US 3821678 A
Description (OCR text may contain errors)
United States Patent [1 1 [111 3,821,678 [4 June 28, 1974 TRANSFORMER HAVING A CAST WINDING STRUCTURE WITH INTEGRAL INSULATING BARRIERS  Inventor: Edgar R. Eley, Athens, Ga.  Assignee: Westinghouse Electric Corporation,
 Filed: Oct. 2, 1973 ] Appl. No.: 402,683
 US. Cl 336/96, 336/192, 336/196 [51 1 Int. Cl. H0lf 27/02  Field of Search 336/96, 196, 198, 205, 336/192  References Cited UNITED STATES PATENTS 3,5l6,040 6/1970 Ripley 336/96 Primary Examiner-Thomas J. Kozma Attorney, Agent, or Firm-J. R. Hanway ABSTRACT A core and winding assembly insulated by a casing constructed of solid insulating material. Insulating barriers project from the casing to prevent electrical arc- 7 ing and creepage between winding terminals and the core, and between certain winding terminals. An insulating barrier includes plates orientated in parallel relationship with a gap therebetween to increase the creepage distance. The barriers are formed as an integral part of the casing.
4 Claims, 5 Drawing Figures PATENTEnJuuza mm FIG. I.
TRANSFORMER HAVING A CAST WINDING STRUCTURE WITH INTEGRAL INSULATING BARRIERS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates, in general, to electrical inductive apparatus and, more specifically, to dry-type transformer insulation structures.
2. Description of the Prior Art Insulating the windings and leads in high-voltage, dry-type power transformers requires special consideration of the fact that no liquid dielectric is present as in oil-filled transformers. In dry-type transformers, it is usually necessary to insulate the electrical components more completely than in oil-filled transformers since air'has a lower dielectric constant than mineral oil. This requirement has deterred the use of cast epoxy insulated windings in dry-type power transformers since the exposed leads from the winding require separate insulation structures for proper electrical performance. Providing such insulation according to conventional arrangements involves extra labor costs and increases the cost of the apparatus. Therefore, it is desirable, and it is an object of this invention, to provide a dry-type power transformer having a cast epoxy insulation structure which conveniently, economically, and adequately insulates the winding structure and the winding leads.
SUMMARY OF- THE INVENTION There is disclosed herein a new and useful dry-type power transformer which is sufficiently insulated by an epoxy material cast around'a winding of the -trans-' BRIEF DESCRIPTION OF THE DRAWING Further advantages and uses of this invention will become more apparent when considered in view of the following detailed description and drawing, in which:
FIG. II is a view of a transformer constructed according to this invention with the enclosure broken away;
- FIG. 2 is a view of a core and winding structure constructed according to this invention;
F IG.-2A is a schematic diagram of the core and winding structure shown in FIG. 2;
F IG'. 3 is a side elevational view of the winding structure shown in FIG. 2; and
FIG. 4 is an end elevational view of the winding structure shown in FIG. 3.
DESCRIPI-IONOF THE PREFERRED EMBODIMENTS Throughout the following description, similar reference characters refer to similar elements or members in all the figures of the drawing.
Referring now to the drawing, and to FIG. l in partic ular, there is shown a dry-type power transformer ltl constructed according to this invention. The trans former enclosure l2 houses the core l4 and the winding structure 116 of the transformer ill. The mounting frame 18 supports the core 114, the winding structure 16, and the terminal board 20. Electrical leads 22 connect the terminals on the terminal board 20 to terminals extending from the winding structure 116, such as the terminals 24, 26 and 28.
The Winding structure l6 is embedded in a casing constructed from an epoxy resin material. Projections,
or plates, conveniently formed in the epoxy insulating material during the casting process, provide the necessary arcing and tracking resistance between various electrical members of the transformer lltl. Various other arrangements of the winding terminals and mounting structure may be used without departing from the scope of the invention. In this specific embodiment, the epoxy casing encapsulates only the highvoltage winding of the transformer 10. Although not shown in FIG. I, a non-encapsulated low-voltage winding is located between the high-voltage winding and the core 14, and is connected to appropriate terminals which are not illustrated. It is also within the contemplation of this invention that both the high-voltage and the low-voltage windings could be encapsulated within the same epoxy casing.
FIG. 2 illustrates the core 14 and the winding structure 16 in greater detail. The magnetic core 14 includes the wound core sections 32 and 34 which each contain an opening through which the winding structure 16 extends. An insulating barrier 42 electrically separates the terminals 24, 26, 28 and 30 from the magnetic core 14. The barrier 42 must provide sufficient dielectric strength and creepage distance to prevent electrical breakdownbetween the terminals and the core 14. This region is stressed by the maximum potential on the high-voltage winding.
FIG. 2A represents schematically the electrical position of the winding terminals. All of the terminals connected to the high-voltage winding 16 must be insulated from the core 14 adequately to protect against the maximum voltage on the winding with respect to ground. The terminal 28 must be insulated from the terminals 24, 26 and 30 adequately to protect against substantially the maximum voltage across the winding 16. The insulation requirements between each of the terminals 36, 38 and 40, and between each of the terminals 24, 26 and 30, are not as stringent as the other insulation requirements since the voltage existing between such terminals is only equal to the voltage developed between a few turns of the winding.
Referring again to FIG. 2, the insulating barrier 44 electrically separates the terminals 36, 38 and 40 from the magnetic core 14, and the insulating barrier 46 electrically separates the terminal 28 from the terminals 24, 26 and 3111i. The insulating barrier42 includes the plates 48 and 50 which are formed from the epoxy material from which the casing 52, which encapsulates the high-voltage winding 16,, is constructed. The plates 48 and Sll'are orientated substantially parallel to each other with a gap 54 located therebetween. The number of plates contained in the barrier 42 depends largely on the creepage distance necessary to prevent electrical creepage between the core 14 and the terminals 24, 26, 28 and 30. The insulating barrier 44 includes the plates 56 and 58 which are formed from the same epoxy material and which have a gap 60 located therebetween. Similarly, the insulating barrier 46 includes the plates 62 and 64 which are also formed from the same epoxy material as the casing 52 and which have a gap 66 located therebetween.
FIG. 3 is a side elevational view of the casing 52 which encloses the high-voltage winding 16. The inside surfaces 70 and 72 of the casing 52 define an opening sufficiently larger than the core 14 to allow for placement of the low-voltage winding. The distance between the inside surfaces 74 and 76 shown in the end elevational view of FIG. 4 is also larger than the portion of the core 14 to be inserted therein for the same reason.
The dry-type transformer disclosed herein provides the required electrical insulation characteristics, with a minimum of additional work, by forming suitably shaped and positioned insulating barriers during the encapsulation of thewinding structure with an epoxy material. Since numerous changes may be made in the above-described apparatus, and since different embodiments of the invention may be made without departing from the'spirit thereof, it is intended that all of the matter contained in the foregoing description, or shown in the accompanying drawing, shall be interpreted as illustrative rather than limiting.
I claim as my invention:
1. A dry-type transformer comprising;
a magnetic core;
a winding assembly inductively coupled to said magnetic core;
a solid electrical insulation structure encapsulating at 4 windingassembly and extending through said solid insulation structure; and
barrier means fomiing an integral part of and being of single unit construction with said insulation structure, said barrier means having a first portion projecting between said terminal means and an exposed portion of said magnetic core to provide electrical insulation between. said terminal means and said core and a second portion which extends between the two individual terminals, said second portion including at least two substantially parallel plates formed of the material from which the insulation structure is constructed, with said plates containing a gap therebetween which does not contain terminals.
2. The transformer of claim 1 wherein the first portion of the barrier means includes at least two substantially parallel plates formed of the material from which the insulation structure is constructed, with said plate containing a gap therebetween which does not contain terminals.
3. The transformer of claim 1 wherein the solid electrical insulation structure and the barrier means are constructed from a material containing epoxy resin.
4. A dry-type transformer comprising:
a wound magnetic core having openings therein;
a tapped winding structure extending through said openings;
an epoxy casing in which said winding structure is encapsulated;
first and second terminals extending from through therebetween'which does not contain terminals.