Question
Download Solution PDFIn an alternator, the nature of armature reaction at zero power factor leading loads is _______.
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFMMF wave diagrams of alternator:
The operation of a synchronous machine may be understood by considering its m.m.f. waves.
There are three m.m.f. waves to be considered that
- Due to the field winding ϕf, which is separately excited with the direct current.
- Due to the 3-phase armature winding flux ϕa.
- Their resultant flux ϕr = ϕf ± ϕa
All the MMFs produced in the motor move at synchronous speed with respect to the stator.
Zero power factor lagging:
The armature reaction is entirely De-magnetising in nature.
ϕr = ϕf - ϕa
The net flux reduces the load to reduce the terminal voltage.
Voltage regulation is positive.
Zero power factor leading:
The armature reaction is entirely Magnetising in nature.
ϕr = ϕf + ϕa
Net flux in the airgap increased to increase induced voltage and the terminal voltage.
Voltage regulation is negative.
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