# EE8501 POWER SYSTEM ANALYSIS ALL 5 UNITS MCQ PART A &amp; B with answers

As per Anna university online exam pattern published this book. Multiple choice questions for all 5 units available. Part A - one mark questions - 50nos. for all units. similarly Part B- 25 questions- two marks- for all 5 units

As per Anna university online exam pattern published this book.

Multiple choice questions for all 5 units available. Part A - one mark questions - 50nos. for all units.

similarly Part B- 25 questions- two marks- for all 5 units

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POWER SYSTEM ANALYSIS

MULTIPLE CHOICE QUESTIONS WITH ANSWERS

ALL 5 UNITS

Department: EEE

Batch/Year: 3 RD

Created by: L.UMASANKAR

Date:

UNIT 1 AND UNIT 2

PART A & PART B

Multiple Choice Questions with Answers

UNIT 1 - PART A

1.The most common generation voltages in India are

a) 440 volt, 6.6 KV, 11 KV

b)440 volt, 220 volt, 110 volt

c) 66 KV, 33 KV, 11 KV

d)11 KV, 13.2 KV, 18 KV.

2.The most common transmission voltages in India are

a) 66 KV, 132 KV, 220 KV

b)132 KV, 220 KV, 440 KV

c) 220 KV, 440 KV, 500 KV

d)11 KV, 132 KV, 500 KV.

3.The type of power station at Bhakra is

a)Nuclear

b)Thermal

c)Hydro

d)diesel.

4.The per capita consumption of electrical energy in India is

a) more than 150 kwh

b)less than 150kwh

c) less than 50 kwh

d)none of these.

5.The per unit impedances of a transformer referred from the primary and secondary side

a) are not equal

b) are equal

c) are varying according to the base voltage and MVA

d) both (b) and (c).

6. The per unit impedance Z(pu) is given by

a) Z Ω * (kVA) b /(KV)² b

b) Z Ω * (MVA) b /((KV)² b *100)

c) Z Ω * (MVA) b *100/(KV)² b

d) Z Ω * (MVA) b /(KV)² b

7. Which among the following assumptions are made in the reactance diagram?

a) The neutral reactance are neglected

b) Static loads are neglected.

c)The capacitance of the transmission lines are neglected

d) Only a and c

e)All of these

8.How are the base values chosen in per unit representation of a power system.

a)base KV & base MVA

b)base KV

c)base MVA

d)None of the above

9. What is the formula to calculate the (kV) B on the LT section?

a) (kV) B on HT section * (HT voltage rating) / (LT voltage rating)

b) (kV) B on LT section * (HT voltage rating) / (LT voltage rating)

c) (kV) B on HT section * (LT voltage rating) / (HT voltage rating)

d) (kV) B on LT section * (LT voltage rating) / (HT voltage rating)

10. What is the formula to calculate the (kV) B on the HT section?

a.) (kV) B on HT section * (HT voltage rating) / (LT voltage rating)

b) (kV) B on LT section * (HT voltage rating) / (LT voltage rating)

c.) (kV) B on HT section * (LT voltage rating) / (HT voltage rating)

d) (kV) B on LT section * (LT voltage rating) / (HT voltage rating)

11. Which among these is the major advantage of per unit computations?

a) Per unit impedance of transformers is the same referred to either side of it.

b) For simulating steady state and transient models in the computer this method is very useful.

c) Manufactures usually specify the impedance of an apparatus in per unit system.

d) All of these

12.What are the approximations made in impedance diagram?

a) Neutral reactances are neglected.

b) Shunt branches in the equivalent circuit of the transformers are neglected.

c) Capacitances of the transmission lines neglected.

d) All of the above.

13) Which among these is the equivalent circuit for the synchronous motor?

a) Only a

b) Only b

c) Only c

d) Only d

e) None of these

14.What is the simplified diagram called, after omitting all resistances, static loads, capacitance

of the transmission lines and magnetising circuit of the transformer?

a) Single line diagram

b) Resistance diagram

c) Reactance diagram

d) Both (a) and (b)

e) None of these

15.. What is the per unit system (PU)?

a) A ratio of actual value in any units to the base or reference value in the same units

b) A ratio of the base or reference value in any units to the actual value in the same units.

c) Ratio of the square of the actual value in any units to the square of base or the reference

value in the same units

d) All of these

16.In a three phase, 5 kv ,5 MVA System, What is the base impedance?

a)5 ohms

b)50 ohms

c)0.5 ohm

d)500 ohms

17. For a given base voltage and base volt-amp, the per-unit impedance value of an

element is X. What will be the per-unit impedance value of this element when the voltage

and volt-amp bases are both doubled?

a)2X

b)4X

c)0.5 X

d)X

18.The per unit impedance of a circuit element of 0.15. If the base KV and base MVA are

halved , then new value of the per-unit impedance of the circuit element will be

a)0.075

b)0.15

c)0.30

d)0.60

19. What is the main purpose of reactance diagram?

a) Load flow analysis

b) Fault analysis

c) Calculation of ratings of Alternators

d) Calculation of ratings of Transformers

20.Which of the following is not neglected during formation of reactance diagram from

impedance diagram?

a) Resistance of various power system components

b) Static loads

c) Shunt component of Transformers

d) Reactance of alternators

21. Impedance diagram is used for analysis of __________

a) Load flow

b) Alternator

c) Fault

d) Transmission Line

22. Reactance diagram contains which of the following ?

a) Resistance of Alternator

b) Resistance of transformer winding

c) Induction motor’s equivalent corcuit

d) Inductive reactance of transmission lines

23. Single line diagram does not represents:

a) Star connection of transformer winding

b) Delta connection of transformer winding

c) Neutral wire of transmission lines

d) Ratings of machines

24. In impedance diagram different power system elements are represented by symbols.

a) True

b) False

25. The percentage reactance is defined as

a) The percentage of the ratio of change in reactance in transient condition to the total

reactance of the machine

b) The percentage of the ratio of change in reactance in transient condition of the total

resistance of the machine

c) The percentage of the ratio of voltage drop due to reactance synchronous machine to the

rated voltage when full load rating current is flowing

d) Either (a) and (c)

26. If the secondary of the transformer having the reactance of 4% is short circuited with

normal voltage applied to the primary the symmetrical short circuit current will be

a) 4 times of the full load current

b) 25 times of the full load current

c) 2 times of the full load current

d) 8 times of the full load current

e) 40 times of the full load current

27. If the base kVA is 25,000 then a 5000 kVA alternator with 8% reactance will have

a) A 4% reactance

b) A 40% reactance

c) A 16% reactance

d) A 20% reactance

28. The percentage reactance can be converted into ohmic value which the following formula

a) X ohms = (X(%) ×100 (kV) 2 )/kVA

b) X ohms = (X(%) ×1000 (kV) 2 )/kVA

c) X ohms = (X(%)×(KV) 2 )/(1000 kVA)

d) X ohms = (X(%)×10(kV) 2 )/kVA

29. When an alternator is short circuited on the three phases, it settles down to the steady

short circuit value and limited by

a) Sub-transient reactance

b) Transient reactance

c) Synchronous reactance

d) Either (a) or (c)

30. The short circuit current of an alternator when short circuited on three phases will be

a) Zero as time goes to infinity

b) Maximum when time goes to infinity

c) Infinity when time goes to infinity

d) Small as time goes to infinity but not zero

e) None of the above

31. The reactors used to limit the short circuit current in the alternators have very small

resistance in comparison to reactance

a) Because the high resistance will not help to limit the short circuit current

b) To avoid the energy waste

c) Because the high resistance will raise the temperature and insulation of reactor

will be spoiled

d) To improve power factor

32.For n bus power system size of Y bus matrix is

a) (n-1)×(n-1)

b) (n-2)×(n-2)

c) n×n

d) (n-1)×(n-2)

33. Which of the following matrix is used for load flow studies?

a) Y bus matrix

b) Z bus matrix

c) Unit matrix

d) null matrix

34. Sum of the elements of row i equal to shunt admittances connected to bus i. If this

summation is zero, indicates there is no

a) shunt admittance

b) mutual coupling

c) both 1 and 2

d) none of the above

35.The value of off diagonal elements is

a) which is connected between bus i and bus j with negative sign

b) which is connected between bus i and bus j with positive sign

c) sum of admittances connected at bus i

d) sum of admittances connected at bus j

36. Which of the following statement is true

a)bus admittance matrix is a sparse matrix

b)Bus impedance matrix is a full matrix

c)Both 1 and 2

d)Neither 1 nor 2

37.Applications of Y-bus Matrix

a)Load flow analysis

b)Optimal Load flow analysis

c)Stability analysis

d)all of the above.

38.What are the approximations made in reactance diagram?

a)All static loads & Induction motor neglected.

b)Resistances are neglected

c)Neutral reactances are neglected

d)all of the above.

39.What is off-nominal transformation ratio?

a) When the voltage or turns ratio of a transformer is not used to decide the ratio of base

KV.

b) When the voltage or turns ratio of a transformer is used to decide the ratio of base KV.

c) When the voltage or turns ratio of a transformer is not used to decide the ratio of base

MVA.

d) When the voltage or turns ratio of a transformer is used to decide the ratio of base MVA.

40.What is the element of the graph that is not included in the tree called?

a. Links

b. Branches

c. Oriented graph

d. All of these

41.Which among the following formulae is used for addition of an admittance element into

the bus?

a. Y ii new = Y ii old - y

b. Y ii new = Y ii old + y

c. Y ii new = Y ii old - Y ij old

d. Y ii new = Y ii old + Y ij old

42.What is an oriented graph?

a. A connection of network topology, represented by replacing all physical elements by lines.

b. A graph in which the direction is assigned to each branch.

c. A graph where at least one path exists between any two nodes of the graph.

d. None of these

43.The Dimension of the bus incidence matrix is

a)e x n

b)e x (n-1)

c)e x e

d)None of the above

44.Off diagonal elements of Ybus

a)Yij= -Yji

b)Yij=Yji

c)Yij=1/Yji

d)None of the above

45. Find Y11

a)-j2.25

b)j1.5

c)1.25

d)2

46.Find Y22

a)0.0443-j0.0595

b)-j4

c)1+j4

d)2-j5

47.The incidence of elements to the nodes away from the node in the connected graph

a)Positive sign

b)Negative sign

48.The incidence of elements to the nodes towards the node in the connected graph

a)Positive sign

b)Negative sign

49.The incidence of elements to the nodes no elements in the connected graph

a)Positive sign

b)Negative sign

c)0

d)None of the above

50.What is the dimension of primitive admittance matrix?

a) 5 X 5

b) 7 X 7

c) 9 X 9

d) 2 x 2

UNIT 1 – PART B - MCQ

1. A three phase transformer has a nameplate rating of 30 MVA, 230Y/69Y kV with a leakage -

reactance of 10% and the transformer connection is wye-wye. Choosing a base of 30MVA

and 230 kV on high voltage side, the transformer reactance referred to the low voltage side

will be _______(in ohms).

a) 15.87 Ω

b) 157.8 Ω

c) 176.33 Ω

d) 17.67 Ω

2. A three phase transformer has a nameplate rating of 30 MVA, 230Y/69Y kV with a leakage -

reactance of 10% and the transformer connection is wye-wye. Choosing a base of 30MVA and

230 kV on high voltage side, the high voltage side impedance ____________

a) 1763.3 Ω

b) 158.7 Ω

c) 15.87 Ω

d) 176.3 Ω

3. A three phase transformer has a nameplate rating of 30 MVA, 230Y/69Y kV with a leakage -

reactance of 10% and the transformer connection is wye-wye. Choosing a base of 30MVA and

230 kV on high voltage side, the low voltage side impedance is ___________

a) 158.7 Ω

b) 176.3 Ω

c) 1763.3 Ω

d) 15.87 Ω

4. A three phase transformer has a nameplate rating of 30 MVA, 230Y/69Y kV with a leakage -

reactance of 10% and the transformer connection is wye-wye. Choosing a base of 30MVA and

230 kV on high voltage side, the transformer reactance referred to the high voltage side will be

_________(in ohms)

.

a) 176.33 Ω

b) 17.67 Ω

c) 158.7 Ω

d) 15.87 Ω

5․ The per unit impedance of a circuit element is 0.30. If the base kV and base MVA are

halved, then the new value of the per unit impedance of the circuit element will be

a)0.30

b)0.60

c)0.0030

d)0.0060

6․ The per unit value of a 2 ohm resistor at 100 MVA and 10 kV base voltage is

a) 4 pu

b) 2 pu

c) 0.5 pu

d) 0.2 pu

7. What will be the per unit impedance of a synchronous motor having a rating of 100 kVA,

13.2 kV and having a reactance of 75 Ω / ph?

a. 0.043 pu

b. 0.057 pu

c. 0.036 pu

d. 0.298 pu

8. A 25 MVA,33 kv transformer has a pu impedance of 0.9. The pu impedance at a new base

50 MVA at 11 kv would be

a)12.2

b)10.4

c)16.2

d)14.4

9․ The per unit value of a 4 ohm resistor at 100 MVA and 10 kV base voltage is

a) 4 pu

b) 2 pu

c) 40 pu

d) 0.4 pu

10.The direct axis reactance Xd of a synchronous generator is given as 0.4 pu based on the

generator name plate rating of 10 KV, 75 MVA. The base for calculation is 11 KV,100 MVA.

What is the pu value of Xd on the new base

a)0.279

b)0.578

c)0.412

d)0.44

11.The per-unit impedance of an aleternator corresponding to base values 13.2 KV and 30 MVA

is 0.2 pu. The pu value of the impedance for base values 13.8 KV and 50 MVA in pu will be

a)0.131

b)0.226

c)0.364

d)0.305

12. If a 250 MVA,11/400 KV three-phase power transformer has leakage reactance of 0.05 per

unit on the base of 250 MVA and the primary voltage of 11 KV, then the actual leakage

reactance of the transformer referred to the secondary side of 400 KV is

a)0.8 ohm

b.0.032 ohm

c)0.03125 ohm

d)32 ohm

13. Determine the reactances of the three generators rated as follows on a common base of

200 MVA,35 KV:

Generator 1:100 MVA,33 KV,10%

Generator 2:150 MVA,32 KV,8%

Generator 3:110 MVA,30 KV,12%

a)j0.1778,j0.089,j0.16

b)j0.2, j0.4, j0.6

c)j1,j5,j8

d)j0.5,,0.25,j0.75

14. A three phase transformer with rating 100 KVA,11KV/400 V has its primary & secondary

leakage reactance as 12 ohms/phase & 0.05 ohms/phase respectively. Calculate the pu

reactance of transformer.

a)j0.04118

b)j0.5

c)j2

d)j0.8

15.A generator is rated 500 MVA,22 KV.Its star conncted windings has a reactance of 1.1 pu.

find the ohmic value of the reactance of windings.

a)j1.0648

b)j2.5

c)j0.95

d)5.2

16. Find Y11,Y22

a)j0.5, j2.3

b)-j2.25, -j8.5

c)j4.5,j2.5

d)j0.2,j0.3

17. .Find Y11

a)0.017-j0.0366

b)1+j4

c)0.5+j10

d)2-j6

18. Find Y22

Line No Bus Code Impedance Line Charging admittance for each line

Ypq/2

1 1-2 j 0.20 j 0.04

2 2-4 j 0.25 j 0.05

3 3-4 j 0.15 j 0.03

4 3-1 j 0.10 j 0.02

5 2-3 j 0.30 j 0.06

a)-j1

b)-j0.8

c)-j12.18

d)-j1.5

19. Find Y44

Line No Bus Code Impedance Line Charging admittance for each line

Ypq/2

1 1-2 j 0.20 j 0.04

2 2-4 j 0.25 j 0.05

3 3-4 j 0.15 j 0.03

4 3-1 j 0.10 j 0.02

5 2-3 j 0.30 j 0.06

a)-j5.6

b)-j2.5

c)-j3.6

d)-j10.59

20. Find Y11

Bus Code

Series Admittance

Half Line Charging admittance for

In pu

each line Ypq/2

1-2 -j 10 j 0.08

2-3 -j 5 j 0.16

3-1 -j 4 j 0.20

a)-j13.72

b)-j2.5

c)-j12.5

d)-j5.9

21.Find Y11

a)j2.0

b)j1.5

c)j5.2

d)j2.25

22. Find Y22

a)j3.0

b)j1.5

c)j0.5

d)j2.0

23.Find Y11

a)3-j7.9

b)4.-j5

c)8-j9

d)2-j4

24.Find Y12,Y13,Y23

a)Y1,Y2,Y3

b)-Y6,-Y3,-Y5

c)Y3,Y4,Y5

d)-Y1,-Y2,-Y3

25.Find Y33

a)-j19.89

b)-j12.59

c)-j5.2

d)-j2.5

UNIT 2 Load flow analysis

PART – A MULTIPLE CHOICE QUESTIONS

1)In load flow studies of a power system, a voltage control bus is specified by

a) Real power and reactive power

b) Reactive power and voltage magnitude

c) Voltage and voltage phase angle

d) Real power and voltage magnitude

2)In power system, the maximum number of buses are

a) Generator buses

b) Load buses

c) Slack buses

d) P-V buses

3) In a load flow analysis of a power system, the load connected at a bus is

represented as

a) Constant current drawn from the bus

b) Constant impedance connected at the bus

c) Voltage and frequency dependent sources at the boss

d) Constant real and reactive power drawn from the bus

4)The voltage of a particular bus can be controlled by controlling the

a) Active power of the bus

b) Reactive power of the bus

c) Phase angle

d) All of the above

5) Gauss-Seidel iterative method can be used for solving a set of

a) Linear differential equations only

b) Linear algebraic equations only

c) Both linear and nonlinear algebraic equations

d) Both linear and nonlinear algebraic differential

equations

6) The Gauss-Seidel load flow method has following disadvantages, select the incorrect

statement

a) Unreliable convergence

b) Slow convergence

c) Choice of a slack bus affects convergence

d) A good initial guess for voltages is essential for convergence

7) Compared to Gauss-Seidel method, Newton-Raphson method takes

a) Less number of iterations and more time per iteration

b) Less number of iterations and less time per iteration

c) More number of iterations and more time per iteration

d) More number of iterations and less time per iteration

8) Regulation transformers are used in power systems for control of

a) Voltage

b) Power factor

c) Power flow

d) All of the above

9) In a load flow study a PV bus is treated as a PQ bus when

a) Voltage limit is violated

b) Active power limit is violated

c) Phase angle is high

d) Reactive power limit is violated

10)Which among the following quantities are to be determined in a voltage controlled bus?

a) P and Q

b) Q and |V|

c) |V| and δ

d) Q and δ

11)Which among these quantities are to be determined in slack bus?

a) P and Q

b) Q and |V|

c) |V| and δ

d) Q and δ

12)Which among the following buses constitute the maximum number in a power system?

a) Slack bus

b) P Q bus

c) P V bus

d) All of these

13) What percentage of buses in the power system are generator buses?

a) 5 %

b) 25 %

c) 70 %

d) 10 %

14) Which among the following quantities are specified at the generator bus?

a) P and Q

b) P and |V|

c) Q and |V|

d) P and δ

15) Which among the following quantities are specified at the load bus?

a) P and Q

b) P and |V|

c) Q and |V|

d) P and δ

16)Why are load flow studies carried out?

a. To study of stability of the system

b. For fault calculations

c. For planning the power system

d. All of these

17) Select the correct statement

a) The higher the initial load, the larger the critical clearing angle.

b) The higher the initial load, the lower the critical clearing angle.

c) The initial load has nothing to do with the critical clearing angle.

d) The higher the operating time of the circuit breaker, the larger will be the critical clearing

angle.

18).For a two-bus system if the change in load at bus 2 is 5 MW and the corresponding

change in generation at bus 4 is MW, the penalty factor of bus 4 is

a) 0.6

b) 4.67

c) 0.625

d) none of these

19) If Pm is the maximum power transferred, the loss on the system is

a) HVDC terminal equipment are inexpensive

b) VAR compensation is not required in HVDC systems

c) system stability can be improved

d) Harmonics problem is avoided

20). In a 400 kV network, 350 kV is recorded at a 400 kV bus. The reactive power absorbed

by a shunt rated for 50 MVAR, 400 kV connected at the bus is

a) 61.73 MVAR

b) 55.56 MVAR

c) 45 MVAR

d) 40.5 MVAR

21) Which of the following is a sparse matrix:

a) Jacobian matrix

b) Y bus matrix

c) Both of these

d) None of the above

22) Which type of convergence takes place in Newton Raphson method:

a) Linear convergence

b) Quadratic convergence

c) Cubic Convergence

d) None of the above

23) The approximate number of iteration required for n-bus system in Newton-Raphson

method is:

a) 1

b) N

c) 3

d) n^2

24) On slack bus ______ and ______ are specified:

a) Voltage Magnitude, Real power

b) Voltage Magnitude, Phase angle

c) Active, Reactive power

d) Active power, Phase angle

25)High-speed breakers impact:

Transient stability

Steady state stability

Both of these

None of these

26)The major cause of voltage instability is:

a) Transformer

b) Generator

c) Load

d) Transmission Lines

27) Initially what will be the voltage at all the PQ buses for solving the load flow problem

using NR method?

a. V i = 1 ∠ 90°

b. V i = 1 ∠ 0°

c. V i = 1 ∠ 180°

d. V i = 1 ∠ 45°

28) What is the size of the sub matrix “H “of the Jacobian, if n 1 is the number of PV buses and

n 2 the number of PQ buses?

a. (n 1 + n 2 ) 2

b. n 1 * n 2

c. (n 1 + n 2 ) n 1

d. (n 1 + n 2 ) n 2

29) What is the main drawback in NR method?

a. Slow to converge

b. A large memory allocation is required to store the jacobian matrix

c. The number of iterations is more

d. All of these

30)Which types of equations are solved using Newton Raphson method?

a. Nonlinear differential equations

b. Linear differential equations

c. Non linear algebraic equations

d. Both (a) and (b)

31)The equation f(x) is given as x3 – x2 + 4x – 4 = 0. Considering the initial approximation

at x=2 then the value of next approximation correct upto 2 decimal places is given as

__________

a) 0.67

b) 1.33

c) 1.00

d) 1.50

32) The Newton-Raphson method of finding roots of nonlinear equations falls under the

category of which of the following methods?

a) Bracketing

b) Open

c) Random

d) graphical

33) The Iterative formula for Newton Raphson method is given by __________

a) x1 = x0-f(x0)/f’(x0)

b) x0 = x1-f(x0)/f‘(x0)

c) x0 = x1+f(x0)/f’(x0)

d) x1 = x0+f(x0)/f‘(x0)

34 In Newton Raphson method if the curve f f(x) is constant then __________

a) f’’(x)=0

b) f(x)=0

c) f’(x)=0

d) f’(x)=c

35) For what values of 0 the initial guess will be equal to the next iterative values?

a) 70 degrees

b) 90 degrees

c) 100 degrees

d) 55 degrees

36)The equation f(x) is given as x2-4=0. Considering the initial approximation at x=6 then

the value of next approximation correct up to 2 decimal places is given as __________

a) 3.33

b) 1.33

c) 2.33

d) 4.33

37) At which point the iterations in the Newton Raphson method are stopped?

a) When the consecutive iterative values of x are not equal

b) When the consecutive iterative values of x differ by 2 decimal places

c) When the consecutive iterative values of x differ by 3 decimal places

d) When the consecutive iterative values of x are equal

38.The Newton Raphson method fails if __________

a) f’(x0)=0

b) f’’(x0)=0

c) f(x0)=0

d) f’’’(x0)=0

39.In the solution of load-flow equation, Newton-Raphson (NR) method is superior to

the Gauss-seidel (GS) method, because

a) Time taken to perform one iteration in the NR method is less than when compared

to time taken in GS method

b) Number of iterations required in the NR method is more when compared to that in

the GS method

c) Number of iterations required is not independent of the size of the system in NR

method

d) Convergence characteristics of the NR method are not affected by the selection of

slack bus

40.Convergence of the transmission load flow is always assured in case of

a) Newton–Raphson method

b) Gauss method

c) Gauss–Seidel method

d) both (a) and (c)

41)In load flow studies, the state variables are

a) P and Q

b) V and δ

c) P and V

d) P and δ

42. Which one of the following is not correct

a) Slack bus is otherwise called as reference bus

b) PQ bus is called as load bus

c) PV bus is called as Generator bus

d) PQ bus violating the limit is called as generator bus

43) Which of the following is true?

a) Gauss-Seidel method is a direct solution method for power flow

b) All iterative methods ensure convergence

c) A generator bus is also called a swing bus

d) If the reactive generation exceeds the limit then the P, IVI bus will become a P, Q

bus

44) The number of iteration required for an n-bus system in Gauss-Seidel method are

approximately

a) N

b) N 2

c) 3

d) n(n + 1)/ 2

45) Identify the buses in the order 1,2,3

a) Slack bus, Load bus, Load bus

b) Load bus, Slack bus, Load bus

c) Slack bus, Load bus, PV bus

d) Load bus, Load bus, Slack bus

46) identify the buses in the order 1,2,3

a) Slack bus, Load bus, Load bus

b) Load bus, Slack bus, Load bus

c) Slack bus, PV bus, Load bus

d) Load bus, Load bus, Slack bus

47.What is the value of flat voltage start?

a) 2-j5

a) 1+j0

b) 0

c) None of the above

48.Slack bus is also called

a) Swing bus

b) PV bus

c) Load bus

d) None of the above

49.Need to select the Slack bus

a) Calculate the magnitude of the voltage

b) Calculate the Phase angle of the voltage

a) Calculate the line losses

b) None of the above

50.Best value of Acceleration factor is

a) 1.2

b) 1.5

c) 1.6

d) 1.8

UNIT 2- PART B

1) A 1000 × 1000 bus admittance matrix for an electric power system has 8000 non-zero

elements. The minimum number of branches (transmission lines and transformers) in

this system are _____ (up to 2 decimal places).

a) 3500

b) 1500

c) 1000

d) 500

2) A 10-bus power system consists of four generator buses indexed as G1, G2, G3, G4 and

six load buses indexed as L2, L2, L3, L4, L5, L6. The generator-bus G1 is connected as a

slack bus, and the load buses L3 and L4 are voltage controlled buses. The generator at bus

G2 cannot supply the required reactive power demand, and hence it is operating at its

maximum reactive power limit. The number of non-linear equations required for solving the

load flow problem using Newton-Raphson method in popular form is________.

a) 5

b) 12

c) 13

d) 14

3) In a load flow problem solved by newton-Raphson method with polar coordinates, the size

of the Jactobian is 100 × 100. If there are 20 PV buses in addition to PQ buses and a slack

bus, the total number of buses in the system is__________.

a) 61

b) 14

c) 12

d) 16

4) In a 100 bus power system, there are 10 generators. In a particular iteration of Newton

Raphson load flow technique (in polar coordinates), two of the PV buses are converted to

PQ type. In this iteration,

a) the number of unknown voltage angles increases by two and the number of unknown

voltage magnitudes increases by two

b) the number of unknown voltage angles remains unchanged and the number of

unknown voltage magnitudes increases by two.

c) the number of unknown voltage angles increases by two and the number of unknown

voltage magnitudes decreases by two.

d) the number of unknown voltage angles remains unchanged and the number of

unknown voltage magnitudes decreases by two.

5) A power system has 100 buses including 10 generator buses. For the load flow analysis

using Newton-Raphson method in polar coordinates, the size of the Jacobian is

a) 189 x 189

b) 100 x 100

c) 90 x 90

d) 180 x 180

6) Determine the correctness or otherwise of the following Assertion [a] and the Reason

[r].Assertion: Fast decoupled load flow method gives approximate load flow solution

because it uses several assumptions. Reason: Accuracy depends on the power mismatch

vector tolerance.

a) Both [a] and [r] are true and [r] is the correct reason for [a].

b) Both [a] and [r] are true and [r] is not the correct reason for [a].

c) Both [a] and [r] are false.

d) [a] is false and [r] is true.

7).A two bus power system shown in the figure supplies a load of 1.0+j0.5 p.u.

The values of V1 in p.u. and δ2 respectively are

a) a)0.95 and 6.00 o

b) b)1.05 and -5.44 o

c) c)1.1 and -6.00 o

d) d)1.1 and -27.12 o

8) A 183-bus power system has 150 PQ buses and 32 PV buses. In the general case, to

obtain the load flow solution using Newton-Raphson method in polar coordinates, the

minimum number of simultaneous equations to be solved is ___________.

a) 110

b) 220

c) 332

d) 500

9) The bus admittance matrix of a three-bus three-line system is

Y = [[−13 10 5 ][10 − 18 10][5 10 − 13]]

If each transmission line between the two buses is represented by an equivalent π-network,

the magnitude of the shunt susceptance of the line connecting bus 1 and 2 is

a) 4

b) 2

c) 1

d) 0

10) The per unit fault feeds from generators connected to buses 1 and 2 respectively are

a) 1.20,2.51

b) 1.55,2.61

c) 1.66,2.50

d) 5.00,2.50

11) Consider two buses connected by an impedance of (0+j5)ohm. The bus 1 voltage is 100

∠30°v and bus 2 voltage is 100∠ 0°v. The real and reactive power supplied by bus 1

respectively is

a) 1000W, 268VAR

b) -1000W, -134VAR

c) 276.9W, -56.7VAR

d) -276.9W, 56.7VAR

12) For the Y-bus matrix of a 4-bus system given in per unit, the buses having shunt

elements are

a) 3 and 4

b) 2 and 3

c) 1 and 2

d) 1,2 and 4

13) A power system consists of 300 buses out of which 20 buses are generator buses, 25

buses are the ones with reactive power support and 15 buses are the ones with fixed shunt

capacitors. All the other buses are load buses. It is proposed to perform a load flow analysis

for the system using Newton -Raphson method. The size of the Newton - Raphson Jacobian

matrix is

a) 553 x 553

b) 540 x 540

c) 555 x 555

d) 554 x 554

14) In load - flow analysis, the load at a bus is represented as

a) a constant current drawn from the bus

b) a constant impedance connected at the bus

c) constant real and reactive powers drawn from the bus

d) a voltage - dependent impedance at the bus

15) In load - flow analysis, the load at a bus is represented as a constant current drawn from

the bus a constant impedance connected at the bus constant real and reactive powers drawn

from the bus a voltage - dependent impedance at the bus in a power system during load flow

studies

(i)there are four variables at each bus

(ii)the voltage magnitude at one bus is specified and this bus is called voltage controlled bus

(iii)at all the load buses P and Q are specified for the loads

(iv)power losses are 'assigned to swing bus.

Which of the above is I are correct?

a) (i) and (ii)

b) (ii) and (iii)

c) (i) (iii) and (iv)

d) (i) (ii) (iii) and (iv)

16) In load flow studies

(i)

convergence of iterative method depends upon the diagonal dominance in Y BUS matrix

(ii) sparsity of Z - bus matrix is well exploited

(iii) for large well conditioned system with n-buses the number of iteration required is

approximately n2

(iv) Z - matrix methods is very sensitive to choice of slack bus.

Which of the above is I are true

a) (i) and (ii)

b) (ii) and (iv)

c) (iii) and (iv)

d) (i) and (iii)

17) In load flow solution by N-R method

(i) the rectangular coordinates method is slower compared to polar - coordinates method

(ii) the Jacobian in case of rectangular coordinates is not symmetric

(iii) the Jacobian with usual formulation in polar coordinates is symmetric

(iv) the N-R method converges in 2-5 iterations

which of the following is correct

a) (i) and (iv) are true

b) (ii) and (iv) are true

c) (i), (ii) and (iv) are true

d) (i), (ii) and (iii) are true

18) In the power system network shown in Figure , bus 1 is a slack bus withV1= 1.0∠0◦per unit

and bus 2 is a load bus withS 2 = 280MW +j60Mvar. The line impedance on a base of 100 MVA is

Z= 0.02 +j0.04per unit. Using Gauss-Seidel method, determine V2. Use an initial estimate of

V 2

(0)

=1.0 +j0.0.

a) 0.8-j0.3

b) 0.92-j0.1

c) 1-j2

d) 2-j5

19) In the two-bus system shown in Figure , bus 1 is a slack bus withV1=1.0∠0◦pu. A load of

150 MW and 50 Mvar is taken from bus 2. The line admittanceisy12= 10∠−73.74◦pu on a base

of 100 MVA. The expression for real and reactive power at bus 2 is given by

P2= 10|V2||V1|cos(106.26◦−δ2+δ1) + 10|V2|2cos(−73.74◦)

Q2=−10|V2||V1|sin(106.26◦−δ2+δ1)−10|V2|2sin(−73.74◦)

Using Newton-Raphson method, obtain the voltage magnitude and phase angle of bus 2. Start

with an initial estimate of |V2|(0)= 1.0pu and δ2(0)= 0◦.

a) -0.09,-0.13

b) 1,-2

c) 2,-8

d) 0.5,-1.8

20) In the two-bus system shown in Figure , bus 1 is a slack bus withV1=1.0∠0◦pu. A load of

100 MW and 50 Mvar is taken from bus 2. The line impedanceisz12= 0.12 +j0.16pu on a base of

100 MVA. Using Newton-Raphson method, obtain the voltage magnitude and phase angle of bus

2. Start with an initial estimateof|V2|(0)= 1.0pu andδ2(0)= 0◦

a) 3,-6

b) 2,-3

c) 1,-2

d) -0.2,-0.1

21)Calculate the magnitude and phase of bus 2 for the figure shown below.

Bus1:slack bus V=1.05∠0°

Bus 2:PV bus V=1 pu Pg = 3 pu

Bus 3:PQ bus PL= 4 QL= 2 pu

a) 5,8.2

b) 1, 6.5

c) 0.5, 5

d) 1, 21.8

22) Calculate the V3 of bus 3 for the figure shown below.

a) 0.9275-j0.15

b) 1-j5

c) 5-j10

d) 0.5-j0.2

23) Calculate the V3 of bus for the figure shown below.

Bus1:slack bus V=1.05∠0°

Bus 2:PV bus V=1 pu Pg = 3 pu

Bus 3:PQ bus PL= 4 QL= 2 pu

a) 5-j10

b) 0.737-j0.257

c) 0.5-j 5

d) 0.2-j0.8

24) Given:

Bus 1 is slack bus: V=1∠0°

Scheduled power at Bus 2 is 1.2 p.u.

Scheduled load at Bus 3 is 1.5 p.u. Compute YBUS model

a) [14 -4 -10 ; -4 9 -5 ; -10 -5 15]

b) [-10 -5 15 ; -4 9 -5 ; 14 -4 -10]

c) [-2 2 2 ; -4 9 -5 ; 14 -4 -10]

d) [12 5 10; 5 8 7 ; 10 7 21]

25) In the two bus system shown in figure, bus 1 is a slack bus with V1=1.0∠0° pu. A load of

100 Mw and 50 MVAR is taken from bus 2.The line impedance is Z12 = 0.12 + j 0.16 pu on a

base of 100 MVA. Using Newton-raphson method, find Jacobian matrix. Start with an initial

estimate of V 2 0 = 1.0 pu and δ 2 0 = 0° . perform two iterations.

a)

b)

c)

d)

4 3

−3 4

1 3

−3 2

5 3

−1 4

0.5 3

−3 0.8

ANSWER KEY

UNIT 1 PART A MCQ ANSWER KEY

1 D 2 A 3 C 4 A 5 B 6 D 7 E 8 A 9 C 10 B

11 D 12 D 13 A 14 C 15 C 16 A 17 C 18 C 19 B 20 D

21 A 22 D 23 C 24 B 25 C 26 B 27 D 28 D 29 C 30 A

31 B 32 C 33 A 34 A 35 A 36 C 37 D 38 D 39 A 40 A

41 B 42 B 43 B 44 A 45 A 46 A 47 A 48 B 49 C 50 C

UNIT 1 PART B MCQ ANSWER KEY

1 A 2 A 3 A 4 A 5 B 6 B 7 B 8 C 9 A 10 D

11 D 12 D 13 A 14 A 15 A 16 B 17 A 18 C 19 D 20 A

21 D 22 B 23 A 24 B 25 A

ANSWER KEY

UNIT 2 PART A MCQ ANSWER KEY

1 D 2 B 3 D 4 B 5 B 6 A 7 A 8 C 9 D 10 D

11 A 12 B 13 D 14 B 15 A 16 C 17 B 18 D 19 B 20 D

21 C 22 B 23 C 24 B 25 A 26 C 27 A 28 A 29 B 30 C

31 B 32 B 33 A 34 C 35 B 36 A 37 D 38 A 39 D 40 C

41 B 42 D 43 D 44 A 45 A 46 C 47 B 48 A 49 C 50 C

UNIT 2 PART B MCQ ANSWER KEY

1 A 2 D 3 A 4 B 5 A 6 D 7 B 8 C 9 B 10 C

11 A 12 C 13 B 14 C 15 D 16 D 17 D 18 B 19 A 20 D

21 D 22 A 23 B 24 A 25 A

UNIT 3 SYMMETRICAL FAULT ANALYSIS

PART – A & PART-B

MULTIPLE CHOICE QUESTIONS

1. A transformer rated for 500 KVA, 1 KV/0.4 KV has an impedance of 10% and is connected to

an infinite bus. The fault level of the transformer is

(A) 500 KVA

(B) 5000 KVA

(C) √3x500 KVA

(D) None of the above

2.In a large interconnected power system, consider three buses having short-circuited capacities

1500 MVA, 1200 MVA and 1000 MVA respectively. The voltages of all the buses are 1.0 pu. If a

3-phase fault takes place on bus 2, the change in bus voltage is described as

(A) ΔV1 > ΔV2 > ΔV3

(B) ΔV1 < ΔV3 < ΔV2

(C) ΔV1 > ΔV3 > ΔV2

(D) None of the above

3. A power system network with a capacity of 100 MVA has a source impedance of 10% at a

point. The fault level at that point is

(A) 10 MVA

(B) 30 MVA

(C) 3000 MVA

(D) 1000 MVA

4. The impedance value of a generator is 0.2 pu on a base value of 11 KV, 50 MVA. The

impedance value for a base value of 22 KV, 150 MVA is

(A) 0.15 pu

(B) 0.2 pu

(C) 0.3 pu

(D) 2.4 pu

5. Four identical alternators each rated for 20 MVA, 11 kV having a sub transient reactance of

16% are working in parallel. The short- circuit level at the bus-bars is

(A) 500 MVA

(B) 400 MVA

(C) 125 MVA

(D) 80 MVA

6. In a power system with negligible resistance, the fault current at a point is 8.00 pu. The

series reactance to be included at the fault point to limit the short-circuit current to 5.00 pu

is

(A) 3.000 pu

(B) 0.200 pu

(C) 0.125 pu

(D) 0.075 pu

7. The bus-bars of each of the two alternators of 15% reactance each, are interconnected through

tie-bar reactors of 15% each. The equivalent impedance to fault current for a 3-phase fault in any

alternator bus-bar will be

(A) 75%

(B) 10%

(C) 11.25%

(D) 15%

8. In case of a 3-phase short circuit in a system, the power fed into the system is

(A) Mostly reactive

(B) Mostly active

(C) Active and reactive both equal

(D) Reactive only

9. Four alternators, each rated at 5 MVA, 11 kV with 20% reactance are working in parallel. The

short-circuit level at bus bars is

(A) 6.25 MVA

(B) 20 MVA

(C) 25 MVA

(D) 100 MVA

10. An isolated synchronous generator with transient reactance equal to 0.1 pu on a 100 MVA base

is connected to the high voltage bus through a step up transformer of reactance 0.1 pu on 100

MVA base. The fault level at the bus is

A) 1000 MVA

(B) 500 MVA

(C) 50 MVA

(D) 80 MVA

11. The load currents in short circuit calculation are neglected because

1. Short circuit currents are much larger than load currents

2. Short circuit currents are greatly out of phase with load currents

Which of these statement(s) is/are correct?

(A) Neither 1 nor 2

(B) 2 alone

(C) 1 alone

(D) 1 and 2

12. Consider the following statements regarding the fault analysis

1. The neutral grounding impedance Zn appears as 3Zn in zero sequence equivalent circuit

2. For faults on transmission lines, 3-phase fault is the least severe among other faults

3. The positive and negative sequence networks are not affected by method of neutral grounding

Which of the statements given above are correct?

(A) 2 and 3

(B) 1 and 2

(C) 1 and 3

(D) 1, 2 and 3

13. A short circuit occurs in a transmission line (neglect line capacitance) when the voltage wave

is going through zero, the maximum possible momentary short circuit current corresponding to

(A) Twice the maximum of symmetrical short circuit current

(B) Maximum of short circuit current

(C) Thrice the maximum of symmetrical short circuit current

(D) Four times the maximum symmetrical short circuit current

14. Which of the following is correct

(A) X" d = X' d = X d

(B) X" d < X' d < X d

(C) X" d = X d ∕ 2

(D) X' d = X d ∕ 2

15. Three phase short circuit MVA to be interrupted by a circuit breaker in a power system is

given by

(A) √3 x post fault line voltage in kV x SC current in kA

(B) 3 x pre fault line voltage in kV x SC current in kA

(C) √3 x pre fault line voltage in kV x SC current in kA

(D) (1/√3) x pre fault line voltage in kV x SC current in kA

16. Fault level means

(A) Voltage at fault point

(B) Fault current

(C) Fault power factor

(D) Fault MVA

17. Fault calculation using computer are usually done by

(A) Y BUS method

(B) Z BUS method

(C) None of above

(D) Any of above

18. The rated breaking capacity (MVA) of a breaker is equal to

(A) Product of rated voltage (kV) and rated breaking current (kA)

(B) Product of rated voltage (kV) and rated symmetrical breaking current (kA)

(C) Product of breaking current (kA) and fault voltage (kV)

(D) Twice the value of rated voltage (kV) and rated current (kA)

19. A short circuit current is identified by

(A) Heavy current flow

(B) Voltage rise

(C) Voltage drop

(D) None of above

20. Short circuit currents are due to

(A) Single phase to earth fault

(B) Phase to phase fault

(C) All three phase to earth fault

(D) Any of above

21. The most serious consequences of a major uncleared short circuit fault can be

(A) Blowing of a fuse

(B) Fire

(C) Heavy voltage drop

(D) None of above

22. Which of the following results in a symmetrical fault?

(A) Single phase to earth

(B) Phase to phase

(C) All the three phase to earth

(D) Two phase to earth

23. Which portion of the transmission system is more prone to faults?

(A) Alternator

(B) Transformer

(C) Overhead lines

(D) Underground cables

24. Which portion of the power system is least prone to faults?

(A) Alternator

(B) Switchgears

(C) Transformer

(D) Overhead lines

25. The magnitude of fault current depends upon

(A) Total impedance up to faults

(B) Voltage at the fault

(C) Load current being supplied before occurrence of fault

(D) Both (a) and (b)

26. The maximum short circuit current occurs in the case of

(A) Three phase fault

(B) Double line to ground fault

(C) Line to line fault

(D) Single line to ground fault

27. For limiting the short circuit current

(A) Reactors are used

(B) Resistors are used

(C) Capacitors are used

(D) Any of above

28. Circuit breaker usually operate under

(A) Steady state short circuit current

(B) Sub transient state of short circuit current

(C) Transient state of short circuit current

(D) None of above

29. For complete protection of a 3-phase line

(A) Three-phase and three-earth fault relays are required

(B) Three-phase and two-earth fault relays are required

(C) Two-phase and two-earth fault relays are required

(D) Two-phase and one-earth fault relays are required

30. When all the three phases are short-circuited, the current thought the system is

(A) zero

(Bi) low

(C) very large

(D) none of above

31. When a short circuit occurs in a power system

(A) the voltage at fault point is zero

(B) a very large current flows in the system

(C) it results in overheating of equipment

(D) all of above

32. The fault on a power system that gives symmetrical fault currents is

(A) line to tine fault

(B) three-phase short circuit fault

(C) single line to ground fault

(D) none of above

33.The use of reactors permits the installation of circuit breakers of

(A) lower rating

(B) same rating

(C) higher rating

(D) none of above

34. If the percentage reactance-of the system up to the fault point is 20% and base kVA is

10,000, then short-circuit kVA is

(A)10.000 KVA

(B) 50,000 KVA

(C) 500 kVA

(D) 30.000 KVA

35. The short-circuit kVA is maximum when fault occurs

(A) near the generator

(B) at the end of transmission line

(C) in the middle of transmission line

(D) none of above

36. A short-circuit may lead to

(A) excessive current

(B) fire or explosion

(C) low voltage in the system

(D) all of above

37. In short-circuit calculations, the selected base kVA is equal to

(A) that of the largest plant

(B) the total plant capacity

(C) any arbitrary value

(D) all above

38. In a balanced star-connected system line voltages are ahead of their respective phase

voltages.

(A) 30°

(B) 60°

(C) 120°

(D) none of the above

39. The benefit of star-connected supply system is that

(A) line current is equal to phase current

(B) two voltages can be used

(C) phase sequence can be easily changed

(D) it is a simple arrangement

40. A 3-phase load is balanced if all the three phases contain the same

(A) impedance

(B) power factor

(C) impedance and power factor

(D) none of the above

41. In a 3-phase system, if instantaneous values of phase R and Y are + 60V and -40

V in that order, then instant voltage of phase B is

(A) -20 V

(B) 40 V

(C) 120 V

(D) none of the above

42. Three identical resistances linked in star carry a line current of 12 A. If the similar

resistances are connected in delta across the similar supply, line current will be ……….

(A) 12 A

(B) 4 A

(C) 8 A

(D) 36 A

43. The algebraic sum of instantaneous phase voltages in a three-phase circuit is

equivalent to

(A) zero

(B) line voltage

(C) phase voltage

(D) none of the above

44. In a three phase circuit, true power

(A) cannot exceed apparent power

(B) can exceed apparent power

(C) data insufficient

(D) none of the above

45. In a 3-phase circuit, the load p.f. is 1. The relation among apparent power (S) and true

power (P) is

(A) P=2S

(B) S=2P

(C) P = S

(D) none of the above

46. A 30 MVA. 11 kV 3-phase alternator supplies full-load at a Lagging power factor of 0.6.

The fraction increase in earning ability as the power factor is raised to 0.9 becomes.

(A) 25%

(B) 30%

(C) 60 %

(D) 50 %

47. In a three-phase circuit, if load p.f. is decrease, line current

(A) decreases

(B) increases

(C) remains the same

(D) none of the above

48. All a.c. equipement is rate in kVA because

(A) kVA>kW

(B) kVA< kW

(C) of temperature rise limitation

(D) none of the above

49. Which among the following methods are generally used for the calculation of

symmetrical faults?

a. Norton theorem

b. Thevnin’s theorem

c. Kirchhoff’s laws

d. Only (b) and (c)

50. Which among the following reactance have a greater value?

a. Sub transient reactance

b. Transient reactance

c. Synchronous reactance

d. All of these

51. What is the expression for the symmetrical short circuit current? If the total short circuit

current consists of two parts namely symmetrical short circuit current and DC offset current.

a. (V m / Z) * sin (ω + αt - θ)

b. (V m / Z) * sin (ωt + α - θ)

c. (V m * Z) * sin (ωt + αt - θ)

d. (V / Z m ) * sin (ωt + α - θ)

PART -B

1. Two synchronous generators are connected in parallel at the low voltage side of a

three-phase D -Y transformer as shown in Fig. 3.2. Machine 1 is rated 50 MVA, 13.8 kV.

Machine 2 is rated 25 MVA, 13.8 kV. Each generator has sub transient reactance,

transient reactance and direct axis synchronous reactance of 25%, 40% and 100%

respectively. The transformer is rated 75 MVA, 13.8 D/69Y with a reactance of 10%.

Before the fault occurs, the voltage on high voltage side of the transformer is 66 kV. The

transformer is unloaded and there is no circulating current between the generators

Determine the Generator1 per unit sub transient reactance.

a)0.425pu

b)0.375pu

c)0.6pu

d)1.5pu

2. Two synchronous generators are connected in parallel at the low voltage side of a

three-phase D-Y transformer as shown in Fig. 3.2. Machine 1 is rated 50 MVA, 13.8 kV.

Machine 2 is rated 25 MVA, 13.8 kV. Each generator has sub transient reactance,

transient reactance and direct axis synchronous reactance of 25%, 40% and 100%

respectively. The transformer is rated 75 MVA, 13.8 D/69Y with a reactance of 10%.

Before the fault occurs, the voltage on high voltage side of the transformer is 66 kV. The

transformer is unloaded and there is no circulating current between the generators

Determine the Generator1 per unit transient reactance.

a)0.425pu

b)0.375pu

c)0.6pu

d)1.5pu

3. Two synchronous generators are connected in parallel at the low voltage side of a

three-phase D-Y transformer as shown in Fig. 3.2. Machine 1 is rated 50 MVA, 13.8 kV.

Machine 2 is rated 25 MVA, 13.8 kV. Each generator has sub transient reactance,

transient reactance and direct axis synchronous reactance of 25%, 40% and 100%

respectively. The transformer is rated 75 MVA, 13.8 D/69Y with a reactance of 10%.

Before the fault occurs, the voltage on high voltage side of the transformer is 66 kV. The

transformer is unloaded and there is no circulating current between the generators

Determine the Generator1 per unit direct axis reactance.

a)0.425pu

b)0.375pu

c)0.6pu

d)1.5pu

4. A synchronous generator and a synchronous motor each rated 20MVA, 12.66KV having 15%

reactance are connected through transformers and a line as shown in fig. the transformers are

rated 20MVA,12.66/66KV and 66/12.66KV with leakage reactance of 10% each. The line has a

reactance of 8% on base of 20MVA, 66 KV. The motor is drawing 10MW at 0.8 leading power

factors and a terminal voltage 11KV when symmetrical three phase fault occurs at the motors

terminals. Determine the thevenin’s voltage at the fault location.

a) 1 pu

b) 0.8078 pu

c)0.8688 pu

d)0.8245 pu

5. A synchronous generator and a synchronous motor each rated 20MVA, 12.66KV having

15% reactance are connected through transformers and a line as shown in fig. the

transformers are rated 20MVA,12.66/66KV and 66/12.66KV with leakage reactance of 10%

each. The line has a reactance of 8% on base of 20MVA, 66 KV. The motor is drawing 10MW

at 0.8 leading power factors and a terminal voltage 11KV when symmetrical three phase fault

occurs at the motors terminals. Determine the thevenin’s Impedance at the fault location.

a)0.1058 pu

b)0.15 pu

c)0.1112 pu

d)0.1010 pu

6. A synchronous generator and a synchronous motor each rated 20MVA, 12.66KV having 15%

reactance are connected through transformers and a line as shown in fig. the transformers are

rated 20MVA,12.66/66KV and 66/12.66KV with leakage reactance of 10% each. The line has a

reactance of 8% on base of 20MVA, 66 KV. The motor is drawing 10MW at 0.8 leading power

factors and a terminal voltage 11KV when symmetrical three phase fault occurs at the motors

terminals. Determine the Fault current at the Motor terminal.

a)-j7.8110 pu

b)-j6.3211 pu

c)-j7.3211 pu

d)-j6.8110 pu

7.Two synchronous generators are connected in parallel at the low voltage side of a threephase

D-Y transformer as shown in Fig. 3.2. Machine 1 is rated 50 MVA, 13.8 kV. Machine 2 is

rated 25 MVA, 13.8 kV. Each generator has sub transient reactance, transient reactance and

direct axis synchronous reactance of 25%, 40% and 100% respectively. The transformer is

rated 75 MVA, 13.8 D/69Y with a reactance of 10%. Before the fault occurs, the voltage on

high voltage side of the transformer is 66 kV. The transformer is unloaded and there is no

circulating current between the generators Determine the Generator2 per unit direct axis

reactance.

a)1.0 pu

b)3.0 pu

c)2.0 pu

d)4.0 pu

8. Two synchronous generators are connected in parallel at the low voltage side of a threephase

D-Y transformer as shown in Fig. 3.2. Machine 1 is rated 50 MVA, 13.8 kV. Machine 2 is

rated 25 MVA, 13.8 kV. Each generator has sub transient reactance, transient reactance and

direct axis synchronous reactance of 25%, 40% and 100% respectively. The transformer is

rated 75 MVA, 13.8 D/69Y with a reactance of 10%. Before the fault occurs, the voltage on

high voltage side of the transformer is 66 kV. The transformer is unloaded and there is no

circulating current between the generators Determine the Generator2 per unit transient

reactance.

a)1.2 pu

b)1.4 pu

c)1.6 pu

d)1.8 pu

9. Two synchronous generators are connected in parallel at the low voltage side of a threephase

D -Y transformer as shown in Fig. 3.2. Machine 1 is rated 50 MVA, 13.8 kV. Machine 2

is rated 25 MVA, 13.8 kV. Each generator has sub transient reactance, transient reactance

and direct axis synchronous reactance of 25%, 40% and 100% respectively. The

transformer is rated 75 MVA, 13.8 D/69Y with a reactance of 10%. Before the fault occurs,

the voltage on high voltage side of the transformer is 66 kV. The transformer is unloaded

and there is no circulating current between the generators Determine the Generator2 per

unit sub transient reactance.

a)0.65 pu

b)0.95 pu

c)0.85 pu

d)0.75 pu

10. Consider the power system shown in figure. The values marked are p.u. impedances. The p.u.

reactances of the generator 1 and 2 are 0.15 and 0.075 respectively. Compute the bus impedance

matrix of the generator – transmission network. When the element 0-2 is included the matrix is

The matrix values are mentioned [Z11 Z12 ; Z21 Z22]

a) [0 0.15 ; 0 0.25]

b) [0.15 0 ; 0 0.075]

c) [0 0.075 ; 0.15 0]

d) [0 0 ; 0.15 0.075]

11. Consider the power system shown in Fig. The values marked are p.u. impedances. The p.u.

reactance's of the generator 1 and 2 are 0.15 and 0.075 respectively. Compute the bus impedance

matrix of the generator – transmission network. When the element 1-2 is included, the Z 33 element

of the matrix is (before applying kron reduction)

a) j0.535

b) j0.438

c) j0.325

d) j0.275

12. Z bus matrix of transmission – generator network is

Symmetrical short circuit fault occurs at bus 3. Find the Fault current.

a) –j 8.5623 pu

b) –j 9.8590 pu

c) –j 7.2164 pu

d) –j 6.5879 pu

13. The Fig. shows four identical alternators in parallel. Each machine is rated for 25 MVA,

11 kV and has a sub transient reactance of 16 % on its rating. Compute the short circuit

MVA when a three phase fault occurs at one of the outgoing feeders.

a) 900 MVA

b) 525 MVA

c) 700 MVA

d) 625 MVA

14. Consider the power system shown in Fig. The values marked are p.u. impedances.

The p.u. impedances are on base of 50 MVA and 12KV. Symmetrical short circuit occurs

at bus 3 with zero fault impedance. Find the base current.

a)2105.6 Amp

b)2114.3 Amp

c)2405.6 Amp

d)2305.6 Amp

15. 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.

a)21.94 KA

b)22.99 KA

c)19.04 KA

d)20.87 KA

16. 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 symmetrical interrupting current of the breaker at 66KV.

a)21.94 KA

b)22.99 KA

c)19.04 KA

d)20.87 KA

17. In the 4-alternator system shown in Fig. The reactance of the current limiting reactor X

required to limit the fault level at F in a feeder to 500 MVA. Each alternator is rated 25 MVA,

11 kV with reactance of 16 %. Find the Fault current in p.u.

a) 10 pu

b) 15 pu

c) 20 pu

d) 25 pu

18. In the 4-alternator system shown in Fig. The reactance of the current limiting reactor X

required to limit the fault level at F in a feeder to 500 MVA. Each alternator is rated 25 MVA,

11 kV with reactance of 16 %. Find the Thevenin’s impedance in p.u.

a) 0.05 pu

b) 0.04 pu

c) 0.06 pu

d) 0.03 pu

19. In the 4-alternator system shown in Fig. Find the reactance of the current limiting reactor

X required to limit the fault level at F in a feeder to 500 MVA. Each alternator is rated 25

MVA, 11 kV with reactance of 16 %.

a)0.04533 pu

b)0.02633 pu

c)0.05333 pu

d)0.03333 pu

20. In the 4-alternator system shown in Fig. Find the reactance (in ohm)of the current

limiting reactor X required to limit the fault level at F in a feeder to 500 MVA. Each

alternator is rated 25 MVA, 11 kV with reactance of 16 %.

a) 0.1954 ohm

b) 0.2581 ohm

c) 0.3684 ohm

d) 0.4158 ohm

21. Calculate the fault current at F in the given figure, consider 100MVA,34.5 KV as the base.

a)1.785 pu

b)0.775 pu

c)1.775 pu

d)0.785 pu

22. Calculate the thevenin’s impedance for the given problem; consider 100MVA, 34.5KV as

the base.

a) 0.0833 pu

b) 0.48 pu

c) 0.5633 pu

d) 0.6466 pu

23. A 5OHz alternator is rated 5OOMVA, 20kV, with Xd = 1 pu and Xd" = 0.2pu. It supplies

a pure resistive load of 400MW at 20kV. The load is connected directly across the generator

terminals when a symmetrical fault occurs at the load terminals. The pre-fault load current

in pu is

a)0.3 pu

b)0.5 pu

c) 0.8 pu

d) 0.75 pu

24. A 5OHz alternator is rated 5OOMVA, 20kV, with Xd = 1 pu and Xd" = 0.2pu. It supplies a

pure resistive load of 400MW at 20kV. The load is connected directly across the generator

terminals when a symmetrical fault occurs at the load terminals. The thevenin’s voltage at the

fault location is

a) 0.8 pu

b)0.765 pu

c)0.95 pu

d) 1 pu

25. A 5OHz alternator is rated 5OOMVA, 20kV, with Xd = 1 pu and Xd" = 0.2pu. It supplies

a pure resistive load of 400MW at 20kV. The load is connected directly across the generator

terminals when a symmetrical fault occurs at the load terminals. The initial rms current in

the generator in pu is

a)1.245 pu

b)2.058 pu

c)4.568 pu

d)5.063 pu

UNIT 4 UN SYMMETRICAL FAULT ANALYSIS

PART – A & PART-B

MULTIPLE CHOICE QUESTIONS

1. Which of the following statement is true?

a) a = 0.5 – j 0.866

b) a = 0.5 + j 0.866

c) a 4 = - a

d) a 2 = - (1 + a)

2. The boundary condition for L-G fault is

a) Ib = 0; Ic = 0; and Va = 0.

b) Ia = 0; Ib = - Ic; and Vb = Vc

c) Ia = 0 and Vb = Vc = 0

d) Ia = 0; Vbb’ = Vcc’ = 0

3. Possible faults that may occur on a transmission line are

1. 3-phase fault 2. L-L-G fault

3. L-L fault 4. L-G fault.

The decreasing order of severity of the fault from the stability point of view is

(a) 1-2-3-4

(b) 1-4-3-2

(c) 1-3-2-4

(d) 1-3-4-2.

4. The following sequence currents were recorded in a power system under a fault condition

I positive = j 1.753 pu, I negative = – j 0.6 pu, I zero = – j 1.153 pu.The fault is

(A) Line to ground

(B) Three-phase

(C) Line to line to ground

(D) Line to line

5. The most common type of fault is

(A) Phase to ground

(B) Phase to phase

(C) Two phase to ground

(D) Three phase to ground

6. For a fault at the terminals of synchronous generator, the fault current is maximum for

(A) Three phase fault

(B) Three phase to ground fault

(C) Single line to ground fault

(D) Line to line fault

7. For measuring positive, negative and zero sequence voltages in a system, the reference is

taken as

(A) Neutral of the system only

(B) Ground only

(C) For zero sequence neutral and for positive and negative the ground

(D) None of the above

8. A system is said to be effectively grounded if its

(A) Neutral is grounded directly

(B) Ratio of X0 ∕ X1 > 3.0

(C) Ratio of R0 ∕ X1 > 2.0

(D) Ratio of X0 ∕ X1 < 3.0

9. For a star-delta transformer with star-side grounded, the zero sequence current

(A) Has no path to ground

(B) Exists in the lines on the delta side

(C) Exists in the lines on the Y side

(D) Exists in the lines on both Y and delta sides

10. Zero sequence currents can flow from a line into a transformer bank if the windings are

in

(A) Grounded star/delta

(B) Delta/star

(C) Star/grounded star

(D) Delta/delta

11. If the positive, negative and zero sequence reactances of an element of a power system

are 0.3, 0.3 and 0.8 respectively, then the element would be a

(A) Synchronous generator

(B) Synchronous motor

(C) Static load

(D) Transmission line

12. For the fault analysis in power system, symmetrical components are used because

(A) Results are required in terms of symmetrical components

(B) Number of equations becomes smaller

(C) Sequence network do not have mutual coupling

(D) All of above

13. For a power transformer

(A) Positive sequence impedance is more than negative sequence and zero sequence

impedance

(B) Positive, negative and zero sequence impedances are equal

(C) Positive and negative sequence impedances are equal

(D) Positive sequence impedance is less

14. For measuring positive, negative and zero sequence voltages in a system, the reference

is taken as

(A) Neutral of the system only

(B) Ground only

(C) For zero sequence neutral and for positive and negative the ground

(D) None of the above

15. In a balanced 3-phase system,

(A) only negative sequence current is zero

(B) only zero sequence current is zero

(C) both negative and zero sequence currents are zero

(D) none of above

16. The operator a rotates the vector in anticlockwise direction by

(A) 90°

(B) 180°

(C) 60°

(D) 120°

17. The vector sum of positive sequence currents is

(A) zero

(B) low

(C) infinite

(D) none of above

18. The zero sequence impedance of different elements of power system is generally

(A) zero

(B) equal

(C) different

(D) none of above

19. The positive and negative sequence impedance of a transmission line are

(A) equal

(B) zero

(C) different

(D) infinite

20. The positive sequence impedance of a feeder is 3 ohm. Its negative sequence impedance

will be

(i) 3 ohm

(ii) 1 ohm

(iii) 9 ohm

(iv) 6 ohm

21. On the occurrence of an unsymmetrical fault, the sequence component which is always

greater than the negative sequence component is

(i) zero sequence component

(ii) positive sequence component

(iii) both (i) and (ii)

(iv) none of above

22.1+a+a 2 is

(i) -1

(ii) 1

(iii) 0

(iv) -1.732

23. 1-a-a 2 is

(i) -1

(ii) 1

(iii) 0

(iv) 2

24. Unsymmetrical faults

(i) introduce unbalance in the system

(ii) indicate abnormal conditions in the System

(iii) are more frequent than symmetrical faults

(iv) all of above

25. Current-limiting reactors in power system have

(i) large resistance and low reactance

(ii) large reactance and low resistance

(iii) large reactance and resistance

(iv) none of above

26. The most severe unsymmetrical fault is

(i) single line-to-ground fault

(ii) line-to-line fault

(iii) double line-to-ground fault

(iv) none of above

27. If one line conductor of a 3-phase line is cut, the load is then supplied through ……..

voltage.

(i) single phase

(ii) two phase

(iii) three phase

(iv) none of the above

28. When 3 phase system is impartial, the neutral wire carries

(i) no current

(ii) one-third of current for each phase

(iii) half of current for each phase

(iv) none of above

29. In a balanced three-phase system, phase voltage is 200 < 30° V with the phase current

is 8 < -20°A. The load p.f. is

(i) 0.707 lagging

(ii) 0.64 lagging

(iii) 0.85 leading

(iv) 0.5 lagging

30. ‘a’ is an operator used to symmetrical component analysis

a) Which rotates the vector, it operates upon, through an angle 90° in the clockwise

direction

b) Which rotates the vector, it operates upon, through an angle 120°, in the

counter-clockwise direction

c) Which rotates the vector, it operates upon, through an angle120°, in the

clockwise direction

d) Which rotates the vector, it operates upon, through an angle 240°, in the clockwise

direction

31. In which of the following given faults, all the sequence currents are equal?

a) LG

b) LLG

c) LLL

d) LL

32. If all the sequence voltages at the fault point in a power system are equal, then the fault

point is a

a) LG

b) LLG

c) LLL

d) LL

33. Which of the following statement is/are true?

a)The neutral grounding impedance Zn appears as 3Zn in zero sequence equivalent circuit

b)The neutral grounding impedance Zn appears as Zn in zero sequence equivalent circuit

c)both 1 and 2

d)nether 1 nor 2

34. The method of neutral grounding affects the

a) positive sequence network

b) negative sequence network

c) zero sequence network

d) all of the above

35. Find the value of a 729 , where "a" is the operator

a) 1

b) 0

c) Α

d) α²

36. The positive (Z1), negative (Z2) and zero sequence (Z0) impedances of a transmission line

follows the relation

a) Z1 = Z2 = Z0

b) (Z1 = Z2) < Z0

c) (Z1 = Z2) > Z0

d) any of the above

37. Which of the following represents the transmission line positive sequence reactance

a) Xs-Xm

b) Xm-Xs

c) Xs+2Xm

d) 2Xs+Xm

38. Symmetrical component method of analysis is more useful when

a) system has unsymmetrical fault and the network is otherwise balanced

b) system has symmetrical fault and the network is otherwise unbalanced

c) system has unsymmetrical fault and the network is unbalanced.

d) None of these

39. For a line to line fault analysis using symmetrical components,

(a) the positive and negative sequence networks at the fault point are

connected in series

(b) the positive and negative sequence networks at the fault point are

connected in parallel

(c) the positive, negative, and zero sequence networks at the fault point are

connected in parallel

d) the positive, negative, and zero sequence networks at the fault point are

connected in series

40.The boundary condition for L-L fault is

a) Ib = 0; Ic = 0; and Va = 0.

b) Ia = 0; Ib = - Ic; and Vb = Vc

c) Ia = 0 and Vb = Vc = 0

d) Ia = 0; Vbb’ = Vcc’ = 0

41.The boundary condition for L-L-G fault is

a) Ib = 0; Ic = 0; and Va = 0.

b) Ia = 0; Ib = - Ic; and Vb = Vc

c) Ia = 0 and Vb = Vc = 0

d) Ia = 0; Vbb’ = Vcc’ = 0

42. The boundary condition for single conductor open fault is

a) Ib = 0; Ic = 0; and Va = 0.

b) Ia = 0; Ib = - Ic; and Vb = Vc

c) Ia = 0 and Vb = Vc = 0

d) Ia = 0; Vbb’ = Vcc’ = 0

43.What is the value of zero sequence impedance in line to line faults?

a. Z0 = 1

b. Z0 = ∞

c. Z0 = 3 Zn

d. Z0 = 0

44.What percentage of fault occurring in the power system is line to line fault?

a. 5 %

b. 30 %

c. 25 %

d. 15 %

45.What is the expression for fault current in line to line fault?

a. If = √3 * (Ea / Z1 + Z2)

b. If = 3 * (Ea / Z1 + Z2)

c. If = √3 * (Ea / Z1 + Z2 + Z0)

d. If = 3 * (Ea / Z1 + Z2 + Z0)

46.What will be the sum of (I B + I Y ) in case of line to line fault, if the fault is occurring in

the B and Y lines?

a. ∞

b. 0

c. 1

d. I R

47.What happens to the value of the fault current in case of SLG fault, if fault impedance is

introduced?

a. The fault current increase

b. The fault current remains same as in case of SLG fault.

c. The fault current becomes zero

d. The fault current is reduced

48.What happens if the neutral is not grounded in case of the single line to ground fault?

a. Only the zero sequence impedance will be zero

b. The zero sequence impedance will be infinite

c. Fault current will be zero

d. Both (b) and (c)

49.What percentage of faults occurring is single line to ground fault?

a. 50 %

b. 60 %

c. 35 %

d. 70 %

50.What are cross country faults?

a. A fault occurring at any point of the power system

b. Two or more faults occurring simultaneously on the power system

c. Line to line fault

d. All of these

PART - B

1.A 3-Phase, 1OOMVA, 25KV generator has solidly grounded neutral. The positive, negative

& zero sequence reactance of the generator are 0.2 pu, 0.2 pu and 0.05pu, respectively (at

machine base quantities) If a bolted single phase to ground fault occurs at the terminal of

the unloaded generator, the fault current in per unit immediately after the fault is?

a)5.23 pu

b)4.13 pu

c) 6.69 pu

d) 2.23 pu

2. A 3-Phase, 1OOMVA, 25KV generator has solidly grounded neutral. The positive, negative

& zero sequence reactance of the generator are 0.2 pu, 0.2 pu and 0.05pu, respectively (at

machine base quantities) If a bolted single phase to ground fault occurs at the terminal of

the unloaded generator, the positive sequence fault current in per unit immediately after the

fault is?

a)5.23 pu

b)4.13 pu

c) 6.67 pu

d) 2.23 pu

3. A 3-Phase, 1OOMVA, 25KV generator has solidly grounded neutral. The positive,

negative & zero sequence reactance of the generator are 0.2 pu, 0.2 pu and 0.05pu,

respectively (at machine base quantities) If a bolted single phase to ground fault occurs

at the terminal of the unloaded generator, find the positive sequence voltage in per unit

immediately after the fault is?

a) 0.256 pu

b) 0.554 pu

c) 0.658 pu

d)0.423 pu

4. A 3-Phase, 1OOMVA, 25KV generator has solidly grounded neutral. The positive, negative &

zero sequence reactance of the generator are 0.2 pu, 0.2 pu and 0.05pu, respectively (at

machine base quantities) If a bolted single phase to ground fault occurs at the terminal of the

unloaded generator, find the Negative sequence voltage in per unit immediately after the fault

is?(Consider positive sign)

a) 0.1115 pu

b) 0.234 pu

c) 0.357 pu

d) 0.446 pu

5. A 3-Phase, 1OOMVA, 25KV generator has solidly grounded neutral. The positive, negative &

zero sequence reactance of the generator are 0.2 pu, 0.2 pu and 0.05pu, respectively (at

machine base quantities) If a bolted single phase to ground fault occurs at the terminal of the

unloaded generator, find the Zero sequence voltage in per unit immediately after the fault

is?(Consider positive sign)

a) 0.1115 pu

b) 0.234 pu

c) 0.357 pu

d) 0.446 pu

6. A Line to Line Fault occurs at the terminals of the generator. Calculate the value of fault

Current in per unit. Z 1 = 0.25pu , Z 2 = 0.35 pu

a) 1.4586 pu

b) 2.887 pu

c) 0.887 pu

d) 0.4586 pu

7. A Line to Line Fault occurs at the terminals of the generator. Calculate the value of

positive sequence fault current and post fault voltages. Z 1 = 0.25pu , Z 2 = 0.35 pu

consider positive sign.

a) 0.897 pu

b) 2.345 pu

c) 3.254 pu

d) 1.667 pu

8. A Line to Line Fault occurs at the terminals of the generator. Calculate the value of

Negative sequence fault current and post fault voltages. Z 1 = 0.25pu , Z 2 = 0.35 pu

Consider positive sign.

a) 0.897 pu

b) 2.345 pu

c) 1.667 pu

d) 3.254 pu

9. A Line to Line Fault occurs at the terminals of the generator. Calculate the value of

positive sequence fault voltages. Z 1 = 0.25pu , Z 2 = 0.35 pu Consider positive sign.

a) 0.584 pu

b) 0.234 pu

c) 0.357 pu

d) 0.446 pu

10. A 30MVA, 3-Phase, 50Hz, 13.8KV star connected synchronous generator has positive,

negative & zero sequence reactance 15%, 15% & 5% respectively. A reactance is

connected between the neutral of the generator and ground. A double line to ground

fault takes place involving phase 'b' & 'c' with a fault impedance of j0.1 pu. The value of

Xn that will limit the positive sequence generator current to 4270A. What will be the per

unit value of positive sequence current?.

a) 2.727 pu

b) 1.161 pu

c) 3.402 pu

d) 0.202 pu

11. A 30MVA, 3-Phase, 50Hz, 13.8KV star connected synchronous generator has positive,

negative & zero sequence reactance 15%, 15% & 5% respectively. A reactance is

connected between the neutral of the generator and ground. A double line to ground fault

takes place involving phase 'b' & 'c' with a fault impedance of j0.1 pu. The value of Xn that

will limit the positive sequence generator current to 4270A will be?

a) Xn = 0.05 pu

b) Xn = 1.07 pu

c) Xn = 2.10 pu

d) Xn = 3.14 pu

12. A 30MVA, 3-Phase, 50Hz, 13.8kv star connected synchronous generator has positive,

negative & zero sequence reactance 15%, 15% & 5% respectively. A reactance is

connected between the neutral of the generator and ground. A double line to ground fault

takes place involving phase 'b' & 'c' with a fault impedance of j0.1 pu. If the value of Xn is

0.06 pu what will be the positive sequence generator current in per unit?

a) 6.452 pu

b) 3.402 pu

c) 5.220 pu

d) 1.078 pu

13. When a 50 MVA, 11 kV, 3-phase generator is subjected to a 3-phase fault, the fault

current is –j5 pu. When it is subjected to a line-to-line fault, the positive sequence current is

j4 pu. The positive and negative sequence reactances are respectively

(A) j0.2 and j0.05 pu

(B) j0.2 and j0.25 pu

(C) j0.25 and j0.25 pu

(D) j0.05 and j0.05 pu

14. When a line to ground fault occurs, the current in a faulted phase is 100 A. The zero

sequence current in this case will be

(A) Zero

(B) 33.3 A

(C) 66.6 A

(D) 100 A

15. In an unbalanced 3-phase system, the currents are measured as I a = zero, I b = 6∠60°

and I c = 6∠–120°. The zero sequence, positive sequence and negative sequence

components will be

(A) Zero, (3 – j√3), (– 3 + j√3)

(B) Zero, ( – 3+ j√3), ( 3 – j√3)

(C) Zero, ( – 9+ j 3√3), (9 – j3√3)

(D) Zero, ( 9 – j3√3), (– 9 + j3√3)

16. At 80°, phase R is - 138 V, and phase Y is + 154 V. The voltage of phase B is

(i) 64 V

(ii) -32 V

(iii) 16 V

(iv) - 16 V

17. Positive, negative and zero sequence impedances of line are 2,2 and 5 pu respectively.

Find self and mutual impedances respectively?

a) 1 and 3 pu

b) 3 and 1 pu

c) 2 and 2 pu

d) 2 and 5 pu

18. A transmission line has self and mutual impedances are 0.8 and 0 pu respectively. Find

the positive, negative and zero sequence impedances respectively?

a) 0.6, 0.8 and 1.2 pu

b) 0.6, 0.6 and 1.2 pu

c) 0.6, 0.6 and 0.6 pu

d) 0.8, 0.8 and 0.8 pu

19. The positive, negative and zero sequence impedances of a transmission line are

0.5,0.5 and 1.1 pu respectively. The self (Zs) and mutual (Zm) impedances of the line

will be given by

a) Zs = 0.7 pu, Zm =0.2 pu

b) Zs = 0.5 pu, Zm =0.6 pu

c) Zs = 0.6 pu, Zm =0.5 pu

d) Zs = 0.2 pu, Zm =0.7 pu

20. The zero sequence current of a generator for line to ground fault is j3 pu. Then the

current through the neutral during the fault is

a) j3 pu

b) j1 pu

c) j9 pu

d) j6 pu

21. A fault occurring at the terminals of an unloaded synchronous generator operating at its

rated voltage has resulted in the following values of currents and voltages. IR0 = j 2.37 pu

IR1 = -j 3.05 pu IR2 = j 0.68 pu VR0 = VR1 = VR2 = 0.237 pu. Which of the following

faults has occurred?

a) LL

b) LG

c) LLG

d) LLL

22. The line currents of 3-phase supply are: IR=3+j5 A; IY=2+j2 A ;IB=-2-j1 A ;The zero

sequence current will be

a) 1 + j 2 A

b) 5 + j 7 A

c) 1 + j 4 A

d) -2 - j 1 A

23. An unloaded generator with a pre-fault voltage 1 pu has the following sequence

impedance: Z0 = j 0.15 pu, Z1 = Z2 = j 0.25 pu The neutral is grounded with a reactance of

0.05 pu. The fault current in pu for single line to ground fault is

a) 7.25 pu

b) 2.5 pu

c) 3.75 pu

d) 4.28 pu

24.The positive, negative and zero sequence per unit impedance of two generators

connected in parallel are X1 = 0.12 pu, X2 = 0.096 pu and X0 = 0.036 pu. For LG fault at

generator terminals (with 1 pu voltage) the positive sequence current will be

a)10.936 pu

b) 7.936 pu

c) 8.936 pu

d) 9.936 pu

25. A 30 MVA, 3-Phase, 50Hz, 13.8kv star connected synchronous generator has positive,

negative & zero sequence reactance 15%, 15% & 5% respectively. A reactance is

connected between the neutral of the generator and ground. A double line to ground fault

takes place involving phase 'b' & 'c' with a fault impedance of j0.1 pu. If the value of Xn is

0.06 pu what will be the positive sequence generator current in Amps?

a) 3485 amps

b) 4500 amps

c) 6551 amps

d) 7400 amps

Answer Key

UNIT 3 SYMMETRICAL FAULTS MCQ PART-A ANSWER

1. B 2.B 3.D 4.A 5.A 6.D 7.C 8.A 9.D 10.B

11.C 12.C 13.A 14.B 15.C 16.D 17.B 18.B 19.A 20.D

21.B 22.C 23.C 24.A 25.D 26.A 27.A 28.C 29.D 30.C

31.D 32.B 33.A 34.B 35.A 36.D 37.D 38.A 39.B 40.C

41.A 42.D 43.A 44.A 45.C 46.D 47.B 48.C 49.D 50.C

51.B 52.D 53.B 54.A 55.A

UNIT 3 SYMMETRICAL FAULTS MCQ PART-B ANSWER

1.B 2.C 3.D 4.C 5.C 6.A 7.B 8.A 9.D 10.B

11.C 12.B 13.D 14.C 15.B 16.D 17.C 18.A 19.C 20.B

21.C 22.C 23.C 24.D 25.D

Answer Key

UNIT 4 UNSYMMETRICAL FAULTS MCQ PART-A ANSWER

1.D 2.A 3.A 4.C 5.A 6.C 7.D 8.D 9.C 10.A

11.D 12.C 13.B 14.D 15.C 16.D 17.A 18.C 19.A 20.A

21.B 22.C 23.D 24.D 25.B 26.C 27.A 28.B 29.B 30.B

31.A 32.B 33.A 34.C 35.A 36.B 37.A 38.A 39.B 40.B

41.C 42.D 43.D 44.D 45.A 46.B 47.D 48.D 49.D 50.B

UNIT 4 UNSYMMETRICAL FAULTS MCQ PART-B ANSWER

1.C 2.D 3.B 4.D 5.A 6.B 7.D 8.C 9.A 10.C

11.B 12.C 13.A 14.B 15.C 16.D 17.B 18.D 19.A 20.C

21.C 22.A 23.C 24.B 25.C

UNIT 5 POWER SYSTEM STABILITY

PART A & PART B MCQ WITH ANSWERS

1. The stability of the power system is not affected by

A. Generator reactance

B. Line reactance

C. Excitation of generators

D. Line losses

2. The Power Systems are operated with power angle around

A. 10 o

B. 30 o

C. 70 o

D. 80 o

3. Power system stability is defined as

A. That attribute of the system or part of the system which enables it to develop restoring

forces between the elements there of equal or greater than disturbing forces so as to

restore a state of equilibrium between the elements

B. The maximum power flow possible through some particular point in the system when

the entire or part of the system is disturbed

C. Both A and B

D. Neither A or B

4. Stability limit of a power system is defined as

A. That attribute of the system or part of the system which enables it to develop restoring

forces between the elements there of equal or greater than disturbing forces so as to

restore a state of equilibrium between the elements

B. The maximum power flow possible through some particular point in the system when

the entire or part of the system is disturbed

C. Both A and B

D. Neither A or B

5. Steady-state stability of a power system is the ability of the power system to

A. Maintain voltage at the rated voltage level

B. Maintain frequency exactly at 50 Hz

C. Maintain a spinning reserve margin at all times

D. Maintain synchronism between machines and on external tie lines

6. Steady-state stability of a power system is improved by

A. Reducing fault clearing time

B. Using double circuit line instead of single circuit line

C. Single pole switching

D. Decreasing generator inertia

7.The critical clearing time of a fault is power system is related to

A. Reactive power limit

B. Short circuit limit

C. Steady-state stability limit

D. Transient stability limit

8. With fault clearing time, the transient stability limit of a power system

A. Increases

B. Decreases

C. First increases then decreases

D. First decreases and then increases

9. Transient disturbances are caused by

A. Sudden load changes

B. Switching operations

C. Fault in the power system

D. All of the above

10. he transient stability limit of a power system can be appreciably increased by introducing

A. Series inductance

B. Shunt inductance

C. Series capacitance

D. Shunt capacitance

11. In load flow studies of a power system, a voltage control bus is specified by

A. Real power and reactive power

B. Reactive power and voltage magnitude

C. Voltage and voltage phase angle

D. Real power and voltage magnitude

12. In power system, the maximum number of buses are

A. Generator buses

B. Load buses

C. Slack buses

D. P-V buses

13. In power system, if a voltage controlled bus is treated as a load bus then which one of

the following limits would be violated ?

A. Voltage

B. Active power

C. reactive power

D. Phase angle

14. In a load flow analysis of a power system, the load connected at a bus is represented as

A.. Constant current drawn from the bus

B. Constant impedance connected at the bus

C. Voltage and frequency dependent sources at the boss

D. Constant real and reactive power drawn from the bus

15. The voltage of a particular bus can be controlled by controlling the

A. Active power of the bus

B. Reactive power of the bus

C. Phase angle

D. All of the above

16. Which among these cannot be determined from equal area criterion?

a. Critical clearing angle

b. Critical clearing time

c. Transient stability limit

d. Both (a) and (b)

e. All of these

17. What are the common assumptions made for the equal area criterion?

a. The transmission line and machine resistances are neglected.

b. Rotor speed of the machine is constant

c. Mechanical input remains constant.

d. All of these

18. Which stability information is obtained from the equal area criterion?

a. Absolute stability

b. Transient stability

c. Steady state stability

d. Both (b) and (c)

19. Under what condition is the system stable under equal area criterion?

a. The area under the curve P a – δ curve must increase to ∞.

b. The area under the curve P a – δ curve must become equal to 1

c. The area under the curve P a – δ curve must reduce to zero.

d. None of these

20. Which among the following methods are used to improve steady state stability?

a. Reducing the reactance between the transmission and receiving points.

b. By using bundled conductors.

c. By increasing the excitation of generator or motor or both.

d. All of these

21. Which curve represents the reluctance power in the following power angle curve of a

machine?

a. Curve A

b. Curve B

c. Curve C

d. Curve A and curve B

22. What is the range of ‘δ’ for stable operation?

a. 0° < δ < 45°

b. 45° < δ < 90°

c. 0° < δ < 90°

d. 0° < δ < 120°

23. At what value of ‘δ’ the maximum power transfer takes place?

a. 45 °

b. 90 °

c. 120 °

d. 180 °

24. What is power angle equation of synchronous machines?

a. An equation between electrical power generated to the angular displacement of the rotor

b. An equation between mechanical power generated to the angular displacement of the rotor

c. An equation between electrical power generated to the angular displacement of stator

Windings

d. An equation between mechanical power generated to the angular

displacement of stator windings

25. Which point on the graph represents the steady state stability llimit of the system?

a. Point A

b. Point B

c. Point C

d. Point D

26. What will be the inertia constant H, for a water wheel generator having a speed less than

200 rpm?

a. 2 – 4

b. 2 – 3

c. 1 – 2

d. 5 - 6

27. What are the main applications of the swing curves?

a. Designing the rotor field windings

b. Designing the protective devices

c. Used to limit the size of the machine

d. All of these

28. What information does the swing curve provide?

a. Stability of the system.

b. Performance of the machine

c. The rotor performance

d. All of these

29.What kind of differential equation is swing equation?

a. Linear second order

b. Non linear first order

c. Linear first order

d. Non linear second order

30.What is / are the major assumptions made in the calculation of swing equations?

a. Damper windings are neglected

b. The machine is lossless

c. The machine has to run at synchronous speed

d. Both (a) and (b)

31. What does the swing equation describe?

a. The relative motion of rotor with the field windings of the machine

b. The relative motion of the rotor with respect to stator field as a function of time.

c. The relative motion of stator field with the rated frequency of the machine

d. The performance curve of the machine

32. Which among the following phenomenon is generally associated with voltage stability?

a. Temporary load reduction

b. Voltage is reduced

c. Voltage collapses

d. All of these

33. What is the main cause of voltage instability?

a. Generators

b. Transformers

c. Loads

d. Line losses

34. What is voltage stability?

a. To maintain steady voltages at all the buses after the occurrence of fault.

b. To maintain steady voltages at all the buses before the occurrence of fault.

c. To maintain the system frequency after the severe disturbances

d. All of these

35. On what factors does the transient stability depend on?

a. Initial operating state

b. Severity of disturbances

c. Voltage instability

d. Both (a) and (b)

36. What is / are the cause(s) for transient disturbance?

a. Sudden load changes

b. Faults in the power system

c. Switching operations

d. All of these

37. Which among these phenomenon's is / are associated with angle stability?

a. Imbalance between the two generator torque

b. Stability or synchronism is lost

c. Surplus energy is stored up in the rotating masses

d. All of these

38. What is the value of transient stability limit?

a. Higher than steady state stability limit

b. Lower than steady state stability limit.

c. Depending upon the severity of load

d. All of these

39. What is transient stability limit?

a. The maximum flow of power through a particular point in the power system without loss of

stability when small disturbances occur.

b. The maximum power flow possible through a particular component connected in the power

system.

c. The maximum flow of power through a particular point in the power system without loss of

stability when large and sudden disturbances occur

d. All of these

40. Which among the following methods is used for improving the system stability?

a. Increasing the system voltage

b. Reducing the transfer reactance

c. Using high speed circuit breaker

d. All of these

41. What is steady state stability limit?

a. The maximum flow of power through a particular point in the power system without loss of

stability when small disturbances occur.

b. The maximum power flow possible through a particular component connected in the power

system.

c. The maximum flow of power through a particular point in the power system without loss of

stability when sudden disturbances occur

d. All of these

42.Which among these is a classification of power system stability?

a. Frequency stability

b. Voltage stability

c. Rotor angle stability

d. All of these

43. The stability of the power system is not affected by which among these?

a. Generator reactance

b. Line losses

c. Excitation of generators

d. All of these

44. __________ are designed on the basis of swing curve:

a) Rotor windings

b) Stator windings

c) Transformer windings

d) Protection devices

45. The major cause of voltage instability is:

a) Transformer

b) Generator

c) Load

d)Transmission lines

46. Equal area criterion is applicable to:

a) Single machine connected to infinite bus

b) Two machines connected to infinite bus

c) Multi machine system connected to infinite bus

d) All of these

47. The quantity H in swing equation is:

a) Kelvin constant

b) motion of synchronous motor/3.55

c) Inertia constant

d) None of these

48. H in swing equation is defined as:

a) KE * S

b) KE/S

c) KE + 2

d) KE/S

49. How can we improve the steady state stability of the synchronous generator for a better

performance?

a) Increasing the excitation

b) Increasing reactance

c) Decreasing moment of inertia

d) Increasing moment of inertia

50. How can we check upon the transient stability of a power system?

a) By checking variation in load angle

b) By checking variation of real power with load angle

c) Checking variation in load angle and real power

d) Checking variation in load angle or real power

UNIT 5 PART B MCQ

1.To maintain the transient stability for a power system _____________

a) dδ

dt < 0 , dP

dδ > 0

b) dδ

dt = 0 , dP

dδ > 0

c) dδ

dt > 0 , dP

dδ > 0

d) dδ

dt < 0 , dP

dδ = 0

2. There is 2-machine model having losses too, with their transfer impedance being resistive.

The maximum value of sending power P 1max and maximum receiving end power P 2max will take

place with power angle ‘δ’ such that

a) Both P 1max and P 2max will occur at δ<90

b) Both P 1max and P 2max will occur at δ>90

c) P 1max occurs at δ > 90 and P 2max will occur at δ<90

d) P 1max occurs at δ < 90 and P 2max will occur at δ>90

3. As per the system given, machine B will receive the active and reactive power from machine

A when ______________

a) δ is positive and Va is more than Vb

b) δ is positive and Va is less than Vb

c) δ is positive and Va is same as Vb

d) δ is negative and Va is more than Vb

4. What is voltage stability?

a. To maintain steady voltages at all the buses after the occurrence of fault.

b. To maintain steady voltages at all the buses before the occurrence of fault.

c. To maintain the system frequency after the severe disturbances

d. All of these

5. If there are two machines having moment of inertia M1 and M2, where M1<M2; The possible

number of equivalent moment of inertia will be

a) 1

b) 2

c) 3

d) 4

6. If there are two machines having moment of inertia M1 and M2, where M1<M2; Then one

is proposing to add more inertia to the system. Then it will be added to _____________

a) Machine 1

b) Machine 2

c) Machine 1 and Machine 2

d) Either of Machine 1 and Machine 2

7. The measure to improve the transient stability of the power system during the unbalanced

or unsymmetrical fault can be taken as ________

a) Single pole switching of CB

b) Excitation control

c) Phase shifting transformer

d) Increasing turbine valve opening

8. What does the steady state stability of a power system signify?

a) Maintaining the rated voltage

b) Maintaining rated frequency

c) Maintaining a synchronism between machines and tie-lines

d) All of the mentioned

9. If a generator of 250 MVA rating has an inertia constant of 6 MJ/MVA, its inertia constant on

100 MVA base is

(a) 15 MJ/MVA

(b) 10.5 MJ/MVA

(c) 6 MJ/MVA

(d) 2.4 MJ/MVA

10. The inertia constant of a 100 MVA, 50 Hz, 4-pole generator is, 10 MJ/MVA. If the mechanical

input to the machine is suddenly raised from 50 MW to 75 MW, the rotor acceleration will be equal

to

(a) 225 electrical degree/s2

(b) 22.5 electrical dgree/s2

(c) 125 electrical degree/s2

(d) 12.5 electrical degree/s2.

11.The inertia constant of a 100 MVA, 11 kV water-wheel generator is 4. The energy stored in the

rotor at the synchronous speed is

(a) 400 MJ

(b) 400 kJ

(c) 25 MJ

(d) 25 kJ.

12. The inertia constant H of a synchronous condenser is

a) greater than that of hydro generator

b) greater than that of turbo alternator

c) equal to that of turbo alternator

d) none of the above

13. The inertia constants of two groups of machines which do not swing together are M1 and M2.

The equivalent inertia constant of the system is:

a) M1 + M2

b) M1 – M2 if M1 > M2

c) (M1 ∗ M2)

d) M1∗M2

M1+M2

14. The inertia constant of two groups of machines, which swing together are M1 and M2.

The inertia constant of the system is

a) (M1 ∗ M2)

b) M1 – M2 if M1 > M2

c) M1 + M2

d) M1∗M2

M1+M2

15. A generator is connected to a synchronous motor. From stability point of view it is

preferable to have:

(a) Generator neutral reactance grounded and motor neutral resistance grounded

(b) Generator and motor neutrals resistance grounded

(c) Generator and motor neutrals reactance grounded

(d) Generator neutral resistance and motor neutral reactance grounded

16. A 50 Hz, four-pole turbo alternator rated at 20 MVA, 13.2 kV has an inertia constant

H = 4 kW sec/kVA. The K.E. stored in the rotor at synchronous speed is:

(a) 80 kilojoules

(b) 80 mega joules

(c) 40 mega joules

(d) 20 mega joules.

17. If the inertia constant H of a machine of 200 MVA is 2 p.u. its value corresponding to

400 MVA will be:

(a) 4 p.u

(b) 2 p.u.

(c) 1.0 p.u.

(d) 0.5 p.u

18. The inertia constant of two groups of machines which do not swing together are M1 and

M2 such that M 1 > M2. It is proposed to add some inertia to one of the two groups of

machines for improving the transient stability of the system. It should be added to:

(a) M1

(b) M2

c) It does not matter whether to add to M1 or M2

d) None of these

19)What are the common assumptions made for the equal area criterion?

a. The transmission line and machine resistances are neglected.

b. Rotor speed of the machine is constant

c. Mechanical input remains constant.

d. All of these

20.The quantity H in swing equation is:

a) Kelvin constant

b) Motion of synchronous motor/3.55

c) Inertia constant

d) None of these

21. For absolute stability of the system we use which criteria?

a) equal area

b) half set

c) transient area

d) none of these

22. What is the range of ‘δ’ for stable operation?

a. 0° < δ < 45°

b. 45° < δ < 90°

c. 0° < δ < 90°

d. 0° < δ < 120°

23 Which curve represents the reluctance power in the following power angle curve of a

machine?

a. Curve A

b. Curve B

c. Curve C

d. Curve A and curve B

24. Under what condition is the system stable under equal area criterion?

a. The area under the curve P a – δ curve must increase to ∞.

b. The area under the curve P a – δ curve must become equal to 1

c. The area under the curve P a – δ curve must reduce to zero.

d. None of these

25. What will be the inertia constant H, for a water wheel generator having a speed less than

200 rpm?

a. 2 – 4

b. 2 – 3

c. 1 – 2

d. 5 - 6

UNIT-5 PART-A MCQ Answer Key

1 B 2 B 3 A 4 B 5 D 6 B 7 D 8 B 9 D 10 C

11 D 12 B 13 A 14 D 15 A 16 A 17 D 18 A 19 C 20 D

21 C 22 C 23 B 24 A 25 A 26 B 27 B 28 D 29 D 30 D

31 B 32 D 33 C 34 A 35 D 36 D 37 D 38 A 39 C 40 D

41 C 42 D 43 A 44 D 45 C 46 A 47 C 48 D 49 A 50 C

UNIT-5 PART-B MCQ Answer Key

1 C 2 A 3 A 4 D 5 C 6 A 7 A 8 C 9 A 10 A

11 A 12 D 13 C 14 C 15 D 16 B 17 C 18B 19 D 20 C

21 A 22 B 23 C 24 C 25 B

Thank you

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