The University of Southampton

Surface discharge measurement using the pockels effect

High Voltage Engineering, Space and surface charge
National Grid plc

The aim of the project is to develop an experiment to measure surface discharge using the Pockels technique. As surface discharge is an inevitable phenomenon leading to failure of the insulation systems in most practical gas-insulated-switchgear (GIS) and high voltage transformers, it is desired to measure surface charge density and distribution. On the other hand, results obtained from measuring surface discharge helps gain insight into the mechanism of streamer formation along the interface of gas and solid insulators. Other measurement techniques in the field include the Lichtenberg figures, dust figures and capacitive probes. However, all of these methods suffer from a number of shortcomings which do not allow charge quantification and capturing of discharge dynamics at the same time as the Pockels technique offers. The principle of the electro-optic system is based on the Pockels effect of some materials such as Bi12SiO20, Bi12GeO20, and LiNbO3, which under an electric stress have the characteristic of retarding the phase of the linearly polarised input light. Other components of the rig include a laser source, beam expander, beam splitter, optical phase modulator (OPM), vacuum chamber, lens, pinhole, CCD camera and synchronisation control circuit. Discharge images are recorded at 1 ms interval during the application of the external voltage and transferred afterwards to a personal computer for further image processing. Results obtained from two cycles of AC voltage in dry air have revealed a number of discharge characteristics namely the polarity effects, back-discharge, residual charge effects etc. In addition, measurements at various pressures have been performed in order to investigate the effects of pressure on the discharge patterns. The influences of electropositive and electronegative gases have also been studied. Other aspects of surface discharge which require further investigations include improving the framing rate, measuring discharge along the solid/liquid interface and studying the electrode shape impacts.

Primary investigators

Secondary investigator

  • Nam Tran

Associated research groups

  • Electrical Power Engineering
  • Electronics and Electrical Engineering
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