A Novel Technique for Estimating the Location of Defect or Inception of Water Treeing in the Semiconducting Screen of a Cable

In this article, a novel method to estimate the location of a defect in the semiconducting layer either for insulation or the conductor screen of a cable is proposed using broadband impedance spectroscopy through sweep frequency response analysis. A relationship between the sum of frequencies of zeroes and the electrical parameters of the cable is established, perhaps for the first time in the case of a cable. Transmission line theory and state-space model are used to establish the relationship of zeroes with the propagation constant and electrical parameters of the cable, respectively. Furthermore, an analytical formula is proposed for the estimation of the location of defects of various sizes in the semiconducting layer using the frequency location of zeros and their cumulative sum and product. Both, finite element method (FEM)-based simulations, as well as experiments on a test cable, were performed to validate the proposed formulae.