52V at 50A is getting tricky to break, and you'd need to use semi-conductor switches to get any kind of sensible reaction time (<1ms) A parallel array of charge pumped N-FETs will probably be required, with suitable current sensing and either analogue comparator based triggering or a small micro etc.
That's assuming you want a simple "when the current exceeds this value, turn off" type arrangement. If you want a constant current control, then the task gets really hard, because the potential power dissipation in the 'switches' becomes large.