In synchronous generator, nature of armature of armature reaction is _________ when it supplies a load at unity power.
Synchronous Generator Armature Reaction at Unity Power Factor
In a synchronous generator, armature reaction refers to the effect of the magnetic field produced by the armature current on the main magnetic field produced by the field winding.
Understanding Armature Reaction Types
The nature of armature reaction depends on the power factor of the load connected to the generator. The three main types are:
- Demagnetizing Armature Reaction: Occurs when the armature MMF opposes the main field MMF, weakening the main field. This happens at lagging power factors.
- Magnetizing Armature Reaction: Occurs when the armature MMF assists the main field MMF, strengthening the main field. This happens at leading power factors.
- Cross-magnetizing Armature Reaction: Occurs when the armature MMF is spatially perpendicular (in quadrature) to the main field MMF. This distorts the main field but does not significantly strengthen or weaken it.
Armature Reaction at Unity Power Factor
When a synchronous generator supplies a load at unity power factor (UPF), the armature current is in phase with the generated EMF. In terms of the magnetic fields:
- The main field flux is produced by the field winding.
- The armature reaction is caused by the MMF produced by the armature current. At unity power factor, the armature MMF ($MMF_{armature}$) is spatially located 90 electrical degrees away from the main field MMF ($MMF_{field}$).
- Mathematically, the spatial relationship can be thought of as:
$$MMF_{armature} \perp MMF_{field}$$
- This spatial displacement means the armature MMF acts along the interpolar axis, distorting the main field flux distribution. It compresses the flux under the leading pole tips and expands it under the trailing pole tips.
- This distortion effect is known as cross-magnetization. It does not add to or subtract from the main field flux linearly, but rather deforms it.
Conclusion
Therefore, when a synchronous generator supplies a load at unity power factor, the nature of the armature reaction is primarily cross-magnetizing.
Important Questions from Armature Winding
What would be the coil span, if the span of the coil is reduced by α electrical degrees?
The chording angle for eliminating fifth harmonic should be:
_______ may be variously defined as the periphery of the armature divided by the number of poles of the generator i.e., the distance between two adjacent poles.
A fractional pitch winding cannot be used to reduce:
In case of two-layer winding in stator of alternators, each slot in stator contains _________.
