Yes, it's surge suppression, usually an MOV that will shunt the protected wire straight to ground; voltage drop does the rest. It's designed to kick in at a certain point above the normal line voltage so as to minimize any transients. Corner-grounding a delta will push the other two legs dangerously close to the threshold for TVSS activation though, at which point it will become a direct short circuit and draw fault current until either a breaker closes or something explodes.
All the high-end UPS systems have this internally. In fact, Powerware engineers cautioned me explicitly about not using a floating delta on one of their 500kVA units lest the delta drift off center and we blow the UPS up.
Although 65A on an undersized neutral can't be good either.
