I. Introduction
Modern power system has been in the stage of huge capacitance, super high voltage and remote distance transmission. The problem of sustained power frequency over-voltage caused by surplus reactive power of long transmission line risks the isolation of system and increases the loss of transmission line, even leads to generators displacement. Also, the stability of long line transmission system is an important problem. The application of asynchronized synchronous motor is not only the popular method of solution of this problem, but also could improve system stability.