Conduction Phenomena of AC- and DC-XLPE Analyzed by Q(t) Method

Relaxation time τ (=ε/k) is one of the important dielectric properties, and the τ can be obtained by Q(t) method with an relatively simple treatment. The procedure of the consideration to obtain τ, and measurement results of AC- and DC-XLPE are shown in this article. To consider τ efficiently and effectively, a parameter “charge ratio” was introduced. The charge ratio means a ratio of Q(tm) which is a charge amount Q(t) at a certain measurement time tm and Q(0) which is an initial rise of voltage application, that is Q(tm)/Q(0). The obtained τ is 300 s for AC-XLPE and more than 28800 s (8 h) for DC-XLPE at 60°C under 60 kV/mm.