Technical Publications

In modern grids, the synergistic effect of sub-threshold harmonics (
) and periodic minor overloads (load factor
) accelerates the thermal fatigue of 110kV oil-immersed transformers. Since these stresses remain within standard compliance boundaries (IEEE Std 519 and IEC 60076-7), they evade static SCADA alarms, creating a critical monitoring blind spot. To address this, this paper formally defines this operational state as the Green-Zone Dual Stress (GZDS) scenario. We propose a white-box dual-engine physics-informed framework tailored for GZDS, integrating the IEEE Std C57.110 eddy current loss factor and the IEEE Std C57.91 Arrhenius thermal aging equation to precisely quantify hidden lifespan losses. Anchored on the standard 20.55-year baseline design life, one million Monte Carlo evolutionary simulations reveal that GZDS synergy induces an average lifespan reduction of 9.83% (2.02 years). Under the extreme compliance limit (constant 105% load, 5% THD), this reduction surges to 22.72% (4.67 years), quantitatively shattering the traditional assumption of “zero damage” in the SCADA green zone. Furthermore, an Equivalent Operating Time (EOT) tracing algorithm based on a 1-year sliding window is proposed to smooth seasonal phase distortions. In exhaustive full-lifecycle traversal tests, this algorithm predicts future extra lifespan losses with an ultra-low average relative error of 0.31% (3.10 days). This framework provides grid dispatchers with computationally lightweight, physically self-consistent indicators for proactive asset management.