EEEB413_exam_sem2_0910

7/17/2019 EEEB413_exam_sem2_0910

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EEEB413, Semester II 2009/2010

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COLLEGE OF ENGINEERING

PUTRAJAYA CAMPUS

FINAL EXAMINATION

SEMESTER 2 2009 / 2010

PROGRAM : BACHELOR IN MECHANICAL ENGINEERING (Hons.)

PROGRAM

MATAPELAJARAN : ELECTRO-MECHANICAL SYSTEMS SUBJECT

KOD MATAPELAJARAN : EEEB413

SUBJECT CODE

TARIKH : MARCH 2010 DATE

MASA : 3 HOURS

TIME

I nstructions to candidates:

1. Answer AL L questions.

2. Total number of questions in this booklet: SIX (6)

3. This is a close book examination. Usage of scientif ic calculator is allowed.

4. All answers and rough work must be done in the examination answer booklet.

5. Useful equations are provided at the last page of this booklet.

DO NOT OPEN THI S QUESTION PAPER UNTI L YOU ARE INSTRUCTED TO DO SO

TH IS QUESTION PAPER CONSISTS OF ?? PRINTED PAGES INCLUDING THI S

COVER PAGE.

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QUESTION 1 [20 marks]

a) Three impedances of value Z = 4 + j3 Ω are connected in Y. For balanced line-to-

line voltages of 208-V, find the line current, the power factor, active power,

reactive power and apparent power for the load. (5 marks)

b) A ferromagnetic core with a relative permeability r of 2000 is shown in Figure 1.

The dimensions are as shown in the diagram, and the depth of the core is 7 cm.

The air gaps on the left and right sides of the core are 0.070 and 0.050 cm,

respectively. Because of fringing effects, the effective area of the air gaps is 5

percent larger than their physical size. If there are 400 turns in the coil wrapped

around the center leg of the core and if the current in the coil is 1.0 A, what is the

flux in each of the LEFT, CENTER , and RIGHT LEGS of the core? What is

the flux density in EACH air gap? Take o = 4 x 10-7

H/m. (15 marks)

[5+15=20 marks]

End of Question 1

Figure 1: Ferromagnetic core

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A 1200V, 750kVA, 50Hz, 4 poles, Y-connected synchronous generator has a

synchronous reactance S X = 0.9Ω and an armature resistance A R = 0.1Ω. Friction and

windage losses at 50Hz are 20kW, and its core losses are 10kW. The Open Circuit

Characteristic (OCC) of this generator is shown in Figure 2.

a) Find the field current ( f I ) required to maintain the terminal voltage at 1200V

during no load. (1 mark )

b) What would be the required internal generated voltage ( A E ), torque angle ( )

and the required field current ( f I ) if the terminal voltage were to be kept at its

rated value 1200V when the generator is loaded with the rated current at unity PF.

(8 marks)

c) Calculate the efficiency of the generator in case b). (6 marks)

[1+8+6=15 marks]

End of Question 2

Figure 2: OCC of a synchronous generator

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A single phase 150-kVA, 2400/240-V transformer has the following parameters

determined:

R1 = 0.2 Ω R2 = 0.002 Ω RC = 10 k Ω

X 1 = 0.45 Ω X 2 = 0.0045 Ω X M = 1.6 k Ω

a) Draw the equivalent circuit referred to the High-Voltage side. (4 marks)

b) Determine the voltage regulation when the transformer is supplying full-load at

0.8 PF lagging. (4 marks)

c) Determine the efficiency of the transformer when the transformer is supplying

full-load at 0.8 PF lagging. (5 marks)

d) Determine primary side current I P when the transformer is supplying full-load at

0.8 PF lagging. (4 marks)

e) Describe the differences between practical transformers compared to ideal

transformers? (3 marks)

[4+4+5+4+3=20 marks]End of Question 3

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a) A 3-phase induction motor has a starting torque of 100% and a maximum torque

of 200% of the full-load torque. Calculate:

(i)

Slip at maximum torque (5 marks)(ii) Full-load slip (5 marks)

b) Complete the diagram below by drawing the direction of the magnetic flux for

ALL 7 (seven) points in Figure 3(b). (5 marks)

[5+5+5=15 marks]

End of Question 4

Figure 3(b): Direction of magnetic flux in accordance to the current

Figure 3(a): Stator windings and current supply

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Company A is designing a 2 roller belt conveyor system for the production line. The

motor that drives the belt conveyor has to be selected to fulfill the requirements above. 4-

pole single phase induction motor is thought to be suitable for the system. Based on the

requirements and the catalog provided in Appendix A, select the appropriate motor.

Justify your answer. Note that no-load speed is approximately 1470 rpm and rated speed

is between 1450 rpm to 1550 rpm for a 4-pole motor at 60 Hz. Use safety factor of 2 and

select a pinion shaft, lead wire type motor.

[20 marks]

End of Question 5


CHOOSE ONE of the following motors and describe it in POINT FORM. The

explanation MUST INCLUDE the working principle, equivalent circuit, torque-speed

curve and the application.

List of motors: DC brushed, DC brushless, AC Induction, AC Synchronous, Linear

Motor, Stepper motor.

[10 marks]

End of Question 6

Total mass of belt and work, m1 = 20 kg

Friction coefficient of sliding surface, = 0.3Roller diameter, D = 100 mm

Mass of roller, m2 = 1 kg

Belt roller efficiency, = 0.9

Belt speed, V = 140 mm/s ± 10%

Motor power supply, Single phase 110 V, 60 Hz

Movement time, 8 hours per day

Required specifications and structural specifications

-END OF QUESTION PAPER-

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LIST OF EQUATIONS

2

2

1 746

120

sync m

sync

F R Ni Hl

l R

A F Bil

e Blv

P

V P I R

R

hp W

fen p

n n s

n

1

1

1

3

3

3

cos

sin

3 3

3 cos 3 cos

3 sin 3 sin

3sin

3sin

A

A

A

A T L

A T L

A T L

A

s

A

m s

S V I

P V I

Q V I

S V I V I

P V I V I

Q V I V I

V E P

X

V E

X

1

22 2

122 12

2

1

2

2

max max2 22 2

2 2

3,

3

2

TH

mTH

m

mind TH

m

sync TH TH

TH

TH

TH TH sync TH TH TH

X V V

X X

RV

X s where R R X X R

R X X s X X

R V s

R X X R R X X

I

V Z

EEEB413_exam_sem2_0910

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