Mansoura UniversityFaculty of Engineering 2nd

- Year Exam.Electrical Eng. Dept. Time: 1.5 Hours

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Good Luck With My Best WishesPROF.Dr. A.R.A.Amin

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Mansoura University.Faculty Of Engineering.Electrical Engineering Dept.

Electric MachineTime allowed: 3 Hours3/6/2012

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Mansoura University.Faculty Of Engineering.Electrical Engineering Dept.

Electric MachineTime allowed: 3 Hours3/6/2012

Final Term ExamFodd Grad Electronic Department

Answer All Question.

First Question: (15 Marks)1-a) Draw phasor diagram for a cylindrical rotor alternator with armature

current lagging, leading, and unity pf. discusses the various parametersinvolved in it. Explain how the diagram can be applied a synchronousmotor.

1-b) A 3 MVA, 11kv, 50 Hz, star-connected cylindrical rotr alternator 4 pole, has60 slot, with 2 conductor/slot and having armature winding of the two layertype, the winding are chorded by 2 slots, the experimental result of open-circuit and short circuit test is plotted.Find flux at full load 0.8 p.f. lagging, by using: Synchronous impedancemethod; ampere-turn method. Neglect armature resistance.

8 T7 1-~3 1-

----- 5J-

> I~r

0 4 +~><l.)Cl)ro-C.0...

3

o

T

300

[250 i~ 200 ~

~150-32

100 -(3t

50 ~eno

5 10 20 25 30 35field current

15 40 45 50 55

Page 10f2

Second Question: (20 Marks)2-a) i- from test of synchronous machine, find equivalent circuit.

ii- from test of induction machine, find equivalent circuit.2-b) Explain the operation principle and draw the power flow of a 3-phase

induction machine at the following operation cases:i- Starting period, ii- No-Load condition,iii- Running at rated load with slip (s) iv- Running at negative slip

then, prove that: Pg: PCU2 : Pm = 1:s : 1-S

Third Question: (20 Marks)3-a) Explain why single phase induction motors are not self starting? State and

compare between the various type of them?3-b) Explain (with help of net diagrams) the starting method adopted for:

i-Three-phase induction motor (squirrel-cage and slip ring).ii-Three-phase synchronous machine.

3-c) A 415 V, 50 Hz, 6 pole, delta connected three phase induction motorconsumes 70 Watt with line current of 112.5A and runs at slip 3 %. If thestator iron losses is 3 KW, windage and friction losses 2 KW and statorresistance 0.1O/ph, and rotor reactance 1O/ph. Calculate:a- Rotor cupper loss; b- Mechanical power;c- Developed shaft torque; d- maximum torque;

d- Efficiency

With my Beast Wishes

Page 2 of2