hi everyone,

I've used Turnigy 2209 28turn 1050kv 15A Outrunner for my quadcopter with 20A esc, kk 5.5 board, Flysky FS-6TB tx rx kit n 400mAh 40C battery.. a wire of one of the motors which was connected to power distribution board came off and the motor on the opposite end of this motor got fried... initially it was fluctuating in clockwise n counterclockwise direction n after a few second i observed white smoke.. Smelled real bad.. I saw that windings on 4 poles were burnt..
what might be the reason for the motor to burn? 

heat build up without load release

Truely speaking, the motor is a 3 phase synchronous motor operation, driven with single phasing fault. Consult any rotating electrical AC machine book with single phasing fault in 3 phase motors.