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Ultrasonic Inspection

ImageWhen electrical apparatus such as switchgear, transformers, insulators or disconnects and splices fail, the results can be catastrophic. This is just as true in industrial plants as it is in the power transmission and distribution side. Electrical discharges such as arcing, tracking or corona are all potential for equipment failure.

If left undetected, these conditions can become a source of an arc flash incident, which can result in severe injury or death. Arcing, tracking and corona can be detected by conducting an Ultrasonic Inspection.

At Powertech Substation Services, Inc. (PSSI), ultrasonic inspection is a part of our approach to a comprehensive preventive maintenance plan.

How Ultrasonic Inspection Works

Arcing, tracking and corona all produce some form of ionization which disturbs the air molecules around it.

PSSI conducts ultrasonic inspections to detect high frequency noise produced by this effect. The specific sound quality of each type of emission can be heard in headphones while the intensity of the signal can be observed on a meter.

Normally, electrical equipment should be silent, although some may produce a constant 60 cycle hum or some steady mechanical noises. These should not be confused with the erratic, sizzling frying, uneven and popping sound of an electrical discharge.

There are three basic electrical problems that can be detected thru airborne ultrasound:

  1. Arcing: An arc occurs when electricity flows through space. Lightning is a good example.
  2. Corona: When voltage on an electrical conductor, such as an antenna or high voltage transmission line exceeds threshold value, the air around it begins to ionize to form a blue or purple glow.
  3. Tracking: Often referred to as "baby arcing", follows the path of damaged insulation.

Although theoretically ultrasonic inspections can be used in low, medium, and high voltage systems, most of the applications tend to be in medium and high voltage systems.

Applications include insulators, cables, switchgears, busbars, relays, contactors, breakers, motor control centers, junction boxes. In substations, components such as power lines, insulators, transformers, arresters, distribution lines, disconnect switches and bushings may be tested.

Ultrasonic inspections are often used for evaluation of electrical components with voltages exceeding 2,000 volts, especially in enclosed switchgears. This is especially useful in identifying tracking problems.

In enclosed switchgear, the frequency of tracking greatly exceeds the frequency of serious faults identified by infrared scanning. It is recommended that both tests be used with enclosed switchgears.

On lower voltage systems, a quick scan of busbars often will pick up a loose connections. Checking junction boxes can reveal arcings.

Corona & tracking often do not generate heat. Scanning with ultrasound & infrared is the best method.

Key Benefits of Conducting an Ultrasonic Inspection

  • No Equipment Down Time
  • Cost Effective
  • Meets or Exceeds Insurance Requirements
  • Non-Intrusive
  • Locates Problems Not Found During Shutdowns
  • Locates Arcing, Corona and Tracking
Last Updated ( Wednesday, 05 December 2012 )
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