Asea Aktiebolag

Asea Brown Boveri Ab

Arne Hjortsberg

Goran Holmstrom

Thommy Karlsson

Lennart Johansson

Erik Sterlund

A tape-formed or sheet-formed insulating material for use in windings and coils of electrical machines includes an insulating layer in the form of a homogeneous film of an organic polymer or in the form of a felt of a paper of fibres of an organic polymer and a protective layer coated on at least one side of the insulating layer which protects the insulating layer against degradation caused by corona. The protective layer comprises an organic polymer containing at least 10 percent by volume of a powdered filler in the form of chromium oxide, iron oxide or a mixture of chromium oxide and iron oxide. The filler preferably has an intrinsic resistivity of 10.sup.4 -10.sup.8 ohm m. The thickness of the protective layer and the total thickness of the protective layer, respectively, are preferably smaller than the thickness of the insulating layer and the resistivity of the protective layer is preferably in excess of 10.sup.10 ohm m.

Electrical insulating material comprising an insulating layer in the

An electrical conductor is provided with an electrical insulation (11) surrounding the conductor (10) and a surrounding protective layer (12) which protects the insulation against degradation caused by corona. The protective layer consists of an organic polymer containing at least 10 percent by volume of a powdered filler in the form of chromium oxide, iron oxide, or a mixture of chromium oxide and iron oxide. The filler preferably has an intrinsic resistivity of 10.sup.4 -10.sup.8 ohm m. The thickness of the protective layer is preferably smaller than the thickness of the underlying insulation (11) and its resistivity preferably exceeds 10.sup.10 ohm m. The conductor is used, among other things, in windings and coils for electrical machines.

Electrical conductor provided with a surrounding insulation

A coil for arrangement in slots in a stator or rotor of an electrical machine, in particular a high voltage coil, comprising a bundle (17) of a plurality of conductors (18) located adjacent to each other and provided with a conductor insulation (19) for insulation of the conductors from each other as well as a main insulation (14) surrounding the bundle for insulation of the bundle against the machine slot. The main insulation consists of a wrapping of a tape- or sheet-formed insulating material wound in several layers around the bundle and comprising a layer with small mica flakes which, as well as the spaces between layers of mica flakes in the wrapping, contains a cured impregnating resin. At least that part of the impregnating resin located in the spaces between mica layers contains particles of a filler with an intrinsic thermal conductivity of at least 5 W/mK, such as aluminium oxide or boron nitride, and with a grain size of the particles of 0.1-15 .mu.m in at least 90 percent of the filler.

Coil for arrangement in slots in a stator or rotor of an electrical

A system for HVDC transmission comprises a conductor, stressed by d.c. voltage, which is insulated from a surrounded grounded casing by pressurized SF.sub.6 gas and along part of its length by at least one solid insulator supporting the conductor in the casing and in contact with the gas. By designing the solid insulator as a core of solid insulating material and a coating, provided thereon, with a high surface resistance, it is possible considerably to reduce the dimensions of the casing. The coating consists of a resinous binder containing a powdered filler in the form of chromium oxide or iron oxide, or a mixture of these substances. The coating preferably has a surface resistance between 10.sup.12 and 10.sup.18 ohm/.quadrature. at an electric field strength of 1 kV/mm.

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Vaster.ang.s, Sweden

Arne Hjortsberg