Electrical inspection
Ultrasound is one of the only ways to capture corona, the ionization of air near an electrical connection. The heat produced by corona is so low that it can not be detected by infrared methods alone, but the high-frequency sound it creates can be captured by ultrasonic equipment.
According to Adrian Messer: "Ultrasound can be used to inspect almost any energized electrical equipment. This may include metal-clad switchgear, transformers, substations, relays, and motor control center, along with many others. Ultrasound can be used to measure equipment voltages from the low end (110 volts) to well over 12,000 volts (12kV).
Traditionally, inspection of energized electrical equipment has been performed using noncontact infrared cameras. However, increasingly, ultrasound is being added to these inspections. One of the main reasons has been safety: An ultrasound inspection of electrical equipment can be done without the need to open the energized cabinet or enclosure. The handheld ultrasound instrument is used to scan openings on the cabinet. The high-frequency sound produced by corona, tracking, and arcing from inside the enclosure will exit through the openings. The inspector will hear the sound via the headset and know an anomaly is present. The sound can then be recorded to determine whether the condition is corona, tracking, arcing, or some type of mechanical looseness."
To learn more, read "Ultrasound for PdM: You heard it here first."
Ultrasound imaging
Ultrasound inspection is not limited to an auditory experience; the data can be recorded and turned into a visual representation. This approach can help you set baselines and alarm levels for various equipment and eliminate the subjectivity often associated with ultrasound.
According to Messer: "Through advancements in airborne and structure-borne ultrasound instruments and software, the user can obtain an ‘image’ of the sound that is being heard to analyze, diagnose, and confirm mechanical fault conditions in rotating equipment. The concept of ultrasound imaging is to record ultrasounds heard via the ultrasound instrument, and then play back those recorded sounds in a spectrum analysis software. This will provide the inspector with the audible sound heard in the field during the inspection and a visual ‘image’ or spectrum of the recorded ultrasound in both the FFT and Time Wave Form view. This method will help to reduce the subjectivity of only relying in changes in the decibel level and changes in the sound tone or quality heard by the inspector."
To learn more, read "Sound analysis: Best practices for condition monitoring using ultrasound"
Bearing maintenance
With its heightened sensitivity, ultrasound is also well suited for detecting issues with rotating equipment. Ultrasonic instruments allow users to listen to the acoustic quality of bearings, helping to diagnose issues of over and under lubrication and helping to extend both bearing and machine life.
According to Messer: "Vibration analysis has long been the instrument of choice to use for bearings and other rotating equipment. More commonly, ultrasound is being used in conjunction with vibration analysis to help technicians confirm the condition of mechanical assets. Because of ultrasound's versatility, if a facility does not have a robust vibration analysis program in place, ultrasound can be implemented to detect early-stage bearing failures as well as other issues.
If the vibration analysis is performed by an outside service provider on a quarterly or monthly basis, ultrasound can be used during the interim. This will help the facility know the condition of some of the more-critical assets before the service provider enters the facility. The service provider’s time thus can be used more efficiently because the plant will know whether there are any eminent problems with the assets that are being monitored by ultrasound. The service provider can then prioritize work based on the ultrasound findings."
To learn more, read "Listen to your bearings."
