Measurements of Internal Fields in Insulants for High Voltage Cables: Possiblity Opened by the Pressure Wave Propagation Method.

During the last few years there has been an evolution of the methods used for studying insulants and particularly those used in high voltage cables. Indeed it appeared that a very direct way to understand the processes taking place in such materials when they were submitted to an electric field, and thus to improve their performances, was to measure the field or charge distributions inside these materials. Non destructive methods for such determination have been developed and particularly one in which the internal electric field is swept by a pressure wave which is propagated in the system under study and which acts as a probe sensitive to this field. Such non destructive measurement allows the determination not only of the field distribution but also of its evolution in function of such parameters as temperature, time, environment and even now applied field. It has become possible to carry out such measurements while a voltage gradient is applied across the insulator.