Note: Descriptions are shown in the official language in which they were submitted.
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 1 -
Dielectric insulation medium
The present invention relates to a dielectric insulation
medium, according to claim 1, and to the use of a
hydrofluoro monoether in a dielectric insulation medium
and to the use of the dielectric insulation medium for an
apparatus for the generation, distribution and/or usage of
electrical energy, according to claims 34 and 36,
respectively. The invention further relates to an
apparatus for the generation, distribution and/or usage of
electrical energy, according to claim 37.
Dielectric insulation media in liquid or gaseous state are
conventionally used for the insulation of an electrically
active part in a wide variety of electrical apparatuses,
such as switchgears or transformers.
In medium or high voltage metal-encapsulated switchgears,
for example, the electrically active part is arranged in a
gas-tight housing, which defines an insulating space, said
insulation space comprising an insulation gas usually at
several bar pressure and separating the housing from the
electrically active part thus preventing flow of
electrical current between housing and active parts.
Metal-encapsulated switchgears allow for a much more
space-saving construction than switchgears which are
mounted outdoors and are insulated by ambient air. For
interrupting the current in a high voltage switchgear, the
insulating gas further functions as an arc extinction gas.
Many of the conventionally used insulation media have
several drawbacks.
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 2 -
On one hand, conventional insulation gases with high
insulation and switching performance often have some
environmental impact when released into the atmosphere. So
far, the high global warming potential (GWP) of these
insulation gases has been coped with by strict gas leakage
control in gas-insulated apparatuses and by very careful
gas handling.
On the other hand, conventional environment-friendly
insulation gases, such as dry air or CO2, have quite a low
insulation performance, thus requiring the gas pressure
and/or the insulation distances to be increased.
For the reasons mentioned above, efforts have been made in
the past to replace the conventional insulation gases by
suitable substitutes.
For example, WO 2008/073790 discloses a dielectric gaseous
compound which - among other characteristics - has a low
boiling point in the range between -20 C to -273 C, is
preferably non-ozone depleting and has a GWP of less than
22,200 on a 100 year time scale. Specifically, WO
2008/073790 discloses various different compounds which do
not fall within a generic chemical definition.
Further, US-A-4175048 relates to a gaseous insulator
comprising a compound selected from the group of
perfluorocyclohexene and hexafluoroazomethane, and EP-A-
0670294 discloses the use of perfluoropropane as a
dielectric gas.
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 3 -
EP-A-1933432 and co-pending US-A-2009109604 refer to
trifluoroiodomethane (CF3I) and its use as an insulating
gas in a gas-insulated switchgear.
The use of a compound of general formula CxHyFzI in
general, and of CF3I in particular, as an insulating
medium for electric power transmitting and distributing
machines is further disclosed in EP-A-1146522.
However, despite of the insulation properties mentioned in
these documents, CF3I has a relatively low thermal
stability: at around 100 C it starts to decompose into
hazardous products, including 12, which can form a solid,
conducting residue.
Considering the drawbacks of the insulation media that are
state of the art, and in particular those of CF3I, the
object of the present invention is thus to provide a
thermally stable dielectric insulation medium which has a
low impact on the environment.
According to claim 1, the object of the present invention
is achieved by a dielectric insulation medium comprising a
hydrofluoro monoether containing at least three carbon
atoms. Preferred embodiments of the invention are given in
the dependent claims.
The term "hydrofluoro monoether" as used in the context of
the present invention, refers to a compound having one and
only one ether group, said ether group linking two alkyl
groups, which can be, independently from each other,
linear or branched. The compound is thus in clear contrast
to the compounds disclosed in US-B-7128133, relating to
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 4 -
the use of compounds containing two ether groups, i.e.
hydrofluoro diethers, in heat-transfer fluids.
The term "hydrofluoro monoether" as used in the context of
the present invention is further to be understood as a
compound which is partially hydrogenated and partially
fluorinated.
The term "hydrofluoro monoether" is further to be
understood such that it may comprise a mixture of
differently structured hydrofluoro monoethers. The term
"structurally different" shall broadly encompass any
difference in sum formula or structural formula of the
hydrofluoro monoether.
The present invention is based on the surprising finding
that by using a hydrofluoro monoether, an insulation
medium is obtained that has high insulation capabilities,
in particular a high dielectric strength (or breakdown
field strength), and at the same time a low GWP.
Due to the use of the specific hydrofluoro monoethers, the
present invention further allows to provide an insulation
medium which is chemically and thermally stable to
temperatures above 140 C, which is non-toxic or has a low
toxicity level, and which in addition is non-corrosive and
non-explosive.
As mentioned above, the hydrofluoro monoethers according
to the present invention have been found to have a
relatively high dielectric strength. Specifically, the
ratio of the dielectric strength of the hydrofluoro
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 5 -
monoethers according to the present invention to the
dielectric strength of SF6 is greater than about 0.4.
The hydrofluoro monoether according to the present
invention can participate in a very efficient tropospheric
removal process which involves hydrogen abstraction by an
OH radical. Ultimately, this results in a relatively low
atmospheric lifetime of the compound.
Due to its relatively low atmospheric lifetime, the
hydrofluoro monoether of the present invention also has a
relatively low GWP, as already mentioned. Specifically, an
insulating medium having a GWP of less than 1'000 over 100
years, more specifically of less than 700 over 100 years,
can be achieved according to the present invention.
The hydrofluoro monoether according to the present
invention has a relatively low atmospheric lifetime and in
addition is devoid of halogen atoms that play a role in
the ozone destruction catalytic cycle, namely Cl, Br or I.
Therefore, the dielectric insulation medium according to
the present invention has the further advantage of zero
ODP, which is very favourable from an environmental
perspective.
According to claim 1, the hydrofluoro monoether of the
present invention contains at least three carbon atoms.
Hydrofluoro monoethers containing at least three carbon
atoms generally have a boiling point of higher than -20 C
at ambient pressure. This is in clear contrast to the
teaching of the state of the art, and in particular of
WO 2008/073790 which teaches a boiling point of -20 C or
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 6 -
lower to be an essential feature of a feasible dielectric
compound.
The preference for a hydrofluoro monoether containing at
least three carbon atoms and thus having a relatively high
boiling point of more than -20 C is based on the finding
that a higher boiling point of the hydrofluoro monoether
generally goes along with a higher dielectric strength.
In the following some exemplary embodiments, which may be
present alone or in combination, of the present invention
are given.
In embodiments, the dielectric insulation medium comprises
a gas component a) different from the hydrofluoro
monoether, and in particular the gas component a)
comprises a mixture of at least two gas component elements
al), a2), ... an).
In embodiments, the dielectric insulation medium comprises
a gas component a) having an atmospheric boiling point of
at least 50 K, preferably at least 70 K, in particular at
least 100 K, below an atmospheric boiling point of the
hydrofluoro monoether.
In embodiments, the dielectric insulation gas component a)
has a dielectric strength of more than 10 kV/(cm bar),
preferably more than 20 kV/(cm bar), in particular more
than 30 kV/(cm bar). In embodiments, the dielectric
insulation gas component a) is a carrier gas which itself
has a lower dielectric strength than the hydrofluoro
monoether. In this regard, the term "dielectric strength"
is to be understood as "pressure-reduced dielectric
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 7 -
strength" or "dielectric strength at standard temperature
and pressure". For example, the standard temperature is
thereby defined as 25 C and the standard pressure as
1 bar.
In embodiments, the dielectric insulation gas component a)
comprises molecules with less atoms than present in the
hydrofluoro monoether, in particular comprises tri-atomic
and/or di-atomic molecules or consists of tri-atomic
and/or di-atomic molecules.
According to an embodiment of the present invention, the
hydrofluoro monoether contains 3 or 4 or 5 or 6 carbon
atoms, in particular three or four carbon atoms, most
preferably exactly three carbon atoms.
More particularly, the hydrofluoro monoether according to
the present invention is thus at least one compound
selected from the group consisting of the compounds
defined by the following structural formulae in which a
part of the hydrogen atoms is substituted by a fluorine
atom:
.õ..---... .----...,
2 0 0 (Oa) ,
..õ---,.. ....--
0 (Ob) ,
0 (Oc) ,
(Od) ,
..õ----.. ....--
0 (Oe),
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 8 -
0 (Of),
(Og) and
0 (Oh).
By using a hydrofluoro monoether containing three or four
carbon atoms, and in specific cases also when containing
five or six carbon atoms, a gaseous insulation medium can
be achieved, which does not liquefy under typical
operational conditions and which at the same time has a
relatively high dielectric strength.
Furthermore, by using a hydrofluoro monoether containing
three or four or five or six carbon atoms, an insulating
medium can be achieved, which is non-explosive and thus
complies even with high safety requirements.
In summary, by using a hydrofluoro monoether containing
three or four carbon atoms a non-explosive dielectric
insulation medium having a high dielectric strength
relative to air and having at the same time a boiling
point of less than 30 C can be achieved. This is of
particular relevance for the targeted use of the
insulation medium in an electrical apparatus, such as for
example gas-insulated switchgear, a gas-insulated
transmission line or a gas-insulated substation. By using
a hydrofluoro monoether containing five or six carbon
atoms non-explosivity and high dielectric strength
together with a boiling point of less than 55 C or less
than 40 C are achievable.
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 9 -
In the context of the present invention, the term "boiling
point" is to be understood as boiling point at atmospheric
pressure, i.e. at about 1 bar.
Considering flammability of the compounds, it is further
preferred that the ratio of the number of fluorine atoms
to the total number of fluorine and hydrogen atoms, here
briefly called "F-rate", of the hydrofluoro monoether is
at least 5:8. It has been found that compounds falling
within this definition are generally non-flammable and
thus result in an insulation medium complying with highest
safety requirements.
According to a further preferred embodiment, the ratio of
the number of fluorine atoms to the number of carbon
atoms, here briefly called "F/C-ratio", ranges from 1.5:1
to 2:1. Such compounds generally have a GWP of less than
1'000 over 100 years, thus leading to a very environment-
friendly insulation medium. It is particularly preferred
that the hydrofluoro monoether has a GWP of less than 700
over 100 years.
In embodiments, the dielectric insulation medium as a
whole has a global warming potential GWP over 100 years of
less than 1000, preferably less than 700, preferably less
than 300, preferably less than 100, preferably less than
50, preferably less than 20, most preferred less than 10.
Regarding the environmental aspect, it is further
preferred that the hydrofluoro monoether also has an ODP
of 0, as mentioned above.
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 10 -
The above mentioned desirable effects can in particular be
achieved by a hydrofluoro monoether having the general
structure (I)
CaHbFc-O-CdHeFf (I)
wherein a and d independently are an integer from 1 to 3
with a + d = 3 or 4 or 5 or 6, in particular 3 or 4, b and
c independently are an integer from 0 to 11, in particular
0 to 7, with b + c = 2a + 1, and e and f independently are
an integer from 0 to 11, in particular 0 to 7, with e + f
= 2d + 1, with further at least one of b and e being 1 or
greater and at least one of c and f being 1 or greater.
It is thereby a preferred embodiment that in the general
structure or formula (I) of the hydrofluoro monoether:
a is 1, b and c independently are an integer ranging from
0 to 3 with b + c = 3, d = 2, e and f independently are an
integer ranging from 0 to 5 with b + c = 5, with further
at least one of b and e being 1 or greater and at least
one of c and f being 1 or greater.
According to a particularly preferred embodiment, exactly
one of c and f in the general structure (I) is 0. The
corresponding grouping of fluorines on one side of the
ether linkage, with the other side remaining
unsubstituted, is called "segregation". Segregation has
been found to reduce the boiling point compared to
unsegregated compounds of the same chain length. This
feature is thus of particular interest for the dielectric
insulation medium, because compounds with longer chain
lengths allowing for higher dielectric strength can be
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 11 -
used without risk of liquefaction under operational
conditions.
Most preferably, the hydrofluoro monoether according to
the present invention is selected from the group
consisting of pentafluoro-ethyl-methyl ether (CH3-0-CF2CF3)
and
2,2,2-trifluoroethyl-trifluoromethyl
ether (CF3-0-CH2CF3).
Pentafluoro-ethyl-methyl ether has a boiling point of
+5.25 C and a GWP of 697 over 100 years, the F-rate being
0.625, while 2,2,2-trifluoroethyl-trifluoromethyl ether
has a boiling point of +11 C and a GWP of 487 over
100 years, the F-rate being 0.75. They both have an ODP of
0 and are thus environmentally fully acceptable.
In addition, pentafluoro-ethyl-methyl ether has been found
to be thermally stable at a temperature of 175 C for
30 days and therefore to be fully suitable for the
operational conditions given in electrical insulation
applications. Since thermal stability studies of
hydrofluoro monoethers of higher molecular weight have
shown that the stability of ethers containing fully
hydrogenated methyl or ethyl groups have a lower thermal
stability compared to those having partially hydrogenated
groups, it can be assumed that the thermal stability of
2,2,2-trifluoroethyl-trifluoromethyl ether is even higher.
Hydrofluoro monoethers in general, and pentafluoro-ethyl-
methyl ether as well as
2,2,2-trifluoroethyl-
trifluoromethyl ether in particular, display a low risk
for human toxicity. This can be concluded from the
available results of mammalian HFC (hydrofluorocarbon)
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 12 -
tests. Also, information available on commercial
hydrofluoro monoethers give no evidence of
carcinogenicity, mutagenicity, reproductive/developmental
effect and other chronic effects of the compounds of the
present application.
Based on the data available for commercial hydrofluoro
ethers of higher molecular weight, it can be concluded
that the hydrofluoro monoethers of the present application
in general, and in particular pentafluoro-ethyl-methyl
ether as well as 2,2,2-trifluoroethyl-trifluoromethyl
ether, have a lethal concentration LC 50 of higher than
10'000 ppm, rendering them suitable for insulation
applications also from a toxicological point of view.
The hydrofluoro monoether according to the present
invention has a higher dielectric strength than air. In
particular, pentafluoro-ethyl-methyl ether has a
dielectric strength about 2.4 times higher than air at 1
bar, as will be shown in connection with the figures
below.
Given its boiling point, which is preferably below 55 C,
more preferably below 40 C, in particular below 30 C, the
hydrofluoro monoether according to the present invention,
particularly pentafluoro-ethyl-methyl ether and 2,2,2-
trifluoroethyl-trifluoromethyl ether, respectively, is
normally in the gaseous state at operational conditions,
as is required for many applications, and in particular
for high voltage switching in gas insulated switchgears
(GIS).
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 13 -
The dielectric insulation medium of this application can
be a gas mixture, which apart from the hydrofluoro
monoether preferably comprises air and/or at least one air
component, in particular selected from the group
consisting of carbon dioxide (002), oxygen (02) and
nitrogen (N2), and/or a noble gas, and/or nitric oxide
(NO), and/or nitrogen dioxide (NO2), and/or nitrous oxide
(N20) as buffer or carrier gas. Alternatively, the
dielectric insulation medium can substantially consist of
hydrofluoro monoether.
By using a suitable admixture gas, a further increase in
the dielectric strength of the insulation medium can be
achieved.
In the case of pentafluoro-ethyl-methyl ether, for
example, a dielectric strength of 68 kV/cm at 1 bar total
pressure can be achieved by adding a small amount of
admixture gas (which has a higher boiling point than
pentafluoro-ethyl-methyl ether and a dielectric strength
higher than SF6). The dielectric strength obtained thereby
is higher than that of SF6 at the same pressure (84
kV/cm), as will be shown in the context of the figures
below.
According to a preferred embodiment, suitable admixture
gases are selected from the group consisting of
fluoroketones containing from 4 to 15 carbon atoms,
preferably from 4 to 12 carbon atoms, more preferably from
4 to 10 carbon atoms, even more preferably from 4 to 8
carbon atoms, even further more preferably from 5 to 8
carbon atoms, and most preferably is a fluoroketone
containing exactly 5 and/or exactly 6 and/or exactly 7
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 14 -
and/or exactly 8 carbon atoms. According to a particularly
preferred embodiment, dodecafluoro-2-methylpentan-3-one
and/or decafluoro-2-methylbutan-3-one, is used as an
admixture gas, as it has been found to have very high
insulating properties and an extremely low GWP. A
dielectric insulation medium comprising such fluoroketones
has been disclosed in the previously
filed
PCT/EP2009/057294 of the same applicant, the total content
of which is herewith enclosed in this application by
reference.
The term "fluoroketone" as used herein shall be
interpreted broadly and shall encompass both perfluoro-
ketones and hydrofluoroketones. The term shall also
encompass both saturated compounds and unsaturated
compounds including double and/or triple bonds. The at
least partially fluorinated alkyl chain of the
fluoroketones can be linear or branched.
The term "fluoroketone" shall also encompass fluoroketones
having a cyclic carbon backbone. The term "fluoroketone"
shall signify a chemical composition that comprises a
carbonyl-group and on each side of it an alkyl-group. The
term "fluoroketone" may comprise additional in-chain
hetero-atoms (i.e. hetero-atoms attached to the chemical
structure comprising a carbonyl-group and on each side of
it an alkyl-group), e.g. may comprise at least one hetero-
atom being part of the carbon backbone and/or being
attached to the carbon backbone. In exemplary embodiments,
the fluoroketone shall have no hetero-atom.
The term "fluoroketone" shall also encompass fluoro-
diketones having two carbonyl-groups or fluoroketones
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 15 -
having more than two carbonyl-groups. In exemplary
embodiments, the fluoroketone shall be fluoromonoketones.
In exemplary embodiments, the fluoroketone is a
perfluoroketone, and/or the fluoroketone has a branched
alkyl chain, in particular an at least partially
fluorinated alkyl chain, and/or the fluoroketone contains
fully saturated compounds. The expression that "the
fluoroketone contains fully saturated compounds" means
that both a single fully saturated fluoroketone, i.e. a
fluoroketone without any double bond or triple bond, or a
mixture of two or more fully saturated fluoroketones may
be comprised.
In an embodiment, the fluoroketone is or comprises at
least one compound selected from the group consisting of
the compounds defined by the following structural formulae
in which at least one hydrogen atom is substituted with a
fluorine atom:
0 (Ia)
0 (Ib)
0 (Ic)
0
cis? (Id).
In embodiments, the fluoroketone is or comprises a
perfluoroketone, in particular has the molecular formula
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 16 -
C5F100, i.e. is fully saturated without double or triple
bonds. The fluoroketone may more preferably be selected
from the group consisting of 1,1,1,3,4,4,4-heptafluoro-3-
(trifluoromethyl)butan-2-one (also named decafluoro-3-
methylbutan-2-one), 1,1,1,3,3,4,4,5,5,5-decafluoropentan-
2-one, 1,1,1,2,2,4,4,5,5,5-decafluoropentan-3-one,
1,1,1,4,4,5,5,5,-octafluoro-3-bis(trifluoromethyl)-pentan-
2-one; and most preferably is 1,1,1,3,4,4,4-heptafluoro-3-
(trifluoromethyl)butan-2-one.
In embodiments, the further fluoroketone is or comprises
at least one compound selected from the group consisting
of the compounds defined by the following structural
formulae in which at least one hydrogen atom is
substituted with a fluorine atom:
0 (IIa),
0 (IIb),
0 (IIc),
\/.r\
0 (IId),
0 (Ile),
>/Y
0 (IIf), and
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 17 -
0
O(hg);
and/or is or comprises at least one compound selected
from the group consisting of the compounds defined by
the following structural formulae in which at least
one hydrogen atom is substituted with a fluorine
atom:
o
II
.----.^.õ--"-- (IIIa),
.,--....--..---.
11
o (IIIb),
o
.--"----.1-------"-- (IIIc),
0
(IIId),
----------,-------__
o (IIIe),
I:11
-------------------- (uhf),
0 (lug),
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 18 -
...----------',_
CI (IIIh),
0
11
---T----....---------..
(IIIi),
0
0
(IIIk),
0
(III1),
0
(IIIm), and
0
6 (IIIn) named dodecafluoro-cycloheptanone.
In embodiments, the fluoroketone has the molecular formula
C6F120, i.e. is fully saturated without double or triple
bonds. More preferably, the fluoroketone can be selected
from the group consisting of 1,1,1,2,4,4,5,5,5-nonafluoro-
2-(trifluoromethyl)pentan-3-one (also named dodecafluoro-
2-methylpentan-3-one),
1,1,1,3,3,4,5,5,5-nonafluoro-4-
(trifluoromethyl)pentan-2-one (also named dodecafluoro-4-
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 19 -
methylpentan-2-one),
1,1,1,3,4,4,5,5,5-nonafluoro-3-
(trifluoromethyl)pentan-2-one (also named dodecafluoro-3-
methylpentan-2-one),
1,1,1,3,4,4,4-heptafluoro-3-bis-
(trifluoromethyl)butan-2-one (also named dodecafluoro-3,3-
(dimethyl)butan-2-one),
dodecafluorohexan-2-one and
dodecafluorohexan-3-one, and particularly is the mentioned
1,1,1,2,4,4,5,5,5-nonafluoro-2-(trifluoromethyl)pentan-3-
one.
Apart from the above gaseous embodiments, it is however
also possible that the insulation medium or at least one
of its components is in liquid form under certain
operational conditions or even permanently. Here, "liquid
form" shall be understood broadly to encompass any state
of matter or mixture which comprises at least partially a
liquid in any form, for example a liquid phase, an aerosol
phase, an over-saturated vapour phase or combinations
thereof. Such liquid form of the insulation medium or at
least one of its components might for example be present
for applications in a low temperature environment. In
particular, the insulation medium can be a two-phase
system comprising the hydrofluoro monoether both in liquid
and gaseous state. More particularly, the insulation
medium can be an aerosol comprising droplets of the
hydrofluoro monoether dispersed in a gas phase comprising
hydrofluoro monoether in the gaseous state.
The insulation properties of the insulation gas, and in
particular its breakdown field strength, can be controlled
by the temperature, pressure and/or composition of the
system. If a two-phase system comprising the hydrofluoro
monoether both in liquid and gaseous phase is used, an
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 20 -
increase of the temperature does not only result in an
increase of the absolute pressure, but also in an increase
of the hydrofluoro monoether's concentration in the
insulation gas due to a higher vapour pressure.
It has been found that for many applications of the
insulation gas, such as applications in the medium or high
voltage range, a sufficient molar ratio, i.e. the molar
ratio of hydrofluoro monoether to the remaining components
of the medium (generally the carrier or buffer gas), and
thus also a sufficient breakdown field strength can be
achieved even at very low operational temperatures e.g. of
down to about -30 C or even -40 C, even without additional
measures such as external heating or vaporization.
Preferably, the
molar fraction of the hydrofluoro
monoether in the insulation medium is larger than 1%,
preferably larger than 2%, more preferred larger than 3%,
in particular larger than 3.5%.
As mentioned, the insulation medium of the present
invention is
particularly useful for electrical
applications. The present invention thus also relates to
the use of the herein-described hydrofluoro monoether in a
dielectric insulation medium for an apparatus for the
generation, the distribution and/or the usage of
electrical energy.
The present invention also encompasses the use of the
dielectric insulation medium as claimed in any of the
claims 1-33 for the dielectric insulation in an apparatus
for the generation, distribution and/or usage of
electrical energy.
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 21 -
Likewise, the present invention further relates to an
apparatus for the generation, the distribution and/or the
usage of electrical energy, said apparatus comprising a
housing defining an insulating space and an electrical
active part arranged inside the insulating space. This
insulating space comprises the insulation medium described
above.
Also, the term "electrically active part" in this context
is to be interpreted broadly including a conductor, a
conductor arrangement, a switch, a conductive component, a
surge arrester, and the like.
In particular, the apparatus of the present invention
includes a switchgear, in particular an air-insulated or
gas-insulated metal (or otherwise)-encapsulated switchgear
or a hybrid (i.e. partially air-insulated and partially
gas-insulated) switchgear or a medium voltage block
switchgear or a ring-main-unit, or a dead tank breaker or
a PASS-module (plug-and-switch module), or a part and/or
component thereof, in particular a bus bar, a bushing, a
cable, a gas-insulated cable, a cable joint, a current
transformer, a voltage transformer, and/or a surge
arrester.
Switchgears, in particular gas-insulated switchgears
(GIS), are well known to a person skilled in the art. An
example of a switchgear for which the present invention is
particularly well suited is for example shown in EP-A-
1933432, paragraphs [0011] to [0015], the disclosure of
which is incorporated herewith by reference.
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 22 -
It is further preferred that the apparatus is a switch, in
particular an earthing switch (e.g. a fast acting earthing
switch), a disconnector, a combined disconnector and
earthing switch, a load-break switch or a circuit breaker,
in particular a medium-voltage circuit breaker, a
generator circuit breaker and/or a high-voltage circuit
breaker.
In another embodiment, the apparatus is a high voltage
circuit breaker having a pressure-build-up chamber for
providing pressurized arc-extinguishing gas, and in a
switching operation the hydrofluoro monoether is
decomposed in the pressure-build-up chamber and/or arcing
region during an arc-extinguishing phase. Such molecular
decomposition allows to further increase the number of
molecules and hence the pressure which is available for
extinguishing the arc. The hydrofluoro monoether is also
helpful in the exhaust region of a circuit breaker,
because its rather low dissociation temperature functions
as a temperature barrier in the exhaust gas. In other
words, thermal energy in the exhaust gas can be absorbed
by dissociation of hydrofluoro monoether in the exhaust,
which prevents further temperature increase in the exhaust
gas above the dissociation temperature of the hydrofluoro
monoether.
According to another embodiment, the apparatus can be a
transformer, in particular a distribution transformer or a
power transformer.
According to still other embodiments, the apparatus can
also be, e.g., an electrical rotating machine, a
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 23 -
generator, a motor, a drive, a semiconducting device, a
power electronics device, and/or a component thereof.
In embodiments, the apparatus has a conventional pressure
design for being filled with sulphur hexafluoride SF6 and
is filled with the dielectric insulation medium as claimed
in claim 1 and the dependent claims and, in particular,
the apparatus does not contain sulphur hexafluoride SF6.
The invention particularly relates to a medium or high
voltage apparatus. The term "medium voltage" as used
herein refers to a voltage in the range of 1 kV to 72 kV,
whereas the term "high voltage" refers to a voltage of
more than 72 kV. Applications in the low voltage range
below 1 kV are feasible, as well.
In order to achieve a desired dielectric rating of the
apparatus, such as a desired dielectric withstand
capability (for example represented by a desired breakdown
field strength) and operating temperature range, the
apparatus can comprise a control unit (also referred to as
"fluid management system") for controlling individually or
in combination: the composition - in particular the
chemical composition or the physical phase composition,
such as a gas/liquid two-phase system - and/or the
temperature of the insulation medium, and/or the absolute
pressure, the gas density, the partial pressure and/or the
partial gas density of the insulation medium or at least
one of its components, respectively. In particular, the
control unit can comprise a heater and/or vaporizer in
order to control the vapour pressure of the hydrofluoro
monoether according to the invention, which is of
particular relevance for applications in a low temperature
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 24 -
environment. The vaporizer can e.g. be an ultrasound
vaporizer, or can comprise spraying nozzles for spraying
the insulation medium into the apparatus.
If a vaporizer is used, it should also comprise a dosing
unit to set the concentration of the hydrofluoro monoether
in the insulation medium according to needs of breakdown
field strength. This will exemplarily be shown in more
detail below for a medium or high voltage gas-insulated
switchgear. Furthermore, the control unit may comprise a
measuring unit for measuring the control parameters, such
as temperature, pressures and/or composition - in
particular the liquid phase level - and/or a monitoring
unit for monitoring such parameters.
As mentioned, the present invention also relates to the
use of a hydrofluoro monoether, as described above and
elsewhere in this application, in a dielectric insulation
medium for an electrical apparatus for the generation, the
distribution and/or the usage of electrical energy, as
also described herein.
In embodiments, the dielectric insulation medium and the
apparatus comprising the dielectric insulation medium and
the use of the hydrofluoro monoether as a dielectric
insulation medium can comprise, in addition to the
hydrofluoro monoether, at least one gas component a) or
gas component element al) selected from the first group
consisting of: air; an air component, in particular
nitrogen, oxygen and carbon dioxide; nitric oxide,
nitrogen dioxide, nitrous oxide N20, CF3I; noble gases and
in particular argon; methane, sulphur hexafluoride SF6;
perfluorocarbons, in particular carbon tetrafluoride CF4,
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 25 -
C2F6, C3F8 or c-C4F8; fluoroketones, in
particular
fluoroketones containing exactly 5 or 6 or 7 or 8 carbon
atoms; perfluoroethers, in
particular perfluoro
monoethers; and mixtures thereof. Such gas components al)
may have several advantages such as: good dielectric
strength; low boiling points, in particular lower boiling
points than hydrofluoro monoethers and preferably boiling
points below 0 C or below -10 C or below -20 C or below -
30 C or below -40 C; thus may extend the range of
operating temperatures to lower values; and may provide,
in particular in the case of SF6 or CF4 when admixed in
smaller quantities, relatively low contributions to an
overall still acceptable GWP value of the gas mixture or
dielectric insulation medium.
In further embodiments, the dielectric insulation medium
and the apparatus comprising the dielectric insulation
medium and the use of the hydrofluoro monoether as a
dielectric insulation medium can comprise, in addition to
the hydrofluoro monoether and optionally the above listed
gas components and/or gas component elements, at least one
gas component a) or gas component element a2) selected
from the second group consisting of: CHF3, (C2F5)20,
(CF3)20; further perfluorocarbons and in particular C2F4,
C3F6, C4F10, C4F6, C4F8, C6F10, C6F12, C6F14, C6F6; C2F5C0F,
C5F802, c-C4F7I, CF3CF (CF3) CF (CF3) CF2I,
CF3CF2CF2CF2I,
CF3CF2CF2I, CF3CF2I, CF3CHFCF2I, CF3SF5, CH2F2, CH3-c-C4F6I,
CH3CF(CF3)CF(CF3)CF2I, CH3CF2CF2I, CH3CHFCF(CF2CF3)CF2I, CO;
noble gases and in particular He, Kr, Ne; N2f
perfluorodiethyl thioether,
perfluoromethyl ethyl
thioether, perhalogenated
organic compounds,
tetradecylfluorohexane, XeF2, XeF4; and mixtures thereof.
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 26 -
According to one embodiment, the gas component a) is a
bulk gas or buffer gas or carrier gas that is present in a
larger mole fraction than the hydrofluoro monoether, in
particular the gas component a) being present in a
quantity of larger than 60%, preferably larger than 70%,
more preferably larger than 80%, even more preferably
larger than 90%, particularly preferred larger than 95%,
even more particularly preferred larger than 97%, of the
insulation medium.
According to an alternative embodiment, the gas component
a), in particular SF6 and/or CF4, is present in a smaller
mole fraction than the hydrofluoro monoether, in
particular the gas component a) being present in a
quantity of less than 40%, preferred less than 30%, more
preferred less than 20%, even more preferred less than
10%, particularly preferred less than 5%, even more
particularly preferred less than 3%, and most preferred
less than 1%, of the insulation medium.
In other embodiments, for a dielectric insulation medium
as described throughout this application and as claimed
hereinafter, an apparatus and a use are disclosed, the
apparatus and use comprising a hydrofluoro monoether
optionally in a mixture with e.g. carbon dioxide and/or
air and/or oxygen. A mixture of the hydrofluoro monoether
with carbon dioxide and/or air and/or oxygen is most
preferably used as an arc-extinguishing gas in a circuit
breaker, in particular in a high-voltage circuit breaker
or medium-voltage circuit breaker. The use of oxygen in
combination with hydrofluoro monoether reduces carbon
deposition on electrodes of the circuit breaker, and/or
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 27 -
reduces the amount of toxic arcing by-products in the
circuit breaker, in particular after switching operations.
The use of carbon dioxide increases the arc extinction
capability of the mixture.
According to a particular embodiment, the present
invention does not relate to the use of a hydrofluoro
monoether as a foam-blowing agent, for example for the
production of polyurethane thermally insulating foams or
for the generation of cellular structures in other
polymers, plastics or metals used as thermal insulating
materials.
According to further embodiments, the present invention
does not relate to the use of a hydrofluoro monoether as a
refrigerant in liquid form, as a coolant for electronic
equipment or as a medium in heat transfer systems.
According to further embodiments, the present invention
does not relate to the use of a hydrofluoro monoether as
cleaning solvent, for example for electronic components,
precision cleaning of medical or analytical equipment, or
for metal finishing.
According to further embodiments, the present invention
does not relate to the use of a hydrofluoro monoether as
carrier solvent for coatings, lubricants or friction-
reduction agents, e.g. on devices such as surgical knife
blades.
According to a further embodiment, the present invention
does not relate to the use of a hydrofluoro monoether for
precision drying in semiconductor applications.
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 28 -
The invention is further illustrated by way of the
following illustrative figures of which
Fig. 1 shows a graphical representation of the electric
breakdown field strengths of embodiments of the
dielectric insulation medium of the present
invention as a function of gas pressure,
compared with conventional reference gases;
Fig. 2 shows a purely schematic representation of a
medium or high voltage gas-insulated switchgear
according to an embodiment of the present
invention comprising a temperature control unit;
and
Fig. 3 shows a purely schematic representation of a
medium or high voltage gas-insulated switchgear
according to an embodiment of the present
invention comprising a fluid handling unit.
Throughout this application, the terms "preferable",
"preferred", "more preferable", "in particular" shall
solely mean "exemplary" and shall therefore signify
embodiments or examples only, i.e. are to be understood as
optional only. The term "characterized in" is no admission
of prior art.
Fig. 1 shows the breakdown voltage or electric breakdown
field strength E bd in kV/cm of an insulation medium
essentially consisting of pentafluoro-ethyl-methyl ether,
here briefly called HFE1, over a given pressure range. As
is apparent from Fig. 1, the breakdown voltage is higher
than the one determined for pure air (shown in circles) at
the respective pressure. By admixing dodecafluoro-2-
methylpentan-3-one as an admixture gas having a partial
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 29 -
pressure of 0.14 bar to pentafluoro-ethyl-methyl ether
having a partial pressure of 0.84 bar, an insulation
medium is obtained which has a breakdown voltage (shown by
the square) that is even superior to the breakdown voltage
obtained with SF6 (shown in triangles) at the respective
pressure of 0.98 bar.
In order to adapt the pressure and/or the composition
and/or the temperature of the insulating medium in the
system, the electrical apparatus can comprise a control
unit (or "fluid management system"), as mentioned above.
This is of particular relevance for low temperature
applications down to -30 C or even -40 C.
As an example, a high voltage switchgear comprising a
temperature control unit is shown in Fig. 2. The
switchgear 2 comprises a housing 4 defining an insulating
space 6 and an electrically active part 8 arranged in the
insulating space 6. The switchgear 2 further comprises a
temperature control unit 10a for setting the housing 4, or
at least a part of the housing 4, of the switchgear and
thus the insulation medium comprised in the insulating
space 6 to a desired temperature. As well, any other part
in contact with the insulation medium can be heated in
order to bring the insulation medium or at least parts of
it to the desired temperature. Thus, the vapour pressure
of the hydrofluoro monoether - and consequently its molar
ratio in the insulation gas - as well as the absolute
pressure of the insulation gas can be adapted accordingly.
As also shown in Fig. 2, the hydrofluoro monoether is in
this embodiment not homogenously distributed throughout
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 30 -
the insulating space due to the temperature gradient given
in the insulation space.
An alternative control unit or fluid management system is
schematically shown in Fig. 3 in which a fluid handling
unit 10b is attributed to the gas-insulated switchgear as
the control unit. According to this control unit, the
composition of the dielectric insulation medium, and in
particular the concentration of the hydrofluoro monoether,
is adjusted in a dosing unit (not separately shown)
comprised in the fluid handling unit 10b, and the
resulting insulation medium is injected or introduced, in
particular sprayed, into the insulating space 6. In the
embodiment shown in Fig. 3, the insulation medium is
sprayed into the insulating space in the form of an
aerosol 14 in which small droplets of liquid hydrofluoro
monoether are dispersed in the respective carrier gas. The
aerosol 14 is sprayed into the insulating space 6 by means
of nozzles 16 and the hydrofluoro monoether is readily
evaporated, thus resulting in an insulating space 6 with
an inhomogeneous concentration of hydrofluoro monoether,
specifically a relatively high concentration in close
proximity of the housing wall 4' comprising the nozzles
16. Alternatively, the insulation medium, in particular a
concentration, pressure and/or temperature of the
insulation medium or of at least one of its components, in
particular the hydrofluoro monoether, can be controlled in
the fluid handling unit 10b before being injected into the
insulation space. In order to ensure circulation of the
gas, further openings 18 are provided in the upper wall of
the housing 4, said openings leading to a channel 20 in
the housing 4 and allowing the insulating medium to be
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 31 -
removed from the insulating space 6. The switchgear 2 with
fluid handling unit 10b, as shown in Fig. 3, can be
combined with the temperature control unit 10a described
in connection with Fig. 2. If no temperature control unit
is provided, condensation of the hydrofluoro monoether can
occur in a low temperature environment. The condensed
hydrofluoro monoether can be collected and reintroduced
into the circulation of the insulation medium.
Furthermore, the apparatus 2 can have a reserve volume of
hydrofluoro monoether and/or of an admixture gas, such as
a fluoroketone containing from 4 to 12 carbon atoms and,
in particular, from 5 to 6 carbon atoms, and/or means for
limiting a maximal permissible operating temperature of
the desired insulation medium such that the absolute
filling pressure is maintained below a given pressure
limit of the apparatus 2.
In the context of the switchgears exemplarily shown in
Fig. 2 and Fig. 3 it is noted that nominal current load
generally facilitates the vaporization of the hydrofluoro
monoether by the ohmic heating of current carrying
conductors.
In embodiments, the apparatus 2 has a dielectric
insulation medium, in which the hydrofluoro monoether is
present in an amount such that a condensation temperature
of the hydrofluoro monoether is below +5 C, preferably
below -5 C, more preferably below -20 C, even more
preferably below -30 C, most preferably below -40 C.
In further embodiments, the apparatus 2 has a dielectric
insulation medium, which comprises gaseous components in
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 32 -
molar volumes such that a condensation temperature of the
mixture of the gaseous components is below +5 C, prefer-
ably below -5 C, more preferably below -20 C, even more
preferably below -30 C, most preferably below -40 C.
For sake of clarity: boiling point or boiling point
temperature relates to the vapour pressure curve of a
component of the insulation medium as a function of
temperature, and in particular to the boiling point
(temperature) at atmospheric pressure, i.e. at about 1
bar. This is a property of the component as such and
describes its vaporization and liquefaction behaviour in
particular under atmospheric surrounding pressure
conditions.
In contrast, condensation temperature relates to a
specific apparatus providing a volume for receiving the
dielectric insulation medium, its filling with a specific
dielectric insulation medium, in particular the type and
amount of the component or components of the dielectric
insulation medium, at a given temperature, e.g. the
operating temperature or the minimal rated operating
temperature, and to the corresponding total pressure of
the dielectric insulation medium and the partial pressures
of its components. In such a specific apparatus
environment filled with a specific choice of dielectric
insulation medium, condensation temperature defines the
temperature at which a gaseous part or phase of the
dielectric insulation medium, in particular a group of
components in gaseous phase of the dielectric insulation
medium, start to condense into droplets that sit down on
inner surfaces of the apparatus and form a liquid "sea"
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 33 -
thereon. Such condensation may occur at a common
condensation temperature, briefly called condensation
temperature, of components of the dielectric insulation
medium, even if the boiling points of such components in
their pure form may differ by e.g. several 10 K or even by
some 50 K. As a result of different boiling points and
common condensation temperature, the molar fractions of
the components in the gaseous phase and in the liquid
phase may vary when condensation starts.
Therefore, the term "condensation temperature" is an
integral parameter describing the specific apparatus
having a specific filling with the dielectric insulation
medium and under specific operating conditions.
In other words, the condensation temperature is determined
solely by the nature and number density or molar volume
(m3/mol) of the dielectric insulation gas component or
components under consideration. The number density or
molar volume corresponds to the partial pressures present
in the apparatus at a given temperature. Thus, the
parameters "type of dielectric gas component or gas
components" and "number density or molar volumes"
determine at what temperature a gas or group of gas
components will condense.
In embodiments, it is intended to avoid condensation by
the choice of the dielectric insulation medium, in
particular choice of its types and amounts of components,
and by the choice of pressures, i.e. partial pressures of
the components and the total pressure, possibly by
additional filling of a carrier gas or bulk gas, and by
the choice of operating conditions, such as temperature.
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 34 -
The avoidance of condensation is expressed by the fact
that the condensation temperature shall be lower than a
minimal operating temperature or a rated operating
temperature of the apparatus, e.g. lower than +5 C, or -
5 C, or -20 C, or -30 C, or -40 C, as stated above.
The term carrier gas or bulk gas or buffer gas, which may
be or may be comprised in the above mentioned gas
component a) or gas component elements al), a2), ... an)
different from the hydrofluoro monoether, shall signify a
gaseous part of the dielectric insulation medium that
contributes to the dielectric strength, but typically has
a dielectric strength weaker than the (dielectrically more
active or stronger) gas components, such as hydrofluoro
monoether(s) and/or fluoroketone(s) and/or
other
"dielectrically strong" gas component species. Such
carrier gas, e.g. air, typically has a condensation
temperature well below the condensation temperature of the
above mentioned dielectrically stronger gas components,
such as hydrofluoro monoether(s) and/or fluoroketone(s).
In embodiments, the dielectric insulation medium is a
dielectric insulation gas under over-pressure of less than
8 bar, preferably less than 7.5 bar, more preferably less
than 7 bar, in particular equal or less than 6,5 bar; or
the dielectric insulation medium is a dielectric
insulation gas under over-pressure of less than 2.5 bar,
preferably less than 2.0 bar, more preferably less than
1.5 bar, in particular equal to or less than 1.2 bar.
Throughout this application, the constituents of the
dielectric insulation medium, such as e.g. various kinds
of hydrofluoro monoethers, fluoroketones and carrier
CA 02821218 2013-06-11
WO 2012/080222 PCT/EP2011/072571
- 35 -
gases, are herewith explicitly disclosed to be possible or
to be present in any combinations, may it be pair-wise
combinations, triplet-wise combinations, quadruplet-wise
combinations, or the like. Therefore, any listings of all
such combinations are herewith made part of the
disclosure. Furthermore, throughout this application, any
disclosure of and claim on the dielectric insulation
medium comprising a hydrofluoro monoether according to the
present invention and any of its embodiments is also a
disclosure of the use of such a hydrofluoro monoether in
or as a dielectric insulation medium, and this use is
explicitly disclosed herewith and may be claimed as a use
claim, in particular by replacing the term "Dielectric
insulation medium comprising a hydrofluoro monoether" with
the term "Use of a hydrofluoro monoether in or as a
dielectric insulation medium".
CA 02821218 2013-06-11
WO 2012/080222
PCT/EP2011/072571
- 36 -
List of reference numerals
2 switchgear
4 housing
4' housing wall
6 insulating space
8 electrical active part
10a temperature control unit
10b fluid handling unit
14 aerosol
16 nozzle
18 opening
channel
