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Typically, corona and tracking do not show up
with an infrared scan in electrical systems below 240 kV.
This point alone demonstrates the need for the inspection
industry to marry temperature imaging and ultrasound
scanning techniques. This paper will discuss the many uses
of airborne ultrasound to record wave files and use an
infrared system with real time photo and/or IR images to aid
the inspector in his/her reports. For Example:
A southeastern chemical plant used airborne
ultrasound and an infrared camera to inspect several 13.8 kv
rectifier panels with the panels closed. No significant
temperature variations could be detected through the closed
panels. There was however significant levels of airborne
ultrasound detected at the lower right corner of one of the
fifteen panels. Ultrasound detectors transform ultrasound
to audible sound while maintaining the tonal characteristics
of the source. Therefore several qualified electrical
technicians were able to safely listen to the signal and
make a definitive action. The “vacuum breaker” was removed,
and by applying a DC current to this breaker a failure was
revealed.
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Ultrasonic Scanning 13.8 Kv
Panels with Flexible Sensor Attachment |
Scanning High kV T&D Lines
with Parabolic Dish Attachment |
Finding this fault averted the loss of
electrical power, a shutdown of the plants compressed air
system, and possible injury to personnel from fire or
shock. This random ultrasound inspection revealed a
potential fault that would have been missed during the
company’s regular inspection. Since then airborne
ultrasound inspection of all switchgear has been added as
part of the regular scheduled infrared PM.
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