Comparative Study Of Short-circuit Impulse Current Based On Electromagnetic Transient Simulation And Practical Calculation

With the continuous construction of UHVAC and UHVDC projects,the scale of power system is expanding,the grid structure is becoming more and more complex,the electrical connection is becoming closer,and the whole grid presents the characteristics of large-scale,complex and heterogeneous.At the same time,the problem of exceeded short-circuit current is getting worse,which restricts the development of power grid in each province.Whether to install the short circuit current limiter or not,and the specification of the limiter requires more accurate results of short-circuit current calculation.Short-circuit impulse current is defined as the maximum possible instantaneous value of short-circuit current,which is an important basis for dynamic stability verification of electrical equipment.With the development of computer technology,it is possible to use electromagnetic transient simulation to get short-circuit current in large-scale systems.In this thesis,the variation of three-phase short-circuit impulse current in power system is studied and an impulse coefficient correction method for practical short circuit calculation is put forward.The short-circuit impulse current calculation based on electromagnetic transient simulation and short-circuit practical calculation is studied in comparison.Firstly,the physical electromagnetic transient process of three-phase short-circuit in a synchronous generator and the method of getting short-circuit current formula based on Laplace approach are analyzed.The variation of the short-circuit impulse current of single large synchronous generator is studied by theoretical analysis,optimizing the short-circuit current calculation formula with PSO and establishing the three-phase short-circuit model of a synchronous generator based on PSCAD/EMTDC.Then,the practical calculation of shortcircuit current based on the power flow calculation and the method of determining impulse coefficient are discussed.An impulse coefficient correction method based on RANSAC is proposed.This correction method can modify impulse coefficient according to the working condition of generator,reduce the computation and quickly get more accurate results based on the power flow.The rationality of the method is verified by the three-phase short-circuit model of a single synchronous generator.Then,the variation of short-circuit impulse current is furtherly studied in the practical multimachine system.The short-circuit impulse current results based on electromagnetic transient simulation and practical calculation are analyzed in detail.It is proved that the maximum shortcircuit impulse current of different synchronous generators can be achieved at almost the same fault time.Because the actual impulse coefficient of each machine is different after the fault,the error between the short circuit impulse current value calculated by the impulse coefficient in practical calculation and the actual result is analyzed.Through the two-machine system,the WSCC9-node system and the New-England39-node system,the short-circuit impulse current results calculated by PSCAD electromagnetic transient simulation and PSASP short-circuit impulse current calculation are compared,and the correctness of the above analysis is verified.