Some technical consideration on very low frequency cable diagnostic

Cable diagnostic with very low frequency (VLF) measurements has gradually evolved from laboratory research to field testing. VLF dielectric test aims to replace DC dielectric test for extruded cables because of the potentially harmful effects and ineffectiveness of DC voltage in polymeric insulation. Furthermore, dielectric loss measurements are often used for insulation diagnostic. Its application at very low frequencies has led to the development of different cable diagnostic methods. However, despite recent technical guide for dielectric tests and existing criteria of dissipation factor measurements for cable diagnostic, field experience remains unconvinced and widely divided. This paper presents some field and laboratory results on VLF testing and measurements to gain a better understanding.