What are the different types of Partial Discharge?

Published 18 Nov 2019

Republished from LinkedIn with kind permission of Neil Davies | EA Technology Australia | Helping Owners and Operators of Electrical Assets Improve Reliability and Efficiency

  • uploaded by Chris Dodds | Thorne & Derrick Sales Marketing Manager

Partial Discharge

Neil Davies

Partial Discharge (PD) can be classified into 3 main types:

Internal Partial Discharge, occurring inside insulation

Surface Partial Discharge, tracking across insulation

Corona Partial Discharge, from a sharp electrode into gas

Internal PD is the silent defect where there will be no sound, smell or visual indication of a problem prior to failure. If you witness the aftermath of a compound insulated cable box failure, you will see how the build-up of pressure can lead to a very disruptive and dangerous explosion.

Surface PD occurs across the surface of insulation. When alternative materials to porcelain started to be introduced into switchgear and dry cable terminations started being widely introduced, some critical aspects of design and installation were not fully appreciated. This led to a spike in failure rates due to surface PD. When developed, it will produce the crackling and ozone smell.

Corona PD is what we often hear in outdoor switchyards, particularly when humid. Corona at sharp points in switchyards isn’t usually detrimental. However, if corona activity occurs inside enclosed chambers and there is no airflow to remove chemical reactions, then it can lead to the onset of surface PD and problems.

Partial Discharge


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