Comparison of OFIL’s Corona Camera & Ultrasonic instruments

What is Corona & What Causes it? Corona is an electrical discharge brought on by the ionization of a fluid (air) surrounding a conductor. It occurs when the potential gradient (strength of the electric field) exceeds a threshold value, but conditions are insufficient to cause complete electrical breakdown or arcing. The ionization process generates, UV light, radio frequency and wide spectrum sound energy, including both audible and ultrasonic components.

How do the technologies works? OFIL’s Corona Camera Ofil’s Corona Cameras pinpoint the ultraviolet light coming form the corona source. The corona location is displayed on real time visible image for analysis by the technician. The corona intensity value is displayed. Video clips & still images can be recorded for further analysis and documentation. Ultrasonic Ultrasonic instruments detect the ultrasonic energy (usually at 40 KHz) created by the corona. The signals are demodulated to audible frequencies so the technician can listen to them to determine presence of corona by sound recognition. Some models can display relative signal strength and also record the signals.

Selectivity to Corona OFIL’s Corona Camera Ofil’s Corona Cameras specifically detect energy in the UVC band related to corona activity. Potential interferences are limited to sources that generate UVC (electrical arcing, etc.) Ultrasonic Ultrasonic instruments detect all ultrasonic signals in the frequency of interest, not just those from corona. The technician must make a qualitative judgment by listening to the demodulated signal to determine if the source is corona or something else. Strong competing ultrasonic energy may mask signals from weak to moderate corona, making detection difficult under some conditions.

Localizing the Corona source Ofil’s Corona Cameras Ofils’s corona cameras uses bi- spectral technology to directly display the location of corona on a live video image. The corona source can be pinpointed to a specific location on a component (valuable information for diagnostic purposes) without having to get close to it. Some models have zoom capability for distances of 100 meters and above. Ultrasonic Ultrasonic is highly directional, making it relatively simple to initially locate the general source of a signal. By decreasing the sensitivity while moving closer, the source may be narrowed down to a specific component. Strong competing ultrasounds and/or other corona sources in the area make localization difficult.

Determining Corona Strength Ultrasonic Some instrument models can display the ultrasonic signal strength (usually in db), which includes all ultrasound energy in the frequency range, not just that from corona. Strong competing ultrasound or other corona sources can make an accurate corona strength measurement very difficult to impossible. Ofil’s Corona Cameras Corona strength is determined by directly counting the photons emitted from the source, then integrating them to generate and display a rate value in photons/minute that is directly proportional to the corona strength.

AN, RI, TVI concern? Decision Chart Photons per Minute Can it be damaged by corona? Corona- where? Critical component? Material type Critical location? Corona intensity? No Yes High> <Medium<5000 Low<1000 Monitor for additional signs Schedule repair or replacement Repair or replace ASAP No Yes Repair or replace ASAP

“…Attempting to measure and trend levels of observed ultrasonic activity and trying to relate them to the potential seriousness of surface partial discharge or end of life is not valid and could potentially lead to misleading conclusions…” “Testing Distribution Switchgear for Partial Discharge in the Laboratory and the Field”, by EA Technology, IEEE2008 Ultrasonic

Enclosed Electrical Equipment Ofil’s Corona Camera Direct line of sight to the corona source is required. Inspection of enclosed equipment requires the enclosure be opened prior to inspection. Ultrasonic Ultrasonic detection of corona does not require direct line of sight to the corona source. Inspection of enclosed equipment can be accomplished by listening via enclosure openings (vents, etc.).

Summary While at first glance it may appear that these are competitive technologies, when you dig a little deeper, you find that they are, in reality, complimentary. Solar blind UV technology adds a new capability to your predictive maintenance toolbox. It allows you to quickly and accurately pinpoint the source of corona and accurately evaluate and trend it’s strength. As a result, you can reduce energy losses, plan maintenance based on equipment condition and keep your electrical transmission/distribution system running at peak efficiency and reliability.

The next slide describes a test, comparing Ofil’s Corona Camera and ultrasonic device results. The white dot is the corona source’s location according to Ofil’s Corona Camera while the red dot indicates about the corona spot’s location according to the ultrasonic device. The red dot is a laser that was placed under the ultrasonic device.

White  Ofil’s Corona Camera Red  Ultrasonic Can you pinpoint, based on the red dot only ( ultrasonic device), the exact corona location?

Can you distinguish, based on ultrasonic device only, between the dead and the live end corona sources ? The picture describes contaminated substation. Can distinguish nearby corona sources and their strength based on ultrasonic device?