Transfer Characteristics Of Electronic Current Transformer And Its Impact On Relay Protection

With modern power system developing towards the direction of the extra high voltage, long distance, large capacity, traditional electromagnetic transformer is difficult to meet the needs of modern development because of its disadvantage of insulation structure complex, magnetic saturation, big volume and high cost and so on. In recent years, the emergence of electronic instrument transformer, which meet the needs of equipment miniaturization, intelligent, good reliability, high safety and quality of economic operation of power system, and play an important role in the digital substation. Therefore, combining the development trend of digital substation and inspection requirements of secondary equipment, requirements of building the model of electronic instrument transformer has become more and more urgent,Research on the transfer characteristics of electronic current transformer and its Impact on relay protection has important theoretical significance and practical application value.Electronic current transformer is regarded as the research main line on this paper. On the basis of analyzing the structure and measuring principle firstly, the modeling work of the sensing head and analog signal processing system of active electronic current transformer has completed through MATLAB software, and the transfer function model has deduced, and the frequency characteristic and error factors has analyzed through the prototype parameters into the simulation model.The simulation method and transfer characteristics test scheme of electronic current transformer has proposed next. The transfer characteristics of electronic current transformer is key to research and analyze from perspective of precision,saturation characteristics, frequency characteristics, the transient characteristics.the results show that the bandwidth of the active electronic current transformer is mainly dependent on sensing head and characteristic parameters of signal processing circuit. Rogowski coil current transformer has unsaturated properties, high precision measurement of a large current, but can’t correct transfer attenuation of dc component, and accuracy is difficult to guarantee in measuring low current; Low power current transformer is high in the steady state accuracy, but has iron core saturation problems in the big current; Fiber optical current transformer has unsaturated properties, and can effectively transfer the aperiodic component and every harmonic, but will show distortion phenomenon in low current measurements that cause a large error.The traditional electro-magnetic transformer with magnetic saturation problem already can’t meet the needs of the development of relay protection that is analyzed finally. The application of new type of electronic transformer can overcome the hidden trouble existing in the traditional transformer, and can bring the advantage for the relay protection. The influence of electronic current transformer on relay protection is further analyzed with the aid of PSCAD simulation platform to built transformer differential protection model. The simulation results show that electronic instrument transformer can greatly improve the sensitivity of the differential protection under guaranteeing the premise of reliability, and improve the performance of the protection system consequently.