📘 Synchronous Motor – V Curves & Inverted V Curves
V-curve explains relationship between armature current and field current at constant load. Very important for power factor control.
🔹 1️⃣ What is V-Curve?
Graph between: Armature Current (I_a) vs Field Current (I_f) At constant mechanical load. Shape resembles letter "V".🔹 2️⃣ Why V Shape?
Case 1: Under Excited Field current low → Back EMF low Motor draws large lagging current. Case 2: Normal Excitation Back EMF equals required value Armature current minimum Power factor = unity. Case 3: Over Excited Field current high Motor draws leading current Armature current increases again. Thus current decreases then increases → V shape.🔹 3️⃣ Inverted V-Curve
Graph between: Power Factor vs Field Current Shape is inverted V. Under excited → Lagging PF Normal excitation → Unity PF Over excited → Leading PF Very important concept.🔹 4️⃣ Practical Importance
Industries operate motor in over excited condition to supply leading reactive power. Used as: Synchronous Condenser🔹 5️⃣ Example Concept Question
If load constant and field current increased: Armature current first decreases then increases. Minimum at unity power factor.🔹 6️⃣ Important Observations
- V curve drawn at constant load
- Minimum current at unity PF
- Over excitation → Leading current
- Used for PF improvement
🎯 GATE Important Points
- Remember V-curve shape
- Know under vs over excitation
- Inverted V shows PF variation
- Common conceptual question area
Minimum Current Occurs at Unity Power Factor
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