CMR Institute of Technology

Jan. - May 2015 | Basic Electrical Engg. (14ELE25) | Sem 2 - I & J | Prof. H. N. ShankarAssignment # 07 Three Phase Circuits

Date of issue: 28 Mar., 2015 | Submission Due: 06 Apr., 2015-----------------------------------------------------------------------------------------

Instructions: ANSWER NEATLY AND LEGIBLY on A4 sheets only and not in sheets torn from a book. Sketch diagrams wherever relevant. Explain your notations explicitly and clearly. An incomplete assignment is not acceptable for submission. Once you submit your assignment, you will be expected to answer all the questions there

INDEPENDENTLY. You may be asked to answer any question of the assignment in the class.

-----------------------------------------------------------------------------------------Part-A: All students are required to answer all questions.

Q1. In a 3-phase system, explain (a) phase sequence; (b) positive sequence; and (c) negative sequence.Q2. What are (a) balanced and (b) unbalanced 3-phase systems? Sketch the waveforms for a balanced system of positive sequence quantities. Sketch the phasor diagrams for both positive and negative sequences.Q3. Explain briefly the generation of 3-phase emf-s.Q4. What are the advantages of 3-phase systems over 1-phase systems? Q5. What are (a) phase and line voltages; and (b) phase and line currents?Q6. In a balanced star, (a) identify the phase and line voltages and show how phase voltages are related to line voltages; and (b) identify the phase and line currents and show how phase currents are related to line currents. Sketch a phasor diagram for voltages. Q7. In a balanced delta, (a) identify the phase and line voltages and show how phase voltages are related to line voltages; and (b) identify the phase and line currents and show how phase currents are related to line currents. Sketch a phasor diagram for currents. Q8. In a balanced system of supply and load, find expressions for the complex power consumed with (a) star load; and (b) delta load.Q9. Explain the two-wattmeter method of measuring 3-phase power. State the NECESSARY CONDITION. Q10. How can the power factor in a 3-phase load be measured by the two-wattmeter method?

Part-BProblems: Courtesy: Basic Electrical Engineering by D. C. Kulshreshtha (See scanned pages)Note: You are required to check the answers to the problems provided in the pages below. Do NOT assume that they are ALL correct.

For I Sec: Problem numbers: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23 & 25.

For J Sec: Problem numbers: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24 & 26.

For your benefit, you are strongly advised to take the assignments very seriously.Topics in this assignment are included for the second Internal Assessment Test.

Submission Due: 06 Apr., 2015Good luck!