Transformer Aging due to High Penetrations of PV, EV Charging, and Energy Storage Applications

High penetrations of photovoltaic (PV) systems, energy storage (ES) devices, and electric vehicle (EV) charging may significantly affect the operational constraints of substation power transformers. In high penetrations these applications can flatten a transformer's daily load profile, which minimizes the cooling down period for the unit's paper insulation. Also, because these applications rely upon power electronics to interface with the electric grid, high penetrations can increase the volume of harmonic currents propagating through the distribution system, which can also impact transformer aging. Although the initial impact of PV and ES applications may reduce a unit's peak energy demand, long-term system planning and emergency operating conditions may require derating of existing capacity limits to prevent aging that impacts overall life expectancy. To identify transformer aging characteristics as a function of load profile and harmonic content, the authors developed a transformer transient model based upon the tested attributes of a 50MVA SPX Waukesha transformer and the modeling methods described in IEEE Std. C57.90 and IEEE Std. C57.110. Utilizing the model, the authors identified the relationship between aging, harmonic distortion, and load profile characteristics associated with high penetrations of PV, ES applications, and EV charging.