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Ultrasonic Inspection of High Voltage Services Equipment

high-voltage-repairWhen combined with infrared thermography, ultrasonic inspections can detect catastrophic arcing while ensuring the reliability of high voltage services. These diagnostic tests can identify and isolate a number of electrical warning signs that produce heat, ultrasonic noise or a combination of interferences.

Ultrasonic inspections are valuable for locating faults and partial discharges that produce abnormal frequencies. Additional thermographic inspections can be used to confirm the diagnosis or detect conditions that generate heat due to resistance caused by corrosion or tracking. Plus, ultrasonic analysis can identify serious problems that do not generate hot spots. Test equipment delivers readings on all types of open and enclosed equipment, including a circuit breaker, power transformer, insulators, switches, relays and contacts.

Advantages of Ultrasonic Testing

Ultrasonic inspections can detect faults and inaudible frequencies in all types of equipment that handle low to high voltages. Sensitive ultrasonic instruments can also pick up mechanical noise and vibrations. For accuracy, results should be visually analyzed using spectrum analysis software to rule out potentially nondestructive conditions. In many cases, the turbulence of spontaneous ionization creates distinctive sounds that can be detected with ultrasonic equipment.

These tests reveal unique sound patterns related to the following problems.

  • Arcing creates irregular acoustic patterns that stop and start spontaneously.
  • Tracking, also called baby arcing, forms similar peaks and valleys.
  • Coronas produce a steady buzzing sound and a uniform sound wave.
  • Partial discharges produce popping and buzzing noises.

Fast track power Field technicians can identify most problems based on the sound profile. Additional computer-based analyses differentiate subtle changes in the pattern and help to determine the extent of the fault. For example, the frequency of primary harmonics shifts when a corona becomes more severe. Similar harmonics can be produced by loose mechanical connections, so it is important to investigate all possible causes.

Field Tests and Computer Analysis

If the discharge generates heat, thermographic imaging can confirm the audio diagnosis. Ultrasonic data can be recorded, analyzed and played back from a computer or a handheld device that produces a spectrum analysis and time series.

Testing modules measure faults in the air and on solid surfaces that conduct sound. Closed-cabinet testing is easier because there are fewer safety requirements and workers do not need to wear cumbersome safety gear in challenging environments.

Inspection Equipment

Ultrasonic inspections can be completed while high-voltage equipment is online, which is a significant advantage. Accessories and field protocols enhance audio signals and reduce interference from nearby equipment. For example, parabolic reflectors can double the signal-reading distance for increased accuracy. Probes and wave-scanning modules detect ultrasonic noise at multiple frequencies. Kilohertz adjustments make it possible to collect readings from a variety of materials. Once the signal is lowered to an audible range, the technician listens for sound fluctuations using headphones or a loudspeaker.

Using Testing Data to Correct Electrical Faults

Tests show ultrasonic anomalies, but they cannot determine when failure will occur. Arc flashing and coronas may happen at any time, so there is no opportunity to compare test results over months or years. If a problem is detected, it should be repaired immediately to ensure worker safety and to prevent catastrophic events from causing prolonged outages. By inspecting degraded areas and faults in insulating materials, high-voltage clients can protect their valuable equipment and transformers.

Continuous ultrasonic monitoring is another method for addressing rapidly changing conditions in enclosed equipment. Once installed, these units have the potential to prevent catastrophic failures and costly repairs by providing a constant stream of real-time data. Units also eliminate the need for testing experts to travel to remote sites.

For more information on field testing equipment and protocols, contact Equisales Associates in Houston by calling 713-733-3999. We provide fast track power substations, equipment rentals and testing services to high-voltage clients in North America and around the world.


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