Effects of PV transformer energization on power quality

The penetration of Distributed Energy Resources (DERs) continues to blur the boundary between the tradition ally held definitions of transmission and distribution systems. Increasingly, DERs are being connected at the sub-transmission and distribution voltage levels. As is the case with any new technology, the proliferation of such generation resources has led to certain unforeseen outcomes. This paper examines the effect on the power system (with regards to power quality), of the transformers that are being used to integrate DERs to the system. Two case studies from two different utilities in the United States, pertaining to Solar PV transformer energization are presented. One case study pertains to transformer energization and system unbalance leading to harmonic resonance issues while the other shows distortion around the zero crossing of the voltage caused by ringing during energization of PV transformers connected to solar inverters. A third, simulation case study examines PV transformer energization that excites resonance in systems containing transmission cables. Detailed analyses of the phenomena, underlying causes and mitigation techniques are presented. Finally, shortcomings with respect to modeling techniques and lessons learned in the process have been described. The paper closes with a description of future research avenues and expected work with regards to Power Quality in this field.