Research On Principle Of Protection And Service Restoration Strategy For Isolated Power System

The power system used on shipboard, airplane or space station, for example, is classified as isolated power system (IPS). IPS with bad operation environment is vulnerable to external disturbances. The important equipments in loop power distribution systems and zone distribution system have the advantages of high power supply continuity and reliability because the systems can obtain power supply from two directions. Moreover, the advanced protection and reconfiguration technology are important means to improve the survivability and reliability of IPS. Based on the ideas of non-communication protection and intelligent restoration, the protection of loop power distribution and the multiobjective intelligent service restoration method of DC zone distribution are studied.Firstly, the network structure characteristics of IPS are analyzed. A typical loop power distribution has been established by MATLAB, and the short circuit situation under different operation modes have been analyzed by simulation. On the basis, the traditional three section current protection method of IPS is analyzed, three kinds of protection methods are presented by using different criteria. The first one is an improved directional over-current based time-graded protection. In this method, the local relay achieves the selectivity by time coordination of protection device after the remote break of the line has been disconnected. The second one is an accelerated action method based on ration signal of current. The changing of current through the local relay is adopted when the fault occurs and the remote breaker of the line is tripped. The method uses the current ratio criterion of the accelerated over-current protection to determine the fault zone, and then accelerated trip of the local break. The last one is a new accelerated action method based on the remote breaker operating time. In the method, the changing of current through the local relay is adopted when the fault occurs and the remote breaker of the line is tripped, and the time characteristics of this changing are used to determine the fault zone, and then accelerated trip of the local break.The restoration process of DC zone distribution of IPS is researched. A multiobjective model for fault restoration of DC zone distribution system is established to maximize numbers of load power supply and minimize the time of switch operation. In this paper, the objective functions of different dimensions are normalized, and these objective functions are integrated by using the analytic hierarchy process (AHP). Then the integer programming (IP) method is used to optimize the integrated objective function, and the optimal switch operation sequence is obtained finally.Compared with the traditional three-section current protection method, the proposed protection methods do not need communication channel, but also can further shorten the time of cutting off the fault line, and ensure the continuity of power supply. This paper develops the theory of non-communication protection for IPS, which could be a powerful tool for enhancing the survival of IPS under complex situations. The work of these protection methods is of great theoretic and practical value. And the reconstruction method of DC zone distribution is a good reference for study on DC power distribution network.