Overcurrent protection schematic: is there any off the shelf solutions?
5us is slow? All others solutions I think they will be ultra slow, then. You can use a reed switch instead of hall sensor, but you'll get an aproximative threshold with long delay (compared to 5us).
Anyway, what is the purpose of this ovecurrent detector, I mean what is the voltage source, because if you are trying to detect SC over mains power supply the current will be far more than 30A, and what load you are trying to protect (resistive, inductive)?