Page 1 of7 Locating Short-Circuit Faults in Underground Networks J. Zhou, B. Ayhan, and C. Kwan Signal Processing, Inc. 9700 Great Seneca Highway Rockville, MD 20850, USA chiman.kwan@signalpro.net Abstract -- In power distribution networks, impedance short circuit faults are hard to detect in their incipient stage, as the fault currents may not be large enough to trip circuit breakers. In this paper, we summarize our research activities in short circuit fault localization in underground power distribution networks. First, a simulation testbed was built. It can emulate power distribution networks with both bolted and impedance faults. Different impedances can be added to different branches. Power injection points, load nodes, and short-circuit fault locations can all be adjusted by users. Second, a hardware testbed corresponding to the simulation testbed was fabricated. Third, two novel fault localization algorithms (fault signature matching and sparisity recovery) were implemented. Results obtained from the simulation and hardware testbeds have excellent agreement. Our fault localization algorithms are validated by extensive numerical and experimental data. It is observed that, standard voltage measurements at a small number of pre-selected nodes are suicient to localize the faults precisely; and hence, our fault localization scheme is of low cost. In addition, since our algorithms require only simple matrix calculations, localization within a few cycles « 50ms) is achievable. Indx Terms-- short-circuit, fault localization, sparsity recovery, impedance fault. I. NOMENCLATURE DTCR - Dynamic Thermal Capacity Rating EPRI - Electric Power Research Institute ERCOT - Electric Reliability Council of Texas NPR: Network Protector Relays SCADA - Supervisory Control And Data Acquisition II. INTRODUCTION How to maintain the integrity of underground power distribution networks is an important and challenging topic for power industry. As an example, Con Edison experiences more than 1600 failures on its distribution feeders and 1000 arcing faults on its secondary distribution system each year [1], resulting in serious consequences like cable bunout, manhole explosions, and service interruption. Accurate, low cost, and automated systems to detect and localize faults in underground power distribution networks have been sought ater for years; but, their developments are still at early stage. High complexity of underground power networks constitutes the primary challenge to arive at eicient fault detection schemes. Fig. 1 shows a typical underground power network where high voltage power transmission lines are connected to O. D. Limaye, M. Lu, and W. Lee University of Texas at Arlington Arlington, TX 76019, USA low voltage underground power mesh networks via transformers and network protector relays. Three complications displayed in Fig. 1 make fault localization in power network dificult. First, the network is fed by power transmission lines via multiple injection points. Hence it is virtually impossible to track the transmission lines to pinpoint the faults. Second, although the faults do have tremendous impacts to their neighborhoods, typically they do not bring up drastic disturbances to the overall behavior of the network, especially at their incipient stages. Third, the faults' signatures are usually attenuated by the large number of loads in the network. In recent years, temperature sensors have been proposed to monitor cable faults [2] and power distribution equipment [5]. For example, Electric Power Research Institute (EPRI) used to execute a program named "Dynamic Thermal Capacity Rating (DTCR)." Several utility companies implemented similar pilot programs as well; for instance, Electric Reliability Council of Texas (ERCOT) initiated a SCADA program in 2007. A major drawback pertinent to using temperature sensors for fault detection is the relatively long lag time; especially, the temperature sensors are very slow [4] to react to impedance faults and low intensity arcing faults [5]. Typical response time is around 1 second [4]. In addition, temperature sensors have to reside in the proximity of the fault locations to achieve suficient sensitivity. Embedding these temperature sensors for fault inspection in large-scale underground networks would require a lot of sensors densely distributed throughout the entire network, which is logistically demanding and cost prohibiting. There are also attempts to apply iber optic sensors for the purpose of cable monitoring [3]. However several years ago, an investigation conducted by Con Edison concluded iber optic sensors an ineffective solution, because of cost and effectiveness (probability of detection and false alarm rates) [7]. protector relays Fig. 1. A typical underground power transmission network. 978-1-4244-9500-9/11/$26.00 © 2011 IEEE