Question
Download Solution PDFIgnoring the effect of armature reaction, if excitation of a synchronous motor running with constant load is increased, its torque angle must:
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFConcept:
Effect of changing field excitation for constant load:
For a synchronous motor, as excitation (E) is increased :
- PF (i.e. cos ϕ) decreases and becomes more and more leading
- Armature current, Ia increases.
As we move from normal excitation ( E = V) to overexcitation (E > V), Ia increases from a minimum at normal excitation (Unity PF)
Explanation:
For synchronous motor:
E = V - Ia (R + j X)
From phasor approach,
Under-excitation (lagging pf)
Over-excitation (leading pf)
As we go from under-excitation → normal excitation → over-excitation, E moves anticlockwise and δ decreases.
Additional Information
| Excitation | Power factor |
| Under excitation | Lagging power factor |
| Normal excitation | Unity power factor |
| Over excitation | Leading power factor |
Last updated on Jul 1, 2025
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