If production slightly exceeded consumption, and production was not reduced, the generators at the powerplants would end up speeding up and the frequency and vo

If production slightly exceeded consumption, and production was not reduced, the generators at the powerplants would end up speeding up and the frequency and voltage of the network would go up. As voltage increases, many loads end producing more power and at some point an equilibrium would be achieved. If something goes wrong and a large part of consumption disappeared (e.g. broken HVDC transmission line) the generators would start overspeeding dangerously, and as voltage went over the limit, things would start breaking downstream (transformers, loads themselves burning due to overvoltage), resulting in a cascade of failures that would end up as far as damaging the generators themselves. Grid balancing is a tough act.