Guidelines for EMT Transmission Line Models for Time-Domain Protection Algorithms

New transmission line protection methods have been proposed for improved speed and dependability in future power systems with new elements such as VSC HVDC converters. These new methods either implicitly assume or explicitly use a transmission line model, which may vary from very simple to very detailed. The absence of a verification of these models may impact dependability and result in unwanted behaviour, especially for those algorithms that do not explicitly filter out a specific frequency (e.g., the fundamental). This paper presents a verification step in the frequency domain to assess the line model accuracy within the bandwidth of the algorithm and applies this with examples. Second, to make algorithm design choices explicit, an analysis of the line model-algorithm interactions is provided. The paper finds that the protection input filter should match the bandwidth for which the line model is accurate. A carefully designed input filter thus depends on algorithm design choices and constraints such as line geometry, line model and sample rate.