EN 61007:1997

SLOVENSKI STANDARD
01-september-2002
Transformers and inductors for use in electronic and telecommunication
equipment- Measuring methods and test procedure (IEC 61007:1994, modified)
Transformers and inductors for use in electronic and telecommunication equipment -
Measuring methods and test procedures
Transformatoren und Drosseln für die Anwendung in elektronischen und
nachrichtentechnischen Einrichtungen - Meßmethoden und Prüfverfahren
Transformateurs et inductances utilisés dans les équipements électroniques et de
télécommunications - Méthodes de mesure et procédures d'essais
Ta slovenski standard je istoveten z: EN 61007:1997
ICS:
29.180 Transformatorji. Dušilke Transformers. Reactors
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

NORME
CEI
INTERNATIONALE
IEC
INTERNATIONAL
Deuxième édition
STAN DARD
Second edition
1994-10
Transformateurs et inductances utilisés
dans les équipements électroniques
et de télécommunications —
Méthodes de mesure et procédures d'essais
Transformers and inductors for use
in electronic and telecommunication
equipment —
Measuring methods and test procedures
© IEC 1994 Droits de reproduction réservés — Copyright - all rights reserved
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—3—
1007 ©IEC:1994
CONTENTS
Page
FOREWORD 7
Clause
1 Scope 9
2 Normative references 9
3 Terminology
4 Test procedures 21
4.1 Test and measurement conditions
4.1.1 Measurement uncertainty
Alternative test methods 21
4.1.2
4.2 Visual inspection
4.2.1 Safety screen position
4.2.2 Quality of solder joints
4.3 Dimensioning and gauging procedure
4.4 Electrical test procedures
4.4.1 Winding resistance 27
4.4.2 Insulation tests
4.4.3 Losses
4.4.4 Inductance
4.4.5 Unbalance
4.4.6 Capacitance
4.4.7 Transformation ratios
4.4.8 Resonant frequency
4.4.9 Signal transfer characteristics
4.4.10 Frequency response
4.4.11 Pulse characteristics
4.4.12 Voltage-time product rating
4.4.13 Total harmonic distortion
4.4.14 Voltage regulation
4.4.15 Temperature rise 89
4.4.16 Surface temperature 91
4.4.17 Phase test (polarity) 93
4.4.18 Screens
4.4.19 Noise 99
4.4.20 Corona test
4.4.21 Magnetic fields
4.4.22 Inrush current 109
— 5 —
1007 ©IEC:1994
Page
Clause
4.5 109
Environmental test procedures
4.5.1 General
4.5.2 Soldering
Robustness of terminations and integral mounting devices 4.5.3
4.5.4 Shock
4.5.5 Bump
Vibration (sinusoidal) 4.5.6
4.5.7 Acceleration, steady state
Rapid change of temperature (thermal shock in air)
4.5.8
Sealing 4.5.9
4.5.10 Climatic sequence
4.5.11 Damp heat, steady state 113
4.5.12 Dry heat
Mould growth 4.5.13
4.5.14 Salt mist, cyclic (sodium chloride solution)
115 4.5.15 Sulphur dioxide test for contacts and connections
4.5.16 Fire hazard
4.5.17 Immersion in cleaning solvents
115 4.6 Endurance test procedures
4.6.1 Short-term endurance (load run)
4.6.2 Long-term endurance (life test)

1007 ©IEC:1994 — 7 —
INTERNATIONAL ELECTROTECHNICAL COMMISSION
TRANSFORMERS AND INDUCTORS FOR USE
IN ELECTRONIC AND TELECOMMUNICATION EQUIPMENT -
MEASURING METHODS AND TEST PROCEDURES
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 cooperation 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, prepared by technical committees on
which all the National Committees having a special interest therein are represented, express, as nearly as
possible, an international consensus of opinion on the subjects dealt with.
3) They have the form of recommendations for international use 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.
International Standard IEC 1007 has been prepared by IEC technical committee 51:
Magnetic components and ferrite materials.
This second edition cancels and replaces the first edition published in 1990, and amend-
ments 1 and 2 (published in 1993), and constitutes a technical revision.
The text of this standard is based on the first edition of IEC 1007, amendments 1 and 2
and the following documents:
DIS Report on voting
51 (C0)309
51(CO)312
Full information on the voting for the approval of this standard can be found in the report
on voting indicated in the above table.

1007 ©IEC:1994 - 9 -
TRANSFORMERS AND INDUCTORS FOR USE
IN ELECTRONIC AND TELECOMMUNICATION EQUIPMENT -
MEASURING METHODS AND TEST PROCEDURES
1 Scope
This standard describes measuring methods and test procedures for inductors and trans-
formers for use in electronic and telecommunication equipment that may be involved in
any specifications for such components, in particular those forming part of the IEC Quality
Assessment System for Electronic Components (IECQ scheme).
2 Normative references
The following normative documents contain provisions which, through reference in this
text, constitute provisions of IEC 1007. At the time of publication, the editions indicated
were valid. All normative documents are subject to revision, and parties to agreements
based on IEC 1007 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 27: Letter symbols to be used in electrical technology
IEC 44-4: 1980,
Instrument transformers - Part 4: Measurement of partial discharges
IEC 50, International Electrotechnical Vocabulary (IEV)
IEC 68-1: 1988, Environmental testing - Part 1: General and guidance
Amendment 1 (1992)
IEC 68-2: Environmental testing - Part 2: Tests
IEC 68-2-1: 1990, Environmental testing - Part 2: Tests - Tests A: Cold
Amendment 1 (1993)
IEC 68-2-2: 1974, Environmental testing - Part 2: Tests - Tests B: Dry heat
Amendment 1 (1993)
IEC 68-2-3: 1969,
Environmental testing - Part 2: Tests - Test Ca: Damp heat, steady
state
IEC 68-2-6: 1982,
Environmental testing - Part 2: Tests - Test Fc and guidance: Vibration
(sinusoidal)
1007 ©IEC:1994 - 11 -
IEC 68-2-7: 1983, Environmental testing - Part 2: Tests - Test
Ga and guidance: Accel-
eration, steady state
Amendment 1 (1986)
IEC 68-2-10: 1988, Environmental testing - Pa rt 2: Tests - Test J and guidance: Mould
growth
IEC 68-2-13: 1983, Environmental testing - Part 2: Tests - Test M: Low air pressure
IEC 68-2-14: 1984, Environmental testing - Part 2: Tests - Test N: Change of temperature
Amendment 1 (1986)
IEC 68-2-17: 1978, Environmental testing - Part 2: Tests - Test Q: Sealing
Amendment 4 (1991)
IEC 68-2-20: 1979, Environmental testing - Part 2: Tests - Test T: Soldering
Amendment 2 (1989)
IEC 68-2-21: 1983, Environmental testing - Part 2: Tests - Test U: Robustness of termin-
ations and integral mounting devices
Amendment 2 (1991), Amendment 3 (1992)
IEC 68-2-27: 1987, Environmental testing - Part 2: Tests - Test Ea and guidance: Shock
IEC 68-2-29: 1987, Environmental testing - Part 2: Tests - Test Eb and guidance: Bump
IEC 68-2-30: 1980, Environmental testing - Part 2: Tests - Test Db and guidance: Damp
heat, cyclic (12 + 12-hour cycle)
Amendment 1 (1985)
IEC 68-2-42: 1982, Environmental testing - Pa rt 2: Tests - Test Kc: Sulphur dioxide test
for contacts and connections
IEC 68-2-45: 1980, Environmental testing - Part 2: Tests - Test XA and guidance: Immer-
sion in cleaning solvents
IEC 68-2-52: 1984, Environmental testing - Part 2: Tests - Test Kb: Salt: mist, cyclic
(sodium chloride solution)
IEC 68-2-58: 1989, Environmental testing - Part 2: Tests - Test Td: Solderability,
resistance to dissolution of metallization and to soldering heat of Surface Mounting
Devices (SMD)
IEC 270: 1981, Partial discharge measurements

1007 ©IEC:1994 - 13 -
IEC 367-1: 1982,
Cores for inductors and transformers for telecommunications - Part 1:
Measuring methods
Amendment 1 (1984), Amendment 2 (1992)
IEC 551: 1987,
Determination of transformer and reactor sound levels
IEC 617, Graphical symbols for diagrams
IEC 651: 1979, Sound level meters
Amendment 1 (1993)
IEC 695-2: Fire hazard testing - Part 2: Test methods
IEC 695-2-2: 1991,
Fire hazard testing - Part 2: Test methods - Section 2: Needle-flame
test
IEC 695-2-4/0: 1991, Fire hazard testing - Part 2: Test methods - Section 4/Sheet 0:
Diffusion type and pre-mixed type flame test methods
IEC 695-2-4/1: 1991,
Fire hazard testing - Part 2: Test methods - Section 4/Sheet 1:
1 kW nominal pre-mixed test flame and guidance
ISO 3: 1973,
Preferred numbers - Series of preferred numbers
ISO 497: 1973,
Guide to the choice of series of preferred numbers and of series contain-
ing more rounded values of preferred numbers
ISO 1000: 1992,
SI units and recommendations for the use of their multiples and of certain
other units
3 Terminology
For the purpose of this standard the following definitions apply in addition to those of
IEC 50:
3.1 component:
A transformer or an inductor.
3.2 peak working voltage: The maximum instantaneous voltage for which the winding
insulation is rated under working circuit conditions.
3.3 pulse waveform parameters (see figure 1)
a) peak pulse amplitude, Urn : The maximum value of an extrapolated smooth curve
through the top of the pulse, excluding any initial "spike" or "overshoot", the duration of
which is less than 10 % of the pulse duration.
b) pulse duration, td : The time interval between the first and last instants at which the
pulse amplitude equals 50 % of the peak pulse amplitude.

Leading edge Pulse top Trailing edge
Pulse crest
Overshooti
% tJmf
Droop
Pulse duration
Rèturn backswing
td
Cycle time
t
Back
–10 —
swing
Rise Fall
time
time
Recovery time
tf
590/90
tr
NOTE - For clarity in illustrating droop, the 80% and 10% points have been used in constructing the line
which determines the border between the pulse top and the trailing edge.
Figure 1 - Pulse waveform parameters

1007 CD IEC:1994 - 17
c) pulse rise time, t
r: The interval between the first instant at which the pulse
amplitude reaches 10 % of the peak pulse amplitude and the first instant at which the
pulse amplitude reaches 90 % of the peak pulse amplitude, excluding any unwanted or
irrelevant po
rtion of the waveform.
d) pulse fall time, tf:
The interval between the last instant at which the pulse
amplitude reaches 90 % of the peak pulse amplitude and the next instant at which the
pulse amplitude reaches 10 % of the peak pulse amplitude, excluding any unwanted or
irrelevant po rtion of the waveform.
NOTE — Where the value of the droop approaches 10 % of the peak pulse amplitude, the upper point
defining fall time may be replaced by the last instant at which the pulse amplitude reaches 80 % of the
peak pulse amplitude.
e) droop:
The difference between the peak pulse amplitude and the amplitude of the
extrapolated smooth curve through the top of the pulse, excluding any initial "spike" or
"overshoot", at its intersection with the straight line through the points defining the
pulse fall time, expressed as a percentage of the peak pulse amplitude.
f) pulse crest:
The maximum amplitude of the pulse.
g) overshoot:
The amount by which the pulse crest exceeds the peak pulse
amplitude. Overshoot is expressed as a percentage of the peak pulse amplitude.
h) backswing: The maximum amplitude of the reverse pulse, i.e. the po
rtion of the
pulse after the zero-crossing, expressed as a percentage of the peak pulse amplitude.
i) return
backswing: The maximum amplitude of the swing that follows the back-
swing, expressed as a percentage of the peak pulse amplitude.
j)
recovery time: The time interval between the end of the pulse fall time and the time
at which the pulse amplitude last reaches +10 % of the peak pulse amplitude. Excep-
tionally, a figure less than 10 % may be used, in which case the interval is termed "the
X % recovery time".
k) pulse
repetition frequency (prf): The average number of pulses in unit time when
this is independent of the period over which it is measured.
3.4 Q factor (quality factor): The ratio of the energy stored to the energy dissipated
during one cycle at a particular frequency in a specified winding. It is expressed in terms
of either the series or the parallel components of reactance and loss resistance.
3.5 harmonic distortion: The square root of the sum of the square of all harmonic
voltages up to and including the seventh harmonic (excluding the fundamental) expressed
as a percentage or as a ratio in decibels of the fundamental.
3.6 maximum winding temperature: The mean temperature rise of any winding of the
component under full load, when thermal stability has been achieved, added to the
specified maximum ambient temperature.
3.7 voltage-time product rating: The voltage pulse amplitude multiplied by the time
elapsed from the start of the pulse within which the non-linearity of the magnetizing
current does not exceed a specified value.
3.8 background (acoustic) noise: The noise measured at a measuring point with the
exclusion of that produced by the component under test.

1007©IEC:1994 - 19 --
3.9 compass safe distance:
The distance from the pivot of the test magnetometer or
compass to the nearest point on the surface of the component under test, at which the
magnetic deviation is limited to a stated value.
3.10 duty ratio; duty factor:
The ratio of pulse duration td to the cycle time.
3.11
current transformer parameters
a) burden:
That property of the circuit connected to the secondary winding of a
current transformer which determines the real and reactive power at the secondary
terminals. It is expressed as total impedance with effective resistive and reactive
components or as the total volt-amperes and power factor at the specified values of
current and frequency.
b) current transformation ratio, k:
The ratio of the r.m.s. value of the primary current
to the r.m.s. value of the secondary current under specified conditions.
c) phase angle:
The angular displacement between the vectors representing the
primary and secondary currents of the transformer. The phase angle is positive when
the secondary current leads the primary current.
d) ratio error:
The difference between the measured current transformation ratio k
and its nominal value
kn, divided by the measured value, and expressed as a percent-
age.
kn - k
ratio error = x 100 (per cent)
k
3.12 electrostatic screen:
A conducting screen inserted between windings that, when it
is connected to earth, considerably reduces the transference of unwanted signals from
one winding to the other via interwinding capacitance.
3.13 safety screen: A conducting screen inserted between windings that, when it is
connected to earth, effectively prevents fault currents flowing between those windings, in
the event of an insulation failure.
3.14
polarity (applicable to single-phase windings): A property of a single-phase
winding such that a terminal on one winding has the same polarity as a terminal on
another winding if, when the other ends of the windings are connected to form a common
terminal and the transformer/inductor is energized with a sinusoidal voltage, the induced
voltage appearing between each of the two terminals and the common terminal is rising
positively through zero at the same instant of time.
3.15 uniformly-
insulated winding: A winding in which the insulation to earth is, at
all points, designed to withstand an electric strength test of a value appropriate to the
insulation of the high-voltage end.
3.16 graded-insulated winding:
A winding in which insulation to earth is graded from
the amount at the high-voltage end to a smaller amount at the low-voltage end.
NOTE – Such a winding should withstand an electric strength test of a value appropriate to the insulation of
the low-voltage end.
1007 ©
IEC:1994 — 21 —
4 Test procedures
4.1 Test and measurement conditions
Unless otherwise specified all tests shall be carried out under standard atmospheric
conditions for testing as specified in IEC 68-1. Where there is a requirement for compo-
nents to attain temperature stability this shall be in accordance with 4.8 of IEC 68-1.
Unless otherwise stated in the detail specification, all voltages and currents shall be
sinusoidal; values shall be taken as r.m.s. and polyphase supplies shall be assumed to be
balanced.
The "information to be stated" that is required to complete the descriptions of test methods
in this clause shall be specified in the relevant detail specification for the component. The
detail specification shall also specify the test fixture to be used in association with a
component, where this is intended for use at frequencies high enough for the length of test
leads to become significant.
4.1.1 Measurement uncertainty
The limits quoted in detail specifications shall be absolute. The tolerance values applying
to the actual measurement system shall be taken into account when the measurements
are assessed against specification limits. Where tolerances in respect of set conditions or
instrument error have been prescribed these shall be regarded as additional minimum
requirements.
4.1.2 Alternative test methods
The test and measurement methods given in the relevant specification shall not be
regarded as the only methods to be used. Special test equipment and automatic test sets
are available, which may also be used. However, the tester shall satisfy the customer or
relevant authority (see Note 1) that any alternative methods which he may use will give
results equivalent (see Note 2) to those obtained by standard methods. In the case of
dispute, for referee and reference purposes the specified methods only shall be used.
Alternative test methods shall not be shown in detail specifications.
NOTES
1 Such as a National Supervising Inspectorate within the IECQ scheme.
2 By "equivalent" it is meant that the value of the characteristic established by such other method and
deemed acceptable in accordance with the limits ascribed to such other method will fall within the specified
limits when measured by the specified method.
4.2 Visual inspection
Visual inspection shall be performed under normal factory lighting without visual aids. The
condition, workmanship, marking and finish shall be
satisfactory.
NOTE — If special lighting and/or visual aids are necessary for the acceptance of particular components
(e.g. very small components), these may be specified as additional tests in the relevant detail specification.

1007 © IEC:1994 - 23 -
4.2.1 Safety screen position
NOTE — Sometimes the term "isolating screen" is used as an alternative to "safety screen".
Purpose:
To determine the position of a safety screen in relation to adjacent windings.
Procedure:
The fitted and positioned safety screen shall be inspected before being
obscured by subsequent windings. The safety screen shall:
a)
totally cover the winding around which it is wrapped such that the "finish" end over-
laps the "start" end by no less than the amount specified in the detail specification;
b)
be adequately insulated so as not to comprise a short-circuited winding;
c) have edges extending sufficiently along the winding being screened to prevent
direct contact between windings.
NOTE — Screens fitted to toroidal transformers may consist of a number of turns of conductive strip
provided that each turn overlaps the adjacent turn by not less than 5 % of the strip width.
Information to be stated:
- minimum overlap.
4.2.2 Quality of solder joints
NOTE — A good solder joint is one that has excellent electrical contact between the parts joined and good
mechanical strength. Examples of good solder joints are shown in figure 2. Figure 3 illustrates defective
joints.
Purpose: To determine the quality of all solder joints.
Procedure:
All solder joints shall be inspected to ensure that the following requirements
are complied with:
Requirements: Soldered joints shall:
a) exhibit good tinning as evidenced by the free flowing of solder with wetting of the
termination;
b) be smooth with no spikes;
c) be bright and shiny;
d) be without rough patches;
e)
shall have a concave surface and the outline of the wire shall be visible under the
surface of the solder;
f)
not have been moved during soldering (such joints exhibit an "orange peel" effect,
as shown in figure 3a);
g)
not be "dry" (that is, shall not exhibit a distinct line where the solder fillet joins the
wire or have a high contact angle between the solder and the wire (see figure 3b));
h)
be wired at terminals in such a way as to leave no residual stress (see figure 3c);
i) not exhibit "wicking" (that is, the joining wire shall not be overheated, leading to the
movement of solder into multi-stranded wires (see figure 3d)).

25 -
1007 © IEC:1994 -
J
591/90
Figure 2 - Examples of good solder joints
ro
_z__-,
X
(
593/90
Figure 3a - Moved joint Figure 3b - Dry joints
Insulation
I
I
I
I
I Solder
in the multistrand wire
i
A I kr makes it brittle
595/90
Figure 3c - Mechanically stressed joint Figure 3d - Wicking
Figure 3 - Examples of defective joints

1007 ©IEC:1994 - 27 -
4.3
Dimensioning and gauging procedure
The dimensions shall be verified as being in accordance with the relevant specification.
4.4
Electrical test procedures
4.4.1
Winding resistance
4.4.1.1 D.C. winding resistance
Purpose: To determine the d.c. resistance of a winding or windings between specified
terminations.
Procedure: The resistance shall be measured by a suitable method.
Where required by the detail specification, the ambient temperature A (in °C) shall be
measured and the result of the resistance measurement R
m (in I) corrected to the
corresponding value at 20 °C, R20 (in by means of the following formula:
k + 20
Rm
R20 k + 0
where k
is a constant related to the thermal coefficient of resistivity. For the purposes of
this standard, the value for copper shall be taken as 234,5 and for aluminium as 228,1.
NOTE – For safety reasons, consideration should be given to short-circuiting windings capable of produc-
ing high voltages at current interruption.
Information to be stated:
a) terminations between which the measurement is to be made;
b) whether the result of measurement should be corrected to 20 °C, and if so, the
value of k to be used for materials other than copper or aluminium.
NOTES
1 The selected method should be determined by the ease of operating the test and the accuracy re-
quired. The accuracy of the equipment should be at least ten times better than the accuracy required of the
test.
2 The measuring current should not be so large as to cause self-heating or to have a significant magnet-
izing effect on the component.
4.4.1.2 Continuity
Purpose: To verify the continuity of a specified winding.
Procedure:
Continuity shall be established using a suitable d.c. or a.c. voltage or current
source, and a suitable detector.
Information to be stated:
- winding to be tested.
1007 © IEC:1994 — 29 —
NOTES
1 The current should not be so large as to have a significant magnetizing effect on the component.
2 Care should be taken in testing a winding with a high inductance value as a high voltage may be
generated.
3 Where there are parallel paths, as with multiple windings or in polyphase components, a d.c.
resistance check may be necessary to ensure that the path under examination is not being influenced by
shunt paths.
4.4.2 Insulation tests
4.4.2.1 Electric strength test
Purpose:
To ensure that the insulation of uniformly-insulated windings and the low-
voltage end insulation of graded-insulated windings are adequate.
NOTES
1 This test is not suitable for the high-voltage end insulation of windings having graded insulation or
designed to have one point earthed*. The high-voltage end insulation of such windings can be tested only
by the application of an appropriate induced voltage test (see item b) of special conditions of test of
4.4.2.2).
2 In ce rt
ain cases it may be appropriate to demonstrate the adequacy of the low-voltage end insulation
of graded-insulated windings during the induced voltage test (see item b) of special conditions of test of
4.4.2.2).
Procedure: A test voltage whose value is selected from the table below, unless otherwise
specified, shall be applied between specified pairs of isolated elements of the component.
All windings shall be short-circuited. Windings and screens on one side of the insulation
system shall be connected to frame, core and earth while windings and screens on the
other side shall be connected together.
Electric strength test voltages
A.C. test voltage, 45 - 65 Hz
Peak working voltage D.C. test voltage
(r.m.s.)
V v V
pk r.m.s.
<25
50 71
>25 to 50 100
>50 to
100 300
>100 to 175 500 707
>175 to 700 2,8 x peak working voltage
4 x peak working voltage
>700
1,4 x peak working voltage
2 x peak working voltage
+ 1 000 + 1 400
The test voltage shall be increased at a convenient rate but not exceeding 2 kV per sec-
ond, from zero to the specified value, maintained at this value for the specified time (un-
less breakdown occurs), then decreased to zero at the same rate.
In the USA, "ground" is used in place of "earth" and "grounded" in place of "earthed".

1007 ©IEC:1994 – 31 –
For fluid-filled components, except for those designed for operation in one plane only and
so marked, approximately half the test sample shall be tested with terminals uppermost
and half with the terminals underneath.
If a specified environmental conditioning is required for this test the component shall be
held for a minimum of 6 h unless otherwise specified in the specified conditions. (See
IEC 68 for information on environmental testing.)
There shall be no evidence of heating, breakdown or deterioration. Ionization shall not be
regarded as a criterion of breakdown. The leakage current shall not exceed the specified
value.
Information to be stated:
a) terminations between which the test is to be made;
b)
test voltage (for a winding having graded-insulation, values shall be given for both
ends of the winding);
c) frequency of a.c. test voltage (if different from the values shown in the table);
d) test duration;
e) maximum leakage current, if specified.
NOTES
3 If breakdown occurs during the test it can at first be detected by sporadic and intermittent increases in
leakage current followed by a significant increase to a constant higher value which, on many electric
strength test sets, is accompanied by a partial or complete collapse of the voltage. This type of breakdown
may be caused by partial breakdown in ionized voids and weakened insulation which then avalanches to
complete breakdown in the form of arc-over or arc-through.
4 Electric strength test voltages may be hazardous. Extreme care should be taken in performing this
test.
4.4.2.2 Induced voltage test
Purpose: To verify the adequacy of inter-turn and inter-layer insulation of transformers
and inductors, and to verify the adequacy of the high-voltage end insulation of windings
having graded-insulation.
Special conditions of test
The following special conditions apply:
a) Uniformly insulated windings are normally tested as in Procedure 1, 2 or 3, as
appropriate. Any point of a winding may be earthed during the test as specified.
b) Windings having graded-insulation are normally tested as in
Procedure 1, 2 or 3,
as appropriate. A point on such a winding may be earthed or raised to a specified volt-
age above earth during the test. The induced voltage shall be such that, when added
vectorially to any applied voltage, the high-voltage end of the winding is raised to the
appropriate peak test voltage given in 4.4.2.1, Procedure.

1007 ©IEC:1994 – 33 –
If the specified voltage above earth is alternating, then it shall be of the same fre-
quency as the induced voltage.
NOTE 1 — In general, during the execution of the induced voltage test, no winding should be permitted to
"float", i.e. to remain unconnected at both ends.
Procedure 1: Applicable to transformers and inductors intended for energizing by
sinusoidal waveforms.
A specified test voltage of not less than twice the rated supply voltage at a frequency of
not less than twice the lowest rated frequency shall be applied across the specified
winding. The duration and manner of application shall be as specified in the detail specifi-
cation.
Procedure 2: Applicable to transformers and inductors intended for energizing by pulse
waveforms.
Specified test voltage pulses of amplitude not less than twice the rated pulse amplitude, at
a specified pulse repetition frequency of not less than 25 % of the maximum rated pulse
repetition frequency and with a specified pulse duration not less than 25 % of the rated
maximum pulse duration and normally* not greater than 50 % of the rated pulse duration
shall be applied across the winding. The duration and manner of application shall be as
specified in the detail specification.
Procedure 3: Applicable to transformers and inductors intended for energizing by
non-sinusoidal periodic waveforms such as those in power supplies operating with semi-
conductors in a switched mode.
A specified sinusoidal test voltage of peak value not less than twice the maximum rated
peak value for the input voltage waveform and at a specified frequency, derived as
follows, shall be applied across the specified winding. The duration and manner of appli-
cation shall be as specified in the detail specification.
The test frequency shall be such that its cyclic period is normally** not greater than the
effective shortest half-cycle period of the operative waveform for which the component is
intended e.g. in the case of pulse width modulated symmetrical or asymmetrical
waveforms the effective half-cycle shall be taken to be the effective minimum on-time of
the electronic switch.
Duration for application of test voltage in Procedures 1, 2 and 3
The duration of application of the test voltage shall be specified as one of the following:
a) The applied voltage shall be raised from one-third of the specified voltage to the full
Pulse durations greater than 50 % of the rated maximum value may be specified provided that core flux
saturation or other abnormalities are shown not to be incurred thereby.
** A lower test frequency may be specified provided that core flux saturation or other abnormalities are shown
not to be incurred thereby.
1007 ©IEC:1994 - 35 -
value which shall then be maintained for 60 s ± 5 s before reducing the voltage to one-
third of its value and hence to zero.
b) 5 s to 10 s (value to be stated).
Requirements:
There shall be no evidence of heating, breakdown or deterioration. Ionization shall not be
regarded as a criterion of breakdown.
Information to be
stated in the detail specification:
a) the test voltage (r.m.s. or peak as applicable);
b) the winding(s) to be energized (see note 2);
c)
the winding point intended to be connected to a known potential and the value of
this potential (if applicable);
d)
the duration of application of test voltage;
e) the test frequency or pulse repetition frequency (as applicable);
f)
the pulse duration (applicable to Procedure 2).
NOTE 2 - A source of test voltage may be connected to windings other than the normal input winding in
order to obtain the necessary voltages.
4.4.2.3
Insulation resistance
Purpose:
To measure the resistance of the insulation between the various parts of the
component.
Procedure:
Unless otherwise specified the insulation resistance shall be measured with a
d.c. voltage of either:
100 V ± 15 V for windings with peak working voltage < 500 V, or
500 V ± 50 V for windings with peak working voltage > 500 V.
The test voltage shall be applied until a steady reading is obtained or, failing that, for 60 s
± 5 S.
If a specified environmental conditioning is required the component shall be held in the
specified condition for a minimum of 6 h, unless otherwise specified. (See IEC 68 for infor-
mation on environmental testing.)
Information to be stated:
a)
terminations between which the measurement is to be made;
b) peak working voltage of each winding;
c)
environmental conditioning.
1007 © IEC:1994 - 37 -
4.4.3 Losses
4.4.3.1 No-load current
Purpose: To verify that the core is of the required quality and is correctly assembled and
that there are no short-circuited parts of the windings.
Procedure: The specified voltage at the frequency or frequencies specified shall be
applied from a low impedance source to the input winding with all other windings open-
circuit. The harmonic distortion of the applied voltage shall be less than 6 %. The input
current shall be measured with a true r.m.s. instrument, whose impedance is sufficiently
low not to affect the applied voltage by more than 1 %. The input current shall be
measured when its value is stabilized. For polyphase components all input currents shall
be measured.
Information to be stated:
a) a.c. voltage;
b) test frequency;
c) winding to be tested;
d) maximum r.m.s. value of input current.
4.4.3.2 No-load loss
Purpose: To verify that the transformer is of the required quality and is correctly
assembled and that there are no short-circuited parts of the windings.
The specified voltage at the specified frequency shall be applied to the input
Procedure:
winding via a suitable wattmeter, all other windings being open-circuit. The harmonic
distortion of the voltage when applied to the winding shall be less than 6 %.
The power loss shall be measured when its value has been stabilized, a correction being
made for the wattmeter losses if these are significant.
Information to be stated:
a) test voltage;
b) test frequency;
c) winding to be connected;
d) maximum power loss.
4.4.3.3 Quality factor, Q
Purpose: To determine the quality factor of a component at a particular frequency.
Q,
Procedure: The quality factor, shall be measured at the specified voltage and
frequency using a suitable method, for example:
a) a suitable inductance bridge;

1007 © IEC:1994 — 39 —
b)
circuit magnification meter (0-meter);
c)
insertion loss measurement (see, for example, appendix H of IEC 367-1);
d) damped oscillation method (see, for example, appendix G of IEC 367-1).
The references given for methods c) and d) above contain the appropriate formulae and
calculations.
The relationships between the effective inductance
L and resistance R of a component
under test, according to whether a series (s) or parallel (p) circuit representation is used,
and the measured value of Q at the frequency f
are given by:
2n f Ls
Q =
Rs
and
Rp
Q
21tfLp
respectively.
Information to be stated:
a) winding connections;
b) a.c. voltage;
c)
measuring frequency;
d) limits of Q value.
NOTE — In tests of high Q components, corrections for capacitor losses and terminating impedance may be
necessary.
4.4.4 Inductance
4.4.4.1 Effective inductance and effective resistance
Purpose: To measure the effective inductance and, if specified, the effective resistance of
a winding.
Procedure:
The inductance and, if specified, the effective resistance of the specified
winding shall be measured on a suitable bridge at the specified voltage and frequency with
polarizing d.c. applied if required.
Information to be stated:
a) winding to be measured;
b) form of measurement (see note);
c) a.c. voltage on the measured winding;
d) measuring frequency;
e) polarizing d.c.
– 41 –
1007 © IEC:1994
NOTES
1 In the case of low Q components, typically 10 or less, it is necessary to specify series or parallel mode
of measurement.
2 There is a difference between the true inductance Lo measured at low frequencies, and the effective
inductance Le measured at a frequency approaching self-resonance.
4.4.4.2 Leakage inductance, Li
Purpose: To determine the leakage inductance between windings of a transformer.
Procedure: The series inductance of the specified winding shall be measured on a
suitable bridge, the remaining windings or a specific winding being short-circuited as
specified.
Information to be stated:
a) winding connections;
b) a.c. voltage;
c) measuring frequency (see note 2).
NOTES
In performing this test the applied voltage should be sufficiently low for the currents in the short-
circuited windings not to exceed their rated values.
2 The selected frequency should ensure that the indicated value of the series inductance falls on the
straight minimum portion of the graph of measured inductance versus frequency (see figure 4).
Measured series
inductance
Test frequency range
Is 1■I
Value corresponding
to leakage inductance L 1
Frequency
IEC 900/94
Figure 4 – Variation of measured series inductance with frequency

1007 ©1EC:1994 - 43 -
4.4.5 Unbalance
NOTE — The following tests are concerned with the various types of unbalance in transformers.
4.4.5.1 Capacitance unbalance
Purpose:
To determine the capacitance unbalance between specified terminations of a
transformer.
Procedure: A suitable circuit for the measurement of this parameter is shown in figure
5.
The test frequency shall be high enough to make the effect of inductance unbalance
negligible.
With no connections to the transformer under test, capacitor C
1 is set to a specified value
(for example 50
pF) and a balance is obtained by varying C 2. The transformer is then
connected as shown and the bridge is rebalanced by varying C
1 . The difference between
the two values of C
1 is the capacitance unbalance.
Information to be stated:
a) initial value of C1;
b) component connections;
c) frequency.
1007 ©IEC:1994 - 45 -
Balanced source
G
D is a high-impedance detector
The 1 ka ratio arms are
non-reactive resistors
t 2
C and C are calibrated
variable capacitors of the same
type, preferably air dielectric
t
Component under test
IEC 90I/9I
NOTE - Terminal letters are for reference only.
Figure 5 — Circuit for measuring capacitance unbalance

1007 ©IEC:1994 - 47 -
4.4.5.2 Common mode rejection ratio
Purpose:
To determine the degree of rejection of the common mode input voltage.
Procedure:
A suitable circuit for this test is shown in figure 6.
Transformer under test
R1
G
u1
598/90
Figure 6 - Circuit for determining common mode rejection ratio
The input terminals of the transformer under test are connected to the high potential
terminal of a voltage source through equal resistors R
1 , each equal to half the input imped-
ance. The output terminals of the transformer under test are connected to a resistor
R2
whose value is specified in the detail specification.
The common mode rejection ratio (CMRR) in decibels is given by:
CMRR = -20 log
(U2/U1)
where
U 1 is the voltage of the common mode source, and
U2
is the voltage of the common mode signal emerging from the component under
test.
Information to be stated:
a)
transformer connections, including earth connections;
b) test frequency;
c) input impedance, 2R1;
d)
load resistor R2.
4.4.5.3 Impedance unbalance
Purpose:
To determine the impedance unbalance between two windings of a transformer,
intended to be equal.
Procedure: A suitable circuit for this test is shown in figure 7.

- 49 -
1007 © IEC:1994
Transformateur en essai
599/90
Figure 7 - Circuit for measuring impedance unbalance
A precision screened and balanced transformer shall be used as the input transformer T
and its symmetry shall be at least 20 dB better than the expected reading for the
transformer under test.
If the voltage caused by unbalance, as measured by the voltmeter V, is U2 , then the
impedance unbalance auz in decibels is given by the expression:
auz = 20 log (U1/2U2)
Information to be stated:
a) component connections;
b) input voltage U1;
c) load impedance ZL;
test frequency.
d)
NOTE — It is recommended that V is a frequency selective voltmeter, tuned to the test frequency.
4.4.5.4 Crosstalk attenuation
To determine the crosstalk attenuation of a telecommunication line transformer
Purpose:
which is for use in a phantom circuit.
Procedure: A suitable test circuit is shown in figure 8.
The attenuator shall be adjusted until U 1 = U2.
The crosstalk attenuation a c in decibels shall then be calculated in terms of the attenuator
setting a from the following expression:
r
a^ = ar + 10 log 2 - 10 log (Z /Z )Ps

1007 ©IEC:1994 - 51 -
Transformer under test
ZP Zs L
R2
R3
U2
A
dB
!EC 907/94
T
is a precision screened and balanced transformer.
L
is
...