Study on High Rsponse Excitation of Superconducting Generator

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Low synchronous impedance of superconducting generators (SCG's) improves power system stability. If high response exitation is possible in SCG, it could improve power system stability much more. For SCG with high response exitation, wer have many problems to be solved. One of the problems is how to design the exiciter. Since time constant of field circuit of SCG is very large, the capacity of the exciter may be very large. Thyristor convertors, which are used as exciters of the conventinal generators bring some problems, that is large capacity, reactive power, current harmonics and so on. Here we propose a new method of exciter with a small power supply and an energy transfer circuit between two superconducting coils. one of them is for storage and the other is field winding of SCG. The power supply, which consists of thyristor converter, supplies energy to the coil for storage. The energy is transfered from the coil for storage to the field winding through energy transfer circuit. The capacity of the power supply is rather small since it supplies only small energy for the loss of the system in the steady state. In rapid change of the field current for high response excitation, the current is supplied from the coil for storage. Though the converer is small from a point of AC side, the exciter looks large capacity for the field winding. The fundamental tests, that is, tests for energy tranfer, step response test, frequency response test and so on, were carried out by use of two superconducting coils. They confirmed that the exciter can operate well.Furthermore, we considered characteristics of field circuit of SCG and power system characteristics of SCG.