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Electric Arc, Corona, Tracking Detection
There are three basic electrical problems that are detected with the Ultraprobe 2000:
Arcing:
An arc occurs when electricity flows through
space. 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, the air around it begins to ionize to form a blue or purple glow.
Tracking:
Often referred to as "baby arcing", follows the
path of damaged insulation.
Although theoretically the Ultraprobe 2000 can be used in low, medium and high voltage systems, most of the
applications tend to be in medium and high voltage systems. 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,
contactors, junction boxes. In substations, components such as insulators, transformers and bushings may be
tested. Ultrasonic testing is often used at voltages exceeding 2,000 volts, especially 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 to perform 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.
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 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-2000 Ultrasonic Waveform Concentrator (a parabolic reflector) which will
double the detection distance of the Ultraprobe and provide pinpoint detection. The UWC-2000 is
recommended for those situations in which it may be considered safer to inspect electrical apparatus at a
distance. The UWC2000 is extremely directional and will locate the exact site of an electrical discharge.
CHECK TRANSFORMERS, SWITCHGEARAND
OTHER ELECTRICAL APPARATUS
