motor problem : no load amps is high

my sorsz 28"/40 " 533 series 2 color unit stops running after a few minutes .
found that the no load amp ( when checked it was 30 amps) is more than the rated current. if the speed is increased up to 6000 sheets per minute, the current consumption is 20 amps.

if we bypass the thermostat the motor runs.

( primary voltage - 425 v , Transformer tapping 380v . Secondary Voltage 190v 50 hz )

couldn't find out the problem, please guide.