Effects and suppression of fast transient overvoltages on transformers applied to solar photovoltaic and BESS

Solar photovoltaic (Solar PV) and Battery Energy Storage Systems (BESS) are recognized as the cheapest and easier to set up renewable energy source in most countries nowadays. The size and rating have grown up to utility-scale and can reach hundreds of MVA. Such large power generation sites require sophisticated protection systems. It’s not due to the intermittence of energy generation, but due to the complexity of all equipment that those installations, especially the unitary transformers, tends t o experience more frequent switching on the medium voltage (MV) side. Furthermore, vacuum circuit brakers (VCB), which are known by its capability to give raise to fast transients, are extensively used. This work presents a comprehensive transient modelling of a large Solar PV site and its main components. Details on the models applied in the simulations are given. The severity of the transients in terms of voltage amplitude and reignition within VCB were evaluated based on several parameters. Finally, transformer internal voltages were computed on conventional transformer and when it is protected through varistors across MV windings.