ASTM A889/A889M-93(1998)
(Test Method)Standard Test Method for Alternating-Current Magnetic Properties of Materials at Low Inductions Using the Wattmeter-Varmeter-Ammeter-Voltmeter Method and 25-cm (250-mm) Epstein Frame
Standard Test Method for Alternating-Current Magnetic Properties of Materials at Low Inductions Using the Wattmeter-Varmeter-Ammeter-Voltmeter Method and 25-cm (250-mm) Epstein Frame
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 (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, 1, 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 a-c 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 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 A34.
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 A340.
1.8 This standard does not purport to address all of the safety problems, 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.
1.9 The 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 parentheses except for the sections concerning calculations where there are separate sections for the respective unit systems. 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 the specification.
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Designation: A 889/A 889M – 93 (Reapproved 1998)
Standard Test Method for
Alternating-Current Magnetic Properties of Materials at Low
Inductions Using the Wattmeter-Varmeter-Ammeter-
Voltmeter Method and 25-cm [250-mm] Epstein Frame
This standard is issued under the fixed designation A 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 1.6 This test method shall be used in conjunction with
Practice A 34/A 34M.
1.1 This test method covers tests for the magnetic properties
1.7 Explanation of terms, symbols, and definitions used may
of basic flat-rolled magnetic materials at power frequencies [25
be found in the various sections of this test method. The official
to 400 Hz] using a 25-cm [250-mm] Epstein test frame and the
list of definitions and symbols may be found in Terminology
25-cm [250-mm] double-lap-jointed core.
A 340.
1.2 The magnetic properties of materials are determined
1.8 This standard does not purport to address all of the
from measurements on Epstein core specimens with the core
safety concerns, if any, associated with its use. It is the
and test coils treated as though they constituted a series-parallel
responsibility of the user of this standard to establish appro-
equivalent circuit (Fig. A1.1) for the fundamental frequency of
priate safety and health practices and determine the applica-
excitation where the apparent parallel inductance, L , and
bility of regulatory limitations prior to its use.
resistance, R , are attributable to the test specimen.
1.9 The values stated in either customary (cgs-emu and
1.3 This test method is suitable for the determination of core
inch-pound) units or SI units are to be regarded separately as
loss, rms volt-amperes, rms exciting current, reactive volt-
standard. Within the text, the SI units are shown in brackets.
amperes, and related properties of flat-rolled magnetic materi-
The values stated in each system are not exact equivalents;
als under ac magnetization.
therefore, each system shall be used independently of the other.
1.4 The frequency range of this test method is normally that
Combining values from the systems may result in nonconfor-
of the commercial power frequencies 50 to 60 Hz. It is also
mance with this test method.
acceptable for measurements at frequencies from 25 to 400 Hz.
This method is customarily used on nonoriented electrical
2. Referenced Documents
steels at inductions up to 10 kG [1.0 T] and for grain-oriented
2.1 ASTM Standards:
electrical steels at inductions up to 15 kG [1.5 T].
A 34/A 34M Practice for Sampling and Procurement Test-
1.5 For reactive properties, both flux and current waveforms
ing of Magnetic Materials
introduce limitations. Over its range of useful inductions, the
A 340 Terminology of Symbols and Definitions Relating to
varmeter is valid for the measurement of reactive volt-amperes
Magnetic Testing
(vars) and inductance permeability. For the measurement of
A 343 Test Method for Alternating-Current Magnetic Prop-
these properties, it is suggested that test inductions be limited
erties of Materials at Power Frequencies Using Wattmeter-
to values sufficiently low that the measured values of vars do
Ammeter-Voltmeter Method and 25-cm Epstein Test
not differ by more than 15 % (Note 1) from those calculated
Frame
from the measured values of exciting volt-amperes and core
loss.
3. Significance and Use
NOTE 1—This limitation is placed on this test method in consideration
3.1 This test method may be used to determine the specific
of the nonlinear nature of the magnetic circuit, which leads to a difference
core loss, specific reactive power, specific exciting power,
between vars based on fundamental frequency components of voltage and
inductance permeability, and impedance permeability of flat-
current and current after harmonic rejection and vars computed from rms
rolled magnetic materials over a wide range of inductions and
current, voltage, and watt values when one or more of these quantities are
at frequencies up to 400 Hz for symmetrically magnetized test
nonsinusoidal.
samples.
3.2 These measurements are used by the producer and user
1 of the flat-rolled material for quality control purposes. The
This test method is under the jurisdiction of ASTM Committee A-6 on
fundamental assumption inherent in these measurements is that
Magnetic Properties and is the direct responsibility of Subcommittee A06.01 on Test
Methods.
Current edition approved Feb. 15, 1993. Published April 1993. Originally
published as A 889 – 88. Last previous edition A 889 – 88. Annual Book of ASTM Standards, Vol 03.04.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
A 889/A 889M
they can be correlated with the electromagnetic characteristics to the secondary winding of the test fixture does not change the
of a core fabricated from the flat-rolled material.
terminal voltage of the secondary by more than 0.05 %. The
input circuitry of the current scaling amplifier must have an
4. Test Specimen
input impedance sufficiently high that the connection of the
4.1 Select and prepare the specimens for this test in accor- circuitry to the potential terminals of the current shunt does not
dance with Practice A 34/A 34M. change the terminal voltage by more than 0.05 %. These
amplifiers should have a linear frequency response up to about
5. Basic Circuit
20 times the test frequency and a gain accuracy of 0.1 % or
5.1 Fig. 1 shows the essential apparatus and basic circuit better since all instrumentation may be, and preferably will be,
connections for this test. Terminals 1 and 2 are connected to a connected to the output of these amplifiers. Care should be
source of adjustable ac voltage of sinusoidal waveform of exercised in the design of the amplifiers so that no phase shift
sufficient power rating to energize the primary circuit without is introduced into either the current or the voltage signal.
appreciable voltage drop in the source impedance. All primary
6.4 Flux Voltmeter—The flux voltmeter for this test shall be
circuit switches and all primary wiring should be capable of
a true average-responsive voltmeter calibrated to read average
carrying much higher currents than are normally encountered
volts times 2 p/4, so that its indications will be identical
=
to limit primary circuit resistance to values that will not cause
with those of a true rms voltmeter on a pure sinusoidal voltage.
appreciable distortion of the flux waveform in the specimen
A high-input-resistance, multirange electronic meter with a
when relatively nonsinusoidal currents are drawn. The ac
full-scale accuracy rating of 0.25 % or better is the preferred
source may be an electronic amplifier which has a sine-wave
instrument.
oscillator connected to its input and may include the necessary
6.5 RMS Voltmeter—A true rms-indicating voltmeter is
circuitry to maintain a sinusoidal flux waveform by using
needed if measurements of exciting current are to be made by
negative feedback of the induced secondary voltage. In this
measuring the voltage drop across the potential terminals of the
case, higher primary resistance can be tolerated since this
current shunt. A high-input-resistance, multirange electronic
system will maintain sinusoidal flux at much higher primary
instrument with a full-scale accuracy of 0.25 % or better is
resistance. Although the current drain in the secondary is quite
required for this instrument. This voltmeter may also be used to
small, especially when using modern high-input impedance
measure the true rms voltage on the secondary of the Epstein
instrumentation, the switches and wiring should be selected to
test frame.
minimize the lead resistance so that the voltage available at the
6.6 Wattmeter and Varmeter—A wattmeter is required for
terminals of the instruments is imperceptibly lower than the
the measurement of core loss, and a varmeter is needed for the
voltage at the secondary terminals of the Epstein test frame.
measurement of reactive power. Since both are needed to make
all measurements, the preferred instrumentation is one high-
6. Apparatus
accuracy watt converter and a 90° phase-shift circuit to be used
6.1 The apparatus shall consist of as many of the following
with the watt converter to measure the reactive power by
component parts as are required to perform the desired
shifting the phase of the secondary voltage. Alternatively, a
measurement functions:
wattmeter and a varmeter may be used as required to make the
6.2 Epstein Test Frame used for this test shall be in
desired measurements. The rated accuracy of the wattmeter at
conformity with Annex A1.1 of Test Method A 343.
the test frequency and unity power factor should be less than
6.3 Voltage and Current Signal Scaling Amplifiers—These
0.25 % of full scale. The power factor encountered by the
amplifiers are used to amplify or attenuate the voltage induced
wattmeter during a core loss test on a specimen is always less
in the secondary winding of the test frame and the voltage
than unity and, at inductions well above the knee of the
appearing across the potential terminals of the current shunt,
magnetization curve, approaches zero. The wattmeter must
R , to ranges that are suitable for electronic circuitry. The input
S
maintain adequate accuracy (1 % of reading) even at the most
circuitry of the voltage scaling amplifier must have an input
severe (lowest) power factor which will be presented to it. The
impedance sufficiently high that the connection of the circuitry
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 the voltage signal by 90°. This can be
done since the secondary voltage is essentially a pure sinusoid
at low-to-moderate inductions, especially if negative feedback
of the secondary voltage is used in the test power supply
FIG. 1 Basic Circuit for Wattmeter-Varmeter Method circuitry. The phase shifter that is used for this purpose should
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
A 889/A 889M
be a modern operational amplifier device which will accurately decrease the voltage slowly and progressively during an
shift the phase of the input signal by exactly 90° (tolerance of elapsed time of 5 to 10 s so that the induction will be reduced
0.1°) without affecting the amplitude of the signal. smoothly to a point below the lowest induction at which tests
6.6.2 Wattmeter—An electronic wattmeter with appropriate are to be performed and near zero induction. This will
voltage and current ratings is the preferred instrument if the demagnetize the specimen which is quite important, since most
separate scaling amplifiers and phase-shift circuits are not highly permeable materials become polarized by handling in
used. The voltage input circuitry of the electronic digital the earth’s magnetic field during loading of the specimens into
wattmeter must have an input impedance sufficiently high that the test frame. After demagnetization, take care not to jar or
the connection of the circuitry to the secondary winding of the move the specimen in any way that will destroy the desired
test fixture does not change the terminal voltage of the reproducible (virgin) magnetic state of negligible flux density.
secondary by more than 0.05 %. The voltage circuit must also Tests should be made immediately after demagnetization
be capable of accepting the maximum peak voltage which is (within 2 to 3 min) for the desired test points.
induced in the secondary winding during testing. The current 7.2.1 Core Loss, Exciting Current, and Reactive Power—
input circuitry of the electronic digital wattmeter must have an
With an appropriate value for R inserted for the induction
s
input impedance of no more than 1 V, and preferably no more range to be tested (see 6.7), connect an appropriate test power
than 0.1 V. The current input circuitry must also be capable of
source to Terminals 1 and 2. Increase the voltage supplied to
handling the maximum rms current and the maximum peak the test frame until the flux voltmeter indicates that the desired
current drawn by the primary winding of the test fixture when
test induction has been reached. Read the wattmeter to deter-
core loss tests are being performed. mine core loss and the rms voltmeter to determine the rms
6.6.3 Varmeter—An electronic instrument with appropriate
exciting current. Then position Switch S to the varmeter
voltage and current ratings is the preferred instrument if the
position (90° phase shift in) and read the wattmeter again to
separate scaling amplifiers and phase-shift circuits are not
determine the reactive power. Make tests at several inductions
used. The accuracy and impedance characteristics for the
in order of increasing induction values.
varmeter should be the same as for the wattmeter described in
6.6.2.
8. Calculation (Modified cgs Units)
6.7 Current Shunt—This should be a noninductive resistor
8.1 Flux Volts—The voltage induced in the specimen by the
with an accuracy rating of 0.1 % or better. This resistor must be
desired test induction is calculated from the following equa-
capable of handling the full exciting current of the test winding
tion. This voltage is also the Voltage E of the equivalent circuit
at the maximum test induction without destructive heating or
of Fig. A1.1 in Annex A1.
more than specified loss of accuracy as a result of self heating.
E 5 =2pB AN f 3 10 ~V! (1)
To avoid intolerable levels of distortion, the value of the 1 2
resistor should be reasonably low. However, a large value of
where:
resistance is desirable to maximize the signal and reduce the
B = maximum intrinsic flux density, G;
effects of noise. Fixed resistors
...
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