IEC 60404-2:1996

IEC 60404-2 ®
Edition 3.1 2008-06
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Magnetic materials –
Part 2: Methods of measurement of the magnetic properties of electrical steel
strip and sheet by means of an Epstein frame

Matériaux magnétiques –
Partie 2: Méthodes de mesure des propriétés magnétiques des bandes et tôles
magnétiques en acier au moyen d'un cadre Epstein

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IEC 60404-2 ®
Edition 3.1 2008-06
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Magnetic materials –
Part 2: Methods of measurement of the magnetic properties of electrical steel

strip and sheet by means of an Epstein frame

Matériaux magnétiques –
Partie 2: Méthodes de mesure des propriétés magnétiques des bandes et tôles

magnétiques en acier au moyen d'un cadre Epstein

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.220.20; 29.030 ISBN 2-8318-9835-8

− 2 − 60404-2 © IEC:1996+A1:2008
CONTENTS
FOREWORD.4
1 Scope and object .6
2 Normative references.6
3 General principles of a.c. measurements .7
3.1 Principle of the 25 cm Epstein frame method .7
3.2 Test specimen .7
3.3 The 25 cm Epstein frame.7
3.4 Air flux compensation .9
3.5 Power supply.9
3.6 Voltage measurement.9
3.7 Frequency measurement .10
3.8 Power measurement.10
4 Procedure for the measurement of the specific total loss.10
4.1 Preparation for measurement.10
4.2 Adjustment of power supply .10
4.3 Measurement of power .11
4.4 Determination of the specific total loss .11
4.5 Reproducibility of the specific total loss measurement.12
5 Procedure for the determination of the peak value of magnetic polarization, r.m.s.
value of magnetic field strength, peak value of magnetic field strength
and specific apparent power .12
5.1 Test specimen .12
5.2 Principle of measurement .12
5.3 Reproducibility.14
6 General principles of d.c. measurements .14
6.1 Principle of the 25 cm Epstein frame method .14
6.2 Test specimen .14
6.3 The 25 cm Epstein frame.14
6.4 Air flux compensation .15
6.5 Power supply.15
6.6 Apparatus accuracy .15
7 Procedure for the d.c. measurement of the magnetic polarization .15
7.1 Preparation for measurement.15
7.2 Determination of the magnetic polarization.15
7.3 Determination of the magnetic hysteresis loop .16
7.4 Reproducibility of the measurement of the magnetic polarization .16
8 Test report.16

Annex A (informative) Digital sampling methods for the determination of the magnetic
properties .21

Bibliography .24

60404-2 © IEC:1996+A1:2008 − 3 −
Figure 1 – Double-lapped joints .17
Figure 2 – The 25 cm Epstein frame.17
Figure 3 – Circuit for the wattmeter method .18
Figure 4 – Circuit for measuring the r.m.s. value of the magnetizing current.18
Figure 5 – Circuit for measuring the peak value of the magnetic field strength
using a peak voltmeter .19
Figure 6 – Circuit for measuring the peak value of magnetic field strength
using a mutual inductor M .19
D
Figure 7 – Circuit for d.c. testing: to obtain discrete values of magnetic polarization.20
Figure 8 – Circuit for d.c. testing: continuous recording method .20

− 4 − 60404-2 © IEC:1996+A1:2008
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MAGNETIC MATERIALS –
Part 2: Methods of measurement of the magnetic properties
of electrical steel strip and sheet by means of an Epstein frame
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of 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, IEC publishes International Standards, Technical Specifications,
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Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
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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 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 IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
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other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
This consolidated version of the official IEC Standard and its amendment has been
prepared for user convenience.
IEC 60404-2 edition 3.1 contains the third edition (2000) [documents 68/119/FDIS and
68/135/RVD] and its amendment 1 (2008) [documents 68/365/FDIS and 68/369/RVD].
A vertical line in the margin shows where the base publication has been modified by
amendment 1.
International Standard IEC 60404-2 has been prepared by IEC technical committee 68:
Magnetic alloys and steels.
60404-2  IEC:1996+A1:2008 − 5 −
This standard supersedes chapters I, II, IV and V of IEC 60404-2:1978.
The standard IEC 60404-11 supersedes chapter VIII of IEC 60404-2:1978.
The standard IEC 60404-13 supersedes chapters VI, VII and IX of IEC 60404-2:1978.
Chapter III of IEC 60404-2:1978 is cancelled.
The committee has decided that the contents of the base publication and its amendments will
remain unchanged until the maintenance result date indicated on the IEC web site under
"http://webstore.iec.ch" in the data related to the specific publication. At this date,
the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
The contents of the corrigendum of March 2018 have been included in this copy.

− 6 − 60404-2 © IEC:1996+A1:2008
MAGNETIC MATERIALS –
Part 2: Methods of measurement of the magnetic properties
of electrical steel strip and sheet by means of an Epstein frame

1 Scope and object
This part of IEC 60404 is applicable to grain oriented and non-oriented electrical sheet and
strip for a.c. measurements of magnetic properties at frequencies up to 400 Hz and for d.c.
magnetic measurements.
The object of this part is to define the general principles and the technical details of the
measurement of the magnetic properties of electrical steel sheet and strip by means of an
Epstein frame.
The Epstein frame is applicable to test specimens obtained from electrical steel sheets and
strips of any grade. The a.c. magnetic characteristics are determined for sinusoidal induced
voltages, for specified peak values of magnetic polarization and for a specified frequency.
The measurements are to be made at an ambient temperature of (23 ± 5) °C on test
specimens which have first been demagnetized.
Measurements at higher frequencies are to be made in accordance with IEC 60404-10.
NOTE Throughout this standard the term "magnetic polarization" is used as defined in IEC 60050(221). In some
standards of the IEC 60404 series, the term "magnetic flux density" was used.
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
the referenced document (including any amendments) applies.
IEC 60050-221, International Electrotechnical Vocabulary – Chapter 221: Magnetic materials
and components
IEC 60404-4, Magnetic materials – Part 4: Methods of measurement of d.c. magnetic properties
of magnetically soft materials
IEC 60404-8-3, Magnetic materials – Part 8-3: Specifications for individual materials – Cold-
rolled electrical non-alloyed and alloyed steel sheet and strip delivered in the semi-processed
state
IEC 60404-8-4, Magnetic materials – Part 8-4: Specifications for individual materials – Cold-
rolled non-oriented electrical steel sheet and strip delivered in the fully-processed state
IEC 60404-8-7, Magnetic materials – Part 8-7: Specifications for individual materials – Cold-
rolled grain-oriented electrical steel sheet and strip delivered in the fully-processed state
IEC 60404-10, Magnetic materials – Part 10: Methods of measurement of magnetic properties
of magnetic sheet and strip at medium frequencies
IEC 60404-13, Magnetic materials – Part 13: Methods of measurement of density, resistivity
and stacking factor of electrical steel sheet and strip

60404-2 © IEC:1996+A1:2008 − 7 −
3 General principles of a.c. measurements
3.1 Principle of the 25 cm Epstein frame method
The 25 cm Epstein frame which comprises a primary winding, a secondary winding and the
specimen to be tested as a core, forms an unloaded transformer whose characteristics are
measured by the method described in the following subclauses.
3.2 Test specimen
The strips to be tested are assembled in a square, having double-lapped joints (see figure 1),
thus forming four branches of equal length and equal cross-sectional area.
The strips shall be sampled in accordance with the appropriate product standard in the IEC
60404-8 series.
They shall be cut by a method which will produce substantially burr-free edges and, if so
specified, heat treated in accordance with the corresponding product standard. They shall have
the following dimensions:
− width b = 30 mm ± 0,2 mm;
− length 280 mm ≤ l ≤ 320 mm.
The lengths of the strips shall be equal within a tolerance of ±0,5 mm.
When strips are cut parallel or normal to the direction of rolling, the edge of the parent sheet
shall be taken as the reference direction.
The following tolerances shall apply for the angle between the specified and actual direction of
cutting:
±1° for grain oriented steel sheet;
±5° for non-oriented steel sheet.
Only flat strips shall be used. Measurements shall be made without additional insulation.
The number of strips comprising the test specimen shall be a multiple of four and is specified
in the corresponding product standard. However, the active mass of the test specimen (see
equation (1)) shall be at least 240 g for strips 280 mm long.
3.3 The 25 cm Epstein frame
The 25 cm Epstein frame (hereinafter referred to as the Epstein frame) shall consist of four
coils into which the strips making up the test specimen are inserted (see figure 2).
A mutual inductor for air flux compensation is included with the Epstein frame.
The winding formers supporting the coils are made of hard insulating material, such as
phenolic paper. They have a rectangular cross-section with 32 mm inner width. A height of
approximately 10 mm is recommended.
The coils shall be fixed to an insulating and non-magnetic base in such a way as to form a
square (see figure 2). The length of the sides of the square formed by the internal edges of the
+ 1
strips of the test specimen shall be 220 m m (see figure 2).
- 0
− 8 − 60404-2 © IEC:1996+A1:2008
Each of the four coils shall have two windings:
− a primary winding, on the outside (magnetizing winding);
− a secondary winding, on the inside (voltage winding).
NOTE An electrostatic screen may be provided between these windings.
The windings shall be distributed uniformly over a minimum length of 190 mm, each coil having
one quarter of the total number of turns.
The individual primary windings of the four coils shall be connected in series, as shall be the
secondary windings. The number of primary and secondary turns may be adapted to the
particular conditions prevailing with regard to the power source, measuring equipment and
frequency.
NOTE The total number of turns generally used and recommended is 700 or 1 000.
In order to reduce the effect of the impedances of the windings as much as possible, the
following requirements shall be met:
R R
1 −6 2 −6
≤⋅1,25 10 Ω ≤⋅510 Ω
2 2
N N
1 2
L L
1 −9 2 −9
≤⋅2,5 10 H ≤⋅2,5 10 H
2 2
N N
1 2
where
R and R are the resistances of the primary and secondary windings, respectively, in ohms;
1 2
L and L are the inductances of the primary and secondary windings, respectively, in
1 2
henrys;
N and N are the total number of turns of the primary and secondary windings, respectively.
1 2
NOTE These requirements are satisfied, for example, if windings with the following characteristics are used:
− total number of turns: N = 700, N = 700;
1 2
− primary (outer) winding: each of the four coils carries 175 turns of two copper wires connected in parallel,
each with a nominal cross-sectional area of approximately 1,8 mm , wound side by side in three layers;
− secondary winding: each of the four coils carries 175 turns of one copper wire with a nominal cross-sectional
area of 0,8 mm wound in one layer.
The effective magnetic path length, l , of the magnetic circuit shall be conventionally assumed
m
to be equal to 0,94 m. Therefore, the active mass, m , that is the mass of the test specimen
a
which is magnetically active, is given by:
l
m
mm= (1)
a
4 l
where
l is the length of a test specimen strip, in metres;
l is the conventional effective magnetic path length, in metres (l = 0,94 m);
m m
m is the total mass of the test specimen, in kilograms;
m is the active mass of the test specimen, in kilograms.
a
60404-2 © IEC:1996+A1:2008 − 9 −
3.4 Air flux compensation
The mutual inductor for air flux compensation shall be located in the centre of the space
enclosed by the four coils, its axis being directed normal to the plane of the axes of these coils.
The primary winding of the mutual inductor shall be connected in series with the primary
winding of the Epstein frame, and the secondary winding of the mutual inductor shall be
connected to the secondary winding of the Epstein frame in series opposition (see figure 3).
The adjustment of the value of the mutual inductance shall be made so that, when passing an
alternating current through the primary windings in the absence of the specimen in the
apparatus, the voltage measured between the non-common terminals of the secondary
windings shall be no more than 0,1 % of the voltage appearing across the secondary winding of
the test apparatus alone.
Thus the average value of the rectified voltage induced in the combined secondary windings is
proportional to the peak value of the magnetic polarization in the test specimen.
3.5 Power supply
The power supply shall have a low impedance and a high stability of voltage and frequency.
During measurements, the voltage and frequency variations shall not exceed ±0,2 % of the
required value.
For the determination of the specific total loss, the specific apparent power and the r.m.s. value
of the magnetic field strength, the form factor of the secondary voltage shall be 1,111 ± 1 %.
NOTE This is possible in several ways: for example by using an electronically controlled power supply or a
negative feedback power amplifier. The form factor of the secondary voltage is the ratio of its r.m.s. value to its
average rectified value.
Two voltmeters, one responsive to r.m.s. values and the other responsive to average rectified
values shall be used to determine the form factor.
NOTE The waveform of the secondary induced voltage should be checked with an oscilloscope to ensure that only
the fundamental component is present.
3.6 Voltage measurement
The secondary voltage of the Epstein frame shall be measured by means of appropriate
voltmeters having an input impedance greater than or equal to 1 000 Ω/V.
NOTE For the application of digital sampling methods, see Annex A.
3.6.1 Average type voltmeter
A voltmeter responsive to average rectified values having an accuracy of ±0,2 % or better shall
be used.
NOTE The preferred instrument is a digital voltmeter.
3.6.2 RMS voltmeter
A voltmeter responsive to r.m.s. values having an accuracy of ±0,2 % or better shall be used.
NOTE The preferred instrument is a digital voltmeter.
3.6.3 Peak voltmeter
A voltmeter responsive to peak values having an accuracy of ±0,5 % or better shall be used.

− 10 − 60404-2 © IEC:1996+A1:2008
3.7 Frequency measurement
A frequency meter having an accuracy of ±0,1 % or better shall be used.
NOTE For the application of digital sampling methods, see Annex A.
3.8 Power measurement
The power shall be measured by a wattmeter having an accuracy of ±0,5 % or better at the
actual power factor and crest factor.
NOTE For the application of digital sampling methods, see Annex A.
The resistance of the voltage circuit of the wattmeter shall be at least 5 000 times its
reactance, unless the wattmeter is compensated for its reactance.
If a current measuring device is included in the circuit it shall be short-circuited when the
secondary voltage has been adjusted and the loss is being measured.
4 Procedure for the measurement of the specific total loss
NOTE For the application of digital sampling methods, see Annex A.
4.1 Preparation for measurement
The Epstein frame and measuring equipment shall be connected as shown in figure 3.
The test specimen shall be weighed and its mass determined to within ±0,1 %. After weighing,
the strips shall be stacked into the coils of the Epstein frame with double lapped joints at the
corners and with the same number of strips in each branch of the frame such that the length of
+1
the internal side of the square so formed is 220 mm. Where strips are cut half parallel and
−0
half perpendicular to the direction of rolling, the strips cut in the direction of rolling shall be
inserted in two opposite branches of the frame and those cut perpendicular to the direction of
rolling inserted in the other two branches. Care shall be taken to ensure that the air gap
between the strips in the overlapping portions is as small as possible. It is permissible to apply
a force of about 1 N to each corner, normal to the plane of the overlapping strips.
The test specimen shall then be demagnetized in a decreasing alternating magnetic field of an
initial level higher than used in previous measurements.
4.2 Adjustment of power supply
The power supply output shall be slowly increased, whilst observing the ammeter in the primary
circuit to ensure that the wattmeter current circuit is not overloaded, until the average rectified
value of the secondary voltage U of the Epstein frame has reached the required value. This
is calculated from the desired value of magnetic polarization by means of:
R
i
$
Uf= 4N AJ (2)
RR+
it
60404-2 © IEC:1996+A1:2008 − 11 −
where
U is the average value of the rectified voltage induced in the secondary winding, in volts;
A is the cross-sectional area of the test specimen, in square metres;
f is the frequency, in hertz;
$
J is the peak value of magnetic polarization, in teslas;
N is the total number of turns of the secondary winding;
R is the total resistance of the instruments in the secondary circuit, in ohms;
i
R is the series resistance of the secondary windings and mutual inductor, in ohms.
t
The cross-sectional area of the test specimen is given by the equation:
m
A = (3)
4 l ρ
m
where
A is the cross-sectional area of the test specimen, in square metres;
m is the total mass of the test specimen, in kilograms;
l is the length of a test specimen strip, in metres;
ρ is the conventional density, or the value determined in accordance with IEC 60404-13, of
m
the test material, in kilograms per cubic metre.
4.3 Measurement of power
The ammeter in the primary circuit shall be short circuited and the secondary voltage
readjusted if necessary. The form factor of the secondary voltage shall be determined in
accordance with 3.5 and then the wattmeter reading shall be recorded.
4.4 Determination of the specific total loss
The power, P , measured by the wattmeter includes the power consumed by the instruments in
m
the secondary circuit. The total loss, P , of the test specimen shall therefore be calculated
c
using the equation:
⎛ ⎞
1,111 U
⎜ ⎟
N
⎝ ⎠
P=−P (4)
c m
R
i
N
where
P is the calculated total loss of the test specimen, in watts;
c
N is the total number of turns of the primary winding;
N is the total number of turns of the secondary winding;
P is the power measured by the wattmeter, in watts;
m
R is the total resistance of the instruments in the secondary circuit, in ohms;
i
U is the average value of the rectified voltage induced in the secondary winding, in volts.
The measured specific total loss, P , is obtained by dividing P by the active mass m of the
s c a
test specimen.
P P 4 l
c c
P== (5)
s
m m l
a m
− 12 − 60404-2 © IEC:1996+A1:2008
where
P is the specific total loss of the test specimen, in watts per kilogram;
s
l  is the length of a test specimen strip, in metres;
l is the conventional effective magnetic path length, in metres (l = 0,94 m);
m m
m is the total mass of the test specimen, in kilograms;
m is the active mass of the test specimen, in kilograms;
a
P is the calculated total loss of the test specimen, in watts.
c
4.5 Reproducibility of the specific total loss measurement
The reproducibility of the results obtained from the procedures described in this subclause is
characterized by a relative standard deviation of 1,5 % for measurements on grain oriented
material at magnetic polarizations up to 1,7 T and for measurements on non-oriented material
up to 1,5 T.
For measurements at higher magnetic polarizations, it is expected that the relative standard
deviation will be increased.
5 Procedure for the determination of the peak value of magnetic polarization,
r.m.s. value of magnetic field strength, peak value of magnetic field strength
and specific apparent power
This clause describes measuring methods for the determination of the following characteristics:
$
− peak value of magnetic polarization J ;
~
− r.m.s. value of magnetic field strength H ;
$
− peak value of magnetic field strength H ;
− specific apparent power S .
s
5.1 Test specimen
The test specimen shall comply with 3.2.
5.2 Principle of measurement
$
5.2.1 Peak value of magnetic polarization J
The peak value of magnetic polarization shall be determined from the average value of the
secondary rectified voltage measured as described in clause 4 and calculated from equation 2.
5.2.2 RMS value of magnetic field strength
The r.m.s. value of the magnetic field strength shall be calculated from the r.m.s. value of the
current, measured by an r.m.s. ammeter in the circuit shown in figure 4. Alternatively a
precision resistor, of value typically in the range 0,1 Ω to 1 Ω of an accuracy of 0,1 %, shall be
connected in place of the ammeter and the voltage developed across this resistor shall be
measured using a voltmeter responsive to r.m.s. values conforming to the requirements of 3.6.
The frequency shall be set to the desired value. The peak value of the magnetic polarization
shall be set by adjusting the secondary voltage of the Epstein frame to the required value
calculated from equation 2. The r.m.s. value of the current shall then be determined and
recorded. The r.m.s. value of the magnetic field strength shall be calculated from the equation:
N
~~
H = I (6)
l
m
60404-2 © IEC:1996+A1:2008 − 13 −
where
~
H is the r.m.s. value of magnetic field strength, in amperes per metre;
~
I is the r.m.s. value of magnetizing current, in amperes;
l is the conventional effective magnetic path length, in metres (l = 0,94 m);
m m
N is the total number of turns of the primary winding.
5.2.3 Peak value of magnetic field strength
The peak value of the magnetic field strength shall be derived from the peak value of the
magnetizing current Î which is obtained by measuring the voltage drop across a known
precision resistor R of an accuracy of 0,1 %, using a peak voltmeter as shown in figure 5. For
this measurement, the form factor of the secondary voltage is allowed to exceed the specified
value (see 3.5).
The peak magnetic field strength shall be calculated from the equation:
N
$$
H = I (7)
l
m
where
$
H is the peak value of magnetic field strength, in amperes per metre;
$
⎛ ⎞
U
$
Î is the peak value of magnetizing current ⎜I = ⎟ in amperes;
1 1
R
⎝ ⎠
l is the conventional effective magnetic path length of test specimen (l = 0,94 m);
m m
N is the total number of turns of the primary winding of the Epstein frame.
Alternatively, the peak value of the magnetizing current Î can be determined by measuring the
average rectified value of the voltage appearing across the secondary winding of a mutual
inductor M of an accuracy of 0,5 %, the primary winding of which is connected in series with
D
the primary winding of the Epstein frame. With this method it is necessary to ensure (e.g. by
observing the waveform on an oscilloscope) that there are no more than two zero crossings per
cycle of the voltage waveform of the secondary winding of the mutual inductor. The circuit is
given in figure 6. The voltmeter can be the same instrument as is used for measuring the
secondary voltage of the Epstein frame. With this method, the peak value of the magnetic field
strength shall be calculated from the equation:
N RR+
1 vm
$
H=⋅ ⋅ U (7a)
m
4fM l R
Dm v
where
M is the mutual inductance in the circuit given in figure 6, page 35, in henrys;
D
R is the resistance of the secondary winding of M , in ohms;
m D
R is the internal resistance of the average type voltmeter, in ohms;
v
U is the average rectified value of the voltage induced in the secondary winding of M ,
m D
in volts.
− 14 − 60404-2 © IEC:1996+A1:2008
5.2.4 Determination of the specific apparent power
For a given value of magnetic polarization and frequency, the corresponding r.m.s. values of
the magnetizing current (see 5.2.2) and the r.m.s. value of the secondary voltage of the Epstein
frame shall be measured. The r.m.s. value of the voltage shall be measured by connecting a
voltmeter complying with the requirements of 3.6 across the secondary winding of the Epstein
frame.
The specific apparent power is given by the following relationship:
N N 4 l
~~ ~~
1 1
SI==U IU (8)
s1 2 12
mN mNl
a2 m2
where
S is the specific apparent power, in voltamperes per kilogram;
s
~
I is the r.m.s. value of the magnetizing current in amperes;
l is the conventional effective magnetic path length, in metres (l = 0,94m);
m
m
l is the length of a test specimen strip, in metres;
m is the total mass of the test specimen, in kilograms;
m is the active mass of the test specimen, in kilograms;
a
N is the total number of turns of the primary winding of the Epstein frame;
N is the total number of turns of the secondary winding of the Epstein frame;
~
U is the r.m.s. value of the voltage induced in the secondary winding, in volts.
5.3 Reproducibility
The reproducibility of the results obtained from the procedures described in this clause
depends essentially upon the accuracy of the instruments used for the measurement and
careful attention to the physical details of the test equipment. When using instruments having
an accuracy of ±0,5 % or better, the reproducibility of the measurements is characterized by a
standard deviation of the order of 2 % except for the specific apparent power where the
reproducibility is characterized by a standard deviation of between 2 % (for values of magnetic
polarization below the knee of the magnetization curve) to 7 % (for values of magnetic
polarization approaching saturation).
6 General principles of d.c. measurements
6.1 Principle of the 25 cm Epstein frame method
The 25 cm Epstein frame which comprises a primary winding, a secondary winding and the
specimen to be tested as a core, forms an unloaded transformer whose d.c. characteristics are
measured by the method described in the following subclauses.
6.2 Test specimen
The test specimen shall comply with 3.2.
6.3 The 25 cm Epstein frame
The 25 cm Epstein frame shall be constructed in accordance with 3.3.

60404-2 © IEC:1996+A1:2008 − 15 −
6.4 Air flux compensation
The effect of the air flux shall be compensated by means of a mutual inductor as described
in 3.4.
6.5 Power supply
The power supply shall have a current rating sufficient to produce the maximum magnetic field
strength required. The ripple content shall be less than 1 % and the current stability shall be
such that the resultant relative magnetic flux variations are not more than 0,2 %.
6.6 Apparatus accuracy
The accuracy of the measuring apparatus shall be as follows:
6.6.1 Magnetic flux integrator
A magnetic flux integrator having an accuracy of ±0,3 % or better shall be used.
NOTE The magnetic flux integrator may be calibrated by one of the methods described in annex B of IEC 60404-4.
6.6.2 Ammeter
An ammeter having an accuracy of ±0,2 % or better shall be used.
7 Procedure for the d.c. measurement of the magnetic polarization
7.1 Preparation for measurement
The Epstein frame and measuring equipment shall be connected as shown in figure 7.
The test specimen shall be weighed and assembled into the Epstein frame as described in 4.1.
The test specimen shall then be demagnetized either in a decreasing alternating magnetic field
or by a series of reversals of a gradually reducing direct current flowing in the primary winding
of the Epstein frame, the frequency of the reversals being about two per second. The initial
value of the magnetic field strength produced by the demagnetizing current shall be of a level
higher than that used in previous measurements.
The cross-sectional area A of the test specimen shall be calculated from equation 3.
7.2 Determination of the magnetic polarization
Discrete values of magnetic polarization can be determined for corresponding values of
magnetic field strength using a circuit as shown in figure 7, or a normal magnetization curve
can be obtained from a series of discrete values. Alternatively, a continuous recording method
may be used. A calibrated four terminal resistor is connected in series with the magnetizing
winding of the Epstein frame. The potential terminals are connected to the X input of an X-Y
recorder and the output of the flux integrator is connected to the Y input of the X-Y recorder as
shown in figure 8. A plotter or computer interface can be used in place of the X-Y recorder.
The magnetic field strength shall be determined by measuring the magnetizing current in the
primary winding of the Epstein frame using the following equation:
NI
H = (9)
l
m
− 16 − 60404-2 © IEC:1996+A1:2008
where
H is the magnetic field strength, in amperes per metre;
I is the magnetizing current, in amperes;
l is the conventional effective magnetic path length, in metres (l = 0,94 m);
m m
N is the total number of turns of the primary winding of the Epstein frame.
To obtain discrete values of magnetic polarization, the magnetic flux integrator shall be zeroed
and the current through the primary winding shall be increased until the desired value of
magnetic field strength is reached.
The magnetizing current and the change in fluxmeter reading shall be recorded. The value of
the magnetic polarization shall be calculated from the change in fluxmeter reading and the
calibration constant of the flux integrator using the following equation:
K α
jj
ΔJ = (10)
NA
where
ΔJ is the measured change of magnetic polarization, in tesla;
A is the cross-sectional area of the test specimen, in square metres;
α is the reading of the flux integrator;
j
K is the calibration constant of the flux integrator, in volt seconds;
j
N is the total number of turns of the secondary winding of the Epstein frame.
7.3 Determination of the magnetic hysteresis loop
If required, the magnetic hysteresis loop shall be determined in accordance with IEC 60404-4
except that the ring shall be replaced by the Epstein frame and test specimen.
7.4 Reproducibility of the measurement of the magnetic polarization
The reproducibility of the results obtained from the procedure described in this clause is
characterized by a relative standard deviation of 1,0 %.
8 Test report
The test report shall include the following, as applicable:
a) type and identity of test specimen;
b) density of material (conventional, or as measured in accordance with IEC 60404-13);
c) length of test specimen strips;
d) number of strips;
e) ambient temperature during the measurements;
f)
...