NASA Technical Memorandum 103164

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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

c_

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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 investigated 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 experimental 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 signalaveraging 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 crosssectional 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 frequencynested 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.

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3.

4.

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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, WrightPatterson Air Force Base, Ohio, August 1958.
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NationalAeronautics and Report Documentation Page

SpaceAdministration

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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