Ultrasonic testing is often used on high-voltage electrical equipment, particularly enclosed switchgear. In enclosed gear, tracking is a particularly serious problem because the distance from current carrying components to ground is usually small. Failure of insulating components can cause switchgear components to vaporize. Ultrasonic testing in enclosed switchgear may be more important than infrared testing.
Heat Seekers Infrared Inspection Services Provides Airborne Ultrasonic Testing
Because ultrasonic sound can pass through small cracks at doors or through ventilation openings, an ultrasonic test can be performed where infrared cannot. Results can reveal extremely high internal ionization. With Heat Seekers night vision glasses, arcing can be visible.
On many types of enclosed high-voltage gear, front or rear panels can be removed to provide access for ultrasonic testing. (All appropriate safety procedures must be observed during removal of panels on energized high-voltage switchgear. See National Fire Protection Association 70E, “Standard for Electrical Safety Requirements for Employee Workplaces”)
However, high-voltage switchgear is often totally enclosed. Access is through interlocked doors that cannot be opened when the gear is energized. This type of gear can be easily tested for insulation breakdown through the use of a listening port. Ultrasound easily passes through an opening but is readily blocked by a solid surface. On switchgear, a listening port can often be provided by removing a few bolts from the housing.
The ultrasonic instrument is then held near the open bolt holes to detect the distinctive buzz of internal tracking or corona. On totally sealed gear, a 4” capped hole can be cut into the switchgear housing during an outage. The port cover can be removed for inspection. The ultrasonic instrument is then positioned at the hole and operated to detect any internal tracking.