Research On Protection Scheme For Distribution Network With Distribution Generations

With the development of the related technology of distributed generations in recent years, it has become a trend for distributed generations to be connected to the power grid. Traditional distribution network is a radial one where power is supplied by single-ended power source. With the increase of penetration level of distributed generations, bidirectional power flow occurs in distribution network, which will bring a series of problems to traditional current protection and control scheme.Firstly, the article analyzes the influence of distributed generations on distribution network protection. Due to bidirectional power flow, assistant current and shunting effect caused by distributed generation, the article analyzes the influence on protection action. Influence on automatic reclosing, including acceleration before reclosing and acceleration after reclosing, is explained in the article. And then the article analyzes influence on the island line protection.Secondly, this paper proposes a distribution network protection scheme based on the coordination of zoned pilot protection and improved genetic algorithm. The distribution network is partitioned according to the location of distributed generation. Directional pilot protection is installed at the zones with distributed generations and the improved genetic algorithm is applied in each zone to locate fault area. This paper proposes an improved fuzzy adaptive simulated annealing genetic algorithm by integrating fuzzy inference and adaptive simulated annealing genetic algorithm. This algorithm improves fault tolerance of the fitness function, adopts the adaptive strategy and the optimal individual reserve strategy in genetic selection, calculates fuzzy adaptive crossover operator and fuzzy adaptive mutation operator by combining fuzzy inference and adaptive strategy, and adopts simulated annealing algorithm to improve convergence speed and local search ability. The case studies demonstrate the feasibility and effectiveness of the proposed scheme which does not need any complicated communication devices.Finally, based on research of relevant new protection schemes, this paper proposes a wide area protection scheme for smart distribution network with distributed generations. The distribution network is partitioned according to the coordination of distributed generation and loads. After the distribution network is partitioned, splitting equipments and advanced feeder terminal units are installed at the borders of the zones with distributed generations. For zones without distributed generations, only advanced feeder terminal units are installed. The proposed scheme includes two parts:advanced feeder terminal units based fault zone identification and intelligent electronic devices based fault section location. Advanced feeder terminal units can detect local real-time information and exchange information with adjacent advanced feeder terminal units. Therefore, the fault zone could be identified. When splitting conditions of splitting equipment are satisfied, the splitting points will be disconnected and the fault zone will be intentionally islanded. intelligent electronic devices installed in the fault sections will exchange information with adjacent ones, and then the fault section could be located and isolated. By theoretical analysis of the island stable operation problem, the intentional islanding scheme considers the capacity of distributed generations and the uncertain distributed generation output. It can ensure the stable operation state of the islanded zone and make full use of generating capacity of distributed generation. The control strategy of reclosing and reconnection of island proposed in this paper can eliminate transient faults and reconnect the island to distribution network without any asynchronous problems. Case analysis is conducted to validate the protection scheme under various fault situations. The feasibility and effectiveness of the proposed scheme is demonstrated by the case studies. The scheme can reduce the power failure area and improve the reliability level of power supply. As to provide theoretical basis for distribution network protection, the protection scheme is straightforward and possesses application value.The two distribution network protection schemes proposed can effectively solve the protection problems caused by distributed generations connected to distribution network, providing theoretical basis for distribution network protection.