Space Charge Measurement Equipment for Full-Scale HVDC Cables Using Electrically Insulating Polymeric Acoustic Coupler

A new, very sensitive device for space charge measurements on full-size cable is proposed. The measurement employs the basis of the pulsed electro-acoustic (PEA) method, in which an acoustic signal is produced due to the interaction between the pulsed electric field and the space charge. A polymeric material was used as an acoustic coupler that also isolates the cable and the measurement device electrically. It was found that the new type of device with polymeric coupler has a four times higher sensitivity than the conventional PEA device. The isolation from the cable body was proven to be advantageous for easily connecting the probing pulse voltage to the measurement section of the cable through its insulation screen (outer screen electrode) while applying a dc high voltage to the conductor. Feasibility of the new PEA device was examined using a cable with 20 mm-thick insulation. It was shown experimentally that PEA measurements performed at a voltage as low as 5 kV provided clear charge patterns. As a result of this, the accuracy of the electric field calculation was estimated to be 0.25 kV/mm or better, which leads to 2% of accuracy at 250 kV operating voltage.