Assignment 02 – AC Machines

 

Assignment – AC Machines 

Course: Electrical Engineering Semester: 4 Subject: AC Machines **Assignment No.: 02 Maximum Marks: 20 Submission Date: 22/04/2026

Instructions

• Answer all questions neatly with proper diagrams wherever required.

• Use standard notation and units.

• Each question carries equal marks unless specified.

• Show all steps in derivations and numerical problems.

Part A – Short Answer Questions (Any five) (2 Marks Each)

1. Explain the construction and working principle of a single‑phase induction motor using the double revolving field theory.

2. Classify single‑phase induction motors based on different starting methods (split‑phase, capacitor start, shaded pole).

3. State the applications of single‑phase induction motors in domestic and industrial use.

4. Explain with neat diagram the construction of a synchronous machine (salient pole and cylindrical rotor).

5. Define synchronous speed and slip in alternators.

6. Differentiate between turbo‑generators and hydro‑generators.

7. What is hunting in synchronous motors? How can it be prevented?

Part B – Long Answer Questions (Any two) (5 Marks Each)

1. Draw and explain the equivalent circuit of a single‑phase induction motor. Discuss its torque‑speed characteristics.

2. Derive the EMF equation of an alternator and explain the significance of chording and breadth factors.

3. Explain the methods of synchronization of an alternator with bus bar (two bright & one dark lamp method, synchroscope method) with neat diagrams.

4. Draw and explain the V and inverted V curves of a synchronous motor. Discuss their significance in power factor correction.

5. Describe the construction, working principle, and applications of any two special electrical machines (Stepper motor, AC servo motor, Linear Induction Motor, Reluctance motor, Hysteresis motor, Universal motor).

                                     OR

 Numerical Problems (Any two) (5 Marks Each)

1. A split‑phase induction motor develops a starting torque of 12 Nm when the auxiliary winding is connected.

   • If the auxiliary winding is disconnected, the starting torque reduces to 4 Nm.

   • Calculate the torque ratio and comment on the effectiveness of the auxiliary winding.

2. A capacitor start induction motor has a main winding current of 5 A lagging the supply voltage by ${40}^{\circ }$.

   • The auxiliary winding current is 3 A leading the supply voltage by ${50}^{\circ }$.

   • Calculate the starting torque (proportional to $I_m{I}_a\sin \theta$).

   • State whether the motor will have high starting torque suitable for heavy loads.

3. A single‑phase induction motor equivalent circuit has the following parameters:

   • Stator resistance $R_1=2\mathrm{\Omega }$,

   • Stator reactance $X_1=4\mathrm{\Omega }$,

   • Rotor resistance (referred to stator) $R_2^{\mathrm{\prime }}=3\mathrm{\Omega }$,

   • Rotor reactance $X_2^{\mathrm{\prime }}=5\mathrm{\Omega }$.

   • Applied voltage = 200 V.

   Calculate the input current and power factor at standstill (blocked rotor condition).

Submission Guidelines

• Attach the assignment sheets with a cover page (Name, Roll No., Semester, Subject).

• Use proper diagrams, equations, and references.

• Late submission will result in deduction of marks.