US2410756A - Process for impregnating condensers - Google Patents

Description

Nov. 5, 1946. B. SPRINGER PROCESS FOR IMPREGNATING CONDENSERS Filed Nov. 15, 1939" 2 Sheets-Sheet 1 l BERT NV E NTOR PEI V652 ATTOQNEYS Nov. 5, 1946. B. SPRINGER PROCESS FOR IMPREGNA-TING CONDENSERS 2 Sheets-Sheet 2 Filed Nov. 15, '1959 LNyENTOIZ 552711040 sPEM/GEE W m ATTORNEYS some.

Patented Nov. 5:, 1946 UNITED STATES rnoonss FOR IMPREGNATING CON DEN SEES Berthold Springer, Berlin W. 30, Germany; vested in the Alien Property Custodian Application November 13, 1939, Serial No. 304,193 In Germany November 19, 1938;

5 Claims. (Cl. 117 .65)

Thepresent invention relates to a process and finished condensers deteriorate Very, much owing to the volume contraction which takes place together with the solidification of the impregnating agents, especially after long storage. This is besides other reasons mainly caused by the fact that owing to the volume contraction during solidification near the ends of the finished roll the solid impregnatin agent shows series of small cracks. The water coming from the air which slowly penetrates into these cracks. causes deterioration of the electric properties of the condenser. With certain kinds of rolling, as for instance the rolling of noninductive condensers, the influence of the cracks can be especially trouble- Till now it has been tried to improve the disadvantage of decreasing the dielectric strength by making the insulating coils considerably larger thanthe metal foils. i

The present invention intends to abolish the appearance of disturbing cracks by suppressing .the volume contraction of the impregnating agent. This contraction takes place during solidification. When impregnating condenserswithimpregnatingagents which are solid at room temperature, according to the present invention, the impregnating'agent is at first, starting at room g the structureshown in Fig. 5.

temperature, liquefied in-a cyclic processandin presence of the condenser submittedto such high temperatures and such high pressures that'the volume of the impregnating agent, whether'toliquid and solid-state of a pure impregnating agent in a diagrammatic drawing. It is to be .understoodthat according to the invention impregnating agents consisting of mirtures canbe Figs. 1, 2 and3 are diagrams showing'volume and temperature change in themateiial' being treated and showing respectively, three'separate Ways in which the cyclic process in accordance with my invention may be carried out.

Fig. 4 is a, diagrammatic view showing one. form of apparatus for carrying out the process in accordance with my invention, v j

Fig. 5 is a sectional view showing an electrical condenser, in the making of which the improved method and apparatus of I my invention may be employed, and

Figs. 5a and 5b are detail views of a portion of Curve 101 shows the isobar of a certain amount of an impregnating agent in solid and liquid state under atmospheric pressure. The volume of this amount at room temperature is called 1 The curves p2 and 103 show the isobars of the same amount at considerably increased pressures p2 and 273, respectively. The changes in volume V which take place at the melting temperatures'Ti, T2 and .T3 are called w1, H72, H23. They decrease, as can be seen in the drawings, with increasing pressures. The process for impregnatin of condensers can be realised according to the invention in many different kinds of cyclic processes that it is cooled to ordinary temperature 'at constant volume.

By reducing the impregnating agent to the desired volume or) ma liquid state; as described above, the solidification occurring at the following cooling as well as thefurther reducing down to ordinary temperaturejtakesfplace without any change in volume, which jcould, be disturbing b the formation of troublesomejc'racks. 1

In the above described performance of the procv ess according to the invention generally comparatively high pressures andlrcorresponding high J temperatures have to, be, used. Thereforegin a preferred method of performiiigrth'e cyclic proc ess according to the invention, the'in'ipreg'nating agent which has to. be t're ted is'exhibited at a ,55

t r tur .a ng???edi ???Pin s-W p c ,I i lust ated; in pl ce at (the exac l 3 of Hg) to such a pressure that it solidifies and then it is cooled at the same or at a higher pressure'isobarically to its volume at ordinary temperature.

Such a cyclic process is shown in Fig. 2, curve 11, of the accompanying drawings.

The impregnatingiagent is hfea'te'dat the pressure in, which may difier from the atmospheric pressure, to the melting temperature T; corresponding to the isobar 122, then exhibited to the pressure m which makes it solidify, and is cooled to such a degree, for instance isobarically, until it assumes the desired volume (or) The above described method has the -effect that owing to the pressurepz being far above atmospheric pressure, thecontractionpf volume (wz) connected with solidification is-considerably smaller than the contraction of volume 1(w1) at the melting point (at 760 mm. of Hg). The contraction connected .with' the isobaric cooling of the solid material at. 'th'epresSure $92,113,816 be kept ,sufiiciently .jsmall ,.Joy choosing sufficiently high pressure ,Qinl order. -to v prevent troublesome cracks. Furthermore,etheiormation .of. undesired cracksatltheen'ds .of thepondenser roll according .to .thelcontractionjof ..volume during .solidification cannot occur .in .the .CGOll-lllg. of the impregnating agent in the'solid state. l j It .is also advantageous .tofsubmitlthe. impreg- V hating. material.j-which'i'sctos betiieated at attemperature abovefthe melting point lat .1160 him.

of Hg) to .,a. pressure-cat, which the impregnating age'ntis still liquid, whereupon it )issolidified by cooling at constant .voliimecjand.reduced..lto the ,volume which it assumes at ordinary temperature. llnrFig. 3,.curve IILLisshown, for instance, one'lway of conductingthis'kind of cyclic process The impregnating.agent islheated at;the pressurefjpi whichfmay be equal orjdiiie fint ,from [I atmospheric pressure to 1a vItemperature 'higher than.the temperature T2. jltisthen su mitted tova pressure higher thanlthemelting pressure I702 corresponding to T2," remaining liquid. 'It is cooled isochoricallyto the ,temperatureTz, wherebyjllthe impregnating jagent' solidifies. I Iheirit is either cooledgisobarically @or, ,at first compressed in the solidflstatlto; the volume (or) .atTz and then'cooled'to ordinary temperature at const ant volume. I ,i'

glnthis method of carrying Voutithejfprocess jacfjoordin'g.,tojheinvention gin-importantpartiofjthe volume. reduction. takes 1place', in", the liquid state before the solidification jof .the impre nating agent starts, and therefore "thelformation of cracks during 'isclidifica i n is gn aflctical ye w natedf" I r In realisingith rocessaccording;to ;th,e..i

ve'ntionjjthe cyclic processes, Tillustratcdg in fthe diagrammatic drawing may generally not be obeyed strictly, ljhe difierent tracksinthe'flc'il lii i may: n t. Lie-com ete y"isotherm 'l oloaric'; for 'ins't ncefthe compress onlin' the; cyclic "12. :ma'ypnq tak enera y thermctic p r or an a vcli. .pri sl s osen. whichi oids e formation of 1 craclgs rand 7 also; wc iksi with temp tures .a dpressu les which.ca ieas yhet 'correspondingto- Figs. 2 and 3.

pnstan tem eratur "T inor" ay t i insffollow strictly a a le j t 'ithe T-axis.

,rf i win s ing the pressures and temperatures used in the process according to the invention. This substance may have the following constants:

The melting temperature at 760 mm. of Hg is 5 Ti=50 C.; the change in melting temperature solid and the liquid state and the thermal expansion coefficient is 510- and the compressibility 2-10 The contraction of volume dur- .ing solidification ,at atmospheric pressure is w1=5-10 cc./gr. and the decrease in the contraction of volume with pressure is 4- 10 cc /atm,

The figures given above correspond roughly to thefigures of known substances, as for instance cetylic-alcohol as can be seen from the tables of Landolt-Brnstein, the International Critical Tables etc, and .fromthe publications on which thesefism areb edhe mpresn naas nts us d..prac ca lvfl no d e prin i ally i their behaviour fromhcmogeneous substances.

Assuming a pure substance with theabove mentionedconstants, the followin picture is obtained for the. cyclic process shown in Fig. l by I, which requires especially high pressures ,and' temperatures as compared with the cyclic processes in Figs.12 and 3.

g .Lgra'mof'the impregnating agent is'heated at apressure of'760-mm. of Hg from ordinary temperature to its meltingpoint of C; expanding .015 cc. ,The changejof volumeduringmelting amountsto cc. *The'molten substance istur- 3 *ther heated to about 61C. expanding -.O06 cc; At

this temperature it is exposed toapressure of about*2500 to"30GO;a*trn., which-makesthe volume fdecrease'to its volumeat ordinary-temperature and TSO mm'oiI-Ig.

' jlffsubstances are used "the volume contraction of which changesstronger withfpressurethan it 'isf the case with the above mentioned; substance,

considerable smaller pressures, "as 'for-instanceup to 10 00, atm., are suii'icientin the-cyclic processes 'jFOI quite different purposes; namely i for renderingyharmlessthe traces of gas-which remain in the badly evacuated condenser 'rolls, -a-- small overpressure of several atmospheres has already 0 been used on -the liquid impregnating agent. It

can be seenthatthepressures jused in the process according to theinventicha-re of a difierent' order of; magnitude.

In "Fig. fl --are {sh0wn -di agrammatically the essential parts of a deviceadapted for performing the process according to the --invention. The impregnatingvessel 1 consists; of a-number of pressure chambers 2, suitable iortaking the condenser rolls-which-can b'e tightly-closedat 3. -Thechambers 2 are connected via'bore holes 4 thepigxg-line 5. This line is connected-with the evacuatingdeviee 9"viavalve -8. By-valve ll) it is separated front-the container-H-which-is filled with the'impregnatingagenh and by valve gr fl Z from the high pressure part i 3 and the medium "pressure part 1 5-'of;the compressor. r I

' *Afterfeed-ing the chambers 2 with condenser rolls, container l is heated by an electric heater 1 "fixedin an insulating envelope 6. At the same time the aireXpands-outof thechambers through =the opening ofvalve 8. Afterclosing-thevalve a theiimpregnating agent--molten in the container H is, allowed'to; enter-by opening the valve v v e H! intdt-helinesiand l which are all'heatable "faliomogeneous substance is used for'demonstrat-7 and heat-insulated. According to the process which has to be carried out, and according to the impregnating agent used, at first a medium overpressure may be produced with the compressor I5 in the chambers 2 which at the same time have to be heated to a suitable temperature. After closing the valve the high pressure devic I3 can be fed under medium pressure with impregnating agent from the compressor I5, valve I 4 being open, and after opening valve 12 the chambers 2 can be put under the desired high pressure. All the auxiliary devices, as thermometers, electrical and mechanical manometers etc. are omitted in the drawings.

As mentioned at the beginning the process according to the invention can be applied with special advantage for impregnating non-inductive condensers of known construction. Such a condenser is shown diagrammatically in section in Figs. 5, 5a and 5?).

One of the electrodes of the condenser is formed by the metal foils l1 interconnected at 19, the other electrode being formed by the foils l8 connected at 20. Adjoining metallic turns are separated by impregnable insulating layers Hi. The higher the wanted dielectric strength of the condenser has to be, the less the layers l1 and i8 can overlap. The free border given by the distance between 2! and 22 has to be sufficiently large, which increases the length of the condenser if the capacity is kept at a constant value. Even with large borders sparking-over cannot be avoided with certainty. For explanation of this fact it is referred to Figs. 5a and 5b which reproduce the inner edge 22 of the border in large scale. Fig. 5a. shows a condenser impregnated according to the known process and Fig. 5b according to the present invention, the impregnating agent being marked 23. In the known process of impregnation small cracks and bigger cavities are formed by the strong volume contraction of the impregnating agent during solidification (compare Fig. 5a).

This does not assure in the region of the border safety against sparking especially after the penetration of moisture into the cracks.

By the process of impregnation according to the invention, however, a considerable uniform filling 23 free from cracks is achieved in the border region (compare Fig. 517). As experiments have shown, by the process according to the invention a multiple increase in strength of breakdown is obtainable. Even with small borders safety against sparks around the border is obtained. Therefore, non-inductive condensers of a certain capacity can be manufactured with considerable smaller length with the present process than with the known processes.

What I claim as new and desire to secure by Letters Patent is:

1. The process for impregnating electrical apparatus with insulation material solid at normal temperature and pressure, which comprises essentially, impregnating the apparatus with the insulation material and bringing the material by application of heat and pressure to substantially that volume which is the normal volume for the material at normal atmospheric pressure and temperature, and then cooling the impregnating material isochorically.

2. The process for impregnating electrical condensers with insulating material solid at normal temperature, which comprises liquefying the impregnating material by heat, applying the liquefied material to the condenser, compressing the liquefied material to that volume which is its normal volume at normal atmospheric temperature and pressure and cooling the material while maintaining it at substantially constant volume.

3. The process for impregnating condensers with impregnating agents solid at normal atmospheric temperature and pressure, which comprises liquefying the impregnating material, compressing the material under a pressure of 1,000 to 3,000 atmospheres and cooling the same, as and for the purposes described.

4. The process as described in claim 3, wherein the pressure used is between 2,000 and 3,000 atmospheres.

5. The process for impregnating electrical condensers with insulating material solid at normal temperature, which comprises heating the impregnating material to fluent condition, impregnating the condenser with the fluent material and. applying pressure suflicient to compress the impregnating material substantially to that vol- 'ume which is the normal volume for the material at normal atmospheric pressure and temperature and then coolin the material at substantially constant volume.

BERTHOLD SPRINGER.

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