Electricity: electrical systems and devices – Safety and protection of systems and devices – High voltage dissipation
Patent
1984-05-18
1986-11-25
Pellinen, A. D.
Electricity: electrical systems and devices
Safety and protection of systems and devices
High voltage dissipation
361212, H02H 322
Patent
active
046252568
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an overvoltage proctector for a device having two parts movable relative to each other, one of which is stationary in relation to a frame at ground potential, said parts being connected with each other via at least one bearing, the movable part being subjected to an electrical voltage and the stationary part being electrically connected to the frame.
BACKGROUND
In apparatus with mutually moving parts which are connected to each other via a bearing and are subjected to different electrical potentials, there is the risk that a current path can occur through the bearing. The current passing the bearing surfaces may be of magnitude that the bearing is damaged by pitting of the bearing surfaces. It is known to protect the bearings by insulating the bearing seatings in the cases where the voltage difference is small, as is the case, for example, for asynchronous machines. This is not satisfactory when there are large voltage differences, since there is the risk of flashover. Examples of this are to be found in wind turbines and radar antennae which are subjected to lightning.
SUMMARY OF THE INVENTION
The problems mentioned above are solved by providing the bearing with insulation while the moving part is provided with a spark discharge gap at the same time.
The bearing is protected by the insulation against electric current up to a given voltage threshold. In order that this voltage threshold will not be exceeded, the spark discharge gap comes into operation and lowers the voltage.
BRIEF DESCRIPTION OF THE DRAWING
The sole FIGURE of the drawing shows, partly in section, an elevational view of one embodiment of apparatus according to the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
The invention will now be described in detail with reference to the appended drawing. Therein is seen a bearing housing 1 with ball bearings 2, 3 and 4, which carry a shaft 5, for example, the shaft of a wind turbine 15. The shaft is insulated from the ball bearings by bearing seatings 6 and 7, consisting of material with high electrical insulation power. The housing is connected to electrical ground potential by a frame 13, and carries at one end a ring 8 having a bevelled outer edge. The shaft supports a ring 9 coacting with, and surrounding the ring 8, and having an inner surface with a bevel corresponding to that of the outer edge of the ring 8, such that a circular gap 10 is formed between the two rings. This gap constitutes an electrical flashover zone during a spark discharge. The shaft 11 of a machine 14 such as a generator, which is driven by the shaft 5, is connected to the shaft via an insulating part 12. The thickness and material of the bering seatings 6 and 7, which determine the dielectric strength, and the axial extension of said seatings, which determines the flashover resistance, are such in relation to the insulation power of the gap 10 that the flashover voltage is lower across the gap than the dielectrical breakdown voltage and the flashover voltage over the bearing seatings. If the shaft is subjected to a voltage lower than the flashover voltage, the insulating bearing seatings prevent current from passing through the bearings. For a voltage exceeding the flashover voltage of the air gap, e.g. lightning, a spark discharge is produced in the gap 10 which limits the voltage which can occur at the bearing seatings.
As an alternative to the described embodiment, instead of insulating bearing seatings, the shaft may be provided with an insulating layer or consist entirely of insulating material at the portion in contact with the bearings. If the shaft is mounted in journal bearings, the bushes themselves may consist of insulating material. The arrangement in accordance with the invention thus protects the bearings from conducting current and thus being destroyed. Bearing damage in a wind turbine or radar antenna results in great inconvenience, since the entire machine must be taken down from its tower and transported to a workshop for repairs. Ot
REFERENCES:
patent: 392400 (1888-11-01), Belfield
patent: 1201328 (1916-10-01), Moran
patent: 2256118 (1941-09-01), Kyropoulos
patent: 2599951 (1952-06-01), Stanton
patent: 2778635 (1957-01-01), Eash
patent: 4177493 (1979-12-01), Bliamptis
Power Engineering, vol. 58, issue No. 5, May 1954, pp. 73 & 74.
Beck, Westinghouse Engineer, vol. 9, issue No. 3, May 1949, pp. 72 & 73.
Akerlund John
Scuka Viktor
Pellinen A. D.
Telefonaktiebolaget LM Ericsson
Wysocki A. Jonathan
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