In a synchronous motor armature current flows due to revolving flux which in turn rotates the load,but in no load condition armature current is zero hence thr is no revolving flux then how motor rotates? pls give books referance.

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  • Oct 16th, 2006

When syn mtr is at no load, armature draws current required for magnetisation.

as supply having some freq. so field flux continues 2 rotate at syn speed.

understand in syn mtr speeed is constant from noload 2 full load.For u r reference "Electrical Machinery by P.S. Bhimbra" is very good book.

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  • Oct 6th, 2007

The question I feel is wrong as current flow in three phase winding causes flux which appears to be revolving. This revolving magnetic field poles get locked with the fixed rotor poles and thus the motor shaft rotates. Hence irrespective of load on the motor, it runs at constant synchronous speed depending on the number of poles and supply frequency.


  • Oct 1st, 2009

In synchronous motor current in armature winding the current doesn't depends on load it is supplied seperately from other means, hence the question asked is wrong for synchronous motor, however induction motor have their rotor circuitary complete and also run on no load condition.


  • Oct 3rd, 2009

Armature winding is 3 phase winding and is supplied with 3 phase supply

Field is supplied with DC supplied

First motor is run at syn speed to lock rotor in syn speed now load is applied

Questioner is confused actually the rotating field is produced by armature not by field.

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  • Jun 19th, 2010

Synchronous motor: we will give dc supply to the armature as a excitation, which causes revolving flux, so that motor will rotate at synchronous speed.

if there is no excitation and the armature coils are shorted at their ends then it is called three phase induction motor.then rotating magentic flux causes current flow in conductor and as per faradays law any current carrying conductor placed in magnetic filed experience force.

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