In a Search for Reliable Methods to Evaluate Resistance to Electrical Treeing in Materials for HVAC and HVDC Cable Insulations

Research activities are reported on developing a new type of test objects and procedures for evaluating the resistance to electrical treeing in various materials for HVAC and HVDC cable insulations. A test object with wire electrode is introduced and its advantageous features are elucidated. One of them is a capacity to form multiple trees in a single test object that significantly increases the amount of data for statistical analyses. Focus is also made on the possibilities to electrically detect electrical initiation and development of electrical trees. A hypothesis is formulated and evidenced that the resistance to formation of electrical trees in materials for DC applications can successfully be tested with time varying voltages of sinusoidal and pulsed types. In addition, electrical treeing tests are reported on specimens cut from a real HVDC cable insulation that aimed to imitate the cable operating environment and the impact of voltage transients appearing during cable joint failures. It revealed that such transients have a certain impact on the insulation resistance to electrical treeing.