| Most of the EHV/UHV transmission line faults are single phase ground faults and mainly to the transient faults. Single phase auto-reclosure technique can greatly improve the reliability of power supply. However, if the breaker is reclosed after a permanent fault, the system will suffer more serious impact and influence. Therefore, before reclosing, discrimination of the fault type correctly to achieve adaptive reclosure is very necessary. That is, reclosing only when the transient fault occurs.EHV/UHV transmission line has become the backbone and hub of the power transmission system. The application of single phase adaptive reclosure is of great significance for improving the stability and reliability overall system. After analyzing the fault phase voltage when single phase ground fault occurs on EHV/UHV transmission line in detail, a new criterion of single phase adaptive reclosure is proposed. The main content is the following:①The EHV/UHV transmission line models of single circuit and double circuit are researched.The compensation level, compensation mode of shunt reactor and the selection interval of neutral point small reactor are discussed. Moreover, the transfer characteristic of capacitor voltage transformer is analyzed. The distribution of EHV/UHV transmission line can not be ignored. In contrast of the characteristics of chain, Bergeron and the time-varying dynamic vector model, Bergeron model is chosen as the single circuit line and double circuit line. As the shunt reactors are commonly used in EHV/UHV transmission line, the compensation principle, installation location, and connectivity of shunt reactor are discussed respectively for single and double circuit transmission lines. The necessity of installation of small neutral point reactance is proved and its range in various compensation forms is qualitative discussed. As a signal sampling device of protection unit, the performance of CVT has a greater influence to the work of protection equipment. In order to study with the actual situation, the CVT model is added in the system, and its working principle and transfer characteristic are also discussed.②After analyzing the physical process when single phase ground fault occurs in EHV/UHV system with shunt reactor, an identification method based on charictoristic of recovery voltage is proposed to achieve single phase adaptive reclosure.The results of research on characteristic of the primary arc, secondary arc and recovery voltage of fault phase are as follow: when transient fault occurs, the fault phase voltage of primary arc is high but the duration is very short, the secondary arc voltage is small and highly nonlinear, and the recovery voltage contains power frequency component and free component whose frequency is slightly lower than 50Hz; when permanent fault occurs, the primary arc and secondary arc voltage are very weak, and the recovery voltage only contains power frequency component. In each stage, the fault phase voltage vary in different characteristic in size, differ about accessing, and the degree of influence by external factors is dissimilar too. After considering the factors above, the recovery voltage is chosen as the characteristic to discriminate the fault type.③Multiple Signal Classification (MUSIC) is used to estimate the power spectrum of fault phase voltage, and the new criterion of single phase adaptive reclosure based on power spectrum is proposed. As the composition of fault phase recovery voltage is different when transient and permanent fault occurs, the power spectrum is also in difference. MUSIC which is one of the power spectrum estimation methods can effectively detect the non-integer frequency component in short length signal, and its resolution is high. Therefore, MUSIC is used to estimate the power spectrum of recovery voltage in fault phase, in order to detect the composition of the recovery voltage. Then the fault type can be distinguished by the difference of power spectrums.④Single circuit line models are established in the platform of MATLAB/ SIMULINK to verify the validity of proposed criterion. The models include a 500kV and a 750kV transmission line, and arc model is added in the fault simulation. The signal of fault phase voltage is obtained through digital simulation under the conditions of different fault types, different fault locations, overload and high resistance grounding fault. The power spectrum of fault phase voltage is estimated by MUSIC to verify the correctness of criterion. Simulation results show that the criterion can improve the success rate of single phase reclosure, using only single-end electric quantity. The criterion which has no effect with high frequency content and transition resistance is of high sensitivity and easy to achieve.⑤The single phase adaptive reclosure criterion is used in EHV double circuit transmission line with shunt reactor on same tower. The simulation is done to verify the vadility. A model of 500kV double circuit transmission line is established in PSCAD / EMTDC.The digital simulation is done under the conditions of individual single-loop compensation for each line and comprehensive compensation for double circuit line by shunt reactor. The vadility of the criterion for double circuit transmission lines on the same tower is verified.
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