dThe effect of armature flux on the flux produced by rotor ampere-turns is called the armature reaction. dIn the case of alternator, the armature flux and the rotor flux moves at the same speed. dStator current and the load power factor determine whether the armature flux opposes, distorts or helps the rotor flux. dFor Unity Power Factor Load, the effect is only distorting. dFor Zero lagging Power Factor Load, the effect is only weakening. dFor Zero leading Power Factor Load, the effect is only strengthening.
v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} p\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);} v\:textbox {display:none;} dWe can use Ohm‘s Law to find out the value of the synchronous impedance. d The open circuit voltage of the synchronous generator is first measured to read Vopen circuit. Then the generator is short circuited to measure Iopen circuit. The value of synchronous impedance is found from Zs = Vopen circuit / Ishort circuit ( at the same excitation ) dThe curve for short circuit current is always a straight line because during short circuit, the short circuit current is a demagnetizing current. As a result, the magnetic field is never saturated. Hence, we can find the value of Ishort circuit by interpolation even the two tests are not carried out at the same value of excitation.
v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} p\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);} v\:textbox {display:none;} dWe often use e.m.f. phasor diagram to illustrate the phase relationship between the various phasors in a synchronous generator d dFor a generator, the generator internal voltage Et is ( physically ) larger than the infinite busbar voltage V, [Et = E1 + I1Xa [E1 = V + I1 Rs + I1 X leakage [Et = V + I1 Rs + I1 Xa  + I1 X leakage [ dIn fact the actual value of Et may be smaller than the actual value of V as in the case of an under-excited generator where the stator current is leading

 


Comments

ankit kumar gupta
08/09/2013 04:22

explain armature reaction of alternator

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