Feasibility study on distribution transformer based urban grid connected energy islands with distributed generation

Abstract

Sri Lanka’s distribution network has been facing drastic changes during recent past due to the continuous addition of distributed renewable generation into the network. Addition of rooftop solar PV into the low voltage distribution feeders has significantly increased during 2016-2017, due to the government initiative “Surya Bala Sangramaya” on promoting rooftop solar generation. As a result, in highly populated urban areas, some distribution transformer service areas now have more than 50% of installed solar rooftop capacity, compared to the connected transformer capacity. These transformers export power to the medium voltage network from low voltage side during daytime due to high solar generation and low energy usage inside these service areas. An increasing number of transformers will experience such reverse power flow in near future with the acceleration of promoting rooftop solar programs. Operating with higher density of rooftop solar in distribution transformer service areas will result in numerous power quality issues and higher distribution losses in spite of the advantages of utilizing household rooftops for solar PV generation. In this study, a futuristic solution is proposed to effectively utilize the daytime solar PV generation in a single distribution transformer service area itself with the formation of smart grid type operation. Distribution transformer based smart grid, which operates with controlling mechanisms, loads, rooftop solar and battery storage systems is discussed in this report. This system can be developed and operated as a community-based smart grid that is formed inside the distribution transformer service area with the contribution of the electricity customers. Other than operating as individual energy customers and energy producers, public can become procumers who operate and control their loads and PV generation together to optimize load flow, power quality and economics in this proposed smart grid. This research is a preliminary study to identify the possibility of such distribution transformer based smart grid for Lanka Electricity Company Private Limited operation area. Extensive simulations were carried out using Matlab Simulink by modeling the three phase four wire LV network for a single transformer area to identify the present behavior of the LV Network. Then the model was upgraded to proposed future smart grid arrangement. Results on the customer behaviors, load flows and power quality on both normal and smart grid type scenarios are presented for several case studies including the present situation, future expected situation and for the proposed smart grid. As the outcome of this research, simulated results were obtained for smart grid arrangement inside an actual transformer service area and technical compatibility of the concept is presented to the Sri Lankan urban distribution transformers.