Selection of VFDs

For example if the motor is 60 HP should we select a drive one rating higher than motor...

Here I was seen one machine and we selected same rating drive and motor but near by same configuration machine using one ratting higher drive. and in the first one drive is getting tripped frequently when ever there is a voltage fluctuation, but the same time other machine is working fine. and once we too replace our drives into higher rating the problem has been sort out ...