electrical technology

MULTIMEDIA COLLEGE

JALAN GURNEY KIRI

54100 KUALA LUMPUR

THIRD, FOURTH SEMESTER FINAL EXAMINATION, 2014/2015 SESSION

EGR2073 – ELECTRICAL TECHNOLOGY

DTEA-E-F-3/12, DTET-E-F-1/13, DTEA-E-F-1/13, DTES-E-F-1/13,

DTEQ-E-F-1/13, DTEW-E-F-1/13

21 SEPTEMBER 2014

2.00 PM – 4.00 PM

(2 HOURS)

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INSTRUCTIONS TO STUDENT

1. This Examination paper has EIGHT (8) printed pages.

2. This question paper consists of ONE (1) section.

Answer FOUR (4) questions ONLY.

3. Please write all your answers in the Answer Booklet provided.

STUDENT IDENTIFICATION NO

EGR2073 ELECTRICAL TECHNOLOGY 21 SEPTEMBER 2014

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TH/BA/KZM/UI/NFCM of 8

INSTRUCTION : ANSWER FOUR (4) QUESTIONS ONLY- (100 MARKS)

Question 1

(a) By referring Figure 1, identify which meter represent:

Figure 1

i. Real power

(2 Marks)

ii. Apparent power

(2 Marks)

iii. Calculate the apparent power value

(2 Marks)

iv. Calculate power factor value

(2 Marks)

v. Draw the power triangle

(3 Marks)

vi. Determine the reactive power value of this load.

(4 Marks)

Continued…


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(b) Fill the table 1 with the suitable answer

(10 Marks)

Table 1

Continued…

Resistive Load Capacitive Load Inductive Load

Phase angle

ϴ = 0

ϴ = ϴ = > 0

Complex Plane

Sketch

Power Factor

Unity

Explanation

The current “lags”

the voltage

Reactive Load

Negative


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Question 2

(a) Figure 2 show a connection of ‘Y’ and ‘Delta’ in three-phase configurations.

Completely label where each of the following electrical quantities would be

found in both the ‘Y’ and ‘Delta’ three-phase configurations in terms of:

i) Phase voltage

ii) Line Voltage

iii) Phase current

iv) Line current

(12 Marks)

Figure 2

(b) In which circuit (Y or Delta) are the phase and line currents equal? In which

answers.

(4 Marks)

Continued…


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(c) Figure 3 shows a balanced Delta-to-Delta connection system. Calculate all the

voltages, current and total power in this balanced system.

(9 Marks)

Figure 2

Figure 3

Continued…

230

V


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Question 3

(a) Define permeability.

(2 Marks)

(b) Magnetic properties of materials are characterized by their relative

permeabilities. Briefly explain the following materials.

i) Ferromagnetic material

ii) Paramagnetic material

iii) Diamagnetic material

(9 Marks)

(c) A steel ring, 20 cm mean diameter and circular cross section of diameter 2.5

cm, has an air gap of 1 mm. The ring is uniformly wound with 500 turns of

copper wire carrying a current of 3A. Calculate:

i) The total magnetomotive force

(2 Marks)

ii) The magnetomotive force of the steel ring

(2 Marks)

iii) The magnetomotive force of the air gap

(2 Marks)

iv) The flux density

(8 Marks)

Continued…


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Question 4

(a) What are the essential parts of a transformer and briefly describe them. You

may add to the diagram to help you to answer.

(7 Marks)

(b) Draw the circuit diagram symbol for a transformer.

(3 Marks)

(c) A transformer has 500 primary turns and 3000 secondary turns. If the primary

voltages is 240V, determine the secondary voltages, assuming an ideal

transformer.

(5 Marks)

(d) A 5KVA single phase transformer has a turns ratio of 10:1 and is fed from a

2.5KV supply. Neglecting losses, determine:

i) The full-load secondary current

ii) The minimum load resistance which can be connected across the secondary

winding to give full load KVA

iii) The primary current at full load KVA

(10 Marks)

Question 5

(a) The main parts of direct current motors and generators are basically the same.

Explain the terms below:

i) Armature

ii) Commutator

iii) Brushes

iv) Field Winding

(4 Marks)

Continued…


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(b) A 8-pole generator has a lap-wound armature with 60 slot with 16 conductors

per slot. The useful flux per pole is 40 mWb.

i) Determine the speed at which the machine must be driven to generate an

e.m.f of 240 V.

(3 Marks)

ii) Determine the generated e.m.f in question b(i) if armature is wave-wound.

(3 Marks)

(c) A shunt generator has an armature-circuit resistance of 0.3 Ω, a field-circuit

resistance of 50 Ω, and a terminal voltage of 150 V when it is supplying a load

current of 40 A. Find the:

i) Field current

ii) Armature current

iii) Copper losses at the above load

iv) If the rotational losses are 400 W, what is the efficiency at the above load.

(15 Marks)

End of Page.

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