Dielectric response measurements in time and frequency domain of differentXLPE homo- and copolymer insulated medium voltage cables

Different structure and chemical composition of the insulating materials of medium voltage XLPE cables lead to various dielectric responses of new (un aged) cables and, therefore, can lead to problems in the diagnosis in the c ase of water tree aged medium voltage cables. With the aim of gaining a bet ter understanding of these problems from a technical point of view, the res ults of dielectric response measurements in the time as well as in the freq uency domain on different new XLPE homo- and copolymer insulated medium vol tage cables and on a pressed sandwich-type test specimen before and after t hermal treatment are presented and discussed. The investigations show that XLPE copolymer materials give higher dielectric responses than XLPE homopol ymer materials. One of the reasons is that XLPE copolymer materials have a higher amount of polar, volatile elements (e.g. crosslinking byproducts), w hich lead especially to a higher voltage dependent conductivity.