Research On Relay Protection Of Hybrid Double-Terminal HVDC Transmission

Hybrid HVDC combines the advantages of traditional HVDC and flexible HVDC,So it has become a new development trend.At present,there are few studies on hybrid HVDC protection.In this paper,a set of integrated configuration method for hybrid two-terminal HVDC system line protection and its reclosure strategy is proposed.The work mainly includes:(1)In this paper,a±500kV hybrid two-terminal DC transmission system model is constructed,and the mathematical model,topology structure and control mode of the rectifier station and inverter station at both ends of the DC transmission line are analyzed.A simulation model of the hybrid two-terminal DC transmission system is built on the PSCAD platform.Simulation results verify the correctness of the model.(2)Based on this model,a protection method based on VMD decomposition combined with energy entropy is studied.The DC filter and the wave reactor on both sides of the DC line are used as the physical protection boundary,and the voltage characteristic signal is extracted from the protection device when a fault occurs.By analyzing the fault characteristics of the voltage signal,the protection criterion is constructed according to the different energy entropy of the voltage fault components inside and outside the DC line.The voltage fault components collected from the measurement points at the time of fault occurring were decomposed by VMD to obtain several inherent modal components and calculate the energy entropy.Internal ant external faults were identified according to the different energy entropy of VMD decomposition.The fault poles were identified according to the different energy entropy ratios of the positive and negative voltage fault components.The influence of different fault location and transition resistance is analyzed.(3)Based on this model,a reclosing strategy using transient energy of electrical signals is studied.When the above protection is started,the circuit breaker is finally disconnected and the reclosing strategy is entered.By analyzing the line reclosing logic,it is necessary to determine the fault type,that is,whether the fault is transient or permanent.If the fault is permanent,it is necessary to determine the fault area again in the reclosing stage.According to this characteristic,a line reclosing scheme using voltage information of one terminal is proposed.The voltage signal within 3ms after the circuit breaker coincidence is extracted,and it is decomposed by VMD to obtain the high-frequency natural modal component to calculate its transient energy value.After the circuit breaker is closed,the transient energy of the voltage signal is different.According to this characteristic,a transient fault or permanent fault can be distinguished.If it is judged as permanent fault,it is necessary to compare the positive and negative transient energy obtained at the same side protection installation so as to selectively isolate the fault.