An adaptive cumulative sum based method for unblocking distance relays in TCSC compensated transmission lines

•Challenges associated with the protection of power networks equipped with TCSCs are summarized.•The proposed fault detection method based on the Adaptive Cumulative Sum is introduced in detail.•It is shown that the proposed method provides high speed and accuracy for all types of faults.•It is shown that the proposed method is not sensitive to nonlinear changes of TCSC. Fault detection in transmission lines with thyristor controlled series compensators (TCSC) can be challenging, in particular during power swing conditions. A reliable unblocking method based on the adaptive cumulative Sum (ACUSUM) is presented in this paper. This method alleviates the limitations of conventional methods and has the capability to detect all asymmetric and symmetric faults with high accuracy and speed. The proposed method measures the negative sequence of the current signal for fault detection. Two simulation case studies consisted of the single machine and infinite bus (SMIB) and the IEEE standard 9-bus and three machine systems are simulated in PSCAD/EMTDC to evaluate the proposed method. It is shown that the non-linear behavior of TCSC will not impact the accurate performance of this method.