US2385460A - Method of insulating electrical apparatus - Google Patents
Method of insulating electrical apparatus Download PDFInfo
- Publication number
- US2385460A US2385460A US475942A US47594243A US2385460A US 2385460 A US2385460 A US 2385460A US 475942 A US475942 A US 475942A US 47594243 A US47594243 A US 47594243A US 2385460 A US2385460 A US 2385460A
- Authority
- US
- United States
- Prior art keywords
- insulators
- insulating
- electrical apparatus
- parts
- cured
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/04—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing coils
- H01F41/12—Insulating of windings
- H01F41/127—Encapsulating or impregnating
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F27/00—Details of transformers or inductances, in general
- H01F27/28—Coils; Windings; Conductive connections
- H01F27/32—Insulating of coils, windings, or parts thereof
- H01F27/327—Encapsulating or impregnating
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/4902—Electromagnet, transformer or inductor
- Y10T29/49073—Electromagnet, transformer or inductor by assembling coil and core
Definitions
- This invention relates to an improved method of insulating electrical apparatus.
- An object of this invention is to provide a method of insulating electrical apparatus by means of insulating material that can be placed in position while in-a pliable state and then hardened or cured in place.
- Another object of the invention is to provide an improved method of insulating electrical apparatus by means of an initially plastic insulating ma terial that may be sheeted or shaped to a particular form required and semi-cured to facilitate handling prior to positioning in or around the apparatus to be insulated and thereafter curing the insulation in situ to a firm or relatively hard final condition.
- An additional object of the invention is to pro vide a method of insulating electrical parts whereby the insulators can be flexed or shaped 1 readily to fit or conform to the parts as desired and are thereafter finally cured in situ by the application of heat such-as the heat oi a potting compound where such is employed.
- Figure 1 is a side elevational view of a laminated core and coil structure of a transformer having improved semi-cured insulating forms or strips in position between ce oithe coils and core portions;
- Fig. 2 is an end elevational view of the apparatus shown in Fig. 1;
- Pig. 3 is a detached perspective view oi an irrsulating shape formed in accordance with the present improvements
- Fig. 4 is a broken side elevational View of a condenser casing containing the apparatus shown in Fig, 1.
- an elec trical condenser comprising a laminated core structure indicated generally by the numeral l0 and. three coils H, H and It.
- the particular form or shape of the core, or the form or number of coils is not pertinent to the present improvements and is to be considered as shown for illustrative purposes only.
- insulating material In the manufacture of condensers, insulating material generally is inserted between certain parts of the condenser such as between the coils and the adjacent portions of core legs I, it, II and ii.
- the insulating material generally heretofore employed is laminated sheet mica, the sheets being formed generally of flakes or smaller portions cemented together as by shellac.
- unfavorable conditions such as moisture or a relatively high degree of heat, especially where the sheets are under stress as when flexed around a part to be insulated, delamination frequentiy occurs which impairs the insulating properties and often results in impaired functioning or breakdown of the electrical apparatus with which such insulation is employed.
- Laminated mica sheet while flexible, can not readily be bent or shaped without fracture to fit closely around numerous parts which it sometimes is desirable to insulate and hence in the present improvements the high insulating character of mica is utilized in the formation of flexible sheets or forms which can be shaped as desired without fracturing and which are thereafter cured or treated to harden or permantize the shape thereof after the sheets or forms are placed in position in or around the part or parts to be insulated.
- a plastic composition including ground mica, the particles thereof being distributed throughout the mass.
- a composition which is suitable comprises principally mics and a rubber base compound, including conventional fillers, vulcanizing agents and accelerators.
- An example of a suitable composition is as follows:
- mice employed preferably is of e par-- ticle size, from 100 mesh to 325 mesh, for exam ple, has been found to be satisfactory.
- the mass may then be sheeted out to the desired thickness. or it can be given other required shapes, depending on the particular parts to be insulated.
- the sheets or forms are then given a partial cure, preferably to the point where they are no longer tacky or adherent one to another to facilitate handling and placement in their positions of use.
- Such partially cured shapes that is, sheets or other special forms, are pliable and can be readily bent, without fracturing, into close contact with numerous parts to be insulated and under conditions where use of laminated mica sheets, fiber and other materials have presented difficulties.
- such a semicured sheet can be given a channel form and is adapted to be inserted between one of the coils of the condenser and the adjacent leg portions of the laminated core as illustrated in Figs. 1 and 2.
- numeral i8 indicates several of such partially cured insulators.
- semi-cured insulators of suitable shapes and sizes may be provided for other parts or portions of transformers or other electrical apparatus, as will be appreciated.
- the semi-cured insulators After the semi-cured insulators are in position in the apparatus, they preferably are treated to further or completely cure or vulcanize the same to harden them suitably to resist deformation or alteration during use and increase their dielectric strength.
- the final hardening or vulcanlzing ofthe insulators is effected by the application of heat to the insulators in situ.
- the insulated apparatus is a transformer or like device which is generally filled with a hot potting compound after assembly of the device within its casing
- the final stage of vulcanization of the semi-cured insulators can be affected generally by the heat of the potting compound.
- the heat is sufficient generally to effect the final vulcanization of the insulators to a suitable degree of hardness where the insulators are of the composition above mentioned.
- sesame Additional heat may, or course, be supplied where necessary to eficct the vulcanization, but preferably the composition of the insulator is such that an adequate degree of hardness is imparted to the insulators by the heat of the potting compound.
- the presentimprovements facilitate the shaping and placement oi. the insulators in close contact with or around the parts to be insulated and when the insulators are finally cured sumciently to a hard or rigid condition. their dielectric values are such as to give satisfactory service in use with relatively high voltage apparatus.
- fully cured insulators of the illustrative composition mentioned above compare favorably in dielectric strength with laminated mica sheets of substantially equal thickness, but since the hot potting compounds generally employed in certain electrical apparatus frequently cause the binder oi the mica laminations to swell and the sheets to delaminate with resulting reduction in their dielectric strength (such reduction sometimes being as much as fifty per cent) the present improvements are of advantage since no delamination of the insulators occurs and the dielectric strength thereof is increased by increasiii) ing the curing temperature up to that required for maximum hardness.
- the method of insulating electrical apparatus having a casing and parts therein adapted to be separated by insulating material which comprises the steps of placing between said parts insulators of curable and pliable rubber base insulating material, and pouring into said casing around said parts and insulators a molten potting compound having a temperature suificiently high to eifect the curing of the insulators.
- the method of insulating electrical elements which comprises forming insulators of heatcurable plastic insulating material, partially curing the insulators to render the same manipulable and non-tacky, placing the partially cured insulators in insulating positions on or about the elements to be insulated, and thereafter applying to the insulators to finally cure the same in situ a potting compound at a temperature sufficiently high to effect said curing.
- the method of insulating parts of electrical apparatus which comprises inserting a partially cured shape of hardenable rubber base compound in position with respect to the part to be insulated. and thereafter finally heat-curing the shape to hardness by pouring therearound a potting compound at a curing temperature.
Description
Sept. 1945- M. OMANSKY 2,385,460
METHOD OF INSULATING ELECTRICAL APPARATUS Filed Feb. 15, 1943 ratented Sept. 25,1945
UNITED STATES PATENT QFFICE Morris Omansky, Brookline, Mara, assignor, by
memo assignments, to Jeflerson Electric Company, Beilwood, Ill., a corporation of Illinois 7 Application February 15, ms, Serial No. 415,942
8 Claims.
This invention relates to an improved method of insulating electrical apparatus.
In electrical apparatus, such as, for example, transformers andhigh tension apparatus, it has been customary to separate and insulate the parts. such as windings, through the use of mica sheets or shields. The mica used for this purpose is customarily built up into sheets from smaller pieces or flakes oi mica held together by a binder such as shellac. There are diiiiculties and disadvanhues connected with the use of such sheet mlca insulation, among which is its tendency to delamihate and deteriorate under the influences of heat or moisture, and the tendency to crack or break when bent.
An object of this invention is to provide a method of insulating electrical apparatus by means of insulating material that can be placed in position while in-a pliable state and then hardened or cured in place.
Another object of the invention is to provide an improved method of insulating electrical apparatus by means of an initially plastic insulating ma terial that may be sheeted or shaped to a particular form required and semi-cured to facilitate handling prior to positioning in or around the apparatus to be insulated and thereafter curing the insulation in situ to a firm or relatively hard final condition.
An additional object of the invention is to pro vide a method of insulating electrical parts whereby the insulators can be flexed or shaped 1 readily to fit or conform to the parts as desired and are thereafter finally cured in situ by the application of heat such-as the heat oi a potting compound where such is employed.
Other objects and advantages of the invention will be apparent from a consideration of the following specification and accomp y n drawing of a transformer selected for the purpose of illustrating the principles of the invention.
In the drawing, Figure 1 is a side elevational view of a laminated core and coil structure of a transformer having improved semi-cured insulating forms or strips in position between ce oithe coils and core portions;
Fig. 2 is an end elevational view of the apparatus shown in Fig. 1;
Pig. 3 is a detached perspective view oi an irrsulating shape formed in accordance with the present improvements;
Fig. 4 is a broken side elevational View of a condenser casing containing the apparatus shown in Fig, 1.
the principles or the present invention, an elec trical condenser is shown comprising a laminated core structure indicated generally by the numeral l0 and. three coils H, H and It. The particular form or shape of the core, or the form or number of coils is not pertinent to the present improvements and is to be considered as shown for illustrative purposes only.
In the manufacture of condensers, insulating material generally is inserted between certain parts of the condenser such as between the coils and the adjacent portions of core legs I, it, II and ii. The insulating material generally heretofore employed is laminated sheet mica, the sheets being formed generally of flakes or smaller portions cemented together as by shellac. When subjected to unfavorable conditions such as moisture or a relatively high degree of heat, especially where the sheets are under stress as when flexed around a part to be insulated, delamination frequentiy occurs which impairs the insulating properties and often results in impaired functioning or breakdown of the electrical apparatus with which such insulation is employed.
Laminated mica sheet, while flexible, can not readily be bent or shaped without fracture to fit closely around numerous parts which it sometimes is desirable to insulate and hence in the present improvements the high insulating character of mica is utilized in the formation of flexible sheets or forms which can be shaped as desired without fracturing and which are thereafter cured or treated to harden or permantize the shape thereof after the sheets or forms are placed in position in or around the part or parts to be insulated.
In carrying out the present improvements a plastic composition is prepared including ground mica, the particles thereof being distributed throughout the mass. A composition which is suitable comprises principally mics and a rubber base compound, including conventional fillers, vulcanizing agents and accelerators. An example of a suitable composition is as follows:
Parts by weight Rubber (smoked sheets) Sulfur 45 Stearic ri 1 Parailln 3 Zing nxirlo 1 du. Pont 808 accelerator s... 2 Ground mica above illustrative composition is one which In the drawing, for the purpose of illustrating 55 can be vulcanized to provide a hard final product.
The mice, employed preferably is of e par-- ticle size, from 100 mesh to 325 mesh, for exam ple, has been found to be satisfactory. The se-= lected materials are mixed in suitable mixers or in a rubber mill in accordance with known rubber manufacturing procedure and thereafter the mass preferably is aged for about twenty-four hours before use. The mass may then be sheeted out to the desired thickness. or it can be given other required shapes, depending on the particular parts to be insulated. The sheets or forms are then given a partial cure, preferably to the point where they are no longer tacky or adherent one to another to facilitate handling and placement in their positions of use. Such partially cured shapes, that is, sheets or other special forms, are pliable and can be readily bent, without fracturing, into close contact with numerous parts to be insulated and under conditions where use of laminated mica sheets, fiber and other materials have presented difficulties.
As shown in Fig. 3 of the drawing, such a semicured sheet can be given a channel form and is adapted to be inserted between one of the coils of the condenser and the adjacent leg portions of the laminated core as illustrated in Figs. 1 and 2. In Fig. 1, numeral i8 indicates several of such partially cured insulators. r
In position, semi-cured insulators of suitable shapes and sizes may be provided for other parts or portions of transformers or other electrical apparatus, as will be appreciated.-
After the semi-cured insulators are in position in the apparatus, they preferably are treated to further or completely cure or vulcanize the same to harden them suitably to resist deformation or alteration during use and increase their dielectric strength.
In accordance with the present improvements, the final hardening or vulcanlzing ofthe insulators is effected by the application of heat to the insulators in situ. Where the insulated apparatus is a transformer or like device which is generally filled with a hot potting compound after assembly of the device within its casing, the final stage of vulcanization of the semi-cured insulators can be affected generally by the heat of the potting compound. In Fig. 4 of the drawing, an assembled transformer is shown in posi-= tion in a casing i9 which has been filled with a potting compound 20. Potting compounds commonly used are asphaltic base material which is poured while hot into the casing to enclose the parts after the latter are positioned within the casing.
Where the potting compound is heated to 400450 F. the heat is sufficient generally to effect the final vulcanization of the insulators to a suitable degree of hardness where the insulators are of the composition above mentioned.
sesame Additional heat may, or course, be supplied where necessary to eficct the vulcanization, but preferably the composition of the insulator is such that an adequate degree of hardness is imparted to the insulators by the heat of the potting compound.
The presentimprovements facilitate the shaping and placement oi. the insulators in close contact with or around the parts to be insulated and when the insulators are finally cured sumciently to a hard or rigid condition. their dielectric values are such as to give satisfactory service in use with relatively high voltage apparatus. For example, fully cured insulators of the illustrative composition mentioned above compare favorably in dielectric strength with laminated mica sheets of substantially equal thickness, but since the hot potting compounds generally employed in certain electrical apparatus frequently cause the binder oi the mica laminations to swell and the sheets to delaminate with resulting reduction in their dielectric strength (such reduction sometimes being as much as fifty per cent) the present improvements are of advantage since no delamination of the insulators occurs and the dielectric strength thereof is increased by increasiii) ing the curing temperature up to that required for maximum hardness.
Whilev an embodiment of the improvement is disclosed for illustrative purposes, it will be apparent that variations thereof may be made use of within the scope and spirit of the invention.
I-claim:
1. The method of insulating electrical apparatus having a casing and parts therein adapted to be separated by insulating material which comprises the steps of placing between said parts insulators of curable and pliable rubber base insulating material, and pouring into said casing around said parts and insulators a molten potting compound having a temperature suificiently high to eifect the curing of the insulators.
2. The method of insulating electrical elements which comprises forming insulators of heatcurable plastic insulating material, partially curing the insulators to render the same manipulable and non-tacky, placing the partially cured insulators in insulating positions on or about the elements to be insulated, and thereafter applying to the insulators to finally cure the same in situ a potting compound at a temperature sufficiently high to effect said curing.
3. The method of insulating parts of electrical apparatus which comprises inserting a partially cured shape of hardenable rubber base compound in position with respect to the part to be insulated. and thereafter finally heat-curing the shape to hardness by pouring therearound a potting compound at a curing temperature.
MORRIS OSKY.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US475942A US2385460A (en) | 1943-02-15 | 1943-02-15 | Method of insulating electrical apparatus |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US475942A US2385460A (en) | 1943-02-15 | 1943-02-15 | Method of insulating electrical apparatus |
Publications (1)
Publication Number | Publication Date |
---|---|
US2385460A true US2385460A (en) | 1945-09-25 |
Family
ID=23889822
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US475942A Expired - Lifetime US2385460A (en) | 1943-02-15 | 1943-02-15 | Method of insulating electrical apparatus |
Country Status (1)
Country | Link |
---|---|
US (1) | US2385460A (en) |
Cited By (23)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2444522A (en) * | 1946-06-15 | 1948-07-06 | Nathanson Max | Ballast unit for fluorescent lamp lighting apparatus |
US2447376A (en) * | 1943-05-28 | 1948-08-17 | Bendix Aviat Corp | Ignition apparatus |
US2477132A (en) * | 1945-12-22 | 1949-07-26 | Gen Electric | Electric ballast |
US2484215A (en) * | 1946-08-30 | 1949-10-11 | Westinghouse Electric Corp | Synthetic resin compositions |
US2514015A (en) * | 1945-07-14 | 1950-07-04 | Tobe Deutschmann Corp | Ballast unit |
US2618689A (en) * | 1948-01-13 | 1952-11-18 | Gen Electric | Electromagnetic induction apparatus |
US2697855A (en) * | 1949-12-10 | 1954-12-28 | Elastic Stop Nut Corp | Manufacture of transformers |
US2709280A (en) * | 1953-12-08 | 1955-05-31 | Beneke Corp | Method for producing molded articles |
US2723933A (en) * | 1950-01-31 | 1955-11-15 | Hans D Isenberg | Method of making preformed insulation for high voltage transformer |
US2725539A (en) * | 1954-05-21 | 1955-11-29 | Elastic Stop Nut Corp | Transformers |
US2725616A (en) * | 1952-04-11 | 1955-12-06 | Louis R Duman | Method of forming air gaps in a transformer |
US2729850A (en) * | 1951-09-01 | 1956-01-10 | Western Electric Co | Methods of and apparatus for making cast articles |
US2810112A (en) * | 1953-01-26 | 1957-10-15 | Gen Electric | Transformer |
US2886854A (en) * | 1955-01-07 | 1959-05-19 | Albert W Franklin | Resistor grid and method of making |
US2899611A (en) * | 1959-08-11 | Capacitor | ||
US2949642A (en) * | 1957-03-14 | 1960-08-23 | Morris S Lieberman | Method of assembling a molded cable connector |
US2971640A (en) * | 1958-04-07 | 1961-02-14 | Charles D Snelling | Plastic foam packaging |
US3240848A (en) * | 1961-07-11 | 1966-03-15 | Gen Electric Canada | Method of making encapsulated transformers containing a dielectric gas |
US4510476A (en) * | 1983-06-21 | 1985-04-09 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | High voltage isolation transformer |
US5440286A (en) * | 1991-03-26 | 1995-08-08 | North American Philips Corporation | Electrical transformer structure with coil covers |
US5742489A (en) * | 1994-12-05 | 1998-04-21 | France/Scott Fetzer Company | Transformer housing and connector bushing |
US6138809A (en) * | 1997-09-17 | 2000-10-31 | Denso Corporation | Insulated electromagnetic coil for electromagnetic clutch |
US20080017686A1 (en) * | 2006-07-20 | 2008-01-24 | Buck William C | Cap nailer and feed system |
-
1943
- 1943-02-15 US US475942A patent/US2385460A/en not_active Expired - Lifetime
Cited By (23)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2899611A (en) * | 1959-08-11 | Capacitor | ||
US2447376A (en) * | 1943-05-28 | 1948-08-17 | Bendix Aviat Corp | Ignition apparatus |
US2514015A (en) * | 1945-07-14 | 1950-07-04 | Tobe Deutschmann Corp | Ballast unit |
US2477132A (en) * | 1945-12-22 | 1949-07-26 | Gen Electric | Electric ballast |
US2444522A (en) * | 1946-06-15 | 1948-07-06 | Nathanson Max | Ballast unit for fluorescent lamp lighting apparatus |
US2484215A (en) * | 1946-08-30 | 1949-10-11 | Westinghouse Electric Corp | Synthetic resin compositions |
US2618689A (en) * | 1948-01-13 | 1952-11-18 | Gen Electric | Electromagnetic induction apparatus |
US2697855A (en) * | 1949-12-10 | 1954-12-28 | Elastic Stop Nut Corp | Manufacture of transformers |
US2723933A (en) * | 1950-01-31 | 1955-11-15 | Hans D Isenberg | Method of making preformed insulation for high voltage transformer |
US2729850A (en) * | 1951-09-01 | 1956-01-10 | Western Electric Co | Methods of and apparatus for making cast articles |
US2725616A (en) * | 1952-04-11 | 1955-12-06 | Louis R Duman | Method of forming air gaps in a transformer |
US2810112A (en) * | 1953-01-26 | 1957-10-15 | Gen Electric | Transformer |
US2709280A (en) * | 1953-12-08 | 1955-05-31 | Beneke Corp | Method for producing molded articles |
US2725539A (en) * | 1954-05-21 | 1955-11-29 | Elastic Stop Nut Corp | Transformers |
US2886854A (en) * | 1955-01-07 | 1959-05-19 | Albert W Franklin | Resistor grid and method of making |
US2949642A (en) * | 1957-03-14 | 1960-08-23 | Morris S Lieberman | Method of assembling a molded cable connector |
US2971640A (en) * | 1958-04-07 | 1961-02-14 | Charles D Snelling | Plastic foam packaging |
US3240848A (en) * | 1961-07-11 | 1966-03-15 | Gen Electric Canada | Method of making encapsulated transformers containing a dielectric gas |
US4510476A (en) * | 1983-06-21 | 1985-04-09 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | High voltage isolation transformer |
US5440286A (en) * | 1991-03-26 | 1995-08-08 | North American Philips Corporation | Electrical transformer structure with coil covers |
US5742489A (en) * | 1994-12-05 | 1998-04-21 | France/Scott Fetzer Company | Transformer housing and connector bushing |
US6138809A (en) * | 1997-09-17 | 2000-10-31 | Denso Corporation | Insulated electromagnetic coil for electromagnetic clutch |
US20080017686A1 (en) * | 2006-07-20 | 2008-01-24 | Buck William C | Cap nailer and feed system |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US2385460A (en) | Method of insulating electrical apparatus | |
US2464029A (en) | Method of making transformers | |
US2464568A (en) | Electrical coil insulated with thermoplastic particles and thermoset polymer | |
CH268951A (en) | Current transformer with windings embedded in a solid insulating compound. | |
US2618689A (en) | Electromagnetic induction apparatus | |
US3318995A (en) | Cast electrical bushing construction having controlled and shielded shrinkage voids | |
EP0008883B1 (en) | Polymer concrete with cast threads and method of producing the same | |
US2925570A (en) | Current transformer | |
US3249658A (en) | Processes for curing rubber compounds | |
US3705372A (en) | Cast-type winding structure for electrical inductive apparatus | |
US3626587A (en) | Methods of constructing electrical transformers | |
US1796421A (en) | Wound electrical device and method of making it | |
US3896406A (en) | Screen for core legs for transformers, reactors and the like | |
US2381163A (en) | Electrical insulating material | |
US2950339A (en) | Method and structure for encapsulating electric apparatus | |
KR100769640B1 (en) | molding method of Voltage transformer for metering of high reliability | |
JPS55120121A (en) | Manufacture of resin-molded coil | |
US2880401A (en) | Means for controlling crack formations | |
US2900611A (en) | A method of restraining forces of noncircular cylindrical coils | |
US3147456A (en) | Current transformer | |
JPH06224064A (en) | Manufacture of electromagnetic induction apparatus winding | |
JPH0629114A (en) | Dust core and manufacture thereof | |
US2836777A (en) | High voltage slug capacitor | |
GB1191624A (en) | Improvements in or relating to Resinous Components for use in Electrical Insulation | |
JPS6221252B2 (en) |