Study Of New Principle And Realization Technology Of Transmission Line Protection

Relay protection for transmission line is very significance for maintaining safe stabilize work of power system and increasing economic benefits. With the expand and development of interconnected huge electric power grid in China, power system capability is more and more large and electric voltage level is more and more high, which causing the problems of distributed capacitance current and current transformer saturation, thus the contradiction between relay dependability and relay security is further aggravated. Obviously, it is quite urgent to study and improve relay protection criterion and performance to meet the demand of power system development. Thus, the study work is valuable and important in theory and application to solve several difficult problems of transmission line protection applied in large scale power grid such as capacitance current compensation, current transformer saturation and trip speed and so on.Transmission line multi differential protection new scheme is proposed according to shortcomings of single principle such as phasor value based differential protection and sampled value based differential protection. In the proposed scheme, the sampled value based differential protection is used to clean most comparative serious internal faults in one cycle reliably and the slight internal fault can be detected by phasor value based differential protection; at the same time, a restraint current criterion is led into the proposed protection to overcome the impact of current transformer saturation on phasor value based differential protection by means of adaptively inserting the time-delay of 200ms while serious external fault occur. As for the proposed protection scheme, its protective criteria are ripe and reliable, and it is not necessary to configure complex detecting element for current transformer saturation. Simulation results show that the reliability, sensitivity trip speed and immunity to current transformer saturation are better than those of the single principle based differential protections.The new method of transmission line Bergeron model based sampled value differential protection is proposed to solve the problem that phasor based capacitance current compensation methods are not suitable for sampled value differential protection. The proposed method can not only compensate capacitance current in time domain completely, but also inherits the merits of traditional sampled value differential protection such as fast trip speed and well immunity ability to current transformer saturation, the vital technology puzzle of high performance sampled value differential protection applied in high voltage long transmission line is solved well.The new principle of phase angle based self adaptive differential protection is proposed, which increases largely the security of differential protection and not influent the sensitiveness to interal fault. The proposed principle uses the fact that current phase angle error caused by current transformer saturation is smaller than current amplitude, and the self adaptive technology is introduced that the restraint coefficient of differential protection is adjust with current phase angle. When internal fault occurs, the phase angle difference of two end currents is small and the restraint coefficient is small, so the sensitiveness of relay is high. On the contrary, when external fault occurs, the phase angle difference of two end currents is large and the restraint coefficient is large, so the immunity ability to current transformer saturation of the proposed principle is increased significantly.The new method of measured impedance convergence based inverse time distance protection is proposed, which decides data window length according to real-time measured impedance convergence result. The convergence speed of measured impedance is faster, the data window length of protective algorithm is shorter and the trip speed is faster. Especially, the comprehensive self adaptive variable data window distance protection has better performance to improve trip speed of the first zone of distance protection, which composes measured impedance convergence based inverse time distance protection with step mode based inverse time distance protection.The dissertation represents the some importance technology such as protection configuration, hardware architecture and software design and so on during developing high performance complete set of protection device for high voltage transmission line. The IEEE C37.94 standard based sampled time adjust method is proposed to solve efficiently data synchronize of optical fibre based differential protection. The dynamic simulation experiment results show that protective performance can meet the design necessity and agree with prospective design goal.At last, the dissertation gives the systematical summarize and points out the further work.