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Ece 372 Electrlcal Power Systems I Question Paper

Ece 372 Electrlcal Power Systems I

Course:Bachelor Of Science In Electrical And Information Engineering

Institution: Moi University question papers

Exam Year:2011

a)
b)
QUESTION ONE
a) What is the effect of load P.F. on regulation of a transmission line? {2.5 mks}
b) State the four key characteristic features that are required of all protection schemes {4 mks}
c) A 3-tjJ overhead line has resistance and reactance per phase of 5Q and 20 Q respectively. The load at the receiving end is 25 MW at 33kV and a p.f of 0.8 lagging. Find the capacity of synchronous condenser required for this load condition if it is connected at the receiving end and the line voltages at both ends are maintained at 33 kV. {5.5 mks}
d) What is the justification in neglecting line capacita.nce in short transmission lines? {2 mks}
QUESTION TWO
c) What is Electric power supply system? Draw a single line diagram of a typical a.c. power supply scheme. {5 mks}
b) .A 3-tjJ transmission line 200 km has the following constants:
Resistance/phase/km=0.16.Q
Reactance/phase/km=0.25.Q
Shunt admittance/phase/km= 1.5 x 10-6S.
Calculate by rigorous method the sending end voltage and current when the line is delivering a load of 20Nf\V at 0.8 p.f lagging. The receiving end voltage is kept constant at 110 KV. {9mk~}
QUESTION THREE
a) Discuss the requirements of a satisfactory electric supply system {6 mks}
b) Deduce an expression for voltage regulation of a short transmission line, giving the vector diagram. {8 mks}
QUESTION FOUR
a) Discuss conditions necessary for successful parallel operation of transformers {5 mks}
b) Explain the construction and working of Brown-Boveri regulator with a neat sketch {9 mks}
QUESTION FIVE
a) The present trend IS towards cu. for generation and distribution and d.e. for transmission. Discuss the reasons for it {4 mks}
b) Tests on 31.5MVA, 132/33KV star/delta 3-phase transformer gave the following results (loss values given are for 3 phases):
c)
-open circuit test: 33KV, 5.5A, 21KW

-short circuit test: 13.2KV, 137.8A, 100K\V Calculate

1. Equivalent circuit parameters refered to LV side {3 mks}

11. Efficiency at full load and half of full load with unit p.f. {4 mks}

111. Regulation at full load with 0.8 p.f lagging. {3 mks}

QUESTION SIX

a) Discuss the importance of voltage regulation in modern power systems {4 mks}

b) A 3-phase, 50 Hz, 16 km long overhead line supplies 1000 KW at llkV, 0.8 p.f. lagging. The line resistance is 0.03Q per phase per km and line inductance is 0.7 mH per phase per km. calculate the sending end voltage, voltage regulation and efficiency of transmission {7 mks}

c) A long transmission line is open circuited at the receiving end. Will there be any current ill the line at the sending? Explain your answer. {3 mks}

QUESTION SEVEN

a) Discuss the terms voltage regulation and transmission efficiency as applied to transmission line {3 mks}

b) A 3-phase, 50Hz transmission line 100km long delivers 20MW at 0.9 p.f. lagging and at 110 KV. The resistance and reactance of the line per phase are 0.2Q and 0.4Q respectively while capacitance admittance is 2.5 10.6 Siemens/km/phase. Calculate:

1. The current and voltage at the sending end

11. Efficiency of transmission. Use nominal T method {11 mks}

Ece 372 Electrlcal Power Systems I Question Paper

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