The Applicability Research on Asynchronous Limit Impedance Circle in Loss of Excitation Protection for Large Turbo-Generator

Loss-of-excitation fault of large turbo-generator poses a serious threat to the security of generator and power system. It is significant to properly set generator´s loss-of excitation protection. Loss-of-excitation protection has many different operating criterions, and their application range and condition should be clarified for good effect. Based on theoretical analysis and simulating calculation, this paper focuses on the asynchronous limit impedance circle criterion of loss-of-excitation protection and analyzes the influence of the contact strength between generators and power system on generators´ dynamic characteristics when the loss-of-excitation fault happens. The critical contact reactance between generator and power system is defined to measure the applicability of the asynchronous limit impedance circle criterion when the operation mode of power system changes, which provides an important reference to the selection of desirable operating criterion of loss-of-excitation protection.