Light emission in XLPE subjected to HV in high vacuum and pressurized gas

The spectral and spatial resolution of electroluminescence, the light emitted from polymeric insulation subjected to high electric field, is studied in a test cell pressurized to 215 kPa with ultra high purity nitrogen gas. The paper also describes light emission from crosslinked polyethylene (XLPE) subjected to HV in an ultra high vacuum test cell. It is shown that the characteristics of light emitted from XLPE in the evacuated test cell are quite different from the light emitted when the test cell is pressurized. The mechanisms responsible for light emission under high vacuum condition are described and it is suggested that care should be taken when interpreting the light detected from polymeric insulation subjected to high electric fields.

I. Introduction

Electroluminescence (EL), the emission of light due to high electric fields, has been observed in insulating materials such as polyethylene, polypropylene and epoxy resin, The EL technique has been employed successfully in the initial development of the 500 kV underground cables. Although a sophisticated setup is required to detect the faint EL light, the technique is sensitive enough to reveal the very early stages of insulation degradation, prior to partial discharge and electrical tree inception.