The information is grossly inadequate. The breaker may have some mechanical problem/pole descrepency trip. give some more details about the size,voltage level,type of protection,breaker details etec.
There is practically nothing that can be done to avoid the drop in voltage for few cycles for a ph-ph fault, if you don't want any costly re-designs. Motors are designed for undervoltages of few 100msec and if drive control is the problem, go for seperate constant voltage source for the same...
some times high resistance earthing will be done for the detection of ground fauls in floating neutral systems. This can also result in the same observation.
