Recovery voltage measurement on oil-paper insulation with simple geometry and controlled environment

Using the recovery voltage of oil-paper insulation to diagnose its state of maintenance is very popular among electrical engineers. Many advantages of using recovery voltage includes non-intrusive, easy to operate, more resistant to noise compare to other non-intrusive diagnostic methods. However, the lack of understanding on the physical process causes dispute over interpretation of measurement results. This also discourages further application of recovery voltage to non-standard insulation systems because there is no known standard reference to which comparison can be made. Experiments have been carried out to study the recovery voltage of oil-paper as a response of insulation material. The variation of recovery voltage in response to sample geometry, temperature and moisture are studied. The results reveal that the traditional Debye polarisation model, implemented as parallel RC-circuit in recovery voltage software, is not a satisfactory description of the physical process. The interfacial charge movements play more dominant role in the formation of recovery voltage in oil-paper insulation systems and the use of exponential function to describe the interfacial charge movements is both uneconomical and unphysical.