LV the P lt values do notexceed 1, according to the stages described in IEC 61000-3-7.


Under normal operating conditions, during each period of one week, 95 % of the 10 min meanr.m.s. values of the negative phase sequence component of the supply voltage shall be withinthe range 0 % to 2 % of the positive phase sequence component. In some areas unbalances upto 3 % occur.



Under normal operating conditions, during each period of one week, 95 % of 10 min meanr.m.s. values of each individual harmonic voltage shall be less than or equal to the value givenin Table 7. Resonances may cause higher voltages for an individual harmonic.

Moreover, the THD of the supply voltage (including all harmonics up to the order 40) shall beless than or equal to 5 %.Limits for harmonic higher than 13 do not apply for HV meshed networks exceeding 90 kV(included) of nominal voltage.

NOTE The limitation to order 40 is conventional. The measurement of higher order harmonics is not reliable; further information is given in Annex A 2 of EN 61000-4-30.


Odd harmonicsNot multiples of 3 Multiples of 3

Even harmonics

Order h

Relativevoltage

Order h

Relativevoltage

Order h

Relativevoltage

5 4 % 3 3 % 2 1,9 %7 3 % 9 1,3 % 4 1 %

11 2 % 15 0,5 % 6 .. 24 0,5 %13 1,8 % 21 0,5 %17 1,5 %19 1,3 %23 1 %25 0,9 %

Formattato: Evidenziato

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a Depending on the network design the value for the third harmonic order can be substantially lower. NOTE No values are given for harmonics of order higher than 25, as they are usually small, but largely unpredictable due toresonance effects.


Due to the low resonance frequency of the HV network, no values are given for interharmonicvoltage.

NOTE: Due to the very low resonant frequency in HV grid (200 500 Hz) caused by high capacities andinductances, interharmonics are of minor relevance in HV networks.


Due to the low resonance frequency of the HV network, no values are given for mains signallingvoltage.

6.3 Voltage events



6.3.2 Supply voltage dips/swellsVoltage dips are typically originated by faults occurring in the public network or in the networkusers installations.Voltage swells are typically originated by switching operations, load disconnections etc.Both phenomena are unpredictable and largely random. The annual frequency varies greatlydepending on the type of supply system and on the point of observation. Moreover, thedistribution over the year can be very irregular.

6.3.2.1 Voltage dip/swell measurement and detectionVoltage dips/swells shall be measured and detected according to EN 61000-4-30, using asreference the declared supply voltage for HV networks. The voltage dips/swells characteristicsof interest for this standard are residual voltage (maximum r.m.s. voltage for swells) andduration 1.Typically, on HV networks, the line to line voltages shall be considered.Conventionally, the dip threshold is equal to 90 % of the reference voltage; the threshold for swells is equal to the 110 % of the nominal voltage. The hysteresis is typically 2 %; referencerules for hysteresis are given in clause 5.4.2.1 of EN 61000-4-30.

Note: For polyphase measurements, it is recommended that the number of phases affected by each event aredetected and stored.


Voltage dips shall be evaluated according to EN 61000-4-30. Post treatment aimed at dipsevaluation depends on the intended purpose.Typically, on HV networks:

1 In this standard, values are expressed in percentage terms of the reference voltage.

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polyphase aggregation is applied; polyphase aggregation consists in defining anequivalent event characterized by a single duration and a single residual voltage;

time aggregation consists in defining an equivalent event in case of multiplesuccessive events; the method used for multiple events aggregation can be setaccording to the final use of data; some reference rules are given in IEC TR 61000-2-8.





20 t 200 200 < t 500 500 < t 1000 1000 < t 5000 5000 < t 60000

90>u>=80 CELL A1 CELL A2 CELL A3 CELL A4 CELL A580>u>=70 CELL B1 CELL B2 CELL B3 CELL B4 CELL B570>u>=40 CELL C1 CELL C2 CELL C3 CELL C4 CELL C5

40>u>=5 CELL D1 CELL D2 CELL D3 CELL D4 CELL D55 >u CELL X1 CELL X2 CELL X3 CELL X4 CELL X5

Voltage dips are, by their nature, very unpredictable and variable from place to place and fromtime to time. For the time being, it is not possible to give fully representative statistical results of measurements of voltage dips frequency covering the whole of European networks.It should be noted that, due to the measurement method adopted, measurement uncertaintyaffecting the results has to be taken into account: this is particularly relevant for shorter events.Measurement uncertainty is addressed in EN 61000-4-30.Dips duration depends generally on the protection strategy adopted on the network, that maydiffer from network to network, depending on network structure and on neutral grounding. As aconsequence, typical durations are not necessarily matching the boundaries of columns of table8.


Voltage swells shall be evaluated according to EN 61000-4-30. Post treatment aimed at swellsevaluation depends on the intended purpose.Typically, on HV networks:

polyphase aggregation shall be applied; polyphase aggregation consists in definingan equivalent event characterized by a single duration and a single maximum rmsvoltage;




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Ta b le 9 : c l a s s i f ic a t ion o f s w e l ls a c c o rd ing to m a x imum vo l t a ge a nd du ra t ion Swell voltage u [%] Duration t [ms]

20 t 500 500 < t 5000 5000 < t 60000u>120 CELL S1 CELL S2 CELL S3

120>u>=110 CELL T1 CELL T2 CELL T3

A voltage swell generally happens in case of switching operations and load disconnections.Faults in the public distribution network, or in a network user's installation, give rise to temporarypower frequency overvoltages between live conductors and earth; such overvoltages disappear when the fault is cleared.Generally, temporary power frequency overvoltages in HV do not cause any network usersconcern as normally any load is connected via transformers with different types of neutralgrounding.


Transient overvoltages in HV supply systems are caused by switching or, directly or byinduction, by lightning. Switching overvoltages generally are lower in amplitude than lightningovervoltages, but they may have a shorter rise time and/or longer duration.

NOTE The network users' insulation coordination scheme must be compatible with that adopted by the supplier.

1 This table reflects the polyphase network performance. Further information is needed to consider events affectingan individual single phase voltage in three -phase systems. To calculate the latter, a different evaluation method hasto be applied.

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Annex A(informative)

Special nature of electricity

Electricity is an energy form which is particularly versatile and adaptable. It is utilised by being

converted into several other forms of energy: heat, light, mechanical energy, and the manyelectromagnetic, electronic, acoustic and visual forms which are the bases of moderntelecommunications, information technology and entertainment.

Electricity as delivered to the network users has several characteristics which are variable andwhich affect its usefulness to the network user. This standard describes characteristics of electricity in terms of the alternating voltage. With respect to the use of electricity it is desirablethat the supply voltage would alternate at a constant frequency, with a perfect sine wave and aconstant magnitude. In practice, there are many factors which cause departures from this. Incontrast to normal products, application is one of the main factors which influence the variationof "characteristics".

The flow of energy to the network user's appliances gives rise to electric currents which aremore or less proportional to the magnitudes of the network users' demands. As these currentsflow through the conductors of the supply system, they give rise to voltage drops. Themagnitude of the supply voltage for an individual network user at any instant is a function of thecumulative voltage drops on all the components of the system through which that network user is supplied, and is determined both by the individual demand and by the simultaneous demandsof other network users. Since each network user's demand is constantly varying, and there is afurther variation in the degree of coincidence between the demands of several network users,the supply voltage is also variable. For this reason, this standard deals with the voltagecharacteristics in statistical or probabilistic terms. It is in the economic interests of the networkuser that the standard of supply should relate to normally expected conditions rather than torare contingencies, such as an unusual degree of coincidence between the demands of severalappliances or several network users.

Electricity reaches the network user through a system of generation, transmission anddistribution equipment. Each component of the system is subject to damage or failure due to theelectrical, mechanical and chemical stresses which arise from several causes, including

extremes of weather, the ordinary processes of wear and deterioration with age, andinterference by human activities, birds, animals, etc. Such damage can affect or even interruptthe supply to one or to many network users.

To keep the frequency constant requires the amount of running generation capacity to bematched instant by instant to the simultaneous combined demand. Because both the generationcapacity and the demand are liable to change in discrete amounts, especially in the event of faults on the generation, transmission or distribution networks, there is always a risk of amismatch, resulting in an increase or decrease of the frequency. This risk is reduced, however,by connecting many systems into one large interconnected system, the generation capacity of which is very great relative to the changes which are likely to occur.

There are several other characteristics that may have a disturbing or damaging effect onnetwork users' equipment, or even on the network users. Some of these disturbingcharacteristics arise from unavoidable transient events in the supply system itself, resulting fromfaults or switching, or caused by atmospheric phenomena (lightning). Others, however, are theresult of various uses of electricity which directly alter the waveform of the voltage, impose aparticular pattern on its magnitude, or superimpose signalling voltages. Coincidentally with themodem proliferation of equipment which has these effects, there is also an increase in theequipment which is susceptible to the disturbances.

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This European Standard defines where possible the variations of the characteristics normally tobe expected. In other cases the standard provides the best possible indication of what, inquantitative terms, is to be expected.

Since there is a considerable diversity in the structures of the distribution networks in differentareas, arising from differences in load density, population dispersion, local topography, etc.many network users will experience considerably smaller variations of the voltage

characteristics than the values given in this standard.It is a particular feature of electricity that, in respect of some of its characteristics, its quality isaffected by the user rather than by the producer or supplier. In these cases the network user isan essential partner, with the supplier, in the effort to maintain the quality of electricity.

It should be noted that this question is addressed directly by other standards, already publishedor in preparation: Emission standards govern the levels of electromagnetic disturbances whichnetwork users' equipment may be allowed to generate. Immunity standards set downdisturbance levels which the equipment should be capable of tolerating without undue damageor loss of function. A third set of standards, for electromagnetic compatibility levels, has thefunction of enabling coordination and coherence of the emission and immunity standards, withthe overall objective of achieving electromagnetic compatibility.

Although this standard has obvious links with compatibility levels, it is important to note that it

relates to voltage characteristics of electricity. It is not a standard for compatibility levels. Itshould be especially noted that the performance of equipment might be impaired, if theequipment is subjected to supply conditions more severe than specified in their productstandard.

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Annex B(informative)

Indicative values for voltage events and single rapid voltage changes

The present Annex B is aimed at providing the reader with some information about indicativevalues currently available at a European level for some of the events defined and described inthe standard. Some information is also given about the way of using values given in thestandard, and about the way of collecting data of further measurement campaigns, in order toallow for comparisons between different systems and to have homogeneous data at a Europeanlevel.

As many monitoring systems are in place in some countries, further information is available at anational level.

At a national level, more precise figures can be found; furthermore, some regulations may exist.

B.1 Long interruptions of the supply voltage

Under normal operating conditions the annual frequency of voltage interruptions longer thanthree minutes varies substantially between areas. This is due to, among others, differences in

system layout (e.g cable systems versus overhead line systems), environmental and climaticconditions etc. To get information about what can be expected, the local network operator should be consulted. In different countries national interruption statistics exist giving indicativevalues. The CEER Benchmarking Reports on Quality Supply give some statistics for a certainnumber of European countries and a review of applicable regulatory standards for longinterruptions.Rules for aggregating events should be considered when comparing statistical values for longinterruptions.

B.2 Short interruptions of the supply voltage

The duration of most of the short interruptions may be less than some seconds. Indicativevalues, intended to provide readers with information on the range of magnitude which can beexpected, can be found in IEC TR 61000-2-8 (UNIPEDE statistics).

When comparing statistical values for short interruptions, the following issues should beconsidered: rules for aggregating events, the possible inclusion of Very Short Interruptions (VSI) or transitory interruptions.

In some documents short interruptions are considered as having durations not exceeding oneminute. Sometimes control schemes are applied which need operating times of up to threeminutes in order to avoid long voltage interruptions.

B.3 Voltage dips and swells

The swells treated in this paragraph are between live conductors.

Use of Table 2, 5 and 8 As detailed in product standards, voltage dips and swells, according to their severity, can impair the operation of equipment.

Classes 2 and 3 are defined in EN 61000-4-11 and in EN 61000-4-34. Although the cells of the table 2,5 and 8 are not exactly coincident with the test levels table, itcan be expected that equipment tested according to the relevant product standard should copewith voltage dips as indicated in the cells:

A1, B1, A2, B2 for class 2;

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A1, B1, C1, A2, B2, A3, A4 for class 3.

Compatibility levels for industrial power networks are defined in EN 61000-2-4.Table 2, 5 and 8 data can help the user to identify the expected performance of the network; inorder to assess the probable behaviour of the equipment connected, its immunity has to beconsidered in accordance with such data.

The specification of immunity requirements (including tests specifications and performancecriteria) is the responsibility of the product committees. Generic EMC standards (EN 61000-6-1and 61000-6-2) apply to products operating in a particular environment for which no dedicatedproduct family /product EMC standards exist. Nevertheless, and for information only, theperformance criteria are reported in the following.

Performance criteriaPerformance criterion A: The apparatus shall continue to operate as intended during and after the test. No degradation of performance or loss of function is allowed below a performance levelspecified by the manufacturer, when the apparatus is used as intended. The performance levelmay be replaced by a permissible loss of performance. If the minimum performance level or thepermissible performance loss is not specified by the manufacturer, either of these may bederived from the product description and documentation and what the user may reasonablyexpect from the apparatus if used as intended.Performance criterion B: The apparatus shall continue to operate as intended after the test. No

degradation of performance or loss of function is allowed below a performance level specifiedby the manufacturer, when the apparatus is used as intended.The performance level may be replaced by a permissible loss of performance. During the test,degradation of performance is however allowed. No change of actual operating state or storeddata is allowed.If the minimum performance level or the permissible performance loss is not specified by themanufacturer, either of these may be derived from the product description and documentationand what the user may reasonably expect from the apparatus if used as intended.Performance criterion C: Temporary loss of function is allowed, provided the function is self-recoverable or can be restored by the operation of the controls."

Currently available indicative values

The vast majority of voltage dips has a duration less than 1 s and a residual voltage above 40%. However, voltage dips with smaller residual voltage and longer duration can occur

infrequently. In some areas voltage dips with residual voltage between 90 % and 85 % of U c canoccur very frequently as a result of the switching of loads in network users' installations.Indicative values, which are intended to provide readers with information on the range of magnitude which can be expected, can be found in IEC TR 61000-2-8 (UNIPEDE statistics).

Methods for reporting measurement campaignsThe data relevant to voltage dips/swells should be presented according to the followingguidelines.The data collected should be homogeneous in terms of voltage levels. Within the same voltagelevel, distinction should be made between networks with prevailing underground cables or aeriallines. To cover all seasonal effects, the observation time should be one year.The data should be collected in tables like 4 and 5; the following data shall be reported:

average dips/swells incidence per bus per year; 90 or 95% dips/swells incidence per bus per year; maximum dips/swells incidence per bus per year.

B.4 Swells (temporary power frequency overvoltages) between live conductorsand earth

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For low voltage systems, under certain circumstances, a fault occurring upstream of atransformer may produce temporary overvoltages on the LV side for the time during which thefault current flows. Such overvoltages will generally not exceed 1,5 kV r.m.s.For medium voltage systems, the expected value of such an overvoltage depends on the typeof earthing of the system. In systems with a solidly or impedance earthed neutral theovervoltage shall generally not exceed 1,7 U c. In isolated or resonant earthed systems theovervoltage shall generally not exceed 2,0 U c. The type of earthing will be indicated by the

distributor.Indicative values about overvoltages on distribution networks can be found in IEC TR 61000-2-14. More information for LV systems can be found in IEC TR 62066.

B.5 Magnitude of rapid voltage changesFor low voltage, under normal operating conditions, rapid voltage changes generally do notexceed 5 % U n, but changes of up to 10 % U n with a short duration might occur some times per day in some circumstances.For medium voltage, under normal operating conditions, rapid voltage changes generally do notexceed 4 % U c, but changes of up to 6 % U c with a short duration might occur some times per day in some circumstances.These indicative values apply to the phenomenon of rapid voltage changes as defined in 3.14.

At a national level, additional values may be available, but in some cases they are referred toanother definition of rapid voltage change ( U max , see EN 61000-3-3 clause 3.3 and fig. 2).

In general, the frequency and magnitude of rapid voltage changes are related to the loadvariation by the users and to the short-circuit power level of the network.

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Bibliography

IEC TR 61000-2-14

2006 Electromagnetic compatibility Part 2-14: Environment Overvoltages on public electricity distribution networks

IEC TR 62066 2002 Surge overvoltages and surge protection in low voltage a.c.power systems - General basic information

EN 50065-1 2001 Signalling on low-voltage electrical installations in thefrequency range 3 kHz to 148,5 kHz Part 1: Generalrequirements, frequency bands and electromagneticdisturbances

CLC/TR 50422 2003 Guide for the application of the European Standard EN 50160

EN 61000-2-2 2002 Electromagnetic compatibility Part 2-2: Environment -Compatibility levels for low-frequency conducted disturbancesand signalling in public low-voltage power supply systems(IEC 61000-2-2:2002)

EN 61000-2-4 1997 Electromagnetic compatibility Part 2-4: Environment -Compatibility levels in industrial plants for low-frequencyconducted disturbances

EN 61000-4-15+ A1

19982003

Electromagnetic compatibility (EMC) Part 4-15 Testing andmeasurement techniques Flickermeter - Functional anddesign specifications (IEC 61000-4-15:1997 + A1:2003)

EN 61000-6-1 2002 Electromagnetic compatibility Part 6-1: Generic standards -Immunity for residential, commercial and light-industrialenvironments

EN 61000-6-2 2000 Electromagnetic compatibility Part 6-2: Generic standards -Immunity for industrial environments

UNIPEDE 91en 50.02

Voltage dips and short interruptions in public medium voltageelectricity supply systems

CEER 20012003

2005

Benchmarking Report on Quality of Electricity Supply - Freelyavailable at http://www.ceer-eu.org

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