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TRANSFORMERS, SWITCHGEAR AND OTHER ELECTRICAL APPARATUS
E. ELECTRIC ARC, CORONA, TRACKING DETECTION
There are three basic electrical problems that are detected with the Ultraprobe 10000:
Arcin
g: An arc occurs when electricity is conducted to “ground”. This is over a high current pathway. 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. This is where air is the only pathway to
ground.
Tracking
: Often referred to as "baby arcing", it follows the path of damaged insulation over a low current pathway.
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.
Typical applications include: insulators, cable, switchgear, buss bars, relays, circuit breakers, pot heads, junction boxes. In substa-
tions, 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 its’ accessories.
The method for detecting electric arc and corona leakage is similar to the procedure outlined in leak detection. 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
wide-band 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
mid-line 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 systems, a quick scan of bus bars often will pick up arcing or the tracking from 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 recommended for those situations in which it may be considered safer to
inspect electrical apparatus at a distance. The UWC-10 is extremely directional and will locate the exact site of an electrical discharge.
