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Cable termination to oil filled bushing - QuickField simulation example

Electric field stress in a cable termination connected to an oil-filled bushing, showing stress reduction from the stress cone and semiconducting deflector.

Engineering question

How to calculate the reduction in electric stress from a stress cone and semiconducting deflector in a cable-to-oil-bushing termination?

Answer
Model the stress cone and deflector with their permittivity and small conductivity in an axisymmetric AC-conduction analysis of the termination.

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Typical applications
transformer cable bushings, cable-to-bushing interfaces, stress cone assemblies

Cable termination to oil filled bushing

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Simulation problem

Problem Type
Axisymmetric problem of AC conduction.

Geometry
Cable termination to oil filled bushing Stress cone with deflector are used to reduce electric field stress in the cable termination. 10 mm 0.1 mm 10 mm Dielectric (XLPE) Conductor (copper) Stress cone Oil Flange Insulation screen Semiconducting insert Deflector

Given
Voltage U = 64 kV (r.m.s.), frequency f = 50 Hz.
Relative permittivity of media: oil 12, insulator 2.3, stress cone 22, deflector 2.5.
Deflector electrical conductivity 0.0002 S/m.

Task
Calculate electric field stress distribution.

Solution
Semiconductors are modeled as materials featuring both electric permittivity and conductivity, though small.
In QuickField we should specify the magnitude of the time-harmonic voltage that is room mean square value times square root of two: 64000*sqrt(2).

Results

Electric field stress distribution in the cable termination
Cable termination to oil filled bushing

Reference:
Simon Dubitsky, George Greshnyakov, Nikolay Korovkin Optimization of Capacitive and Resistive Field Grading Devices for Cable Joint and Termination. INTERNATIONAL JOURNAL OF ENERGY. volume 9. 24-30.

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