Non-Intrusive Detection Of Partial Discharge Activity - EA Technology UTL2 Operating Manual

EA Technology
1.2

Non-Intrusive Detection of Partial Discharge Activity

Partial discharges are electric discharges that do not completely bridge the electrodes. The
magnitude of such discharges is usually small however they do cause progressive deterioration of
insulation that may lead to eventual failure.
Non-intrusive partial discharge detection provides a means for identifying these potential sources
of insulation failure that result not only in loss of supply to customers but can also endanger staff.
A partial discharge emits energy in the following ways:
Electromagnetic:
•
Radio
•
Light
•
Heat
The most practical techniques for non-intrusive testing are based on the detection of the radio
frequency part of the electromagnetic spectrum and ultrasonic emissions. The UltraTEV range has
been specifically developed to enable electromagnetic and ultrasonic activity to be detected in a
single simple to use instrument.
Airborne Ultrasonic Discharge Activity
Acoustic emission from partial discharge activity occurs over the whole acoustic spectra. Audible
detection is possible but depends on the hearing ability of the individual. Using an instrument to
detect the ultrasonic part of the acoustic spectra has several advantages. Instruments are more
sensitive than the human ear, are not operator dependent and operating above the audible frequency
are more directional.
The most sensitive method of detection is using an airborne ultrasonic microphone centred at 40
kHz. This method is very successful at detecting partial discharge activity provided there is an air
passage between the source and the microphone.
Electromagnetic Discharge Activity
When partial discharge activity occurs within high voltage switchgear it generates electromagnetic
waves in the radio frequency range which can only escape from the inside of the switchgear through
openings in the metal casing. These openings may be air gaps around covers, or gaskets, or other
insulating components. When the electromagnetic wave propagates outside the switchgear it also
impinges on the metal casing of the switchgear producing a transient in the earth potential. The
Transient Earth Voltage (TEV) is only a few millivolts and lasts only a short time with a rise time of a
few nanoseconds.
UltraTEV Locator Probe Operating Manual
Acoustic:
•
Audio
•
Ultrasonic
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Gases:
•
Ozone
•
Nitrous oxides