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Transformer bushing electric stress

QuickField simulation example

A solid-type oil-impregnated paper bushing is used to lead a 36 kV conductor inside a transformer tank.

Engineering question
How to find electric stress distribution in transformer bushing?

Engineering answer
Set up an axisymmetric QuickField Electrostatics problem for a transformer bushing and evaluate electric stress distribution from computed field results.

Typical applications
high-voltage transformer bushings, oil-paper bushings, graded insulation bushings

Problem Type
Axisymmetric problem of electrostatics.

Geometry
Transformer bushing Solid-type oil-impregnated paper bushing used in transformers Oil Metallic flange Conductor Porcelain Paper

Given
Relative permittivity of media: air 1, transformer oil 2.1, porcelain 5, paper 3.
Conductor potential 36 kV (r.m.s)

Task
Calculate the electric field stress distribution in the cross-section shown by the dashed line.

Solution
Problem features a rotational symmetry so it could be simulated as 2D Axisymmetric.
To calculate the peak value of electric potential we should multiply the root mean square value by the square root of two.

Results
Electric field strength distribution is presented in the picture below. Electric field stress at the oil-paper interface is 15.2 kV/cm.
Transformer bushing electric stress

Reference
The idea of this example, media physical properties and insulator dimensions were taken from the book by Sivaji Chakravorti Electric Field Analysis, Problem 7.2.