Adding Vsd To Motors And Bearing Failure

Hi.
I need to add VSDs to 2 x 150kW motors. They are currently started by old large orange cabineted Turnbul and Jones liquid starters. However the power company is disturbed with the voltage droop we are causing at start up in the incoming 11kV lines. Hence the need to go to VSD's. Now both these motors will run at 50Hz. do i need shaft earthing brushes to eliminate bearing failure caused by stray induced currents?

Rotor Bar Failure

Hi. Just had a 150kW (old type) WEG motor fail due to rotor bars collapsing. Bars are copper section welded at ends. Bars have burnt through laminations at the ends in places. Debris has cut windings. Motor is soft started and drives a high inertial load. Soft start is AB. Start time is 20 secs. Is this just old motor problems or has the high rotor currents flowing for protracted periods caused the rotor bars to overheat The second failure is a 90kW weg motor. In this case the rotor assembly has shifted along the shaft and hit the endbell. Motor is vertically mounted. My beleif this would be a warranty case but motor is 10 yrs old.

Motor tails

How do i identify the correct conections of an unlabelled 6 wire motor. Is there a test to establish which is U1V1W1 or U2V2W2