Influence of Field Grading in Setup for Electric Breakdown Testing of Polyethylene Films

Abstract

High dielectric strength of solid electrical insulation materials for high voltage applications is essential for high reliability and long-term performance.The IEC 60243 and ASTM D149 both describe very similar test methods to determine the short-term electric strength of solid insulation materials. A test sample, usually thin plaque, is placed in an electrode system with surrounding insulating oil. The voltage is then steadily increased until an electric breakdown occurs. Despite the relatively simple test setup, testing materials with high electric strength can be difficult. The breakdown channel is often located outside the active testing area of the electrodes and found at the electrode edge at the triple point between the electrode, test object, and surrounding oil.In this study, we have investigated different possibilities to control the electrical field enhancement in the vicinity of the electrode edges using silicone rubber, field grading silicone rubber, and a high permittivity oil. The testing was performed with semi-spherical electrodes and electrodes as recommended in IEC 60243 on polyethylene films. Electrodes covered with the field grading rubber increased the short-term breakdown strength compared to standard testing without modification. The high permittivity oil and silicone rubber seemed to have limited effect on the breakdown strength.

Intrinsic AC Dielectric Breakdown Strength of Polyimide Films at the Extreme: New Breakthrough Insights on Thickness Dependence

“…This has, indeed, been recently reported by Li et al and by Andersson et al in crosslinked polyethylene (XLPE) and low-density polyethylene (LDPE), respectively, for other applications. [27,28] To illustrate the reduced fringing due to encapsulation, Figure 3 shows the variation in the E-field enhancement factor 𝜂 calculated at an electroplated Au electrode edge (5 μm thick and 0.5 μm radius of curvature) as a function of the PI insulating film thickness in the case where the encapsulation is either an insulating oil or a subsequent PI capping overlayer. The enhancement factor 𝜂 increases monotonically with the PI insulating film thickness.…”

“…This has, indeed, been recently reported by Li et al and by Andersson et al in crosslinked polyethylene (XLPE) and low‐density polyethylene (LDPE), respectively, for other applications. [ 27,28 ]…”