Research Of Short Circuit Current Calculating Method Of Marine Looped Electric Power System

As ships developing on the direction of becoming bigger and more automatic, the requirement of high level marine electric power station has become greater. In order to meet the requirement of the high power quality and reliability of the future electric propulsion ships, the power supply style of marine electric power station will change variously. Among these styles, the research of the looped power system is a very important part.The main content of this paper is the research of short circuit current of marine looped electric power system, which is a part of research of transient stability. Three points of view are used to research the characteristics of short circuit current of marine looped electric power system, such as applied calculating method, digital simulation and dynamic simulating experiment. And in order to select the switch correctly, the peak value of the three-phase short circuit current under the most serious condition is calculated.Firstly, this paper sets out from the fundamental equations of synchronous generator and asynchronous motor, analyses the physics process of short circuit and educes the expression of the whole short circuit current. And then, according to the features of the looped power supply network, the paper educes the applied calculating methods of two-node power system and more-than-three-node power system respectively. In the method of two-node power system, equivalent generators are used to calculate the influence of the line. In the method of more-than-three-node power system, transfer impedance of each generator to the short circuit point is calculated respectively, so the system has no current coupling. And we can know the whole short circuit current by usingadding principle. This method breaks the limit that the previous calculating method of the marine ac electric power system only suits tree-style network.In digital simulation, after mastering the simulating models of the main parts of the system such as generators, exciting systems and lines, a two-node and a four-node looped power system are simulated by four-order RUNGER-KUTTA method. The peak value of the simulation is compared with the result of applied calculation and the result is satisfied.In addition, the dynamic simulating is also experimentalized, including single generator with no load test, single generator with load test, single generator in series with impedance test and four-node system with four generators short circuit test. These tests validate the applied calculating method from the view of physics simulation.In order to calculate conveniently, a software is developed on the platform of VB6.0 under the foundation of the applied calculating method. The software is based on the typical looped electric power system and is modular programmed which is more convenient to extend.