SKR Engineering College 2006 B.E Electrical and Electronics Engineering EE 1211- ELECTRICAL MACHINES - Question Paper

S.K.R. ENGINEERING COLLEGE
POONAMALLEE, CHENNAI-602103.

Third Semester
Electronics & Communication Engineering
EE 1211- ELECTRICAL MACHINES
Model exam
Date: 18.10.2006
Time: three Hrs Maximum: 100
ans ALL ques.
PART A [10X2=20]
1.Express the emf formula of DC generator?
2.What does starter mean? What is the necessity of having starter with DC motor?
3.What are the losses had happen in transformer?
4.Define voltage regulation of transformer? provide the expression for the same?
5.Draw the equivalent circuit of a three-phase induction motor?
6.A six pole, 3 phase induction motor runs at 800 rpm at load. Determine the value of
slip at this load condition?
7.Define pitch factor and distribution factor as applied to alternator?
8.Write down any four advantages of short pitch winding in synchronous machines?
9.What is the voltage range for transmission and distribution system?
10.Give the advantages of cables compared with overhead transmission lines?
PART B [5X16=80]
11.(i) List the advantages and disadvantages of EHVDC transmission system? [8]
(ii) Draw the layout and single line diagram of a main power-receiving substation with
the subsequent details,
2 Nos of 220kV incoming lines, Duplicate bus bar with bus coupler arrangement
2 Nos of 110kV outgoing lines
3 Nos of 66kV lines, necessary CB’s and Lighting arresters? [8]
12. A. (i) A four pole, lap wound, 750 rpm, dc shunt generator has armature resistance of
0.4 ohm and field resistance of 200 ohm. The armature has 720 conductors and
flux per pole is 30 mWb. If the load resistance is 15 ohm, obtain the terminal
voltage? [8]
(ii)Draw and discuss the load characteristics for all kinds of dc generator? [8]
OR
B. (i) discuss the speed control methods of DC motor? [8]
(ii) Derive the torque formula for dc motor? [8]
13. A. (i) Derive the emf formula of a transformer? [4]
(ii) A five KVA, 500/2500 V, 50 Hz, single phase transformer gave the subsequent
readings,
O.C. test: 500V, one A, 50W(LV Side open)
S.C. test: 25V, 10A, 60 W (LV side Shorted)







Determine,
I. The efficiency on full load, 0.8 lagging power factor.
II. The voltage regulation on full load, 0.8 leading power factor.
III. The efficiency on 60 % of full load, 0.8 leading power factor.
IV. Draw the equivalent circuit referred to primary and inserts all the values.[12]
OR
B. (i) discuss the constructional details of single phase transformer [6]
(ii) Draw how the simplified equivalent circuit of a transformer can be found
without introducing much error? [10]
14. A. (i) Sketch and discuss the typical torque slip characteristics of a three phase
Induction motor? [8]
(ii)The power input to a 500 V, 50 Hz, six poles, 3-phase induction motor
running at 975 rpm is 40 kW. The stator losses are one kW and friction and
windage losses total two kW. Calculate,
I. Slip II. Rotor Cu Loss III. O/P Horse power IV. Efficiency [8]
OR
B. discuss the different kinds of starters used in 3-phase induction motor [16]
15. A. (i) discuss the principle of operation of permanent magnet stepper motor [8]
(ii) discuss the principle of operation of hysteresis motor [8]
OR
B. describe voltage regulation of an alternator? How it can be computed by
Means of EMF and MMF methods? [16]

Earning:   Approval pending.