Up Time Magazine - February/March 2009 - (Page 29) scan technique. If you have any question about the safety of opening a switchgear cabinet, do not open it until an outage can be secured. If no noise is heard during the initial scan, do not assume that a problem does not exist. The interior geometric design of the cabinet may not allow the signal to reach the ultrasound collector or may allow a partial and weak signal to be heard. Likewise, mild cases of corona may have a very weak discharge signal that cannot be heard until the cabinet is open. Other problems that may affect the initial scan are competing ultrasonic noises generated by 60Hz electrical cycle generated by transformers, moving air from cabinet and overhead fans, and mechanical vibration from inside switchgear cabinets. Mechanical vibration signals can sound similar to electrical discharge. If you are in doubt, apply light pressure on the side of the cabinet and/or door to see if you can reduce or eliminate the ultrasound signal. The noise will dissipate or change if you are picking up mechanical vibration. This technique will quickly rule out any confusion between mechanical vibration and electrical discharge. arch-flash face shields make it next to impossible to use an eyepiece viewer, but the LCD screen can be easily viewed while wearing a face shield. Keep in mind that small delta-temperature rises on cables and bushing may be indicators of larger problems. Once a problem is detected, it should be described and photographed. Because of the dangers involved with getting too close to the equipment, having a telephoto lens on your visual camera will help get a closer look at a problem and see details that may otherwise be missed. Also, a bright flashlight will help overcome reduced vision caused by face shield tinting and will also illuminate dark and tight areas where corona and tracking may be hiding. If there is any doubt, or you lack the expertise in-house, contracting these specialized services to a qualified consultant is the best choice. However, if you are considering this type of inspection program in-house, receiving the proper training is always to best way to assure that you are not only receiving the best return on your investment and efforts, but keeping your personnel safe. Acknowledgements The author would like to thank the following people who were instrumental in compiling this paper. They have provided technical input, guidance for field work and ultrasound training: James Hall – Ultra-sound Technologies, www.ultra-soundtech.com; Dan Ninedorf - Ox Creek Energy Associates Inc., www. corona-technology-course.com and Dale C. Rossman Inc. – High-Voltage Switchgear and Maintenance, 1-863-559-4613 Jim Brady of Brady Infrared, Liane Harris with ECS2 Group and Jim Hall with Ultra-Sound Technologies work together in a limited partnership to bring together the use of Airborne Ultrasound, Vibration and Infrared. This group is committed to teaching others how to use and integrate these technologies. You can contact Jim Hall, Ultra-Sound Technologies for any questions or comments. As well, any request for training or services. Jim Hall, Ultra-Sound Technologies, (770) 517-8747 or jim.hall@ultra-soundtech.com or www.UltraSoundTech.com Performing a Switchgear Inspection Working around energized high-voltage switchgear should only be performed by a qualified person wearing the appropriate arc-flash personal protection equipment (PPE) as prescribed by NFPA 70-E guidelines. As these guidelines continue to move front and center in our industry, it is becoming easier to find qualified switchgear professionals that are familiar with, and more importantly wear, the necessary PPE when opening and closing cabinets. There are some things that you can do to reduce the risk of arch-flash. If you are an “in-house” technician with high-voltage switchgear, consider installing hinges on panels and modifying bolts that can be easily handled while wearing gloves. Once a cabinet is open, the inspector should slowly scan the entire interior of the cabinet with the ultrasound listener. Both front a back compartments, if accessible, should be scanned on rack-in breakers and load interrupter switches. Never should the ultrasound instrument or any body parts break the plane of the cabinet or exceed the approach distance for the given voltage class. Although I’m not a huge fan of LCD screens on infrared cameras, they do have their place when conducting this type of inspection. The www.uptimemagazine.com 29 http://www.ultra-soundtech.com http://www.corona-technology-course.com http://www.corona-technology-course.com http://www.ultraSoundTech.com http://www.ultraSoundTech.com http://www.globalreliability.com/r2r http://www.globalreliability.com/r2r http://www.uptimemagazine.com
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