SIST EN 61620:1999

Insulating liquids - Determination of the dielectric dissipation factor by measurement of the conductance and capacitance - Test method

Describes a method for simultaneous measurement of conductance G and capacitance C enabling the calculation of the dielectric dissipation factor tan delta of insulating liquides. Method applies to both unused insulating liquids and insulating liquids in service in transformers and in other electrical equipment.

Isolierflüssigkeiten - Bestimmung des Permittivitäts-Verlustfaktors durch Messung der Konduktanz und Kapazität - Prüfverfahren

Isolants liquides - Détermination du facteur de dissipation diélectrique par la mesure de la conductance et de la capacité - Méthode d'essai

Décrit une méthode de mesure simultanée de la conductance G et de la capacité C permettant le calcul du facteur de disspation tan d'isolants liquides. La méthode s'applique aussi bien aux isolants liquides neufs qu'aux isolants liquides en service dans les transformateurs ou autres appareils électriques.

Insulating liquids - Determination of the dielectric dissipation factor by measurement of the conductance and capacitance (IEC 61620:1998)

General Information

• Status: Published
• Publication Date: 30-Nov-1999
• ICS: 29.040.01 - Insulating fluids in general
• Technical Committee: TPD - Fluids for electrotechnical applications
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Dec-1999
• Due Date: 01-Dec-1999
• Completion Date: 01-Dec-1999
• Ref Project: EN 61620:1999 - Insulating liquids - Determination of the dielectric dissipation factor by measurement of the conductance and capacitance - Test method

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN 61620:1999
01-december-1999
Insulating liquids - Determination of the dielectric dissipation factor by
measurement of the conductance and capacitance (IEC 61620:1998)
Insulating liquids - Determination of the dielectric dissipation factor by measurement of
the conductance and capacitance - Test method
Isolierflüssigkeiten - Bestimmung des Permittivitäts-Verlustfaktors durch Messung der
Konduktanz und Kapazität - Prüfverfahren
Isolants liquides - Détermination du facteur de dissipation diélectrique par la mesure de
la conductance et de la capacité - Méthode d'essai
Ta slovenski standard je istoveten z: EN 61620:1999
ICS:
29.040.01 Izolacijski fluidi na splošno Insulating fluids in general
SIST EN 61620:1999 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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NORME
CEI
INTERNATIONALE
IEC
61620
INTERNATIONAL
Première édition
STANDARD
First edition
1998-11
Isolants liquides –
Détermination du facteur de dissipation
diélectrique par la mesure de la conductance
et de la capacité –
Méthode d’essai
Insulating liquids –
Determination of the dielectric dissipation factor
by measurement of the conductance
and capacitance –
Test method
 IEC 1998 Droits de reproduction réservés  Copyright - all rights reserved
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PRICE CODE S
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Pour prix, voir catalogue en vigueur
For price, see current catalogue

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61620  IEC:1998 – 3 –
CONTENTS
Page
FOREWORD . 5
INTRODUCTION .7
Clause
1 Scope . 9
2 Normative references . 9
3 Definitions.11
4 Principle of operation . 13
5 Apparatus.15
6 Sampling.19
7 Labelling.19
8 Procedure.21
9 Expression of results. 25
10 Test report.25
11 Precision.27
Annex A (normative) Exhaustive cleaning procedure for the test cells. 29
Annex B (normative) Simplified cleaning procedure for test cells devoted
to only one type of liquid. 31
Annex C (informative) General considerations on the factors influencing
the conduction of liquids. 33
Annex D (informative) Bibliography . 43

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61620  IEC:1998 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
INSULATING LIQUIDS –
DETERMINATION OF THE DIELECTRIC DISSIPATION FACTOR
BY MEASUREMENT OF THE CONDUCTANCE AND CAPACITANCE –
TEST METHOD
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International Organization
for Standardization (ISO) in accordance with conditions determined by agreement between the two
organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61620 has been prepared by IEC technical committee 10: Fluids for
electrotechnical applications
The text of this standard is based on the following documents:
FDIS Report on voting
10/446+446A/FDIS 10/458/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
Annexes A and B form an integral part of this standard.
Annexes C and D are for information only.

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61620  IEC:1998 – 7 –
INTRODUCTION
The conductivity σ is a characteristic of a liquid only if it is measured at thermodynamic
equilibrium.
To fulfil this requirement high electric stress and/or prolonged voltage application is to be
avoided, this is not the case in IEC 60247 for the d.c. resistivity measurement (electric stress
–1
up to 250 Vmm , conventional arbitrary time of electrification 1 min).
There is a simple relationship between the dielectric dissipation factor tan δ, the conductivity σ
and the permittivity ε of the liquid with no (or negligible) dipolar losses, which is the case of
most liquids for electrotechnical applications:
σ
tan δ =
εω
where ω = 2 πf and f is the frequency of the voltage.
Therefore, the measurement of either tan δ or σ gives the same information on the conduction
properties of the liquid. In fact, very often in practice, there are large discrepancies between
the resistivity calculated from the measurement of tan δ with conventional apparatus and the
d.c. resistivity measured following the recommendation of IEC 60247.
New devices for the measurement of the conductivity σ at thermodynamic equilibrium are
currently available. They are able to measure easily and with precision very low values of σ.
The capabilities of this new equipment allow measurements of σ of unused insulating liquids
even at room temperature.

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61620  IEC:1998 – 9 –
INSULATING LIQUIDS –
DETERMINATION OF THE DIELECTRIC DISSIPATION FACTOR
BY MEASUREMENT OF THE CONDUCTANCE AND CAPACITANCE –
TEST METHOD
1 Scope
This International Standard describes a method for the simultaneous measurement of
conductance G and capacitance C enabling the calculation of the dielectric dissipation factor
tan δ of insulating liquids. The proposed method applies both to unused insulating liquids and
insulating liquids in service in transformers and in other electrical equipment.
The standard is no substitute for IEC 60247; rather it complements it insofar as it is particularly
suited to highly insulating liquids and it recommends a method of measurement for these
–6
liquids. This method allows values of the dielectric dissipation factor as low as 10 at power
δ
frequency to be determined with certainty. Moreover, the range of measurements of tan lies
–6
between 10 and 1 and can be extended up to 200 in particular conditions.
2 Normative references
The following normative documents contain provisions which, through reference in this text,
constitute provisions of this International Standard. At the time of publication, the editions
indicated were valid. All normative documents are subject to revision, and parties to
agreements based on this International Standard are encouraged to investigate the possibility
of applying the most recent editions of the normative documents indicated below. Members of
IEC and ISO maintain registers of currently valid International Standards.
IEC 60247:1978, Measurement of relative permittivity, dielectric dissipation factor and d.c.
resistivity of insulating liquids
IEC 60475:1974, Method of sampling liquid dielectrics
ISO 5725-1:1994, Accuracy (trueness and precision) of measurement methods and results –
Part 1: General principles and definitions
ISO 5725-2:1994, Accuracy (trueness and precision) of measurement methods and results –
Part 2: Basic method for the determination of repeatability and reproducibility of a standard
measurement method
ISO 5725-3:1994, Accuracy (trueness and precision) of measurement methods and results –
Part 3: Intermediate measures of the precision of a standard measurement method
ISO 5725-4:1994, Accuracy (trueness and precision) of measurement methods and results –
Part 4: Basic methods for the determination of the trueness of a standard measurement method

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61620  IEC:1998 – 11 –
3 Definitions
For the purpose of this International Standard, the following definitions apply
3.1
conductivity (σσ)
quantity related to the electric field strength E and to the conduction current density j by
jE= σ
3.2
resistivity (ρρ)
reciprocal of the conductivity σ , given by
1
ρ =
σ
3.3
resistance (R)
the resistance of the liquid-filled test cell is the ratio of the voltage V applied to the cell to the
direct or in-phase current I , and is given by
R
V
R =
I
R
In the simplest case of plane parallel electrodes of area A and with a gap distance L,
ρL
=
R
A
3.4
conductance (G)
reciprocal of the resistance, given by
1
G =
R
3.5
capacitance (C)
the capacitance of the liquid-filled test cell is the ratio of the charge Q of the electrodes to the
voltage V applied to the test cell. For a plane capacitor,
εA
C =
L
where ε is the permittivity of the liquid.
3.6
dielectric dissipation factor (dielectric loss tangent tan δδ)
for a material subjected to a sinusoidal voltage, tan δ is the ratio of the value of the absorbed
active power to the value of the reactive power. In the simple case of a capacitance C shunted
by a resistance R,
G
tan δ =
Cω
where ω = 2πf and f is the frequency of the voltage.
Details about the factors influencing the conduction of liquids can be found in annex C.

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61620  IEC:1998 – 13 –
4 Principle of operation
The principle of operation is to measure both the capacitive current and the conduction current
by applying an alternate square wave voltage to the test cell. The capacitive current is
measured during the rise time and the conduction current is measured during the stable period
of the voltage, but prior to any possible disturbance of the electric field due to ion
accumulation. The currents can be measured at both positive and negative half-waves of the
alternate square wave voltage for a number of cycles to increase the accuracy of the
*
measurement (see figure 1 and [6] to [12] ).
V (t)
V
t
I (t)
I = C dV/dt I = V/R = GV
C R
t
IEC  1 562/98
Figure 1 – Principle of operation using the square wave method
The square wave voltage V(t) of amplitude ±V, is periodically reversed with a slope dV/dt. The
current I during the rise and fall of the voltage is the sum of the capacitive current
(displacement current) and the conduction current, i.e.
dV V
 
IC=×   +
 
dt R
The capacitive current I is measured during the rising and falling periods of V(t).
C
The conduction current I is measured at the flat parts of V(t), since V/R< R C
has settled for a time at the beginning of each flat period. The capacitance C, the resistance R
(or conductance G) and tan δ at a given angular frequency ω can be determined from the
following relations:
I
C
=
C
 dV 
 
 
dt
I
V R
= =
R or G
I V
R
1
tan δ =
ω
CR
___________
*
 Figures in square brackets refer to the bibliography in annex D.

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61620  IEC:1998 – 15 –
5 Apparatus
Apparatus specifically constructed or assembled from stand-alone instruments can be used to
realize this measurement method. The block diagram shown in figure 2, and the following
subclauses illustrate an appropriate equipment.
1
5
2
3 4
6
IEC  1 563/98
Key
1Test cell
2 Heating device
3 Square wave generator
4 Measurement chain
5 Meter
6 Recorder
Figure 2 – Block diagram for the measuring apparatus
5.1 Test cell
Three terminal test cells designed according to the recommendations given in IEC 60247 are
generally suitable for this measurement.
An additional type of cell in which there is no bridge made by any solid insulating material
between the measurement electrodes, as shown in figure 3, can be used. This type of cell
often proves more accurate on highly insulating liquids.

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61620  IEC:1998 – 17 –
6
1
2
3
5
4
IEC  1 564/98
Key
1 Cover
2 Inner electrode
3 Outer electrode
4 Stainless steel vessel
5 Sheath for temperature measurement
6 BNC plugs for electrical connection
Figure 3 – Example of a test cell designed for highly insulating liquids
The distance between the outer and the inner electrode is typically 4 mm; the minimum
distance should not be lower than 1 mm. The material recommended for the electrodes is
stainless steel. As an example, the diameter of the inner electrode is 43 mm, that of the outer
electrode is 51 mm; the height of the electrodes is 60 mm; the diameter of the stainless steel
vessel is 65 mm.
This type of test cell was designed to minimise the effects of contamination from the surfaces
in contact with the liquid: although the surface in contact is large, the ratio χ = "electrode
–1
surfaces" / "liquid volume" is rather small (χ = 2,6 cm ) due to the large volume of liquid
3
(v = 200 cm ).
NOTE – It is recommended to restrict the use of a given cell to a particular type of liquid.
5.2 Heating device
The heating device shall be adequate to maintain the temperature of the measurement cell
within ±1 °C of the prescribed value. It may consist of a forced draught air oven or an oil-filled
thermostatically controlled bath fitted with a shelf to support the cell.
The heating device shall provide screened electrical connections to the cell.

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61620  IEC:1998 – 19 –
5.3 Square wave generator
The square wave generator shall deliver a highly stable quasi-rectangular voltage. The
following characteristics are suitable:
– amplitude: 10 V to 100 V;
– frequency: 0,1 Hz to 1 Hz;
– ripple: <1 %;
– rise time: 1 ms to 100 ms.
5.4 Measurement chain
The conduction current I through the test cell is measured during the second part of each
R
half-wave and averaged over a number of periods depending on the range of measurement.
The measuring chain gives the conductance G of the test cell.
I
R
=
G
V
–6 –14
As an example, the range of measurable conductance values is 2 × 10 S to 2 × 10 S with
a margin of error of less than 2 %.
The capacitance C of the test cell is deduced from the current measured during the rise
of the voltage. The measurable capacitance values are between 10 pF and 1 000 pF with an
uncertainty of less than 1 %.
–14
As an example, for a liquid of relative permittivity ε = 2, a conductance value of 2 × 10 S
r
–6
gives tan δ = 0,8 × 10 at 50 Hz.
6 Sampling
The insulating liquid samples shall be taken in accordance with IEC 60475 by qualified
personnel. During transportation and storage the samples shall be protected from direct light.
7 Labelling
Insulating liquid samples shall be properly labelled before being dispatched to the laboratory.
The following information is necessary:
– customer or plant;
– identification of the liquid (type and grade);
– identification of equipment;
– date and time of sampling;
– temperature when sampling;
– point of sampling;
– other pertinent information.

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61620  IEC:1998 – 21 –
8 Procedure
In order to get a significant measurement of dissipation factor tan δ, it is essential to follow
precise rules concerning
– the careful cleaning of the test cell;
– the careful filling of the test cell and handling of the liquid samples and of the test cell itself.
8.1 Cleaning of the test cell
8.1.1 Operating procedure
According to the state of cleanliness of the test cell and the level of conductivity of the liquid to
be measured, the cleaning procedure of the test cell can be more or less sophisticated and
take more or less time.
If the cleanliness of the test cell is unknown or if there is any doubt, a cleaning procedure shall
be applied.
Many different types of cleaning procedure can be used provided they have proved to be
efficient.
In annex A, a reference procedure is given. It shall be used in case of dispute between two
laboratories.
In annex B, an appropriate simplified cleaning procedure is given as an example.
NOTE – For routine testing and when a number of samples of the same type of unused liquid are to be tested
consecutively, the same test cell may be used without intermediate cleaning, provided that the value of the property
for the sample previously tested is better than the specified value. If such is not the case, the test cell must be
cleaned before being used for further tests.
8.1.2 Checking the cleanliness of the empty cell
To obtain a significant measurement it is necessary that the electrical losses of the empty cell
be much lower than those of the liquid to be measured.
NOTE – Nevertheless, the walls of the vessel and the electrodes may retain impurities liable to dissolve eventually
in the liquid.
8.1.3 Checking the cleanliness of the filled cell for measurement at room temperature
If the test cell is perfectly clean and if the temperature of the liquid is constant, σ and tan δ are
independent of time. The measurement can thus be taken as soon as it is practically possible.
...