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Second Year Second Semester Examination Question Paper
Second Year Second Semester Examination
Course:Bachelor Of Electrical And Computer Engineering
Institution: Moi University question papers
Exam Year:2012
COURSE CODE: ECE 272
COURSE TITLE : BASIC ELECTRICAL POWER
QUESTION ONE
1 a)(i)Explain the essential factors that influence the choice of the site for a hydro-electric plant. (4mrks)
(ii)Explain the functions of the following; dam, spillways, surge tank, headworks and penstock. (5mrks)
b)A hydro-electric power station has a reservoir area of 2.3 km2 and capacity 5 x 106M3. The effective head of water is 100M. The penstock, turbine and generator efficiencies are respectively 95%, 90% and 85%. Find;
(i)The total electrical energy that can be generated from the power station.
(ii)If a load of 15,000 kw has been supplied for 3 hrs, find the fall in reservoir level.(5 mrks)
QUESTION TWO
2 a)Explain the meaning of the following terms as applied to power generation;
(i)Load Curve.
(ii)Maximum Demand.
(iii)Load Factor.
(iv)Diversity Factor. (4mrks)
b) An equipment in a power station costs Ksh. 1,560,000 and has a salvage value of Ksh. 60,000 at the end of 25 years. Determine the depreciated value of the equipment after 20 years using the following methods;
(i)Straight line method
(ii)Diminishing value method
(iii)Sinking fund method at 5% compound interest annually. (6mrks)
c) Explain two advantages of having a high load factor. (4 mrks)
QUESTION THREE
a) Give five desirable characteristics of a tariff. (5 mrks)
b)Calculate annual bill of a customer whose maximum damand is 100 kw,p.f=0.8 lagging and a load factor of 60%. The tariff is Ksh.75 per Kva of maximum demand plus 15 cts per kWh consumed.(3 mrks)
c) Explain the followings methods of tariff;
(i) Block rate
(ii) Two-part tariffs (2 mrks)
d) A tariff in force is Ksh. 50 per kVA of maximum demand per year plus 10 cuts per k Wh. A consumer has a maximum demand of 10 Kw with a load factor of 60% and a p.f of 0.8 lag. Show the effect of improving the load factor to 80% with the same maximum demand and p.f on the total cost per k Wh (4 mrks)
QUESTION FOUR
4 a) Explain four disadvantages of low power factor. (4 mrks)
b)A 3-phase induction motor operates of full load with efficiency of 89% and a p.f of 0.85% lagging. Calculate the kVA rating of capacitor bank required to raise full load the power at 0.95% lagging. What will be the capacitance per phase if the capacitors are connected in (i)delta(ii)star (6 mrks)
c)Show that for consumer taking power of P Kw at a power factor cos?1 charged at Ksh. A per kVA maximum demand plus a flat rate per Kwh , most economical power factor after installing a power factor improvement equipment should be;
cos?2=v(1- (B/A)2)
where cos?2=power factor after correction
B=the cost of per K va of the p.f correction equipment. (4 mrks)
QUESTION FIVE
5 a)With respect to phases name six systems that are available for A.C distribution; (6mrks)
b)(i)Why is electrical power normally transmitted at high voltage?(1 mrk)
(ii)A single-phase line has an impedance of 5< 60°O and supplies a load of 120A, 3 300V at 0.8 p.f lagging. Draw a vector diagram and use it to calculate the sending-end voltage. (3 mrks)
c)An overhead, single phase –phase transmission line delivers 1 100Kw at 33 kV at 0.8 p.f lagging. The total resistance of the line is 10O and a total inductive reactance is 15O. Determine;
(i)Transmission efficiency
(ii)Sending-end voltage
(iii)Sending-end p.f (4 mrks)
QUESTION SIX
6 a)With a help of a heat sketch give a brief outline of a typical A.C power supply scheme showing the following parts;
(i)Generating station
(ii)Primary transmission
(iii)Secondary transmission
(iv)Primary distribution
(v)Secondary distribution (7 mrks)
b)Give any four advantages of high voltage D.C transmission over high voltage A.C transmission. (4mrks)
c)Give any three disadvantages of high voltage D.C transmission over high voltage A.C transmission. (3 mrks)
QUESTION SEVEN
7 a)Outline six advantages of electric heating over other methods of heating. (6 mrks)
b)With the help of a well labelled diagram explain the working principle of fluorescent mercury-vapour lamps. (5 mrks)
c)Explain the formation of electric arc. (3 mrks)
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