In 2015, ZTZ commissioned a 6-channel BMS on three single-phase 230/115 kV transformers using the adjacent phase method (test tap currents ~22 mA high-side, ~10 mA low-side). By 2019, after four years, the customer noted H2 PF concerns. 

ZTZ’s Technical Expertise: ZTZ performed in-depth historian data analysis, correlating PF elevation with ambient temperature and using the High-to-Low algorithm to isolate the H2-X2 bushing pair as defective. ZTZ recommended offline Doble testing and high-side oil sampling, which confirmed the issue and revealed gas anomalies. This multi-algorithm approach (e.g., imbalance calculations) demonstrated ZTZ’s proficiency in phasor-based diagnostics. 

Evidence of Monitoring Use: 

C1 trends remained ~100% baseline, but H2 was 0.5% higher than peers. 

PF charts showed H2 elevation vs. stable H1/H3; high-side imbalance reached 1.3%, with steady increases over time. 

DGA results post-recommendation: H2 had >5,000 ppm hydrogen, 12 ppm water, and elevated ethylene (34 ppm)/methane (2,694 ppm), far exceeding H1/H3 baselines—directly tied to BMS alerts. Offline tests matched: H2 PF at 0.724% (vs. nameplate 0.32%), proving the system’s predictive value in averting failure.