What is a PRPD diagram, and how does it support the analysis of electrical partial discharges?

PRPD stands for Phase Resolved Partial Discharge. A PRPD diagram displays detected partial-discharge events in relation to the phase of the line voltage.

Electrical partial discharges often do not occur evenly throughout the entire voltage cycle. Instead, events may accumulate within specific phase ranges. The resulting pattern provides additional information about the type and behavior of the discharge.

PRPD display on the SONASCREEN 2

In Partial Discharge mode, the SONASCREEN 2 displays the PRPD diagram live. At the same time, the position of the acoustic sound source is shown in the camera image.

During a measurement, the detected partial discharge is kept within the specified measurement area until sufficient data has been collected. The measurement can then be saved for further evaluation.

The PRPD diagram supports:

• assessing whether the detected acoustic events are related to the line frequency,
• identifying recurring phase-related patterns,
• distinguishing partial discharges from non-synchronous background noise,
• documenting and comparing measurements.

Evaluation using PDReport

Saved measurements can be analyzed and documented further using PDReport. The software automatically detects the line frequency and displays the acoustic signal as a PRPD diagram.

PDReport also supports automatic differentiation between corona and surface partial discharge.

Limitations of the assessment

A PRPD pattern is an important evaluation tool, but it does not provide a final diagnosis of the electrical equipment on its own.

The assessment should also consider:

• the position of the sound source,
• the acoustic signal,
• the PRPD pattern,
• the condition and operating state of the system,
• comparison with previous measurements,
• results from additional electrical testing methods where required.

The evaluation must be performed by appropriately qualified personnel.