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Machine Riddle No.44 - Starting of synchronous motor
If we start a synchronous motor with field winding short circuited (no exitation) then we are sure that it will start as induction motor but, will this motor run as synchronous motor ??? or it will run as induction motor. pls explain in detail.
Author : RAMJEE KUMAR - From: India
Sat, June 30th, 2012 - 09:36
Starting of synchronous motor as a 3-Phase squirrel cage induction machine is the one of synchronous motor starting methods with using of damper windings or amortisseur windings not shorted exiting winding. The most of the large synchronous motors are provided with dampe windings, in order to nullify the oscillations of the rotor whenever the synchronous machine is subjected to a periodically varying load. Damper windings are special bars laid into slotscut in the pole face of a synchronous machine and then shorted out on each end by a large shorting ring, similar to the squirrel cage rotor bars. Once the motor picks up to a speed near about its synchronous speed, the DC supply to its field winding is connected and the synchronous motor pulls into step i.e. it continues to operate as a Synchronous motor running at its synchronous speed. The mentioned winding should be design for withstanding of induction starting current. 
Author : Hamid - From: Iran
Thu, October 11th, 2012 - 05:47
Why Field winding is excited when generator is rotated near to synchronous speed not at lower speed OR what will happen is Turbo-generator field winding is excited at around 1000rpm.  Is there any protection provided to avoid this? 
Author : rakesh kumar - From: India
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