Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF INVENTION:
IRON POWDER ENCAPSULATED LIQUID-COOLED REACT~
FIELD OF INVENTION:
This invention relates to large KVA, water-cooled iron
core reactors and reactors of such type having a powdered iron
core.
The invention is also directed to a low-loss liquid-
cooled, large KVA reactor, for example, in the range of 10 KVA
to 30 ~VA The units may be either single-phase or three-phase
and are used as part of filter circuits and for current limiting
applications.
BACKGROUND OF INVENTION:
The method usually used to construct these reactors is
to place coils constructed of insulated conductors around the legs
of laminated steel cores of conventional C-, U- or E-shape. The
laminated steel structures which form the magnetic path of the
reactor may or may not have an air gap in order to linearize the
lnductance. Such reactors are bulky and difficult to cool and
difficult to cool uniformly. Furthermore, a considerable inventory
of iron-steel laminations is required if a variety of sizes of
reactors is to be produced. Also, in the conventional reactors
it is difficult if not impossible to optimize the shape and design
of the reactor for each of various different applications.
For examples of what is known in the prior art with regard
to the present invention, reference may be had to the following:
Powdered Core:
Canadian Patents 1,106,926 issued November 8, 1981 to
Nippon Konzoku Co, Ltd.
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895,781 issued March 21, 1972 to N. V. Philips'
Gloeilampenfabrieken;
772,131 issued November 21, 1967 to The International
Nickel Company of Canada, Limited;
510,769 issued March ~, 1955 to N. V. Philips'
Gloeilampenfabrieken;
238,555 issued March 11, 1924 to International Western
Electric Co. Inc.;
343,199 issued July 17, 19~4 to Radio Corporation of
America;
404,935 issued May 19, 1942 t~ C. Larenz Aktienyesell-
schaft;
428,569 issued July 3, 1945 to Johnson Laboratories Inc.
Coil Embedded in Powdered Core:
Canadian Patents 674,649 issued November 26, 1963 to
Serge Blanchi, Le Vesinet, S ~ O, and Roger Lacour;
239,901 issued May 6, 1924 to The Radio Service
Laboratories, Inc.;
765,130 issued August 8, 1967 to Peter A. Klaudy;
United States Patent 3,201,729 issued August 17, 1965
to Serge Blanchi and Roger Lacour.
Current Limitin~ Reactor Coil Embedded in Sand:
Canadian Patent 291,951 issued August 6, 1929 to ~ondit
Electrical Mfg. ~orporation.
Liquid Cooled_Inductive Devices:
Canadian Patents 1,052,875 issued April 17, 1979 to
Tioxide Group Limited;
1,007,311 issued March 33, 1977 to Westinghouse
Electric Corporation;
1,005,537 issued February 15, 1977 to Allmanna
Svenska Elektriska Aktiebolaget;
1,029,450 issued April 11, 1978 to ASES Aktiebolag,
Sweden;
819,280 issued July 29, 1969 to Alsthom-
Savoisienne, Saint-Ouen;
818,748 issued July 22, 1969 to Siemens-
Schuckertwerke Aktiengesellschaft;
715,198 issued August 3, 1965 to Epsco, Incorporated;
613,948 issued February 7, 1961 to Allmanna
Svenska Elektriska Aktiebolaget;
493,554 issued June 9, 1953 to The Ohio Crankshaft
Company;
448,007 issued April 20, 1948 to Radio Corporation of
America;
417,262 issued December 21, 1943 to Induction ~eating
Corporation;
436,985 issued September 17, 1946 to Edward G. Budd
Manufacturing Company.
239,901 issued May 6, 1924 to The Radio Service
Laboratories, Inc.
United States Patents 3,946,349 issued March 23, 1976 to
The United Sta-tes of America as represented by the Scretary of the
Air Force;
2,782,386 issued February 19, 1957 to The Ohio Crankshaft
Company.
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The process of embedding coils in an iron powder mass
using a binder like epoxy has been used previously, but has be~n
applied exclusively to reactors and transformers with small KVA
capacities. Examples of the, same are found in the foregoing
United States Patent 3,201,729 and Canadian Patents 674,649 and
239,901. In all of these cases, no provision is made to extract
the heat from either the windings of the device or from the core
and thus the method is limited to devices having a small capacity.
Additional prior art discloses the use of pot cores which are
assembled around small windings wound on bobbins to form both
high-frequency reactors and high-frequency transformers. The
pot cores themselves are formed from ferrite which are formed
under great pressure and sintered. The maximum size available
is a diameter approximately three inches. Once again, these
devices are only useful to form reactors and transformers of
very low KVA since there is no provision for cooling the devices
except on their external surfaces.
SUMMARY OF INVENTION:
One object of the present invention is to substantially
reduce the weight and size of the reactor relative to a conventional
reactor having the same capacity.
Another object of the present invention is to provide a
reactor design which can be made in various shapes and sizes with-
out engaging in elaborate and/or expensive manufacturing tech-
niques.
A further object of the present invention is to dispense
with the use of conventional laminated iron-steel core structures
while at the same time providing a reactor of superior quality.
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A still further object cf the present invention is to
provide a low-loss liquid-cooled reactor of large capacity, for
example, in the range of 10 KVA to 30 ~VA on a 60 cycle basis.
Summary of Invention:
In keeping with the foregoing objects, there is provided
in accordance with one aspect of the present invention an elec-
trical reactor having coils constructed of a hollow insulated con-
ductor and embedded in a solid core made of powdered metal and a
binding agent therefore, said hollow conductors providing means
for circulating a cooling fluid therethrough.
In accordance with another aspect of the present inven-
tion there is provided an iron core reactor having at least one
coil formed from a hollow, insulated, low-loss conductor embedded
in a powdered, metal, rigid core. The coils are preferably water-
cooled and formed from a low-loss water-cooled conductor described
in more detail hereinafter and illustrated in the accompanying
drawings.
Reactors of the present invention are substantially
smaller and lighter compared to conventional iron core reactors
of comparable capacity. The reactors of the present invention
are also less expensive to construct than conventional iron core
reactors having cores made of laminated steel.
In the reactors of the present invention the liquid
in the coils cools not only the conductor but the core as well,
and they overcome the problem of having to stock iron-s-teel
laminations of various shapes and sizes to build reactors of
different sizes. Since the core is made of a metallic powder and
binder therefore, the cores for each design may be op~imumly
shaped as each unit is designed and built in optimum form.
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Forming the core of powdered metal and a binder th~refor~
permits locating taps if required at any point and it is even
possible to obtain partial turns by bringing the tap lead out
through the sides of the unit. When one or more units is en-
capsulated in the same container, for example, in three-phase
units, the coupling between the units is small since each
coil is surrounded by the powdered metal.
LIST OF DRAWINGS:
The invention is illustrated by way of example with
reference to the accompanying drawings, wherein:
Figure 1 is a top plan view of one embodiment of the
reactor provided in accordance with the present invention;
Figure 2 is a vertical sectional view taken along line
2-2 of Figure l;
Figure 3 is a top plan view of another embodiment of
a reactor provided in accordance with the present invention;
Figure 4 is an elevational sectional view taken
essentially along line 4-4 of Figure 3;
Figure 5 is a vertical elevational view illustrating
a minor modification to the reactor;
Figure 6 is a top plan view of Figure 5;
Figure 7 is a vertical elevational view illustrating
another modification;
Figure 8 is a. top plan view of Figure 7;
Figure 9 is a graph illustrating the characteristics
of a reactor provided in accordance with the present invention;
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Figure 10 is a top plan view illustratiny further modi-
fications;
Figure 11 is a vertical sectional view taken essentially
along line 11-11 of Figure 10;
Figures 12-18 are various views illustrating different
embodiments of low-loss liquid-cooled conductors for the reactors
disclosed in the foregoing embodiments and in which
Figure 12 is an elevational view of one form of
conductor;
Figure 13 is a right hand elevational view of Figure 12;
Figure 14 is similar to Figure 13 illustrating modifi-
cations to the conductor;
Figure 15 is similar to Figures 13 and 14 illustrating
further modifications;
Figure 16 is similar to Figures 13-15 inclusive, but
illustrating a further modification;
Figure 17 is a side elevational view of a portion of
a length of a conductor; and,
Figure 18 is an end elevational view of Figure 17.
Referring to the drawings there is illustrated in
E'igures 1 and 2 an electrical reactor having a coil 10 embedded
in a solid core 20. The coil 10 is wound using one or more
insulated, hollow conductors 11 which may be copper tube or a
special low-loss liquid-cooled conductor described hereinafter
with reference to Figures 12-18 inclusive. The coil 10 has
leads 12 and 13 which, in the embodiment illustrated in Figures
1 and 2, project upwardly from the reactor but obviously, and as
will become more apparent hereinafter, may be located at any
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position, for example, radiate outwardly from the reactor.
Furthermore, they may termina~e at any peripheral location
relative to the coil permitting use of fractional turns should
the same be necessary. The coil 10 and leads 12 and 13 therefrom
are provided with insulation 1~ to prevent electrical contact
between the conductors 11 and the core 20.
The core 20 is made from metal powder and a binding
agent, the metal being preferably iron but may be other metals
or mixtures thereof providing suitable characteristics for an
electrical induction apparatus. The binder for the metal powder
is preferably an epoxy resin, but obviously, other suitable
binding agents may also be employed.
The reactor is made by winding the hollow copper tube
or special low-loss liquid-cooled conductor into a cylindrical coil
whereafter water connections 15 and electrical terminals 16 are
added. The conductor is insulated on the outer surface thereof
to prevent contac-t between the conductors wound into the coil.
The completed coil and its leads are lightly encapsulated, for
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example, in a ~}b~es~ar~ tape dipped in epoxy resin designated
by the reference numeral 14 in order to isolate the coil from
the iron powder core which is later added. After the encapsu-
lated coil is cured it is placed inside a tubular form 30 made
31~s j'`l'b re
-- 1 ' of, for example, fibrcgl~cs, and a mixture of iron powder and
epoxy is tapped or rammed into place around the coil so as to
completely encapsulate the coil. If required, the core may be
provided with an air gap 21 readily formed by using a disc-
shaped, non-me~allic filler piece of required thickness placed
inside the coil when the iron powder/epoxy mixture is partially
in place.
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Since the core is formed from a powdered mixtu~e the
leads 12 and 13 can be brought out at any position on the unit
as previously mentioned, for example, out of the top as illus-
trated or through the circular side of the unit.
The leads 12 and 13 are provided with suitable couplings
15 for connection to a fluid cooling source circulated through the
coil during operation of the device. The cooling fluid is pre-
ferably a liquid, such as water, but obviously any cooling fluid
may be utilized.
After the iron powder resin mixture has been appropriately
rammed into place to encapsulate the coil the unit is then oven-
cured. After curing, if desired, an insulating layer 40 may be
added to the top of the unit to isolate the terminals away from
the iron core. The insulating layer 40 may be any suitable
material, for example, an air-curing plastics material and if
desired to prevent oxidation of the iron core, the unit can be
completely coated with a moisture impervious material.
The size and shape of the coil and the size and shape of
the iron powder encapsulation is chosen to optimi7e the design of
the unit in terms of cost and/or size. In particular, the dimen-
sions designated A, B and C are so related that the magnetic flux
density in the three locations is approximately equal. This pre-
vents one part of the core from going into saturation before the
main body of the core, thereby using the material in an optimum
way. Tests conducted on a unit constructed in accordance with
the foregoing have been found not to saturate nearly as easily
as a normal reactor having a laminated iron core.
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The unit may be provided with lifting and mounting
brackets 50 which may be placed in the mold before the mixture
of iron powder and epoxy is added. The lifting brackets 50 are
L-shaped straps of, for example, steel, secured to the form ~s by
bolts 51 or other suitable fastening means. Each mounting bracket
has respective legs 52 and 53 each provided with an aperture 54
therein.
A more complex embodiment of the invention is illustrated
in Figures 3 and 4, Figure 4 being a cross-sectional view of a
three-phase reactor. This three-phase reactor unit is contructed
in exactly the same manner as the single-phase unit described in
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the foregoing except that the form or ~ibrcgla33 tube or cylin-
drical casing 30 is much longer and the three coils 10 are encap-
sulated successfully in the iron powder epoxy mix. The individual
phases of a-~ree-phase system have low interface couplin~s
as each phase is surrounded with an iron path. It should be
noted that the thickness of the iron powder between the phases
(distance A in Figure 4) may be made exactly the same size as the
thickness of the iron path at the top and bottom of the three-
phase reactor, i.e., thickness B in Figure 4 since the flux in
all o~ these regions is identical. This is the result of the fact
that currents in the three phases are separated by 120 electrical
degrees.
Referring to Figures 5 and 6 there is illustrated
therein a metal supporting structure 60 at each of opposite ends
of the reactor unit. The metal supporting structures 60 are
spiders consisting of a plurality of arms 61 (four being illus-
trated) radiating outwardly from a central hub 62. The outer end o~
the arms are bolted as at 62 to the tubular outer f~rm 3~ in ~rder
to form a strong integrated structure. The metal supporting
structures 60 are convenient for very large and heavy react~r
units. The completed reactor unit may be mounted either verti-
cally as illustrated, that is with the axis of the cylinder
structure in the vertical direction or alternatively in the hori-
zontal position.
For smaller alterna-ting current reactor units and even
for quite large DC smoothing reactors the water circulating
through the coil is able to remove both the heat generated by the
coil and the heat generated by the losses in the iron powder mag-
netic structure. However, in large a1ternating current units it
may sometimes be necessary to add auxiliary coaling to remove
heat energy from the iron powder core itself. Figures 7 and 8
show a typical arrangement using copper tubing~ as seen therein~
a bifiler type of coil 70 is used in order to keep the voltages
generated at the ends of the cooling tubes small by preventing
the formation of large loops which would enclose a significant
amount of flux.
As previously mentioned, an air gap 21 as shown in
Figure 1 may be incorporated into the design. In any case,
because of the dis~rete nature of the iron particles forming
the core and of their isolation from each other due to the epoxy
resin the reactor as formed according to the method described in
the foregoing have a distributed air gap incorporated in the
magnetic structures. This tends to make their characterlstics
very linear as may be seen by a typical curve shown in Figure 9.
As a result o~ this there is a significant flux leakage from the
iron powder structure which may cause ~roblems when the reactor
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is used in alternating current circuits and are placed close to
conducting materials such as enclosures In order to prevent this,
another embodiment of the invention is illustrated in Figures 10
and 11. In this embodiment strips 80 of laminated core steel are
grouped together and located at selected spaced apart positions
around the periphery of the reactor unit. Because of their much
higher effective permeability and therefore flux density capacity
they are able to capture and con-tain most of the leakage flux and
prevent it from entering surrounding structures. The groups of
laminated strips are separated one from the other by iron powder
and epoxy mixture designated 2OA and which is part of the powdered
iron core.
The low-loss liquid-cooled conductor for the coil is
illustrated in Figures 12-18 inclusive. Referring to the same
there is illustrated in Figures 12 and 13 a plurality of electrical
sub-conductors 100 of solid cross-section and preferably either
circular or trapeæoidal in cross-sectional shape cabled in unilay
spiral fashion over a hollow, generally circular in cross-section,
cooling tube 102 through which a fluid or liquid coolant such as
water may be circulated-.- The cooling tube 102 may be made of
metal such as copper or stainless steel or may be of a non-
electrical conducting material such as plastic, for example
TEFLON~. The sub-conductors 100 are generally metallic and
preferably copper or aluminum. The choice of sub-conductor
material and cooling tube material depends upon the application.
For low frequency applications, i.e., DC or line frequency 50 or
60 hertz, copper conductors over a coppex cooling tube may be used.
For intermediate frequencies of the order of several hundreds of
hertz, copper or aluminum sub-conductors over a stainless steel
cooling tube may be used to reduce the eddy losses in the cooling
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tube. For higher frequencies of the order of ki,lohertz ïn above
or where very low eddy losses are required, copper or aluminum
sub-conductors are wound over a non-conducting thermoplastic
material such as TEFLON~.
The sub-conductors 100 are electrically insulated from
each other by a coating 103. The fact that the conductors are
cabled in spiral fashion around the cooling tube 102 they are
effectively continuously transposed so that they share the total
current equally. The entire assembly is coated with an outer
insulation layer 104 which may be applied by winding a filament
material around a conductor or by extruding an insulating thermo-
plastic or thermosetting material over the assembly.
In certain applications the apparatus size and/or
configuration and the frequency of operation may mean that even
with the arrangement of sub conductors 100 described hereinabove,
the eddy losses may be unacceptably large. In such circumstances
the sub-conductors 100 may themselves be sub-divided into smaller
sub-conductors 106 as shown in Figure 14. The number and size of
the sub-conductors may be selected to make the eddy current losses
as low as is required within practical limits. The sub-conductors
106 may be transposed by bunch cabling or by regular cabling and
then by roll forming into trapezoidal segmental shapes either
before they are wound over the cooling tube 102 or while they are
being wound over the coolirlg tube.
In an alternative embodiment illustrated in Figure 15
a second layer of sub-conductors 107 is cabled over the ~irst
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layer 100 before the insulating material 104 is a~i4~. ','he
sub-conductors in both layers are insulated individually and
the sub-conductors may be further sub-divided into insulated
strands as explained above to further reduce eddy losses.
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A further, more complex embodiment, is illu trated in
Figure 16 wherein there is illustrated a composite cable 110
comprising seven sub-cables 109, each of which is fabricated as
described in the foregoiny with reference to Figures 13, 14 or
15. The composite cable 110 is formed by spiralling six outer
sub-cables 109 about a central sub-cable lO9a. If desired,
another layer (not illustrated) of 12 sub-cables 109 may be
unilayed over the seven sub-cables in the conventional ~ay of
making cables. The entire assembly is insulated with a layer
108 of insulating material as hereinbefore described. In having
the insulation layer 108, the layer 104 about each of the sub-
cables 109 may be omitted if desired.
As an alternative to the composite cable illustrated
in Figure 16, a large flat cable 111 may be used and which is
illustrated in Figures 17 and 18. The large flat cable 111
comprises a plurality of sub-cables 109 continuously transposed
without the use of a central core cable. The cable 111 is roll
or otherwise formed, after cabling to provide the flat shape as
seen in Figure 18. The flattened form of cable provides an
improved space factor and because of the continuous transposition
eddy current losses are very low.
There are a number of beneficial characteristics de-
rived from the invention described in the foregoing. The reactors
may be made small, light and less expensively than conventional
iron core reactors made from laminated steel. The units are very
efficient because of low core loss resulting from the use of iron
powder and special low-loss cable described with reference -
~Figures 12-18. The liquid in the coils cools not only the --c~^
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ductor, but also the core in all units except those which may
be exceptionally large in which case additional cooling is provided.
Because of the distributed air gap which is also a result from the
use of the powdered iron core, the units have a very linear
characteristic and saturate very slowly. Reactors of all possible
shapes and sizes can be readily constructed without having to
carry a large amount of iron core laminations as is required for
conventional reactors. The cores for each design may be optimumly
shaped since each unit is designed and built in optlmurn form.
~hen required, the units are shielded by the use of thin core
steel laminations in which case the resulting units can be placed
very close to metal walls of enclosures without causing any over-
heating problems. The units are inheren~ly very strong and not
easily damaged by short circuit currents. If taps are required,
the unit may be tapped at any point. It is also possible to
o~tain partial turns by bringing the tap leads out through the
sides of the unit.
