About
Partial Discharge (PD) is a dielectric breakdown of a insulation system
under high voltage stress which bridges between two conducting
electrodes. It can be found at any point of an insulation system, where
the electric field strength is over the breakdown strength of the
insulation material. It occurs as symptoms of a number of failure
mechanisms related to motors, generators, cable, transformer and
switchgear.
PD can be destructive if it is not handled properly. It causes
deterioration of components which may lead to catastrophic outcomes,
such as power outage, employee injury, production loss and etc. are all
possible consequences when PD is not discovered or handled properly in
time.
PD testing and monitoring of in-service high voltage equipments and
plant is a new trend of service which notifies the user immediately
with any possible faults and deterioration in the high voltage
insulation system. Then users can take action to the PD activity in
order to prevent any destructive result from happening. Testing can
correctly identify and warn of active failure mechanisms as below:
- Contamination
- System aging
- Loose stator windings
- Poor manufacturing
- Poor installation
- Thermal deterioration
By time-based maintenance (TBM), the equipment would be replaced at the
end of its lifetime expectancy regardless of its insulation condition.
Once the insulation aging is slower than expectation (orange line in
Fig.1), the equipment is still replaced beyond its real poor insulation
condition. By condition-based maintenance ( CBM ), the equipment would
be replaced only if its insulation condition lowers than acceptance
level. On-line PDM is one approach to implement CBM.
PDCare first came out in 2010 as a concept which integrated all
resources, technology and field experience of decades; it remedies the
drawback of both traditional diagnostic test and on-line monitoring
equipment on insulation breakdown maintenance. Traditional diagnostic
test can discover defects of an insulation deterioration, but it is
unable to minimize the risk of potential failure which may lead to
catastrophic results. Although increasing the test frequency can
successfully lower the failure rate, the cost of maintenance would
raise dramatically. On the other hand, on-line monitoring equipment, a
convenient device that detects and informs the user of any partial
discharge activity; however, it is not able to distinguish noise or PD
activity. In addition, it is unable to evaluate risk level and locate
PD source. With PDCare, all these problems can be resolved.