PULSED ELECTROACOUSTIC METHOD FOR MEASUREMENT OF SPACE-CHARGE DISTRIBUTION IN POWER-CABLES UNDER BOTH DC AND AC ELECTRIC-FIELDS

A modification of an earlier technique, to measure the distribution of space charge in the insulation of a coaxial cable, under both DC and AC electric fields, is described. The mathematical analysis is developed on the basis of acoustic waves propagating in media with cylindrical geometry. In order to measure the charge distribution in AC electric fields at any phase angle, a phase shift technique has been employed. The method of calibration of charge density is given, and the charge distribution in the insulation (2 mm in thickness) of XLPE cable has been measured under DC voltages (+/-40 kV, at room temperature) and AC voltage (17 kV peak, at 24-degrees-C and 105-degrees-C).