Study On N-X Verification For High And Medium Voltage Distribution Networks

Power supply security is a main index in network planning, including the ability to avoid large scale outage and maintain constant power supply for loads after outage. From the view of planning urban distribution network, this paper proposes different N-X verification methods for high and medium voltage network, based on their specific configuration characteristic.High voltage distribution network plays an important role in connecting transmission networks and medium and low voltage distribution networks. Components (such as transmission lines, main transformers and substations) in high voltage distribution networks may be disconnected from the network when fault occurs. This operation leads to power off of main transformers in related load substation. So load transfer must be considered in N-X verification. This paper proposes a high voltage network N-X verification method considering load transfer. According to different substations'connecting mode and number of main transformers, this method uses different load transfer ways to promise constant power supply for loads. This method can simulate the operation in power system correctly.Transmission feeders in medium voltage distribution networks are very long, and they are connected through connecting switches. As a result, configuration of medium voltage distribution networks is very complicated, which results in much difficulty in load transfer. The existing N-X verification in CNP software is mainly for the network within three-sectioned and three-linked,But for the multi-sectioned and Multi-linked medium voltage distribution network, the loads transfer can not be achieved accurately. In order to avoid this shortcoming, this paper proposes an N-X verification method based on feeder partition: divide the feeders into different zones through switches, and then carry out load transfer according to feeder partition. This method not only maintain correct load transfer within three-sectioned and three-linked,but also can offer a proper way to transfer loads, how to operate and the related line load ratio after loads transfer, thus offer great help to urban network's planning.In this paper, the algorithm function components have been preliminarily applied in"Computer-aides Decision-making System for Urban Power Network". It has been verified by calculation actual and samples data.