Distance Protection of Transmission Lines with High Levels of Series Compensation
A study on frequency and time domain communication independent distance protection for series compensated lines
Time: Fri 2023-03-03 10.00
Location: F3, Lindstedtsvägen 26 & 28, Stockholm
Video link: zoom link for online defense
Subject area: Electrical Engineering
Doctoral student: Md Tanbhir Hoq , Elektroteknisk teori och konstruktion
Opponent: Professor Claus Leth Bak, Aalborg universitet
Supervisor: Associate Professor Nathaniel Taylor, Elektroteknisk teori och konstruktion; Jianping Wang, Elkraftteknik, Elektroteknisk teori och konstruktion
Series capacitors are used in electric transmission lines to increase their power transfer capacity. They compensate for the inductive reactance of the line. They offer a useful alternative to building new lines, in view of economic and environmental constraints. However, during transmission line faults, the presence of series capacitors causes problems for distance protection relays. Distance protection is the most widely used protection method in transmission lines, due to its relatively simple working principle and its ability to work with only local measurements of voltage and current. As the number of series compensated transmission lines is increasing, and the typical compensation level is also increasing, it has become essential to investigate protection methods that can be employed in place of traditional distance protection in series compensated lines.
This thesis addresses the problems associated with line protection in the presence of series capacitor compensation. The first part is an assessment of the performance of traditional distance relays in cases with high levels of series compensation. This was based both on simulation studies and on published works describing research studies and industry experience with series capacitor projects and the related line-protection issues. It is concluded that traditional distance protection cannot be used reliably with high levels of series compensation. The second part of the thesis describes some alternative protection methods that are developed and studied as candidates for better single-ended protection of series-compensated lines. These are based on incremental quantities, Lissajous curves and RL/RLC line models. These methods show positive results for single ended protection of series compensated lines.The incremental-quantity based method is fast and operates reliably, but faces under-reach problems with fault resistance. The Lissajous-curve basedmethod can be used as an alternative to the Fourier transform and has some advantages in overcoming inversion situations, but it requires at least a cycle of data to operate. The RL- and RLC-model based solutions can also operate fast, but lose accuracy with higher fault resistances. All the proposed protection methods are extensively tested, using data from fault test cases generated with PSCAD, and algorithms developed in Matlab.