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Transformers, switchgear another electrical apparatus
Electric arc, Corona, Tracking Detection
There are three basic electrical problems that are detected with the Ultraprobe 10000:
Arcing: An arc occurs when electricity is conducted to “ground”. Lightning is a good example.
Corona: When voltage on an electrical conductor, such as an antenna or high voltage transmission line
exceeds the threshold value of the air around it, air begins to ionize and form a blue or purple glow.
Tracking: Often referred to as „baby arcing“, it follows the path of damaged insulation.
The Ultraprobe 10000 can be used in low (below 15 kV), medium (15 kV – 115 kV) and high voltage
systems (above 115 kV).
When electricity escapes in high voltage lines or when it „jumps“ across a gap in an electrical
connection, it disturbs the air molecules around it and generates ultrasound. Most often this sound will
be perceived as a crackling or „frying“ sound, in other situations it will be heard as a buzzing sound. Typ-
ical applications include: insulators, cable, switchgear, buss bars, relays, circuit breakers, pot heads,
junction boxes. In substations, components such as insulators, transformers and
bushings may be tested.
Ultrasonic testing is often used in enclosed switchgear. Since ultrasound emissions can be detected by
scanning around door seams and air vents, it is possible to detect serious faults such as arcing, tracking
and corona without taking the switchgear off line as in an infrared scan. However, it is recommended that
both tests be used with enclosed switchgear.
NOTE: When testing electrical equipment, follow all your plant or company safety procedures. When in
doubt, ask your supervisor. Never touch live electrical apparatus with the Ultraprobe or it’s
accessories.
The method for detecting electric arc and corona leakage is similar to the procedure outlined in leak de-
tection. Instead of listening for a rushing sound, a user will listen for a crackling or buzzing sound. In
some instances, as in trying to locate the source of radio/TV interference or in substations, the general
area of disturbance may be located with a gross detector such as a transistor radio or a
wideband interference locator. Once the general area has been located, the scanning module of the
Ultraprobe is utilized with a general scan of the area. The sensitivity is reduced if the signal is too strong
to follow. When this occurs, reduce the sensitivity to get a midline reading on the meter and continue
following the sound until the loudest point is located.
Determining whether a problem exists or not is relatively simple. By comparing sound quality and sound
levels among similar equipment, the problem sound will tend to be quite different. On lower voltage sys-
tems, a quick scan of bus bars often will pick up arcing or a loose connection. Checking junction boxes
can reveal arcing. As with leak detection, the closer one gets to the emission site, the louder the signal.
If power lines are to be inspected and the signal does not appear to be intense enough to be detectable
from the ground, use UE Systems UWC-10 Ultrasonic Waveform Concentrator (a parabolic reflector)
which will double the detection distance of the Ultraprobe and provide pinpoint detection. The UWC-10 is
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