Electrical Installation And Principles Question Paper

Electrical Installation And Principles

Course:Diploma In Electrical And Electronics Engineering (Electrical And Electronics )

Institution: Kenya Power & Lighting Company Training School question papers

Exam Year:2010

2521/104
ELECTRICAL INSTALLITION AND PRINCIPLES
Oct/Nov 2010
Time: 3 hours

THE KENYA NATIONAL EXAMINATION COUNCIL
DIPLOMA IN ELECTRICAL AND ELECTRONICS ENGINEERING
(POWER)
MODULE 1
ELEETRICAL INSTALLITIONAND PRINCIPLES
3 HOURS
INSTRUCTIONS TO CANDIDATES
You should have the following for this examination:
Answer booklet;
Mathematical tables/Electronics calculators
Take E =8.85×10-12
This paper consists of TWO sections A and B.
Answer any THREE questions from section A and TWO from section B.
All questions carry equal marks.
Maximum marks for each part of a question are as shown.
SECTION A: ELECTRICAL AND INSTALLITION SOLAR
Answer any THREE questions from this section.

1. (a)With the aid of a sketch the loop-in-method used for wiring final lighting circuits.

(6 marks)
(b) Explain why the following tests are carried out in installations.
i. Polarity;
ii. Insulation resistance test;
iii. Earthling test.
(9 marks)
© A two – core cable 50 metres long and cross – sectional area 2.5mm2 supplies current to a 240v single phase load of 10kW and 0.8 power factor determine the:
i. Voltage drop;
ii. Power loss in the cable
Take resistivity of copper as 17.5 µO mm.

2. (a) (i) State the IEE regulations requirements at consumers intake point;
(ii) With the aid of a labelled diagram, show the sequence of control at consumers intake points to meet the requirement in 2a (i)
(7 marks)

(b) Draw a labelled diagram of a typical grid system applicable in Kenya and indicate standard voltage levels.
(8 marks)
(c) Describe the Haloger Nielson method for treatment of electric shock to begin artificial respiration.
3. (a) Describe the following wiring methods.
i. Steel conduct ;
ii. Ducting system.
(6 marks)
(b) i. State three advantages of a trunking system;
ii. Draw a labelled diagram showing the distribution of electricity in a storied building by raising mains.
(6 marks)
(c) Explain the difference between closed and open type of alarm system.
(8 marks)
4. (a) State two:
i. Functions of earthling ;
ii. Types of earth electrodes.
(4 marks)
(b) With aid of a labelled diagram, show how the earth electrode resistance is determined.
(10 marks)
(c) Determine the following types of electrical control devices:
i. Contactor,
ii. Thermostat
(6 marks)

5. (a) With the aid of a labelled block diagram, describe the photovoltaic solar wiring system:
i. Battery does not charge ;
ii. Battery voltage too high;
iii. A.c loads not working
(6 marks)

(c) With aid of a circuit diagram, show how a test is carried out on a solar panel to determine its output and performance.
(4 marks)

SECTION B: ENGINEERING PRINCIPLES
Answer any TWO questions from this section.
6. (a) Define the following terms as used in electromagnetism:
i. Relative permeability;
ii. Reluctance
(4 marks)
(b) A closed magnetic circuit of cast steel contains an 8 cm long path of cross – sectional area 2cm2 and 2cm path of cross – sectional area 4cm2. A coil of 200 turns is wound around the 8 cm long path of the circuit and a current of 0.5A flows. Determine the flux density in the 2cm long path if the relative permeability of cast steel is 750.
(10 marks)

(c) For the series – parallel connected resistor shown in the figure 1 calculate
i. The supply current;
ii. Current following through each resistor;
iii. P.d across the parallel branch.
(6 marks)

F

FIGURE 1

7. (a) State two:
i. Advantages of an alkaline cell over a lead acid cell;
ii. Indication of fully charged lead acid cell;
(4 marks)

(b) Distinguish between :

(i) Electrolysis and electroplating;
(ii) Polarizarion and local action
( 4 marks)

( c) With the aid of labelled diagram show the construction of a mercury cell.
(5 marks)
(d) A miliameter of 2O resistance reads up to 150mA. With the aid of sketches, show how the miliameter can be used to read:
i. 20 volts;
ii. 20 Amperes
(7 marks)
8. (a) Define the following a.c terms:
i. Period;
ii. Rms value

(b) (i) sketch the following waveforms:

I rectangular;
II saw tooth
(2 marks)

(ii)An alterernating voltage V has a periodic time of 0.01 s and a peack voltage of 50V. When time t is zero V= -10V express the instantaneous voltage in the form.
V=Vmsin (?t ± ? )
(5 marks)

(c ) (i) Show that for a series connected circuit, resonance frequency is given by
fr= 1/2p vLCHz
(3 marks)
(ii)A coil of inductance 150Mh and negligible resistance is connected in series with capacitance of 3µF and resistance of 10O across a 60V variable frequency supply. Determine :
a) Resonant frequency;
b) Current at resonance ;
c) Voltages across the coil and capacitor at resonance;
d) Q factor of the circuit.
(8 m

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