Fast verification of remote backup capability of transmission line phase-tophase distance protection based on impedance matrix

The loss of secondary dc power in a substation will disable all protections, making them fail to trip when faults occur on power equipments. The remote backup capability of protections deployed in the upstream stations will become a crucial issue for the secure operation of power grids. In this paper, an impedance matrix-based method to efficiently verify the remote backup capability of phase-to-phase distance protection is proposed. The measuring impedance formula of the protection based on the impedance matrix is deduced. An analytical equation is established through combining the formula with the setting value of the protection. The remote backup capability is fast verified according to the characteristics of the equation solutions. The effectiveness of the method is demonstrated through case studies of a typical 500 kV substation.