Synchronous condensers as a viable inertia support mechanism on the future South African grid

Abstract

Modern electricity networks may face inertia shortages based on increasing inverter-based renewable energy penetration, along with the (often concurrent) decommissioning of aging synchronous thermal generators. In the South African network, the market share of coal generation is projected to decrease significantly based on the country's energy policy, primarily to be replaced by wind and solar PV. In this paper the inertia adequacy on the future South African network is evaluated, and the viability of converting retired synchronous generators to synchronous condensers is assessed based on sufficiency of inertia support provided and economic viability. It is found that by 2030, the South African network will have insufficient inertia for a significant portion of the year. However, significant improvements in Rate of Change of Frequency and frequency nadir are observed when incorporating inertia from converted synchronous condensers during multiple-contingency trip events. Finally, the conversion of synchronous generators to synchronous condensers is found to be the least-cost solution when compared to the installation of new synchronous condensers or of large-scale battery systems. The contributions made in this paper highlight the importance of considering network inertia in establishing a national energy policy, while also informing solutions to future inertia constraints.