TRANSIENT SIMULATION OF SUPERCONDUCTING SYNCHRONOUS MACHINES

In this dissertation, a computer model is developed to study the electromechanical interactions between superconducting generators and power systems during various fault conditions. A large set of equivalent circuits is used to represent the eddy currents on the finite length electromagnetic cylindrical shields which surround the superconducting field winding. The armature and field windings are represented by coupled circuits as in conventional generator models. The rotor-turbine shaft dynamics are introduced in the model by a set of lumped masses representing the various stages of the turbine and the rotor, connected by springs representing the shaft. The electrical and mechanical equations of the machine are related by the air gap torque equation in a large system of simultaneous, nonlinear differential equations. The model is much larger in analytical size than conventional generator models, because of the presence of more than one hundred equivalent circuits representing the electromagnetic shields. Efficient integration methods (Predictor Corrector) and matrix inversion techniques (Triangular Decomposition) are used to perform the calculation in a reasonable amount of computer execution time. A conventional two axis representation of the machine is used. However, the model has been expanded to allow for the simulation of electromagnetic interactions between the outer rotor cylinders which include the warm damper, and the inner rotor which carries the field winding and the cold shield. The conventional d-q axis transformation is expanded to connect the machine to a delta-wye transformer and simulate unbalanced faults in the transmission line.;The developed computer algorithms are used to study the transient behavior of a 300 MVA superconducting generator and the results are reported here.;A frequency domain analysis of the generator behavior is also performed to derive closed form expressions for the eddy currents in the shields, the field shielding and the transient reactances at different frequencies. This type of analysis is useful in the design process since it provides quick answers to critical points of the design. Then, a Nyquist stability test is used to determine the stability of the machine at various operating conditions in the respect of real and reactive load instead of using a direct eigenvalue method which would require to solve for the eigenvalues of a very large matrix ((TURN)100 x (TURN)100).