Space Charge Measurement of Thick Insulating Materials

A proto-type pulse electro-acoustic (PEA) measurement system with a polymeric acoustic coupler for space charge measurement of thick insulating materials has been proposed. The thickness of insulating material available to be measured in the past was limited to less than 1mm, in order to maintain sufficient sensitivity. In this presentation, we propose a new type of PEA device for evaluating the insulation performance of full-size insulation system like HVDC cables and GIS, of which insulating materials are over 10 mm in thickness. The new device employs a non-metallic acoustic coupler (e.g., polystyrene) of which acoustic impedance is close to the specimen to improve the acoustic matching and sensitivity. Additionally, an A/D converter with 15-bit resolution and a pulse generator with a high repetition rate to perform waveform averaging as much as 100,000 times were used to reduce random noise. With the above improvements, it could be demonstrated that PEA space-charge distribution measurements are possible on specimens with thicknesses of up to around 88 mm.