Variable water load for dissipating large amounts of electrical power during high voltage power supply test

Littlejohn, D. P.

Reed, A. E.

English

NASA Technical Reports Server

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON, D C 20546 
REPLY TO 
ATTN OF: March 27, 1971 
TO : USI/Scientific & Technical Information Division 
FROM: GP/Office of Assistant General 
Attention: Miss Winnie M. Morgan 
Counsel for Patent Matters 
SUBJECT: Announcement of NASA-Owned 
U.S. Patents in STAR 
In accordance with the procedures contained in the Code GP 
to Code US1 memorandum on this subject, dated June 8, 1970, 
the attached NASA-owned U.S. patent is being forwarded for 
abstracting and announcement in NASA STAR. 
The following information is provided: 
U.S. Patent No. : 3,350,671 
Corporate Source : Jet Propulsion Laboratory 
Supplementary Vasian Associates 
Corporate Source : 611 Hansen Way, Palo Alto, C a l i f ,  
NASA Patent Case No.: XNP-05381 
Please note that this patent covers an invention made by an 
employee of a NASA contractor. Pursuant to Section 305(a) of 
the National Aeronautics and Space Act, the name of the 
Administrator of NASA appears on the first page of the patent; 
however, the name of the actual inventor (author) appears at 
the heading of Column No. 1 of the Specification, following the 
words 'I. . . with respect to an invention of. . . ." 
Gayle Parker 
Enclosure: 
Copy of Patent 
L/ 
(NASA CR OR TMX OR AD NUMBER) 
https://ntrs.nasa.gov/search.jsp?R=19710011367 2020-03-17T02:55:47+00:00Z
3,350,671 Oct. 31, 1967 R. C. SEAMANS, JR 
DEPUTY ADMINISTRATOR OF THE NATIONAL 
AERONAUTICS A N D  SPACE ADMINISTRATION 
Filed July 27, 1966 
, HIGH POWER-HIGH VOLTAGE WATERLOAD 
cv 
M 
723 
ATTORN EY S 
United States Patent -Office Patented Oct. 31, 1967 
3,350,671 
Robert C. Seamans, Jr., Deputy Administrator of the Na- 
tional Aeronautics and Space Administration, with re- 
spect to m invention of Duane P. Littlejohn, Santa 
Clara, and Arthur E. Reed, Sunnyvale, Cali. 
Filed July 27, 1966, Ser. No. 568,352 
HIGH POWER-HIGH VQLTAGE WATERLOAD 
6 Claims. (C1. 338-82) 
This invention relates to a variable high power water 
load for dissipating large amounts of electrical power 
during testing of high power output electrical apparatus. 
The invention is particulayly suitable for testing high volt- 
age, high power DC power supplies of the type used in 
powering communications transmitters. 
In order accurately to test high power output power 
supplies it is necessary to operate such power supplies at 
the rated output thereof. Provisidn of a dummy load for 
the power supply is desirable in order to avoid transmis- 
sion of unnecessary radiation as would occur if the power 
supply were connected to a transmitter. The present inven- 
tion provides a dummy load suitable for such purpose. 
The principal object of the invention is to provide such 
dummy load in which the current capacity, and hence the 
power dissipating capacity, of the load can be readily 
and oonveniently varied during operation of the apparatus. 
Variability of the load permits operation of the power 
supply in a stable condition at the rated current, voltage, 
and power levels at which the power supply operates when 
it is connected into the operative circuit with which it is 
used. 
The specific embodiment of the invention that is ex- 
plained in more detail hereinafter includes an electrically 
conductive hollow tube that is provided with fluid open- 
ings at opposite ends thereof, an electrically conductive 
rod mounted in the tube approximately coaxially thereof, 
and an insulative sleeve mounted in the tube between the 
inner tube wall and the rod with provisions for sliding 
the sleeve within the tube to  vary the radial current path 
through fluid from the rod to the tube interior. Fluid con- 
ducted through the tube is heated by passage of current 
therethrough and is cooled at an externally located heat 
exchanger for recirculation through the tube. 
Known prior art techniques for controlling the power 
dissipation capabilities of such apparatus typically em- 
ploy devices for varying the flow rate of fluid through 
the dummy load, and while such systems afford variability 
of the total power dissipation, they do not afford variabil- 
ity of the current capacity of the load. The adjustable in- 
sulative sleeve of the present invention permits variatioii 
in current flow, and hence, power dissipation, whereby 
power supplies can be tested under conditions that ac- 
curately correspond to actual operating conditions. 
A feature and advantage of the present invention is that 
current flow through the load can be adjusted while power 
is applied to the load. As power is supplied to water loads, 
the temperature of the water and the apparatus contain- 
ing the water increases. The increased temperature causes 
a change in the resistance of the water, as a consequence 
of which the amount of current flow changes. Because the 
load of the present invention is adjustable during opera- 
tion, the system can be readily stabilized at the rated 
current and power output of the power supply under test. 
Another feature and advantage of the present invention 
is that fluid flow controlling and cooling accouterments 
employed with the apparatus can be significantly simpli- 
fied since the invention affords an internally disposed cur- 
rent flow adjustment structure. 
A further feature and advantage is that the dummy load 
of the present invention is particularly suitable for high 
voltage operation since it employs coaxially oriented con- 
5 
ductive members. Such structure is substantially free of 
sharp edges and/or corners that would, if present, con- 
tribute to aroing under high voltage operation. 
Other objects, features and advantages will be apparent 
after referring to the following specification and accom- 
panying drawing in which: 
The sole figure is a side view in partial cross section 
of a dummy water load according to the present invention, 
portions of the drawing beina shown in schematic form. 
10 
15 
20 
25 
30 
35 
40 
45 
50 
55 
60 
65 
70 
Referring more partkulari; to the drawing, reference 
numeral 12 indicates an electrically conductive fluid im- 
pervious hollow tube, centrally and coaxially of which 
is mounted a conductive rod 14. Tube 12 and rod 14 form 
electrodes to which the terminals of a high voltage power 
source S under test are connected; the tube and rod were 
constructed of #304 stainless steel tubing in one appa- 
ratus constructed according to the invention. 
Tube 12 is provided with fluid tight end caps 16 and 
18, thereby defining a fluid tight chamber; the tube is 
further provided with a fluid inlet fitting 20 and a fluid 
outlet 22 for communicating fluid through the chamber. 
Intermediate fluid outlet opening 22 and end cap 16 a 
molded high voltage insulator 24 is supported centrally 
of the tube on a mounting collar 26 for mounting rod 14 
centrally of tube 12. An O-ring 28 is provided between 
insulator 24 and collar 26 to form a fluid tight seal there- 
between. A conductor 30 extends through insulator’24 and 
is connected at the inner end thereof to rod 14 and at  the 
outer end to a connecting terminal 32 to which one output 
terminal of power source S is connected. A corona ring 34 
is provided inwardly of terminal 32 to avoid arcing be- 
tween the terminal and end plate 16 and/or tube 32. 
Mounted within tube 12 for slidable axial movement 
therein is a hollow insulative sleeve 36. The outer diam- 
eter of insulative sleeve 36 is approximately equal to the 
inner diameter of tube 12 so that little or no fluid flows or 
resides between the inner surface of the tube ,and the 
outer surface of the sleeve. Because tube 36 is formed of 
insulative material, polyvinyl chloride for example, it inter- 
rupts a portion of the radially oriented current path be- 
tween rod 14 and tube 12. The portion of the current path 
interrupted by sleeve 36 is adjustable, and for this pur- 
pose a threaded shaft 38 is supported in a thrust bushing 
40 carried in end cap 18. An apertured disc 42 is joined 
to the axial end of sleeve 36 and is formed centrally 
thereof with a threaded hole 44 for threaded engagement 
with shaft 38. An O-ring 46 is provided for affording a 
fluid tight joint between bushing 40 and end cap 18. I t  
will thus be seen that rotation of shaft 38 mwes sleeve 36 
axially of tube 12. 
Disc 42 is exemplary of any suitable element for op- 
eratively connecting shaft 38 to sleeve 36 without re- 
stricting fluid flow between inlet opening 20 and out- 
let opening 22. Disc 42 is provided with one or more 
apertures 48 to permit such fluid flow. It can therefore 
be seen that fluid entering inlet ing 20 will flow axi- 
ally of the annular space bet.ween sleeve 36 and rod 
14, thence through the annular space between tube 12 and 
rod 14, and thence out through outlet opening 22. 
A pump 50 is connected to the apparatus through a 
suitable conduit 52 for circulating fluid, such as water, 
through the system. Such fluid is conveyed through a 
conventional heat exchanger depicted schematically at 54 
to cool the fluid and is further conveyed through a de- 
ionizer 56 of conventional form. A metering valve 58 is 
provided in parallel with de-ionizer 56 so as to assure 
that any electrochemical change in the fluid caused by 
flow through the tube 12 will be obviated before recircu- 
lation of the fluid. 
The operation of the apparatus can be understood by 
assuming that high voltage power source S has one out- 
3,350,671 
3 
put terminal thereof connected to tube 12 and the other 
output terminal thereof connected to rod 14 through ter- 
minal 32 and conductor 30. Assuming a conventional cur- 
rent flow, as contrasted with electron flow, the current 
will pass from rod 14 through the fluid F flowing through 
the annular chamber between the rod and tube 12 and 
thence through the tube wall back to the power source. 
Because the fluid F affords a resistance to current flow, 
power is dissipated and power source S is loaded. Power 
dissipation in the fluid creates heat which causes the 
temperature of the fluid to increase and the resistance of 
the fluid to decrease. Should such decrease in resistivity 
cause an increase in current above the current desired, 
shaft 38 is rotated to move sleeve 36 inwardly, toward 
the left as viewed in the drawing, to decrease the cross- 
sectional area of the radial current path from rod 14 to 
tube 12 through the fluid. Reduction of the cross-sec- 
tional area of the current path increases the resistance 
thereof, and therefore, decreases the current flow. Until 
the temperature of the system is stabilized, adjustments 
of sleeve 36 by rotation of shaft 38 will maintain cur- 
rent flow at the desired amount. As a complement to 
adjustment of sleeve 36, the rate of flow afforded by 
pump 50 and the rate of cooling afforded by heat ex- 
changer 54 can be adjusted in accordance with well- 
known criteria. 
A more complete understanding of the operation of the 
present invention can be had by a quantitative consid- 
eration of a specific apparatus designed in accordance 
with the invention. Such apparatus is capable of dissi- 
pating one megawatt of power. In the apparatus, pump 
50 operates to maintain a flow, Q, of 200 gallons per 
minute (g.p.m.) and heat exchanger 54 operates to per- 
mit a temperature rise (AT) between inlet opening 20 
and outlet opening 22 of 19" C. That such parameters 
afford 1 megawatt dissipation can be deprived from the 
equation: 
P=.264xQ x A T  ( 1 )  
in which: 
P is power dissipated in kilowatts; 
.264 is a constant determined by system geometry and 
the characteristics of fluid F; 
Q is rate of fluid flow in gallons per minute; and 
A T  is temperature rise in degrees centigrade between 
inlet opening 20 and outlet opening 22. 
Adjustment for a given resistance value may be calcu- 
The resistance: 
lated from the following equations. 
P 
where: 
p=resistivity (ohm-cm.) 
L=exposed length of electrode (cm.) 
As seen from the above equation, the resistance (RL) 
varies directly as resistivity ( p ) .  
During a normal operation ( p )  can be expected to vary 
over a comparatively wide range due to a number of 
causes. The first order cause can be expected to be a re- 
sult of temperature change in the relation: 
K P=F ( 3 )  
in which K is a constant and T is the temperature of 
fluid F in degrees centigrade. 
In view of these facts, an example of adjustment for 
a particular (RL) will assume a fixed ( p )  of 1 megohm- 
an. at a fixed temperature and 
R~=5000n (4) 
4 
From Equation 1: 
10 
5 or: 
L= in. 
2 r (  2.54) RL 
A combination of Equations 4 and 6 yields: 
lxloo =12.55 in. 
2r (2 .54 ) (5X103)  L= 
The length of rod 14 exposed by adjustment of sleeve 
36 in the exemplary apparatus has the following adjust- 
Maximum exposed electrode for minimum resistance- 
31.1 in.; 
Minimum exposed electrode for maximum resistance- 
0.625 in. 
When voltage is first applied to  the load design as de- 
scribed hereinabove, a given current will flow depending 
on the length of rod 14 exposed by movement of sleeve 
36, resistivity p, and temperature of the water at inlet 
opening 2Q. As the power to the load is increased, the 
25 average temperature over the length of the rod 14 will in- 
crease causing a further increase in current due to the 
drop in resistivity. At any particular power level and 
fixed inlet temperature, the current will stabilize and re- 
main essentially constant. Total adjustment of the sleeve 
30 36 is possible during any level of operation to allow 
manual adjustment of the length L of rod 14 exposed to 
tube 14 until stabilization occurs. The adjustment of 
sleeve 36 permits stable operation at any level of opera- 
tion and the control of pump 52 and heat exchanger 54 
35 permits establishment of a constant temperature at inlet 
fitting 20. The exemplary apparatus described above is 
satisfactory for loading a 50,000 volt DC power supply 
at one megawatt. 
Thus it will be seen that the present invention pro- 
40 vides a d m m y  load capable of stable operation at high 
power levels in which load the current and the total pow- 
er dissipated are adjustable. Because of the coaxial con- 
figuration of tube 12 and rod 14 the appgratus is suit- 
able for high voltages such as 50 kv. Thus testing of power 
45 supplies under actual operating conditions is made pos- 
sible without: causing spurious and unwanted electro- 
magnetic radiations. 
While one embodiment of the present invention has 
been shown and described it will be apparent that other 
50 adaptations and modifications can be made without de- 
parting from the true spirit and scope of the invention. 
What is claimed is: 
1. A test load for a direct current power supply of the 
type having first and second output terminals, said load 
55 comprising an elongate hollow conductive tube for con- 
nection to said first terminal, an elongate conductive rod 
mounted in said tube centrally and along the longitudinal 
axis thereof for connection to said second terminal, said 
rod having an outer cross-sectional extent less than the 
60 inner cross-sectional extent of said tube to  define a 
chamber therebetween, means for conveying a conductive 
fluid through said chamber to establish a current path 
between said rod and said tube, an elongate insulative 
hollow sleeve mounted in said chamber, said sleeve hav- 
65 ing an outer configuration substantially congruent to the 
inner configuration of said tube to afford relative sliding 
movement therebetween in fluid tight relation, and 
means for adjustably positioning said sleeve to vary the 
area of the path between said tube and said rod through 
2. A test load according to claim 1 wherein said tube 
and said sleeve are of hollow cylindric form and wherein 
said rod has a cylindric exterior surface concentric with 
said tiube and sleeve to define an annular fluid chamber 
15 ment range: 
20 
70 said fluid. 
75 therebetween. 
. . c  
3,350,671 
5 6 
3. A test load according to claim 1 having means in- the outlet opening, current flow between said rod and 
cluding an insulator at one end of said tube 'for support- said tube can be adjusted by adjusting the longitudinal 
ing said rod therein, a bushing at the opposite end of said position of said sleeve. 
tube, a threaded shaft carried in said bushing and having 6. In a power supply test load of the type including a 
an inner end extending into said tube, means for attach- 6 conductive hollow fluid impervious tube, an elongate con- 
ing said inner end to said sleeve, and means for threaded- ductive rod having an outside diameter less than the in- 
ly engaging said shaft so that rotation thereof effects side diameter of said tube, means for mounting said rod 
positioned adjustment of said sleeve longitudinally of said in said tube coaxially thereof, said mounting means be- 
tube. ing insulative so that said rod is electrically isolated from 
4. A test load according to claim 1 in combination said tube, and inlet and outlet fittings for conveying fluid 
with means for delivering fluid to said conveying means through said tube to provide an eleotrically conductive 
including a pump, a heat exchanger in series with said medium between the rod and the tube; the improvement 
pump, and means for connecting said pump and said comprising a hollow insulative sleeve mounted in said 
heat exchanger to said tube. tube, said sleeve having an outer diameter substantially 
5. A test load for a direct current power supply com- 15 equal to the inner diameter of said sleeve to support said 
prising a conductive hollow fluid impervious tube having sleeve in said tube for sliding axial movement and means 
an inlet opening at one end thereof and an outlet opening for adjustably positioning said sleeve within said tube to  
at the opposite end thereof, an elongate conductive rod vary the area of said rod that directly confronts the in- 
having an outside diameter less than the inside diameter ner surface of said tube. 
References Cited of said tube, means for mounting said rod in said tube 20 coaxially thereof, said mounting means being insulative 
so that said rod is electrically isolated from said tube, a UNITED STATES PATENTS 
hollow insulative sleeve mounted in said tube, said sleeve 2,983,145 5/1961 H~~~ et _ _ _ _ _ _ _ _ _ _  73-193 
having an outer diameter substantially equal to the inner 3,167,957 2/1965 ziviani _ _ _ _ _ _ _  73-193 
diameter of said sleeve to support said sleeve in said 25 
tube for sliding axial movement, means for adjustably 
positioning said sleeve within said tube to  vary the area 101,381 7/1937 Australia. 
of said rod that directly confronts the inner surface of 107,266 5/1939 Australia. 
FOREIGN PATENTS 
said tube, whereby when a high voltage power source is 
connected between said tube and said rod and a fluid js 30 
circulated through said tube fram the inlet opening to 
ROBERT K. sc,FER, 
H. J. NOHAUSER, Assistant Examiner. 
Examiner. 


High power-high voltage waterload Patent

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