Process Design and Optimisation
Ablation between Metal Sheath and Buffer Layer of High Voltage XLPE Insulated Power Cable
Eifelkabel has helped to develop a test method and a design that does not show this problem.
The corrugation aluminium is a common sheath structure of high voltage cross-linked polyethylene (XLPE) insulated cable due to its good bending performance. However, some problems, especially buffer layer ablation, have occurred frequently in cables due to such corrugated structure. Some further studies are carried out around the ablation morphology. The morphology of the ablated buffer layer from laboratory is observed by optical-microscopic, which shows great similarity with the ablation points in failure cables, verifying discharge is one of the causes of ablation.
Degassing optimisation
The main purpose of the degassing process for AC application is to remove methane. Methane is a gas that is created during the cross linking process and should be removed safely afterwards. After installation of the cables methane will only diffuse in the direction of the joints or terminations.
Certain companies recommend an upper limit of 30 ppm of methane.
The degassing process depends on many parameters.
Naturally the thickness of the complete insulation and the temperature play the most significant role. The temperature should be limited to the deformation temperature of the outer semi-conductive layer.
Ultrascreen™
Ultrascreen is an equipment measuring the thickness of all different layers inside the cable online from various angles.
We were involved in the start up of one of these equipments at a big cable maker.
In the first step he monitored only the accuracy of the measurement in correlation with the x-ray, where he saw differences.
Variation in the Ultrascreen measurement were afterwards correlated to overall cable testing results. With the help of the measurement we could locate potential cable faults much easier.
In the second step we regulated the extrusion conditions with these measurements and reduced the failures during testing significantly.
