In December 2015, ZTZ added BMS to the high-side bushings of a 17-year-old 270 MVA generator step-up (GSU) unit, using 3 C1 taps and 3 CCVT inputs. 

ZTZ’s Technical Expertise

Over four months, ZTZ tracked worsening trends and asserted high-confidence alarms, enabling reliance on the system over labor-intensive offline testing. Their polar plot analysis of leakage currents showed strong polarization, building operator trust for timely action. 

Evidence of Monitoring Use

Two months post-install: H2 C1 at 0.5% above nominal (blue trace in 2-month plot). 

PF peaked at 1.5% (red trace), escalating to 8% by month four. 

High-side imbalance current rose steadily to 8.0% (polar plot), confirming imminent failure risk. This data-driven progression allowed bushing replacement, preventing outage in a critical power plant setting.