US 3588607 A
Description (OCR text may contain errors)
United States Patent  Inventors Donald J. Rlstuccia Sharpsville, Pm; Kenneth R. Klein, Niles, Ohio  Appl. No. 860,672
 Filed Sept. 24, 1969  Patented June 28, 1971  Assignee Westinghouse Electric Corporation Pittsburgh, Pa.
 ELECTRICAL TRANSFORMER APPARATUS FOR GROUND LEVEL INSTALLATION HAVING FUSED MEANS ACCESSIBLE FROM OUTSIDE THE APPARATUS 6 Claims, 4 Drawing Figs.
 [1.8. CI 317/15, 3 37/201  Int. Cl H0211 7/04, H01h 85/02  Field of Search 317/15; 337/201, 204, 224, 202
[5 6] References Cited UNITED STATES PATENTS 3,014,158 12/1961 Nelson 317/15 3,350,526 10/1967 Anderson 317/15X -mazemcuwn 12 Primary Examiner.lames D. Trammell Assistant Examinerl-iarvey Fendelman Attorneys-A. T. Stratton and F. E. Browder ABSTRACT: Electrical conductive apparatus such as a transformer adapted for mounting at ground level, including a casing filled to a predetermined level with liquid dielectric, a magnetic core-winding assembly disposed within said casing, protective fuse means disposed through one wall of said casing, and at least one high voltage bushing assembly disposed through one wall of the casing. The high voltage bushing is electrically connected in series circuit relationship with the protective fuse means and the fuse means is electrically connected in series circuit relationship with the high voltage windings of the winding assembly. The protective fuse means includes a longitudinal tubular receptacle having a longitudinal opening therein. The tubular receptacle extends through a wall of the casing with one end located inside the casing and with the other end extending outside of the casing. The protective fuse means also includes a removable fuse accessible from the end of the fuse assembly located outside the casing. The end of the fuse assembly extending inside the casing is closed to prevent liquid dielectric from entering the longitudinal opening in the fuse receptacle. The end of the fuse receptacle positioned outside of the casing is closed by a weathertight closure. A current limiting fuse is attached to the weathertight closure member and is removed or inserted into the longitudinal opening in the fused receptacle by means of the weathertight closure member.
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ELECTRICAL TRANSFORMER APPATHJS FOR GROUND LEVEL INSTALLATHON HAVING FUSED MEANS ACCESSIBLE FROM OUTSIDE THE APPARATUS CROSS REFERENCES TO RELATED APPLICATIONS This application is related to application Ser. No. 654,220, filed July 18, 1967, by Donald J. Ristuccia, now US. Pat. No. 3,475,693, which application is assigned to the same assignee as the present application.
BACKGROUND OF THE INVENTION l Field of the Invention This invention relates to electrical inductive apparatus, such as distribution transformers adapted to be installed at ground level, and more particularly to transformers of the type having fusible means connected between the high voltage bushings and a high voltage winding.
2. Description of the Prior Art The related application hereinbefore referred to discloses a protective link suitable for use in electrical inductive apparatus, such as transformers. The related application discloses a protective link wherein the fusible element of the link is surrounded by the liquid dielectric of the transformer. It is possible with this type of apparatus that when the fusible link melts due to a fault in the apparatus a gas bubble could be formed which could short the high potential to ground and completely destroy the apparatus. Apparatus such as disclosed in the related application also has certain disadvantages in that in some instances when the link fuses pressure builds up in the casing of such magnitude that when the fuse structure is being removed this pressure will blow the fuse holder from the receptacle and carry with the fuse holder hot dielectric which could be injurious to maintenance personnel and adjacent equipment.
Apparatus such as disclosed by the related application has a further disadvantage in that are products result when the fuse blows, and these are products are injurious to the transformer apparatus. A high are in the liquid dielectric tends to decompose the liquid dielectric into water and carbon products. This decomposition of the liquid dielectric into water and carbon products reduces the insulating quality of the liquid dielectric.
Other are products such as bits of metal or insulating material are also created which fall into the transformer casing and create trouble by shorting the winding or obstructing the flow of liquid dielectric. Another objection to the apparatus of the related application is that the fuse contacts located inside the transformer casing are not visible to service personnel from outside the casing. It is entirely possible to remove the fusible element carrying mechanism from the apparatus of the related application, but still leave parts such as fused metal are products inside the tube, which parts will maintain the contacts closed so that the circuit is really not open although the fuse holder has been removed.
The invention provided by this application eliminates the above-referred-to objections to the invention of the related application. The apparatus of the present invention of the related application. The apparatus of the present invention uses a current limiting fuse. This fuse can handle large fault currents, of the order of 40,000 amperes, without any disturbance, electrical or mechanical, external to the fuse casing. Therefore, the apparatus is not subject to mechanical shock or arcing when the fuse blows. The only time the apparatus is subjected to arcing or mechanical shock is during a close-in on a faulted transformer, but if this occurs the current limiting fuse will operate in a small fraction of a cycle and keep the energy at a very low level.
When the current limiting fuse is used to break the load to a transformer an arc will be drawn; however, the arc extinguishing material carried by the fuse will quickly extinguish the arc and no damage will be caused to the apparatus. Furthermore, because of the large central opening in the fuse holder for receiving the fusible element the apparatus provided by this invention permits service personnel to look into the end of the fuse holding compartment and see without too much difficulty whether or not the contacts in the fuse holding compartment are clear and not shorted by some foreign material left in the fuse holding compartment when the blown fuse is removed.
SUMMARY OF THE INVENTION The invention provided by this application is a new and improved electrical inductive apparatus of a type having a casing filled to a predetermined level with liquid dielectric means and a magnetic core having high and low voltage windings associated therewith disposed within the casing. The apparatus is equipped with protective fuse means having a tubular receptacle for receiving a removal fusible link, and at least one high voltage bushing. The high voltage bushing is sealed through an opening in the casing. The tubular receptacle of the protective fuse means also seals through an opening in the casing, with its fusible link insertable and removable from outside the casing. One end of the tubular fuse receptacle extends into the casing and is positioned below the liquid dielectric level. The other end of the tubular fuse receptacle extends outside of the casing and the fusible link is insertable and removable into the tubular fuse receptacle from outside'of the casing. The end of the tubular fuse receptacle extending into the casing is fitted with fuse contact means and the fuse contact means are electrically connected to the high voltage bushing. A cylindrical longitudinal electrode surrounds the longitudinal tubular opening in the tubular fuse receptacle and extends from a point near the fuse contact means located in the sealed end of the fuse receptacle to the outer end of the fuse receptacle, which is located outside of the casing. Electrical connection is made to the longitudinal tubular electrode from a point inside the casing to the high voltage winding. It is thus seen that both high voltage connections to the tubular fuse holder receptacle are made inside of the casing. A current limiting fuse is attached to a closure member which closure member is carried by a weather shed or cover and the closure member is used to close the end of the fuse receptacle located outside of the transformer casing and also makes electrical contact between the end of the fuse member located outside of the transformer casing and the end of the tubular electrode located outside of the transformer casing.
The current limiting fuse is inserted or removed into the tubular fuse holder element by means of the weather shed located on the outside of the transformer casing. Thus when the fusible element of the fusible apparatus melts, all live parts are within the transformer casing. When the fusible element melts no are products are deposited in the liquid dielectric. When the fuse element is removed from the tubular fuse receptacle an operator may readily look into the end of the tubular fuse receptacle and see that the high voltage circuit is clearly open.
The end of the current limiting fuse adjacent to the fuse contact means located at the end of the tubular fuse holding element which is inside the transformer tank carries arc extinguishing material. This are extinguishing material generates a gas when exposed to an are which will assist in extinguishing any are which may occur. With the construction provided by this invention there is no possibility of an air bubble being created when the fusible member melts, which air bubble could possibly contact high voltage terminals and create a short circuit to ground which would destroy the transformer.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view of a transformer provided according to this invention, with the front cover removed;
FIG. 2 is a partial sectional view of a transformer provided by this invention showing the front cover in closed position;
P10. 3 is a longitudinal sectional view of a fuse holder as provided by this invention; and
FIG. 4 is a sectional view taken along lines IV-IV of FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENT In the description which follows, like reference characters refer to like parts in the various FIGS. of the drawing.
Referring to FIG. 1, which shows a front elevational view of a transformer as provided by this invention which is intended for installation at ground level, the reference character indicates a casing which encloses a core and coil assembly. The casing 10 contains fluid dielectric for cooling and insulating the transformer. In FIG. 1 the upper part 11 of the casing 10, which is called the terminal compartment, is shown with the terminal cover removed. The lower part 14 of the casing 10 is provided for bringing in the cables for connection to the terminals. In FIG. 1 there are shown two high voltage terminals 16 and 18 extending through the front wall 12 of an upper part 11 of the casing 10. There is also shown three low voltage terminals 20, 21 and 22 extending through the front wall 12 of the casing 10. Also shown in FIG. I is a front view of a fuse assembly 24 as provided by this invention. The fuse assembly extends through the front wall 12 of the casing 10 and one end of the fuse assembly 24 is covered by the fluid dielectric in the casing 10 and the other end of the fuse assembly 24 extends into the terminal compartment 11 and is accessible from the front of the terminal compartment 1 1.
FIG. 2 is a sectional view of the transformer apparatus shown in elevation in FIG. 1 and shows a cover 26 in position over the terminal compartment 11. This cover 26 may be locked in place by some arrangement such as a hasp 28 which is adapted to receive a padlock. from the outside front of the casing 10. Also shown in FIG. 2 is a core and coil assembly comprising a laminated magnetic core 30 having a high voltage winding 32 and low voltage windings 34 and 36 associated therewith. As better seen in FIG. 2 the fuse holder assembly 24 extends through the wall 12 of the casing 10 and an end 38 projects into the casing 10 and is located below the level of the liquid dielectric in the casing 10. Another end 40 of the fuse assembly 24 extends into the terminal compartment 11 of the casing 10. As seen in FIG. 2 the high voltage terminal 16 is electrically connected to the fuse holder assembly 24 by an electrical conductor 42. The fuse holder assembly 24 is electrically connected to one end of the high voltage winding 32 by an electrical conductor 44. The other end of the high voltage winding 32 is connected to the other high voltage bushing 18 by means of an electrical conductor 46. As illustrated in FIG. 2 the upper end of the low voltage winding 34 is connected to the low voltage bushing 20 with a conductor 48. The lower end of the low voltage winding 34 and the upper end of the low voltage winding 35 is connected to the low voltage bushing 22 by means of a conductor 50. The lower end of the low voltage winding 36 is connected to the low voltage bushing 21 by means ofa conductor 52.
Referring to FIG. 2, the high voltage circuit is traced from the high voltage bushing 16 through the fuse assembly 24 through the highvoltage winding 32, and the conductor 46 back to the other high voltage bushing 18. This circuit places the fuse holder assembly 24 in series circuit relationship with the high voltage circuit of the transformer.
In FIG. 2 a series of knockout plugs 52 are indicated in the end of the terminal compartment 11 to permit running the required cables into the terminal compartment 11 to connect to the high and low voltage terminals located in the terminal compartment 11. When the cover 26 is locked in place over the terminal compartment 25 all of the live terminals of the transformer are covered.
Referring specifically to FIG. 3, this FIG. shows a longitudinal sectional detail of the fuse holder assembly 24 illustrated in FIGS. 1 and 2. The fuse holder assembly 24 comprises an elongated molded or cast member 60. This member 60 has therein an elongated chamber or cavity 62 for receiving a fuse 82. Also cast or molded into the member 60 is an elongated metallic electrode member 64. This member 64 is insulated from the chamber or cavity 62 but completely surrounds the cavity 62. The electrode member 64 extends from a point on the member 60 which would be mounted inside the casing 10 to substantially the end of the fuse holder assembly 20 which is located in the terminal compartment 11. This electrode member 64 serves several functions. One function is to provide means for making an electrical connection to one end of a fuse installed in the cavity or opening 62. An important function of the cylindrical longitudinal electrode member 64 is to distribute the electrical field due to the difference in voltage between the fuse and the tank wall 12; and, thereby prevent starting of corona and generation of radio interference because of poor field distribution or undue stress. If corona is produced it would cause objectional radio interference and would also erode the cast member 60 and cause electrical failure of the member 60. The field distribution and stress reduction is improved also by a stress grading coating or shield 61 which surrounds a portion of the member 60 and is electrically connected to a flange member 66. The flange member 66 is connected to ground potential. The stress grading coating 61 may be silicon carbide paint, or any other suitable stress grading material, or instead of stress grading, the element 61 could be a sprayed on metallic, electrical, conducting coating.
As shown in FIG. 3 the cast or molded member 60 has formed therein the flange 66 which is used to attach the fuse assembly 24 to the transformer tank wall 12 by welding. The casing 10, including wall 12, is connected to ground. The end 66 of the cast or molded member 60 of the fuse assembly 24 which extends into the transformer casing is normally covered with the liquid dielectric in the casing 10. A fuse clip or contact means 68 is mounted in the end portion 66 of the member 60 by means of a bolt 70 which is welded to the fuse contact means 68 and extends to the outer end of the member 60. The high voltage lead 42 which connects to the high voltage terminal bushing 16 is fastened to the bolt 70 by means of a nut 72. A bolt 74 is fastened to the cylindrical electrode 64 and extends to the outside of the cast or molded member 60 of the fuse assembly 24. The lead 44 which connects to the upper end of the high voltage winding 32 of the transformer is fastened to this bolt 74 by means of a nut 76.
The cylindrical electrode member 64 extends to the end 78 of the cast or molded member 60 which extends into the terminal compartment 11 of the casing and this end of the electrode 64 terminates in a threaded portion 80. A current limiting fuse 82, is installed in the cavity or central opening 62 in the cast or molded portion 60 of the fuse assembly 24. This current limiting fuse may be of the type covered in U.S. Pat. No. 3,134,874. One end of the fuse 82 has thereon a stud 84. This stud serves to attach the fuse 82 to a contact member 86. The contact member 86 is permanently attached to a weather shield or shed 84. The other end of the fuse 82 has attached thereto by means of a bolt 88 and a nut 90 a piece of material which when exposed to an electric arc will generate gas to assist in extinguishing the arc. The material 80 may be any suitable high molecular weight polyoxymethylene material, such as that sold under the trademark Delrin."
It is emphasized that although the elongated anode 64 has been described as cylindrical this shape is not critical and may be of any desired shape as long as it serves the functions described thereinbefore.
The molded member 60 may be made of material such as epoxy filled resin, glass polyester, glass filled nylon, rubber, or any other suitable material which may be molded into the desired shape economically.
The weather shed or protective cover 84 is formed from some suitable insulating material. The weather shed 84 is permanently attached to the contact member 86 and the weather shed 84 is provided within an eye 104 which may be engaged by a hook stick for inserting the fuse 82 into or removing the fuse 82 from the longitudinal cavity or opening 62 in the fuse assembly. The weather shed 84 has extended sides 106 which extend down and protect substantially all of that portion of the molded or cast member 60 which extends into the terminal compartment 11.
A gasket 108 is also provided between the ends of the member 60 which extends into the terminal compartment 11 and the contact element 86 for providing a moisture-tight seal for the cavity 62.
From the foregoing description taken in connection with the drawings it is seen that this invention has provided a transformer adapted for installation at ground level which is provided with an improved fuse assembly for protecting the high voltage circuit of the transformer; wherein, should a fuse blow, all are retained in the fuse body itself which is sealed from the liquid dielectric and cannot be deposited in the liquid dielectric to contaminate the liquid dielectric, and all high voltage terminals connected to the fuse assembly are below the liquid dielectric level. A fuse assembly by this invention also prevents air bubbles from contacting the high voltage connections and ground which condition would cause flashover or explosions which would destroy the transformer. This invention also provides an improved fuse assembly wherein all connections from high voltage terminals to the fuse assembly are made inside the transformer casing and are maintained under the liquid dielectric and one connection from the fuse to the high voltage leads is made outside of the transformer casing where it is visible to a Serviceman who can visually inspect the connections when the fuse assembly is removed to be sure that the circuit is open before contacting the high voltage terminals of the transformer. Although this invention has been described in connection with liquid dielectric filled apparatus, it is understood that it is equally applicable to other types of apparatus, such as dry-type transformers.
It is therefore seen that this invention has provided a transformer adapted for ground level installation which is a substantial improvement over the referenced patent application in that it provides a fusing arrangement which adequately protects the apparatus and ensures safety for maintenance personnel or anyone who might accidentally contact the outside of the transformer casing.
1. A transformer comprising a tank, a magnetic core in said tank, said core having high voltage and low voltage coils associated therewith, at least one high voltage bushing connected through a wall of said tank, an elongated fuse holder connected through a wall of said tank with one end of said fuse holder inside said tank and the other end of said fuse holder outside said tank, said fuse holder having a central longitudinal cavity with a closed end, fuse contact means in said central cavity adjacent the closed end of said cavity, electrical circuit means connecting said fuse contact means to said high voltage bushing, hollow electrical conducting means embedded in said fuse holder, said hollow conducting means being spaced from and surrounding said cavity, said hollow electrical conducting means extending from a point inside said tank to substantially said end of said elongated member located outside said tank, means closing the end of said cavity in said member located outside said tank, and electrical conducting means connecting from a point on said hollow conductor located inside said tank to said high voltage winding.
2. The apparatus of claim 1 including an elongated fuse in said longitudinal cavity, said fuse having one end electrically connected to said fuse contact means and the other end connected to said means closing the end of said cavity in said fuse holder located outside said tank, said means closing the end of said cavity in said fuse holder located outside said tank being electrically conductive and making electrical connection to said hollow conducting means at a point located outside said tank.
3. The apparatus of claim 2 wherein said fuse is a current limiting fuse.
4. The apparatus of claim 2 wherein the end of said fuse connected to said fuse contact means has a member comprised of arc extinguishing material attached thereto.
5. The apparatus of claim 1 wherein said means closing the end of said cavity in said fuse holder located outside said tank is an electrical conductor and makes electrical connection with said hollow electrical conducting means.
6. The apparatus of claim 5 wherein an electrically insulating weather protector is attached to the means closing the end of said cavity in said fuse holder located outside said tank, said weather protector surrounding and protecting a major portion of the end of the fuse holder located outside said tank.