Motor Excitation
Motor Excitation
(OP)
Why do we apply DC excitation on Synchronous Motor at nearly 95% of the sync speed, why not at 60 or 70%?
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RE: Motor Excitation
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: Motor Excitation
RE: Motor Excitation
With a generator you want to match the grid frequency and voltage, then close the generator breaker.
With a synchronous motor, you close the motor breaker and the motor is accelerated to speed via a squirrel cage winding built into the rotor pole faces (other starting systems are possible). The rotor field breaker is then closed to apply the field when the rotor is at maximum speed (could be 90% as you say). The motor then accelerates to synchronous speed and full load can be applied. Larger motors have to be started unloaded, as the squirrel cage often has relatively poor torque.
If you apply the field at too low a speed the motor will try and draw a high current from the supply and will trip on over current.
RE: Motor Excitation
Higher the deviation from the synchronous speed, higher the stress.
This is the reason why one would like to interlock Field DC application with motor speed (not less than 95% rated).