Study On Travelling Wave Transfer Characteristics And Application Techniques Based On Rogowski Coils

Electronic transducers have been widely used in smart substations. They have some excellent characteristics such as wide response frequency band, broad dynamic measurement range, accurate transfer characteristics, non magnetic saturation, better insulation characteristics and so on. These non-traditional transducers can realize local sampling and the digital outputs, which is beneficial to data sharing. They are considered as the next generation of transducers for smart grids. Currently, because of lacking better understanding to both travelling wave transfer characteristics of electronic transducers and data processing techniques, they are only be used for transferring power frequency and some harmonic signals, but not be used for transferring higher frequency travelling wave. Consequently, neither travelling wave fault location nor protection hasn’t been used in smart substations. In order to solve the above problems, the following works are investigated in this paper:(1) High frequency transient equivalent circuits of Rogowski coils and broadband integrator are established. Their travelling wave transfer characteristics are analyzed and verified by simulations. Based on structure features and induction principle of Rogowski coils, factors influencing transfer accuracy and electromagnetic shield technologies have been discussed. And results reveal Rogowski coils have accurate travelling wave transfer characteristics. Then, two kinds of equivalent circuits, lumped parameters model and distributed parameters model, are built and compared through their transfer functions and frequency response curves. Meanwhile, initial voltage distribution characteristics when travelling wave arrives are analyzed by distributed parameters model. Travelling wave transfer characteristics of two models are simulated and it is proved that Rogowski coils have an excellent response to travelling wave. The following analog circuits of Rogowski coils, including amplifying circuit, integral circuit and filter circuit, are also established. And a compound integral circuit composed of passive integrator and active integrator is designed to ensure an integral broadband response. Eventually, simulations of whole circuit, including Rogowski coils and its following analog circuits, demonstrate that the whole circuit can meet demands of travelling wave transfer.(2) Based on theoretical analysis, a special Rogowski coils for transferring travelling wave is developed, and corresponding tests are done. Firstly, based on its two working mode, self-integral and differential, a design method of differential Rogowski coils is proposed. Then, a group of coil’s physical and electromagnetic parameters are designed, and according to these parameters, a suitable Rogowski coils is made. Meanwhile, its response characteristics of steady-state, lighting surge, fault generated travelling wave are tested by different testing systems. The experiment results indicate that Rogowski coils have an excellent performance to transfer travelling wave.(3) Based on differential characteristics of Rogowski coils, a travelling wave front identification method is proposed. The key to realize fault location is to obtain break-points of travelling wave surge accurately, especially initial surge. Output of Rogowski coils is differential signal, which can be perfectly used for identifying surge’s break-point. Using differential outputs of coils directly can improve the ability to identify travelling wave. Meanwhile, integral circuit can be deleted. So, features of differential travelling wave are analyzed firstly. Fault location criterions based on differential travelling wave are designed correspondingly. Finally, the criterions are demonstrated to be feasible by simulations of single-end and double-end fault location.(4) In order to realize fault location and protection based on travelling wave in smart substations, schemes of data sampling and transmission are investigated. Based on layered structure features and data transmission mode in smart substations, an overall scheme is proposed. Because of the difficulty to realize a high rate sampling of travelling wave, a method on how to determine the lowest sampling rate which should meet the demand for travelling wave protections is presented. Then, a high-speed sampling circuit composed of a high speed A/D converter, a FPGA and a DSP is designed. A/D converter’s connection form is analyzed in the following. Synchronization scheme for travelling wave signals based on UillE1588is investigated. Considering high synchronous error of current interpolation algorithm for travelling wave data, a modified interpolation algorithm is presented by modifying basic sampling time, and is proved to work well.(5) The communications of IEDs in smart substation should follow IHC61850. In order to meet application requirements, logical nodes for travelling wave fault location and protection is established and their data objects are completed. The communication model for travelling wave application is established. Based on standard9-2, transfer frame of travelling wave is designed and investigated.