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Main >> Applications >> Sample problems >> Stress control tube

Stress control for cable termination

QuickField simulation example

33kV single core cable termination has design measures to control the electric stress near the screen end. Special mastic with a field-dependent electrical conductivity is used.

Problem Type
Axisymmetric problem of transient electric.

Geometry
Stress control for cable termination Calculate the effect of electric stress reduction. Conductor GND Insulation Copper screen Semi-conducting Jacket Stress relief mastic Ø 20.4 mm Ø52 mm 8 mm

Given
AC frequency f = 50 Hz, conductor potential V = 33 kV (r.m.s.).
Screen potential - 0 V (grounded).
XLPE permittivity 2.5.
Insulation materials electrical conductivity 1e-15 S/m.
Yellow mastic permittivity is 15, electrical conductivity is field-dependent:

Task
Calculate the effect of electric stress reduction.

Solution
To represent sinusoidal varying electric potential we can use the equation: V*sqrt(2) * cos(360° * f * t).
In fact we are interested in the peak stress values, so we can apply peak voltage value of V*sqrt(2).

To improve convergence we added two points to the end of the curve to artificially limit the conductivity value at extremely high electric field stress: [54 kV/mm, 14 pS/m], [73 kV/mm, 15 pS/m]
Later the results revealed that the electric field stress is within the limits of the original data.

Results
With a stress control mastic the maximal electric stress along the insulation surface reduces from 58 kV/mm to 25 kV/mm.


Stress control for cable termination