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Transformer bushings

Transformers with ElecNet

Capacitive bushings are often used to improve the field distribution inside of transformers. They can be used to grade the voltage down gradually from high voltage conductors. The design and simulation of transformer bushings have always been challenging because modeling these structures was computationally quite expensive, especially in 3D, due to the fine mesh required for long and very thin pieces of foil that are present in these devices. Presented here is a two-dimensional 2D ElecNet model of capacitive bushings placed inside of an oil insulated transformer using floating electrodes on component surfaces which readily solves the computational time aspect of the problem.

In this example, the transformer bushing consists of twenty foils of various lengths that are placed inside of epoxy-resin impregnated paper (ERIP) at specific locations in order to minimize the maximum electric field, E.

transformer busing consisting of nine foils

METHODS and RESULTS

2D MODEL and MESH

Taking advantage of axial symmetry, a 2D model is considered here. Each foil inside of the paper is defined as a floating electrode.

A detailed view of the model and the mesh can be seen on the right.

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Resulting FIELDS

Presented on the left are two shaded field plots -- the electric field |E| with units of volts/m and the voltage distribution in the model. The displayed field plot was restricted to the values between 0 and 5.28e6 V/m.

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EFFECTS of BUSHING - COMPARATIVE GRAPH

The graph on the right is of |E| along a line through the ERIP at the top of the model. Data for a transformer with no bushings is also plotted to act as a reference.

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