A closed-form solution to Estimate Parameters of Three-terminal Hybrid Transmission Lines

Abstract

—Accurate transmission line parameter values are essential to set the line protection relay applications. The ex isting parameter estimation methods for three-terminal hybrid lines require multiple measurement sets and employ iterative techniques to solve non-linear equations. Implementation of such methods requires high computation burden, and it is difficult to implement in protection relays. To mitigate these challenges, we proposed a closed-form solution for parameter estimation in three-terminal hybrid transmission lines using two sets of terminal voltage and current measurements recorded at 1 percent power difference. Nonlinear equations are formed by equating junction voltages calculated from two terminals. The hyperbolic terms present in nonlinear equations are replaced with corresponding Taylor’s expansion to arrive at a closed-loop form. Line parameters are directly calculated using the closed loop equation. The proposed method is verified with lines at three different voltage levels connecting conventional systems and inverter based renewable resources simulated in PSCAD/EMTDC and found to be accurate.