EN 60099-5:1996/A1:1999

SLOVENSKI STANDARD
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
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

NORME CEI
INTERNATIONALE IEC
60099-5
INTERNATIONAL
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
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Commission Electrotechnique Internationale
Q
PRICE CODE
International Electrotechnical Commission
Pour prix, voir catalogue en vigueur
For price, see current catalogue

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.
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.

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.

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
High harmonic content
in system voltage
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
capacitors, if applied. The specific capacitance of a resistor element is typically 60 pF.kV/cm
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
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
60099-5 Amend. 1 © IEC:1999 – 13 –
resistive current
third harmonic current
power loss
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
resistive current
8 third harmonic current
power loss
-40 -20 0 20 406080 100 120 140
IEC  1186/99
Temperature - °C
Figure 7 – Typical normalized temperature dependence at U
c
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 resist
...