Electrical Breakdown of Epr-Insulated Cables at DC and Impules Voltages

The electric strengths of three EPR-compounds are investigated using dc, impulse and impulse with dc bias voltages. To see whether dc and impulse strengths are affected by vulcanization residues, breakdown tests are carried out at different times after vulcanization. Different levels of dc perstress cause a considerable influence on the impulse breakdown strength, whereas the duration of dc prestress seems to be without effect. The applied mode of test procedure affects the breakdown results considerably: the breakdown strength measured in a step test procedure is lower than that obtained by the application of a single impulse with high amplitude. This behavior is valid for both polarities of dc prestress. Finally, the effect of repeated impulse discharges on the long-term performance of dc stressed cables is studied. The coherence between cable length, transient voltages, and cable failures is investigated and discussed.