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10.9 Armature Reaction in Alternator
When an alternator is running at no-load, there will be no current flowingthrough the armature winding. The flux produced in the air-gap will be only dueto the rotor ampere-turns. When the alternator is loaded, the three-phase currentswill produce a totaling magnetic field in the air-gap. Consequently, the air-gapflux is changed from the no-load condition.The effect of armature flux on the flux produced by field ampere-turns (i. e.,rotor ampere-turns) is called armature reaction.Two things are worth noting about the armature reaction in an alternator. First,the armature flux and the flux produced by rotor ampere-turns rotate at the samespeed (synchronous speed) in the same direction and, therefore, the two fluxesare fixed in space relative to each other. Secondly, the modification of flux inthe air-gap due to armature flux depends on the magnitude of stator current andon the power factor of the load. It is the load power factor which determineswhether the armature flux distorts, opposes or helps the flux produced by rotorampere-turns. To illustrate this important point, we shall consider the followingthree cases:(i) When load p.f. is unity(ii) When load p.f. is zero lagging(iii) When load p.f. is zero leading
(i) When load p.f. is unity
Fig. (10.10 (i)) shows an elementary alternator on no-load. Since the armature ison open-circuit, there is no stator current and the flux due to rotor current isdistributed symmetrically in the air-gap as shown in Fig. (10.10 (i)). Since thedirection of the rotor is assumed clockwise, the generated e.m.f. in phase R
1
R
2
isat its maximum and is towards the paper in the conductor R
1
and outwards inconductor R
2
. No armature flux is produced since no current flows in thearmature winding.
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Why DC suuply used in Excitation of Alternator?
for torque improvement in armature and create n-pole or s-pole in armature a dc source is used in alternator armature.
What are the effect of armature reaction in DC machine and how the armature reaction is minimise?
Armature reaction is the interaction between the magnetic flux produced by armature current and that of the main magnetic field in an electric motor or generator.
What is the difference between armature reaction and armature reactance?
armature reactant means loss in armature associated with inductive properties of the coil, while armature reaction include losses due to magnetizing component of current flowing through armature.
Why the induction motor does not have armature reaction?
Because the armature (or rotor) has no external connection. The currents that produce torque from the rotor are induced by the magnetic field in the machine, so there is no commutator, no brushes and no armature reaction.
Why pole face are chamfered in dc machine?
in order to reduce armature reaction.
What is mean by armature reaction?
armature reaction means when load is added to the armature then current is passed through armature conductors then in armature creates flux. It is demagnetize and cross magnetize the main field flux. in other ward it is effect of armature field on main field.
What are compensating winding?
compensating windings are used to overcome armature reaction
What are the components in an alternator?
Stator, armature, rectifier, bearings, brushes,
How many components makes an alternator?
stator armature recertifier
What is armature reaction in dc machines?
The armature reaction is the interaction between armature flux and field flux when current is introduced to a dc motor. It results in a cross-magnetizing effect and a demagnetizing effect.
What is armature reactions in a synchronous machine?
Armature reaction is the effect of armature flux on the flux generated by the fied windings.Cross magnetisation and Demagnetising are its consequences.
Armature reaction in a DC generator?
ARMATURE REACTION in DC MachineAll current-carrying conductors produce magnetic fields. The magnetic field produced by current in the armature of a dc generator affects the flux pattern and distorts the main field. This distortion causes a shift in the neutral plane, which affects commutation. This change in the neutral plane and the reaction of the magnetic field is called armature reaction.
