Technical performance and stability analysis of eskom power network using 600kv, 800kv, and 1000kv hvdc.

Abstract

In designing electric power networks or implementing major expansions to existing networks, a number of the key issues regarding the technical performance of the network at both transmission and distribution level must be ascertained, namely: voltage regulation, voltage fluctuations, electrical losses, transmission/distribution plant loading and utilization, fault level, generation stability, harmonics, phase balancing, supply availability and system security. System studies and analysis conducted from time to time to ascertain the operating state of a network, taking into account, load growth projections for the future. Undue stresses on the system or anticipated problems are determined from power flow analysis or during operation and maintenance. Using a modified Eskom network (KwaZulu-Natal sub-grid) as a case study, the technical and stability analysis for different high voltage direct current (HVDC) transmission voltages: 600kV, 800kV and 1000kV were carried out using DIgSILENT PowerFactory engineering software tool, as an alternative for bulk power transfer using high voltage alternating current (HVAC) link along the major corridors. Static analysis using PV and QV curves; dynamic analysis using RMS time domain and electromagnetic EMT analysis were carried out. Dynamic analyses were performed to determine the system fault levels and critical fault clearing time. Results obtained from this investigation show that 600kV and 800kV HVDC transmission systems have greater power capacity than equivalent HVAC line. HVDC delivery systems were observed to have lower electrical losses, better voltage profile, increase fault clearing time, enabling robust protection schemes to be installed. Voltage distortion due to harmonic content and imperfect current waveform in Cahosa-Bassa LCC-HVDC link were also investigated, and re-engineering with the use of VSC-HVDC technology has been proposed. This option provides reduced harmonic content, excellent sinusoidal waveform and minimal vulnerability to commutation failure. A financial and economic analysis of a 500kV HVAC double circuit and ±600kV HVDC transmission network were compared. HVDC system was proposed the most suitable scheme for bulk transmission of electric power over long distances due to high efficiency and better economics.