Estimating the location of faults and damaged parts in cable during offline and online condition

Abstract

Condition monitoring in high voltage (HV) cables is essential to ensure reliability, prevent failures, and enhance safety. It helps in the early detection of faults, reduces downtime, and extends the cable's lifespan. By monitoring, maintenance can be planned proactively, avoiding costly emergency repairs and ensuring continuous, efficient power supply. In this thesis , analytical methods are proposed for the location of a short circuit fault and damaged insulation and conductor screen parts in a power cable using impedance spectroscopy (IS) obtained from sweep frequency response analysis (SFRA). The driving point impedance function (DPIF) construction of a power cable is introduced as an initial step toward using the SFRA technique for power cable condition monitoring. It is proposed that SFRA data be used to generate the DPIF. Furthermore, the DPIF of the cable is generated analytically using the knowledge of the cable's frequency-dependent characteristics, material qualities, and dimensions, while the impedance spectroscopy is estimated using conventional transmission line theory. For the first time in the instance of a cable, a relationship is established between the sum of frequencies of zeroes and the electrical properties of the cable. The relationship between zeroes and the electrical parameters of the cable and the propagation constant is established using the state space model and transmission line theory, respectively. This thesis achieves the location of defects of different sizes in the semiconducting layer by using the frequency location of zeros and their cumulative sum and product to locate defects, and by using the proposed analytical formulae to locate a short-circuit fault using the location of poles and zeros of the impedance function before and after the fault. Further, a novel method is proposed to estimate sheath-to-ground (SG) faults at any arbitrary locations in a cross-bonded (CB) and non-cross-bonded cable (NCB) by only measuring the earthing current from both grounding boxes during online conditions. In CB cable system, the range of grounding current in SG fault condition is estimated for a cable having SG fault at different minor sections using the analytical method which is based on the proposed circuit model of the CB cable. The measured grounding current is compared with the analytical fault current range, and if the measured current is in the proposed analytical range, the SG fault is confirmed and the location of the same is estimated by the proposed analytical formulae. In NCB cable system, the healthy condition grounding current is estimated for different types of bonding using the analytical method which is based on the proposed circuit model of the cable. The measured grounding current is compared with the