Research On New Energy Transmission Line Protection Scheme Based On Fault Transient Characteristics

To achieve the "dual carbon" goal,promoting the transformation of the power system to clean and low-carbon,and building a new type of power system with new energy as the main body are important measures in response to national policies.The new power system and traditional power system have significant differences in power generation principles,control methods,grid connected equipment,and external characteristics.They have characteristics such as limited amplitude and controlled phase angle.The unclear fault characteristics lead to the risk of rejection of traditional power frequency based protection schemes,which cannot meet the requirements of power system relay protection.Therefore,it is urgent to study protection schemes suitable for high proportion new energy transmission lines.The transient components generated during faults in high-voltage transmission lines contain rich fault information such as fault type,direction,location,and duration.The protection scheme composed of fault transient characteristics can act before the system control strategy responds,effectively solving the problems faced by existing protection schemes for new energy transmission lines.This article mainly focuses on the transient process and protection schemes of faults in new energy transmission lines.Firstly,the source of transient signals in the power system is explored,and the basic theory of traveling waves is analyzed,including the generation of traveling wave signals,the transmission process of traveling waves,and the calculation of refraction and reflection coefficients.This provides theoretical support for the subsequent calculation of voltage traveling wave amplitude,polarity,and energy,and introduces the extraction method of transient signals,When the low-frequency component is the main frequency signal,using wavelet transform is more advantageous,while when the high-frequency signal is the main component.using wavelet packet transform is more advantageous.Secondly.due to the disadvantage of traveling wave protection being greatly affected by the initial phase angle of faults in AC systems,when a fault occurs at the time of voltage zero crossing,this scheme has the problem of being unable to capture the fault traveling wave and causing the protection scheme to fail.In response to the above issues.this article first uses wavelet packet transform with better time-frequency analysis ability and higher resolution for high-frequency signals to extract fault information.By introducing frequency components into the energy,the difference in the ratio of high to low frequency energy during faults inside and outside the area is amplified.Furthermore,a new energy transmission line protection scheme based on the ratio of high to low frequency energy of transient traveling waves during faults is proposed,This scheme reduces the requirements for sampling rate and wave head extraction accuracy,can adapt to faults at different positions,has strong resistance to transition resistance,and has high sensitivity and reliability.Finally,the effectiveness of the designed scheme was verified on the PSCAD/EMTDC simulation platform.Finally,the structure of new energy transmitted through multi terminal DC is a key research direction in China and a future trend in the development of power grid technology.However,for multi terminal DC power grids where reactors are installed at the outlet of converter stations and there is no clear boundary between lines,the protection scheme based on boundary characteristics is ineffective,posing a threat to the safe and stable operation of the power system.In response to the above issues,this article starts from the perspective of traveling waves and first analyzes the propagation process of voltage traveling waves when faults occur at different locations.The expression of voltage traveling waves is derived,and it is found that there is a difference in the polarity of the second voltage traveling wave at the two ends of the protection installation during internal and external faults.Based on this,a traveling wave protection scheme based on voltage polarity comparison is proposed.Finally,the effectiveness of the designed scheme was verified on the PSCAD/EMTDC simulation platform.