Mastering the Benefits and Applications of Heat Shrinkable Stress Tubes

Mastering the Benefits and Applications of Heat Shrinkable Stress Tubes

Heat shrink stress tube refers to the sleeve used to shield the electrical stress at the cut end of a cable.

The stress control theory of high voltage cable terminal has been developed, and the heat shrink stress tube with suitable impedance value has been developed. The heat shrink stress tube suitable for different voltages and various sections of cable has been prepared.

It has been proved that the electrical and thermal properties are stable and reliable even after regular operation. The cable terminal designed by the heat-shrink semiconductor stress tube can meet the test standards.

Introduction

There have been successful experiences with the installation of stress ball capacitance vertebrates or capacitance cakes in the terminals of high-voltage cables to reduce the density of power lines.

It is known that the absence of the above devices to control the electric field stress will lead to dissociative discharge at the end of the shielding layer close to the ground, thus shortening the life of the cable terminal.

The time of terminal damages depends on the strength of the electric field at the end of the shielding layer and the anti-ionization performance of the insulating material. Generally, it is within one year.

Function

The function of the heat shrink stress tube is to evacuate the electrical stress at the end of the outer shield of the 10-35kV crosslinked power cable.

Electrical Stress Control

Electrical stress control is an important part of the design of medium and high-voltage cable accessories.

Electric stress control is to control the electric field distribution and electric field intensity inside the cable accessories, which is to take appropriate measures to make the electric field distribution and electric field intensity in the best state, so as to improve the reliability and service life of the cable accessories.

For the end of the cable, the distortion of the electric field is the most serious. The most important factor affecting the reliability of terminal operation is the cut-off point of the cable outer shield. The influence of the electric field distortion of the middle connector of the cable is not only the shielded cut-off of the cable, but also the insulation cut-off of the end of the cable.

Material

The material composition of heat shrink stress tube is composed of a variety of polymer materials blending or copolymerization.

General substrate is polar polymer, and then add high dielectric constant filler and so on.

The heat shrink stress tube in the cable accessories is mainly used to relieve the electrical stress at the outer shield cut-off point of the shield end distributed crosslinked power cable.

Relevant standards (such as JB/T10740) stipulate that the parameters of the stress tube are composed of two parts. One is the dielectric constant, which is required to reach 15, and the other is the volume resistivity, which is required to reach 10^10~10^12.

Improvement of stress-core

The traditional stress control measures include wrapping or installing an olive-shaped vertebra on the cable insulation layer with insulating tape, paper roll or molded material at the end of the shield layer. Because the thickness of the insulation layer outside the end of the shield layer has increased, the electric field distribution is relatively uniform.

The disadvantage of using stress vertebrae is that the outside diameter of the cable terminal must be enlarged, which is not commensurate with the tendency of miniaturization of power equipment.

Besides, wrapping stressed vertebrae by hand is time-consuming, and pre-molded stressed vertebrae lack versatility.

Therefore, after the 1970s, an innovative semiconductor rubber belt for stress control was successfully researched. Furthermore, a kind of heat-shrinkable nonlinear semiconductor rubber stress tube is developed, which can meet the requirements of small volume and simple construction.

Around the whole world, this semiconductor material is widely used as a new stress control device in cable terminals of kV and below, especially in the accessories of rubber, plastic and non-drip cables.

Service Life

The requirement for the stress layer material is that it should remain stable even if there are different electric field intensities and due to conductor or ambient temperature changes.

Check the life of cable accessories is the same as the cable, not simply through the above several tests to make a reliable judgment. The most effective measure is the same as the cable, which needs to pass the load cycle test.

Main Application

Although the structure of cable products in different countries is not completely consistent, such as the insulation of crosslinked polyethylene, ethylene propylene rubber and oil paper, the shielding layer also has extrusion semiconductor, semiconductor tape, and graphite powder.

However, the use of stress tubes can be applied as long as they are slightly modified according to the differences in terminal design.

But the problem is that the test standards are not the same.