power system analysis-be(pt)new

7/30/2019 Power System Analysis-BE(PT)NEW

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VINAYAKA MISSIONS UNIVERSITY

V.M.K.V ENGINEERING COLLEGE, SALEM

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

POWER SYSYEM ANALYSISQUESTION BANK

UNIT - I

PART A

1. What is the need for system analysis in planning and operation of power system?

2. What are the components of power systems?

3. What are the major parts of the power system?

4. What is single line diagram?

5. Define the per unit value of any electrical quantity.

6. What is called stabilization winding in transformer?

7. Define the per unit value of any electrical quantity

8. What is the need for base values?

9. Write the equation for converting the p.u impedance expressed in one base to another?

10. What is Impedance and reactance diagram?

11. What is the advantage of per-unit method over percent method?

12. Define steady state stability.

13. Define Transient state stability.

14. What is steady state stability limit?

15. Name the different types of stability.

16. Define dynamic stability.

17. Name any two methods of reducing short circuit current.

18. List the methods of improving the transient stability limit of a power system.

19. What are advantages of per-unit computations?

20. Write down the classification of power system components?

21. A generator rated at 30 MVA, 11KV, has a reactance of 20%. Calculate its per

unit reactance for a base of 50 MVA and 10KV.


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22. A connected generator rated at 300MVA, 33KV has a reactance of 1.24 p.u .

Find the ohmic value of reactance.

23. The base KV and Base MVA of a 3 transmission line is 33KV and 10 MVA

respectively. Calculate the base current and base impedance.

24. What is the purpose of increasing a resister or reactor between the neutral of Y (star)

& ground?

25. Define reactor.

PART B

1. Explain the need for system analysis in planning & operation of power system

2. What are the steps to be followed to draw the per phase reactance diagram.

3. Define per unit quantities, derive expression for single phase and three phase system.

4. Draw the reactance diagram for the power system shown in fig. Neglect resistance and

use a base of 100 MVA,220KV in 50 line. The ratings of the generator, motor and

transformer are given below.

Generator: 40 MVA, 25KV, X11=20%

Synchronous motor: 50MVA, 11KV, X11 = 30%

Y-Y Transformer: 40 MVA, 33/220KV, X = 20%

Y- Transformer: 30 MVA, 11/220KV (/Y), X = 15%

5. A three phase, -Y transformer with rating 100 KVA, 11KV/400V has its primary and

Secondary leakage reactance as 12/phase and 0.05/phase respectively. Calculate the

p.u reactance of transformer.


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6. A three phase transformer is connected in the star to star connection. The rating of

transformer is 220KV/400V, 60MVA base current 4000A and slot leakage reactance

are X1=12, X2=8. Find out the i)transformation ratio, ii)total leakage reactance, iii)

p.u reactance of the transformer side.

7. A 15 MVA, 3.5kv, 3 phase generator has a sub transient reactance of 20%. It is

connected through a transformer to a high voltage transmission line having a

total series reactance of 70. The load end of the line has Y-Y step down

transformer. Both transformer banks are composed of 3, 1 transformer connected

for 3 operation. Each of three transformers composing 3 bank is rated 6667

KVA, 10/100 KV with a reactance of 10%.The load represented as impedance is

drawing 10MVA at 12.5KV and 0.8PF lagging .Draw the single line diagram of

power network. Choose a base of 10MVA, 12.5KV in the load circuit, and determine

the reactance diagram. Determine also the voltage at the terminals of the generator.

8. Draw a reactance diagram for the power system shown in figure

T1 T2

G1 T.L M2

Xn1 Xn2

Generator: 40MVA, 25KV, X11=20%

Synchronous motor:50MVA, 11KV, X11=30%

Transformer1(Y-Y): 33KV/220KV, 40MVA, X1=15%

Transformer1(Y-): 11KV/220KV(-Y), 30MVA, X1=15%

9. A 3 transformer is constructed using three identical 1 transformer of

rating 200 KVA, 63.51KV/11KV transformer. The impedances of primary and

secondary are 20+j 45 and 0.1 +j 0.2 respectively. Calculate the p .u

impedance of the transformer.


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10. A 120 MVA, 19.5 KV generator has a synchronous reactance of 0.15 p. u and it is

connected to a transmission line through a transformer rated 150MVA, 230/18KV (

/ ) with x =0.1 p .u.

a) Calculate the p .u reactance by taking generator rating as base values.

b) Calculate the p .u reactance by taking transformer rating as base values.

c) Calculate the p .u reactances for a base value of 100MVA and 220KVon HT

side of the transformer.

UNIT - II

PART A

1. Define primitive network.2. What are the disadvantages in primitive network?

3. Define bus in a power system network

4. What is called as oriented graph?

5. Define CO-TREE.

6. How loop impedance matrices are formed?

7. What is a bus impedance matrix?

8. What are the methods available for forming bus impedance matrix?

9. What is off nominal transformer ratio?

10. Why the reactors are connected in series with the system?

11. What is a tap changing transformer and what are the types of tap changing

transformers?

12. What are symmetrical components?

13. How power system studies are carried out?

14. How the power system network can be studied using mathematical model?

15. Write the performance equations of the primitive network

16. Define bus in a power system network

17. What is called as a branch in an electric network?

18. Define node in the power system network.

19. Define loop.


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20. Define graph.

21. Define oriented graph of a power system network?

22. What is a sub -graph? (or) Define a sub -graph?

23. What is called as a tree in the network? (or) Define Tree

24. What are the properties of TREE?

25. What is building block Matrix? Where it is used?

PART B

1. Derive the performance equations in impedance and admittance form for a power

system network?

2. Obtain the expression for nodal admittance equation.

3. Derive the equations to find the - equivalent circuit of transformer with off-

nominal tap ratio.

4. Explain the modelling of generator, load and transmission line for short circuit,

power flow and stability studies.

5. Explain in detail about the formation of network equations.

6. Obtain the expression for YBus & ZBus matrix (or) How YBus & ZBus matrix are

formed from the electrical network?

7. Explain in detail about the successive elimination method to solve the unknown

voltages of YBus.

8. Eliminate bus (3) & (4) in the given bus admittance matrix and form new bus

admittance matrix.

=

5

4

0

8.9

j

j

j

yBus

5

5..2

3..8

0

j

j

j

8

14

5..2

4

j

j

j

j

18

8

5

5

j

j

j

j

9. Explain the procedure to form basic loop incidence matrix.

10. Obtain the expression for nodal admittance equation.

UNIT - III

PART A


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1. What is the need for short circuit studies or fault analysis?

2. What is meant by a fault?

3. Write the expression for the short circuit current i(t).

4. Define subtransient reactance.

5. Find the fault current if the prefault voltage at the fault point is 0.97 p.u.

6. Define Doubling effect.

7. Define positive sequence components.

8. Write the symmetrical components of 3 system.

9. Define power invariance?

10. Prove that 01 2 =++ aa .

11. What is the need for short circuit studies or fault analysis?

12. Why faults occur in a power system?

13. How the faults are classified?

14. What are the classifications of shunt fault?

15. State the frequency of occurrence of various types of faults?

16. What are the assumptions made in short circuit analysis?

17. How symmetrical faults are analysed ?

18. Name the main differences in representation of power system for load flow and short

circuit studies?19. Rank the various fault in the order of severity?

20. What is meant by fault calculations?

21. Define DC-off set current

22. Differentiate between subtransient and transient reactance.

23. Define negative sequence components

24. Define zero sequence components

25. What is an unsymmetrical fault? List the various unsymmetrical faults

PART B

1. Derive the equation for internal voltages and fault current of synchronous machines

under loaded and unloaded transient conditions.

2. Explain the procedure for making short circuit studies of a large power system network using digit


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computers

3. Derive algorithm for single line to ground fault analysis of a multi machine power system using bu

impedance matrix

4. What are the points to be considered while selecting Circuit Breakers?

5. Explain the procedure to remove a branch impedance Zb from the given network

under fault condition.

6. A salient pole generator without dampers is rated 20 MVA, 13.8 KV and has a

direct axis subtransient reactance of 0.25 per unit. The negative and zero sequence

reactances are respectively, 0.35 and 0.10 per unit. The neutral of generator is

solidly grounded. With the generator operating unloaded at rated voltage with

Ean 000.1 = per unit, a single line to ground fault occurs at machines terminals,

which then have per unit voltages to ground, ,0=aV ,25.102013.1 0=bV

025.102013.1 =cV .Determine the subtransient current in the generator and the

line to line voltages for subtransient conditions due to the fault.

7. A synchronous generator and motor are rated 30, 000 KVA, 13.2 KV and both have

subtransient reactances of 20%. The line connecting them has a reactance of

10% on the base of the machine ratings. The motor is drawing 20,000 KW at 0.8

pf leading and the terminal voltage of 12.8 KV when a symmetrical 3 fault

occurs at the motor terminals. Find the subtransient currents in the generator, the

motor and the fault by using internal voltages of the machines. using Thevenins

theorem.

8. A 69 KV circuit breaker having a voltage range factor K of 1.21 and a continuous

current rating of 1200 A ,has a rated short circuit current of 19000 A at the

maximum rated voltage of 72.5 KV. Determine the maximum symmetrical

interrupting capability of the breaker and explain its significance at loweroperating voltages.

9. Derive the relation betweenY

Z and

Z

10.Obtain the Thevenins equivalent circuit under fault calculations using ZBus


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UNIT IV

PART A

1. Why power flow analysis is made?

2. Define voltage controlled bus.

3. What is PQ bus?

4. What is Swing bus?

5. What is the need for slack bus?

6. What are the operating constraints imposed in the load flow studies?

7. Write the expression for complex power injected to a bus?

8. What are the advantages of Gauss-Seidel method?

9. What is Jacobian matrix?

10. What is an acceleration factor?

11. What is power flow study or load flow study?

12.What are the informations that are obtained from a load flow study?

13. What is the need for load flow study?

14.What are the works involved in a load flow study?

15.What are the quantities that are associated with each bus in a system?

16.What are the different types of buses in a power system ?

17. What are the iterative methods mainly used for the solution of load flow problems?.

18. Write the expression for complex power injected to a bus ?.

19. Write the load flow equation of Newton Raphson method.

20. What do you mean by a flat voltage start?

21. When the generator bus is treated as load bus?

22. What are the advantages of Gauss-Seidel method?

23. What are the disadvantages of Gauss Seidel method?

24. What is an acceleration factor?

25. What is decoupled power flow method?

PART B

1. What are the types of buses in power flow studies? Explain in detail.


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2. Explain the iterative procedure of gauss seidel method used in power folw

analysis. Draw the flowchart.

3. Explain the Newton Raphson Method for load flow problem with a neat flow

chart.

4.

(i) What is load flow study

(ii) What are the methods of load flow analysis

(iii) Compare NR Method and Gauss seidel method of load flow studies.

Give its advantages and disadvantages?

5. Derive Gauss Seidel flow algorithm and give step-by-step procedure for

implementing this algorithm. State the relative merits of this method

6. Derive Static load flow equation.

7. Consider the three bus system. Each of the three lines has a series impedance of

0.02 + j0.08pu and a total shunt admittance of j0.02 pu. The specified quantities

at the buses are tabulated

Bus Real load

demand PD

Reactive

load

demand QD

Real power

generation

PG

Reactive

power

generation

QG

Voltage

specification.

1 2.0 1.0 Unspecified Unspecified V1 = 1.04 +

j0(Slack bus)

2 0.0 0.0 0.5 1.0 Unspecified (PG

Bus)

3 1.5 0.6 0.0 QG3=? (04.13 PVbusV =

Controllable reactive power sources of available at bus 3 with the constraint

puQG 5.10 3

Find the load flow solution using the Use decoupled method to obtain one iteration of

load flow solution. Use a tolerance of 0.01 for power mismatch.

8.State the approximations made in load flow solution.


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9. The system data for a load flow solution are given. Determine the voltages at the

end of first iteration by Gauss seidel method. Take 6.1= .

Line admittances

Bus code Admittance

1-2 2-j8

1-3 1-j4

2-3 0.666-j2.664

2-4 1-j4

3-4 2-j8

Bus specifications

10. Give a note on state variables.

UNIT V

PART A

Bus code P Q V Remarks

1 - - 1.060

0 Slack

2 0.5 0.2 - PQ

3 0.4 0.3 - PQ

4 0.3 0.1 - PQ


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1. Define stability

2. Define steady state stability

3. Write any three assumptions made up on transient stability.

4. What is transient stability limit?

5. What is a first swing?

6. Define swing curve. What is the use of swing curve?

7. What is damper winding?

8. State equal area criterion.

9. Give the expression for critical clearing time.

10. Define critical clearing angle.

11. What is Voltage Collapse?

12. What is the synchronizing power coefficient?

13. How the stability studies are classified?

14. Give an expression for swing equation.

15. What are the assumptions made by solving swing equation?

16. For the swing equation Ma

Pdt

d=

2

2

. What will be the value of P a during steady

state operation?

17. What is excitation system?

18. What is damper winding

19. Define H constant used in stability studies

20. What are all the control schemes included in the stability control techniques

21. What are coherent machines?

22. State equal area criterion

23. Define critical clearing angle.

24. What are the two methods of representing load buses

25. What is meant by classical stability model and classical stability studies?

PART B

1. Derive the swing equation of a synchronous machine swinging against an infinite

bus.


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2. Explain the computational algorithm for solving Swing Curves Using Modified Eulers

method.

3. A 50HZ, four pole turbo generator rated 100MVA; 11KV has an inertia constant of 8.0

MJ/MVA. Find

(a). The stored energy in the rotor at synchronous speed

(b). If the mechanical input is suddenly raised to 80MW for an electrical

load of 50MW, find rotor acceleration, neglecting mechanical and

electrical losses.

(c). If the acceleration calculated in part (b) is maintained for 10cycles,

find the change in torque angle and rotor speed in rev per min at the

end of this period.

4. Describe the equal area criteria for Transient stability analysis of a system.

5. Obtain the expression for power when

(i)Machine connected to infinite bus

(ii) Two machine System

6. Derive the Power Angle Equation.

7. What are the bus elimination techniques used in Stability studies.

8. A 50HZ, four pole turbo generator rated 100MVA; 11KV has an inertia constant of

8.0 MJ/MVA. Find (a). the stored energy in the rotor at synchronous speed (b). If

the mechanical input is suddenly raised to 80MW for an electrical load of 50MW,

find rotor acceleration, neglecting mechanical and electrical losses.(c). If the

acceleration calculated in part (b) is maintained for 10cycles, find the change in

torque angle and rotor speed in rev.per min at the end of this period.

9. A 2pole 50HZ, 11KV turbo alternator has a ratio of 100MW,pf 0.85 lagging. The

rotor has a moment of inertia of 10,000 Kgm2.calculate H and M.

10. 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 increases the

reactance between the generator and the infinite bus to 500% of the value before the


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fault, when the fault is isolated the maximum power that can be delivered is 75% of

the original maximum value. Determine the critical clearing angle for the condition

described.

power system analysis-be(pt)new

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