What Is The Theory Of Ultrasound?

Your company has just decided to replace the calendar based, open panel electrical inspections with safer, closed panel Condition Based Maintenance programs. Historically, your maintenance team has only relied on infrared thermography to inspect electrical components and equipment. As a result of moving to a Condition Based Maintenance program, the decision was made to add ultrasound inspection capabilities to the program. As the director of the maintenance team, you are researching the topic of ultrasound to understand how this technology can benefit the maintenance inspection program. The first step is to understand the theory behind ultrasound. Let’s see what information you have found?

Sound is a mechanical wave that travels in a straight line.  A mechanical wave is a local oscillation in a medium and it transfer its energy through that medium. These waves can move over long distances and the energy propagates in the same direction as the wave travels through the medium.  Common examples of mechanical waves are seismic waves, sound waves and water waves.

Sound is a vibration that travels through the air or another medium and can be heard when that vibration reaches the human or animal’s ear.  Sound is a type of energy made by vibrations.  When an object vibrates, it causes movement in the medium particles.  These particles start to bump into particles that are close, and this continuous bumping makes them vibrate into more medium particles – a sound wave is born.

                                                                             The Critical Angle of Ultrasonic Electrical Inspection of Transmission Lines

There are several components of a sound wave:

  • Amplitude:   the height of a wave’s crest which determines its loudness.
  • Compression: a region in a sound wave where particles have been pushed together making the densest part of the wave.
  • Frequency:  the number of waves produced in a given period of time and usually measured in Hertz (Hz) or cycles per second named after the German physicist who produced the first artificial electromagnetic waves.
  • Loudness: the intensity of the pressure wave resulting in the levels intensity perceived by someone and measured in Decibels (dB).
  • Pitch: describes the perceived highness or lowness of a sound wave and the difference between them Higher frequency sounds have a higher perceived pitch.
  • Rarefaction: the region in the sound wave where the particles have been spread out and are the least dense part of the wave.
  • Wavelength: the measurement of a sound wave from compression to compression or from rarefaction to rarefaction.

An ultrasound wave is a wave with a frequency exceeding the upper limit of human hearing greater than 20 kHz (20,000 Hertz).  Ultrasound waves can be produced by friction inside a motor, gear box, bearing housings, pistons, hydraulic rams and fan housings.  Exterior friction can create ultrasound waves on conveyor rolls, belts, belt splices, finger guards, chains and sprockets.  Internal turbulence occurrences within steam traps, vacuum leaks, valve leaks, pump cavitation and back pressure issues can create ultrasound waves.  On electrical equipment, ultrasound is generated due to Partial Discharge phenomenon including arcing, tracking and corona.  So, on electrical assets, Infrared inspections lets you see heat from loose or overloaded connections that you could not see with the naked eye while ultrasound allows you to hear signs of defects that would be impossible to hear otherwise but that may not generate any appreciable heat.  The two inspection technologies work extremely well together to ensure that the most common problems with electrical equipment can be detected early.

Detecting ultrasound waves using handheld ultrasound testing devices play a critical role when used in a Condition Based Maintenance Inspection program.  Anomalies in equipment or components of equipment may create ultrasound waves, when detected, could alert the maintenance team that a component or machine needs to be further assessed for deterioration.  The goal is to find the anomaly and determine the health of the equipment and fix it if needed before that equipment fails.  Condition Based Maintenance programs are growing in popularity as companies look for ways to proactively detect and fix equipment before costly repairs or full replacements are needed.  


Detecting ultrasound waves is gaining popularity as a tool within Condition Based Maintenance programs.  Companies recognize that preventing equipment failures by performing proactive maintenance inspections saves them time and money in the long run.


The Critical Angle of Ultrasonic Electrical Inspection of Transmission Lines

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