High-Voltage Transmission Line and SF6 Gas-Insulated Substations Inspection Using Computed Radiography

Edmundo A. LINS 1, Adroaldo M. FERREIRA 2, Mardonio S. CARVALHO 2

1 BB&E Engineers and Consulting Associates; Lauro de Freitas, Bahia, Brasil

Phone: +55 71 21373414, Fax: +55 71 21373414; e-mail: bbe@bbesolutions.com.br, bbe@terra.com.br 2 SENDCONTROL Industrial Inspections; Lauro de Freitas, Bahia, Brasil

E-mail: adroaldo@sendcontrol.com.br, mardonio@sendcontrol.com.br

Abstract Considering the world scenario, the thermography inspection has been extensively used to evaluate the integrity of electric equipment. Although thermography equipment has become more efficient, there is a series of operational and environmental factors which interfere in the obtained results, especially when the tests are carried out on the ground, as is more common. Besides, the thermography presents a non-conclusive, merely indicative nature, hence it is not possible to define the precise amplitude or gravity of the problem. This article demonstrates the efficacy of wi-fi remote operated computed radiography systems, which makes the internal visualization of equipment possible while they operate, specially with emphasis to the possibility of its use in transmission lines inspection. The quality of the obtained information allows one to evaluate, in a conclusive way and not only symptomatic, the integrity of the equipment, avoiding operational failures and achieving a better planning of the assets maintenance activities. Keywords: Thermal NDT, radiographic testing (RT), other methods, structural health monitoring (SHM), maintenance, integrity, inspection, computer radiography, thermography 1. Introduction Ensure continuity of power supply is a global concern. Regardless of the energy source: hydroelectric, nuclear, wind, etc., it is necessary ensure the continued operation of transmission and distribution systems which are composed essentially of electrical equipment and transmission lines. Today we see around the world several projects of developments in most of them coordinated by CIGRE in order to provide systems and methods of assessment, inspection and analysis that can more accurately verify the integrity of the equipment and transmission lines. Specifically in relation to the inspection of transmission lines, are being done projects drones and robotic systems. However, the inspection tools what are still used extensively are the visual inspection and thermography, in most cases, from the ground. Some projects currently under development are intended to load them in drones and robots, but these goals are going to collide with little capacity and autonomy of these systems. In the case of transmission lines has been used on a much smaller scale inspection by electromagnetics when evaluating corrosion of steel cores of cables, however, this technique can not be applied to cables made entirely of aluminum. Considering the limitations of the above techniques and the use of DRONES, we are proposing as a complementary tool, especially taking into account the reliability of their results and the possibility embed it on a robotic system for inspection of transmission lines, the use of computed radiography controlled remotely. This paper also shows the tests made in Gas-Insulated-Substations (GIS).

2. Computer Radiography Remote in Power Sector. Real-time radiography 2.1 Applications in Gas-Insulated-Substations (GIS). It is all important to the workings of a GIS that contacts installed on your driver are in perfect condition and properly attached. The breaking of springs these contacts can cause improper opening or even causing it to fall inside the conductor. Contacts with malfunctioning can cause discharges that reach the wall of the outer shell, responsible for containment of insulating gas (SF6) causing a merger on his wall until reaching the outside (hole) with consequent leakage of gas and loss of insulation. We should emphasize that in the case of GIS what was inspected the operating current was 2000 A. The application of remote computed radiography allowed the inspection of hard to reach places without the need for scaffolding providing a high productivity gains, and have identified mergers walls before the occurrence of the hole in the outer casing. Through simulations we found that in the case of falling contacts inside the conductor would also be possible to identify not only the occurrence but also locate the broken contact.

Figure 1. GIS inspected. The largest GIS of the world in extension continues.

Figure 2. Details of the contact's positioning to be inspected inside the conductor

Figure 3. Detail of the body of the electrical conductor with the occurrence of fusion caused by lightning

Figure 4. Radiographic image indicating the occurrence of fusion and the fall of the contact inside the electrical conductor.

Figure 5. Detail the positioning of the computed radiography system in the place to be inspected.

Figure 6. Radiographic image of the region of Figure 5

Figure 7. Radiographic image indicating the presence of fragments inside the conductor

2.2 Termography x Radiography As shown previously, the inspection tools massively used currently comes down to visual inspection and thermography, and much smaller scale analysis of the condition of corrosion of steel core through electromagnetism, not entirely applicable to aluminum cables. The visual inspection has many known limitations however, regarding thermography, despite the significant supply of increasingly modern and efficient equipment, the international literature presents studies that we list several factors that directly influence its results. It is not the object of this article discuss these factors in view that this matter has already been detailed in other articles however, given the large number, diversity and possibility of interference in the results of thermographic testing it behooves us to list them: convective cooling, electrical loads, component emissivity, thermal gradiente, ambient conditions, ambient air temperature, solar absorption, precipitation, wind speed, temperature/resistance relationship, limitations of the infrared system, resolution, waveband detected. It is important to emphasize that thermography provides qualitative information, suggestiveness, since it can only observe but not diagnose the cause of warming. Studies we conducted associating the 02 techniques demonstrated the perfect correlation of the results being that the radiographic indications could provide information for identifying the cause of the temperature rise.

Figure 8. Thermographic image of a splice with indication of temperature rise and radiographic image

showing the increased density of the material in the heated point. Similar indications

2.3 Applications in Overhead Lines (OHLs) The efficiency of detection of discontinuities by computed radiography is unquestionable. The various possibilities for image analysis and measurement of discontinuities usando software (with a minimum scale of 0.1 mm) is an important tool for evaluation of the indications. The possibility of activation and production of images remotely allows inspection in hard to reach places like stretches of transmission line cables.

Our current state of development allows us to radiograph on energized lines or not. In these situations we are still positioning equipment systems from the ground (underground) but we are developing a robotic system that will allow us to move and position the equipment directly on the transmission line. Part of the development of robotic design is a transmission system of satellite imagery and inspection tools for dynamic computed radiography able to inspect sections of transmission lines continuously.

Figure 9. Positioning of computed radiography equipment in OHL

Figure 10. Radiographic image obtained remotely in OHL

3. Conclusions It is absolutely important and it is a global concern ensure the smooth operation of the electric transmission systems regardless of the source generating energy systems. This objective involves the evaluation of the equipment integrity as well substations as transmission lines. The efforts in this direction are been developed around the world and a reliable evaluation involves the joint analysis of information provided by various techniques. Within this context the remote computed radiography seeks to add resources for a more efficient analysis. The information provided by this technique are accurate and conclusive and has not only suggestive or indicative nature. The possibility of obtaining real-time images with remote control and detailed analysis by software gives to the system great confidence and a wide range of applications. The addition of a robotic system that will allow greater flexibility of movement of inspection equipment as well as the source of transmission of satellite imagery will make it a inspection tool for high potential for use. Reference 1. Hotline inspection and control of joints, Ormin & Bartsch, Paper 22-203, Cigre, Session 1998. 2. IEEE Standard 738, Institute of Electrical and Electronics Engineers, PO Box 1331, Piscataway, NJ 08855-1331. 3. Guidelines for thermographic inspection in electrical installations, Danish Technological Institute, 1994 (Taastrup, Denmark). 4. Snell, J., Fritz, J., Improving temperature measurements for electrical inspections, Proceedings of Thermosense XX, SPIE, Bellingham, WA, 1995. 5. Snell, J., Renowden, J., Improving results of thermographic inspections of electrical transmission and distribution lines, IEEE 9th International Conference on Source, 2000