Sizing up a drive transformer

[tajin23]

As per my Manager instructions I always sized up a drive isolation(voltage match) transformer for continuous operation based on KVA load demanded from the controllers for continuous mode S1 operation, controller load in some cases were bigger than drive HP. Now my Manager have instructed me to sized them up according to machine cycle, one of our customer have complained, their machine cycle Amperage average readings are around 10~15% of rated transformer amperage. Trying to find a method to sized them, with a DACQS I grabbed the amperage readings(1000) of an existing machine during the working cycle 1.7 seconds, I rms the readings, and verify the overloading amperage peaks as per IEEE std C57.12.59 and I2t = 1250, the transformer is 75 KVA, 600/460VAC 3ph, dry type delta-wye, with this new method it should be 10 KVA, the controller input voltage is 400..500 VAC. Based on the information I have grabbed(I have done with other machines also) and different scenarios the machine can run I can predict the amperage profile of new machines during it's machine cycle and make the transformer size more according to the load, can you feedback to me if this is the way of doing it, or if I am missing something here, with this number is any factor to oversize it?