What is the minimum RPM for the 2.2kW spindle?

Spindles with 2 poles, which is typically for these types of spindles will have a minimum RPM of 6000 RPM or 100Hz; however, I would not run the spindle below 15000 RPM or 250Hz to give a safety factor and no damage will occur. If you have a 4 pole spindle, then much lower RPMs can be achieved, and with higher torque than a 2 pole spindle. The 4 pole spindle will require more power than 2 pole spindles and will not be able to achieve as high maximum RPMs.