US3792528A

US3792528A - Process of for manufacturing electrical apparatus such as casing-enclosed transformers and reactors

Info

Publication number: US3792528A
Application number: US00250060A
Authority: US
Inventors: J Schober
Original assignee: BBC Brown Boveri France SA
Current assignee: BBC Brown Boveri AG Switzerland; BBC Brown Boveri France SA
Priority date: 1971-05-19
Filing date: 1972-05-03
Publication date: 1974-02-19
Anticipated expiration: 1991-02-19
Also published as: DE2128627A1; IT955541B; FR2137996A1; SE387469B; CH532307A; AT318068B; CA981887A

Abstract

In a process and apparatus for manufacturing encased electrical equipment such as transformers or reactors, the windings are first formed and insulated by a wrapping of insulating material, e.g. paper applied to the conductor bars; the insulated windings are then dried in an oven, pressed to their final size and then sealed with a sealing agent. e.g. paraffin. Thereafter, the dried, pressed and sealed windings are assembled with their magnetic structure and installed in the casing, and apparatus is then utilized to wash out the sealing agent from the windings and dry them, after which the casing is filled with the usual insulating oil. The apparatus for washing the sealing agent from the windings and drying them includes a combined boiler-still in which the washing medium, e.g. kerosene, is heated to vaporization and delivered hot to the casing which serves to wash out the sealing agent and form a slurry with the latter. The heat from the vapor also serves to heat up and dry the windings. This slurry is pumped from the casing, passed through a filter and delivered to a combined storage tank-still from which it is pumped back to the boiler-still for re-vaporization of the washing medium and recovery of the sealing agent which is then drained off for re-use to seal other windings. A vacuum pump connected to the casing through a cooling trap serves to maintain the casing under a vacuum and also deliver water drawn off at the same time, from the cooling trap to the storage tank-still. Vaporized washing medium is also selectively delivered from the boiler-still to a condenser, and the condensed washing medium is then passed into a storage tank having an outlet by means of which the washing medium can be delivered through an equalizing conduit to the storage tank-still. The function of the storage tank for the condensed washing medium and equalizing conduit is to enable the apparatus to be operated selectively, i.e. with or without balance of the washing medium.

Description

United States Patent Schober PROCESS OF FOR MANUFACTURING ELECTRICAL APPARATUS SUCH AS CASING-ENCLOSED TRANSFORMERS AND REACTORS [75] Inventor: Johannes Schober,Mellinge n,

Switzerland [73] Assignee: Aktiengesellschaft Brown, Boveri &

' Cie, Baden, Switzerland [22] Filed: May 3, 1972 [21] Appl. No.: 250,060

[30] Foreign Application Priority Data Berberich et a1. 29/605 Primary Examiner-Richard J. Herbst Assistant Examiner-Carl E. Hall Attorney, Agent, or Firm-Pierce, Scheffer & Parker [57] ABSTRACT In a process and apparatus for manufacturing encased electrical equipment such as transformers or reactors, the windings are first formed and insulated by a wrap- [451 Feb. 19, 1974 ping of insulating material, e.g. paper applied to the conductor bars; the insulated windings are then dried in an oven, pressed to their final size and then sealed with a sealing agent. e.g. paraffin. Thereafter, the dried, pressed and sealed windings are assembled with their magnetic structure and installed in the casing, and apparatus is then utilized to wash out the sealing agent from the windings and dry them, after which the casing is filled with the usual insulating oil. The apparatus for washing the sealing agent from thewindings and drying them includes a combined boiler-still in which the washing medium, e.g. kerosene, is heated to vaporization and delivered hot to the casing which serves to wash out the sealing agent and form a slurry with the latter. The heat from the vapor also serves to heat up and dry the windings. This slurry is pumped from the casing, passed through a filter anddelivered to a combined storage tank-still from which it is pumped back to the boiler-still for re-vaporization of the washing medium and recovery of the sealing agent which is then drained off for re-use to seal other windings. A vacuum pump connected to the casing through a cooling trap serves to maintain the casing under a vacuum and also deliver water drawn off at the same time, from the cooling trap to the storage tank-still. Vaporized washing medium is also selectively delivered from the boiler-still to a condenser, and the condensed washing medium is then passed into a storage tank having an outlet by means of which the washing medium can be delivered through an equalizing conduit to the storage tank-still. The function of the storage tank for the condensed washing medium and equalizing conduit is to enable the apparatus to be operated selectively, i.e. with or without balance of the washing medium.

'11 Claims, 6 Drawing Figures

PATENTEDFEBI slam sum

2 or 4 Fig.2b

PATENTEU FEB 1 9 m4 SHEET t UP 4 I This invention relates to an improved process for manufacturing electrical apparatus such as transformers and reactors consisting of coil windings mounted within oil-filled casings and to a novel apparatus by which the process can be practiced.

The primary object of the invention is to provide an improved process and related apparatus by means of which one is enabled to manufacture in a particularly economic manner and using production cycle techniques with substantial savings in assembly work and time, casing enclosed high-voltage transformers and reactors and with particular emphasis on the production of high quality, paper-insulated windings for such apparatus which is achieved at a much lower production time than has been heretofore possible, and especially with respect to furnace time necessary for drying of the windings to remove moisture.

It is known to insulate electrical conductors with paper and to produce electrical windings from conductors which have been so insulated. The windings, prefabricated in this manner, are then dried to remove moisture and pressed in order to arrive at their final, stabilized dimensions. However, for technical reasons, for example, when manufacturing multi-phase windings forhigh-load transformers, it becomes necessary to store the dried and pressed windings, or banks of windings before being installed in their casings, with the result that the paper insulation on the windings will again absorb moisture from the ambient atmosphere until a balance is reached. The higher thehumidity of thestorage space the higher will be the amount of moisture absorbed by the insulation. Also, even during assembly of the individual windings into banks of coils, will the windings absorb moisure fromthe surrounding air thus making it necessary to again subject them to heat treatment in a drying oven, so that by a single, or if necessary a multiple drying operation such contraction of the coils is attained that it becomes possible to install the yoke. Final assembly of the active component, i.e. the windings andtheir magnetic structure, is again accomplished at ambient humidity, especially its wiring, requiring a rough drying of the active component, the respacing and re-pre ssing again taking place at ambient humidity, so that finally a full drying and additional pressing of the. active component becomes necessary. Installation of the active component in its casing is also accomplished at ambient humidity, thus requiring another, or final drying of the active component. The final step in the manufacturing process is to impregnate the active component in its casing with insulating oil, under vacuum.

Previous attempts have been made to reduce the wetting of the windings by impregnating them with oilafter compression to their final, stabilized size, and to complete the processing of the windings in such state. Another known attempt to solve the problem, especially in the case of small transformers, of decreasing mois ture absorption, has been to soak or impregnate the winding insulation with paraffin.

impregnation of the windings with oil is not a satisfactory solution since oil continuously drips off the windings onto the floorof the work space and thus creates a vexing cleaning problem. Moreover, handling of the oil impregnated windings is rather troublesome, and windings treated in this manner obviously tend to pick up and hold rather large-sized dust particles. Also, the oil absorbed by the paper insulation will become fouled by absorption of gases, or by oxidation, and especially so during the still necessary final drying operation whereby impregnating oil will remain within the insulation, and causes a greater fire hazard.

lmpregnation of the paper insulation on the windings with paraffin likewise is no solution to the problem because paraffin is brittle and therefore cannot be subjected to great mechanical stress, and a lasting impregnation will'show a great tendency to form cracks. lmpregnation of the windings with insulating oil, which follows in the usual manner after such specific treatment, becomes quite difficult due'to the prior impregnation with paraffin because even traces of paraffin will prevent full saturation of the insulation, thus leading to formation of air pockets and consequently to a much greater chance for glow-discharge with all the undesirable consequences thereof. I

In order to at least somewhat shorten the abovedescribed multi-step manufacturing operation which requires a very long time, it has recently been suggested to use kerosene vapor instead of hot air, as the heat transfer agent for heating the windings to be dried, or for heating of the completed active component, thus supplying more quickly the relative greatiquantities of heat required by the active copper and iron. However, this method does not result in any improvement concerning the above-described impregnating process,v or concerning the protection of the electrical windings against moisture penetration, especially during the manufacture of the windingsas well as the active components. i

The primary objective of the present invention is not only to avoid the deficiencies of the above-described manufacturing process but also to establish an improved process which requires fewer steps in the manufacture of the windings, including their assembly with the magnetic structure thereby to complete the active component of the apparatus such as a super-voltage transformer or compensation reactor and the insulation on the winding will be maintained free. from air, gases,

- moisture, foreign matter or entrapped matter up to the its casing will, under no circumstances be hindered.

In accordance with .the invention, these previously existing problems are solvedin that the conductors forming the windings after being wrapped with their insulation, usually paper, are dried and pressed into their final stabilized dimensions, the windings are then sealed with a sealing agent and assembled with their magnetic structure (core and yoke) to form the active component of the apparatus, the active component is then installed in the permanent casing provided therefor, a hot washing agent in vapor form is then circulated through the casing to wash out the sealing agent from the insulation, as well as heat up and dry the active component, and insulating oil is then introduced into the casing to impregnate the active component.

As explained above, paper is the most common material used for insulating the conductors from which the windings for the apparatus are formed. Various types of sealing agents can be used to seal the insulation on the coil windings against moisture penetration including, fluoro-chloro telomerization products, or paraffines. For washing out the sealing agent from the windings, several different mediums have been found to be satisfactory including kerosene, fluorinated organic compounds such as a carbon fluoride, chlorocarbon fluoride, fluorinated amines or ethers having the proper boiling points. If desired, an oxidation inhibitor can be admixed with the sealing agent as a protection against oxidation, and in the case where paraffin is used as a sealing agent, the oxidation inhibitor admixed with it can be either ditertiarybutyl-p-cresol (DBPC) or B phenylnaphthylamine. Other oxidation inhibitors can be utilized.

For performing the improved process in a particu larly advantageous manner, a novel apparatus has been developed. This includes a combined boiler and still for vaporizing the washing agent which is conducted in vapor form from one outlet thereof by way of a conduit and shut-off valve to an inlet at theupper endof the evacuated casing containing the active component (windings and magnetic structure). The vaporized washing agent washes out the sealing medium from the windings, and the slurry of washing agent and sealing medium is pumped off from an outlet at the bottom of the casing through a conduit including a shut-off valve and a pump, the slurry then being passed through a filter and from the latter to a combined storage tank and still. The slurry is then fed back from the latter into the combined boiler and still through a conduit including another pump where the washing agent and sealing medium are separated, the washing agent then being revaporized and the sealing medium being drawn off for re-use.

The vacuum within the casing is produced by a vacuum pump connected to an inlet to the casing at the upper end thereof through conduit means including a shut-off valve at the casing side and a cooling trap intermediate the shut-off valve and vacuum pump. Moisture within the casing and drawn off through the conduit connected to the vacuum pump is separated out in the cooling trap and this liquid is delivered through a conduit containing a shut-off valve to the conduit which carries off the slurry of the washing agent and sealing medium from the casing. The liquid moisture i.e. water, is removed from the combined storage tankstill by a drain pipe.

A second outlet from the boiler-still delivers some of the washing agent in vapor form through conduit means including a shut-off valve, the valve being followed by a condenser which liquifies the washing agent for delivery to a storage tank which is maintained under vacuum by another vacuum pump, and this storage tank is connected by way of an equalizing conduit to the combined storage tank and still for the slurry of washing agent and sealing medium. The function of the storage tank for the liquidified washing agent is to enable one to achieve a balance" for the agent, if desired. The apparatus can be operated with, or without balance of the washing agent, this being controlled by means of the shut-off valves provided at the two outlets from the boiler-still.

This apparatus which can, of course, be modified in certain respects will ensure continuous handling of insulated windings of the type described, even in the case where large compact banks of coils are involved, thus guaranteeing that the redried winding insulation will possess the same impregnation capacity for absorbing the impregnating oil or other dielectric medium in the same manner as would a new and dry winding which is free from inclusions of gases and foreign matter.

The improved process in accordance with the invention and especially in conjunction with the apparatus developed for its practice is particularly advantageous and applicable in connection with the manufacture of high and super'high voltage windings insulated with paper, and particularly for transformer and reactor coils of large size, at substantial savings in labor and time, and which so far as quality is concerned are at least equal to thatachieved by other processesof treatment heretofore known.

The paper-insulated conductor bars which are to form the windings are bundled and preferably ovendried under a vacuum' at a temperature of approximately 1 10C and simultaneously pressed, for example, at a pressure of 30 kg/cm to achieve their final, stablizied size. While still in their heated state they are the impregnated with a moisture-proof sealing agent e.g. paraffin heated to C by immersion. This immersion can take place in the heating oven by dipping the conductor bars in a vessel containing the liquified paraffin and which is located within the oven. After final assembly and installation within the permanent casing provided for the transformer or reactor, or other similar device as the case may be, the sealed conductors are subjected for approximately 40 hours to treatment under vacuum with the vaporized washing agent e.g. kerosene at llOto C whereupon after stopping the supply of kerosene vapor, the liquid kerosene present within the insulation is vaporized by additional evacuation.

It has been found that paper insulation treated in the above-described manner, is capable of absorbing the impregnating medium, i.e. insulating oil, in the same manner as untreated, i.e. a completely fresh and dry paper insulation, a fact proved by measurement of the capillary rise of insulating oil within the paper tape unwrapped from the conductor, the tape being placed in a vertical position and with the lower end dipped into the insulating oil. Such measurements, using an insulating oil with a viscosity of 20 centistokes, show, after ten minutes, a capillary rise of 3.5 mm for the outer paper layer of the outer conductors of a conductor bundle, and a capillary rise of 4 mm for the inner paper layer of such conductors. The outer paper layer of the inner conductors of the conductor bundle showed a capillary rise of 4 mm, and the inner paper layer of these same conductors likewise showed a capillary rise of 4 mm. In comparison, the capillary rise of insulating oil, in the case of untreated paper is likewise 4 mm after ten minutes. The indicated capillary risc values of 3.5, 4, 4,4,

and 4 mm'change to 7, 7, 8,8, and 9 mm if the time is increased to sixty minutes. Although, during the sealing of the conductors, the paper insulation canabsorb paraffin in quantities up to 70 percent of its own weight, it becomes feasible, by a step in the process, to wash, melt or dissolve this paraffin from the insulation inan economic manner so that the paraffin is recovered and becomes re-usable. For this purpose the mixture of washing agent and sealing medium, e.g. kerosene and paraffin bleeding off the winding in the casing, is returned to the boiler, serving also as a still, the kerosene being distilled off the paraffin into the storage tank, and the paraffin settling in the boiler being drawn off in its hot and still liquid state and passed through a filter and r'e-used to seal other windings to be treated in accordance with the process of the invention. Cooling of the kerosene, which occurs during this operation, will not cause any clogging of the conduit system employed for conveying the various mediums so long as the kerosene-paraffin slurry does not contain more than 40 percent paraffin. This holds true because only a small portion of the paraffin will dissolve in the cold kerosene, or will precipitate during the cooling off period in the form of a fine-crystalline clurry of crystals and can thus be pumped without difficulties. If the paraffin retains a kerosene residue of no more than to percent, its properties which are significant for the technological processes, for example, adhesion, will for all practical purposes not be effected when it is'in a solidified state at room temperature. Above all, the windings treated with the paraffin will retain their full capacity of being impregnated with insulating oils, after the paraffin has been removed. Furthermore, the kerosene is very stable, so far as insulating oil is concerned due to its chemical structure, and the oil is not therefore adversely affected by the kerosene. Also, since oxidation inhibitors can be admixed with the paraffin, it becomes possible to prevent formation of organic acids, or acid products, which may occur in particular, at the surface of the oil.

Theinvention is advantageous in particular due to the fact that the time required for treatment of the windings or compact banks of windings can be reduced by approximately 30 percent.

Furthermore, when the process in accordance with the invention is utilized it becomes possible to establish a work synchronization process for making the windings which permits manufacture of various types of windings at different times and to assemble them in final form without intermediate drying steps due to the stabilization built into them by application of the sealing medium. The sealing technique, accomplished in accordance with the invention prevents, primarily repetitious wetting of the winding or of the winding insula-- tion so that it becomes possible to dispense with many of the intermediate steps required by previously known or standard processes, namely, repeated oven treatment of the windings, repeated tightening by the pressing components, and spacing of the windings by means of washers, to overcome shrinkage caused by dring of he Pa ,iy l eaths yire ev n time, n the case of largesized transformers, lasts up to 14 days, representing a highly work-intensive treatment of the windings, the improved process in accordance with the present invention will be greatly advantageous because the winding units manufactured thereby will become stabilized at the time when theyare first dried, with the result that up to the time of the final drying operation, all intermediate heat treatment steps heretofore required in connection with other processes, and including also the re-spacing steps and interruptions of the drying operations will have been omitted. 1 The result is therefore considered to represent an advantageous and significant savings in winding assembly and calibration work, savings which are particularly important for the manufacture of windings which consists of banks of coils, and particularly those which are required to operate a super high voltage ratings.

The foregoing as well as other objects and advantages of the invention will become more apparent from the following detailed description of the process and an apparatus by which it may be performed, and from the accompanying drawings wherein:

FIG. 1 is a diagrammatic representation of the sequential steps involved in a known process for the manufacture of insulated winding components in comparison with the much fewer steps required in the practice of the improved process in accordance with the present invention;

FIGS. 2a and 2b are elevation and plan views respectively of a known arrangement for affecting stabilization of a winding;

FIG. 3 is a diagrammatic illustration of an apparatus by which the process in accordance with the present invention is performed;

FIG. 4 illustrates a bundle of paper insulated electrical conductor bars for which the process in accordance with the invention may be practiced; and

FIG. 5 illustrates a portion of a transformer structure with its high and low voltage paraffin-sealed windings in final assembled form on the related part of the core and yoke components of the magnetic supporting structure and as it would be installed in its permanent casing and treated in accordancev with the process of the invention by the apparatus depicted in FIG. 3.

With reference now to FIG. 1 and to the known process illustrated at the left side of this view, the various sequential steps involved are indicated by rectangles, and in those steps where heating is involved to dry out the windings, the rectangle has been drawn with dual lines. In step 1, the initial oven drying and pressing of the paper insulated conductor is carried out. Step 2 indicates temporary storage of the initially dried and pressed winding, i.e. in a storage room at ambient humidity until further needed. In step 3, shrink treatment of the winding in an oven takes place by means of which sufficient contraction takes place in order to permit the winding to be assembled with the core and yoke components of the magnetic structure. Step 4 indicates final assembly of the shrunkwinding with its core and yoke structure, this likewise taking place in a workroom at ambient humidity. Step 5 indicates rough drying of the final assembly of windings and magnetic structure in an oven. Re-spacing of the windings after rough drying is carried out in step 6 also under ambient humidity conditions. Thorough drying of the re-spaced windings is carried out in an oven in step 7. Installation of the finally dried assembly of re-spaced windings and magnetic structure in the casing is indicated at 8, and in step 9 of the known procedure, re-drying of the encased winding'and magnetic structure and impregnation of the winding with insulating oil takes place.

The steps involved in the improved procedure in accordance with the present invention are shown at the right on FIG. 1. In step 1', initial drying, spacing and stabilization of the insulated windings by application of the sealing medium thereto takes place. Step 2 which corresponds with step 4 of the prior art shown at the left, involves assembly of the stabilized windings with their core and yoke structureand which is done in a workroom under ambient humidity conditions. In step 3', which corresponds somewhat with step 8 of the known procedure, the assembly of windings and magnetic structure in the permanent casing takes place. However, distinctly different from step 8 is that treatment of the assembled winding and magnetic structure with the washing agent, e.g. kerosene, takes place in the casing, so as to remove all of the sealing medium,

e.g. paraffin from the windings. In the final step 4', which corresponds somewhat to step 9 of the known procedure, the assembly of winding and magnetic structure, now also dired by the hot washing agent is then impregnated with insulating oil.

FIG. 2 illustrates a known arrangement for mounting prefabricated paper insulated windings for storage prior to their assembly on their magnetic structure. The winding 1 is mounted between a lower supporting ring 2 and an upper supporting ring 3. The winding and supporting rings are then pressed together by means of a clamping arrangement including lower and upper pres

sure plates

5,6 and a plurality of tension rods provided with compression springs 8 and tightening nuts 9. Preferably woodenv spacer blocks 7 are inserted between the upper end of winding 1 and the upper pressure plate 6. The winding mountingstructure as depicted in FIG. 2 is utilized in connection with the manufacture of medium and also large sized windings which are stabilized in the clamped and dry condition by application of a sealing medium, e.g. varnishes, especially on a plastic base, and this is done preferably by a soaking or dipping operation. However, such method cannot be utilized for windings which will be subjected to high and super high voltages since the sealing medium, i.e. the varnish utilized to protect the winding against ambient humidity will remain permanently in the insulation and hence will not permit extremely high voltage stresses in the winding for the reasons hereinbefore explained.

In the practice of the present process, the insulated windings can be mounted in essentially the same manner as depicted in FIG. 2 and pressed to their final dimensions, after which they are placed in an oven, and perhaps under a vacuum, and impregnated with the sealing medium, e.g. paraffin which is in a hot liquid state. The insulated windings thus become sealed against absorption of moisture from the ambient air and thus are no longer subjected to any changes in dimension; i.e. the windings become completely stabilized.

With reference now to FIG. 3, which illustrates a particularly advantageous apparatus by which the process can be performed, a combined boiler and still 1 serves for vaporizing the washing agent e.g. kerosene which is conducted in vapor form. from one outlet thereof by way of a conduit and shut-off valve 2 to an inlet connection 3 at the upper end of the evacuated casing 4' containing the assembled active component (windings and magnetic structure). The vaporized washing agent washes out the sealing medium e.g. paraffin from the windings, and the slurry of washing agent and sealing medium is pumped off from the drain outlet at the bottom of the casing through a conduit including a shut-off valve 6 and a pump 5, the slurry then being passed through a filter 11 and from the latter to a combined storage tank and still 12. The slurry is then fed back from the latter into the combined boiler and still 1 through a conduit including another pump 14 where the washing agent and sealing medium are separated, the washing agent then being re-vaporized and the sealing medium being drawn off from a bottom drain pipe 15 for re-use. I I

The vacuum within the casing 4 is produced by a vacuum pump 7 connected to an inlet, to the casing at the upper end thereof through conduit means including a shut-off valve 8 and a cooling trap 9 intermediate the shut-off valve 8 and vacuum pump 7. Moisture within the casing and drawn off through the conduit connected to the vacuum pump is fseparated out in. the cooling trap 9 and this liquid is delivered through a conduit containing a shut-off valve 10 to the conduit which carries off the slurry of the washing agent and sealing medium from the casing 4. The liquid moisture i.e. water, is removed from the combined storage tankstill 12 by a drain pipe 13.

A second outlet from the boiler-still l delivers some of the washing agent in vapor form through conduit means including a shut-off valve 16, the valve being followed by a condenser 17 which liquifies the washing agent for delivery to a storage tank 18 which is maintained under vacuum by another vacuum pump 19, and this storage tank is connected by way of an equalizing conduit 20 to the combined storage tank and still 12 for the slurry of washing medium and sealing agent. The function of the storage tank 18 for theliquified washing medium is to enable one to achieve a balance for the medium, if desired. The apparatus can be operated with, or without balance of the washing medium, this being controlled by means of the shut-off

valves

2,16 provided at the two outlets from the boiler-still 1.

This apparatus which can, of course, be modified in certain respects will ensure continuous handling of insulated windings of the type described. Moreover, and what is also important, the apparatus assures recovery of the sealing agent, e.g. paraffin having a quality which makes it re-usable for sealing other windings to be installed in other casings after the one being processed has been completed. After the supply of vaporized washing medium, e.g. kerosene to the casing 4 has been cut off, e.g. after a 40 hourtreatment under vacuum with vaporized kerosene at a temperature of from 1 l0to C, the vacuum pump 7 is contained in operation to assure removal of all liquid kerosene within the winding insulation and casing. Simultaneously with washing out of the sealing agent, the hot vapor also serves as a heat transfer agent to heat up and effect final drying of the windings. The casing 4 is now disconnected from the apparatus, followed by impregnation of the windings with insulating oil with which the casing is filled.

Another casing with the windings therein protected by the sealing agent is then connected to the apparatus and the process repeated.

FIG. 4, which is a cross-sectional view, depicts a bundle of nine conductor bars having a rectangular configuration which can be treated in accordance with the process of the invention. The eight outer conductor bars are denoted by numeral 1 and the inside conductor bar, surrounded by the outer bars, is denoted by numeral 2. The individual copper conductor bars are insulated by winding the same with paper tape, the paper insulation 3 consisting, for example, of 24 layers of paper, each with a thickness of 0.05 'mm. and wound onto the conductor bar in helically manner such as to establish an overlap factor of one-third. FIG. 4 also illustrates the structure of the stabilized conductor bundle after treatment with kerosene, but without indicating the kerosene-paraffin residues, if any, and without showing the structural components which hold the conductors of the bundle in place. Any space not occupied by the conductor material itself and by the paper insulation can, therefore, be taken up fully by the insulating 9 oil during the final re-drying'and impregnation operation in accordance with the invention.

FIG. illustrates one portion of a high-power transformer structure which can be manufactured in a particularly advantageous manner when the process and apparatus of the invention are utilized. The upper yoke of the magnetic structure is designated by numeral 1, the lower yoke by 2, the core column by 3, the yoke lamination by 4 and the lower yoke lamination by 5. Upper and lower rings 6 support all of the windings, the supporting base is shown at 7, the upper and lower rings supporting the inner winding at 8, the outer winding by 1 l, supporting parts for the outer winding by 10, the inner winding by 12, the main insulation between the inner and outer windings at 9, horizontally extending oil ducts at 13, vertically extending oil duct at 14, the foot at 15, and the components for fine adjustment between the upper yoke laminations 4 and the upper support ring 6 being indicated at 16. The active part of the transformer, as depicted, for example, in part in FIG. 5 would be enclosed within evacuated casing 4', the windings l1 and 12 having previously been stabilized by sealing with the selected sealing agent, e.g. paraffin, so that the paraffin can then be washed out by the kerosene vapor.

Stabilization of the windings by sealing with the sealing agent takes place before the windings are assembled into banks of coils on the magnetic structure. That is, the individual windings may be pre-fabricated at various times, especially if they are mass-produced, and sealed with the sealing agent, and thus can then be assembled without regard to the humidity factor of the ambient air in which the assembly takes place.

The unexpected and surprising technological improvements, which can be attained by the process of the invention, are caused by the product itself as well as by the process for the manufacture of this product. In contrast to the methods used heretofore, especially in contrast to the concept that it is not feasible to provide a preliminary impregnation of the prefabricated or assembled coils or banks of coils, and to remove such preliminary impregnation or sealing in such manner that it would not affect detrimentally the final impregnation of the windings, the newprocess discloses a relatively simple and economic method which solves not only the problem of a temporary seal, held to be incapable of being solved, but also the other above discussed problems, with all advantages as offered by the process and resulting in a product of high quality. This product of a multi-step, time-oriented manufacturing process which can be produced, without being affected, under all humidity conditions which may arise after the drying operation of the prefabrication process, is distinguished by its freedom from impairment by humidity, especially so far as the paper insulation and the windings are concerned, with the result that the characteristics of the windings, stabilized in this manner, are solely determined by the properties as conditioned by the materials used and the production designs desired, and that these windings no longer are subject to uncontrolled influences which heretofore could not be eliminated by the protracted and costly production methods, but have now become feasible due to the fast and compact method of construction as proposed by the invention.

1 claim:

1. The process for manufacturing electrical apparatus such as transformers and reactors consisting of coil windings mounted within oil-filled casings which comprises the steps of:

a. wrapping the electrical conductors which are to form the windings with a tape of insulating material;

b. winding the tape-insulated conductors into coils of the desired configuration;

c. drying the coils;

d. pressing the coils to their final size;

e. sealing the coils with a sealing agent;

f. assembling the dried, pressed and sealed coils with their magnetic structure to form the active component of the electrical apparatus;

g. installing the assembled active component within the casing providedtherefor;

h. washing out the sealing agent from the coils by means of a hot medium in its vapor state which condenses at and within the tape insulation material and which also serves as a heat transfer agent to dry the coils; and

' i. impregnating the dried coils with the insulating oil.

2. The process as defined in claim 1 for manufacturing electrical apparatus wherein the insulating material used for wrapping the electrical conductors is paper.

3. The process as defined in claim 1 for manufacturing electrical apparatus wherein moisture-proof means are used as the sealing agent.

4. The process as defined in claim 1 for manufacturing electrical apparatus wherein paraffin is used as the agent for sealing the coils.

5. The process as defined in claim 1 for manufacturing electrical apparatus wherein fluoro-chloro telomerization products are used as the agent for sealing the coils.

6. The process as defined in claim 1 for manufacturing electrical apparatus wherein the medium in its vapor state used for washing out the sealing agent from the coils is kerosene.

7. The process as defined in claim 1 for manufacturing electrical apparatus wherein the medium in .its vapor state used for washing out the sealing agent from the coils is a fluorinated-organic compound.

8. The process as defined in claim 7 for manufacturing electrical apparatus wherein the fluorinated organic compound used for washing out the sealing agent is taken from the group consisting of carbon fluorides, chlorocarbon fluorides, and fluorinated amines or ethers with the required boiling points.

9. The process as defined in claim 1 for manufacturing electrical apparatus and wherein the sealing agent includes an oxidation inhibitor admixed therewith.

10. The process as defined in claim'8 for manufacturing electrical apparatus wherein said oxidation inhibitor is ditertiarybutyl-p-cresol (DBPC).

l l. The process as defined in claim 9 for manufacturing electrical apparatus wherein said oxidation inhibitor is B-phenylnapthylamine.

Claims

1. The process for manufacturing electrical apparatus such as transformers and reactors consisting of coil windings mounted within oil-filled casings which comprises the steps of: a. wrapping the electrical conductors which are to form the windings with a tape of insulating material; b. winding the tape-insulated conductors into coils of the desired configuration; c. drying the coils; d. pressing the coils to their final size; e. sealing the coils with a sealing agent; f. assembling the dried, pressed and sealed coils with their magnetic structure to form the active component of the electrical apparatus; g. installing the assembled active component within the casing provided therefor; h. washing out the sealing agent from the coils by means of a hot medium in its vapor state which condenses at and within the tape insulation material and which also serves as a heat transfer agent to dry the coils; and i. impregnating the dried coils with the insulating oil.

7. The process as defined in claim 1 for manufacturing electrical apparatus wherein the medium in its vapor state used For washing out the sealing agent from the coils is a fluorinated organic compound.

10. The process as defined in claim 8 for manufacturing electrical apparatus wherein said oxidation inhibitor is ditertiarybutyl-p-cresol (DBPC).

11. The process as defined in claim 9 for manufacturing electrical apparatus wherein said oxidation inhibitor is Beta -phenylnapthylamine.