CA1210464A - Iron powder encapsulated liquid cooled reactors - Google Patents

Abstract

A B S T R A C T

A low loss, liquid-cooled, large KVA reactor that includes a cylindrical coil wound from a hollow insulated conductor and embedded in a solid core made of powdered metal and a binding agent therefor. The conductor is preferably a low loss conductor and the entire unit is preferably enclosed in a moisture-impervious material.

Description

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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.

~4 895,781 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.

--` 3 Z~04~i4 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;

' .,~-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 ~210~

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 _71~s~ ,~ihf~
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 ~ ~J~5~ f ~'bre 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 - 12 -~
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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 - 13 ~

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 ~ ~G~
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.

Claims (11)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An electrical large KVA power reactor comprising at least one cylindrical coil wound from at least one hollow insulated conductor of high amperage capacity embedded in a solid core made of powdered metal and a binding agent therefor, said hollow conductor providing means for circulating a cooling fluid therethrough.

2. A reactor as defined in Claim 1, wherein said conductor is a low-loss conductor.

3. A reactor as defined in Claim 1, including an air gap in said core within said coil.

4. A reactor as defined in Claim 1, wherein said core is located in a cylindrical glass fibre sleeve in tight, intimate contact therewith.

5. A reactor as defined in Claim 1, including an additional fluid flow path through said core for use in cooling the same.

6. A reactor as defined in Claim 1, including additional strips of laminate steel core around said solid core.

7. A reactor as defined in Claim 6 wherein said strips of steel are arranged in groups at positions spaced apart from one another around the periphery of the core.

8. A reactor as defined in Claim 7 wherein the space between said groups is filled powdered metal and binding agent therefor.

9. A reactor as defined in Claim 1 including a metal spider at each of opposite ends thereof.

10. A reactor as defined in Claim 1 wherein said coil is encapsulated in an insulating material.

11. A reactor as defined in Claims 1, 2 or 3 wherein said conductor comprises a plurality of sub-conductors cabled in unilay spiral fashion over a circular in cross-section tube.