Failure of synchronous motor to start up on no load

I have a synchronous motor rated 2025HP,11KV,82.44A Excit: 43.6V, 112.3A,750RPM with a field resistor of 1 ohm which is a main drive motor for the winder,at first when this motor was run on no load it ran ok but when we tried to test run it in presence of the end users it couldn't start it was just humming.we have carried out all the necessary tests,we haven't found any open circuit in the power and rotor circuit, we have injected dc voltage in the rotor and all the pole voltage drops are equal.what can cause this motor to behave the way it is behaving?
Original Post
Dez,
When you say when in ran no load it was ok, then when you started it the second time was is still at a no load condition? I assume necessary tests include:
Voltage present and balanced on stator
No grounding of the stator or rotor.
Resistance is balanced on the stator/surge test
Resistance is balanced on the rotor/armature
Brushes, brush shunts, spring tension, slip ring circuit, resistor all check good?
Sounds like a single phase condition or no voltage getting to the rotor/armature, what about the fuses, breaker, wires to motor, junction box on side of motor.
Dave
what is really happening is that the motor will run on no load untill you switch it off but when you want to start it again it will just hum when you rotate the rotor manually and switch it on it runs so its like on certain positions it is locking itself( like stator north-rotor north)we have checked to see if there is any reversed connection on the stator and also checked the polarity on the rotor poles,all is ok but i don't know what is causing the motor to fail to start at certain postions.

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