Research On Reclosing Device On Synchronization Line Of Small Hydropower Stations

With the development of small hydropower station and its unique advantages, it has gradually become one of the most important power energy. Parallel operation between small hydropower station and distribution network solves a series of problems of isolated network which are poor reliability of power supply, poor power quality and load-carrying capacity and so on. However, a large number of small hydropower stations have been incorporated into distribution network, which changed the structure and the power flow of distribution network. It obviously has adverse effects on the operation, relays and control of distribution network, which may destroy the coordination between the original reclosing device and the relays.At present, with a relatively weak single transmission line connected to the distribution network, the small hydropower stations tend to be isolated from the power grid and to be operated in isolated island when a failure occurs, in which reclosing always fails. Moreover, overvoltage in transmission line always takes place in high water season. This thesis mainly studies the existing problems of parallel operation. The main text is listed as the following:Firstly, model of IEEE5 power network is adopted for simulation and theoretical study on the effect of the parallel operation on the original three-step current relays of the distribution network based on fault location, access position and the capacity of small hydropower. The impact mechanism such as sensitivity and setting of relays is analyzed when non-selective removal of small hydropower stations takes place.In addition, based on requirements of automatic reclosing device and operation of distribution networks in faults, the research focuses on the example simulation to obtain the basic parameters and operation characteristics of reclosing operation under the terms of permanent fault, non-voltage verification and variation characteristics of bus voltage.Furthermore, according to the impact mechanism of three-step current relays, the basic operating characteristics of the reclosing operation, combined with the operational experience of spot small hydropower stations, the problems of the low success rate of reclosing and overvoltage of the connected bus in high water season is solved to a certain extent. Buses of 35 kV and 10 kV are used as examples and the improvement of auto-reclosing are proposed. Also the control flow is designed.Finally, distribution power network of 35 kV is used as an example. Based on the improvement in measures, the design scheme of the automatic reclosing device is proposed. According to reclosing control process, control logical diagram is designed. The hardware and software is designed and implemented. Debugging and trial operation of the device is finished.The running of the device shows the following results: it improves the success rate of the reclosing, improves voltage quality of the bus, enhances the reliability and stability of the power supply area containing small hydropower stations and achieves certain engineering significance in parallel operation of small hydropower station.