vidya digital library - sudhinpk critical clearing angle for the condition described. (15 marks) (b)...

Vidya Digital Library


C 6129 (Pages 2) Name .

Reg. No .

SIXTH SEMESTER B.TEeH. (ENGINEERING) DEGREEEXAMINATION, JUNE 2010

EE 04 604-P OWER SYSTEMS-TI

(2004 Admissions)

Time : Three Hours Maximum: 100 Marks

1. (a) Define per unit Representation. Give the advantages of use ofp.u. values.

(b) Draw the one-line diagram for (i) Rotating MlC ; (ii) Two winding power transformer; (iii ) Aircircuit-br eaker ; (iv) 3 ~ Y connection ; (v) Power circuit-breaker.

(c) Define Economic Dispatch and unit commitment problem. Explain the differ ence between thetwo problems.

(d) Two turbo alternators rated for 100 M\ry and 160 MW hare governor drop characte ristic of 4%from no load to full load. They are connected in parallel to share a load of 250 MW. Dete rmine

->("-

the load shared by each machine, assuming free governor action."

(e) List types of fault in power system and explain double line to ground fault in detail.

(f) What is the need of short circuit studies ?

(g) Define voltage instability. Explain the cause of voltage instability.

(h) Derive the exp ression for the determination of critical clearing time.(8 x 5 =40 marks)

2. (a) Explain clearly with the aid of a flowchart th e computational problem of load flow solutionusing Newton Raphson method when the system contain all types of buses .

(15 marks)

(b) Carry out one iteration of load flow solug<;>n.by Gauses Seidal method;

Bus (1) slack bus, Especified =1.05 l.Q:Bus (2) PV bus, IE Ispec =1.2 p.u. PG =3 p.u .

Bus (3) PQ bus, PL =4 p.u, QL =2 p.u.

Take Q limits of generator 2 as a ~ Q s 4. Ybus for given system is :

l3-j9 - 2 + ffi -1 +j4 ]

Ybus = - 2 + j5 5-j14 - 3+ j9

-I + j4 -3 + j9 4 - j l 3

(15 marks)

Turn over

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2 C 6129

3. (a) Explain the different parts of speed governing system. Derive the transfer function model for

speed governing system.

(15 marks)

(b) What is meant by Economic load dispatch? Derive the conditions for optimal load dispatchincluding transmission lines.

(15 marks)

4. (a) A 25 MVA, 11 kV, generator has a Xd" = 0.2 p.u, Its negative and zero sequence reactance are

respectively 0.3 and 0.1 p.u. The neutral of the generator is solidly grounded. Determine thesub transient current in the generator and the line to line voltages for subtransient conditionswhen an line to ground fault occurs at the generators terminals. Assume that before the

occurrenceofthe fault. The generator is operating at no load at rated voltage. Ignore re sistance.

(15 marks)

(b) Determine the fault currents in each phase following double line to ground short circuit atthe terminals of a star-connected synchr onous generator operating initially on an open circuit

voltage of 1.0 p.u. The positive negative and zero sequence reactance of generator are jO.35 ,j 0.25 and j 0.20 respectively and its star point is isolated from ground.

(15 marks). ' .

5. (a ) A 50 Hz generator is delivering 50% of the power that it is capable of delivering through a

transmission line to an infinite bus. A fault occurs that increase the reactance between thegenerator and the infinite bus to 500% of the value before the fault. When the fault is isolated,the maximum power that can be de livered is 75% of the original maximum value. Determinethe critical clearing angle for the condition descri bed.

(1 5 marks)

(b) Explain briefly what is meant by Swing equation. Derive an expression for Swing equati on .

(1 5 marks)

{4 x 15 =60 marks]

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C 58372 (Pages 3) Name .

Reg. No .

SIXTH SEMESTE R B.TECH. (ENGINEERING) DEGREE EXAMINATIONJ UN E 2009

Electrical Engineering

EE 04 604- ·POWER SYSTEMS-II

(2004 Admissions)

Time : Three Hours

A ns /,ver all questions.

Maximum : 100 Marks

, 1. (a) What are the advantages and disadva ntages of the de-coupled Power flo~v over the Newton

Power.t1ow?

(b) Briefly explain t he load flow solution by Gauss-Seidel method.

(e) The increme ntal fue l costs of two plants are :

dt1)' 1 =-- =0.012Pg1 + 8.0d Pg 1

dtz'A. , = -- =0.008 Pg z + 9.6- d Pg2

Where l is in Rs .! hour and Pg is in MW. If both units operate at all timesandmaximum a nd

minimum loads on each u n it are 550 and 100 MW respectively, Plot I, of the p la nt in

Rs. / MWh versus plant output in MW for economic dispatch as total load varies from 200 to

1l00MW.

(d) Explain in detail about automatic load dispatching.

(e) Discuss briefly the concept of shoot circuit capacity of a bus. How doe~ the shOl:t ~i rcuit capa city

affect the circuit-breaker rating?

(D Three 10 lVIVA generators each hav ing a reactance of 0.2 pu are Operatin g in pa rall el. They

feed a transmission lin e t hrough a 30 MVA transformer having a pe r uni t re acta nce of 0.05.

Find the fault MVA for a fault a t the sending end of the line.

(g) Derive Swing equation and dis cuss its application is the study and Power system stability.

(h) How the transient stability of a system can be improved ? Discuss the various approaches to

the problem.

(8 x 5 =40 marks)

Turn ov e r

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2 C 58372

2. (a) Explain in detail the algorithm for the formation of Bus Impedance matrix. How can thematrix to be modified for addition or removal of a branch?

Or

(b) A two bus system in shown in the figure. below. Determine the voltage at the end of third

iteration by Gauss-Seidel method . .The elements of bus impedance matrix are

YI I = Y22 = 1.5~6 p.u, and Y2 1 = Yl2 =1.811 \00 p.u.

Vl=1.1~ V2

0.5 + j 0.31.1 + j 0.2P1 + j Q l

3. ' (a) What is meant by economic load dispatch? Derive the condition for optimal load dispatchincluding transmission lines, what are the assumptions made in deriving the same?

Or

(b) The fuel cost in Rs.lhour of three thermal plants of a power system are:

C1 = 200 + 7.0 PI + 0.008 Pf Rs./hr.

C2 =180 + 6.3 P2 + 0.009 pi Rs.lhr.

C3 = 140 + 6.8 P3 + 0.007 p& Rs ./hr.

where Pi' P2 and P3 are in MW. Plant outputs are subject to the following limits :

10 MW:s; 85 MW

10 MW:s; 80 MW

10 m s 70 MW.

For this problem, assume the real power loss is given by :

PL (pu) =0.0218 Pf (pu) + 0.0228 pi (pu)

2+ 0.0179 P3 (pu).

where the loss Coefficients are specified in per unit on a 100-MVA base . Determine the optimaldispatch of generation when the total system load is 150 MW.

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3 C 58372

4. (a) Derive the equation for the total fault current in terms ofSymmetrical Components and Phase

equation for the line to line fault at a bus.

Or

(b) Explain in brief about the various unsymmetrical faults occurring in Power System.

5. (a) Explain in detail the point by point method method for determining the critical clearing time .

Or

(b) A synch ronous generator having a reactance of 1 p .u . is connected to an infinite bus through

a transmission system with a reactance of 0.7 p.u. The generator is running on noIoad with

a voltage of 1.1 p.u. Take H =4.5. MW-s / MVA.

The voltage of infinite bus is 1 ~ p.u. and its frequency is 50 Hz .

Calculate the frequency of natural oscillation if the machine in suddenly loaded to :

(i) 60 % and

(iii) 75 % of its maximum power limit.

Neglect resistance and machine da mping.

(4 x 15 =60 marks)

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vidya digital library - sudhinpk critical clearing angle for the condition described. (15 marks) (b)...

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