To mechanical / electrical engineers,how to supply 3-phase motor with a single-phase supply using steinmetz?

First of all the motor if rated at 230v, IS single phase otherwise it will be rated at 415v if 3 phase. I am not familiar with the term steinmetz so I cannot help you there. however, microfarads @ 50 Hz = 3180 X Amperes Divided by Applied Voltage So, a 1/4 HP motor drawing approx. 3.2 Amps at 240 Volts (if the start winding is also operating at 240 Volts), the required capacitor would be in the neighbourhood of 38-42, or 43-48 mf.