Transformer bushing application

ElecNet, Infolytica's electric field simulation package, allows for fast, accurate modeling of bushings inside of transformers in both two and three dimensions. Previously, modeling these structures was computationally expensive, especially in 3D, due to the fine mesh required for long and very thin pieces of foil. Presented here is a two-dimensional analysis of capacitive bushings inside of an oil insulated transformer using ElecNet's floating electrodes. 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.

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

Results

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Due to the axial symmetry present in this device, ElecNet's 2D Static solver is used. Each foil inside of the paper is represented in ElecNet as a floating electrode, which is a conductor that is not fixed to a known potential and has a zero charge. A floating electrode, or an electrode with a specified voltage, can be applied to a body, such as the high voltage electrode, or on a surface, such as one of the foils. If these thin foil electrodes were made out of bodies, the mesh used would contain an inordinate number of elements. By applying the foils only to surfaces, the mesh needed by ElecNet is much smaller and is generated in a fraction of the time.

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

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Once the simulation is complete, the user can view the results calculated by ElecNet. Presented on the right are two shaded field plots -- the electric field |E| with units of volts/m and the voltage field V with units of volts. ElecNet also reports the potential for each of the floating electrodes, which can easily be referenced by the user.

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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.

Solution Data

• Solver used: ElecNet Static 2D.

• CPU: AMD Athlon© 2800+.
• Number of unknowns: 5 395.
• Solving time: less than 1 second.
• Number of mesh elements: 2 598.
• Time to generate mesh: less than 1 second.