978-1-4799-6422-2/14/$31.00 2014 IEEE

Robotic Systems Applied to Power Substations A State-of-the-Art Survey

Jean-Francois Allan1, Julien Beaudry2 Hydro-Qubec Research Institute (IREQ)

Robotics and Civil Engineering Varennes, Qubec, Canada

1 allan.jean-francois@ireq.ca, 2 beaudry.julien@ireq.ca

Abstract-- This paper presents a state-of-the-art survey of robotic systems applied to power substations. Bibliographic research for this paper identified some 75 scientific publications and 39 patents dating from the late 1980s to 2013. Aside from recent work at Hydro-Qubec (IREQ) in Canada on a field robot for power substations, almost all the R&D work identified comes from Asia, especially during the last decade, with the main research developments involving a mobile robot named SmartGuard from State Grid Corporation of China (SGCC). The first section of the paper presents robotic systems dedicated to inspection and security in power substations, while the second part of the paper looks at robots for operation and maintenance tasks in substations. A list of patents for robots for substations is also provided.

Index Terms-- Inspection, navigation, robot, substation.

I. INTRODUCTION

A literature review of robotic and remote control systems for maintenance of transformer substations and overhead transmission and distribution lines was conducted about 20 years ago [1]. At the time, robotics for power substations was not a major research and development topic for electric utilities; most robot applications were for teleoperated robots used for live-line maintenance of overhead power lines. In addition, there were no satisfactory technical solutions for robot inspections of substations in 1993 [2]. The technology has evolved over the last two decades, however, paving the way for new robotic applications.

Furthermore, with the modernization of power grids, there is a drive to include autonomous devices in substations [3]. In this new context, robotics can play a role in the inspection, maintenance and operation of substation equipment. The following sections present existing robotic systems applied to substations as described in the published literature.

II. INSPECTION AND SECURITY TASKS

This section covers robotic systems that inspect and monitor substations, often by using cameras (the robots are not in contact with the equipment).

A. Terrestrial robots

Two of the earliest publications on mobile robotics applied to substations describe a patrolling robot developed by the Chubu Electric Power Co. in the 1980s [4] [5]. This mobile robot (1.3 m wide, 1.4 m long and 1.7 m high) was equipped with an infrared camera, a color camera, an abnormal pulse detector and a microphone, and it patrolled the substation with the help of an electromagnetic detection system that followed a guide wire buried 1 cm below the surface. Battery-powered, the robot operated for 2.5 hours and could be recharged at a charging station in the substation. A Japanese paper published in 1999 describes the development of this patrolling robot [6]. In the 1990s, Hitachi, Toshiba and Mitsubishi developed inspection robots for substations; a picture of a robot named Big Mouse is presented in [15].

1) State Grid Corporation of China (SGCC)

A report published in 2004 describes the main R&D advances in robotics for transmission and distribution in China [7]. The work done between 2002 and 2005 was supported by the National High Technology R&D Program of China, with the first three years of the program dedicated to prototypes and the last to their industrial application. A mobile robot for a 500-kV substation is described. The robot is equipped with a visible and an infrared camera as well as a directional microphone [8][9].

The Web site of the Electric Power Robotics Laboratory of SGCC recaps the history of the robotics project supported by the Chinese R&D program [10]. The first robots were used for inspection tasks, and they went into operation in 2005 [11]. These SGCC robots are called SmartGuard, and several generations have been developed since 2002. Fig. 1 shows different versions of this substation robot and more detailed information is given in [12], [13] and [14]. Technical specifications for the robot are given in [15]. The robot has two independent motorized wheels in front and two omni-directional wheels at the rear. Several scientific publications since 2008 describe the development of the SmartGuard robot. One paper discusses the software control architecture under Linux that improves performance and stability in real time, allowing implementation of complex control algorithms [16].

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Fig. 1. Different versions of the SmartGuard robot described by Guo et al. in [12] (2010; 2010 IEEE) and Wang et al. in [13] (2010; 2010 IEEE)

A number of papers discuss methods of navigation for a robot in a substation. A method of monocular navigation, with the robot following a yellow line 10 cm wide on the ground by processing image and ground markers indicating commands the robot must carry out, is described [17] [18]. Robot navigation using differential GPS navigation (DGPS) and dead reckoning (DR) principles has also been investigated [19][20][21][22]. Use of an omni-directional vision system with infrared illumination is described, the system using a Frontier-II robotic platform (Fig. 2) and having a positioning error of 4 cm and 2.5 [23]. Details of this omni-directional infrared vision system are provided by researchers from Shanghai Jiao Tong University [24][25].

Fig. 2. Navigation with infrared omni-directional vision, Guo et al. in [23] (2009; 2009 IEEE)

A navigation system based on magnetic guidance is also described [26]. A series of magnetic markers are placed on the roadway, and sensors on the robot pick up signals; localization is based on radio frequency identification (RFID) technology. Positioning error is 0.22 cm with this method of navigation. By the end of 2010, there were 13 SmartGuard robots serving SGCC and the China Southern Power Grid: 12 SmartGuard robots in 11 substations equipped with magnetic guidance navigation, and one robot equipped with GPS-DR navigation [15].

Two studies investigated navigation by laser (commonly used in industrial robotics for autonomous guided vehicles) using a Sick NAV200 laser sensor [27] [28].

For the inspection of equipment in substations, the SmartGuard robot uses a vision system composed of a visible light camera, an infrared thermal imager, a pan-and-tilt mechanism and an image processing module. An algorithm was developed for visual and infrared image fusion invariant to changes in scale and illumination (see result in Fig. 3) [29]. Two SmartGuard robots have been equipped with this technology [30]. A method for isolator status recognition was also developed [31] [32] [33].

Fig. 3. Fusion of visible and infrared substation equipment images, Li et al. in [29] (2010; 2010 IEEE)

2) Hydro-Qubec Research Institute (IREQ)

In 2012, field tests were performed in Hydro-Qubec substations using a mobile robot developed by IREQ [34]. This robot (Fig. 4) was built on a Clearpath Robotics Husky A200 mobile platform and uses a visible camera and a Jenoptik thermographic camera for substation inspection tasks.

Fig. 4. IREQ mobile robot, Beaudry et al. in [34] (2012)

3) Other research developments

An article published in 2006 by the Chongqing Electric Test and Research Institute introduced the concept of an automatic guided vehicle (AGV) with laser guidance to inspect substations [35]. A study by the Sichuan Electric Power Research Institute and the Guangxi University of Technology looked at navigation and positioning of the robot using color vision (detection of edges by following a yellow line on the road as a guide) and RFID technology (tags installed on the road at desired locations that give commands to the robot) [36]. Also, use of a line on the ground as a navigation guide with an Uptech Voyager II mobile robotic platform was studied at the University of Science and Technology Beijing [37][38][39] and Jinan University [40]. A paper issued by the Northeast Electric Power University and the Heilongjiang Electric Power Co. describes the use of graph theory in patrolling robot technology for unattended substations [41]. RFID tags are used during navigation to command a robot created at the Southwest University of Science and Technology, and a visual camera is used for edge detection [42]. Use of a Bumblebee2 stereo vision system mounted on a robot for 3D reconstruction and obstacle detection is also described [43] [44].

Described as well are a visual servo system for adjusting robot gesture to center an image [45] and an algorithm for path planning [46]. Studies at Chongqing University propose a path planning strategy that considers road attributes [47] [48]; a Pioneer 3-AT robot platform was used [49]. At the 2012 CIGRE Congress, researchers from the Instituto de Investigaciones Elctricas (IIE) in Mexico presented a

computer-simulated navigation algorithm based on a Markov Decision Process that can be used to obtain an optimal robot path [50].

B. Robots moving along cables

A mobile robotic system that moves on a steel cable and uses an infrared camera to detect hot spots in a substation was developed at the University of Sao Paulo [51]. This technology is similar to that used for robots developed for inspection of power transmission lines, but without the ability to cross obstacles.

C. Aerial robotics

Orthophoto maps are used to manage the transmission assets of the National Grid Corporation of the Philippines (NGCP): power cables, transmission towers, substations, etc. [52]. Orthophoto maps can also be used, in conjunction with field data and satellite images, for other critical applications such as vegetation management.

The use of unmanned air vehicles (UAV) and remote sensing technologies seems a viable option for inspection and condition assessment of overhead transmission lines [53], and it is probably just a matter of time till these technologies are transferred to substation applications.

D. Image processing

1) Security and surveillance

An article published in 1990 by authors affiliated with Hiroshima University, the Tokyo Electric Power Co. and the TOKO Electric Corp describes a system for real-time detection of trespassers in substations [54]. Composed of a video camera, an image processor system and a microprocessor, this system detects intruders by measuring changes of intensity level, with different thresholds for an alarm signal.

Researchers from Hong Kong Polytechnic University and the China Light & Power Co. report on the use of remote vision for substation monitoring (real-time status of equipment), security and fire safety [55] [56] [57].

An article published in 2001 [58] describes a Swedish pilot project testing use of a movement detector that generates an alarm when movement is detected in the substation together with a camera that shows a picture of what occurred.

A study at Wuhan University looked at a multi-agent architecture for intelligent video monitoring of unattended substations using moving object detection and tracking methods [59]. Researchers at the Shanghai University of Electric Power describe a substation perimeter safety monitoring system based on ZigBee communication technology [60].

2) Inspection of substation equipment

Researchers at the North China Electric Power University used a computer vision technique (a non-contact method that allows remote meter reading) to monitor the condition of substation equipment [61]. Another study describes the use of image processing and recognition to monitor high-voltage

equipment running status [62], and yet another describes the application of video image recognition technology to solve problems of meter display information recognition (see Fig. 5), switch position recognition and transformer fan working state recognition in substations [63].

Fig. 5. Meter display recognition, Sun et al. in [63] (2011; 2011 IEEE)

Researchers at Sabzevar Tarbiat Moallem University in Iran used thermography images to detect electrical equipment faults [64] [65]. And researchers at the State Grid Corporation of China used fusion of visible and infrared pictures together with an intelligent environment surveillance system to enhance substation operation security, stability and reliability [66] [67].

3) 3D reconstruction

The use of laser and optical geotechnologies to create CAD models of substations is the main subject of a paper published in 2012 [68]. These technologies provide the high level of detail required to reconstruct existing models (reverse engineering) and to establish control and security status over time. One of the main goals with geotechnologies is semi-automatic modeling of three-dimensional CAD objects to conceptualize a substation and define it dimensionally, manage enlargements and maintain or replace equipment. An experiment using a Trimble GX laser scanner, a digital camera and computer vision algorithms (A-SIFT: affine scale-invariant feature transform; and RANSAC: random sample consensus) in an outdoor electrical substation in Jumilla, Murcia, Spain, is described [68]. A comparison was established with the constructed CAD models using the data provided by the manufacturer, Iberdrola: an average discrepancy of 9 mm was obtained, giving an overall accuracy better than 98% for the CAD models.

Another paper also looks at 3D reconstruction applied to a substation [69]. Two of the authors of this paper are associated with Eletrobras Furnas Brazil. Discussed in another paper are LiDAR (light detection and ranging) technologies and their role in 3D modeling of substations, with the possible advantage of virtual substation visits without ever leaving the office [70].

III. OPERATION AND MAINTENANCE TASKS

This section describes the literature on robots that perform maintenance or operation tasks on power network equipment in substations (involving physical contact between robotic systems and substation equipment).

A. Cleaning insulators

A mobile HVCR (High-Voltage Cleaning Robot) system was developed at Shanghai Jiao Tong University to clean porcelain insulators of 220/330-kV substations. Incorporating a scissor lift telescopic mechanism, the robot can reach a height of 8 metres. The cleaning is done with a brush-spinning

device. Two papers discuss the robotic system architecture [71] [72], and two others look at the insulation of the robot given the high voltages concerned [73] [74]. Another paper describes version II of the robot (HVCR-II) but does not detail the differences between versions I and II [75]. A radius variable manipulator for the HVCR that changes radius continuously to adapt to the contour of the pyramid insulators is described as well [76]. And in a paper published in 2010, a new live-line work robot capable of ultrasonic detection of flaws in porcelain insulators of 220-kV substations is described [77].

Researchers at the Korea Electric Power Research Institute (KEPRI) developed a robotic system to clean power insulator suspension chains of transmission towers and substations [78].

B. Activating 735-kV disconnect switches

A Kinova Jaco robotic manipulator arm was integrated in IREQs terrestrial mobile robot (initially as in Fig. 4) so it could perform operation tasks in a power substationactivating 735-kV disconnect switches, for example. A field test was performed in July 2013 at a Hydro-Qubec substation, with the robot teleoperated to get it to its destination in the substation, open a cabinet door and activate 735-kV disconnect switches (see Fig. 6).

Fig. 6. IREQ mobile robot with manipulator arm to activate 735-kV disconnect switches at Hydro-Qubec power substation

IV. PATENTS ON ROBOTS FOR SUBSTATIONS

Innographys patent search software and database were used to draft a list of patents involving robots and substations. As shown in Table 1 and Table 2, 39 Chinese patents were identified. No worldwide (WO), U.S. or Canadian patents were found. Most of the patents are for technologies developed at the Shandong Electric Power Research Institute or the Shandong Luneng Intelligence Technology Co. Ltd., organizations with ties to the SGCC.

V. CONCLUSION

This paper presents a state-of-the-art survey of robotics applied to power substations through a literature review of some 75 scientific publications. Though terrestrial mobile robotics applied to substations emerged in Japan in the 1980s, the vast majority of the work was done in China in the last decade, with considerable R&D effort devoted to SmartGuard robot technology by the State Grid Corporation of China. In fact, apart from the field robot system recently developed at IREQ (Hydro-Qubec) for inspection, maintenance and operation tasks, virtually all other initiatives were in Asia, mainly in Chinaand all 39 identified patents are for Chinese territory. In addition, other tasks that could potentially be

robotized (including inspections for partial discharges and detection of SF6 gas leaks) have been identified for future development [15]. Also, EPRI in the United States seems interested in the development of robot technologies for substation applications [79]. Clearly, we can expect more studies on robots applied to power substations in the years to come, and these could be added to this survey.

TABLE I. PATENTS FOR TECHNOLOGIES DEVELOPED AT THE SHANDONG ELECTRIC POWER RESEARCH INSTITUTE OR THE SHANDONG LUNENG INTELLIGENCE TECHNOLOGY CO., LTD. IN CHINA

CN101604825 A, 12-16-2009, Robot used for intelligent substation patrol CN101957325 A, 01-26-2011, Substation equipment appearance abnormality recognition method based on substation inspection robot CN202041851 U, 11-16-2011, Intelligent routing inspection robot of laser navigation transformer substation CN102255392 A, 11-23-2011, Method for controlling switching operation sequences of full-automatic transformer substation based on mobile robot CN202058039 U, 11-30-2011, Combined positioning system for substation intelligent inspection robot with integrated multi-sensors CN202166895 U, 03-14-2012, Laser navigation system of intelligent patrol robot at transformer substation CN202167774 U, 03-14-2012, Transformer substation patrolling and examining robot system based on smart antenna technology CN202171746 U, 03-21-2012, Transformer substation patrol robot based on wireless local positioning system CN202176206 U, 03-28-2012, Automatic door control system for charging room of intelligent patrol inspection robot in substation CN202205099 U, 04-25-2012, Intelligent inspection robot navigation and control system for transformer substation CN202230635 U, 05-23-2012, Transformer substation inspection robot simulation system based on virtual reality technology CN101957325 B, 05-23-2012, Substation equipment appearance abnormality recognition method based on substation inspection robot CN202282566 U, 06-20-2012, Transformer substation patrol inspection robot with bi-directional voice communication function CN202285342 U, 06-27-2012, Intelligent polling robot charging device for transformer substation CN202334810 U, 07-11-2012, Two-way voice communication device for inspection robot system in transformer substation CN102566576 A, 07-11-2012, Many scanning test robots for sequential control system of transformer substation, in coordination with the method of operation CN202333477 U, 07-11-2012, Charging room for intelligent inspection robot of substation CN202333525 U, 07-11-2012, Intelligent robot inspection system with long-distance video instruction function for transformer substation CN202333860 U, 07-11-2012, Charging docking assembly of transformer substation intelligent polling robot system CN202423926 U, 09-05-2012, Transformer substation polling robot gesture driving system based on electronic map CN202443332 U, 09-19-2012, Intelligent routing-inspection robot environmental information measurement and control system of transformer substation CN202495798 U, 10-17-2012, Automatic charging mechanism for transformer substation inspection robot CN102314615 B, 11-07-2012, Substation inspection robot-based circuit breaker state template-matching identification method

TABLE II. OTHER PATENTS FOR ROBOT APPLICATIONS IN SUBSTATIONS

CN101984382 A, 03-09-2011, Method for intelligently inspection substation equipment by using robot, Chongqing Power Company Extra High Voltage Bureau CN102082466 A, 06-01-2011, Intelligent inspection robot system for transformer substation equipment, Ultra-hv Transmission Bureau of Chongqing Electric Power Company CN102097860 A, 06-15-2011, Intelligent robot patrol system for safety detection of substation, Guodong Fengjie Science And Technology Co., Ltd. CN201897822 U, 07-13-2011, Transformer substation inspection robot, Chongqing Chuangge Technology Co., Ltd. CN102169602 A, 08-31-2011, Structural design of inspection robot of transformer substation, Shenyang Ultra-hv Bureau of Northeast China Grid Company Limited CN102170146 A, 08-31-2011, A battery intelligent management system used for a patrol robot in a transformer substation, Beijing Huadian Fengniao Technologies Co., Ltd. CN202025365 U, 11-02-2011, Structural design of patrol robot in transformer substation, Northeast China Grid Company Limited. Shenyang Ehv Bureau CN101604825 B, 12-14-2011, Robot used for intelligent substation patrol CN202092653 U, 12-28-2011, Navigation system for substation inspection robot, North China Electric Power University CN102430546 A, 05-02-2012, Insulating sub-band electro-cleaning robot of transformer substation, Inner Mongolia Electric Power Science Research Institute CN202238790 U, 05-30-2012, Live-line cleaning robot for substation insulator, Inner Mongolia Electric Power Science Research Institute CN202474607 U, 10-03-2012, Automatic patrol inspection robot system of intelligent transformer substation, Hohai University, Changzhou

CN102736624 A, 10-17-2012, Intellectual scanning test robot of wall-mounted type of a kind of transformer substation, Shenyang Institute of Automation, Chinese Academy of Sciences CN202534975 U, 11-14-2012, Transformer substation inspection robot with infrared obstacle-avoiding function, Changzhi Power Supply Branch of Shanxi Electric Power Company CN202649815 U, 01-02-2013, Transformer substation panorama automation inspection system based on robot technology, Kunming Nengxun Technology Co., Ltd. CN202686368 U, 01-23-2013, Various track type carrier cart for transformer substation patrolling robot, Liaoyuan Power Supply Co., Ltd. of Jilin Electric Power Co., Ltd.

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