A Life Cycle Comparison of Medium Voltage Fault Level Management Technologies Employed by Power Utilities and Recommendations on Future-Proofing the South African Electrical Grid

摘要

Fault levels are reported to be increasing on most networks due to a combination of network interconnectivity and the popular rise of embedded renewable generation projects. Since a high fault level is an indication of the strength and robustness of a power system, this increase is not inherently undesirable but becomes so when the increase is larger than that for which the installed equipment is rated thus necessitating a costly equipment upgrade project or network reconfiguration. When utilities are confronted with the scenario where fault levels are set to rise above those specified by installed equipment, they traditionally considered one of two options. Either replace the installed equipment with suitably rated equipment or install a series reactor to the busbar in an effort to reduce the fault level. The Superconducting Fault Current Limiter and the utilization of 'high' impedance transformers have now also evolved to a position wherein it too is being considered as an effective means of fault level management. This study will begin by discussing fault level trends in South Africa and then by utilising fault level data from existing utility networks in the South African power pool (ESKOM), this paper aims to contextualize the risk present in South Africa today. It will then present some key findings from a case study that investigated the impact of localised generation on MV busbars and undertook an 'asset life' financial comparison of various fault level management options considered. This comparison also considered the energy cost over the duration of the asset service life. The results make it clear that when considering fault level management techniques, a utility cannot rely on only one solution but must decide from a pre-determined basket of solutions as the most appropriate solution is largely determined by the cost of energy, the age of the asset, network configuration and the space available at the existing site. Finally, recommendations are made on strategies that may be employed to future-proof the South African power grid from costly fault level reduction strategies.