Electricity: conductors and insulators – Conduits – cables or conductors – Single duct conduits
Reexamination Certificate
2000-01-12
2001-08-07
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Single duct conduits
C174S068300, C174S135000, C174S1520GM, C174S15300A, C174S016100, C174S002000, C174S489000, C174S657000
Reexamination Certificate
active
06271470
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an insulating liquid filled power bushing for high voltage apparatus and particularly to an insulating liquid filled power bushing for a transformer.
BACKGROUND OF THE INVENTION
In insulating liquid filled power bushings for high voltage apparatus such as oil filled bushings for transformers, the oil in the oil filled bushings is in contact with a cushion of gas that allows the oil to expand and contract due to thermal changes. When the oil expands, the gas is compressed and when the oil contracts, the gas expands to fill the space. As the pressure in the gas space varies and the temperature varies, the tendency for the oil to absorb and contain gas changes. As a result, gas is cyclically entering and leaving the oil over the life of the bushing. In some cases, the giving up of gas is so quick that it results in bubbles forming in the oil below the surface. These bubbles can occur in locations of high stress and produce partial discharge, which interferes with transformer testing and may reduce the life of the bushing in severe cases.
It would be desirable to provide an oil filled bushing where the oil is prevented from contacting the gas cushion. In this way, the oil can't absorb gas and remains devoid of large quantity of gas which make gas bubble evolution impossible.
SUMMARY OF THE INVENTION
It is an object of the present invention to incorporate a piston in the head of a power bushing to prevent the insulating oil from contacting the nitrogen gas and absorbing it. This prevents the nitrogen from being absorbed into the oil and later being released as bubbles, which causes partial discharge.
Accordingly, it is an object of the present invention to provide an insulating liquid filled power bushing for a transformer or other high voltage apparatus including an insulator having a chamber therein for receiving insulating liquid. An expansion chamber communicates with the insulator chamber for receiving insulating liquid and gas. A movable piston is mounted within the expansion chamber for dividing the expansion chamber into a liquid filled section and a gas filled section. A conductor extends through the insulator piston and the expansion chamber. A sealing means is provided for sealing the piston with respect to the conductor and the expansion chamber so as to prevent the gas in the gas filled section from communicating with the liquid in the liquid filled section thereby allowing the liquid to expand and contract due to thermal changes while preventing the liquid from absorbing the gas and making gas bubble evolution impossible. In one form of the invention a sight glass communicates with the insulator chamber and the expansion chamber for receiving insulating liquid and the conductor extends through the insulator, the sight glass, the piston and the expansion chamber. In one form of the invention the insulating liquid is an insulating oil and the gas is nitrogen.
For a more detailed disclosure of the invention and for further objects and advantages thereof, reference is to be had to the following description taken in conjunction with the accompanying drawings.
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ABB Power T&D Company Inc.
Patel Dhiru R
Reichard Dean A.
Woodcock Washburn Kurtz Mackiewicz & Norris LLP
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