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God Bless America 09/11/2001
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 Corona refers to the faint glow, which surrounds an electrical conductor of 3500 volts or greater as a result of the ionization of air as the nitrogen in the air breaks down. This corona has one by-product of ozone that is detrimental to the human lungs and eyes. The corona produces electric discharges that disrupt the molecules around it and generates ultrasound. A by-product of the corona will be tracking on the high voltage component and eventual phase to ground and failure.
Ultrasound Technology detects sounds above the normal range of human hearing, which ranges from 20 Hz to 20 kHz. A frequency range between 20 kHz to 40 kHz normally covers all of the ultrasonic applications used for predictive maintenance applications; such as leak detection, steam traps, bearings and lubrication, and electrical discharge. High voltage electrical areas of concern are insulators, electrical terminations, stress cones, transformers, breakers, contactors and many others.
At Massey Technical Services, LLC we provide the latest in ultrasonic testing for transmission lines, substations, and industrial switchgear in plants. We use the latest UE Systems test equipment, and provide a digital picture of each anomaly with it’s associated spectral time waveform. An example ultrasound inspection is shown below by Jody McCrystal Mechanical Engineer.
Conclusion: Unlike resistance problems associated with current flow that can be detected by infrared, corona is a voltage problem that seldom generates heat. Corona and tracking problems can be easily missed by infrared and remain enigmatic until a major fault occurs that destroys switchgear equipment. The use of ultrasonic technology compliments an infrared inspection program by increasing the ability to locate these destructive problems and take corrective action. |
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