Ahh interesting so if the ratio stays the same then the OP's motor would perform the same as at 50hz? He'd have to run it off 265V somehow.
It still going to run about 17-18% faster because of the frequency, which will cause the centrifugal fan to demand more power at that speed (if nothing is changed there). Now if this motor were designed/intended to be run at that frequency then it might be ok, but it will not give same performance at both frequencies.
VFD's do vary voltage as well as frequency and will maintain V/F ratio no matter what speed they are running at, it is part of the basics of how and why they will work on a given motor. They can be tweaked to vary that ratio a little while accelerating or decelerating to get some torque boost but you can't leave it out of the base V/F ratio range for long or it is hard on the motor windings.
If you are running a 60 Hz 460 volt motor at 30Hz, the drive output will be ~230 volts, full load HP at that speed is half the HP it is at full speed, if it is running at this halved full load current will be same as nameplate full load current. V x A will be half the nameplate V x A - half the speed can deliver half the power, slight variances is because of efficiency aspects but will be pretty close to half the power as at full speed. Where it gets more complex is with variable torque loads like centrifugal fans and pumps, constant torque loads are mostly linear as speed changes.