Practical Impact of Not Self-disconnected VSPP During Faults and Unintentional Islanding on Distribution System Reliability

The promotion of small-scaled distributed generation (DG), commonly known as Very Small Power Producer (VSPP) in Thailand's electric power industry, is derived from its incentive policy, energy efficiency, and environmentally friendly attribute. For this reason, distribution networks have seen a high penetration level of VSPPs powered by conventional or renewable energy resources. Although VSPPs have economic and environmental benefit of the sustainable energy, they have imposed technical barriers and established new requirements for control and protection system of the distribution networks. This paper investigates the possible negative impacts of VSPPs on control and protection systems of distribution networks located in a metropolitan area. Three case studies of real, existing VSPP in 24 kV distribution network are practically presented with short-circuit analysis and dynamic analysis primarily focusing on undisconnected VSPP during faults, and unintentional islanding. The study results show that without proper measures to address the issues on the existing control and protection system, the distribution network would be unable to maintain its integrity of electricity power supply for disturbance incidents.