US2547045A - Means for cooling magnetic cores of electrical apparatus - Google Patents

Description

J. -r. SABOL 2,547,045

MEANS FOR COOLING MAGNETIC CORES OF ELECTRICAL APPARATUS April 3, 1951 2 Sheets-Sheet 1 Filed Dec. 4, 1947 Fig. 2 INVENTOR.

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AfTO/PNEK J. 1-. SABOL April 3, 1951 MEANS FOR COOLING MAGNETIC CORES OF ELECTRICAL APPARATUS 2 Sheets-Sheet 2 Filed Dec. 4, 1947 INVENTOR. Jon/v SAEDL A TTORNEX Fig; 5

Patented Apr. 3, 1951 MEANS FOR- COOLING MAGNETIC CORES OF ELECTRICAL APPARATUS John T. Sabol, Cleveland, Ohio, assignor to The Ohio Crankshaft Company, Cleveland, Ohio Application December 4, 1947, Serial No. 789,620

6 Claims. (Cl. 175-356) The present invention pertains to electrical transforming equipment having E-shaped magnetic cores and more particularly 'to electrical transforming equipment wherein a considerable amount of heat is generated within the center leg of the magnetic core. The invention is particularly-well adapted to an electrical transformer for high frequencies although it will be appreciated that the invention is not limited to such specific uses.

' Maximum permissible loading of a transformer is limited entirely by its temperature. Sinceit has no moving parts its life depends upon the life of the insulation, insulation deterioration being a function of temperature and time. Maximum temperatures usually occur in the laminations of the center leg of the E and from experience should not exceed 250 F. for continuous operation with conventional core plating materials 'and insulation. The temperature of this center leg thus definitely limits the maximum loading of the transformer and establishes the percentage of time during which load can be applied. For instance, with a transformer having a 4" x 4" center le and a 5 turn primary, tests have shown that a duty-cycle ofonly 21% can be maintained when 220 volts at 10,000 cycles is applied to the primary, i. e., power can be applied for 13. seconds during each minute Without exceeding the 250 temperature. When 440 volts at 10,000 cycles is applied, the duty-cycle drops to 6% or 4 seconds on and 56 seconds oif." Under such conditions, a large amount of time is thus wasted or a much larger transformer is required. Such larger transformer is not only more expensive to construct but requires a large amount of space which frequently is diilicult to provide in many installations where a compact structure is necessary.

Artificial cooling of this center leg has proven to, be a difficult problem. Because of the coil windings, circulation of the air over the center leg is restricted. No water-cooledlamination was known which, when interleaved with the magnetic laminations, would provide satisfactory cooling and rapidly remove the heat developed.

Accordin ly, the chief object of this invention is to provide a transformer core having new and improved means for cooling its laminations. A further object is to provide a transformen core having novel cooling means which can be readily assembled with the laminations. An additional object is to provide improved means for controlling a rate of flow ofheat into the cooling means of a transformer. A still further object is toprovide improved coolingmeans for a transformer as will permit the transformer to bereadlly' assembled. Another object is to provide an l-shaped laminated core of high powerca-rrying capacities for electro-magnetic apparatu which canbe constructed inexpensively and which occupies a greatly reduced space. Yet another object is to provide an E-shaped, core-type transformer having an improved duty cycle.

Another object of theinvention. is the provision of a new and improved cooling lamination for E-shaped transformer cores, the edges of the center leg having interconnected cooling tubes associated therewith so that cooling fluid may be continuously flowed to, along and away-from the edges from one end thereof to provide a maximum of cooling therefor.

Other and more specific objects will become apparent upon an understanding of the preferred embodiments of the invention described hereinafter taken in conjunction with the attached drawings which form a part hereof and wherein:

Figure l is a perspective view partly in section of a transformer core showing a preferred embodiment of the invention.

Figure 2 is an elevational view partlyin section of a cooling lamination used in the core shown in Figure 1.

Figure 3 is a fragmentary sectional viewon the line 33 of Figure l.

Figure 4 is a view similar to Figure 1 showing a modification of the preferred embodiment.

Figure 5 is an elevational view of a cooling lamination used in the embodiment shown in Figure 4.

Referring now to the drawings, Figure 1 shows a water cooled transformer core which comprises a main or winding supporting portion A and a keeper or I bar portion B embodying the present invention. The portion A is generally E-shaped when viewed from the side, and comprises a plurality of E-shaped laminations H, each having a base 10, outer legs 12 and I3, and a center leg [4, thelegs extending for an equal distance per.- pendicularly from the base ill in spaced parallel relationship. The laminations H are stacked in aligned relationship to a considerable thickness to provide the assembled Winding supportin portion A. The winding is normally positioned on the center leg [4. The I or keeper bar portion B comprises a plurality of rectangularly shaped laminations I6 stacked in aligned relationship to the same thickness as the portion A. The keeper bar B, as shown, is disposed across the ends of the legs l2, l3 and I4 and in abutting relationship therewith. An insulating spacer (not shown) may be provided therebetween if desired. The thickness and the actual dimensions of the laminations II and IE will depend upon the use to which the transformer will be put, the, frequency, and the amount of power which it must carry, All'of the design factors are known to those skilled in theart. The material from which thelaminations II and I6. are made may be of anygrade of magnetic material although-it; has been found sistance to its flow. the cooling plates are made may be as desired 3? that with the invention a lower grade of magnetic material may be employed with equivalent results.

Since high frequency alternations of the flux induce high frequency current in the laminations of all members of the magnetic circuit and because of certain unavoidable core losses, these laminations rise in temperature, particularly those in the center leg it, because the winding assembly prevents any circulation of air over these laminations and thereby reduces cooling by convection. This rise in temperature limits the continuous duty rating of the transformer. In the preferred embodiment selected groups of the iron laminations are replaced by suitable shaped he'atconducting plates 20 of a metal preferably having higher heat conducting qualities than the conventional core materials.

The present invention contemplates a method and means of preventing, controlling or limiting this temperature rise whereby the continuous kva. rating of the transformer may be increased without changing or enlarging the physical dimensions of the core. The cooling plates 2!] are similarly shaped to the laminations H and comprise a base 2 i, outer legs 22 and 23, and a center leg 24, the legs all extending in spaced parallel relationship fromand perpendicular to the base 2]. The cooling plates 28 are preferably of the identical size to the laminations I I, so that when interleaved with or substituted for some of the laminations l i, all edges will be flush.

In the embodiment of the invention shown in Figures 1 to 3, a passage 21 is formed internally of the periphery of the plate 29, and going from left to right, extends across the end and thence down the inner edge of the leg 22, across the upper edge of the base 2|, up the left edge, across the end and down the right edge of the center leg 24, across the upper edge of the base 25 and thence up the left edge and across the end of the leg 23. Cooling medium flowing through this passage is thus in contact with a major portion of the periphery of the plate and particularly on three sides of the center leg 2% where the heating problems. of the transformers are most pronounced. The passage 21 may be formed in any desired. manner]. In the preferred embodiment, thesolid portion of the cooling plate 28 has the dimensions, along which the cooling passages are to extend, reduced and a plurality of short lengths of tubing 26 having a squareouter cross section are, ,then suitably brazed or otherwise affixed to theseedges as shown. The ends of the tubing befor e .,assembly are mitered so that when in the position shown provide a continuous internal passage. Ifdesired, a channel or groove could 'be milled or otherwise cut in the edges of the terial suitably brazedor soldered in position. The

passages could also be formed internally of the plate 20, i. e., away from the periphery.

The thickness of each cooling plate 28 may be as desired depending upon the amount of heat which must be dissipated from the internal portion of the transformer core. Preferably it should have a thickness as thinas possible but such that the area of the passage 27 may be sufficient to carry the cooling medium without excessive re- The material from which but are preferably made'from material having high heat conductivity such as copper or silver.

"Copper would, of'course, be normally used because ofits'lower cost. 3 c

In Figure 1, two cooling plates 20, are shown assembled with the transformer core. The passages 21 of these laminations maybe connected in series whereby the cooling medium enters one of the passages, flows the length thereof, enters the other passage and flows the length thereof before being discharged to the drain or otherwise. It is, however, preferred that the passages be connected in parallel as shown to provide a maximum cooling effect for the transformer core and particularly for the center leg l4. Pipes 32 and 33 are shown provided for this purpose.

No cooling plates are shown in the keeper bar B although it should be appreciated that if undesirable heating occurs in this member, a cooling plate of similar construction to that shown in Figure 2 but of a shape corresponding to the shape of laminations "5 could be provided. Alternatively, the legs of the cooling plates 20 could be extended into the keeper bar as shown in the embodiment of the invention shown in Figure 4.

In the alternative construction shown in Fig ures 4 to 5, like parts have been given like numbers and similar parts have been given the same number with a prime mark added. The laminations ll are identical to the laminationsshown in Figure l and need not be describedfurther. In the preferred embodiment, the edges of the cooling plates were flush with the edges of the laminations l I. In this embodiment the base 2| and the outer legs 22, 23 have a width greater than the laminations H and their edges extend there.- beyond a substantial distance providing elonfgated lugs 30, 3|, 32 respectively which extend as shown entirely along the outer perimeter of the E-shaped core. Generally the cooling plates in this embodiment may be of a narrower or thinner construction as no provision must be made for an internal cooling-medium passage. Also the legs 22, 23, 24' are lengthened so as to eX- tend upwardly through and beyond the keeper bar B.

The center leg 2% is provided with laterally extending lugs 34 and 35 of a length less than the length thereof, providing a space 31 and 38 at the lower and upper ends respectively of the leg 24, as viewed in Figure 5.

As shown when the transformer core is assembled, edges of the cooling plate 20 project outwardly of the edges of the magnetic core substantially around the entire edge of the core. The purpose of the lugs is to provide a surface externally of the core to which tubing may be soldered or brazed. The tubing is to provide a continuous passage of a cooling medium.

To assemble the transformer core shown in Figure 4, the E-shaped cooling plates ZBfQand the laminations ll are assembled as showuany number of cooling plates desired being usedfjTh'e electrical windings (not shown) are then assembled on the center leg. An'irregularly shaped tubing 46 of integral or built up construction and having preferably a rectangular cross section is then brazed or soldered to the lugs extending beyond the core. It is to be noted that portions of the length of tubing &6 pass through the spaces 31 and'38. The keeper bar 13 is then assembled by sliding the individual laminations in lengthwise or sidewise,=as thev case may be. .As-in the preferred embodiment, an insulating spacer 48 may be provided between the ends of the lamination legs and the keeper bar laminations-l6. In

the embodiment shown, short lengths of tubing are employed, each having mitered ends which abut and are brazed together when assembled.

b It will be appreciated that the tubing 46 could be formed in one continuous length and bent to form the corners.

It will be noted from an examination of the drawings that the sides of the tubing adjacent to the edges of the laminations Ii and I B are spaced slightly therefrom. Such a spacing prevents the tubing 46 from shorting or providing an electrical contact between the individual laminations H and Hi. It will be appreciated that in normal transformer construction the laminations ordinarily have sufficient scale or other foreign material on their sides to provide a fairly high electrical resistance therebetween which prevents undue leakage currents from flowing between the individual laininations.

In the preferred embodiment, the cooling plates 20 have dimensions identical with the laminations II and the entire transformer core may be assembled in the conventional manner and after assembly suitable water or other cooling medium connections made to the water passages where it extends laterally from the edge of the core.

It will be appreciated that core clamps or otherwise can be provided to maintain the laminations in firm side by side or abutting relationship. Such clamps are not shown in the drawmgs.

It has been found for a given size transformer that substituting the cooling laminations shown does not materially affect the operation of the transformer even though there is a less amount of iron or magnetic material in the core. In fact, because of the cooling ei fect obtained, the power rating of a transformer may be increased by 200% or 300% as the one factor, that is, internal heating which limited the rating of a transformer before, is no longer a problem. The cooling plates themselves while being somewhat thicker than the conventional lamination, do not materially interfere with the operation of the transformer. The electrical resistance of the cooling plates if made of copper, is much lower than that of the magnetic laminations and, therefore, the FR loss is much less.

In accordance with the patent statutes, the preferred embodiments of the invention have been described as a means of illustrating the invention. It will be appreciated that modifications or alterations in the structures shown will occur to others upon the reading and understanding of this specification. It is my intention to include all such modifications and alterations insofar as they come within the scope of the appended claims.

Having thus described my invention, I claim:

1. An electrical transformer having an E- shaped core member which tends to heat when in use, said member comprising a plurality of juxtadisposed magnetic laminations, each having a plurality of spaced parallel legs including an intermediate leg adapted to receive an electrical winding, the space between said legs defining a winding window, means for cooling at least said intermediate leg comprising a plurality of cooling laminations of relatively high heat conductivity with respect to said magnetic laminations interleaved with at least the center leg of said magnetic laminations, said cooling laminations including hollow tubes attached to exposed edges thereof adjacent said winding window and means interconnecting the ends of said tubes in a continuous manner, whereby a cooling fluid may be continuously flowed along said exposed edges to carry away heat generated in said intermediate leg of said magnetic laminations and conducted to said cooling laminations.

2. The combination of claim 1 wherein said magnetic laminations extend beyond said cooling laminations at all sides and wherein said tubes extend continuously at least over one exposed edge adjacent said winding window across the end and over the other exposed edge adjacent said winding window of the center leg of the cooling laminations.

3. The combination of claim 1 wherein the exposed edges of the center leg of the cooling laminations extend beyond the exposed edges or" the center leg of the magnetic laminations and said cooling tubes are attached to said extending portions.

4. The combination of claim 1 wherein the exposed edges of at least the center leg of said cooling laminations extend beyond the exposed edges of the center leg of the magnetic laminations, said extending portions having a length less than the length of the center leg or" the magnetic laminations, and said hollow tubes passing through the space formed thereby from one exposed edge of one cooling lamination to another exposed edge of another cooling lamination.

5. The combination of claim 1 wherein said core includes a keeper bar comprised of a plurality of juxtadispcsed laminations extending across the ends of said legs and said cooling laminations extend into said keeper bar and are interleaved with the magnetic laminations thereof.

5. An electrical transformer having an E- shaped core member which tends to heat when. in use, said member comprising a plurality of juxtadisposed magnetic laminations, each having a plurality of spaced parallel legs including an intermediate leg adapted to receive an electrical winding, the space etween said legs defining a winding window, means for cooling at least said intermediate leg comprising a plurality of cooling laminations of relatively high heat conductivity with respect to said magnetic laminations interleaved with at least the center leg of said magnetic laminations, said cooling laminations having passages associated with the exposed edges thereof adjacent said winding window and means interconnecting the ends of said passages in a continuous manner whereby a cooling fluid may be continuously flowed along said exposed edges to carry away heat generated in said intermediate leg of said magnetic laminations and conducted to said cooling laminations.

JOHN T. SABOL.

REFERENCES CETED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 513,420 Rowland Jan. 23, 1894 834,148 Lord Oct. 23, 1906 1,331,896 Brand Feb. 24, 1920 1,789,229 Gebhard Jan. 1931 1,790,906 Eckman 1- Feb. 3, 1931 1,819,481 Pearson Aug. 18, 1931 FOREIGN PATENTS Number Country Date 166,613 Great Britain July 28, 1921

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