What diagnostic technique is most effective at detecting insulation degradation in a hydro-generator's stator winding while the machine is in operation?

Partial Discharge (PD) monitoring is the most effective diagnostic technique for detecting insulation degradation in a hydro-generator's stator winding while the machine is in operation. Partial discharges are localized electrical discharges that occur within insulation systems when the electric field stress exceeds the dielectric strength of a small portion of the insulation. These discharges are often the first sign of insulation deterioration and can lead to eventual insulation failure. PD monitoring systems detect these discharges by sensing the high-frequency electrical pulses, acoustic emissions, or electromagnetic radiation they generate. Unlike offline tests such as insulation resistance tests, PD monitoring can be performed continuously while the generator is online, providing real-time information about the condition of the insulation. This allows for early detection of developing problems, enabling proactive maintenance to prevent costly unplanned outages. By analyzing the magnitude, frequency, and location of PD events, engineers can assess the severity of the insulation degradation and identify specific areas of concern within the stator winding.