Answer / abysen

when a synchronous machine operates at no load,Ia=0,therefore Fa=0.Neglecting the leakage impedance,then Ff=Fr & Ef=Er=Vt.Under this condition the machine is neither in motoring nor in generating mode.This condition is called Floating on the line.
Fa=mmf due to arm current
Fr=air gap mmf,Ff=field mmf,Ef=excitation emf,Er =air gap emf.

Answer / iamdon

The 3 phase synchronous machines(alternator as well as
motor) has a special capability of working on different
power factors(lagging,leading and unity) depending upon the
excitation of DC field as mentioned below.

Overexcited----Motor will take leading current
Underexcited---Motor will take lagging current
Normal excited-Motor will take unity pf current.

So, overexcited motor can be used for power factor
improvement in large industrial plants where many Induction
motors and like wise loads are running.Under this situation
motor is not driving any mechanical load.Such state of
working of synchtronous motor is termed as 'A synchronous
motor floating on line'.

Author:arbelectbit@yahoo.com

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