Research On Distance Protection Method For EHV Transmission Line

With the establishment of the large-scale joint system and rapid increase of system capacity in the modern power system,EHV transmission lines get development fast,the distance protection which performance more perfect than current protection won the wide application in EHV transmission line,while the problem of influence by power swing and transition resistance of short dot is difficult to solve in the distance protection.In this paper,starting from the two angles of algorithm and distance relay to solve the above problems,The main contents are as follows:Detailedly the paper have studied the wavelet neural network algorithm,design and construct the structure of wavelet neural network.The current energy extracted by multi-resolution analysis as feature vector to identify the system fault and the re-occurred fault during power swing,which applied to the wavelet neural network algorithm to complete protection.This paper presents a multi-phase compensation distance relay free from power swing,and symmetrical components and the phase diagram method analysis are used to analyze the operating characteristics of the relay in different operating conditions.Through the analysis,it shows that the relay is not affected by system oscillation and has a definite action range for the asymmetric metallic short circuit fault,which in the local failure the relay can reliably move,and outside the region and reverse faults it can reliably not work,but the relay also has the shortcoming that not reflect symmetrical short circuit fault and weak ability to resist transition resistance.For the weak ability to resist transition resistance of the relay,this paper proposes a method based on BP fixed network to overcome the influence of the relay by the transition resistance,and the effectiveness of the proposed method is validated by computer simulation.For the shortage of the relay that can't reflect the symmetrical short circuit fault and can't select completely the fault phase,this paper designed the improved scheme,and put forward a distance protection method based on improved multi-phase compensation distance relay,and verified the feasibility of this method by analysis of an example.