Characterisation of Acrylic Lightguides for an Optical Partial Discharge Measurement System for Gas-Insulated Gear

Unconventional partial discharge (PD) measurements can be advantageous in terms of sensitivity and noise-rejection capabilities. While ultra-high-frequency (UHF) measurements are nowadays common for gas-insulated gear, they have the shortcoming of being unable to detect discharge with slow rise and fall times and glow-discharges [1]. Optical measurements can overcome this issue and are able to detect light emissions from continuous light-sources. Therefore, a minimal-invasive, retro-fittable optical measurement system with the capability to detect near infrared and ultraviolet light has been developed. It incorporates acrylic lightguide elements like those used in commercially available arc-detection systems for gas-insulated gear. In a GIS/ GIL the distance between the location of discharge and the optical sensor may be large and the incident angle of the light will vary. In such a case, light emission can still be detectable indirectly from reflections at the inner enclosure walls. To investigate the influence of the lightguide geometry and alignment on the sensitivity in more detail, multiple acrylic lightguide elements with different shapes have been manufactured. Furthermore, a test fixture has been built to allow the determination of angle- and distance-dependent sensitivity. The results of those measurements are presented and discussed in this paper.