It is always possible to correct a motor to unity
power factor, but total correction is normally not
recommended. The influence of other reactive forces
on the power line, such as changing motor or transformer
load, is unpredictable, and if the power factor
is over-corrected, it can cause high currents, high
magnetic side pull forces on the motor rotor, high
voltage, and transient motor over-torque much greater
than full load motor torque. Whether overcorrection
will cause motor damage is uncertain, but
there is evidence that motor life can be shortened by
voltage spikes caused by over-correction. A safer
course is a more conservative one, limiting correction
to the .9 (or 90%) level.