A protection algorithm for TA saturation countermeasure based on principle of unified pilot protection

A unified pilot protection system is proposed. By virtue of optical fiber communication system, unified pilot protection system can deliver multi-information such as current and voltage sample value, all kinds of digital information. Applying these information, the protection system can not only accomplish many criteria in one system to enhance the performances of pilot protection, also can achieve some other auxiliary functions such as reclosure cooperation, line parameters calculation and so on. Based on the idea of unified pilot protection, this paper studies the solutions of using fault direction information to overcome the problem that differential protection is easily influenced by TA property differences and TA saturation, and gives a detailed analysis of the effect of TA saturation on the performances of current differential component and positive sequence fault direction component. The results show that TA saturation gives limited influence on fault direction component, so it can detect fault direction reliably and provide auxiliary information for current differential protection to distinguish internal fault from external one, accordingly, the paper proposes the corresponding criterion. The results of dynamic simulation experiments verify the feasibility and effectiveness of the proposed scheme. This work is supported by National Natural Science Foundation of China (NO.50807032).