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Several methods of controlling electric field stress

2022-10-25
Electrical stress control is a very important part in the design of medium and high voltage cable accessories. Electric stress control is to control the electric field distribution and electric field strength inside the cable accessories, that is, to take appropriate measures to make the electric field distribution and electric field strength in the best state, so as to improve the reliability and service life of the cable accessories.

For the cable termination, the electric field distortion is the most serious, which affects the operation reliability of the cable terminal most, and the influence of the electric field distortion of the middle joint of the cable is not only the cable shield cut off, but also the cable end insulation cut off. In order to improve the electrical stress distribution at the cable insulation shield cut, the following methods are generally used to control the electric field.

Method of geometric shapes. Stress cone is used to relieve the stress concentration of electric field.

Parameter control method. High dielectric constant material and nonlinear resistance material were used to alleviate the electric field stress concentration.

Integrated control method. The capacitance cone is used to relieve the electric field stress concentration.

At present, the products of stress control materials have heat shrinkable stress control tubes, stress control tapes and so on. Generally, the dielectric constant of these stress control materials is greater than 20, and the volume resistivity is 10*8-10* 12ω.cm. Stress control and volume resistance should be taken into account in the application of stress control materials. Although the higher permittivity is the better in theory, the capacitor current caused by the excessive permittivity will also generate heat and promote the stress to control the material aging.

Stress control material at the same time, as a kind of multiphase polymer composite material structure, running in the field for a long time, temperature and external environmental changes will make the stress control material aging, aging stress control after the material volume resistivity will happen very big change, volume resistivity is more bigger, stress control material into insulation materials, no control of an electric field, As the volume resistivity decreases, the stress control material becomes a conductive material, causing cable failures.

This is the reason why heat shrinkable cable accessories that use stress control materials to improve the electric field can only be used for medium-voltage power cable lines and heat shrinkable cable accessories often fail. Cable accessories that also use stress control tapes have similar problems.


Stress Control Tube

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Insulation breakdown of Heat Shrinkable Termination and its analysis
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