Investigation of the acoustical material properties of polymers used in power cable insulation systems and their temperature dependency

Summary

For the electrical insulation of modern medium voltage and high voltage power cables a sophisticated three layer insulation system is used, which consists of an inner and outer semiconductive layer and the cross-linked polyethylene (XLPE) insulation layer in between. To ensure a high quality of the insulation system the production of the insulation system is monitored, while certain tests can only be done after finishing the production step. Especially during cooling of the cross-linked insulation system, ultrasonic diagnosis can be used for monitoring purposes as a non-destructive measurement technique. Ultrasonic technique offers a variety of information about the production quality, including the detection of defects and checking of the layer thicknesses. Furthermore, a method for the online measurement of the conductor temperature has recently been developed. A substantial basis for the different applications of ultrasonic diagnosis is the exact knowledge of the acoustical properties of the materials used in the cable core over the temperature range which occurs during production. The properties include sound velocity, acoustic impedance and sound attenuation and are used to interpret the ultrasonic impulses. Published values for the acoustical material properties of XLPE and the semiconducting compound can only be found up to 75 °C. This paper presents values for the acoustical material properties of XLPE and semiconducting compound for temperatures up to 110 °C. Using the investigated acoustical material properties, a model for the transmission and reflection coefficients at the interface between XLPE and inner semiconducting compound is developed and the implication on the temperature measurement method is presented.

Additional informations

Authors

Zhao Ni, Nie Yongjie, Guo Can, van de Ploeg