Fault contribution of grid-connected inverters

The distribution grid is mainly built on a radial configuration where power is coming from one transformer substation to supply clients. Up to recently, in the rare cases where distributed generation existed, it was almost exclusively constituted of rotating machines, which have quite a different behaviour under fault than inverter-based sources. Consequently, current connection impact assessments rules were built on years of rotating machines experience and often misrepresent inverter-based sources. This paper presents an overview of the issue of short-circuit contribution with respect to distributed generation and highlights the distinctions between rotating and inverter-based sources in this regard. A typical inverter and synchronous machine short-circuit current model is presented as well as simulation results for a 7.5 MW implementation on a typical Canadian network.