Practical impact of VSPP in distribution networks: Intentional islanding operation

The promotion of small-scaled distributed generation, commonly known as Very Small Power Producer (VSPP) in Thailand's electric power industry, is derived from its incentive policy and environmentally friendly attribute. For this reason, distribution systems have seen a high penetration level of distributed generation powered by conventional or renewable energy resources. One of the main benefits for having VSPPs is the improvement of system reliability perceived by customers due to the availability of additional backup generations. Such a positive impact can, nevertheless, be only achieved when intentional islanding operation is permitted. That is, without the local utility grid, an isolated system is formed and local loads obtain electricity supply from the VSPPs located in the connected area. This paper investigates the impact of VSPPs based on intentional islanding operation aspects. Two case studies with 12 and 24 kV distribution systems are practically presented with dynamic analysis for the different types and locations of VSPPs. The study results show that the VSPPs are useful as alternative generation backup during the loss of the main supply as a result of equipment outage. It can be seen that after the occurrence of a fault and an islanding subsystem has been subsequently formed, the generation is redispatched to meet the local demand, and the VSPPs can maintain its frequency and voltage of the subsystem within the standard criteria. Electric utilities should, therefore, pay special attention on their existing control and protection systems in order to have their system to remain integrity.