Self-Sustaining Autonomous System for High Voltage Transmission Line Inspectionand Fault Detection in Sri Lanka

Pasika Ranaweera, Thamashi Malaviarachchi, Thadeesha Perera, Supun PereraDepartment of Electrical & Information Engineering

Faculty of Engineering, University of RuhunaSri Lanka

Email: pasika@eie.ruh.ac.lk, thamashi.u@gmail.com, thadeesha@gmail.com, supunclemont@gmail.com

Abstract—High Voltage Transmission line inspection andmaintenance is an extremely dangerous employment due to thereason that such tasks are performed at high altitudes aroundhigh magnitude voltages. In countries like Sri Lanka, thisemployment has caused the demise of experienced techniciansover the years. As a solution to this timely matter on powerdistribution sector, an autonomous approach is introduced toperform the inspection through remote operation. A RemotelyOperated Vehicle (ROV) prototype was implemented to testthe proposed approach in a single transmission line span.The intended functions of the proposed ROV are positioning,live video transmission and the sag template indication of thetransmission line which are being explicated in this paper. Theprototype was tested in a high voltage laboratory environment toverify the feasibility of operation. A magnetic energy harvestingcircuit was designed and implemented to satisfy the powerrequirement of the proposed autonomous system.

Keywords– fault detection; high voltage; magnetic energyharvesting; ROV; transmission line; video streaming;

I. INTRODUCTION

Transmission lines are essential to transfer the electricityproduced in power plants to cities and homes. Any failurein such lines may bring severe consequences to peoplesdaily lives by affecting transportation, health, security andsanitation. Therefore, the proper maintenance of high-voltagetransmission lines is extremely important. However, the trans-mission lines are laid in high altitudes, and the lines transmitcurrent at higher voltages such as 132 kV and 220 kVaccording to Sri Lankan standards. Hence, transmission linesinevitably require routine maintenance.

In Sri Lanka, the transmission network is distributedthroughout the island, which is approximately 2000 km.The transmission line inspection and maintenance work iscurrently performed by specialized workers for once every3 years. Inspection procedure includes checking insulatorstatus, measuring transmission line clearances, etc.

In other countries, use of robots to accomplish this taskis an active research area [1]. But in Sri Lanka, researcheshaven’t been carried out to automate this process till now.So, our focus is directed to implement an inspection robotwhich would be compatible for the transmission lines laidacross national grids island wide.

In this paper, the basic concept of the proposed ROValong with its mechanical design and the control systemis introduced. The validity of the proposed concept will beconfirmed with results of experiments, discussed at the endof this paper.

II. INSPECTION OF TRANSMISSION LINES

High-voltage transmission lines are usually arranged insingle or 2 wires, supported by transmission towers. Thedistance between the towers is usually between 300 m and500 m, which are laid across forests, mountains or any otherisolated places. The suspended transmission lines are oftencomposed of a metallic core and metallic casing. Whenexposed to the elements, the lines may suffer from corrosion,damages by lightning bolts, or even rupture of the core. Inorder to inspect the lines, workers must walk on the lines; inmany cases suspended 20 m above the ground. The currentlyused methods require skilled workers, and expose the workersto unnecessary levels of danger and stress. In addition, whenthe lines are being inspected, the transmission of electricitymust be temporarily suspended, which means that other linesmay be overcharged in order to compensate for the line thatis undergoing maintenance as well as it takes a high cost.Moreover, it takes approximately 3 years to carry out theinspection procedure in the entire transmission network. Thisis due to the lesser availability of the specialist employeeswho are willing to take the risks.

Insulators in the transmission lines could be damaged bylightning bolts and surface corrosion. Therefore the insulationlevel will become lower than the expected level. Mostly inSri Lanka these insulators are inspected by Binoculars or bynaked eye. This scenario is not accurate and it can resultin severe damages inflicted to the transmission network. So,there should be a proper method to inspect insulator status.

Although there are many forms of robots existing fortransmission line inspection over the world, they are notsuited for line configurations and atmospheric conditions inSri Lanka [1],[2]. Moreover, measurements taken from suchrobots are exclusive of parameters such as ground clearance,sag template and insulator condition. Additionally, they aretoo expensive to purchase and maintain for a developingcountry.

2016 First International Conference on Micro and Nano Technologies, Modelling and Simulation

978-1-5090-2406-3/16 $31.00 © 2016 IEEE

DOI 10.1109/MNTMSim.2016.14

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2016 First International Conference on Micro and Nano Technologies, Modelling and Simulation

978-1-5090-2406-3/16 $31.00 © 2016 IEEE

DOI 10.1109/MNTMSim.2016.14

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III. PROPOSAL FOR AUTOMATION

A. Proposed Model for the ROV

This study is focused on designing a transmission lineinspection robot that will operate only in a single span. Theprototype requires at least two supporting points and a bodyto hold all the electronic circuits of the ROV. To keep thestability of the robot when moving on the lines, the centreof mass must be positioned as low as possible, ideally underthe transmission line. Therefore, the body is constructed tobe light weighted and the supporting points are placed inbalanced positions in order to be stable on the transmissionline.

Hence, the robot is composed of two supporting points andpulleys that move on the transmission line. Each supportingpoint is equipped with one motor for motion on the cable andthey are connected to the body by a belt and an arm. Thebody is to be protected from electromagnetic interferences.Therefore a proper enclosure is implemented on the robot.Since the proposed ROV is exposed to open air while inoperation, it is constructed to withstand any climatic distur-bances occurring during the inspection period. A magneticenergy harvesting method is proposed to recharge the batteryof the model.

B. Simulations

The basic design was modeled and simulated usingSOLIDWORKS®. For the stability of the robot on theline which is about 20m high, the wheel configuration isimportant. The simulation was carried out by consideringseveral configurations. Taking into account dynamic effects,the configuration that presented the best results is displayedin Fig 1. The simulation results revealed that the motion ofthe robot will be stable if the two wheels were placed onopposite sides of the conductor.

The enclosure design proposed for the ROV was alsosimulated using ViziMag®. Several materials with magneticshielding properties [3] were simulated. The simulation re-sults revealed that the most suitable material for magneticshielding is low carbon steel, which reduce the magneticinterference to the structure by a factor of 600, which is morethan the expected value. The simulation results are shown inFig 2.

IV. MECHANICAL DESIGN

A. Motion Units

The proposed ROV consists of two motion units, eachwith one pulley and a shaft. A DC motor is embedded in tothe top surface of the body. And the torque is transmitted tothe pulley using a timing belt. The pulleys (P1 in Fig 3) aremade of Nylon, with two grooves, one for clinging on thetransmission line and the other for the belt which connectsto the gear motor. The clinging groove diameter is matchedto the diameter of the transmission line conductor while the

Fig. 1. Overall view of the proposed ROV and its components

Fig. 2. Simulated magnetic shield for the proposed model

other groove diameter is chosen as 5 mm to be suited forthe motors. Each shaft (S1 in Fig 3) is made of iron to getthe strength required to hang the robot on the transmissionline. And it is insulated with high voltage insulation tapeto prevent resulting formation or electric arcs between thelines and the body of the robot.

Fig. 3. Arrangement of a single wheel in the ROV prototype

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B. Structure of the prototype

The structure which contain all the electronic circuits ofthe ROV is made of Perspex to lighten the total weight. Forthe driving mechanism, two DC motors operating at 120 rpmand produces a maximum torque of 60 Ncm is connected tothe upper plate of the structure along with a 12 V battery.This range of rpm is required with a better gear system toreduce the wheels backward motion on upper part of the sag.

The middle plate of the structure is equipped with anArduino UNO board for RF communication and a motorcontroller. The bottom plate consists of the main processor,Raspberry pi, Accelerometer for sag measuring and a GPSmodule for fault location tracking. A fish eye lens camerais also included in the front of the structure to take a videofeed of the inspection.

C. Enclosure of the structure

To overcome the difficulties appeared in the presenceof magnetic and electrical fields of high voltage lines, awell-insulated enclosure box is constructed. This enclosureconsists of a magnetic shield, an electrical shield along witha roof to withstand the climatic conditions. According toAmpere’s law, a higher magnetic field exists in high voltagetransmission lines. To avoid magnetic field interferences, aproper magnetic shielding material should possess a lowpermeability. Therefore for the construction of the magneticshields shown in Fig 4, the material is selected as low carbonsteel which attributes a permeability of 4000 H/m. As the bestshape for the structure, a cylindrical shape is chosen to avoidinterferences that might occur in the presence of magneticfields with higher magnitudes [4].

In order to avoid electro-static forces, the structure iswrapped with aluminum foil paper as shown in Fig 5. Acooling fan is used to prevent the overheating of electroniccomponents inside the prototype. Since the ROV shouldbe light weighted for proper operation of motors in thetransmission line, polyvinyl chloride (PVC) is used forimplementing the enclosure of it. And to overcome climaticdisturbances, a cover is made using PVC as illustrated inFig 6.

Fig. 4. Magnetic shielding Enclosure of the ROV prototype

Fig. 5. Electric shielding of the ROV prototype

Fig. 6. The complete enclosure of the ROV prototype

D. Magnetic Energy Harvesting Circuit

A power harvesting method is developed to recharge thebattery bank that would provide continual power supply forthe operation of the robot [5]. The power supply operatingprinciple is based on the harvesting of the magnetic energyaround the power supply lines using an electric currentsensor. The circuit design is shown in Fig 7.

Fig. 7. Magnetic energy harvesting circuit

The regulated output voltage of the prototype circuit devel-oped in relation to Fig 7, is tabulated against the controlledinput bus current in TABLE I for a burden resistor of 470ohms. The variation is plotted in Fig 8.

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TABLE IOUTPUT VOLTAGE OF ELECTRIC ENERGY HARVESTING

MODULE FOR THE RESISTOR VALUE OF 470 OHMS

Bus Input Rectified Regulatedcurrent (A) voltage (V) voltage (V) voltage (V)

5.0 2.64 2.24 0.167.5 3.64 3.12 2.32

10.0 4.24 3.72 2.4812.5 4.68 4.12 3.2815.0 4.96 4.40 3.9217.5 5.20 4.96 4.4020.0 5.60 5.12 4.8022.5 5.60 5.52 5.0425.0 6.00 5.76 5.0427.5 6.40 6.08 5.0430.0 6.80 6.40 5.0432.5 7.20 6.64 5.0435.0 7.20 6.88 5.0437.5 7.60 7.12 5.0440.0 7.60 7.36 5.04

When the bus current of the transmission line is in therange of 5.0-40.0 A, a stable 5 V DC voltage source issupplied to the monitoring module.

Fig. 8. Experimental output of the developed magnetic energy harvestingcircuit

The simulated power harvesting circuit design plotted us-ing PROTEUS®simulator considering the actual transmissionline parameters (Lynx conductor 360 A) is shown in Fig 9.According to this simulation, a stable 12 V DC voltage isobserved at the output.

V. CONTROL SYSTEM

The ROV can be controlled remotely, which means the useris always in charge of the operation and all the processed datais transmitted using wireless communication.

Fig. 9. Simulated magnetic energy harvesting circuit using PROTEUS®

A. Portable Control Unit

A Radio Frequency (RF) transmitter kit with 433 MHz isused to remotely operate the movements of the ROV. Theseinput RF signals are directed to the Raspberry Pi and thencontrol the motors using motor controllers. The LCD screendisplays the current movement of the ROV which helps theuser to get the required visual of insulators and conductors.

B. Wireless Communication

The access method to main processing unit of the ROV isestablished through a 2.4 GHz Wireless Local Area Network(WLAN) connection. Since Raspberry pi 2 B unit is installedas the main processing unit, the WLAN is accessed using aWi-Fi Universal Serial Bus (USB) adapter at the ROV end.The operations of the ROV requires internet access sincesome tools used for implementation (plotly and google maps)uses online data streaming. This feet is achieved by sharingan active network connection at user end to the WLAN.This enables feature of accessing ROV data over internet toauthorized remote users.

The real time video feed is streamed using Real TimeStreaming Protocol (RTSP) and encoded with the VLCencoder. The users can access this stream by connecting tothe media network via VLC plug-in at port no. 8554, whichwas defined for this implementation. The Raspberry pi isconfigured to work as a server (Apache Tomcat), so that GPSdata is hosted as HTML data to the user end. Therefore toacquire GPS data, HTTP connection is established betweenthe user end and the ROV end. The internet connection isused to plot data obtained from sensors online. The datais also pushed to Plotly API through HTML GET POSTrequests. Distance measuring data is obtained by Raspberrypi through GPIO pins whereas the Sag data is obtained fromI2C protocol.

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C. Main Web Interface

The main web interface of this system contains the realtime video feed, GPS plot, sag template and the groundclearance plot which are obtained by the acquired sensordata from the robot as shown in the Fig 10. The interface isdeveloped using html5 and PHP.

Fig. 10. GUI for inspecting line condition

VI. FIELD TESTING

A. Results of Experiments

1) Outdoor Testing: The ROV prototype was tested in atesting environment for its proper operation.

• Speed: 5.655 m/min, the robot can complete a 300 mlong single span inspection within 53.05 minutes.

• Operation on inclined lines: The robot was able to climbcables with an inclination of up to 30 degrees. Sincethe wheels were made of Nylon, it was able to operatewithout the interference from slippage of the wheels.But at the top of the sag, slippage of wheels occurred.This issue can be corrected by enhancing the frictionthrough including trails on the wheel surface.

• Data analyzing: All the data including sag template,GPS location, video feed and ground clearance wassuccessfully fed into the GUI.

• The video feed was obtained from the VLC plug-invery clearly and accurately.

2) Electromagnetic Shield Testing: The prototype wastested for proper operation of its electromagnetic shield witha 220 V:100 kV step up transformer, which was available inthe high voltage laboratory where the tests were conducted.The robot was mounted on a Lynx conductor using insulationrods and a measuring capacitor of 100 pF is used as they arewell-suited for the reduction of high alternating voltages tovalues easily measurable with instruments.

A spark was observed when the voltage reached 56.2kV between a non-insulated nut on the top of the structureand the conductor. This restriction could be addressed byinsulating all the nuts and metallic pieces with epoxy resin[6].

VII. CONCLUSIONS

A prototype of high voltage transmission line inspectionrobot was developed with higher reliability and higher accu-racy with minimal cost using available resources. This pro-totype can be operated up to 56 kV at any weather conditionon Lynx conductor, which is the mostly used conductor typein Sri Lanka. This system is capable of transmitting a livevideo feed, sag template, ground clearance map and the GPSlocation of the robot positioning. The magnetic field energyharvesting unit is capable of recharging the battery used in theROV and provides a low cost solution than renewable energysources. The implemented prototype proves the feasibility ofadopting autonomous systems in transmission line inspectionand fault detection.

The proposed design is supposed to be operated in asingle span. But for the industrial applications, span tospan operation is a compulsory requirement. Therefore, anenhanced structure should be designed which consists ofthree wheels to successfully operate on multiple spans.

The ground clearance is expected to be in a standard rangeof 15-20 m. Hence a sensor with more than 20 m is required.Currently the prototype operates with an ultra-sonic sensorwhich has a maximum range of 5 m. Therefore to achieve therequired range with actual transmission lines, high precisionLIDAR system [7] can be implemented.

Another major aspect of this design is to inspect insulatorand transmission line conductor conditions. Currently theprototype is equipped with a single camera with a fish eyelens in front. More cameras can be installed at the back andtop of the ROV structure to improve the perspective. Thecommunication ranges can be further extended with the useof RF modules and installing long range antennas at bothends. For industrial applications a better magnetic shield canbe implemented as mentioned in [8].

REFERENCES

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[2] Xiaohui Xiao, Gongping Wu, and Sanping Li, Dynamic CouplingSimulation of a Power Transmission Line Inspection Robot with itsFlexible Moving Path when Overcoming Obstacles, Proceedings of the3rd Annual IEEE Conference on Automation Science and EngineeringScottsdale, AZ, USA, Sept 22-25, 2007.

[3] Magnetic Shielding Materials : Magnetic Properties [Online], Available:http://www.amuneal.com/magnetic-shielding/theory-design/magnetic-shielding-materials.

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[4] Peter Sergeant, Mauro Zucca, Luc Dupr, and Paolo Emilio Roccato: Magnetic Shielding of a Cylindrical Shield in Nonlinear HystereticMaterial, IEEE Transactions on Magnetics, VOL. 42, NO. 10, October2006.

[5] W.M.M.S.C. Perera, U.L.J.T. Perera, T.U. Malaviarachchi and P.S.Ranaweera: ”Developing a Power Generation Technique for High Volt-age Environments through Electromagnetic Energy Harvesting”, ThirdAnnual Research Symposium (ARS 2016) of Faculty of Engineering,University of Ruhuna, Sri Lanka, E/14, 14 January 2016.

[6] Imai.T, Sawa F. , Ozaki T., Shimizu T. , Kido R., Kozako M., TanakaT., Evaluation of insulation properties of epoxy resin with nano-scalesilica particles, in proc. of 2005 International Symposium on ElectricalInsulating Materials, 2005 (ISEIM 2005), 239 - 242 Vol. 1, 5-9 June2005.

[7] How LIDAR works homepage on LIDAR-UK. [Online]. Available:http://www.lidar-uk.com/how-lidar-works/.

[8] Devender; Ramasamy, S.R., ”A review of EMI shielding and suppres-sion materials,” in Electromagnetic Interference and Compatibility ’97.Proceedings of the International Conference on , vol., no., pp.459-466,3-5 Dec 1997, doi: 10.1109/ICEMIC.1997.669850.

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