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ID.No./Seat No.

MEHRAN UNIVERSITY OF ENGINEERING AND TECHNOLOGY,JAMSHORO.

FIRST TERM FINAL YEAR (7 TH TERM) B.E.(ELECTRICAL) SUPPLEMENTARYEXAMINATION 2012 OF 05 TO 08-BATCHES.

Dated: 13-03-2012 Time allowed: 03 Hours. Max Marks:80 NOTE: ATTEMPT ANY FIVE QUESTIONS. ALL QUESTIONS CARRY EQUAL MARKS.

Q.No.

01. A one-line power system is shown in the figure. Draw the impedance diagram for thesystem. Choose a base of 132 KV for transmission line and base KVA of 20 MVA.

02. (a) Describe voltages, currents and power in a balanced three circuit.

(b) In a balanced three-phase circuit the voltage V ab is 173.2 OoV. Determine all the

voltages and currents in a Y-connected load having Z L=10 20 o . Assume that the phasesequence is abc.

03. A balanced star-connected load takes 25 A from a balanced 3-phase, 4-wire supply. If thefuses in the two lines are removed, find the symmetrical components of the line currents

before and after the fuse removal and current in neutral line before and after.

04. Explain the concept of sequence impedance and sequence network of the three phase power system and show thatVa1 = E a I a1Z1, Va2 = 0 I a2Z2, V a0 = 0 I a0Z0, Z 0 =3Z n + Z 0 Va1 = E a I a1Z1

05. A 30 MVA, 11 KV, 3-phase synchronous generator has a subtransient reactance of 30%.The negative and zero sequence reactances are 40% and 15% respectively. The neutral of the generator is solidly grounded. Determine the sub-transient current in generator andline to line voltage for sub transient conditions when line to line fault occurs atgenerator terminals with generator operating unloaded at rated voltage.

Contd on P/-2.

POWER SYSTEM ANALYSIS

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06 (a) Explain Gauss-Seidal method for the solution of non-linear algebraic equations.

(b) An incomplete nodal admittance matrix for a 4-bus system with negligible shunt

admittance is given below. Find the missing terms to complete the Y-bus and draw theappropriate 4-bus system

0.8-j4 0.35+j1.5 -0.45+j25 Y 14

Y21 Y22 0.35+j2.5 -0.3+j3

Y31 Y32 Y33 -1.2+j4

Y14 Y24 Y34 Y44

07. Define steady state and transient stabilities. Derive expression for max. power delivered by synchronous generator connected to infinite bus.

08. The ABCD constants of a nominal network representing a three phase transmissionline are

A = D = 0.97 0, B = 60 0 , C = 0.001 0 S

Find the steady state stability limit if the both sending end and receiving end voltages areheld constant at 132 KV: (a) with the ABCD constants as given, (b) with the shuntadmittance neglected, and (c) with both the series resistance and shunt admittanceneglected.

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