Challenges of Fault Current Analysis using IEC 60909 and ENA G74 in Grids Dominated by Converter Fed Generation

Abstract

Fault current analysis is a key part of designing, managing and analysing an electrical network. The traditional IEC 60909 calculation method has been well established in standards for many decades, however it is based on a number of simplified assumptions to make the computational process simple and efficient. A comparison is also included with the ENA G74 short circuit calculation method. The assumptions used in these methods are creating misleading results in large renewable energy generation plants that have a significant portion of Converter Fed Generation (CFG), by overstating the retained voltages and increasing the calculated fault levels. This paper shows how these assumptions break down in generation sites dominated by CFG, and can produce unrealistic results, due to the constant current output of the CFG. The paper also outlines some of the shortfalls in assessment of Grid Forming Inverters fault contribution.