IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 61, NO. 1, JANUARY 2012 267 Fault Detection on Transmission Lines Using a Microphone Array and an Infrared Thermal Imaging Camera Hyunuk Ha, Sunsin Han, and Jangmyung Lee, Senior Member, IEEE Abstract—This paper proposes a hierarchical fault detection method for transmission lines using a microphone array to detect the location of a fault and thermal imaging and charge coupled de- vice (CCD) cameras to verify the fault and store the image, respec- tively. There are partial arc discharges on faulty insulators which generate specific patterns of sound. By detecting these patterns using the microphone array, the location of the faulty insulator can be estimated. A sixth-order bandpass filter and an autocorrelation scheme were applied to remove the noise signals caused by the wind, bird chirpings, or other external influences. When a mobile robot carries the thermal CCD cameras to the possible location of the fault, the faulty insulators or power transmission wires can be detected by the thermal images. The CCD camera then captures an image of the faulty insulator for the record. This detection scheme has been proved to be effective through experimentation. As a result of this research, it will be possible to use a mobile robot with integrated sensors to detect faulty insulators instead of using a human being. Index Terms—Infrared image sensors, inspection, insulator testing, microphones, power distribution faults, power transmission lines. I. I NTRODUCTION W ITH THE current economic growth, the need for power is continuously increasing. Currently, there are several efforts to provide high-quality power in various fields [1]. With this trend, research works into the diagnosis of high-voltage equipment are actively being performed to discover fault symp- toms and to analyze the faults in order to not allow the same fault in the future [2]. Most of the monitoring and analysis are done for the insulators and power lines [3]. Insulators are used to isolate the naked power lines and to support the lines mechanically [4]. According to their functions, the insulators are classified as porcelain insulators, distribution line post insulators, dead- end suspension bells, pin post insulators, pin insulators, spool Manuscript received December 17, 2010; revised March 29, 2011; accepted March 30, 2011. Date of publication July 22, 2011; date of current version December 8, 2011. This work was supported by the Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (2010-0024129). The Asso- ciate Editor coordinating the review process for this paper was Dr. George Xiao. The authors are with the Department of Electrical Engineering, Pusan National University, Busan 609-735, Korea (e-mail: jmlee@pusan.ac.kr). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIM.2011.2159322 insulators, and guy strain insulators. Depending on its material, there are ceramic insulators, glass insulators, and polymer insulators; ceramic insulators are mostly used in Korea. When faulty insulators exist in the transmission lines, the power transmission efficiency becomes low, resulting in a tremendous national loss. The partial arc discharges also cause fires and unexpected security problems to social life. Notice that faulty insulators are a safety issue for personnel working on the line. There are several tools and methods used to detect the faulty insulators: thermal imaging cameras [5], human eyes, electric fields, corona cameras, ultrasonic sensors, and neon lamp meth- ods [6]. However, each of these methods has shortcomings in detection. For example, the human eye is not a good sensor during the night. Most of the methods are neither accurate nor quantitative [7]. Very recently, the electric field harmonics have been used for the detection of faulty insulators [8], [9]. This method is relatively accurate, reliable, and able to be commer- cialized as the signal detection circuits are not too expensive and not too heavy to be carried by a mobile robot moving along the power transmission lines. The transmission lines vary according to the line voltage and designated load. Therefore, the fault conditions also vary depending on the environment and fixtures [1]. Since there are a variety of malfunctions and faults at the insulators and the transmission lines, the inspection needs to be done without stopping the power transmission. Currently, most of the inspections are done periodically for each electric pole, relying on human visual detection by an expert in the task [10], [11]. Even though the electric power companies in South Korea spend U.S. $ 50 million per year, inspection has been done for only 7% of the power transmission system. There are also security problems for the inspectors on the lift truck, which limits the detection of faulty insulators to an irregular sampling inspection. This is a real situation with low reliability and high risk inspections [4]. To prevent accidents and to improve the inspection reliability, it is time to replace the human operators with inspection robots. In this research, the area for the possible faulty insulators is detected by the microphone arrays while the mobile robot is moving along the transmission line quickly. Once the faulty area is detected, the mobile robot approaches the area slowly, and the thermal imaging camera captures the suspected insu- lators and wires [12]–[16]. The microphone array is used to detect the location of the partial discharge with the audible arcing noise “Zee-Zig” [17]–[19]. The raw signal includes a lot of noise, which need to be filtered out to make the signal 0018-9456/$26.00 © 2011 IEEE