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This paper compares different provisions to protect a special high power switching power supply from internal short-faults, in particular internal short-circuits. The power supply is based on a five three-phase NPC inverters, with common dc-link, rated for a total power of about 60MW and for an output voltage of 6.5kV, using IGCTs as switching components. A large, distributed, capacitor bank is connected at the dc-link side of the inverters, with huge amount of stored energy, as high as 760kJ during nominal operation. In case of internal short-circuit of one inverter leg, due for example to a failure of one IGCT, this energy is discharged into the faulty leg, potentially leading to explosion and fault propagation. Simulations have been performed in order to analyze, select and design the most suitable protection to avoid this risk.

The Acceleration Grid Power Supply (AGPS) is a system devoted to supply the acceleration grids of the MITICA experiment, the full scale prototype of the ITER Neutral Beam Injector (NBI), being built in Padova (Italy) to test the NBI in advance of the operation in ITER. The procurement of the AGPS is split in two parts: the low voltage conversion system, namely the AGPS-Conversion System (AGPS-CS,) being procured by the European domestic agency, and the high voltage DC Generators (AGPS-DCG), being procured by the Japanese domestic agency. After the contract award, in late 2015, the executive design phase of the AGPS-CS has been finalized. The paper will present the final design of the AGPS-CS and will discuss the main choices in particular concerning the protection from internal faults of the inverters.