Year: 1895

page_text: арготещения ш
A communication to me from abroad by Professor RICHARD THRELFALL, of the
University of Sydney, New South Wales.
I, GEORGE THRELFALL, of 95 Finsbury Pavement, London E.C. Engineer,
do hereby declare the nature of this invention to be as follows:-
It having been found difficult with electric condensers constructed in the usual
manner, to keep down the production of beat due principally to imperfect
insulation of the dielectric, leading to small conduction currents with their
accompanying losses; to the presence of small air bubbles between the armatures
across which discharges may occur; and to the phenomena of "electric" absorption
or "residual charge"; and my correspondent having discovered that an essential
condition of success in making condensers is the exclusion of air and water
especially if condensers are to be used with alternating currents, he communicated
to me an invention based on that discovery for the manufacture or construction
of electric condensers with a dielectric such as paper of a pure and uniform
description impregnated with oil at a suitable temperature, and specially adapted
by practically total exclusion of air and water to prevent or mitigate dielectric
losses and to work satisfactorily with alternating currents of electricity of high
voltage in respect of which invention I made application for Letters Patent
No. 8328 of 1894; and the present invention relates to improvements according
to which a condenser is made with a dielectric consisting of material such as
paper, silk, cellulose or other fibrous material in the form of sheets, of a pure
and uniform description, impregnated at a suitable temperature say from 130°-
150° C. with an insulating material that is capable of being readily liquefied by
heat to facilitate impregnation of the sheet dielectric and displacement therefrom
of air and moisture, but which is solid or semi-solid at ordinary atmospheric
temperature.
In carrying out the present invention that kind of gray paper known in
commerce under the name of Swedish filter paper may advantageously be used.
It is important that the paper shall be uniform in texture and free from size.
A sheet of such paper having a thickness of say about 0.3 mm is able to withstand
an electrical pressure of about one thousand volts, applied in an alternating
manner. For condensers designed for an alternating pressure of two thousand
volts, as ordinarily defined, a double thickness of paper may with advantage be
used. Two thicknesses at least may in all cases be used, so as to minimise any
danger of short-circuiting that may arise from the accidental presence of holes in
the paper.
The paper is cut into sheets of the required size, care being taken that the
edges are cut clean so that the sheets will lie uniformly one upon another. The
paper thus prepared is then impregnated with insulating material of the nature
referred to and which may consist for example of paraffin wax or vaseline or a
mixture. Satisfactory results have been obtained by using a mixture of one part
of hard paraffin wax melting at 50° C. and two parts of ordinary vaseline (pure),
but the melting point of the mixture and its cost are both in excess of what are
desirable from a manufacturing point of view. The insulating material which up
to the present has been found to give the most satisfactory results, consists of soft

page_text: paraffin wax having a melting point of about 30° C. and obtained as a bye-product
beretofore of little value, in shale or oil distillation works. Although in the
following description I speak of the use of this soft paraffin wax, it is to be
understood that this invention is not limited to the use of such material, as any
other suitable material having sufficiently good insulating properties, which is
solid or semi-solid, at ordinary temperature and can be readily liquefied by heat
and maintained in a liquid condition without undergoing such change as will
impair its insulating properties, at a temperature of say from about 130° C.
to 150° C., can be used.
In order to impregnate the paper with the soft paraffin wax, a suitable vessel
such as a flat dish made from thin metal plate and somewhat larger than the sheets
of paper and two or three inches deep, is about half filled with the wax which
is raised by appropriate means to a temperature of say from 130° C. to 150° C.
or even higher provided the paper is not thereby injuriously affected or the wax
caused to volatilize to an inconvenient extent. The bath being maintained at the
temperature mentioned, the sheets of paper are introduced one by one, in such a
manner that at first the paper floats on the surface of the liquid wax. The hot
wax soaking through the paper will drive the air before it so that when, after.
say about ten seconds, the paper is thrust beneath the melted wax, the effervescence
will be so small as to cause no inconvenience. Usually it will not be advisable to
have more than about one hundred papers in the dish at once, for they tend to
float up to the top of the liquid wax and thus prevent the dipping of fresh
sheets.
When say a hundred sheets have been collected, a small weight is placed upon
them and they are left to soak, say for about an hour or until no further evolution
of gas occurs, the temperature being maintained approximately constant and care
being taken not to burn the lower sheets. The dish and its contents are then
allowed to cool slowly.
It
In
The condenser is then built up of these prepared sheets and sheets of metal
arranged alternately in a suitable metallic box in the usual manner, there being
preferably two sheets of prepared paper between adjacent sheets of metal.
does not matter whether the sheets of paper be allowed to cool in the air before
placing them between the sheets of metal, or be lifted direct into the condenser
box, provided that they are taken out of the bath of wax at a sufficiently low
temperature to prevent the wax draining away to any considerable extent.
building up the coudenser it is advisable but not necessary to keep the temperature
sufficiently high to prevent the wax setting. The sheet metal used with the sheets
of dielectric prepared as described, may advantageously consist of the thin
pewter foil such as is commonly used for covering bottles, as it possesses the
advantage of not taking up so much room as the thicker varieties of sheet metal
commonly employed in condensers, and of being less expensive than tin foil.
These however may be used if desired. The inside of the condenser box may
advantageously be lined with mica, though other insulating substances such as
glass, and asbestos sheet have been found to give satisfactory results. In
building up the condenser it is necessary to avoid-as far as possible-introducing
air between the successive sheets of dielectric and metal foil. With a very little
care, each sheet of metal foil can be rubbed down after being placed on a prepared
sheet of paper so as to get rid of most of the air bubbles that might otherwise be
left between the two. When the desired number of sheets have been introduced,
soft wax in a heated and in a liquid condition is poured into the box in sufficient
quantity to cover the condenser, say to a depth of about half an inch. The condenser
box with condenser therein, is then removed to a vessel heated to a temperature of
say about 130° C. and is exhausted by means of a pump capable of producing a
vacuum in which the pressure is not more than say that corresponding to half an
inch of mercury. The exhausting, which according to experience will occupy
several hours, must be continued until there is an almost complete cessation of the

page_text: delivery of gas from the condenser. The degree to which the exhaustion of gas
should be carried, which must in every case be almost complete, will depend upon
the degree of loss of power permissible in the condenser being manufactured. I£
paraffin wax be the insulating material used, a few bubbles of gas will be obtained
almost continuously, but these are mostly due to slight decomposition of the
paraffin and the exhausting operation should not on that account be continued.
Three exhaustions each followed by readmission of air and occupying altogether
say about ten hours have been found sufficient for a practically complete expulsion of
air and moisture from the condenser when the sheet dielectric therein has been
previously treated as hereinbefore described. The exhausting operation may be
carried on at a temperature as low as 110° C., but the operation will then take
longer than at the higher temperature mentioned.
The condenser after being exhausted as described, should be allowed to cool
slowly and then tested for insulation.
The ends of each of the two series of sheets of tin foil forming each one of the
armatures of the condenser, should be smoothly rubbed together and doubled on
themselves so as to insure a perfect contact; want of the due observance of this
precaution is a very common source of heating.
The actual terminals making contact with the foil ends of the finished condenser may
conveniently be passed through tubes soldered to the lid of the box. The terminals
may consist of stout wire armed at their lower ends with springs and so placed as to
bear on the tiu foil ends of the armatures when the lid of the box is placed in
position.
Dated this eth d..
100%
Improvements in Electric Condensers,
A communication to me from abroad by Professor RICHARD THRELFALL, of the
University of Sydney, New South Wales.
1. GEORGE THRELFALL, formerly of 95 Finsbury Pavement, but now of
50 Fenchurch Street, London, E.C. Engineer, do hereby declare the nature of this
invention and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement:-
6
It having been found difficult with electric condensers constructed in the usual
manner, to keep down the production of heat due principally to imperfect insulation
of the dielectric, leading to small conduction currents with their accompanying
losses; to the presence of small air bubbles between the armatures across which
discharges may occur; and to the phenomena of "electric" absorption or residual
charge" and my correspondent having discovered that an essential condition of
success in making condensers is the exclusion of air and water especially if
condensers are to be used with alternating currents, he communicated to me an
invention based on that discovery for the manufacture or construction of electric
condensers with a dielectric such as paper of a pure and uniform description
impregnated with oil at a suitable temperature, and specially adapted by practically
total exclusion of air and water to prevent or mitigate dielectric losses and to
work satisfactorily with alternating currents of electricity of high voltage, in
respect of which invention 1 made application for Letters Patent No. 8328 of 1894 ;

page_text: and the present invention relates to improvements according to which a condenser
is made with a dielectric consisting of material such as paper, silk, cellulose or
other fibrous material in the form of sheets, of a pure and uniform description
impregnated at a suitable temperature say from 130°-150° C. with an insulating
material that is capable of being readily liquefied by heat to facilitate impregnation
of the sheet dielectric and displacement therefrom of air and moisture but which
is solid or semi-solid at ordinary atmospheric temperature.
In carrying out the present invention that kind of gray paper known in commerce
under the name of Swedish filter paper may advantageously be used. It is
important that the paper shall be uniform in texture and free from size. A sheet
of such paper having a thickness of say about 0.3 mm is able to withstand an
electrical pressure of about one thousand volts, applied in an alternating manner.
For condensers designed for an alternating pressure of two thousand volts, as
ordinarily defined, a double thickness of paper may with advantage be used. Two
thicknesses at least may in all cases be used, so as to minimise any danger of
short-circuiting that may arise from the accidental presence of holes in the paper
The paper is cut into sheets of the required size, eare being taken that the
edges are cut clean so that the sheets will lie uniformly one upon another. The
paper thus prepared is then impregnated with insulating material of the nature
referred to and which may consist for example of paraffin wax or vaseline or a
mixture. Satisfactory results have been obtained by using a mixture of one part
of hard paraffin wax melting at 50° C. and two parts of ordinary vaseline (pure),
but the melting point of the mixture and its cost are both in excess of what are
desirable from a manufacturing point of view. The insulating material which up
to the present has been found to give the most satisfactory results, consists of soft
paraffin wax having a melting point of about 30° C. and obtained as a bye-product
heretofore of little value, in shale or oil distillation works. Although in the
following description I speak of the use of this soft paraffin wax, it is to be
understood that this invention is not limited to the use of such material, as any
other suitable material having sufficiently good insulating properties, which is solid
or semi-solid, at ordinary temperature and can be readily liquefied by heat and
maintained in a liquid condition without undergoing such change as will impair its
insulating properties, at a temperature of say from about 130° C. to 150° C., can
be used.
In order to impregnate the paper with the soft paraffin wax, a suitable vessel
such as a flat dish made from thin metal plate and somewhat larger than the sheets
of paper and two or three inches deep, is about half filled with the wax which is
raised by appropriate means, such for example as a steam or gas heated oven, to a
temperature of say from 130° C. to 150° C. or even higher, provided the paper is
not thereby injuriously affected, or the wax caused to volatilize to an inconvenient
extent. The bath being maintained at the temperature mentioned, the sheets of
paper are introduced one by one, in such a manner that at first the paper floats on
the surface of the liquid wax. The hot wax soaking through the paper will drive
the air before it so that when, after say about ten seconds, the paper is thrust
beneath the melted wax, the effervescence will be so small as to cause
inconvenience. Usually it will not be advisable to have more than about
one hundred papers in the dish at once, for they tend to float up to the top of the
liquid wax and thus prevent the dipping of fresh sheets.
no
"When say a hundred sheets have been collected, a small weight is placed upon
them and they are left to soak, say for about an hour or until no further evolution
of gas occurs, the temperature being maintained approximately constant and care
being taken not to burn the lower sheets. The dish and its contents are then
allowed to cool slowly.
The condenser is then built up of these prepared sheets and sheets of metal
arranged alternately in a suitable metallic box in the usual manner, there being
preferably two sheets of prepared paper between adjacent sheets of metal. It does

page_text: not matter whether the sheets of paper be allowed to cool in the air before placing
them between the sheets of metal, or be lifted direct into the condenser. box,
provided that they are taken out of the bath of wax at a sufficiently low temperature
to prevent the wax draining away to any considerable extent. In building up the
condenser it is advisable but not necessary to keep the temperature sufficiently
high to prevent the wax setting. The sheet metal used with the sheets of dielectric
prepared as described, may advantageously consist of a thin pewterfoil such as is
commonly used for covering bottles, as it possesses the advantage of not taking up
so much room as the thicker varieties of sheet metal commonly employed in
condensers, and of being less expensive than tin foil. These however may be used
if desired. The inside of the condenser box may advantageously be lined with
mica, though other insulating substances such as glass, and asbestos sheet have
been found to give satisfactory results. In building up the condenser it is necessary
to avoid as far as possible-introducing air between the successive sheets of
dielectric and metal foil. With a very little care, each sheet of metal foil can be
rubbed down after being placed on a prepared sheet of paper so as to get rid of
most of the air bubbles that might otherwise be left between the two. When the
desired number of sheets have been introduced, soft wax in a heated and in a liquid
condition is poured into the box in sufficient quantity to cover the condenser, say
to a depth of about half an inch. The condenser box with condenser therein, is
then removed to a vessel heated to a temperature of say about 130° C. and is
exhausted by means of a pump capable of producing a vacuum in which the
pressure is not more than say that corresponding to half an inch of mercury. The
exhausting, which according to experience will occupy several hours, must be
continued until there is an almost complete cessation of the delivery of gas from
the condenser. The degree to which the exhaustion of gas should be carried,
which must in every case be almost complete, will depend upon the degree of loss
of power permissible in the condenser being manufactured. If paraffin wax be the
insulating material used, a few bubbles of gas will be obtained almost continuously,
but these are mostly due to slight decomposition of the paraffin and the exhausting
operation should not on that account be continued.
Three exhaustions each followed by re-admission of air and occupying altogether
say about ten hours have been found sufficient for a practically complete expulsion
of air and moisture from the condenser when the sheet dielectric therein has been
previously treated as hereinbefore described. The exhausting operation may be
carried on at a temperature as low as 110° C., but the operation will then take
longer than at the higher temperature mentioned. The condenser after being
exhausted as described, should be allowed to cool slowly and be then tested for
insulation.
The ends of each of the two series of sheets of tin foil forming each one of the
armatures of the condenser, should be smoothly rubbed together and doubled on
themselves so as to insure a perfect contact; want of the due observance of this
precaution is a very common source of heating.
The actual terminals making contact with the foil ends of the finished condenser
may conveniently be passed through tubes soldered to the lid of the box. The
terminals may consist of stout wire armed at their lower ends with springs and so
placed as to bear on the tin foil ends of the armatures when the lid of the box is
placed in position.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed I declare that what I
claim is
1. In the process of manufacturing electric condensers wherein a dielectric is
treated by floating immersing and soaking it in an insulating material, the use at a
suitable temperature as set forth and in a condition of liquefaction produced by
heat, of an insulating material which at ordinary atmospheric temperatures would

page_text: be solid or semi-solid, and of a dielectric consisting of sheets of paper, silk,
cellulose or other fibrous material in the manner hereinabove described.
2. The hereinabove described improved manufacture of electric condensers.
Dated this 15th day of October 1895.
W. Lloyd Wise,
G. THRELFALL.
46, Lincoln's Inn Fields, London, W.C., Agent for the Applicant.