Online Partial Discharge Testing of a 10 MVA, 6.6 kV Synchronous Generator
Detecting Insulation Defects Before They Become Failures
Partial Discharge (PD) monitoring is one of the most effective diagnostic tools for assessing the condition of high-voltage rotating machines. Recently, an online PD assessment was performed on a 10 MVA, 6.6 kV synchronous generator, providing valuable insight into the health of the stator insulation system while the machine remained in service.
Why Perform Online PD Testing?
Stator insulation degradation is one of the leading causes of unexpected generator outages. Online PD testing allows asset owners to identify developing defects at an early stage, enabling condition-based maintenance and reducing the risk of costly failures.
Common insulation defects that can be detected include:
Slot discharge
Delamination within insulation layers
Surface discharge
Sparking and loose components
Contamination-related insulation stress
Because measurements are performed during normal operation, the results reflect the actual electrical stresses experienced by the machine.
Measurement Setup
The assessment was carried out using dedicated PD sensors and coupling capacitors installed on the machine terminals. Data was collected and analyzed in accordance with IEC 60034-27, the international standard for online partial discharge measurements on rotating electrical machines.
The monitoring system captured:
PD magnitude and activity levels
Phase-resolved partial discharge (PRPD) patterns
Trending information
Noise separation and source identificatio
PRPD Pattern Analysis
A key part of any PD investigation is interpretation of the Phase Resolved Partial Discharge (PRPD) patterns.
Different insulation defects generate unique PD signatures. By evaluating discharge activity relative to the AC voltage waveform, specialists can distinguish between:
Internal void discharges
Slot discharges
Surface tracking
Corona activity
Sparking defects
The measured PRPD patterns indicated the characteristic behavior required to identify the dominant discharge sources and assess the severity of insulation deterioration.
Continuous Monitoring for Critical Assets
Beyond periodic inspections, permanent PD monitoring systems provide continuous visibility into insulation performance.
Modern monitoring platforms enable:
Real-time condition monitoring
Automated alarm functions
PD trending and analytics
Remote access and diagnostics
Early warning of insulation degradation
For critical generators, this approach supports predictive maintenance strategies and helps maximize equipment availability.
Benefits of Online PD Testing
Online generator PD diagnostics offer several advantages:
No interruption of operation
Early detection of insulation defects
Reduced risk of unplanned outages
Improved maintenance planning
Support for life extension decisions
Compliance with IEC 60034-27 recommendations
How NEKA Can Help
NEKA provides specialized Partial Discharge testing, monitoring, and diagnostics for high-voltage cable systems, generators, motors, transformers, and GIS installations. Our services range from short-term diagnostic campaigns to permanent condition monitoring solutions, helping asset owners make data-driven maintenance decisions and improve network reliability.
Interested in assessing the condition of your rotating machines? Contact NEKA to discuss PD testing, continuous monitoring, and condition assessment solutions tailored to your assets.
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