Techniques used to protect a DC system with more than 100kA short circuit current capacity

With today´s new battery technology and power hungry devices that may need many hours of emergency battery backup, there is the danger of short circuit currents reaching more than 100kA and exceeding the short circuit current ratings of existing DC fuses. Until manufacturers design, test and certify DC fuses with higher short circuit current rating, excessive short circuit currents pose a danger to both personnel and property. This paper discusses solutions to manage short circuit currents and make a system safe using available current limiting devices and techniques. An energy storage system project was deployed which consists of 3 sites with a total of 1MW hours of distributed lithium-ion batteries. These batteries provide stored energy to be used for uninterruptable power supply (UPS) back up and peak shaving (PS) applications. The biggest site, of the3, contains a distributed energy storage system with 64 lithium-ion batteries, rated at 416 kWh, installed in parallel, with a potential of 384kA of short circuit current and this is almost 4 times more current than a 100kA rated fuse can handle. In circuit measurements were used to determine the inductance and resistance of the system. Computer simulations were used to verify the rise times, RMS, and peak current levels required to safely interrupting the current in the fuses. Increasing the Impedance (resistance and inductance), along with proper fusing, were used to limit the short circuit current in a system. Using this combined approach, the required protection to limit the potential short circuit current, flowing through any fuse, could be shown to be reduced to fewer than 100kA.