Kilowatt KW is active power.
Kilowatts (KW) = kilovolt-amperes (KVA) times power factor.
Active power P, reactive power Q, apparent power S has the following relationship P = S × cos Φ (Φ is the power factor)
The regulator labeled 150KVA is the apparent power, and you look at your machine power factor (cos Φ) is how much? (Generally in 80%-95%)
Specifically, we also need to consider the voltage regulator's transient load rate, generally require the rated only 80% of the long-term load,
Specific calculations: 90KW ÷ 80% ÷ power factor (cos Φ) = is the answer you want
Practical application of the 90kW load with a 150KVA is more appropriate.