Research On Configuration Techniques In Loss Of Excitation And Out Of Step Protection Of Generators Connected With Power System

Coordination of power system and generator is a significant method to enhance stability of modern power system. And it has been research focus at present. Because grid-related protection for generating unit is an important part of coordination of power system and generator, it is meaningful to explore the coordination of its constant value and protection scheme aiming at improving security, quickness, selectivity, and delicacy of the protection. Loss of excitaion protection and out of step protection are two of the important components in grid-related protection. But protection schemes are generally set according to experience. There is lack of enough attention to the adaption in operation mode and fault form of actual power grid. In this paper, researches involves how to consider coordination of power system and generator in loss of excitaion protection and out of step protection and propose configuration techniques.From perspective of change of electrical connection between computer network, this paper research on adaption of typical criterion, asynchronous limit impedance circle criterion with time delay, and risk of not action in time. Based on PSD-FDS simulation software, loss of excitaion dynamic process and its protection is simulated in this system. Analyzing characteristic of impedance track viewed from the generator terminal entering into asynchronous limit impedance circle, it difines the critical contact reactance to evaluate the adaptation of the typical criterion to the contact strength between generator and power system and proposes relevant configuration techniques. If the contact reactance between generators and power system is greater than the critical contact, the time that the generator terminal impedance track keeps in the asynchronous impedance circle after the loss-of-excitation fault occurs can’t meet the requirement of time delay for the typical criterion. The protection will not act in time in this case. And it should consider other stator impedance criterion as a supplement. This paper verifies with actual data that critical contact reactance can be a risk indicator to evaluate the adaptation of the typical criterion to operation mode. Through the compare of critical contact reactance of the same generator in single-machine infinite-bus system, three-machine infinite-bus system and real system, it clears and definites the characteristic that critical contact reactance decreases with the reduction of system voltage supporting ability after the loss of excitation.In the local power system with new energy and concentrated thermal power generating units, to avoid that loss of excitation protection may be unsuitable for disconnection operation mode, this paper researches on the time delay of loss-of-excitation protection in disconnection operation mode. Based on simulation, it compares the diffenence of loss of excitaion dynamic process in the local power system with new energy and concentrated thermal power generating units under operation mode of connection and disconnection. It gives a detailed analysis on the influence of disconnection operation mode. And considering coordination of power system and generator, configuration techniques in loss of excitation protection of generators under disconnection operation mode that the time delay should be as small as possible in the allowable range is proposed.To avoid that out of step may not act punctually, this paper researches on two significant questions in parameters setting of out of step protection based on di-keep back principle.(1) Parameter value ofAX. Based on the simulation, it compares the different movement situation of out of step protection after generator out of step oscillation with the different AX and proposes configuration techniques that AX should not be small considering coordination of power system and generator.(2) Minimum system oscillation periodusT. Based on generator out of step scene simulation, it compares the difference of minimum system oscillation periodusT in the out of step protection based on di-keep back principle and three-impedance element principle. It proposes configuration techniques that minimum system oscillation period should not be large considering coordination of power system and generator.