| Three phase synchronous generator is characterized with good electric supply quality, high capacity for carrying loads and outputting both active power and reactive power, which is the most popular equipment of electric power generation. To provide theoretical foundation for generator optimization design and multiple scheme comparison, the finite element method is carried out to calculate generator parameters and analyze operating performance. Compared with the traditional analytical formula and the magnetic circuit method, finite element method gives more accurate results because it is based on actual model, has less assumption, meshes more flexible and the core nonlinear can be taken into account.Under static field operation, the iterative algorithm is used to calculate the value of exciting current with generator running in different operation mode, according to the expression about magnetic flux destiny in air gap and the induced electromotive force. The heuristic current is loaded on exciting winding to obtain the electromotive force, which is compared with the theoretical voltage. Keep on correcting the value of exciting current until the voltage error within specified tolerance, actual current is obtained at last. The magnetic energy method is applied to solve the stator and rotor slot leakage inductance, besides that the expression about three-phase leakage magnetic energy and slot leakage inductance is given.The time stepping finite element method with coupled field-circuit analysis is carried out to calculate the three phase sudden short circuit current under transient field operation. By coupled with the external circuit, the voltage source is series connected in the exciting winding to realize the abrupt change of current at the moment of sudden short circuit. To consider magnetic conductance change of tooth harmonic caused by relative motion between stator and rotor, the transient field operation is applied to obtain the rotor iron loss, aiming to analyze the slotted core effect on rotor iron loss. To simulate rotor rotation, the nodes on air gap are coupled and motor speed is controlled by changing time step length. The rotor iron loss curve with variation of time is given and the average loss in a period of time is obtained.The motor parameters, exciting current, three phase sudden short circuit current and rotor eddy flow loss calculation are calculated by finite element method, and some results by the finite element method are compared with that by the analytical method, and the validity of the finite element method is checked. Researches in this paper provide theoretical foundation to optimization design for the large capacity and high performance synchronous generator. |
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