Enhancing PV Penetration in LV Networks Using Reactive Power Control and On Load Tap Changer With Existing Transformers

Abstract

Voltage rise beyond statuary limits in low voltage (LV) ac networks due to high photovoltaic (PV) penetration and its mitigation using multiple techniques was assessed. Investigations using a real rural domestic overhead LV network were done through load flow simulations. A three-phase four wire medium length LV network with a fixed tap transformer and PV inverters operating at unity power factor was able to host PV between 79%–98% of transformer ratings for five different PV configurations. For the case studied at this penetration level three, limiting factors (voltage, thermal loading limits of lines, and transformer) come together. Three techniques were utilized to control the voltage across the LV network. On load tap changer (OLTC) control was found more robust than reactive power control (RPC). Hybrid control (OLTC and RPC) was found beneficial only for extra high PV penetration scenarios. Replacement of a few critical line spans and the existing transformer with higher capacity conductors and an OLTC equipped transformer (higher size) enabled the network to host an additional 50%–90% PV. The unequal distribution of single-phase PV systems among three phases has negative effects on penetration. Consideration of PV integration while planning new LV networks and retrofitting of OLTCs with existing transformers, could make the LV system more PV friendly. The RPC option, though less effective than OLTC due to increased current, can be beneficial at medium penetrations where OLTC may become a costly solution.