Agreed no where near that current goes directly thru the regulator, but if it sets up the alternator for full charge, well, the current back into the battery could exceed 30A. Fact that the alternator is making current likely indicates that it is working, could have an internal fault that is fully energizing the fields at all times. I'm wondering about this 30A fuse. If I'm right, there is a fusible link in the primary battery supply to the car, but this is a bear to change. Any fuse that is easily replaceable and kills the entire electical system sounds like an add on to me. Can you detail which fuse this is?
Maybe check to make sure the field and stator wires are not reversed at the alternator?