In discussing the application of advanced materials to rotating machinery, the following topics are covered: the torque speed characteristics of ac and dc machines, motor and transformer losses, the factors affecting core loss in motors, advanced magnetic materials and conductors, and design tradeoffs for samarium cobalt motors

Triner, J. E.

English

NASA Technical Reports Server

• N84 100G3 "
APPLICATION OF ADVANCEDMATERIALSTO ROTATINGMACHINES
Jame_ E. Triner
National Aeronautics and Space Administration
Lewis Research Center #
Cleveland, Ohio 44135
In discussing the application of advanced materials to rotating machin-
ery, we will cover the following topics: the torque-speed characteristics of
ac and dc machines, motor and transformer losses, the factors affecting core
loss in motors, advanced magnetic materials and conductors, and design trade-
offs for samarium-cobalt motors.
Figure I shows the torque-speed characteristics for various types of
motors. The series motor has a high starting torque for very low speeds. The
shunt motor and the permanent-magnet motor can be used as control devices for
many of the components within the all-electric airplane. Many of the charac-
teristics of the shunt and permanent-magnet motors can be duplicated with a
wound-rotor motor by varying the rotor resistance.
Figure 2 compares the losses within a 5-hp, three-phase motor and a 15-
kVA transformer. The basic difference is that the m_tor has friction and
windage losses in addition to core (iron) loss and I_R loss. However, as
the load on the transformer increases, t_e copper loss (the 12R Inss) pre-
__ dominates. Similarly in the motor the ! R loss is the major loss at higherfoods.
Figure 3 shows weight and efficiency as functions of frequency for a 50-
kVA transformer. It illustrates the advantage of using higher frequencies.
Of course, from 60 Hz to 400 Hz there is a dramatic change. At slightly
i higher frequencies, around 1000 Hz, there is another significant drop in
weight. However, at too high a frequency, the weight gain is not that signif-
icant. The peak efficiency for this particular design is at 5 kHz. Ti_iscon-
tradicts the old adage of copper loss and iron loss being the same. For this
particular design the copper and iron losses are the same at I0 kHz, which is
' not the optimum efficiency point. The figure shows that significant trade- :_
: offs can be made in designing both transformers and motors for advanced all- .
el_ctric airplanes.
i Figure 4 shows some of the factors affecting core _oss. For a simple
i two-segmentcommutator (on the left) if we look at one phase, it is essen-
tially a pulsating square wave; if we combine a number of elements (lower "
._ left),we get a high-frequencyvoltage ripple. This would translate into a
loss within the material. The diagrams on the right show that under the pole
faces, without any rotor current, the magnetic fielo is constant. However,
when current is applied in either a generating or a motoring mode, the distri-
bution :_ flux density tends to increase in one pole face and to decrease in
the other pol_ face as the machine goes through a cycle. This would limit the
flux density at which the motor or generator could be operated.
Figure _ shows this even more significantly. The current flowing in the
rotor actually decreases the flux density in the left side of the pole pieces
(shown by path 2). Through path I the flux density is essentiallyconstant.
Through path 3 the current actually enhances the flux density within the
machine. Thereforeflux density changes linearly across th_ pole face as cur-
rent is applied. At higher flux densities magnetic saturation is approached,
as shown by the flattened tip of the flux waveform. This would result in ad-
ditional _ore loss.
PRECEDINGPAGE_.ANK NOTFILMED 93 _-_" _ -
1984001988-090
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Figure b compares three materials wlth the properties required in rotat-
ing machinery. A fairly high flux density is required to get the windings of
the machine smaller and reduce the accompanying I_R loss. Armco M-4 steel
is presently being used in most rotating machinery. The new Metglas 2605 sig-
nificantly reduces core loss to about one-fourth that of M-4. However, this d
may not be a fair comparison because the M-4 is _luchthicker than the
Metglas - 4 mil as compared to I mil. Another material, Supermendur, also has
high flux density characteristics,but its losses are greater than those of
M-4 even though it is thinner. Thus from a loss standpoint,M-4 is better
than Supermendur at this point. However, Metglas may be a formidable con-
tender as a new material for rotating machiner).
Metglas has been applied to some transformer designs with a significant
reduction in iron loss (fig. 7). Also because of the reduction in iron loss
and the higKer flux density characteristics,the copper loss could be re-
duced. Since this is a phenomenon that increaseswith the squ_re of the cur-
rent, the reduction in copper loss is fairly significant.
Lewis is investigatinga new material called intercalatedgraphite.
Table I shows that intercalatedgraphite can achieve the same levels of resis-
tivity as copper and aluminum at one-third of the weight. It also has a much
higher strength than copper, so that it could be integrallywound as part of
the structure of either the rotor or stator of the machine. This should sig-
nificantlyreduc_ the weight and increase the strength of the motor.
Samarium-cobaltmotor studies have been performed for electric vehicle
research. Figure 8 shows the percentageof total weight for the different
components for a current and two advanced samarium-cobaltmotor designs. The
current motor weighs 1.7 lb/hp, Using the Metglas, a lightermaterial with
less loss than the iron presently used for motor designs, significantlyre-
duces the percentage of total weight of iron while keeping the same amount of
copper used in the current design. The specific weight decreases to 0.74
Ib/hp. Incorporatingintercalatedgraphite fibers changes the weight distri-
bution again. Here intercalatedgraphite would also be used in the frames.
The weight of the machine is again significantlyreduced, to 0.57 lb/hp.
These machines operate at 8000 to 9000 rpm. Raising the operating speed to 20
000 to 26 000 rpm would decrease specific weight further',to around 0.31
Ib/hp. It appears that quite a bit of design work could be done in this area
to support an all-electricairplane motor.
In summary, the major motor losses are core (iron) loss and 12R
(copper) loss. With Metglas, core loss can be reduced by a factor of 4, and
Metglas is lighter than conventional electrical steels. Intercalatedgraphite
conductors may have resistivityequal to that of copper at one-third of the
weight. Also high-speedsamarium-cobaltmotors have high efficiency and low
specificweight. Therefore significant latitude is available in designing
rotating machinery for an a11-electricairplane.
94
1984001988-091
JORI(_iN,_L ?,'_C;_. :'"-., "
OF POOR QUALFI'Y
TABLE I. - CHARACTERISTICS OF INTER_LATED GPJ_PHITEAS COMPARED
WITH COPPER, ALUMINUM, AND GRAPHITE
Material Denslt#, Resistivity, (Figure of merit) -I, Cost,
glcm_ a-cm m #Icm3
Copper 8.9 1.8xi0-6 16 19.6
Aluminum 2.7 2.8 7.6
Graphite 1.7 40 68
a1,8 4.9
Intercalated 2.7 b2.8 7.6 10.5
graphite c6 16
Material Density, Strength, Ratio of strength Thermal e_pansion,
g/c_" psi to weight "C "1
" Copper 8.9 32x10-3 3 600psi 16x10-6
: Aluminum 2.7 16x10 -3 6 000 psi 14 :_
Steel 7.9 600000 76000 7 ,
Intercalated 2.7 (300 to 1000)xlO 3 (180 to _'_)xlO-3 -i
graphite
aposslble.
': bNeeded to compete with aluminum.
i CNeeded to compete with copper.
!
;_
1984001988-092
p_,_. _._
OF POOR QUALrFf "_
T_clUe _ Terque
Slmilht_ _. T,fll_l _ nN,
_md __._pee4 gt c_
, £ 2ell
_'| , -
-a 1. - Torque-speed charecter;st|cs _ .... "
,| .
.ll
96
1984001988-093
ORIGfl_ALPAG_I:_
OF POORQUALITY
1600_
1400--
1200
1000
12Rand
_ Core_oss-_,,\'_\\\_\\\\\\_
0 25 50 75 lO0 125/' 150
Load,percentoffulload
lO0 _ 700 "Friction
and
windage
-- 600 "--Efficiency loss
gO -- 500 Totalosses-_
R
._ v__
._-
¢:
" 80 -- 300
Copper
15 -- 200 loss
%
" : 70 L._ 100
. i Eddycurrentloss Iron r-Hysteresislossloss -i I I,,,t I I I I
;7_ 0 5 lO 15 20 25 30
(a)5-hp,three-phasemotor.
:"_ (b)lS-kVktransformer.
_,iI FigureZ - Comparisonflosscharacteristicsfor5-hpmotorand15-kVA
transformer.
!l °'
1984001988-094
OF POOR Q_jALfl"_
lO0 -- .50
.,,_ EfficiencygS-- 40
m
e,o- i 30 _\ ;
85- 20
Weight .
8o- lo I I
0 l0 20 30 40
Frequency,kHz r
: Figure3. - 50-kVAtransformerdesignfor constantfluxdensity. Primary
voltage, a4OV;secondaryvoltage,lIN.
i f
)
k98
] 98400 ] 988-095
OR:GINALPAGe.|3
OF POOR QUALn_(
I-- 1"" ,=-
_ .i_____ '
o _
__ (b; I
" ^..'.-..=_=_''=0'"=_""_" ='_" "_'='"' i_E--_" c=d_,
,-=---_" ruthcurrent%
L_
._'._'// • I I n(--7
\' t S=_ m=w
A o ,p
_, _ .4'r._ _ltclm " F:oduc_theFn=n_d _ol'-p e..
Figure 4. - Core loss factors. ;
4 i
i
.ql
.!
:i
i
99
1984001988-096
f WithioB_ ia - 0"_ "-(note reduction
_, (c) iIJl orB)
' I J/® ® ®
LJ I 1... I _---tt
• r
F_gure 5. - Effect of a_ture magnetomot_veforce.
------- Metc_as2605SC._llmthick6-
---- _ ArmcosteelM-4,275pmthick
- .... Supermendur,102pmthick
_._" _ Szturzti_n
. _ 2 j....- _,--
_..,o "_
• .8 _
_ .®= r i i i i ! i
.6 .8 1.0 l,l 1.4 1.6 l.I 2,0
klductk_.T
Fkjure6. - Corelossis afunctimd In(lucttonfor
vertousmallrlels. Frequency,_HZ.
100 ,"
,I
1984001988-097
35o-- OF _%_.. -+- -.
.,
/
300--
250--
CopperJoss
_= 200--
a. 150 --l
I
l_ -- _/'/,_//_ Copperloss
5O
Commercial Metglas
Figure7. - Improvementon]5-kVAtransformerusing
Ai,etglas.
ZOOI--" Frirne{graphite Frame(graphite "i'
| Frame relnforcedl reinforced)
I Magnet
80b Maqnet Magnet
/
J Copper60I--- Intercalated
+r...
/ "on ' i
20[-- Iron Iron
L
_ 0 Prtstnt, _rdnced, Advanced(In_rcalat_l
l. 7l Ib/hp O.74Ib/hp graphitl).O.5"/_hp
figureIL -Weightdsamarlum.-cobaltmotors.(ffk:llncy,93
percmt;horsepomr,15hp. ,,,_
101
1984001988-098


Application of advanced materials to rotating machines

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