Predicted dynamic performance of a possible AC link between SaskPower north and south systems

Abstract

SaskPower has two separate systems, namely the North and the South systems. The South system contains SaskPower major generation and system load. The North system load is located relatively far from its generation (200 to 300 km). The North system is considered, therefore, to be electrically weaker than the South system. Recently there has been an interest in connecting the two systems to improve the security, stability and reliability of the integrated system. Grid interconnections, however, especially between weak and strong systems, often result in the arising of low-frequency oscillations between the newly connected areas. These oscillations that are termed “inter-area oscillations” exhibit, generally poor damping and can severely restrict system operations by requiring the curtailment of electric power transfers level as an operational measure. There are two options for SaskPower North and South systems interconnection, namely HVAC and HVDC interconnections (tie-lines). This thesis reports the results of digital timedomain simulation studies carried out to investigate the dynamic performance of a proposed 260 km, 138 kV double-circuit HVAC tie-line incorporating a hybrid three-phase Thyristor- Controlled Series Capacitor (TCSC) compensation scheme that would connect the SaskPower North and South systems. The potential problems that might arise due to such an interconnection, namely power flow control and low-frequency oscillations are studied and quantified and a feasible solution is proposed. In this context, the effectiveness of the TCSC compensation scheme in damping power system oscillations in the tie-line is investigated. Time-domain simulations were conducted on the benchmark model using the ElectroMagnetic Transients Program (EMTP-RV). The results of the investigations demonstrate that the proposed HVAC link that incorporates a TCSC compensation scheme is effective in mitigating the low-frequency oscillations between the North and South systems for different system contingencies and operating conditions.