Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to the field of dielectric fluids as used in freely breathing,
electrical power l,d,lsrur"~ers, more particularly to a method and appardt-Js to sub-
stantially eliminate fluid oxidation.
It is well known, although perhaps not so well understood, that inlimale conlac~05 between power tran~rur",er insulating oils and air results in oxidation and degrada-
tion of the oil by absor~Jlion of air borne conlaminanls such as moisture.
It is not surprising, then, that considerable inventive ingenuity has been applied
to the resolution of this problem, resulting in the design of several transformer oil
containment systems specifically intended to reduce or eliminale entirely, inlimale
10 contact between the oil and the air.
Such systems range from the relatively simple, e.g., a sealed tank containing, in
addition to the oil, an inert gas under pressure which effectively excludes air from the
system, to the moderately complex conservator/diaphragm systems which, as the
name implies, utilizes a flexible bladder capable of following the expansion and con-
15 traction of the oil.
An example of a sealed tank system is exemplified in Soviet patent number1334196 which issued to Bratus et al in August, 1987 and wherein is disclosed a tank
containing dielectric fluid (transformer oil) with the cover of the tank separated from
the mirror surface of the fluid by an inert gas (nitrogen~ introduced and captured
20 under pressure.
Another example of a sealed tank system may be found in South African patent
number 7701020 which issued to Lampe et al in November, 1977 and wherein is
disclosed a method of operating a power transformer within the confines of an oil
filled sealed tank with the oxygen content of the oil maintained at less than 300 ppm
25 by continuously de~Assing the oil during operation of the transformer.
Sealed systems, not unlike those described above, are a widely accepted solu-
tion to the problem of oil oxidation when applied to relatively small distribution trans-
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formers but are gener~lly regarcled as u"acceptable for use with the mostly freelybreathing, large, very high voltage, power l,~"~rur",ers.
Since the electrical safety of such very high voltage transformers is para",ount,
the mechanical systems utilizing sealed tanks or collapsible bladders are of limited
os use beG~use of their negative impact on the reliable Gperability of the primary safety
device employed in such transformers, i.e., the pressure dirrere"lial responsiveBucholtz relay.
At present, then, it is normal practice to sacrifice the integrity of the insulating oil
in favour of electrical safety. Of course, oil inlended for use in power tran~r."",er:j
10 may be, and commonly is, pre-treated with antioxidant in an ~llelllpt to retard the
oxidation process which treatment, while undoubtedly an improvement over nothingat all, nevertheless serves only to slow the oxidation process.
The addition of antioxidant - usually in the form of Ditertiary Butyl Para-Cresol
and Ditertiary Butyl Phenol - does little or nothing to prevent the occurrence of oxida-
15 tion in the first place.
The methods for the prevention of oxidation of transformer insulating oilsheretobefore known suffer, then, from the following sllo, lcor"ings:
a) they require the use of a gas tight, sealed transformer tank thus increasing manu-
facturing costs and i,nposi"g a relatively high quality control regime;
20 b) inert gas introduced to the transformer tank under pressure negatively impacts the
operability of existing and commonly employed electrical safety devices such as a
Bucholtz relay; and
c) pre-treatment of the oil with aromatic cor"pounds merely retards oil oxidation but
does not prevent its occurrence.
It is an object of the present invention to provide an economically viable, simple,
safe and efficient method and apparatus to substantially eliminate insulating oil decay
caused by oxidation of the oil in the presence of air.
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a) to provide a method and apparal.ls to s~hsl~rllially elil"indle oxidation of trans-
former insulating oils, thus increasing the useful lifespan of such oils and hence,
reducing mainlenance costs to the operator;
b) to provide a melhocl and apparatus to sl ~hsl~"lially eliminate oxid~tion of trans-
05 former insulating oils without adverse effects on the oper~bility of existing electrical
safety devices cor"",o, lly used in conjunction with power lldnsrur",er~; and
c) to provide a method and apparalus to 5~lhsl~nlially eliminate oxidation of trans-
former insulating oils which s~lhst~ntially removes the need for pre-treatment of such
oils with antioxidant.
Further objects and advantages will become apparent from a consideration of
the ensuing description and drawing wherein:
According to one aspect, then, the present invention is a method for the sub-
stantial elimination of oxidation of dielectric fluid used in high voltage power trans-
formers comprising the steps of:
15 generating a continuous flow of inert gas;
introducing said continuous flow of said inert gas to one end of an expansion chamber
of said l,ansror"~ercontainmentvessel; and
evacuating said continuous flow of said inert gas at an end of said expansion cham-
ber opposite the end wherein the said continuous flow of said inert gas is introduced
20 so that said flow is across the surface of said dielectric fluid and displaces and elimi-
nates any air in intimate conlact with said surface of said dielectric fluid.
According to another aspect, the present invention is an apparatus for the sub-
stantial elimination of oxidation of dielectric fluid used in high voltage power trans-
former comprising:
25 a dielectric fluid filled high voltage transformer containment vessel having an expan-
sion chamber connected to an upper end of said containment vessel via a constricted
channel, said expansion chamber containing a slight head of said dielectricfluid; and
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means for gener~ g a continuous flow of inert gas at al"~ospheric pressure said
means located in close proximity to said co"la..,ment vessel and connected by atleast one conduit to said ex~ansion chal,lber so that said continuous flow of said inert
gas is introduced via said conduit into said expansion chamber at one end flows
05 across the surface of said ~ielectric fluid and is ev~cl l~ted at the other end of said
expansion chamber.
The present invention is desclibed in further detail having rerere"ce to the ac-companying drawing in which;
Figure 1 is a schematic representation of the apparatus showing the flow of gas
within a transformer tank expansion chamber.
Nitrogen 16 at aL",ospheric pressure is generaled in a nitrogen generdlor 10
of conventional design and known to those skilled in the art and conveyed to a trans-
former tank 24 expansion char"ber 14 via conduit 12 where it enters to one side of the
expansion chamber 14 at the top; fills the space between the inner top surface of the
expansion chamber 14 and the surface of a transformer insulating oil 20.
The nitrogen 16 still at at",ospheric pressure is preferably eV~cll~te~l from the
opposite side of the expansion chamber 14 and returned to the nitrogen generalor 10
via conduit 18.
Aller"alely the nitrogen 16 may be simply vented from the expansion chamber
14 at the opposite end of the chamber 14 from the inlet conduit 12 and dissipated in
the surrounding atmosphere.
It will be understood that the flow of nitrogen 16 into and out of the expansionchamber 14 is continuous while the maintenance of the flow at atmospheric pressure
ensures the unimpaired operability of a Bucholtz relay 22 in the event of electrical
failure.
It will be seen then that the present invention offers a safe simple efficient and
cost effective means for the substantial elimination of oxidation of transformer insulat-
ing oils as commonly used in freely breathing high voltage power transformers byproviding within the transformer tank expansion chamber a continuous flow of inert
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gas at atmospheric pressure across the surface of the transformer oil thereby dis-
placing and eliminating air from inlimdle conlacL with the oil surface while leaving the
operability of electrical safety devices unimpaired.
The description contained herein should not be construed as limiting the scope
05 of the invention but rather as an illusl~dlion of the presently prerer,ed embodiment.
Thus the scope of the invention should be dete""ined by the appended claims and
their legal equivalent.
