Abstract
One of the challenges in laboratory investigation of degradation and ageing of HVDC cable insulation is related to securing, or in other words, imitating the real service environment of the material specimens. So far, the published data refer to experiments conducted in thermo-oxidative conditions, which is not the case during normal cable operation. In service, the cable insulation is protected by a metallic barrier that blocks the transfer of any substances in and out of the construction. By-products from the cross-linking reactions cannot diffuse out and any foreign substances are blocked from entering the insulation. Thus, in order to generate results that are valid, these conditions must be replicated in laboratory experiments. This contribution presents a methodology elaborated for performing ageing experiments in a hermetically sealed environment. Degradation of the material is evaluated through changes in the electrical tree inception voltage and test object capacitance over time. Securing the environmental isolation is accomplished with an isolation system consisting of a glass enclosure with attached metallic electrodes. Indium is used to create a glass-to-metal seal between the glass and the electrodes. The electrode geometry is of needle–plane type and the needle injection process is semi-automated to ensure specimen repeatability.
Highlights
Understanding the effects on HVDC cable insulation caused by long-term exposure to in-service stresses is key to evaluating current and emerging materials
The voltage required for experimentation on this scale is typically in the lower range of tens of kilovolts, as opposed to the hundreds of kilovolts required for the full-scale tests
For ageing experiments to be valid, the actual environmental conditions of the insulation must be replicated. This contribution presents a methodology elaborated for performing ageing experiments in a hermetically sealed environment based on measurements of capacitances of the material samples during development of electrical trees
Summary
Understanding the effects on HVDC cable insulation caused by long-term exposure to in-service stresses is key to evaluating current and emerging materials Experiments which yield such results can be carried out in a number of different ways, for example, by conducting full-scale tests using actual or model cables, by using cables that have already been in-service or by carrying out laboratory experiments on miniature specimens with artificial defects. In electrical treeing experiments where a static sinusoidal voltage is used, the inception time has been shown to decrease significantly when the temperature is raised from 25 to 90 ◦ C. This effect becomes weaker with higher excitation voltages [4]. This contribution presents a methodology elaborated for performing ageing experiments in a hermetically sealed environment based on measurements of capacitances of the material samples during development of electrical trees
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call