Electronic Instrument Transformer Stability Research On The Influence Of The Relay Protection

Electronic instrument transformer is an important facility for signal collection in intelligent substations.There are three key factors that affect the stability of electronic instrument transformers,which are electronic instrument transformer self-transmission error,resampling error and abnormal data.This essay aims to analyze the influence mechanism of those important elements on the relay protection.In the meanwhile,the PSCAD model,consisting of no-load closing,line differential protection and distance protection model,will be created in this article in order to through the related simulation to prove the correctness of the theoretical analysis regarding improving the stability of the electronic instrument transformer.The main work of this paper includes the following three aspects:First of all,using Simulink to establish the Rogowski coil transformer model,and analyzing the characteristics of electronic instrument transformer self-transmission error.This essay applies the simulation data from PSCAD model to the Rogowski coil transformer model in order to obtain the secondary side data,at the same time,the collecting data from the primary side and the secondary side would be used respectively to do distance protection and bus differential protection.In conclusion,the transmission error of the electronic instrument transformer may result in the malfunction of bus differential protection,but it would not influence the normal operation of the distance protection.In addition,this article detailedly analyzes the process of linear interpolation in the digital resampling part,which introduces the concept of “interpolation assistant signal” to analyze the error of the linear interpolation process,and giving the relevant suggestion of improving the linear difference method.In the meanwhile,according to that analysis,this essay also concludes that in the process of using linear interpolation to achieve the synchronization of data,after interpolation,the signal amplitude is related to the position of the interpolation point.The amplitude is the largest when the position of the signal before interpolation is exactly the same as the position of the discrete signal point after interpolation;However,when interpolating in the middle of two consecutive data points,the amplitude is the smallest;When the other places are selected to do interpolation,the amplitude of the obtained signal is between the maximum and the minimum.Furthermore,PSCAD simulation results show that digital resampling has absolutely no affect on the distance protection model and bus differential protection model in this experiment.Finally,the influence of abnormal data on the relay protection is analyzed,and gives the method of eliminating abnormal data.In this paper,the control variable method is used to research the influence on the relay protection,from the location when abnormal data happened,the degree of migration of abnormal data and the duration of abnormal data and so on.According to those relevant researches,there are some conslusions could be obtained.At the sine wave peak point,data anomaly is easier to make the distance protection malfunction,at the zero crossing point,data anomaly is easier to make the differential protection malfunction;the greater the degree of misregistration of the abnormal data and the longer the duration of abnormal data,the easier the protection make malfunction.At the end of this essay,the method of eliminating the abnormal data is proposed,and compared with some existing relevant methods,the method in the article has an advantage over those current methods.