SIST EN 60099-5:1998/A1:2002

SLOVENSKI STANDARD
SIST EN 60099-5:1998/A1:2002
01-november-2002
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Surge arresters -- Part 5: Selection and application recommendations
Überspannungsableiter -- Teil 5: Anleitung für die Auswahl und die Anwendung
Parafoudres -- Partie 5: Recommandations pour le choix et l'utilisation
Ta slovenski standard je istoveten z: EN 60099-5:1996/A1:1999
ICS:
29.240.10 Transformatorske postaje. Substations. Surge arresters
Prenapetostni odvodniki
SIST EN 60099-5:1998/A1:2002 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 60099-5:1998/A1:2002

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SIST EN 60099-5:1998/A1:2002

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SIST EN 60099-5:1998/A1:2002

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SIST EN 60099-5:1998/A1:2002
NORME CEI
INTERNATIONALE IEC
60099-5
INTERNATIONAL
1996
STANDARD
AMENDEMENT 1
AMENDMENT 1
1999-10
Amendement 1
Parafoudres –
Partie 5:
Recommandations pour le choix et l'utilisation –
Section 1: Généralités
Amendment 1
Surge arresters –
Part 5:
Selection and application recommendations –
Section 1: General
 IEC 1999 Droits de reproduction réservés  Copyright - all rights reserved
International Electrotechnical Commission 3, rue de Varembé Geneva, Switzerland
Telefax: +41 22 919 0300 e-mail: inmail@iec.ch IEC web site http://www.iec.ch
CODE PRIX
Commission Electrotechnique Internationale
Q
PRICE CODE
International Electrotechnical Commission
Pour prix, voir catalogue en vigueur
For price, see current catalogue

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SIST EN 60099-5:1998/A1:2002
60099-5 Amend. 1 © IEC:1999 – 3 –
FOREWORD
This amendment has been prepared by IEC technical committee 37: Surge arresters.
The text of the amendment is based on the following documents:
FDIS Report on voting
37/224/FDIS 37/230/RDV
Full information of the voting of the approval of this amendment can be found in the report on
voting indicated in the above table.
Page 73
Section 6: Monitoring (supervision)
Replace the title and text of this section by the following:
Section 6: Diagnostic indicators of metal-oxide surge arresters in service
6.1 General
Apart from brief occasions when a surge arrester is functioning as an overvoltage-limiting
device, it is expected to behave as an insulator. The insulating properties are essential for the
length of life of the arrester and for the operation reliability of the power system.
Various diagnostic methods and indicators for revealing possible deterioration or failure of the
insulating properties have been utilized since the introduction of surge arresters. The
diagnostic methods range from fault indicators and disconnectors for indication of complete
arrester failures, to instruments that are able to measure slight changes in the resistive
leakage current or the power loss of metal-oxide arresters.
The aim of this section is to provide guidance to the user if use of any diagnostic method is
considered, and to present an overview of common diagnostic methods. It also gives detailed
information about leakage current measurements on metal-oxide arresters.
NOTE 1 – Diagnostic devices should be designed and handled in order to provide personal safety during
measurement. Permanently installed devices should be designed and installed with the operational and short-circuit
stresses taken into consideration.
NOTE 2 – For several diagnostic methods, an insulated earth terminal is required on the arrester. The earth
terminal should have a sufficiently high withstand voltage level to account for the inductive voltage drop appearing
between the terminal and the earthed structure during an impulse discharge.
6.1.1 Fault indicators
Fault indicators give a clear visual indication of a failed arrester, without disconnecting the
arrester from the line. The device may be an integrated part of the arrester, or a separate unit
installed in series with the arrester. The working principle is usually based on the amplitude
and duration of the arrester current, or on the temperature of the non-linear metal-oxide
resistors.

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SIST EN 60099-5:1998/A1:2002
60099-5 Amend. 1 © IEC:1999 – 5 –
6.1.2 Disconnectors
Disconnectors, often used on medium-voltage arresters, give a visual indication of a failed
arrester by disconnecting it from the system. The typical working principle is an explosive
device triggered by the fault current; however, the disconnector is not intended to extinguish
the fault current. The disconnector may be an integral part of the arrester or insulating bracket,
or a separate unit installed in series with the arrester. The advantage of the device is that the
line remains in operation after disconnection of the arrester. The major disadvantage is the
lack of overvoltage protection until the failed arrester has been discovered and replaced.
6.1.3 Surge counters
Surge counters operate at impulse currents above a certain amplitude, or above certain
combinations of current amplitude and duration. If the interval between discharges is very short
(less than 50 ms), surge counters may not count every current impulse. Some counters require
power follow current and may not count the short impulse currents through metal-oxide
arresters.
Depending on the operating principle and sensitivity of the counter, it may give an indication
about overvoltages appearing in the system, or it may provide information on the number of
discharges corresponding to significant arrester energy stresses. The counter provides no
specific information about the condition of the arrester.
For safety reasons, the surge counter should be installed beyond easy reach of personnel, It
shall be located where it can be read from ground level with the arrester in service. The
installation should be done without considerably lengthening the earth connection or reducing
its cross-section. The arrester shall be equipped with an insulated earth terminal and a
conductor between the arrester and counter that is insulated from earth.
6.1.4 Monitoring spark gaps
Monitoring spark gaps are used to indicate the number and estimate the amplitude and
duration of discharge currents through the arrester. Special experience is necessary to properly
interpret the marks on the gap. Some spark gaps can be examined with the arrester in service,
while other types require that the arrester is de-energized. It is required that the arrester be
equipped with an insulated earth terminal. Alternatively, the device may be an integrated part of
the arrester. Spark gaps give no direct information about the actual condition of the arrester,
but may help to make decisions about continued operation.
6.1.5 Temperature measurements
Remote measurement of the arrester temperature can be carried out by means of thermal
imaging methods. The measurements are only indicative with regard to the condition of the
arrester, since the temperature drop between the resistors and the housing surface may be
substantial. Nevertheless, comparative measurements made on adjacent arresters or arrester
units may indicate excessive heating.
Direct measurements of the metal-oxide resistor temperature give an accurate indication of the
condition of the arrester, but require that the arrester be equipped with special transducers at
the time of manufacturing. Therefore, this method is used only in special arrester applications.

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SIST EN 60099-5:1998/A1:2002
60099-5 Amend. 1 © IEC:1999 – 7 –
6.1.6 Leakage current measurements of metal-oxide arresters
Any deterioration of the insulating properties of a metal-oxide arrester will cause an increase in
the resistive leakage current or power loss at given values of voltage and temperature. The
majority of diagnostic methods for determining the condition of gapless metal-oxide arresters
are based on measurements of the leakage current.
The measuring procedures can be divided into two groups: on-line measurements, when the
arrester is connected to the system and energized with the service voltage during normal
operation, and off-line measurements, when the arrester is disconnected from the system and
energized with a separate voltage source on site or in a laboratory.
Measurements off-line can be made with voltage sources that are specially suited for the
purpose, e.g. mobile a.c. or d.c. test generators. Good accuracy may be obtained by using the
off-line methods, provided that a sufficiently high test voltage is used. The major disadvantages
are the cost of the equipment and the need for disconnecting the arrester from the system.
Measurements carried out on-line under normal service voltage is the most common method.
For practical and safety reasons, the leakage current is normally accessed only at the earthed
end of the arrester. To allow measurements of the leakage current flowing in the earth
connection, the arrester must be equipped with an insulated earth terminal.
NOTE – The insulation of the earth terminal must, also after long-term degradation, be sufficient to prevent
circulating currents caused by electromagnetic induction, since these currents may interfere with the measurement
of the leakage current.
On-line leakage current measurements are usually made on a temporary basis using portable
or permanently installed instruments. Portable instruments are usually connected to the earth
terminal of the arrester by means of a clip-on, or permanently installed, current transformer.
Long-term measurements of the leakage current may be necessary for closer investigations,
especially if significant changes in the condition of an arrester are revealed by temporary
measurements. Remote measurements may be implemented in computerized systems for
supervision of substation equipment.
6.1.6.1 Properties of the leakage current of non-linear metal-oxide resistors
The a.c. leakage current can be divided into a capacitive and a resistive part, with a pre-
dominant capacitive component and a significantly smaller resistive part. This can be seen in
figure 3, which shows a typical laboratory measurement of the leakage current of a single non-
linear metal-oxide resistor when energized at a voltage equivalent to U for the complete
c
arrester. In figure 4 are shown the results of leakage current measurements carried out on two
different arresters in service at voltage levels slightly below U . Figure 4 also illustrates the
c
influence of different levels of harmonic content in the system voltage.

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SIST EN 60099-5:1998/A1:2002
60099-5 Amend. 1 © IEC:1999 – 9 –
dU/dt = 0
Voltage
U = U
c
Resistive current
i = 10.600 μA
r
Leakage current
i = 0,2.3 mA
IEC  1182/99
Time
Figure 3 – Typical leakage current of a non-linear metal-oxide resistor
in laboratory conditions
4
High harmonic content
3
in system voltage
2
1
0
Low harmonic content
-1
in system voltage
-2
-3
-4
Time IEC  1183/99
Figure 4 – Typical leakage currents of arresters in service conditions
6.1.6.1.1 Capacitive leakage current
The capacitive leakage current measured at the earth terminal of an arrester is caused by the
permittivity of the non-linear metal-oxide resistors, the stray capacitances and the grading
2
capacitors, if applied. The specific capacitance of a resistor element is typically 60 pF.kV/cm
2
to 150 pF.kV/cm (rated voltage), resulting in a capacitive peak leakage current of about
0,2 mA to 3 mA under normal service conditions.
Test voltage, leakage current
Leakage current - mA

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SIST EN 60099-5:1998/A1:2002
60099-5 Amend. 1 © IEC:1999 – 11 –
There is no evidence that the capacitive current would change significantly due to deterioration
of the voltage-current characteristic of the non-linear metal-oxide resistors. Therefore, it is
unlikely that measurements of capacitive current can reliably indicate the condition of metal-
oxide arresters.
6.1.6.1.2 Resistive leakage current
At given values of voltage and temperature, the resistive component of the leakage current is a
sensitive indicator of changes in the voltage-current characteristic of non-linear metal-oxide
resistors. The resistive current can, therefore, be used as a tool for diagnostic indication of
changes in the condition of metal-oxide arresters in service. Typical resistive and capacitive
voltage-current characteristics for a.c. voltages are shown in figure 5. For comparison, typical
characteristics for d.c. voltages are also shown in figure 5.
1,2
1,0
0,8
DCDC, +2, +200° °CC
0,6
DC, +40 °C
AC resistive, +20 °C
0,4
AC resistive, +40 °C
AC capacitive
0,2
0,0
0,01 0,10 1,00 10,00 100,00
Current - mA IEC  1184/99
Figure 5 – Typical voltage-current characteristics for non-linear metal-oxide resistors
The resistive component under a.c. voltage is defined as the current level at the instant of
voltage maximum (dU/dt = 0), as indicated in figure 3. The resistive leakage current of a non-
linear metal-oxide resistor is in the order of 5 % to 20 % of the capacitive current under normal
operating conditions, corresponding to about 10 μA to 600 μA peak resistive current at a
temperature of +20 °C.
In the leakage current region, the resistive current depends on the voltage and temperature.
Typical values of voltage and temperature dependencies under a.c. voltage are indicated in
figures 6 and 7, normalized to U and at +20 °C, respectively.
c
U / U
r
U/U
r

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SIST EN 60099-5:1998/A1:2002
60099-5 Amend. 1 © IEC:1999 – 13 –
6
5
resistive current
4
third harmonic current
power loss
3
2
1
0
0,5 0,6 0,7 0,8 0,9 1,0 1,1 1,2 1,3
U / U
c
IEC  1185/99
Figure 6 – Typical normalized voltage dependence at +20 °C
12
10
resistive current
8 third harmonic current
power loss
6
4
2
0
-40 -20 0 20 406080 100 120 140
IEC  1186/99
Temperature - °C
Figure 7 – Typical normalized temperature dependence at U
c

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SIST EN 60099-5:1998/A1:2002
60099-5 Amend. 1 © IEC:1999 – 15 –
The voltage distribution along an arrester may be uneven, primarily due to the influence of
stray capacitances to earth and to adjacent equipment. The voltage across the non-linear
metal-oxide resistors at the earthed end of the arrester may, therefore, deviate in both
magnitude and phase from the average value along the arrester. This phenomenon affects the
measurement of the resistive leakage current in two ways: First, the resistive current measured
in the earth connection depends on the magnitude of the voltage across the non-linear metal-
oxide resistors at the earthed end, therefore, the measured resistive current may differ from
the average resistive current along the arrester. Secondly, the phase shift of the voltage across
the non-linear metal-oxide resistors at the earthed end influences the result of resistive current
measurement for methods that are using the voltage across the complete arrester as a
reference for the phase angle.
Another similar phenomenon that may influence the measurement of the resistive current when
using certain methods, is the capacitive current induced in the earth lead of the arrester by the
adjacent phases.
6.1.6.1.3 Harmonics in the leakage current
The non-linear voltage-current characteristic of a metal-oxide arrester gives rise to harmonics
in the leakage current when the arrester is energized with a sinusoidal voltage. The harmonic
content depends on the magnitude of the resistive current and the degree of non-linearity,
which is a function of voltage and temperature. As an example, the third harmonic content of
the resistive current is typically 10 % to 40 %. The harmonic content can, therefore, be used as
an indicator of the resistive current. Typical values of the variations with voltage and
temperature of the third order harmonic component are shown in figures 6 and 7.
Another source of harmonics, beside negligible ones, that may considerably influence the
measurement of harmonics in the leakage current, is the harmonic content in the system
voltage. The capacitive harmonic currents produced by the voltage harmonics may be of the
same order of magnitude as the harmonic currents created by the non-linear resistance of the
arrester. An example of harmonics in the leakage current caused by system voltage harmonics
is seen in figure 4.
6.1.6.1.4 Power loss
The power loss may be used for diagnostic indication of arresters in the same way as the
resistive leakage current. Typical values of power losses are 5 mW/kV to 300 mW/kV (rated
voltage) at U and +20 °C. The temperature and voltage dependencies are practically the same
c
as for the resistive current, as seen in figures 6 and 7.
6.1.6.2 Surface leakage current
As with any other outdoor insulator, external surface leakage current may temporarily occur on
the arrester housing in rain or in conditions of high humidity combined with surface pollution. In
addition, internal surface leakage current may appear due to moisture penetration. During
measurements, the surface currents may interfere with the leakage current of the resistors,
however, the sensitivity to external and internal surface currents may be different for the
various measurement methods. The influence of the external surface leakage current can be
avoided, either by performing the measurements in dry conditions, or by any other suitable
method, e.g. bypassing the surface leakage current to ground.

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SIST EN 60099-5:1998/A1:2002
60099-5 Amend. 1 © IEC:1999 – 17 –
6.2 Measurement of the total leakage current
The total leakage current depends mainly on the capacitive current, since the resistive part is
only a fraction of the capacitive current component. Furthermore, the capacitive and resistive
current components differ in phase by 90°; therefore, a large increase in the resistive current of
the non-linear metal-oxide resistors is needed before a significant change can be noticed in the
total leakage current level. In addition, the total leakage current is sensitive to the installation,
since the capacitive current depends on the stray capacitances.
On-line measurements of the total leakage current are extensively used in practice by means
of conventional mA-meters built into the surge counters or into portable instruments, showing
the r.m.s., mean or peak value of the total leakage current.
The sensitivity of the r.m.s, mean, and peak values of the total leakage current to variations in
the resistive current is illustrated in figure 8. The low sensitivity to changes in the resistive
current level makes the measurement of total l
...