WHAT ARE PARTIAL DISCHARGES?
Partial Discharges (PD) are "sparks", surges of electrons and ions occurring in voids and gaps within or adjacent to the insulation of High Voltage machines.
Partial Discharges are significant contributors to the progressive deterioration (aging) of the High Voltage insulation and its failure.
Partial discharge creates Ozone which bonds with Nitrogen and moisture from the air, creating Nitric acid that destroys the insulation.
PDA testing is used to monitor quality of the stator insulation while the generator is in service.
By detecting rapid deterioration in insulation, PDA gives an early warning and helps prevent catastrophic in-service failures, costly repairs, and unplanned outages.
PDA test can identify the severity of main winding problems such as:
Stator winding is the most expensive electrical element of a generator or motor. According to the hydro utilities statistics, stator winding is the most common electrical problem and is the most expensive to fix.
Any in-service failure of generator winding is catastrophic and very costly to repair. PDA test allows maintenance to be based on the actual winding condition rather than time based maintenance.
How do we test for the PD activity?
Test is taken on-line during regular "normal" working regimes and does not need outages.
The on-line test is not destructive like some off-line tests and can be performed when needed, without interrupting normal operation.
Multimillion dollar damage on a stator winding
In the event of an in-service failure, there would be tremendous repair costs as well as loss of production cost, which could be much greater.