Transient Simulation Of Stator'sInternal Faults In Synchronous Generatorand Protection Analysis

The stator's internal faults, which often occur in the synchronous machine, will cause serious damages to machines and power system. In order to predict the destructive effects of internal faults and design the protection schemes, the behavior of machine after internal faults should be analyzed in detail. By means of the multi-loop method, the steady-state analysis of internal faults in stator windings of synchronous machine has been made, but as to the transient analysis, research only limited to single machine with no-load.The mathematical model of multi-loop, which is improved through selecting new stator loops in this paper, can be used to simulate the transient behavior of external short circuit at machine's terminal and internal short circuit in the stator, not only under no-load condition with single machine but also under load condition connected to power network. Regarding the discrete magnetic vector potential and loop currents as the state variables, and combining the FEM with the multi-loop method, a mathematical model of the synchronous machine with internal faults is set up in this paper. This model not only reckons in the effects of the space distribution and the connection pattern of the windings, the position of the short circuit point and the space harmonics of the gap magnetic field, but also takes into account the pole geometry, slot effects, saturation and eddy current in the rotor.On the 12kW, 4-pole salient pole synchronous machine, three phase symmetrical short circuit experiments and kinds of typical internal faults experiments are carried out in case of single machine with no-load and with resistance load at terminal. Based on the above two mathematical model, simulations are also made under the same conditions. The transient solution obtained from the multi-loop mathematical model are in agreement with experiment results approximately under the conditions that saturation is not severe. Though the errors of currents in some non-fault branch seem a little large, the fundamental components of the simulation current are accurateenough for engineering requirements such as verification the protection sensitivities. As to the mathematical model of FEM coupled with electric circuit, the simulation currents of all stator branches and excitation agree well with the experiments data in case of normal operation as well as kinds of faults conditions, especially in saturation conditions.Using the mathematical model of FEM coupled with multi-loop method, the fault of single branch shutdown is simulated on several generators with different number of poles under load condition connected to power network. Simulation shows that huge circulating currents will arise in the stator when a branch shutdown occurs in the turbo-generator with two poles and two branches per phase, which will not happen in the hydro-generator. And a physical explanation is presented in this paper.Since the capacity of a single generator becomes larger and larger, more requirements for protection are demanded relating to the security, reliability, sensitivity and quick-response. In the past, the design of main protection scheme usually depends on the concept, experience and habituation, which lacks in the scientific quantitative analysis. Based on the accurate calculation of internal faults and verification of protection sensitivities, this paper designs the main protection schemes of internal faults for the 150MW hydro-generator in Etan power station according to the principle of advantage complementation and comprehensive utilization, which could protect most of the possible internal faults of the generator.