When considering corona inspection with Ultrasonic it is important to take into account:

  • Distance of detection
  • Pinpointing corona sources
  • Disturbances
  • Detection capabilities from helicopters
  • Price
  • Ultrasonic equipment are sensitive corona detectors but for short distances. The detection capability of those equipment deteriorates drastically as the distance from the corona source increases. This technology is safe and satisfying for very intense coronas. The DayCor®  corona camera, on the other hand, detects corona easily even from distances of 150m and more.

  • The exact location of corona discharge indicates severity of damages and leads to the actions needed to be taken by maintenance teams. Ultrasonic equipment does not pinpoint corona sources though it directs experienced operators towards suspicious defective insulators of high voltage pylons. With a corona camera pinpointing corona on insulators, conductors or any other substation component is straightforward and immediate.

  • Whether a discharge is on an arcing horn, on a corona ring, on an end fitting of a polymer insulator or on the cap of a porcelain insulator etc… can easily be revealed by an optical device like a corona camera.

  • Ultrasonic detector has an advantage when there is no direct line of sight to the corona source. As any other type of camera, Corona cameras require line of sight to the target.

  • Noisy environments, as in urban locations, distract ultrasonic devices yet do not affect corona cameras. Corona cameras, on the other hand are disturbed by UV emission from non-corona sources such as welding arcs and fires. Corona, however, is characteristically a recurring flickering event and thereby is clearly distinctive from surrounding noise. Camera operators with only little experience easily distinguish between “UV noise” and real corona signals.

  • Due to noise ultrasound detectors cannot be used from helicopters. Corona cameras, on the other hand, fit airborne inspections and become popular throughout transmission and distribution sectors of utilities.

  • Ultrasonic equipment is cheaper to buy than a corona camera but the trade-off is in saving labor cost. Inspection team using a corona camera spend less time finding problems.
Ultrasonic Waves, UHF Antennae
Corona UV Cameras
Targets for corona PD detection
Ultrasonic waves and electromagnetic waves
UV radiation, photons
Analysis methods
Subjective to users’ interpretation
Objective, seeing the dynamic flow and direction of corona discharge
Locating targets
Wide scope & general
Getting pinpointed image of the discharge shape, location & direction
Sensitive to enviroment
Cameras use noise reduction function and corona amplification to distinguish sporadic noise from corona
General overview of electric facilities
Predictive maintenance; Condition based maintenance; Solving customers’ complaints Investigating electrical faults; Research in laboratories; Aerial scanning of overhead lines and more
Kil-Mok Shong, Young-Seok Kim, and Sun-Gu Kim, “Images Detection and Diagnosis of Corona Discharge on Porcelain Insulators at 22.9kV D/L”, IEEE International Symposium on Diagnostics for Electric Machines, Power Electronics and Drives, Cracow, Poland, September, 2007