Time Reversal for Partial Discharge Localization on Power Lines with Different Termination Impedances Antonella Ragusa, Hugh Sasse, Alistair Duffy School of Engineering and Sustainable Development De Montfort University Leicester- United Kingdom antonella.ragusa@dmu.ac.uk, hgs@dmu.ac.uk, apd@dmu.ac.uk Abstract—This paper describes a new method for the on-line location of partial discharges (PDs) in power transmission and distribution networks based on Electromagnetic Time Reversal (EMTR) theory and on the Transmission Line Matrix (TLM) method in order to describe the time reversed propagation. In particular, the paper shows the effectiveness of the method in localizing the PD source when the impedances at the terminations of the line are unknown and describes the procedure to be followed in this case. The analysis is performed in simulation, and a model of the PD signal propagation that is able to reproduce the distortion phenomenon that affect the PD signal propagation on power lines and thus the accuracy of the on-line PD location methods is also described. Keywords—Partial discharges, cable system, electromagnetic time reversal, TLM, high voltage power grid reliability. I. INTRODUCTION High voltage power grids are subject to a wide range of electromagnetic disturbances, both natural, such as lightning strikes, geomagnetic effects, and man-made disturbances, such as harmonics, partial discharges (PD), overvoltages, intentional electromagnetic interference (IEMI), that affect the power quality and the reliability of the power networks. This aggressive on-line environment causes the acceleration of the aging and deterioration of the power cables insulation[1]. The insulation failure of a power cable has severe social and economic consequences since the statistics indicate that more than 85% of equipment failures are related to insulation damage[2]. The deterioration of cable insulation is often caused by partial discharge (PD) events, that are localized electrical discharges, partially bridging the insulation between conductors [3] and starting in defects of the insulator. Thus, the adoption of methods for the on-line localization of PD, widely considered as one of the best early warning indicators of insulation degradation, is regarded as one of the most suitable methods to perform the network integrity assessment useful to improve its reliability and to guarantee electricity supply security[1]. The authors have designed a new on-line PD location method based on the electromagnetic time reversal theory and on the use of the Transmission Line Matrix (TLM) numerical method [4]. The proposed method overcomes the shortcomings of the currently adopted reflectometry or traveling wave-based PD location methods [5]-[7]. These methods, based on the principle that PDs produce electromagnetic waves travelling in either direction towards the cable ends, perform simultaneous multi-end measurements of the PD signals at different points of the line and evaluate the PD source from the times of arrival of the measured signals (time of arrival, ToA, methods). Their practical implementation is difficult due to the need for synchronised measurements and their accuracy is strongly influenced by the distortion phenomenon that affect PD signals during their propagation on power cables and by the presence of EMI on power networks. The use of wavelet techniques [6][7] is usually adopted to solve these problems but they require a considerable amount of computational effort. The EMTR-based PD location technique proposed by the authors in [4] and experimentally validated in [8] has shown a significantly improved performance with respect to the traditional location techniques, presenting the following advantages: the use of a single observation point, applicability to inhomogeneous networks [9][10] and robustness against the presence of EMI[8]. The new method is under development and its effectiveness in more complex networks is under analysis. The basic steps of the method are: 1. Measuring of the electromagnetic signal generated by the PD at one observation point (OP) along the line; 2. Simulating using a lossless 1D TLM model the time-reversed injection of the measured PD signal for different guessed PD locations (GPDLs); 3. Localizing the PD source by identifying the GPDL characterized by the maximum energy concentration. In this paper the method is briefly described and its effectiveness in localising PD sources in power networks when the impedances at the line terminations are unknown and the procedure to be followed in this case is described. In particular, in Section II a model of the power line, that is able to reproduce the distortion of the PD signals, is described. This model is used to perform the direct time (DT) simulation that takes place in step 1, related to the PD signal measurement on a real system, and it is useful to design, in simulation, new on- line PD location methods. Section III gives a brief description of the EMTR-based method and, finally, in Section IV the analysis of the simulation results is presented. II. MODEL OF THE SYSTEM UNDER STUDY To perform the DT simulation, a model of the system under study is developed that is able to reproduce the PD signal distortion that is the most significant phenomenon in the real system that can affect the accuracy and effectiveness of the on-line PD location methods. To this aim, the simple power line shown in Fig. 1 is considered. It is formed by a 11kV single-phase coaxial cable[11], 1km long, with aluminum conductor and a Cross-Linked Polyethylene (XLPE) insulator. Table I shows the cable characteristics. The ends of the line are connected to the impedances, Z1 and Z2. The PD event occurs at a location, xPD, of the line and This work was supported by the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Skłodowska- Curie Grant under Agreement 838681. Fig. 1. Schematic of the power transmission line under study.