US3621426A

US3621426A - Transformer with bushing compartment

Info

Publication number: US3621426A
Application number: US88711A
Authority: US
Inventors: Saul Bennon; Harold R Moore
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1970-11-12
Filing date: 1970-11-12
Publication date: 1971-11-16
Anticipated expiration: 1988-11-16
Also published as: FR2113911B1; JPS5528209B1; ES396019A1; BE775081A; YU269771A; YU33231B; FR2113911A1

Abstract

Electrical inductive apparatus of the shell-form type, having a tank filled with a liquid dielectric, and a magnetic core winding assembly disposed in the tank and immersed in the liquid dielectric. The magnetic core winding assembly includes a magnetic core, and one or more windings formed of a plurality of axially spaced pancake coils which link the magnetic core and extend outwardly therefrom above and below the magnetic core, towards the cover and bottom portions of the tank, respectively. At least the connection to the high-voltage winding is made by a lead assembly connected to a pancake coil at a point below the magnetic core. The other end of the lead assembly is connected to the encased end of high-voltage bushing assembly which is mounted in a separate bushing compartment attached to a sidewall portion of the tank, through aligned openings in the tank and bushing compartment.

Description

United States Patent 72] inventors Saul Bennon;

Harold R. Moore, both of Muncle, Ind. [21] Appl. No. 88,711 [22] Filed Nov. 12, 1970 [45] Patented Nov. 16, 1971 [73] Assignee Westinghouse Electric Corporation Pittsburgh, Pa.

[54] TRANSFORMER WlTl-l BUSHING COMPARTMENT 8 Claims, Drawing Figs.

[52] U.S. Cl 336/58, 174/18, 336/60. 336/84, 336/90 I511 Int. Cl ..H011 15/04, H01127/ 150] Field of Search 336/55, 58, 60, 84,90, 92, 65; 174/18. BH, 16BH, 142, 73 R [56] References Cited UNITED STATES PATENTS 2,355,169 8/1944 Lehman et al.. 336/60 X 3,073,891 1/1963 Barengoltz 336/ UX Walling et al Primary Examiner-Thomas J. Kozma Attorneys-A. T. Stratton, Donald R. Lackey and F. E.

Browder ABSTRACT: Electrical inductive apparatus of the shell-form type, having a tank filled with a liquid dielectric, and a magnetic core winding assembly disposed in the tank and immersed in the liquid dielectric. The magnetic core winding assembly includes a magnetic core, and one or more windings formed of a plurality of axially spaced pancake coils which link the magnetic core and extend outwardly therefrom above and below the magnetic core, towards the cover and bottom portions of the tank, respectively. At least the connection to the high-voltage winding is made by a lead assembly connected to a pancake coil at a point below the magnetic core. The other end of the lead assembly is connected to the on cased end of high-voltage bushing assembly which is mounted in a separate bushing compartment attached to a sidewall portion of the tank, through aligned openings in the tank and bushing compartment.

PATENTEDNUV 1s |97l 3, e21 .426

SHEET 1 OF 2 FIG. I.

PATENTEDIIIII I s IIIII 3,621 .426

SHEET 2 0F 2 BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates in general to electrical inductive apparatus, such as power transformers, and more specifically to HIV transformers of the shell-form type.

2. Description of the Prior Art The demand for electrical inductive apparatus, such as power transformers, with higher and higher voltage and power ratings, increases the physical size of the apparatus and the length of its insulating bushings, creating shipping problems for the manufacturers of such apparatus, as well as increasing the substation cost for the user. Removal of the bushings from the apparatus for shipment alleviates the shipping problem at the lower end of the present El-IV range, which is about 230 kv., but higher voltage apparatus usually requires sectionalizing the tank for shipment, such as disclosed in U.S. Pat. No. 3,27 l ,7 [4, which is assigned to the same assignee as the present application.

Sectionalizing the tank of shell-form inductive apparatus may be averted by constructing the magnetic core winding assembly such that it is rotated 90 from its usual position, which is the construction usually used for mobile transfonners, such as disclosed in U.S. Pat. No. 3,258,524, which is assigned to the same assignee as the present application. This construction, however, makes it necessary to force-cool the apparatus. When the magnetic core winding assembly is turned on its side, from its usual position, the openings through the magnetic core assembly, through which the pancake coils extend, are horizontal, instead of vertical, and little oil flow takes place through the horizontal openings due to natural or thermal syphon flow of the oil, as there is little thermal heat to force circulation through horizontal ducts.

Thus, it would be desirable to be able to reduce the tank height of power transformers of the shell-form type, during shipment and also the installed height, and the installed height of thehigh-voltage bushing, or bushings, from the ground, but it would be desirable to be able to do this without resorting to sectionalizing the tank, and without mounting the magnetic core winding assembly such that force-cooling is essential to proper cooling.

SUMMARY OF THE INVENTION Briefly, the present invention is a new and improved electrical inductive apparatus, such as power transformers, which are constructed to provide a tank having reduced shipping and installed height, and a reduced installed height of the highvoltage bushing, or bushings,,from the ground, compared with similarly rated apparatus of the prior art, while orienting the magnetic core winding assembly such that it may be efficiently cooled by the natural thermal syphon flow of the liquid dielec tric. This result is accomplished by bringing at least the highvoltage lead, orleads, out of the bottom of the high-voltage winding assembly, instead of the top. A separate bushing compartment is provided which is attached to one of the sidewall portions of the tank, and a new and improved shielded lead assembly is connected from the high-voltage winding to the encased end of the high-voltage bushing, through aligned openings in the casing and bushing compartment. The construction of the lead assembly enables the clearances from the lead assembly to the casing to be substantially reduced. Since the length of the encased end of the high-voltage bushing determines the tank height in conventional inductive apparatus, bringing the high-voltage lead out of the bottom of the high-voltage winding enables the tank height to be substantially reduced, as other cover mo nted apparatus, such as low-voltage and neutral bushings, and no-load tap changers, do not require as much clearance ,above the magnetic core winding assembly. Further, the bushing height is substantially reduced, reducing the cost of the associated substation, as the bushing is mounted in a separate compartment and not over the magnetic core winding assembly, enabling the height of the upper end of thebushing to the ground to be markedly reduced.

BRIEF DESCRIPTION OF THE DRAWINGS The invention may be better understood, and furtheradvantages and uses thereof more readily apparent, when considered in view of the following detailed description of exemplary embodiments, taken with the accompanying drawings, in

which:

FIG. I is an elevational view, partially in section, illustrating an electrical power transformer constructed according to the teachings of the prior art;

FIG. 2 is an elevational view, partially in section of an electrical transformer constructed to reduce thetank and bushing height by turning the magnetic core winding assembly illustrated in FIG. I on its side;

FIG. 3 is an elevational view, partially in section, illustrating an electrical power transformer constructed according to the teachings of the invention, in which the tank and bushing height are reduced, compared with the transformer shown in FIG. 1, while maintaining the same orientation of the magnetic core winding assembly as illustrated in FIG. 1;

FIG. 4 is an elevational view, in section, of the lead assembly shown in FIG. 3, taken in the direction of arrows IV- IV; and

FIG. 5 is an elevational view, in section, of the lead assembly shown in FIG. 4, taken in the direction of arrows V V.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, and FIG. 1 in particular, there is shown an elevational view, partially in section, of a transformer of the shell-form type, constructed according to the teachings of the prior art. Transformer 10 includes a tank or casing 12 having sidewall portion 14, a cover 16 and a bottom portion 18, with the tank being filled to a predetermined level 20 with an insulating and cooling liquid dielectric, such as mineral oil, or askarel. A magnetic core winding assembly 22 is disposed in tank 12 and immersed in the liquid dielectric. The magnetic core winding assembly is of the shellform type, having a magnetic core 24 which includes first and second

similar sections

26 and 28, and electrical windings, shown generally at 29, which are constructed of a plurality of axially spaced pancake-type coils, such as pancake coil 30.

Each of the

magnetic core sections

26 and 28 include a plurality of stacked or superposed layers of flat, metallic, magnetic laminations, such as layers 32 in magnetic core section 25, which layers of laminations are arranged to provide openings or

windows

34 and 36 through

sections

26 and 28, respectively. The

magnetic core sections

26 and 28 are disposed in adjacent side-by-side relation, such that their adjacent portions form a winding leg 38, with the pancake coils of the winding 29 linking the magnetic core 24 through the

openings

34 and 36, and thus encircling the winding leg 38.

The magnetic core winding assembly 22 is oriented relative to the tank 12 such that the outennost layers of laminations of the magnetic core 24 provide horizontal upper and

lower surfaces

40 and 42, respectively, with the major planes of the layers being substantially perpendicular to the sidewall portions 14 of the tank 12. The plurality of pancake coils which make up the winding 29, extend above and below the iron or magnetic core 24, from the upper and

lower surfaces

40 and 42, thereof, toward the cover 16 and bottom portion I8, respectively, of the tank 12.

The winding 29 may be single or polyphase, and either of the isolated type or of the autotransformer type, with the specific winding construction determining the number of highand low-voltage bushings. For purposes of example, it will be assumed that the transformer I0 is of the autotransformer type having a single high-voltage bushing 50, a single low-voltage bushing 52, and a neutral bushing, which is not illustrated. High-voltage bushing has first and

second terminals

54 and 56, with terminal 56 being connected to the high-voltage winding via a lead 51, and low-voltage bushing 52 has first and

second terminals

58 and 60, with terminal 60 being connected to the low-voltage winding via a lead 53.

High-voltage bushing 50 includes an axially extending electrical conductor connected to the first and

second terminals

54 and 56, a mounting flange and ground shield portion 62, and first and second

insulating portions

64 and 66 disposed to surround the axially extending electrical conductor, between the first terminal 54 and the mounting flange portion 62, and between the mounting flange portion 62 and the second terminal 56, respectively. The

insulating portions

64 and 66 may be porcelain housings which surround a condenser section constructed to have a plurality of capacitor plates or foils for more uniformly distributing electrical stresses across the bushing. A liquid insulating and cooling dielectric, such as mineral oil, may be contained by the insulating portions to insulate and cool the bushing assembly 50. The insulating portions may have weather sheds disposed on their external surfaces to extend the creep distances from the terminals to the grounded flange portion 62 and the tank 12.

The low-voltage bushing 52 may be of similar construction, with its specific constructional details depending upon the voltage and BIL rating of the bushing, but it will have a shorter longitudinal dimension than the high-voltage bushing 50. As illustrated in FIG. I, both the high-voltage bushing 50 and the low-voltage bushing 52 are connected to the portion of winding 29 which extends towards the cover 16.

Cooling of the transformer is accomplished by circulating the liquid dielectric upwardly through ducts formed between the spaced pancake coils, which ducts extend through the

openings

34 and 36 in the

sections

26 and 28, respectively, of the magnetic core, with the circulation being due either to the natural thermal syphon effect, or due to pumps. Some transformers have dual ratings, being cooled by the natural thermal syphon effect until the temperature of the windings and liquid dielectric indicates that forced cooling is required, at which time pumps and fans are automatically energized, with the former increasing the circulation rate of the liquid dielectric. The arrows shown in FIG. 1 illustrate the upward flow of the liquid through the magnetic core winding assembly. At the top portion of the tank 12, it is directed into external heat exchangers (not shown), and returned to the bottom portion of the tank.

The high-voltage bushing assembly 50 and the low-voltage bushing assembly 52 are sealingly mounted through

openings

70 and 72, respectively, in the cover 16, with the length dimension 74 of the high-voltage bushing from its bottom or second terminal 56 to the mounting flange 62 being a major factor in determining the height dimension of the tank 12. In EHV-rated transformers, this dimension is quite long, with the dimension being determined by the BIL rating of the bushing in kilovolts. For example, a bushing rated 1,550 kv. BIL for use with a system voltage of 500 kv., would have a length dimension below the cover of about 8| inches, and an overall length from terminal to terminal of 271 inches. A bushing assembly rated 1,800 kv. BIL for a system voltage of 765 kv. would have a length dimension below the cover of about 93 inches, and an overall length of 340 inches. A bushing rated 2,l75 kv. BIL for a system voltage of l,l50 kv. would have a length dimension below the cover of about 98 inches, and an overall length of about 37l inches.

Thus, the length of the high-voltage bushing assembly inside the tank, for the EHV voltages, substantially increases the tank height, which causes shipping problems, and the installed height of the high-voltage bushing, as well as the height of the tank, increases the cost of the substation due to the height of the superstructures for mounting insulating supports for carrying electrical conductors.

Shipping problems created by the height dimension of the tank may be alleviated by sectionalizing the tank, and removing the bushings for shipment, as the tank height required by only the magnetic core winding assembly 22 is substantially less than the tank height required when the high-voltage bushing is mounted on the cover thereof, enabling the magnetic core winding assembly to be shipped only in a bottom section of the tank, with an upper section of the tank and the bushings being installed at the operating site. Another approach to the shipping problem is to remove the bushings and turn the entire transformer on its side for shipment. The sectionalized tank approach has the disadvantage of adding additional manufacturing and installation costs, and extreme care must be taken at the operating site to prevent contamination of the liquid dielectric when the upper portion of the tank is installed on the lower portion, and the bushings are installed on the upper portion of the tank. Shipping the transformer by turning it over on its side has the disadvantage of requiring large cranes at the operating site, to return the transformer to its upright position. Both of these approaches do nothing to reduce substation cost, as the installed tank and bushing heights have not been changed.

Still another approach is to change the orientation of the magnetic core winding assembly 22 within the tank 12, such that the magnetic core winding assembly is turned" 90 on a horizontal axis, compared with its orientation in FIG. 1. This arrangement is illustrate in FIG. 2, with like reference numerals in FIGS. 1 and 2 indicating like components, and like reference numerals with a prime mark indicating similar but modified components.

More specifically, FIG. 2 is an elevational view, partially in section, of a transformer 10' having a tank 12' which includes sidewall portions 14', a cover 16 and a bottom portion 18'. An insulating and cooling liquid dielectric is disposed in tank 12 to level 20' and a magnetic core winding assembly 22 is disposed in tank 12' and immersed in the liquid dielectric. Magnetic core winding assembly 22 is similar to magnetic core winding assembly 22 shown in FIG. I, except for its orientation relative to the tank 12. The magnetic core winding assembly 22' includes a magnetic core 24 having first and second

adjacent sections

26 and 28, respectively, each of which include a plurality of layers 32 of flat, metallic, magnetic laminations. The plurality of layers 32 are stacked or superposed, with the

outermost layers

40 and 42 of the magnetic core 24, instead of facing the cover and bottom portions of the tank 12, face the sidewall portions 14, and the

openings

34 and 36 through the

magnetic core sections

26 and 28, respectively, instead of being vertically oriented, are horizontal. The high-voltage lead 51 thus emanates from the side of the magnetic core winding assembly, and the high-voltage bushing 50 is mounted in a special bushing compartment which is attached to one of the sidewall portions 50. An opening 82 is provided in the sidewall portion of the tank 12', adjacent to the location of the high-voltage lead 51. The bushing compart' ment 80 has a first opening which is oriented with the opening 82, and the bushing compartment 80 is disposed to seal the opening 82 in the casing. The bushing compartment 80 has a second opening 70 for receiving the bushing assembly 50. Since the encased end of the high-voltage bushing 50 does not dictate the height of the tank 12, it may be reduced to than dimension which will provide the clearance required for the low-voltage bushing, and other cover mounted apparatus, such as a no-load tap changer. Further, since terminal 56 of the high-voltage bushing 50 may be disposed at the height where the high-voltage lead 51 leaves the high-voltage winding, the height of the bushing 50 from the ground may be substantially reduced. Thus, by removing the bushings, this tank may be more easily shipped than the transformer of FIG. 1, without sectionalizing, and the installed tank height, and the height of the bushing is reduced, unlike the transformer of FIG. 1. The disadvantage of the arrangement shown in FIG. 2 is the fact that the liquid dielectric must be circulated by pumps, including baffles disposed to direct the forced coolant through the horizontally disposed

openings

34 and 36 in the

magnetic core sections

26 and 28, respectively, and thus between the axially adjacent pancake coils which make up the winding 29. The natural thermal syphon flow of coolant will not effectively cool the transformer shown in FIG. 2, as the thermal head at opposite ends of the horizontally disposed ducts is substantially the same, resulting in little flow of the liquid dielectric past the portions of the pancake coils which extend through the openings in the magnetic core sections.

FIG. 3 is an elevational view, partially in section. of a transformer 10'' which is constructed according to the teachings of the invention, which reduces the shipping height of the tank. and the installed height of the tank and bushing, compared with the prior art construction shown in FIG. 1, without sectionalizing the tank for shipment, and without requiring that the transformer be forced cooled, as dictated by the construction shown in FIG. 2. Like reference numerals in FIGS. 1 and 3 indicate like components, while like reference numerals with a double prime mark indicate similar but modified components.

More specifically, FIG. 3 illustrates a transformer 10 having a casing or tank 12" which includes sidewall portions 14", a cover 16" and a bottom portion 18". The tank 12" is filled to a predetermined level 20 with a liquid dielectric, such as mineral oil or askarel, and a magnetic core winding assembly 22" is disposed in the tank 12" and immersed in the liquid dielectric. The magnetic core winding assembly 22" includes a magnetic core 24 having first and second

adjacent sections

26 and 28, respectively. Each of the

magnetic core sections

26 and 28 have a plurality of stacked layers 32 of metallic laminations arranged to provide

openings

34 and 36 therein, respectively, with the layers 32 being stacked or superposed. The magnetic core 24 is oriented with respect to the tank 12" such that the outermost layers of laminations provide

surfaces

40 and 42 which face the top of cover 16" and bottom portion 18", respectively, and the axes of

openings

34 and 36 through the magnetic core sections are vertical, i.e., perpendicular to the bottom portion l8" of the tank 12 The tank height, as well as the installed high-voltage bushing height is reduced, according to the teachings of the invention, by bringing the high-voltage lead assembly 90 from the portion of the high-voltage winding located below the surface 42 of the magnetic core. This construction is made practical, by a new and improved construction for the high-voltage lead assembly 90, which enables the clearance between the tank bottom 18" and lead assembly 90 to be substantially reduced.

The high-voltage bushing 50 is mounted in a bushing compartment 92 which has a first opening oriented with an opening 94 disposed in one of the sidewall portions of the tank 12'', with the liquid dielectric in the tank flowing freely into the high-voltage bushing compartment 92 through the opening. The bushing compartment 92 is attached to the tank 12", such as by welding, to preclude any leaks at the joint.

A second opening 96 is provided in the high-voltage bushing compartment 92, through which the high-voltage bushing assembly 50 is mounted and sealed, with the encased end of bushing 50 extending into the liquid dielectric. Bushing 50 may be mounted with its longitudinal axis vertical, if desired, but as illustrated in FIG. 3, the height of the bushing from the ground may be reduced by mounting it at an angle of less than 90 relative to the ground plane.

Since the high-voltage lead assembly 90 may be brought closer to the bottom portion 18" of the tank 12'', than the construction shown in FIG. 2, wherein the high-voltage lead 51 in FIG. 2 proceeds from the side of the magnetic core winding assembly, the overall height of the bushing 50 from the ground may be reduced, compared with the construction shown in FIG. 2, using the same mounting angle and the overall height of the bushing is substantially lower than in the construction shown in FIG. 1. For example, a single-phase transformer for a 1,150 kv. system voltage would require a high-voltage bushing approximately 3l feet long, with 23 feet being outside of the tank. With the construction shown in FIG. I, the upper end of the bushing would be approximately 48 feet from the ground. With the construction shown in FIG. 2, the upper end of the high-voltage bushing would be approximately 38 feet from the ground, and with the construction shown in FIG. 3, theupper end of the high-voltage bushing would be about 35 feet from the ground. Thus, the construction shown in FIG. 3 results in a 13-foot reduction in bushing height, compared with the construction shown in FIG. I and the 3 -foot reduction compared with the construction shown in FIG. 2.

The arrangement shown in FIG. 3, not only reduces the shipping and installed tank height, without sectionalizing the tank, and reduces the installed height of the high-voltage bushing, it also provides the advantages of the FIG. 1 construction, as the transformer may be self-cooled if desired. As illustrated by the arrows in FIG. 3, the liquid dielectric coolant may enter the tank 12" near the bottom thereof, from external heat exchangers (not shown) and circulate upwardly through the tank due to the natural thennal head, through the vertically oriented

openings

34 and 36 in the

magnetic core sections

26 and 28, respectively, thus efficiently cooling the portions of the pancake coils which extend through the magnetic core sections, as well as those portions which are outside of the magnetic core.

FIG. 4 is an elevational view, partially in section, of the high-voltage lead assembly shown in FIG. 3, which contributes to the successful reduction in tank and bushing heights, with the view shown in FIG. 4 being taken in the direction of arrows IV-IV. FIG. 5 is a fragmentary elevational view of the high-voltage lead assembly 90 shown in FIG. 4, taken in the direction of arrows VV.

As illustrated in FIG. 4, winding 29" has at least one highvoltage section 200 including one or more pancake coils. such as pancake coils 102 and 104, which are connected to the high-voltage lead assembly 90. One or more low-voltage winding sections, represented by pancake coil 106, are disposed adjacent to the high-voltage winding 100.

Static plate members, such as static plate members 105 and 107, may be disposed between the high-voltage winding I00 and the adjacent low-voltage windings, in a manner well known in the art.

Lead assembly 90 includes first and second electrically connected main conductor portions and 112, respectively, formed of a good electrical conductor. such as copper, with conductor 110 being connected to pancake coils 102 and 104, such as by a tubular metallic crimp-type connector 114. The leads from the pancake coils 102 and 104, and conductor 110 are inserted into opposite ends of the connector 114 and securely fastened thereto by a suitable crimping tool. Main conductor 110 extends vertically downward, away from the high-voltage winding 100, toward the bottom portion of the transformer, with the conductor 110 being supported by the leads which are connected to the pancake coils of the highvoltage winding. Suitable insulating bands may be disposed about the outer turns of the pancake coils to securely hold these turns adjacent to the point where the leads diverge from the coils to make the connection to conductor 110.

Solid insulating means 116, such as paper tape, may be disposed on the outer surface of conductor 110, in order to provide insulation with a higher electrical strength than the liquid dielectric, immediately adjacent to the outer surface of conductor I10, and also to space the liquid dielectric from the outer surface of conductor 110, in order to prevent ionization of the liquid dielectric. The electrical field about conductor 110 is further controlled by shielding means, to prevent corona discharges adjacent to conductor 110, as will be hereinafter explained. A terminal 117 is connected to the lower end of conductor 110, which may have a tubular portion 119 into which conductor 10 is inserted prior to crimping the tubular portion, and a solid portion 121 having openings therein for receiving fastening means, such as bolts I22 and 124.

Conductor 112 is a tubular metallic conductor, such as copper, having an end portion 118 which has tapped openings therein for receiving

bolts

122 and 124, after the bolts have been inserted through the openings in portion 121 of terminal 1 l7.

The first conductor 110 has an outside diameter which facilitates its connection to leads from the pancake coils 102 and 104, while the second conductor 112 has a much larger outside diameter, selected to reduce the potential gradient adjacent to its outer surface below the ionization level of the surrounding insulation, without the necessity of employing auxiliary field-shaping means, such as shielding members. Conductor 112 may be connected to the lower terminal 56 of the high-voltage bushing 50, without reducing its outside diameter, thus ensuring that the electrical stresses will be below the ionization level of its environment. Solid insulating means 130 may be disposed about the outer surface of conductor 112, to further preclude ionization of the surrounding liquid dielectric, and the inside of the hollow tubular conductor 112 is filled with the liquid dielectric. As illustrated in FIG. 3, the opening 94 through which conductor 112 extends may be shielded and insulated with a plurality of spaced curved shields and insulating barriers, with this structure being indicated generally at 132. The number of insulating barriers disposed between the lead assembly 90 and points of lower potential depends upon the potential difference, and the dimensions of the conductors and insulating clearances.

The smaller diameter conductor 110 must be shielded to prevent electrical stress concentrations in the surrounding liquid dielectric which may ionize the liquid, and this shielding must be accomplished without interfering with the cooling of conductor 110, or with the cooling of the pancake coils to which the lead assembly 90 is connected. These results are obtained by providing first, second, and third shielding means 132, 134, and 136, respectively, with the first and second shielding means 132 and 134 being insulated tubular conductive members, and with the third shielding means being an insulated bowllike conductive member. The first shielding means 132 includes a tubular conductive member 140. Tubular conductive member 140 may be constructed of conductive cloth, or ribbon, formed of a suitable material, it may be formed by disposing a metallic coating or paint on the outer surface of an insulating tubular member, with solid insulating means 142 disposed to surround conductive member 140, such as paper or a synthetic resinous insulating system, or it may be fonned of a metallic tube insulated with suitable insulating means. The specific conductive material selected depends upon the desired resistivity, with materials such as copper, aluminum, stainless steel, carbon, silver, and the like, being typical. The inside diameter of the first shielding means 132 is selected to be larger than the insulated outside diameter of conductor 110, providing space 144 between them for circulation ofthe liquid dielectric.

The first shielding means 132 has a length dimension sufficient to enable it to extend from a point above the crimp-type connector 114, to about the start of the lower terminal 117. The conductive portion 140 of the first shielding means 132 is connected to terminal 117 via electrical lead 146.

The second shielding means 134 is disposed concentrically with the first shielding means 32 and the conductor 110, and it may be constructed in a manner similar to the first shielding means 132, having a tubular conductive portion 148 which is insulated with solid insulating means 150. The insulated inside diameter of the second shielding means is slightly greater than the insulated outside diameter of the first shielding means 132, however, and the second shielding means is telescoped over the lower end of the first shielding means to provide a uniform space between their adjacent outer and inner diameters, The second shielding means 134 has a length dimension selected to enable it to overlap the lower end of the first shielding means by 3 to 4 inches, and to extend downwardly to the second conductor 112, and extend along the end portion 118 of conductor 112 for approximately half of the outside diameter thereof. The conductive portion 148 of the second shielding means is connected to terminal 117 via electrical lead 152. The third shielding means 136 includes a conductive portion 154, solid insulating means 156 disposed to surround the conductive portion 154, and an electrical lead 158 which connects the conductive portion 154 to the terminal 117. The third shielding means 136 is substantially bowl-shaped, and dimensioned to overlap the lower extending end of the second shielding means 134. Unlike the spaced overlap of the first and second shielding means, the second and third shielding means are overlapped and placed tightly together to prevent circulation of oil between the overlapped portions thereof. The second shielding means 134, along with the curved third shielding means 136, provide an effective shielding structure for the connection between the second and

third conductors

110 and 112, respectively.

As illustrated by the arrows in H0. 3, the liquid dielectric flows upwardly through the tank 12", whether under the influence of a natural thermal syphon effect, or due to pumping means. To force this upwardly flowing liquid dielectric to circulate past the conductor 110, and upwardly through the pancake coils which are connected to conductor 110, an insulating tubular member 160 is provided which has an inside diameter larger than the outside diameter of the second shielding means 134, which extends coaxially about conductor 110 from the bottom portion of the winding 100 to a point substantially adjacent to the start of tenninal 117, providing a space between its inner diameter and the adjacent outer diameter of the second shielding means 134. The upwardly flowing liquid dielectric, as illustrated by the arrows in FIG. 4, is thus forced between the lower end of the insulating tubular member 160 and the outer surface of the second shielding means 134, into the space 162 between the insulating tubular member 160 and the first shielding means 132. Space 162 is blocked at its upper end, forcing the liquid dielectric downwardly between the spaced first and second shielding means, cooling terminal 117 at the point where it is connected to conductor 112, and then the liquid dielectric is free to flow upwardly through space 144 and into the cooling ducts provided adjacent to the pancake coils 102 and 104 by suitable insulating washer members having insulating blocks attached thereto, in a manner well known in the art. Additional insulating barrier members may be provided, such as member 166, to aid in distributing electrical stresses about the conductor 1 10.

It should be noted that the first shielding means 132, and the insulating tubular means 160 and 166 all have integral extensions at their upper ends. These extensions extend into the stack of axially aligned pancake coils and are held in place and supported by the axial compression of the pancake coils due to the frictional contact of their relatively large surfaces with the immediately adjacent and contacting insulating members of the composite insulating structure.

Lead assembly provides an interconnecting link between the high-voltage winding and the high-voltage bushing 50, which economically reduces the electrical stresses adjacent thereto, enabling this interconnecting lead to be brought closer to the bottom portion of the tank 12", than would otherwise be possible, enabling the arrangement of bringing the high-voltage lead out of the bottom of the high-voltage winding below the iron to substantially reduce the tank height. Further, the lead assembly 90 and its associated pancake coils are adequately cooled, even when the natural thermal syphon effect is used, due to the disclosed structure of insulating and shielding members.

In summary, there has been disclosed new and improved electrical apparatus of the shell-form type, which may be advantageously used for inductive apparatus constructed to operate with system voltages in the EHV range. The disclosed construction not only substantially reduces the shipping and installed tank height, without sectionalizing the tank, and reduces the installed bushing height, compared with conventional prior art practices, it accomplishes these objects without interfering with the natural thermal syphon cooling of the magnetic core winding assembly. Thus, the apparatus may be shipped and assembled more economically, the user may save on the cost of the substation since the height of the connecting electrical lines may be reduced, and the apparatus may be self-cooled, or it may have a self-cooled rating on dual rated apparatus.

We claim as our invention:

1. Electrical inductive apparatus, comprising:

a tank having bottom, sidewall and top portions,

liquid insulating and cooling means disposed in said tank,

a magnetic core winding assembly disposed in said tank and immersed in said liquid-insulating means,

said magnetic core winding assembly including a magnetic core having a plurality of superposed layers of metallic laminations, with the laminations being arrange to provide at least two magnetic loops which define at least two magnetic loops which define at least two spaced openings through said magnetic core, and a winding having a plurality of axially spaced pancake coils which link said at least two magnetic loops,

said magnetic core winding assembly being oriented in said tank such that the two outermost layers of metallic laminations provide upper and lower surfaces on said magnetic core, with said plurality of pancake coils extending outwardly from said upper and lower surfaces toward the cover and bottom portions of said tank, respectively,

said tank having an opening in one of its sidewall portions, between the lower surface of said magnetic core and the bottom portion of said tank, a bushing compartment mounted on the sidewall portion of said tank having the opening therein, with said bushing compartment having a first opening aligned with the opening in said sidewall portion, and a second opening for receiving an electrical bushing,

an electrical bushing assembly having first and second terminals, said bushing assembly being mounted through the second opening in said bushing compartment, with its second terminal being encased, and an electrical lead assembly disposed to connect the second terminal of said electrical bushing assembly to at least one of said pancake coils, with the connection to said at least one pancake coil being made to the portion thereof which extends outwardly from the lower surface of said magnetic core.

2. The electrical inductive apparatus of claim 1 wherein the electrical lead assembly includes at least first and second electrically connected conductors having first and second outside diameters, respectively, said first conductor being connected to and supported by the at least one pancake coil, extending from the pancake coil towards the bottom portion of the tank, and said second conductor being connected to the outwardly extending end of said first conductor, forming a substantially right angle therewith, and shielding means disposed in spaced relation about at least said first conductor and its interconnection with said second conductor.

0 with the first and second tubular conductive members being disposed coaxially about the first electrical conductor of the electrical lead assembly, with one end of one of the tubular conductive members extending into an end of the other tubular conductive member for a predetermined dimension, to provide an effectively continuous shield, but with a space between them to allow free circulation of the liquid insulating and cooling means.

5. The electrical inductive apparatus of claim 4 wherein the first tubular conductive member is disposed above the second tubular conductive member, with its lower end extending into the upper end of the second tubular conductive member, and including a tubular insulating member disposed about the first tubular conductive member and a portion of the second tubular conductive member, said tubular insulating member having an inside diameter larger than the outside diameter of the second tubular conductive member, to provide a tortuous path for the liquid insulating and cooling means which directs the liquid upwardly between the second tubular conductive member and tubular insulating member, downwardly between the first and second tubular conductive members, and upwardly between the first tubular conductive member, and the first conductor of the electrical lead assembly.

6. The electrical inductive apparatus of claim 2 wherein the shielding means is electrically connected to the electrical lead assembly.

7. The electrical inductive apparatus of claim 1 including a second electrical bushing assembly having first and second tenninals, said second electrical bushing assembly being disposed through the cover of the tank, with its second terminal inside the tank, and an electrical lead disposed to connect the second terminal of said second electrical bushing as sembly to at least one of the pancake coils, with the connection to said at least one pancake coil being made to the portion

Claims

1. Electrical inductive apparatus, comprising: a tank having bottom, sidewall and top portions, liquid insulating and cooling means disposed in said tank, a magnetic core winding assembly disposed in said tank and immersed in said liqUid-insulating means, said magnetic core winding assembly including a magnetic core having a plurality of superposed layers of metallic laminations, with the laminations being arrange to provide at least two magnetic loops which define at least two magnetic loops which define at least two spaced openings through said magnetic core, and a winding having a plurality of axially spaced pancake coils which link said at least two magnetic loops, said magnetic core winding assembly being oriented in said tank such that the two outermost layers of metallic laminations provide upper and lower surfaces on said magnetic core, with said plurality of pancake coils extending outwardly from said upper and lower surfaces toward the cover and bottom portions of said tank, respectively, said tank having an opening in one of its sidewall portions, between the lower surface of said magnetic core and the bottom portion of said tank, a bushing compartment mounted on the sidewall portion of said tank having the opening therein, with said bushing compartment having a first opening aligned with the opening in said sidewall portion, and a second opening for receiving an electrical bushing, an electrical bushing assembly having first and second terminals, said bushing assembly being mounted through the second opening in said bushing compartment, with its second terminal being encased, and an electrical lead assembly disposed to connect the second terminal of said electrical bushing assembly to at least one of said pancake coils, with the connection to said at least one pancake coil being made to the portion thereof which extends outwardly from the lower surface of said magnetic core.

3. The electrical inductive apparatus of claim 2 wherein the diameter of the second conductor of the electrical lead assembly is substantially larger than the diameter of the first conductor, with the diameter of the second conductor being selected to reduce the potential gradient adjacent to its outer surface below the ionization level of its environment.

4. The electrical inductive apparatus of claim 2 wherein the shielding means includes at least first and second insulated tubular conductive members having different inside diameters with the first and second tubular conductive members being disposed coaxially about the first electrical conductor of the electrical lead assembly, with one end of one of the tubular conductive members extending into an end of the other tubular conductive member for a predetermined dimension, to provide an effectively continuous shield, but with a space between them to allow free circulation of the liquid insulating and cooling means.

7. The electrical inductive apparatus of claim 1 including a second electrical bushing assembly having first and second terminals, said second electrical bushing assembly being disposed through the cover of the tank, with its second terminal inside the tank, and an electrical lead disposed to connect the second terminal of said second electrical bushing assembly to at least one of the pancake coils, with the connection to said at least one pancake coil being made to the portion thereof which extends outwardly from the upper surface of the magnetic core.

8. The electrical inductive apparatus of claim 7 wherein the second electrical bushing assembly has a substantially shorter length than the bushing assembly mounted through the bushing compartment.