Test Current Effect on Reliability of Dynamic Contact Resistance Measurements for Circuit Breakers

Dynamic Contact Resistance Measurement (DRM), especially when combined with motion analysis and high-current portable test equipment (up to 1 kA), provides an effective, noninvasive way to assess the state of arcing contacts.

In this paper, it is analyzed how the amplitude of test current influences the reliability and repeatability of DRM measurements at rated operating speed, the typical field test condition.

It notes that while DRM devices commonly use several hundred amperes of DC, using a too low test current results in unstable curves, which can cause incorrect evaluation of arcing contact condition.

Tests on circuit breakers using portable high‑current sources (up to 1 kA) evaluated DRM‑based diagnostics (main/arcing contact resistance, timing, wipe). Higher test currents substantially improve DRM curve stability, repeatability, and diagnostic usefulness. At least 400 A is recommended for reliable results, 800 A or higher provides even better accuracy and lower phase‑to‑phase variation. However, motion measurements remain necessary to determine wipe and contact position, so they are still required for a complete contact condition assessment.

The study stresses that test results are only comparable when conducted under identical conditions, specifically using the same test current and similar assets. It proposes further measurements on both new and aged sister units to assess how wear and contamination affect DRM parameters and to develop reliable diagnostic thresholds.

These findings offer practical site-testing guidance and support standardized DRM practices, improving condition-based maintenance for high-voltage circuit breakers.