A Short Circuit Current Study For Ship Power System

Short-circuit is a usual fault which is one of the faults destroy the ship electric power system badly. The short-circuit current calculation result can provide necessary data for setting delay protection strategy, choosing electrical devices, and checking the stability of the electrical equipments and the breaking capacity of switches, in ship electric power system. So it is very important to get accurate short-circuit values.The national military standard short-circuit current calculation method(GJB-173), which is published in 1986, is widely used in ships especially naval ships. But, in order to make the calculation carry on easily, GJB-173 ignores so much, that the calculation result is larger , which brings troubles to setting protection disposition, and selecting appropriate devices, so it is necessity to improve the GJB-173 method, and give out a new calculation method, which is more accurate.The main task of this paper is to analyze the GJB-173 calculation method and find out the reasons which make the calculation result so larger, then, the calculation method is improved, and a new one is offered, whose accuracy is validated, and, a software is supplied for simulation.1. The periodic current subtransient attenuation of generator is taken into consideration, when calculating the short-circuit of generators, and the decay time constant is corrected in view of the line impedance when the short-circuit point is away from the bus-bar.2. When calculating the short-circuit current of motors, the parallel running motors are replaced by some same type equivalent motors, and the parameters of the equivalent motor such as the quantity, the power, and the attenuation time constant are calculated by square root method. And the total values of the motors short-circuit current equals to the sum of equivalent motors'.3. A visual calculation software is provided based on VC++6.0. 4.According to the ship power system grid, the short-circuit current of the system is calculated by improved calculation method, GJB-173 and GB-3321, respectively, and compared with the others', the improved calculation method's results are proved to have higher accuracy, and the error is reduced effectively.