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While there are numerous literatures that have addressed the impact of mutual coupling on the reliability and security of protection schemes and have provided possible mitigation solutions, there has not been adequate research and documentation presenting a comprehensive analytical approach to 1) estimate the magnitude of mutual coupling and 2) quantify the adverse impact of mutual coupling in real-life scenarios under several system faults across various types of protective elements. This should be considered as the first stage of any mutual coupling related study preceding the second stage in which the mitigation against mutual coupling is to be developed. The proposed methodology can be used to study the impact of mutual coupling on ground overcurrent relays, ground and phase distance as well as pilot protection schemes. As part of the proposed approach, EMT simulation is utilized to quantify the extent of sub-transient overshoot and current reversal that may have adverse impact on the performance of studied relays. A real-life case study within the ERCOT network has been used to demonstrate the proposed study approach.

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While transmission expansions are planned to have positive impact on reliability of power grids, they could increase the risk and severity of some of the detrimental incidents in power grid mainly by virtue of changing system configuration, consequently electrical distance. This paper aims to evaluate and quantify the impact of transmission expansion projects on Sub-Synchronous Resonance (SSR) risk through a two-step approach utilizing outage count index and Sub-synchronous damping index. A graph-theory based SSR screening tool is introduced to quantify the outage count associated with all grid contingencies which results in radial connection between renewable generation resources and nearby series compensated lines. Moreover, a frequency-scan based damping analysis is performed to assess the impact of transmission expansion on the system damping in sub-synchronous frequency range. The proposed approach has been utilized to evaluate the impact of recently-built transmission expansion project on SSR risk in a portion of Electric Reliability Council of Texas (ERCOT) grid.