ASTM A889/A889M-03(2008)
(Test Method)Standard Test Method for Alternating-Current Magnetic Properties of Materials at Low Magnetic Flux Density Using the Voltmeter-Ammeter-Wattmeter-Varmeter Method and 25-cm Epstein Frame
Standard Test Method for Alternating-Current Magnetic Properties of Materials at Low Magnetic Flux Density Using the Voltmeter-Ammeter-Wattmeter-Varmeter Method and 25-cm Epstein Frame
SIGNIFICANCE AND USE
This test method may be used to determine the specific core loss, specific reactive power, specific exciting power, inductance permeability, and impedance permeability of flat-rolled magnetic materials over a wide range of inductions and at frequencies up to 400 Hz for symmetrically magnetized test samples.
These measurements are used by the producer and user of the flat-rolled material for quality control purposes. The fundamental assumption inherent in these measurements is that they can be correlated with the electromagnetic characteristics of a core fabricated from the flat-rolled material.
SCOPE
1.1 This test method covers tests for the magnetic properties of basic flat-rolled magnetic materials at power frequencies (25 to 400 Hz) using a 25-cm Epstein test frame and the 25-cm double-lap-jointed core.
1.2 The magnetic properties of materials are determined from measurements on Epstein core specimens with the core and test coils treated as though they constituted a series-parallel equivalent circuit (Fig. A1.1) for the fundamental frequency of excitation where the apparent parallel inductance, L1, and resistance, R1, are attributable to the test specimen.
1.3 This test method is suitable for the determination of core loss, rms volt-amperes, rms exciting current, reactive volt-amperes, and related properties of flat-rolled magnetic materials under ac magnetization.
1.4 The frequency range of this test method is normally that of the commercial power frequencies 50 to 60 Hz. It is also acceptable for measurements at frequencies from 25 to 400 Hz. This test method is customarily used on nonoriented electrical steels at inductions up to 10 kG [1.0 T] and for grain-oriented electrical steels at inductions up to 15 kG [1.5 T].
1.5 For reactive properties, both flux and current waveforms introduce limitations. Over its range of useful inductions, the varmeter is valid for the measurement of reactive volt-amperes (vars) and inductance permeability. For the measurement of these properties, it is suggested that test inductions be limited to values sufficiently low that the measured values of vars do not differ by more than 15 % (Note 1) from those calculated from the measured values of exciting volt-amperes and core loss.
Note 1—This limitation is placed on this test method in consideration of the nonlinear nature of the magnetic circuit, which leads to a difference between vars based on fundamental frequency components of voltage and current and current after harmonic rejection and vars computed from rms current, voltage, and watt values when one or more of these quantities are nonsinusoidal.
1.6 This test method shall be used in conjunction with Practice A 34/A 34M.
1.7 Explanation of terms, symbols, and definitions used may be found in the various sections of this test method. The official list of definitions and symbols may be found in Terminology A 340.
1.8 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard. Within this standard, SI units are shown in brackets.
1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to its use.
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Designation: A889/A889M − 03(Reapproved 2008)
Standard Test Method for
Alternating-Current Magnetic Properties of Materials at Low
Magnetic Flux Density Using the Voltmeter-Ammeter-
Wattmeter-Varmeter Method and 25-cm Epstein Frame
This standard is issued under the fixed designationA889/A889M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
current and current after harmonic rejection and vars computed from rms
1. Scope
current, voltage, and watt values when one or more of these quantities are
1.1 This test method covers tests for the magnetic properties
nonsinusoidal.
ofbasicflat-rolledmagneticmaterialsatpowerfrequencies(25
1.6 This test method shall be used in conjunction with
to 400 Hz) using a 25-cm Epstein test frame and the 25-cm
Practice A34/A34M.
double-lap-jointed core.
1.7 Explanationofterms,symbols,anddefinitionsusedmay
1.2 The magnetic properties of materials are determined
befoundinthevarioussectionsofthistestmethod.Theofficial
from measurements on Epstein core specimens with the core
list of definitions and symbols may be found in Terminology
andtestcoilstreatedasthoughtheyconstitutedaseries-parallel
A340.
equivalent circuit (Fig.A1.1) for the fundamental frequency of
1.8 The values stated in either SI units or inch-pound units
excitation where the apparent parallel inductance, L , and
are to be regarded separately as standard. The values stated in
resistance, R , are attributable to the test specimen.
each system may not be exact equivalents; therefore, each
1.3 Thistestmethodissuitableforthedeterminationofcore
system shall be used independently of the other. Combining
loss, rms volt-amperes, rms exciting current, reactive volt-
values from the two systems may result in non-conformance
amperes, and related properties of flat-rolled magnetic materi-
with the standard. Within this standard, SI units are shown in
als under ac magnetization.
brackets.
1.4 The frequency range of this test method is normally that
1.9 This standard does not purport to address all of the
of the commercial power frequencies 50 to 60 Hz. It is also
safety concerns, if any, associated with its use. It is the
acceptable for measurements at frequencies from 25 to 400 Hz.
responsibility of the user of this standard to establish appro-
This test method is customarily used on nonoriented electrical
priate safety and health practices and determine the applica-
steels at inductions up to 10 kG [1.0 T] and for grain-oriented
bility of regulatory limitations prior to its use.
electrical steels at inductions up to 15 kG [1.5 T].
2. Referenced Documents
1.5 Forreactiveproperties,bothfluxandcurrentwaveforms
introduce limitations. Over its range of useful inductions, the
2.1 ASTM Standards:
varmeter is valid for the measurement of reactive volt-amperes
A34/A34M Practice for Sampling and Procurement Testing
(vars) and inductance permeability. For the measurement of
of Magnetic Materials
these properties, it is suggested that test inductions be limited
A340 Terminology of Symbols and Definitions Relating to
to values sufficiently low that the measured values of vars do
Magnetic Testing
not differ by more than 15 % (Note 1) from those calculated
A343/A343M Test Method for Alternating-Current Mag-
from the measured values of exciting volt-amperes and core
netic Properties of Materials at Power Frequencies Using
loss.
Wattmeter-Ammeter-Voltmeter Method and 25-cm Ep-
stein Test Frame
NOTE 1—This limitation is placed on this test method in consideration
of the nonlinear nature of the magnetic circuit, which leads to a difference
3. Significance and Use
between vars based on fundamental frequency components of voltage and
3.1 This test method may be used to determine the specific
core loss, specific reactive power, specific exciting power,
This test method is under the jurisdiction of ASTM Committee A06 on
MagneticPropertiesandisthedirectresponsibilityofSubcommitteeA06.01onTest
Methods. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved May 1, 2008. Published June 2008. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1988. Last previous edition approved in 2003 as A889/A889M-03. Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/A0889_A0889M-03R08. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A889/A889M − 03 (2008)
inductance permeability, and impedance permeability of flat- 6.2 Epstein Test Frame used for this test shall be in
rolled magnetic materials over a wide range of inductions and conformity with Annex A1.1 of Test Method A343/A343M.
at frequencies up to 400 Hz for symmetrically magnetized test
6.3 Voltage and Current Signal Scaling Amplifiers—These
samples.
amplifiers are used to amplify or attenuate the voltage induced
3.2 These measurements are used by the producer and user
in the secondary winding of the test frame and the voltage
of the flat-rolled material for quality control purposes. The
appearing across the potential terminals of the current shunt,
fundamentalassumptioninherentinthesemeasurementsisthat
R , to ranges that are suitable for electronic circuitry.The input
S
they can be correlated with the electromagnetic characteristics
circuitry of the voltage scaling amplifier must have an input
of a core fabricated from the flat-rolled material.
impedance sufficiently high that the connection of the circuitry
to the secondary winding of the test fixture does not change the
4. Test Specimen
terminal voltage of the secondary by more than 0.05 %. The
input circuitry of the current scaling amplifier must have an
4.1 Select and prepare the specimens for this test in accor-
input impedance sufficiently high that the connection of the
dance with Practice A34/A34M.
circuitry to the potential terminals of the current shunt does not
change the terminal voltage by more than 0.05 %. These
5. Basic Circuit
amplifiers should have a linear frequency response up to about
5.1 Fig. 1 shows the essential apparatus and basic circuit
20 times the test frequency and a gain accuracy of 0.1 % or
connections for this test. Terminals 1 and 2 are connected to a
better since all instrumentation may be, and preferably will be,
source of adjustable ac voltage of sinusoidal waveform of
connected to the output of these amplifiers. Care should be
sufficient power rating to energize the primary circuit without
exercised in the design of the amplifiers so that no phase shift
appreciable voltage drop in the source impedance.All primary
is introduced into either the current or the voltage signal.
circuit switches and all primary wiring should be capable of
6.4 Flux Voltmeter—The flux voltmeter for this test shall be
carrying much higher currents than are normally encountered
a true average-responsive voltmeter calibrated to read average
to limit primary circuit resistance to values that will not cause
volts times 2π/4, so that its indications will be identical with
=
appreciable distortion of the flux waveform in the specimen
those of a true rms voltmeter on a pure sinusoidal voltage. A
when relatively nonsinusoidal currents are drawn. The ac
high-input-resistance, multirange electronic meter with a full-
source may be an electronic amplifier which has a sine-wave
scale accuracy rating of 0.25 % or better is the preferred
oscillator connected to its input and may include the necessary
instrument.
circuitry to maintain a sinusoidal flux waveform by using
negative feedback of the induced secondary voltage. In this
6.5 RMS Voltmeter—A true rms-indicating voltmeter is
case, higher primary resistance can be tolerated since this
needed if measurements of exciting current are to be made by
system will maintain sinusoidal flux at much higher primary
measuringthevoltagedropacrossthepotentialterminalsofthe
resistance.Although the current drain in the secondary is quite
current shunt. A high-input-resistance, multirange electronic
small, especially when using modern high-input impedance
instrument with a full-scale accuracy of 0.25 % or better is
instrumentation, the switches and wiring should be selected to
requiredforthisinstrument.Thisvoltmetermayalsobeusedto
minimize the lead resistance so that the voltage available at the
measure the true rms voltage on the secondary of the Epstein
terminals of the instruments is imperceptibly lower than the
test frame.
voltage at the secondary terminals of the Epstein test frame.
6.6 Wattmeter and Varmeter—A wattmeter is required for
the measurement of core loss, and a varmeter is needed for the
6. Apparatus
measurement of reactive power. Since both are needed to make
6.1 The apparatus shall consist of as many of the following
all measurements, the preferred instrumentation is one high-
component parts as are required to perform the desired
accuracy watt converter and a 90° phase-shift circuit to be used
measurement functions:
with the watt converter to measure the reactive power by
shifting the phase of the secondary voltage. Alternatively, a
wattmeter and a varmeter may be used as required to make the
desired measurements. The rated accuracy of the wattmeter at
the test frequency and unity power factor should be less than
0.25 % of full scale. The power factor encountered by the
wattmeter during a core loss test on a specimen is always less
than unity and, at inductions well above the knee of the
magnetization curve, approaches zero. The wattmeter must
maintain adequate accuracy (1 % of reading) even at the most
severe (lowest) power factor which will be presented to it. The
accuracy requirements for the varmeter are the same as for the
wattmeter.
6.6.1 Watt Converter and Phase Shifter—An electronic watt
converter that has two high impedance inputs and an output
FIG. 1 Basic Circuit for Wattmeter-Varmeter Method thatisproportionaltotheproductofthesignalsthatareapplied
A889/A889M − 03 (2008)
to these inputs is the preferred instrument for the measurement 7. Procedure
of both power and reactive power. Such devices will probably
7.1 The first steps of procedure for this test method concern
require the use of scaling amplifiers for the voltage and current
the preparations for testing Epstein specimens which are the
signals. This device, which is used for the measurement of
same for this method as given in 6.1, 6.2, and 6.3 of Test
power, is also used for the measurement of reactive power by
Method A343/A343M.
shifting the phase of the voltage signal by 90°. This can be
7.2 Demagnetization—Connect the required apparatus as in
done since the secondary voltage is essentially a pure sinusoid
Fig. 1 with the air-flux compensator in the test frame and
at low-to-moderate inductions, especially if negative feedback
Terminals 1 and 2 connected to a suitable power source. With
of the secondary voltage is used in the test power supply
Switch S closed in the position to short R , increase the
1 S
circuitry. The phase shifter that is used for this purpose should
voltage supplied to the test frame from zero to a value in which
be a modern operational amplifier device which will accurately
the flux-voltmeter indicates an induction above the knee of the
shift the phase of the input signal by exactly 90° (tolerance of
magnetization curve (where the exciting current increases
0.1°) without affecting the amplitude of the signal.
sharply for a small increase in induction). At this point,
6.6.2 Wattmeter—An electronic wattmeter with appropriate
decrease the voltage slowly and progressively during an
voltage and current ratings is the preferred instrument if the
elapsed time of 5 to 10 s so that the induction will be reduced
separate scaling amplifiers and phase-shift circuits are not smoothly to a point below the lowest induction at which tests
used. The voltage input circuitry of the electronic digital are to be performed and near zero induction. This will
demagnetize the specimen which is quite important, since most
wattmeter must have an input impedance sufficiently high that
highly permeable materials become polarized by handling in
the connection of the circuitry to the secondary winding of the
the earth’s magnetic field during loading of the specimens into
test fixture does not change the terminal voltage of the
the test frame. After demagnetization, take care not to jar or
secondary by more than 0.05 %. The voltage circuit must also
move the specimen in any way that will destroy the desired
be capable of accepting the maximum peak voltage which is
reproducible (virgin) magnetic state of negligible flux density.
induced in the secondary winding during testing. The current
Tests should be made immediately after demagnetization
input circuitry of the electronic digital wattmeter must have an
(within 2 to 3 min) for the desired test points.
input impedance of no more than 1Ω, and preferably no more
7.2.1 Core Loss, Exciting Current, and Reactive Power—
than 0.1Ω. The current input circuitry must also be capable of
With an appropriate value for R inserted for the induction
s
handling the maximum rms current and the maximum peak
range to be tested (see 6.7), connect an appropriate test power
current drawn by the primary winding of the test fixture when
source to Terminals 1 and 2. Increase the voltage supplied to
core loss tests are being performed.
the test frame until the flux voltmeter indicates that the desired
6.6.3 Varmeter—An electronic instrument with appropriate
test induction has been reached. Read the wattmeter to deter-
voltage and current ratings is the preferred instrument if the
mine core loss and the rms voltmeter to determine the rms
separate scaling amplifiers and phase-shift circuits are not
exciting current. Then position Switch S to the varmeter
used. The accuracy and impedance characteristics for the
position (90° phase shift in) and read the wattmeter again to
varmeter should be the same as for the wattmeter described in
determine the reactive power. Make tests at several inductions
6.6.2.
in order of increasing induction values.
6.7 Current Shunt—This should be a noninductive resistor
8. Calculation (Modified cgs Units)
withanaccuracyratingof0.1 %orbetter.Thisresistormustbe
capable of handling the full exciting current of the test winding 8.1 Flux Volts—The voltage induced in the specimen by the
desired test induction is calculated from the following equa-
at the maximum test induction without destructive heati
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation:A 889/A889M–93 (Reapproved 1998) Designation:A889/A889M–03
(Reapproved 2008)
Standard Test Method for
Alternating-Current Magnetic Properties of Materials at Low
Inductions Magnetic Flux Density Using the Wattmeter-
Varmeter-Ammeter-VoltmeterVoltmeter-Ammeter-Wattmeter-
Varmeter Method and 25-cm [250-mm] Epstein Frame
This standard is issued under the fixed designationA 889/A 889M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers tests for the magnetic properties of basic flat-rolled magnetic materials at power frequencies [25(25
to 400 Hz]Hz) using a 25-cm [250-mm] Epstein test frame and the 25-cm [250-mm] double-lap-jointed core.
1.2 The magnetic properties of materials are determined from measurements on Epstein core specimens with the core and test
coils treated as though they constituted a series-parallel equivalent circuit (Fig.A1.1) for the fundamental frequency of excitation
where the apparent parallel inductance, L , and resistance, R , are attributable to the test specimen.
1 1
1.3 Thistestmethodissuitableforthedeterminationofcoreloss,rmsvolt-amperes,rmsexcitingcurrent,reactivevolt-amperes,
and related properties of flat-rolled magnetic materials under ac magnetization.
1.4 The frequency range of this test method is normally that of the commercial power frequencies 50 to 60 Hz. It is also
acceptable for measurements at frequencies from 25 to 400 Hz. This test method is customarily used on nonoriented electrical
steels at inductions up to 10 kG [1.0 T] and for grain-oriented electrical steels at inductions up to 15 kG [1.5 T].
1.5 For reactive properties, both flux and current waveforms introduce limitations. Over its range of useful inductions, the
varmeter is valid for the measurement of reactive volt-amperes (vars) and inductance permeability. For the measurement of these
properties, it is suggested that test inductions be limited to values sufficiently low that the measured values of vars do not differ
by more than 15 % (Note 1) from those calculated from the measured values of exciting volt-amperes and core loss.
NOTE 1—This limitation is placed on this test method in consideration of the nonlinear nature of the magnetic circuit, which leads to a difference
between vars based on fundamental frequency components of voltage and current and current after harmonic rejection and vars computed from rms
current, voltage, and watt values when one or more of these quantities are nonsinusoidal.
1.6 This test method shall be used in conjunction with Practice A 34/A 34M.
1.7 Explanation of terms, symbols, and definitions used may be found in the various sections of this test method. The official
list of definitions and symbols may be found in Terminology A 340.
1.8This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to its use.
1.9The values stated in either customary (cgs-emu and inch-pound) units or SI units are to be regarded separately as standard.
Within the text, the SI units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each
system shall be used independently of the other. Combining values from the systems may result in nonconformance with this test
method.
1.8 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the
two systems may result in non-conformance with the standard. Within this standard, SI units are shown in brackets.
1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to its use.
This test method is under the jurisdiction ofASTM CommitteeA-6A06 on Magnetic Properties and is the direct responsibility of SubcommitteeA06.01 onTest Methods.
Current edition approved Feb. 15, 1993.May 1, 2008. Published April 1993.June 2008. Originally published as A889–88.approved in 1988. Last previous edition
A889–88.approved in 2003 as A 889/A 889M-03.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
A889/A889M–03 (2008)
2. Referenced Documents
2.1 ASTM Standards:
A 34/A 34M Practice for Sampling and Procurement Testing of Magnetic Materials
A 340 Terminology of Symbols and Definitions Relating to Magnetic Testing
A 343/A 343M Test Method forAlternating-Current Magnetic Properties of Materials at Power Frequencies Using Wattmeter-
Ammeter-Voltmeter Method and 25-cm Epstein Test Frame
3. Significance and Use
3.1 Thistestmethodmaybeusedtodeterminethespecificcoreloss,specificreactivepower,specificexcitingpower,inductance
permeability, and impedance permeability of flat-rolled magnetic materials over a wide range of inductions and at frequencies up
to 400 Hz for symmetrically magnetized test samples.
3.2 These measurements are used by the producer and user of the flat-rolled material for quality control purposes. The
fundamental assumption inherent in these measurements is that they can be correlated with the electromagnetic characteristics of
a core fabricated from the flat-rolled material.
4. Test Specimen
4.1 Select and prepare the specimens for this test in accordance with Practice A 34/A 34M.
5. Basic Circuit
5.1 Fig. 1 shows the essential apparatus and basic circuit connections for this test. Terminals 1 and 2 are connected to a source
of adjustable ac voltage of sinusoidal waveform of sufficient power rating to energize the primary circuit without appreciable
voltage drop in the source impedance. All primary circuit switches and all primary wiring should be capable of carrying much
higher currents than are normally encountered to limit primary circuit resistance to values that will not cause appreciable distortion
of the flux waveform in the specimen when relatively nonsinusoidal currents are drawn. The ac source may be an electronic
amplifier which has a sine-wave oscillator connected to its input and may include the necessary circuitry to maintain a sinusoidal
fluxwaveformbyusingnegativefeedbackoftheinducedsecondaryvoltage.Inthiscase,higherprimaryresistancecanbetolerated
since this system will maintain sinusoidal flux at much higher primary resistance. Although the current drain in the secondary is
quite small, especially when using modern high-input impedance instrumentation, the switches and wiring should be selected to
minimizetheleadresistancesothatthevoltageavailableattheterminalsoftheinstrumentsisimperceptiblylowerthanthevoltage
at the secondary terminals of the Epstein test frame.
6. Apparatus
6.1 Theapparatusshallconsistofasmanyofthefollowingcomponentpartsasarerequiredtoperformthedesiredmeasurement
functions:
6.2 Epstein Test Frame used for this test shall be in conformity with Annex A1.1 of Test Method A 343/A 343M.
6.3 Voltage and Current Signal Scaling Amplifiers —These amplifiers are used to amplify or attenuate the voltage induced in
the secondary winding of the test frame and the voltage appearing across the potential terminals of the current shunt, R , to ranges
S
that are suitable for electronic circuitry. The input circuitry of the voltage scaling amplifier must have an input impedance
sufficientlyhighthattheconnectionofthecircuitrytothesecondarywindingofthetestfixturedoesnotchangetheterminalvoltage
of the secondary by more than 0.05 %. The input circuitry of the current scaling amplifier must have an input impedance
Annual Book of ASTM Standards, Vol 03.04.
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volume information, refer to the standard’s Document Summary page on the ASTM website.
FIG. 1 Basic Circuit for Wattmeter-Varmeter Method
A889/A889M–03 (2008)
sufficiently high that the connection of the circuitry to the potential terminals of the current shunt does not change the terminal
voltage by more than 0.05 %. These amplifiers should have a linear frequency response up to about 20 times the test frequency
and a gain accuracy of 0.1 % or better since all instrumentation may be, and preferably will be, connected to the output of these
amplifiers. Care should be exercised in the design of the amplifiers so that no phase shift is introduced into either the current or
the voltage signal.
6.4 Flux Voltmeter—The flux voltmeter for this test shall be a true average-responsive voltmeter calibratedtoread averagevolts
times 2 p/4, so that its indications will be identical with those of a true rms voltmeter on a pure sinusoidal voltage. A
=
high-input-resistance, multirange electronic meter with a full-scale accuracy rating of 0.25 % or better is the preferred instrument.
6.5 RMS Voltmeter—Atruerms-indicatingvoltmeterisneededifmeasurementsofexcitingcurrentaretobemadebymeasuring
the voltage drop across the potential terminals of the current shunt.Ahigh-input-resistance, multirange electronic instrument with
a full-scale accuracy of 0.25 % or better is required for this instrument. This voltmeter may also be used to measure the true rms
voltage on the secondary of the Epstein test frame.
6.6 Wattmeter and Varmeter—A wattmeter is required for the measurement of core loss, and a varmeter is needed for the
measurement of reactive power. Since both are needed to make all measurements, the preferred instrumentation is one
high-accuracy watt converter and a 90° phase-shift circuit to be used with the watt converter to measure the reactive power by
shifting the phase of the secondary voltage.Alternatively, a wattmeter and a varmeter may be used as required to make the desired
measurements. The rated accuracy of the wattmeter at the test frequency and unity power factor should be less than 0.25 % of full
scale. The power factor encountered by the wattmeter during a core loss test on a specimen is always less than unity and, at
inductions well above the knee of the magnetization curve, approaches zero.The wattmeter must maintain adequate accuracy (1 %
of reading) even at the most severe (lowest) power factor which will be presented to it.The accuracy requirements for the varmeter
are the same as for the wattmeter.
6.6.1 Watt Converter and Phase Shifter— An electronic watt converter that has two high impedance inputs and an output that
is proportional to the product of the signals that are applied to these inputs is the preferred instrument for the measurement of both
power and reactive power. Such devices will probably require the use of scaling amplifiers for the voltage and current signals.This
device, which is used for the measurement of power, is also used for the measurement of reactive power by shifting the phase of
thevoltagesignalby90°.Thiscanbedonesincethesecondaryvoltageisessentiallyapuresinusoidatlow-to-moderateinductions,
especially if negative feedback of the secondary voltage is used in the test power supply circuitry. The phase shifter that is used
forthispurposeshouldbeamodernoperationalamplifierdevicewhichwillaccuratelyshiftthephaseoftheinputsignalbyexactly
90° (tolerance of 0.1°) without affecting the amplitude of the signal.
6.6.2 Wattmeter—Anelectronicwattmeterwithappropriatevoltageandcurrentratingsisthepreferredinstrumentiftheseparate
scaling amplifiers and phase-shift circuits are not used. The voltage input circuitry of the electronic digital wattmeter must have
aninputimpedancesufficientlyhighthattheconnectionofthecircuitrytothesecondarywindingofthetestfixturedoesnotchange
the terminal voltage of the secondary by more than 0.05 %. The voltage circuit must also be capable of accepting the maximum
peak voltage which is induced in the secondary winding during testing. The current input circuitry of the electronic digital
wattmeter must have an input impedance of no more than 1 V, and preferably no more than 0.1 V.The current input circuitry must
also be capable of handling the maximum rms current and the maximum peak current drawn by the primary winding of the test
fixture when core loss tests are being performed.
6.6.3 Varmeter—Anelectronicinstrumentwithappropriatevoltageandcurrentratingsisthepreferredinstrumentiftheseparate
scaling amplifiers and phase-shift circuits are not used. The accuracy and impedance characteristics for the varmeter should be the
same as for the wattmeter described in 6.6.2.
6.7 Current Shunt—This should be a noninductive resistor with an accuracy rating of 0.1 % or better. This resistor must be
capable of handling the full exciting current of the test winding at the maximum test induction without destructive heating or more
than specified loss of accuracy as a result of self heating. To avoid intolerable levels of distortion, the value of the resistor should
be reasonably low. However, a large value of resistance is desirable to maximize the signal and reduce the effects of noise. Fixed
resistorsof100,10,and1 Vareusefulvalues.Theselectionofshuntshouldbeguidedprimarilybytheprimarycurrentandshould
be the lowest value which retains an adequate signal-to-noise ratio.
6.8 Power Supply—A source of sinusoidal test power of low-internal impedance and excellent voltage and frequency stability
isrequiredforthistest.Voltagestabilitywithin0.1 %andfrequencyaccuracywithin0.1 %shouldbemaintained.Electronicpower
sources using negative feedback from the secondary winding of the test fixture to reduce flux waveform distortion have been found
to perform quite satisfactorily in this test method.
7. Procedure
7.1 The first steps of procedure for this test method concern the preparations for testing Epstein specimens which are the same
for this method as given in 6.1, 6.2, and 6.3 of Test Method A 343/A 343M.
7.2 Demagnetization—Connect the required apparatus as in Fig. 1 with the air-flux compensator in the test frame and
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