Digital Partial Discharge Testing: A Comprehensive Guide to Measurement Interpretation and Analysis

Proper interpretation of partial discharge measurements is crucial for accurate assessment of insulation condition in high-voltage equipment. This guide provides essential knowledge for technicians and engineers to effectively analyze PD data obtained from digital testers and make informed maintenance decisions.

Understanding Partial Discharge Patterns

Different types of insulation defects produce distinctive PD patterns that can be identified through phase-resolved partial discharge analysis. Common patterns include:

• Surface Discharges: Typically appear as rabbit-ear patterns symmetric in both half-cycles

• Internal Voids: Show as rounded patterns occurring mainly in first and third quadrants

• Corona Discharges: Display as sharp peaks at voltage zero-crossings

• Floating Potential Discharges: Appear as narrow bands in phase-resolved patterns

Key Parameters for PD Assessment

When evaluating partial discharge activity, consider these critical parameters:

• Apparent Charge (pC): Magnitude of discharge pulses

• Repetition Rate: Frequency of discharge occurrences

• Phase Position: Location within voltage cycle

• Pulse Shape: Rise time and duration characteristics

• Temperature Dependence: Behavior changes with temperature variations

Trend Analysis and Historical Comparison

Effective PD monitoring requires tracking changes over time. Key aspects include:

• Establishing baseline measurements for each asset

• Monitoring rate of change in PD magnitude

• Tracking pattern evolution and shape changes

• Correlating PD activity with operational parameters

• Comparing similar equipment performance

Noise Identification and Suppression

Accurate interpretation requires distinguishing true PD signals from noise sources:

• External Interference: Radio transmissions, switching operations

• Measurement System Noise: Ground loops, cable disturbances

• Non-PD Signals: Arcing, sparking, or other electrical phenomena

Severity Assessment and Action Limits

Establishing appropriate action levels based on:

• Equipment type and voltage level

• Insulation system design and age

• Criticality of the asset

• Industry standards and manufacturer recommendations

• Historical performance data

Reporting and Documentation

Comprehensive reporting should include:

• Test conditions and environmental factors

• Measurement setup and calibration data

• PD patterns and statistical analysis

• Comparative data with previous measurements

• Recommended actions and follow-up schedule

Mastering PD measurement interpretation enables maintenance teams to make data-driven decisions, prioritize interventions, and optimize asset management strategies. Regular training and practical experience remain essential for developing expertise in this critical aspect of high-voltage equipment maintenance.