## 1 Introduction
The new load profile, which is flatter than the historical profile, can possibly lead to increased operating temperatures given the same peak demand. The increased transformer temperatures can lead to higher than expected losses, aging, and damage when compared to the operation of a power transformers serving a historical cyclic load profile. As the energy demand approaches the pre-established capacity limit of a transformer, internal operating temperatures increase at an exponential rate, which inherently increases the temperature at the hottest spot and thereby the aging of the transformer insulation [2]. As evident in Figure 1, which represents the aging of a 50 kVA transformer unit as a function of per unit load, aging increases nonlinearly when the peak demand is greater than 0.95 per unit at rated ambient temperature. For a flattened load profile, which is considered abnormal by IEEE Std. 57.91, this excessive aging occurs for longer periods of time when compared to that of a traditional cyclic load profile [2]. For operations beyond the established capacity limit, sustained internal temperatures beyond recommended IEEE limits can result in equipment damage and/or catastrophic failure [2]. The research performed by [PERSON] illustrated how a flattened load profile will increase the aging of a 50 MVA SPX Waukesha power transformer due to increased temperatures at the hottest spot [6]. The goal of the research was to determine if high penetrations of PV, ES applications, and EV charging would affect the aging of a typical substation transformer in the US. Utilizing the results from various research endeavors focusing on the grid impact of PV, ES applications, and EV charging, the authors established two test load profiles, one representing the historical load profile and a second representing the effects of high penetrations of PV, ES applications, and EV charging. Transformer aging due to both load profiles were analyzed and compared with the methods described IEEE Std. C57.91-2011 [2]. The analysis revealed that given the same peak demand, a flattened profile can age transformer insulation at a rate 50% greater than expected [6]. With aging identified previously, the author's goal for this manuscript is to determine how to mitigate the excessive aging induced by high penetrations of PV, ES applications, and EV charging. Although the initial impact of increased penetration rates of renewable energy devices and ES applications may lower the peak energy demand on substation transformers, long-term system planning dictates that utility companies utilize substation transformer units to their full capacity [1; 9]. Consider the long-term options when a substation unit fails on a system serving flattened load profiles. If ES applications have severely reduced the peak demand as compared to the historic demand, the utility would have no incentive to install a unit with the same peak capacity. The load is picked up indefinitely by a neighboring unit or the unit is replaced with a smaller and less expensive unit. From a power system planning perspective, there are still thousands of units in existence on the grid that should be utilized to their full potential [10; 11; 12]. Therefore, over time \"underloaded\" units would be phased out as the equipment fails or is upgraded. Integration of PV, ES applications, and EV charging requires the implementation of power electronics, which increase the harmonic distortion on the grid. The heat generated from harmonic distortion also contributes to the internal heating of a transformer, which increases aging and can thereby impact capacity limits [9; 13; 14]. Although there are equipment standards that limit the amount of harmonic distortion induced by a single device, system values exceeding IEEE Std. 519-2014 harmonic voltage limits have been recorded on power systems even though the induced harmonic current levels are considered acceptable [15; 16; 17; 18].