Design and development of electric generator for space power syste

Cooper, D. W.

Kuhns, P. W.

English

NASA Technical Reports Server

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REPLY TO 
ArrN OF: GP/43 03 6 
T o t  
FROM: 
SUBJECT: 
~ A T ~ O ~ A L  AERONAUTICS AND SPACE AD 
WASHINGTON, D.C. 20546 
usI/Scientif i c  & 
Attention: Miss 
5 4  
J 
Technical Information Division 
Winnie M. Morgan 
GP/Office of Assistant General Counsel for 
Patent Matters 
Announcement of NASA-Owned U. S. Patents i n  STAR 
I n  accordance w i t h  the procedures agreed upon by Code GP 
and Code  U S I ,  the attached NASA-owned U. S. Patent is being 
forwarded f o r  abstracting and announcement i n  NASA STAR. 
The following information is provided8 
U. S. Patent No. 8 3,447,003 
Government or  
Corporate Gmployee t Government 
Supplementary Corporate 
Source ( i f  applicable) : 
NASA Patent C a s e  No. : 
NOTE - If  this  patent covers an invention made by a corporate 
employee of a NASA Contractor, the following is applicable: 
Pursuant t o  Section 305(a) of the National Aeronautics and 
Space A c t ,  the name of the Administrator of NASA appears on 
the first page of the patent; however, the name of the actual  
inventor (author) appears a t  the heading of Column No. l of 
yes 0 N o  
the Specification, following the words e with res to 
e4 an invent O f . . .  
https://ntrs.nasa.gov/search.jsp?R=19710010971 2020-03-17T02:54:21+00:00Z
GENERATOR FOR A SPACE POWER SYSTEM 
Filed March 2, 1967 
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(NASA CR OW TMX OR AD NUMBER) s 
3,447,003 
US. cC1.310--54 10 Claims 
10 
ABS 
A space power generating system having a rotor in the 
form of a slotted armature of electrically insulating ma- 
terial. Each slot is filled with small diameter copper l' 
wires. Rotation of the armature moves these wires 
through the field of a k e d  superconducting magnet which 
forms the stator. 
20 
Origin of the invention 
The invention decribed herein was made by employees 
of the United States Government and may be manufac- 
tured and used by or for the Government for govern- 25 
mental purposes without the payment of any royalties 
thereon or therefor. 
Background of the invention 
These and other objects of the invention will be 'ap- 
parent from the specification which follows and from the 
drawings wherein like numerals are used throughout to 
identify like parts. 
In the drawings, 
FIG. 1 is an axial section view of an electric generator 
constructed in accordance with the invention, and 
FIG. 2 is an enlarged section view taken along the 
line 2-2 in FIG. 1. 
A power generating device embodying the feature of 
the present invention is shown in the drawings. This 
generator has a stator PO around a rotor 12 which is 
mounted on a shaft 14. A pair of spaced bearings 16 and 
IS mount the shaft 14 for rotation about its normal axis. 
In an ordinary A.C. alternator, the magnetic field is 
the rotor, but in a superconducting magnet generator 
many problems arise if the rotor is superconducting. Heat 
from the driving source, such as a turbine, is conducted 
to the cryogenic rotor through the support shaft. Another 
problem is the complicated structure required for a rotat- 
ing refrigeration and insulation system. 
As shown in the drawings, the structure of the present 
invention differs from the usual alternator in that, like a 
D.C. generator, the stator 10 is the field while the rotor 
I2 is the armature. This superconducting magnet gen- 
erator is similar to a salient pole alternator with brushes, 
and by applykg superconductivity to this type of gen- 
erator both weight conservation and high efficiency are 
realized. 
This invention relates to a superconducting magnet 30 For superconducting magnets to Ibe useful a high mag- 
generator for producing a greater amount of electrical netic field is generally desired. Such a field should be 
power for a given input power and having a smaller above about 10 kilogauss where magnetic materials 
weight than a conventional generator. The invention is saturate. Thus, the present invention is contrary to con- 
particularly directed to such a generator which is capable ventional generators in that it has no magnetic materials. 
of being used in a space environment. The rotor 12 is of an electrical insulating material to 
A vast amount of electrical power is required for cer- prevent eddy current loss in areas where no conductors 
tain space missions, such as those utilizing electric pro- are present. By minimizing the eddy current loss in the 
pulsion. Low weight and high efficiency are both rotor 12, it can be operated at lower temperatures, and 
mandatory for power rotating mechanical to electrical radiation of heat to the superconducting magnet on the 
conversion systems for use in space. Salient pole alterna- 40 stator 10 is minimized. 
tors of the type used in power generating stations have Both the rotor 12 and the shaft 14 are made of 99 
been proposed for space applications \because of their percent alumina. Armature slots 20 are cut axially about 
high efficiency and low weight. To reduce the weight even the periphery of the rotor 12. Small diameter copper wires 
more cylindrical rotators have been substituted for the 22 are placed in the armature slots 20 as shown in FIG. 
salient pole rotors in this type of alternator to produce 45 2. These wires 22 provide a small rotor eddy current loss, 
higher speed generators. However, these devices utilize and because these wires are paralleled in each slot 20 
graphite brushes which exhibit excessive wear at high the effective resistance which yields the rotor copper loss 
altitudes. is therefore also very low. By not having magnetic ma- 
Brushless generators are proposed as a solution to the terial present in the rotor 12 a larger cross section of 
brush wear problem. These brushless machines have 50 copper armature conductors is utilized. To minimize the 
weights about twice those of the cylindrical rotor alterna- heat flow 'from the rotor 12 to the superconducting stator 
tor which operate at the same speed. Also, brushless PO, a layer 2 of polished aluminum having a thickness 
generators utilize solid rotor construction which pro- of a few mils is plated on the alumina rotor 12. A very 
duces greater hysteresis and eddy current losses with thin silver coating on the rotor surface will likewise re- 
decreased efficiency. 55 duce radiation. 
These space requirements have been met, and the prob- The removal of rot is a necessary function of 
lems of the prior art devices have been solved with the the rotor P2 and the s The material for the rotor 
superconducting generator constructed in accordance with and shaft should have hermal conductivity as well 
the present invention. This generator has a superconduct- as a high strength to withstan'd the high rotor stresses 
ing field as the stator, and its rotor is capable of operat- 60 encountered. As stated above, a high grade alumina has 
ing at very high temperatures. A larger cross section of been found to be tory for this purpose, and the 
armature conductors can be utilized because no magnetic rotor 12 and shaft fabricated from a single solid 
materials are used in the rotor. The alumina rotor and shaft 
It is, therefore, an object of the present invention to provide a good heat path for cooling which may ibe done 
provide a space power generating device which is light 65 at the bearings 16 and 18. It is also contemplated that 
in weight and has increased efficiency. silicon oil can be circulated inside 
Another object of the invention is to provide an im- The magnetic field on the stator 
proved electrical generator for an electric propulsion 26 of a hard superconducting material which is niobium- 
space mission having no magnetic material in its rotor. tin. A silver, copper, or conductor coating is necessary to 
A further abject of the invention is to provide a space 70 prevent current degradation of the magnet coil. It is also 
power generator having a nonmagnetic rotor which contemplated that gadolinium and holmium may be used 
utilizes armature conductors having large cross sections. as flux shaping materials. No outside back iron is neces- 
35 
3,447,003 
4 
sary on the stator 10, and so bf the magnetic field lines said rotor being of an electrically insulating material 
extend to intlnity. thereby minimizing eddy current loss, 
A housing 28 encloses the stator IO as shown in FIGS. 1 a plurality of parallel electrical conductors mounted in 
and 2. The housing 28 includes insulating material 30 such said slots, said conductors being small diameter 
as pearlite. A stainless steel jacket 32 supports the insula- copper wires for minimizing rotor eddy current loss, 
tor 30. Stainless steel rods 34 extending from the housing means for rotating said rotor whereby said conductors 
28 support the stator 18. are moved through the field of said circuit conduct- 
The main armature power is developed on the rotor ing 'magnet, and 
2 and is extracted on brushes 36. Ordinary graphite a polished coating on said armature for minimizing 
rushes 36 may be used in an enclosed section where an heat flow from said rotor to said stator. 
oil with a vapor pressure about 10-6 torrs is placed. At 2. Apparatus as claimed in claim 1 including a housing 
this pressure the high wearing rate of the ibrushes 36 for enclosing said stator for insulating the same. 
does not occur. In the preferred embodiment rhenium 3. Apparatus as claimed in claim 1 wherein the stator 
brushes 36 slide on a silver commutator 38 or slip rings. has a field above about 10 kilogauss. 
In operation, the shaft I4 is rotated in the bearings 15 4. Apparatus as claimed in cl 
16 and 18 by a hollow drive shaft 40 connected to a ture comprises an alumina rotor 
prime remover, such as the tupbine. A coolant may be shaft supported by space bearings. 
be circulated through the hollow shaft 5. Apparatus as claimed in claim 1 wherein the 
aluminum cooling rod 42 because the rotor 12 operates polished coating is aluminum. 
at a temperature of about 300" K. 20 6. Apparatus as claimed in claim 1 wherein the 
The superconducting magnet formed by the coils 26 polished coating is silver. 
must be continuously cooled by a cryogenic refrigerator 7. Apparatus as claimed in claim 1 including means 
44. The cryogenic cooling fluid i s  circulated through in- for cooling the armature to a temperature below about 
d a t e d  conduits to the coils as shown in FIG. 1. An- 300" K. 
other aluminum cooling rod 46 further aids in the cool- 25 8. Apparatus as claimed in claim 2 including a stain- 
ing operation by cooling the end of the shaft 14. less steel jacket enclosing the housing. 
While a preferred embodiment of the generator has 9. Apparatus as claimed in claim 2 Including a 
been shown and described, various modifications may be plurality of support rods extending inwardly from said 
made to the disclosed structure without departing from housing to mount the stator. 
the spirit Qf the invention and the scope of the subjoined 30 10. Apparatus as claimed in claim 1 including means 
claims. for removing electric power from the armature including 
What is claimed is : a silver member mounted on the armature shaft, and 
1. In a space power generating system of the type stationary rhenium brushes in sliding contact with said 
which converts rotating mechanical energy to electrical member thereby enabling said generator to be used 
energy by moving an electrical conductor through a mag- 35 in a space environment. 
netic field, the improvement oomprising 
a stator comprising stationary coils of a superconduct- 
ing material, UNITED STATES PATENTS 
means for cryogenically cooling said material to super- 3,242,418 3/1966 Mela et al. _ _ _ _ _ _ _ _ _ _  310-52 
conducting temperatures whereby said coils form a 40 3,368,087 2/1968 Madsen _ _ _ _ _ _ _ _ _ _ _ _ _  310-52 
supercondwting magnet, 
a rotor comprising an armature having a plurality of 
axia nding slots about the periphery thereof, 
References Cited 
O. HZRSHFIELD, lZxaminer. 
R. SKUDY, Assist~ptt Examiner. 


Generator for a space power system Patent

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