Limitations of Angle-Based Faulty Line Identification Logic in Series-Compensated Parallel Transmission Lines

Distance relay protecting series-compensated parallel transmission lines may maloperate due to the presence of zero-sequence mutual coupling. In case of the line terminating at the same bus at both ends, one practically feasible option is to exchange zero-sequence information between relays. This information can be used in impedance estimation and to estimate fault location in relays. However, the presence of series capacitors in both lines may further aggravate the problem. The existing magnitude-based logic to classify healthy and faulty lines may fail in the presence of the series capacitor owing to the fault location and compensation level. Recently, angle-based logic was proposed, but the analysis was limited to steady-state fundamental frequency-sequence impedance information. This paper analyzes the performance of this angle information by time-domain simulation studies. The performance is analyzed by considering different compensation levels, fault location, and for varying in-feed conditions for the capacitor located at one end of the line. Analysis based on time-domain simulation studies along with the nonswitched positive-sequence polarized distance relay shows that the angle-based logic is able to classify healthy and faulty lines.