🔍 Key Concepts

• AC generator field circuit and rheostat function – what happens to field current if the rheostat goes open? • Effect of short‑circuiting alternator terminals – how does this affect current and power factor when the field is healthy vs. when it is open? • Wattmeter behavior and alternator voltage – relation between field excitation, terminal voltage, and power flow indication

💭 Think About

• When you short‑circuit an alternator with a healthy field, what happens to armature current and the wattmeter reading? Now, if the field rheostat is open (no excitation), how will that change both the current and the indicated power? • Compare what you would expect for terminal voltage with and without excitation. Would an alternator with an open field rheostat be able to build up normal voltage or only a residual value? • Think about whether power can be delivered (positive or negative) when there is no magnetic field to link the stator and rotor. What kind of wattmeter deflection, if any, would be meaningful in that situation?

✅ Before You Answer

• Verify what field excitation is required for an alternator to build up normal voltage under any load condition. • Consider whether an alternator with an open field circuit can deliver real power into a short circuit, and how that would appear on a wattmeter pointer. • Check if the expected symptom is primarily a change in voltage level or a change in power indication (wattmeter deflection) when the field rheostat is open.