Limited experimental data exists for the specific core loss and dynamic B-H loops for soft magnetic materials for the combined conditions of high frequency and high temperature. This experimental study investigates the specific core loss and dynamic B-H loop characteristics of Supermalloy and Metglas 2605SC over the frequency range of 1 to 50 kHz and temperature range of 23 to 300 C under sinusoidal voltage excitation. The experimental setup used to conduct the investigation is described. The effects of the maximum magnetic flux density, frequency, and temperature on the specific core loss and on the size and shape of the B-H loops are examined

Niedra, J. M.

Schwarze, G. E.

Wieserman, W. R.

English

NASA Technical Reports Server

NASA Technical Memorandum 103164
-- _: j ,: ___rL Jll %_r :7i
High Frequency, High Temperature Specific
Core Loss and Dynamic B-H Hysteresis
Loop Characteristics of Soft
Magnetic Alloys
W.R. Wieserman
University of Pittsburgh at Johnstown
Johnstown, Pennsylvania
G.E. Schwarze
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio
and
J.M. Niedra
Sverdrup Technology, Inc.
Lewis Reseach Center Group
Brook Park, Ohio
Prepared for the
25th Intersociety Energy Conversion Engineering Conference
cosponsored by the AIChE, SAE, ACS, AIAA, ASME, and IEEE
Reno, Nevada, August 12-17, 1990
https://ntrs.nasa.gov/search.jsp?R=19900014347 2020-03-19T21:58:53+00:00Z

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HIGH FREQUENCY, HIGH TEMPERATURE SPECIFIC CORE LOSS AND DYNAMIC
B-H HYSERESIS LOOP CHARACTERISTICS OF SOFT MAGNETIC ALLOYS
W.R. Wieserman
University of Pittsburgh at Johnstown
Johnstown, Pennsylvania ]5902
G.E. Schwarze
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135
J.M. Niedra
Sverdrup Technology, Inc.
Lewis Research Center Group
Brook Park, Ohio 44142
ABSTRACT
Limited experimental data exists for the specific
core loss and dynamic B-H loo_s for soft magnetic
materials for the combined conditions of high
frequency and high temperature. This experimental
study investigates the specific core loss and
dynamic B-H loop characteristics of Supermalloy and
Metglas 2605SC over the frequellcy range of 1-50 kHz
and temperature range of 23-300 C under sinusoidal
voltage excitation. The expermental setup used to
conduct the investigation is described. The
effects of the maximum magr_etic flux density,
frequency, and temperature oI_ the specific core
loss and on the size and shape of the B-H loops are
examined.
INTRODUCTION
The Power Conditioning, Contr(_l, and Transmission
(PCC&T) subsystem of future high power space
systems will need to meet the requirements of high
efficiency, low specific mass and high reliability.
To meet these requirements, the power and control
components for the PCC&T will need to operate at
high frequencies to reduce the reactive-type
component masses and at high temperatures to reduce
the size of the cooling radi_itor. The magnetic
component designer will need to know the high
temperature and high frequency performance
characteristics of soft magnetic materials in order
to design and develop components such as
transformers, inductors, and _otors for the PCC&T
subsystem, and power generator:_ for the electrical
conversion subsystem. Magnetic components for
sensors and instrumentation in the control
subsystem will also need this high frequency and
high temperature magnetic data
Under the Power Management[iLl element of the
Civilian Space Technology IniLiative (CSTI) High
Capacity Power Program an experimental program has
been initiated by the NASA-Lewis Research Center to
characterize the electrical and magnetic properties
of soft ferromagnetic materials under various
operating conditions. A survey of the literature
prior to the program's initiat'on clearly showed a
sparsity of electrical and magnetic data for soft
magnetic materials under the :ombined effects of
high temperature and high frequency. Thus, the
objective of this experimenial program is to
investigate candidate commercially available
magnetic materials up to 50 kHz and temperatures to
300 C under both sinusoidal and non-sinusoidal
voltage excitation. The materials to be investi-
gated include alloys of nickel-iron, cobalt-iron,
and silicon-iron and the new class of amorphous
alloys. This paper gives the high frequency, high
temperature results for two different soft magnetic
materials. The measuring, computing, and plotting
system developed to experimentally determine the
specific core loss and dynamic B-H hysteresis loop
characteristics under sinewave voltage excitation
of these two materials is also described.
EXPERIMENTAL SYSTEM
The circuit diagram in Figure I shows the experi-
mental setup used to measure, compute, plot, and
display the electrical and magnetic characteristics
of the test core material. Two key elements in
this setup are the digital storage oscilloscope and
the power amplifier. A high slew rate, high
frequency, variable-amplitude power amplifier
having very low amplitude and phase distortion is
a necessity if the amplifier's output drive signal
is to faithfully reproduce the waveshape of the
oscillator's input signal. The digital storage
oscilloscope along with the system controller
replaces the wattmeter that is generally used for
core loss measurements. Significant improvements
have been made in high frequency wattmeters but
they still have limitations, especially for the
condition of non-sinusoidal core excitation. The
digital oscilloscope used in this investigation
provides a sampling rate of 20 megasamples
persecond, an equivalent-time bandwidth of 400 MHz,
and 14-bit vertical resolution in the signal-
averaging mode.
Thottuvelil, et al [2,3] have developed a high
frequency measuring system which uses a digital
oscilloscope to obtain core loss and B-H loop
characteristic data. The setup in Figure I has
many Features similar to {2,3].
In Figure I the output of the oscillator is
connected to a frequency counter and the input of
the power amplifier which provides the voltage
excitation to the primary winding N_ of the test
core. A coaxial current-sensing resistor trimmed
to give R -0 10 ohms is connected between Np and the¢
low side of the amplifier. The excitation or
primary current in(t) is sensed by measuring the
voltage drop across R . The voltage e,(t) induced
in the secondary win_ing N, is used to sense the
changing flux. ip(t) ana e,(t) are captured,
digitized andstored in the digital oscilloscope
and then transferred to the system controller for
further processing and plotting.
A high temperature oil bath with its integrated
controller regulates the test core's temperature
environment. This bath is filled with a special
high temperature silicone oil into which the test
cores are immersed. Local heating of the cores,
particularly for the test condition of high flux
density at high frequency, is reduced by
circulating the silicone oil. Precautions were
taken to prevent local heating under all test
conditions. Uniform heating of the core is the
desired condition, otherwise the material's
electrical and magnetic characteristics can be
adversely affected and thus, possibly lead to
incorrect interpretations of the experimental data.
By Ampere's Law the magnetizing field strength H(t)
is given by
H(t) = _ A/m (I)
lm
where 1 is the mean path length of the magnetic
core. Lrnder the assumption that N, has a negligible
voltaqe drop, it follows from Faraday s Law that
e,(t) = NmA© dB(t) V (2)
dt
where B(t) is the instantaneous flux density in the
core material and Ac is the magnetic cross-
sectional area of the core. Integration of Eq. (2)
gives
B(t) = N-1Ac J e.(t)d, T (3)
By means of Eqs. (I) and (3) the dynamic B-H loop
can be plotted. The area enclosed by the B-H loop
is a graphical representation of the core loss, but
more importantly, the size and shape of the loop
gives a very good visual display of how the test
core characteristics change as a function of
temperature, frequency, excitation and core
geometry. The B-H loop also provides additional
information such as the remanence and coercivity
points.
The instantaneous power p(t) dissipated by the
magnetic material is
p(t) : ( Pip _ Ip(t)em(t), W (4)
N. I
The time average of p(t) over one period of either
ip(t) or e:(t) gives the core loss. e:(t) was chosen
because it provided well defined zero crossings for
determining the period. The specific core loss is
the core loss divided by the core mass.
MATERIALS AND TEST CORE DESCRIPTION
The soft magnetic materials selected for this
investigation were Supermalloy (79% Ni, 17% Fe, 4%
Mo) and Metglas 2605SC (B]% Fe, 13.5% B, 3.5% Si,
2% C). According to reference 4, Supermalloy has
a range of maximum flux density between 0.65 and
0.82 T, a Curie temperature of 460 C and a mass
density of 8.7 gms/cm_. This same reference states
that Metglas 2605SC_as a range of maximum flux
density between 1.5 and 1.6 T, a Curie temperature
of 370 C and a mass density of 7.32 gms/cm z.
The magnetic core geometry was a toroid wound from
0.001 inch thick by 0.25 inch wide tape with
nominal dimensions of I.D.-I.O inch and 0.D.-I.25
inches. The toroids were supplied by the
manufacturer in unsealed core cases and without
damping material. The magnetic cores were removed
from the aluminum cases for measuring their mass
and cross-sectional area. The core mass was
measured with an analytical balance and the core
cross-sectional area was measured with a
micrometer. The epoxy impregnated fibrous washer
normally used for sealing the aluminum case during
manufacturing was replaced with Teflon fabricated
washers. The size of these washers was such that
they rested on the outer edges of the open end of
the aluminum case and no contact existed between
the magnetic core and washer.
Each test core was prepared by placing the magnetic
core in the aluminum core case, covering the open
end with the Teflon washers and then wrapping the
assembly with several layers of high temperature
mica impregnated tape. The mica tape provided the
necessary electrical insulation between the core
case and the windings. The primary and secondary
windings were wound on the insulated assembly using
a high temperature (Class 220) magnet wire Even
though the test cores were tested up to 300 C, no
electrical breakdown of the insulation was
detected. Each core was fully immersed in the oil
while suspended by its leads from a Teflon terminal
board mounted above the bath. A set of three cores
of the same core material was prepared for each
data run. Separate data runs were made for each
material.
EXPERIMENTAL RESULTS
The specific core loss (SCL) as a function of
maximum flux density B, with frequency f,
temperature, excitation and tape thickness as
parameters, is shown for Supermalloy in Figure 3a
and for Metglas 2605SC in Figure 3b. Each figure
gives four sets of curves with three curves for
each set. The sets are for the frequencies of S,
10, 20 and 50 kHz and the three curves within each
set are for the temperatures of 23, 150 and 300 C.
The data given in Figures 3, 4 and S are for a
single core and are representative of the results
obtained for 3 cores of that particular material.
Figures 4 and 5 show the frequency-nested set of
B-H loops for Supermalloy and Metglas 2605SC,
respectively. If an examination of the temperature
effects on the size and shape of a particular
frequency loop is desired, then the frequency-
nested loops for that material must be plotted for
the same B,. The Bm used for these B-H plots was
selected on the basis of the highest value of Bm
obtainable over the range of frequencies and
temperatures tested.
TheB-HSupermalloyloopsin Figure4a {23C) and
Figure4b (300C)areall plottedfor B,-0.4T and
f=I kHz (inner loop), 5, 10, 20, and 50 kHz (outer
loop). Both figures show that the loop area
increases with frequency, particularly from 20 to
50 kHz. Comparison of these two figures shows how
temperature affects the loop's size and shape
characteristics. The shape of the 300 C loops
indicate flux saturation w_ile the elliptical
shaped 23 C loops indicate no,n-saturation. For a
given frequency, the enclosed area or size of a 300
C loop is always larger than a 23 C loop. This
result is unexpected since the loss is expected to
decrease with temperature [41i. Since these test
cores experienced prolonged heating at ]00 C and
above, i.e. see Figure 2a, it is possible that the
cause is due to temperature ageing effects. The
effects of temperature ageing on this material will
require additional investigat=on.
The Metglas 2605SC loops in i:igure 4a (23 C) and
Figure 5b (300 C) are plotted for B =0 8 T and f-1
m '
kHz (inner loop), 5, ]0, 20, and 50 kHz (outer
loop). Comparison of these f'gures shows that the
loop size increases with frequency for each
temperature and decreases in .,,izewith temperature
for each frequency. These are the expected
results. The temperature-time profile for the
Metglas 2605SC test cores is shown in Figure 2b.
DISCUSSIO_
Each of the two magnetic materials investigated
clearly showed the effect of ,_aximum flux density,
frequency, and temperature oi the specific core
loss. The curves in Figures 3a and 3b show the
expected tendency for the SCL Lo increase as either
B, or f increases. However, fo _ both materials, the
expected tendency for the SCL to decrease for an
increase in temperature for a given Bm and f did
not always hold true.
Clark and Fritz [5] investigz=ted Supermalloy for
f-60, 400 and 1000 Hz over a temperature range of
-55 C to 250 C and found that an increase in
temperature caused a decrease in the SCL. In this
investigation of Supermalloy it was found that for
a given B, and f, the SCL did indeed decrease from
23 C to ]50 C but then increased from 150 C to 300
C so that the SCL is greater ;Lt 300 C than at 23
C. It is felt, as previo=(sly noted, that a
possible cause for this increase in SCL from 150 C
to 300 C is temperature ageing effects. If indeed,
Supermalloy is susceptible to temperature ageing
effects, then the cause and l_ate of this effect
must be determined if this material is to be
considered for high temperatur_ applications. The
SCL for the other two Supennalloy cores tested
showed the same trends as the curves in Figure 3a.
The effect of temperature on the SCL for Metglas
2605SC follows the normal pattern of showing a
decrease in SCL for an increase in temperature with
the following exception. For B < 0.2 T and f=5, 10
and 20 kHz, the SCL is slighl_y higher at 150 C
than at 23 C. Similar SCL results were found for
the other two Metglas 2605SC o)res tested.
A comparison of Supermalloy and Metglas 2605SC
shows that Supermalloy gives a lower SCL than
Metglas 2605SC for comparable values of B., f, and
temperature. For example, at Bm=_O.4T, f- 20 kHz and
T= 150 C, the SCL is 16 W/lb for Supermalloy and 60
W/Ib for Metglas 2605SC. For this same B. and f at
T= 300 C, the SCL is 2] W/Ib for SupermalToy and 30
W/Ib for Metglas 2605SC.
ACKNOWLEDGMENT
lhis research was sponsored by the NASA Lewis
Research Center under the High Capacity Power
Element of the Civilian Space Technology
Initiative.
I.
.
3.
4.
5,
REFERENCES
Schwarze, G. E., "Overview of Space Power
Electronics Technology Under the CSTI High
Capacity Power Program*, Proceedinqs Seventh
Symposium on Soace Nuclear Power Systems,
Conf-go0109, Albuquerque, New Mexico, January
7-10, 1990.
Thottuvelil, V. J., Wilson, T. G. and Owens,
H. A., Jr., "High-Frequency Measurement
Techniques for Magnetic Cores', IEEE Power
[lectronics Soecialists Conference, June
1985, pp 412-425.
Thottuvelil, V. J., Wilson, T. G., Miyazaki,
I. and Owens, H. A., Jr., "High-Frequency
Characteristics of Amorphous Metallic-Alloy
Tape-Wound Cores", |EEE Power Electronics
Specialists Conference, June ]983, pp 168-
180.
"Design Manual Featuring Tape Wound Cores",
TWC-3OOT, Magnetics Components Division,
Butler, Pennsylvania, 1987, p ]4.
Clark, J. J. and Fritz, J. F., "The Effect of
Temperature on the A-C Magnetic Properties of
Nickel-lron Alloys", Wright Air Development
Center Technical Note 58-277, Wright-
Patterson Air Force Base, Ohio, August 1958.
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Report Documentation PageNational Aeronautics and
Space Administration
1. Report No.
NASA TM-103164
2. Government Accession No.
4. Title and Subtitle
High Frequency, High Temperature Specific Core Loss and Dynamic
B-H Hysteresis Loop Characteristics of Soft Magnetic Alloys
7. Author(s)
W.R. Wieserman, G.E. Schwarze, md J.M. Niedra
9. Performing Organization Name and Address
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135-3191
12. Sponsoring Agency Name and Address
National Aeronautics and Space Administration
Washington, D.C. 20546-0001
3. Recipient's Catalog No.
5. Report Date
6. Performing Organization Code
8. Performing Organization Report No.
E-5536
10. Work Unit No.
590-13-31
11. Contract or Grant No.
13. Type of Report and Period Covered
Technical Memorandum
14. Sponsoring Agency Code
15. Supplementary Notes
Prepared for the 25th Intersociety Eqergy Conversion Engineering Conference cosponsored by the AIChE, SAE,
ACS, AIAA, ASME, and IEEE, Reno, Nevada, August 12-17, 1990. W.R. Wieserman, University of Pittsburgh
at Johnstown, Johnstown, Pennsylvania. G.E. Schwarze, NASA Lewis Research Center. J.M. Niedra, Sverdrup
Technology, Inc., Lewis Research (enter Group, 2001 Aerospace Parkway, Brook Park, Ohio 44142.
16. Abstract
Limited experimental data exists for the specific core loss and dynamic B-H loops for soft magnetic materials for
the combined conditions of high frequency and high temperature. This experimental study investigates the specific
core loss and dynamic B-H loop ch_kracteristics of Supermalloy and Metglas 2605SC over the frequency range of
1-50 kHz and temperature range of 23-300 C under sinusoidal voltage excitation. The experimental setup used to
conduct the investigation is described. The effects of the maximum magnetic flux density, frequency, and
temperature on the specific core loss and on the size and shape of the B-H loops are examined.
17. Key Words (Suggested by Author(s)) 18.
Specific core loss; B-H hysteresis lo,)p; High frequency; I
High temperature; Magnetic measurements; Transformers;]
Power conditioning [
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Unclassified Unclassified I 8
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High frequency, high temperature specific core loss and dynamic B-H hysteresis loop characteristics of soft magnetic alloys

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