Amplitude Considerations for Transformer UHF PD Measurements

Bridging the Gap Between UHF Detection and Conventional PD Assessment

Ultra High Frequency (UHF) partial discharge monitoring is rapidly gaining acceptance for transformer diagnostics, with new transformers increasingly manufactured with multiple UHF sensors installed. Yet a critical question remains unanswered: How do you assess transformer risk using UHF measurements when conventional IEC 60270 standards define failure thresholds in picocoulombs—a calibration that's impossible with UHF retrofit sensors?

This technical whitepaper from Qualitrol tackles the industry's most contentious UHF measurement challenge: relating amplitude readings in dBm or percentage to the established picocoulomb risk assessment framework that defines when partial discharge becomes destructive.

What You'll Discover:

Understand why conventional PD monitoring methods—electrical measurements at bushing taps and acoustic detection—have fundamental limitations in sensitivity, localization, and susceptibility to external interference. See how these challenges have driven the adoption of UHF technology despite its amplitude calibration limitations.

Explore detailed experimental results comparing IEC 60270 apparent charge measurements with simultaneous UHF readings in both test tanks and transformer models. Discover the surprising variability: even from the same discharge source, apparent charge fluctuates between 100 and 600 pC for different pulses, yet UHF measurements show consistent repeatability.

Learn the four critical conditions that enable meaningful UHF amplitude assessment: knowing the discharge source location, establishing sensitivity verification procedures, identifying defect type through pattern analysis, and understanding signal propagation paths through transformer geometry.

The research demonstrates that while direct dBm-to-pC conversion remains controversial and complex, accurate localization of the PD source using time-of-flight techniques becomes the linchpin for effective risk assessment—enabling correlation between UHF display ranges and established CIGRE failure thresholds.

Download this essential whitepaper to understand how proper UHF implementation and localization strategies enable meaningful transformer condition assessment despite calibration limitations.