US3295084A

US3295084A - Transformer having a magnetic core comprising a main flux path having one definite grain orientation and a shunt flux path having a different definite grain orientation

Info

Publication number: US3295084A
Application number: US417325A
Authority: US
Inventors: Clifford C Horstman
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1964-12-10
Filing date: 1964-12-10
Publication date: 1966-12-27
Anticipated expiration: 1983-12-27
Also published as: DE1538250A1

Description

- Dec. 27, 1966 c c. HORSTMAN 3,295,084

TRANSFORMER HAVING A MAGNETIC CORE COMPRISING A MAIN FLUX PATH HAVING ONE DEFINITE GRAIN ORIENTATION AND A SHUNT FLUX PATH HAVING A DIFFERENT DEFINITE GRAIN ORIENTATION Filed Dec. 10, 1964 2 Sheets-Sheet 1 INVENTOR WITNESSES JZW JK W Clifford C. Horsrmon Dec. 27, 1966 c. c. HORSTMAN 3,295,084

TRANSFORMER HAVING A MAGNETIC CORE COMPRISING A MAIN FLUX PATH HAVING ONE DEFINITE GRAIN ORIENTATION AND A SHUNT FLUX PATH HAVING A DIFFERENT DEFINITE GRAIN ORIENTATION Filed Dec. 10, 1964 2 Sheets-Sheet 2 l6 F|G.2.

22 B A l8 United States Patent 3,295,034 TRANSFORMER HAVING A MAGNETIC CORE COMPRISING A MAIN FLUX PATH HAVING ONE DEFINITE GRAIN ORIENTATION AND A SHUNT FLUX PATH HAVING A DIFFERENT DEFINITE GRAIN ORIENTATION Clifiord C. Horstman, Sharpsville, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa, a corporation of Pennsylvania Filed Dec. 10, 1964, Ser. No. 417,325 2 Claims. (Cl. 336165) iary or shunt magnetic circuit or flux path were attempted using cold roller magnetic sheet steel having the grains of the steel oriented in the direction of rolling. In these attempts to build a core of this type, at the point where the shunt magnetic circuit connected to the main magnetic circuit, in some of the devices the laminations of sheet steel were interleaved, in others, a transition piece was used to connect the shunt magnetic circuit to the main magnetic circuit. All of these devices were unsatisfactory since at the point where the flux passes from the main magnetic circuit into the shunt magnetic circuit, and vice versa, the fiuX had to travel in a direction transverse to the direction of orientation of the grains of the elec trical sheet steel. The direction transverse to the direction of orientation is a high reluctance path. This meant that the reluctance of the joints at the point where the shunt magnetic circuit connected to the main magnet cir cuit was very high. This introduced many objectionable characteristics into the core. It was impossible to determine the reluctance which the various paths of the core would have which made it impossible to build a satisfactory transformer usin the core with anticipated results. The joints between the main magnetic circuit and the shunt magnetic circuit had high reluctance because the flux had to travel tranverse to the direction of orientation of the grains of the magnetic steel, this caused hot spots which were objectable, since such hot spots would cause the insulation on the coils to rapidly deteriorate and destroy the transformer and furthermore the core had high loss and low permeability.

It is accordingly an object of this invention to provide an improved magnetic core made from grain oriented sheet steel comprising a main magnetic circuit or flux path having a shunt magnetic circuit or flux path attached thereto wherein the above objections of the prior art cores of this type have been eliminated.

It is another object of this invention to provide an improved magnetic core made from grain oriented sheet steel comprising a main magnetic circuit or flux path having a shunt magnetic circuit or flux path attached thereto wherein the flux always travels in the direction in which the grains of the magnetic sheet steel are oriented, which is the low reluctance direction of travel for the flux.

It is a further object to provide an improved magnetic core which has a plurality of flux paths of different reluctance values.

It is a further object to provide an improved magnetic core for a transformer which has a primary flux path and .a secondary flux path in shunt magnetic circuit relationship to the primary flux path.

ice

It is a still further object to provide an improved magnetic core adapted to be used with a primary coil and a secondary coil wherein said core provides a flux path of one reluctance value for the flux due to current flowing in the primary coil and a second flux path of another reluctance value for most of the flux due to current flowing in the secondary coil.

It is still another object to provide an improved transformer having primary and secondary windings and a primary magnetic circuit or flux path for the flux provided by the primary winding and a shunt magnetic circuit connected to the main magnetic circuit or flux path for providing a magnetic circuit for most of the fiuX due to the secondary winding if it reaches excessive values.

Other objects and advantages of this invention will be apparent from the following description, when taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a perspective view of a core provided according to this invention, with primary and secondary windings shown thereon;

FIG 2 is a second embodiment of the core shown in FIG. 1; with primary and secondary windings shown thereon;

FIG. 3 is a perspective view of the shunt magnetic circuit of the general type used in FIGS. 2 and 5,

FIG. 4 is a third embodiment of the core provided according to this invention with primary and secondary windings shown thereon; and

FIG. 5 is a fourth embodiment of the core provided according to this invention showing primary and secondary windings thereon.

Throughout the various figures of the drawings, like reference characters refer to like parts.

Referring to the drawings, FIG. 1 illustrates one embodiment of the improved magnetic core having a shunt circuit as provided by this invention. FIG. 1 shows a magnetic core 10. The magnetic core 10 is comprised of a pair of

core sections

12 and 14. The

core sections

12 and 14 are provided from magnetic sheet steel by winding the required number of layers of laminations to form a core loop. After the core loop has been wound to the required thickness, the core is cut as indicated at 16. The purpose of cutting the core is to enable placing of preformed windings thereon as will be explained hereinafter. The faces of the cut at 16 are worked by grinding and chemically etching to make the faces very smooth so that the

sections

12 and 14 of the core may be fitted back together so that joint at 16 will be a low reluctance joint. The cold rolled magnetic sheet steel from which the

core sections

12 and 14 are formed is preferably oriented in at least two dimensions, that is in the direction of cold rolling and in a direction transverse to the direction of rolling. In the specific embodiment shown in FIG. 1 the magnetic sheet steel from which the

core sections

12 and 14 is formed is oriented in three directions, that is, in the direction of rolling as indicated by the arrow A, transverse to the direction of rolling as indicated by the arrow B and perpendicular to the sheet as indicated by the arrow C. This type of multiple oriented magnetic electrical sheet steel is now commercially available.

The core 10 also comprises a shunt or auxiliary flux path provided by the member 18. The shunt or auxiliary member 18 is also made up of a plurality of laminations of cold rolled electrical sheet steel. In the embodiment shown in FIG. 1, the laminations from which the shunt element 18 is constructed are oriented in the direction of cold rolling only as indicated by the arrow D. The faces of the laminations of the shunt element D are also ground and chemically etched to make the ends of the laminations very smooth. The

points

20 and 21 where the shunt element 18 connects to the sides of the laminations of the

elements

12 and 14 are also ground very smooth and chemically etched so that the ends of the laminations of the shunt element 18 will make very good magnetic contact with the edges of the laminations of the

core elements

12 and 14. Before the

core elements

12, 14 and 18 are assembled into their final assembled relationship a primary winding 22 having terminals 23 is fitted onto one section of the el ment 12 and a secondary winding 24 having terminal 25 is fitted onto one section of the core section 14. Then the

core sections

12 and 14 are fitted together and the shunt circuit 18 is placed in position and a metallic band 26 is placed around the ,

core sections

12 and 14 and tensioned to provide a good joint between the

elements

12 and 14 at 16. Then this band 26 is clamped so as to maintain a constant tension on the joint between the

elements

12 and 14. Next, another metallic band 28 is placed around the shunt element 18 and tensioned to provide good contact between the ends of the laminations of the shunt element 18 and .the sides of the iaminations of the

elements

12 and 14.

When proper tension has been provided to the band 18, the band is clamped so as to maintain constant tension in the joints between the laminations in the

elements

12 and 14 and the ends of the laminations in the shunt element 18.

The

core elements

12 and 14 provide the main flux path for flux set up due to current flowing in the primary winding 22. It is seen that the magnetic circuit provided by the

core elements

12 and 14 for flux caused by current flowing in the primary winding 22 is shorter than the flux path provided by the element 12 and the shunt 18. This means that the flux path provided by the

core elements

12 and 14 has less reluctance than the flux path provided by the core element 12 and the shunt element 18. This means that most of the flux due to the current flowing in the primary winding 22 will flow through the magnetic circuit provided by the

core elements

12 and 14. On the other hand it is seen that the flux path provided by the core element 14 and the shunt 18 is shorter than the flux path provided by the

core elements

12 and 14. This means that the flux path provided by the core elements 14 and shunt 18 has less reluctance than the flux path provided by the

core elements

12 and 14. This means that most of the flux due to abnormal current flowing in the secondary winding 24 will travel the flux path provided by the core elements 14 and the shunt 18, rather than through the main core provided by the

core elements

14 and 12.

In some apparatus it is impractical to provide enough reluctance in the shunt element 18 by proportioning the length of the shunt element 18 relative to the flux path provided by the

core elements

12 and 14. In such instances where more reluctance is required in the shunt element 18, the physical length of the shunt element 18 may be kept reasonable by providing an air gap 19 in the shunt element 18. This air gap 19 may be filled with an insulating material such as micarta, glass or paper. The air gap 19 provides lumped reluctance in the shunt element 18. Under normal operating conditions most of the flux due to current flowing in the primary winding 22 and the secondary winding 24 will flow through the magnetic path provided by the

core sections

12 and 14, because of the high reluctance of the shunt element 18. However, if the current in the secondary winding should become abnormally high, such as happens when a short circuit occurs on the secondary side of the transformer, then most of the flux due to the high current flowing in the secondary winding 24 will be forced through the shunt element 18 and the current in the primary winding 22 will not rise to an abnormal value to overcome the flux due to the high current in the secondary winding 24. In fact, under these conditions the primary winding 22 and its magnetic circuit functions merely like a reactor and the current in the primary winding is limited to its normal value.

It is seen from the foregoing that the structure described as shown in FIG. 1 provides a magnetic core having a main flux path provided by the

core elements

12 and 14 of very low reluctance and also a shunt flux path provided by the shunt 18 which also has very low reluctance. The low reluctance of these flux paths is accomplished because as described hereinbefore the magnetic sheet steel laminations used in the

core sections

12 and 14 are oriented in such direction that all flux flowing in the main magnetic circuit provided by the core sections Hand 14 is always flowing the direction of orientation of theg'r'ains of the steel and the flux flowing in the shunt ci'rcuit is also always flowing in the direction of orientation of the grains of magnetic sheet steel in the shunt section. From an examination of FIG. 1 it is seen that in the core sections in the main magnetic circuit provided by the

core sections

12 and 14 when flux travels from the main magnetic core section into the shunt section 18 that regardless of wethe'r the flux is traveling perpendicular to the laminations, parallel to the direction of rolling, or transverse to the direction of rolling, that the flux is always traveling in the direction in which the grains of the steel are oriented, which is always a low reluctance direction. This structure provides a core having high permeabality with low watts loss.

A transformer as described in FIG. 1 will in effect be a current regulating transformer. The transformer provided according to FIG. 1 is especially desirable and has special utility in installations wherein short circuits frequently occur on the secondary winding. A particular application for this type transformer is found in the electrostatic air cleaning equipment where the plates or dust collectors of the air cleaner constitute the load on the secondary winding and frequent short circuits occur on these plates or dust collectors due to foreign matter passing through the air cleaners.

In the transformer illustrated in FIG. 2 as explained hereinbefore most of the flux due to the primary winding 22 flows through the magnetic circuit comprising the

core elements

12 and 14. Because this magnetic circuit is shorter and has less reluctance than the magnetic circuit provided by the core element 12 and the shunt 18. Also most of the flux due to current flowing in the secondary winding 24 flows through the magnetic circuit comprising the core element 14 and the shunt 18. This is because this magnetic circuit is shorter and has less reluctance than the magnetic circuit comprising the

core elements

12 and 14. In case of a short circuit on the secondary winding 24 high currents will be drawn and a large amount of flux will be set up due to the high current in the secondary winding. If this flux should flow through the primary winding this means that the current in the primary wind ing would normally increase to counteract the flux set up in the core due to current flowing in the secondary winding. However, in the normal core where a single core loop is used for both the primary and secondary windings, the current in the primary winding in order to produce flux to counteract the flux due to the high current in the secondary winding would rise so high and so fast that it would normally burn up the primary winding and destroy the transformer. However, in the transformer shown in FIG. 1, this is prevented because if a short should occur on the secondary winding to cause current in the secondary to rise abnormally and produce an abnormal amount of flux this flux would flow through the magnetic circuit provided by the core section 14 and the shunt 18 and would not pass through the primary winding 22 and therefore the primary winding current would not rise to a value high enough to burn out the primary winding 22.

In FIG. 2 the main magnetic circuit or flux path is shaped identical to that illustrated in'FIG. 1, however, the shunt circuit in FIG. 2 instead of being a C-shaped section as shown in FIG. 1 is merely a bundle of straight laminations fitted in between the C-legs of the

core sections

12 ,and 14.

In FIG. 2 the secondary winding 24 is fitted onto the shunt section 18. In the operation of the transformer built according to FIG. 2, it is seen that the flux due to current flowing in the primary winding will flow through the core section 12, through the shunt section 18 back through the primary winding 22. In this embodiment the secondary winding 24 is placed on the shunt element 18 so that most of the flux set up due to the current flowing in the primary winding 22 will link the secondary winding 24. This is true because the core section 12 and the shunt 18 is shorter and has less reluctance than the magnetic circuit comprising the

core section

12 and 14. This will force most of the flux due to the current flowing in the primary winding 22 to traverse the shunt 18 in the secondary coil 24. However, the magnetic circuit comprising the core section 14 and the shunt 18 is much shorter than the magnetic circuit comprising the core sections 12 and the shunt 18. Therefore, if the current in the secondary winding 24 should rise abnormally high, most of the flux due to the current flowing in the secondary winding 24 will flow through the magnetic circuit comprising the core section 14 and the shunt 18 and will not link with the primary winding 22 to cause the current in the primary winding 22 to rise abnormally high to counteract the flux due to the current flowing in the secondary winding.

FIG. 4 illustrates still another embodiment of the core and transformer as provided by this invention. In FIG. 4, the

core sections

12 and 14 are constructed from cold rolled magnetic sheet steel which is oriented in a single direction, that is, the direction of rolling as indicated by the arrow H. Also in this embodiment, the shunt element 18 is constructed from laminations of magnetic electrical sheet steel which is oriented in a plurality of directions. In the embodiment shown in FIG. 4 the magnetic sheet steel of the element 18 is oriented in the direction of rolling as indicated by the arrow E, in the direction transverse to the direction of rolling as indicated by the arrow F, and in the direction perpendicular to the sheets as indicated by the arrow G. In this embodiment, all of the joints between the

main elements

12 and 14 of the main magnetic circuit or core loop and between the shunt element 18 are ground and chemically etched to provide good electrical joints, the same as for the embodiments shown in FIGS. 1 and 2. Also, in this embodiment, after the

primary windings

22 and 24 have been placed on the

core sections

12 and 14 and the shunt element 18 has been placed in position between the

core sections

12 and 14, as illustrated in FIG. 4, a metal band 28 is placed around the

core sections

12 and 14 and properly tensioned and clamped to maintain proper tension on all of the joints of the core to provide low reluctance joints.

In FIG. 4 the main flux path provided for flux due to current flowing in the primary coil 22 is through the core section 12, through the section 30 of the shunt element 18, through the core section 14 and back through the winding 22. This is true because the magnetic circuit path through the core element 12, through the section 30 of the shunt 18, and through the core section 14 is the shorter flux path and has less reluctance than the flux path through the core section 12 and through the shunt element 18. From this it is seen that most of the flux set up due to current flowing in the primary winding 22 links with the secondary winding 24. However, the main path for flux due to current flowing in the secondary winding 24 will be through the core section 14, through section 30 of the shunt 18, and back through the coil 24. This is true because this path is much shorter and has much less reluctance than the flux path through the core element 14 through the section 30 of the shunt and through the core element 12. In this embodiment also, if a short circuit should occur on the secondary winding 24 which would cause abnormal flux in the core, this flux would traverse 6 the core section 24 and the shunt 18 and would not link with the primary winding 22 to cause the current in the primary to rise to abnormal value which often burns out and destroys the primary winding of the transformer.

It is :also seen in this structure illustrated in FIG. 4 that when the flux passes from the

main core sections

12 and 14 into the shunt and vice versa from the shunt into the main core sections, that the flux is always traveling in the direction of orientation of the grains of the magnetic sheet steel, which is the low reluctance direction of flux flow, because the

main core sections

12 and 14 are constructed from singly oriented steel which has the grains oriented in the direction of rolling, which is the direction in which the flux travels in the

main core sections

12 and 14, and that the shunt section 18 has the grains of the sheet steel oriented in the direction transverse to the direction of rolling and the direction perpendicular to the sheets, which insures that all fiux traveling from the main sections of the

core

12 and 14 into the shunt always travels in a direction of orientation of the grains of the sheet steel in the shunt 18, which is a low reluctance direction of travel of the flux. This construction also provides a core having low watts loss and high permeability.

FIG. 5 illustrates a second embodiment of the core described above for FIG. 4. This embodiment is identical to the embodiment of FIG. 4 except that the shunt element 18 is made from a stack of laminations of cold rolled electrical sheet steel oriented in the direction of rolling as indicated by the arrow E, in the direction transverse to rolling, as indicated by the arrow F and in the direction perpendicular to the sheets as indicated by the arrow G. Also, in FIG. 5, the secondary winding 24 is placed on the shunt element 18. In this embodiment it is also seen that the flux due to current flowing in the primary winding 22 flows through the core section 12 and through the shunt element 18 thereby linking the seconddary winding 24. However, the main flux path for the flux due to current flowing in the secondary winding is through the core element 14 and through the shunt element 18. The core element 14 and the shunt 18 provides a much shorter flux path than the core element 12 and the shunt 18; therefore, the flux path provided by the core element 14 and the shunt element 18 has much less reluctance than the flux path provided by the core element 12 and the shunt element 18 and therefore most of the flux due to current flowing in the secondary winding will flow through the core element 14 and the shunt element 18 rather than through the shunt element 18 and the core element 12. Consequently, in case of short circuits or other conditions where the current would rise abnormally in the secondary winding 24 flux due to this current will not link with the primary winding 22 to cause the current in the primary winding 22 to rise to an abnormal value which would destroy the transformer.

An air gap 19 is also illustrated in the shunt element 18, shown in the transformer of FIG. 4, and in the core section 14 for the transformers shown in FIGS. 2 and 5. The air gap 19 shown in these figures function the same as the air gap 19 explained hereinbefore for FIG. 1. In these figures the air gap 19 forces most of the flux under normal operating conditions to flow through the magnetic circuit linking the primary winding 22 and the secondary winding 24. However, if the current flowing in the sec ondary winding 24 should become abnormal, most of the flux due to this abnormal current in the secondary winding 24 would be forced through the shunt magnetic circuit and would not link with the primary winding 22. This limits the current flow in the primary winding 22 in case of short circuits or abnormal current flow in the secondary winding 24 and prevents the primary winding 22 from burning out under these conditions. The shunt element 18 used in the embodiments shown in FIGS. 2 and 5 is illustrated in FIG. 3. The shunt element 18 of FIG. 3 is built by stacking a bundle of straight laminations. However, it is understood that in the embodi- 7 ment of FIG. 3 the laminations of the shunt element 18 are grain orientated in only one dimension of the sheet, the direction of rolling; whereas, in the embodiment of FIG. 5 the laminations of the shunt element 18 are orientated in a plurality of directions, as explained hereinbefore.

It is emphasized that in all of the various embodiments, all abutting surfaces in all of the butt-joints are ground and etched so that the part of the core may be assembled with a minimum of reluctance in the joints due to the air gaps between the abutting parts.

From the foregoing description it is seen that this invention has provided an improved magnetic circuit or core for use with induction electrical apparatus comprising a main magnetic circuit or flux path and a shunt magnetic circuit or flux path wherein the core has high permeability and low watts loss: It is also seen that a transformer built with the core provided by this invention is essentially a current regulating transformer which has built in protection which will prevent the transformer from burning out or becoming damaged in case of abnormal rise of secondary current, such as happens when a short circuit occurs on the secondary.

It is also seen that this invention provides a magnetic circuit or core for use with induction electrical apparatus wherein the core has a main magnetic circuit or flux path with an auxiliary or shunt magnetic circuit or flux path attached thereto and all of the joints between the main flux path and auxiliary flux path are arranged so that the fiux is always traveling in a direction of orientation of the grains of the magnetic sheet steel from which the main flux path and auxiliary flux path are constructed, thereby providing a core with low rcluctance joints and a core which has high permeability and low watts loss.

Since numerous changes may be made in the abovedescribed embodiments of the invention without departing from the spirit and scope thereof, it is intended that all of the matter contained in the foregoing description and illustration shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. A transformer comprising a four sided main magnetic circuit for carrying flux, said main magnetic circuit being formed from laminations of magnetic sheet steel having a definite grain orientation, a primary winding for carrying current on one side of said main magnetic circuit, a secondary winding for carrying current on the opposite side of said main magnetic circuit from said primary winding, a shunt magnetic circuit connected to said main magnetic circuit intermediate said two winding sides, said shunt magnetic circuit comprising laminations of magnetic sheet steel having a definite grain orientation, the laminations of at least one of said magnetic circuits being grain oriented in at least two directions,

the'magnetic circuit from said primary winding through said secondary winding and back through said primary winding having less reluctance than the magnetic circuit from said primary winding through said shunt magnetic circuit and back through said primary winding, and the reluctance of the magnetic circuit from said secondary winding through said shunt magnetic circuit and back through said secondary winding being of such magnitude relative to the reluctance of the main magnetic circuit from said secondary winding through said primary wind-- ing that upon abnormal current flow in said secondary winding that most of the flux due to abnormal current flow in said secondary winding flows through said shunt magnetic circuit and back through said secondary winding.

2. A transformer comprising a four sided main magnetic circuit for carrying flux, said main magnetic circuit being formed from laminations of magnetic sheet steel having a definite grain orientation, a primary winding for carrying current on one side of said main magnetic circuit, a secondary winding for carrying current on the opposite side of said main magnetic circuit from said primary winding, the laminations of said primary winding leg having a different grain orientation from the grain orientation of the laminations of said secondary winding leg, the laminations of one of said winding legs being oriented in at least two directions, a shunt magnetic circuit connected to said secondary winding leg, said shunt magnetic circuit comprising laminations of magnetic sheet steel having a definite grain orientation, the magnetic circuit from said primary winding through said secondary winding and back through said primary winding having less reluctance than the magnetic circuit from said primary winding through said shunt magnetic circuit and back through said primary winding, and the reluctance of the magnetic circuit from said secondary winding through said shunt magnetic circuit and back through said secondary winding being of such magnitude relative to the reluctance of the main magnetic circuit from said secondary winding through said primary Winding that upon abnormal current flow in said secondary winding most of the flux due to abnormal current flow in said secondary winding flows through said shunt magnetic circuit and back to said secondary winding.

References Cited by the Examiner UNITED STATES PATENTS 2,558,110 6/1951 Stein 3362l8 X 2,771,587 11/1956 Henderson 336- 3,195,090 7/1965 Burkhardt et al. 3362l8 LEWIS H. MYERS, Primary Examiner.

LARAMIE E. ASKIN, Examiner.

T, I. KOZMA, Assistant Examiner.

Claims

1. A TRANSFORMER COMPRISING A FOUR SIDED MAIN MAGNETIC CIRCUIT FOR CARRYING FLUX, SAID MAIN MAGNETIC CIRCUIT BEING FORMED FROM LAMINATIONS OF MAGNETIC SHEET STEEL HAVING A DEFINITE GRAIN ORIENTATION, A PRIMARY WINDING FOR CARRYING CURRENT ON ONE SIDE OF SAID MAIN MAGNETIC CIRCUIT, A SECONDARY WINDING FOR CARRYING CURRENT ON THE OPPOSITE SIDE OF SAID MAIN MAGNETIC CIRCUIT FROM SAID PRIMARY WINDING, A SHUNT MAGNETIC CIRCUIT CONNECTED TO SAID MAIN MAGNETIC CIRCUIT INTERMEDIATE SAID TWO WINDING SIDES, SAID SHUNT MEGNETIC CIRCUIT COMPRISING LAMINATIONS OF MAGNETIC SHEET STEEL HAVING A DEFINITE GRAIN ORIENTATION, THE LAMINATIONS OF AT LEAST ONE OF SAID MAGNETIC CIRCUITS BEING GRAIN ORIENTED IN AT LEAST TWO DIRECTIONS, THE MAGNETIC CIRCUIT FROM SAID PRIMARY WINDING THROUGH SAID SECONDARY WINDING AND BACK THROUGH SAID PRIMARY WINDING HAVING LESS RELUTANCE THAN THE MAGNETIC CIRCUIT FROM SAID PRIMARY WINDING THROUGH SAID SHUNT MAGNETIC CIRCUIT AND BACK THROUGH SAID PRIMARY WINDIND, AND THE