Everything you need to know about partial discharges

                                                                                         

Discharges prevent the equipment from working properly and therefore it eventually breaks down. To avoid this and to have a proper usage of the electrical equipment, it can be verified and maintained using partial discharge testing and partial discharge analysis.

A partial discharge is defined as a small electrical spark that takes place inside the electrical insulation of cables, transformers and other electrical components of engines and generators. These partial discharges may occur in liquid, solid or gas installations due to: the deterioration of the insulation condition or to the improper installation, faulty design or handicraft (in the case of joints and terminations created on the spot). After occurring once, partial discharges may develop into electrical trees that eventually lead to serious malfunctions and breakdowns.

Partial discharge analysis is a tool for predictive maintenance for some switchgear systems, like the medium-voltage ones. This partial discharge analysis is the latest technology that is being applied to electrical equipment, being able to detect malfunctions like corona or surface tracking.

Partial discharge testing is used in order to verify the integrity of installations and its testing uses Partial Discharge (PD) measurements that can safely indicate which part from the system is in need of assistance or maintenance. However, there are both dangerous and partially beneficent PD testing techniques and this is why a proper recognition must be done by experts. The PD testing may be done online or offline and it consists, practically, in measuring the breakdown currents in insulating materials.

Online PD testing helps the partial discharging analysis by determining the trends in partial discharges activity and the conditions that determine them: environmental (humidity, temperature) or service conditions. The partial discharge testing has proved, especially in the last ten years, to be highly effective in determining insulation degradation before the breakdown.

The partial discharge analysis method is the most used is the phase-resolved (PRPDA), in connection with the phase-resolved partial discharge (PRDA) patterns.

The online PD testing and analysis have become in the last 10 years crucial tools in motor maintenance; they have lead to a database that can already offer information about which factors are more (like voltage class) or less (insulation type and age of the winding) important, to significant risks for motors, and, newly, to a rough assessment of the stator winding insulation condition, without being necessary to wait for them to take place inside the equipment. So, this type of testing and analyzing is without doubt very useful and deserves your attention!

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