Introduction; General; Airborne Ultrasonic Discharge Activity; Electromagnetic Discharge Activity - EA Technology UltraTEV Monitor Operating Manual

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2

Introduction

2.1

General

Partial discharges are electric discharges that do not completely bridge the electrodes.
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
Acoustic:
 Audio
 Ultrasonic
Gases:

Ozone

Nitrous oxides
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 Monitor has
been specifically developed to enable electromagnetic and ultrasonic activity to be monitored in a
single simple to use instrument.
2.2

Airborne Ultrasonic Discharge Activity

Acoustic emissions from partial discharge activity are normally at a frequency too high for the human
ear, i.e. ultrasonic. As the partial discharge progresses towards failure the frequency sometimes
decreases into the audible range.
Using an instrument to detect the ultrasonic signal has several advantages: instruments are more
sensitive than the human ear, are not operator dependent and ultrasonic frequencies are more
directional. The most sensitive method of detection is using an airborne ultrasonic microphone. This
method is very successful at detecting partial discharge activity provided there is an air path between
the source and the microphone. However, in the case of sealed switchgear with no air path, an
ultrasonic contact probe can be magnetically attached to the external surface of the switchgear to
monitor internal activity.
2.3

Electromagnetic Discharge Activity

When partial discharge activity occurs within high voltage switchgear it generates Transient Earth
Voltages (TEV) and electromagnetic waves in the radio frequency range.
UltraTEV Monitor Operating Manual
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