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Electrical apparatus and insulation fluid for an electrical apparatus Disclosure Number: IPCOM000243114D
Publication Date: 2015-Sep-16
Document File: 36 page(s) / 84K

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Abstract Present invention relates to electrical apparatuses for generation, transmission, distribution and/or usage of electrical energy and is rated for operating temperature Top ranging from minimum Top,min to maximum Top,max and operating pressure pop up to maximum pop,max. The apparatus comprises a housing enclosing electrical apparatus interior space having insulation space containing an electrical component and an insulation fluid comprising insulation fluid component A, which at standard ambient temperature and pressure is gaseous and has characteristic particle number density nAc which is maximal under constraints that component A a) is single-phase for all temperatures between Top,min and Top,max and b) has pressure not exceeding pop,max at Top,max. Additionally, insulation fluid comprises insulation fluid component B, which has characteristic particle number density nBc which is maximal under constraints a) and b). The insulation fluid fulfills constraints a) and b) and has particle number density nI higher than each of nAc and nBc.

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Page 01 of 36


Electrical apparatus and insulation fluid for an electrical

The present invention relates to an electrical apparatus for
the generation, the transmission, the distribution and/or the
usage of electrical energy, as well as to an insulation fluid
for such an electrical apparatus.

Dielectric insulation media in liquid or gaseous state are
conventionally applied for the insulation of an electrically
conductive part in a wide variety of apparatuses, and in
particular also in gas-insulated switchgear or parts thereof.

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In medium or high voltage metal-encapsulated switchgear, for
example, the electrically conductive part is arranged in a
gas-tight housing, which defines an insulating space, said
insulation space comprising an insulation gas and separating
the housing from the electrically conductive part without
letting electrical current to pass through the insulation
space. For interrupting the current in e.g. high voltage
switchgear, the insulating medium further functions as an arc-
extinction medium (or arc-quenching medium).

    In conventional high-voltage gas-insulated switchgears,
sulphur hexafluoride (SF6) is typically used as dielectric
insulation medium and/or arc-quenching medium.

Alternative insulation media, such as air, have the advantage
of a low Global Warming Potential (GWP). However, their
insulation capabilities are generally rather poor compared to
the insulation capability of SF6.

In order to provide an insulation medium having both a low GWP
and at the same time high insulation capabilities, the use of
organofluorine compounds in an insulation medium has recently
been suggested.


Page 02 of 36

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   Despite of high dielectric strengths theoretically achievable
with these alternative insulation media, they often have a
relatively high boiling point. When the temperature in the
insulation space falls below a predetermined threshold
temperature, liquid droplets can form as a result of partial
condensation of the medium. This inhomogeneity may sometimes
be considered detrimental, since it has been found to go along
with a higher tendency for electric breakdown.

    Inhomogeneities also occur when a liquid insulation medium,
such as oil, is used. Without wanting to be bound by the
theory, it is assumed that at sites with a locally enhanced
field, field emission and subsequent impact ionization can
occur resulting in the formation of gas bubbles in the
insulation liquid. Streamer inception and propagation can then
occur which finally leads to electric breakdown.

In addition to aiming at an environment-friendly way of achie-
ving a high withstand capability against electrical breakdown,
efforts are at the same time made for designing increasingly
compact apparatuses, especially in urban environments.

    Taking the above into consideration, the problem of the
present invention is thus to provide an electrical apparatus
which is environmentally-friendly and which at the same time
has a low tendency for electric breakdown even when...