Table of Contents
Advertisement
3660-MANUL-V01.01.00-CDC3 Operating Manual
1.
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(s).
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
•
When the partial discharge event occurs in a cable, there will be a resulting voltage pulse coupled to the
earth sheath of the cable. These pulses will propagate away from the PD side in both directions. Once the
pulse reaches a change in impedance, this will cause a partial reflection. This results in the pulses travelling
back down the cable several times (dependent upon cable length) as they decay away.
Measurement is taken using the High-Frequency Current Transformer (HFCT) at one end of the cable. This will
reveal a pattern of pulses, where the first pulse is the direct pulse from the PD event. The second pulse is the
reflected pulse from the far end. If the PD site is at the far end of the cable, then the direct pulse and the
reflection will be very close to each other, or perhaps superimposed on each other. Conversely, if the PD site is
at the near end of the cable, the direct pulse will be received first, and then there will be a longer gap as the
pulse travelling away will have to travel nearly twice the length of the cable until it is detected.
Page 1 of 30
Advertisement
Table of Contents
