Monday, August 31, 2020

Chapter 3 : Electromagnetism

Chapter 3 : Electromagnetism

1. Scalar or dot product and B indicated by A of two vectors A(Sin 𝛳B) of Where 𝛳. is the angle between the vector A

A.  AB tan 𝛳
B. AB cot 𝛳.

C. AB sin 𝛳.
D. AB cos 𝛳.


... Answer is (D)

 

 
 

2. Vector or cross product of two vectors A and B indicated by A X B equals where 𝛳 is the angle between the two vectors A and B

A. AB tan 𝛳
B. AB cot 𝛳.

C. AB sin 𝛳.
D. AB cos 𝛳.

... Answer is (D)

 
 
 

3. Line integral around a closed path is

A. circulation around the path
B. density around the path

C.
vector around the path
D. intensity around the path

... Answer is (A)

 

 
 

4. Surface integral of a surface is

A. integral o f surface
B. double integral of surface
 

C.
differential of weight
D. differential of volume

  ... Answer is (B)

 

 
 
5. Volume integral of a volume is
A.  triple integral of volume
B. integral of weight is the gradient of V
C. integral of volume
D. double integral of volume
 
  ...
Answer is (A)

 
 
 

6. D . (V x A) is equal to
A.1
B.-1
C.0
D. ∞

  ... Answer is (B)

 

 
 

7. Electric flux inside a conducting spere is

A. minimum
B. maximum

C.
zero
D. uniform

... Answer is (C)

 
 

8.. Electric field on equipotential surface is

A. always perpendicular to the surface
B. always parallel to the surface

C.
zero
D. infinity

... Answer is (A)

 
 

9. Surface integral of the electric intensity is

A. differential of volume flux
B. net flux emanating from the surface
C. electric charge
D. none of these
 
  ... Answer is (A)

 
 

10. Displacement density D and electric field strength E are related by


A.
D= εE
B. D=
E /ε  

C. D=ε/ E
D. none of above

  ... Answer is (D)

 

 

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Chapter 5 : Harmonics and Transients - Page 5

Chapter 5 : Harmonics and Transients

41. Harmonics in transformer result in
A. increased core losses
B. increased 12R losses
C. magnetic interference with communication circuits
D. all of the above


... Answer is (D)

 

 

42. Which fractional pitch will eliminate the seventh harmonic from the voltage waveform of an alternator?
A. 6/7
B. 7/8
C. 5/6
D. None of the above

... Answer is (A)

 
 

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Chapter 5 : Harmonics and Transients - Page 4

Chapter 5 : Harmonics and Transients

31. The magnetising-inrush-current in a transformer is rich in
 

A. 7th harmonics
B. 2nd harmonics
C. 3rd harmonics
D. 5th harmonics


... Answer is (B)

 

 
 

32. The in-rush current of a transformer at no load is maximum if the supply voltage is switched on
A. At V/2 value
B. At ,6 /2V value
C. At zero voltage value
D. At peak voltage value

... Answer is (C)

 
 
 

33.  Pure inductive circuit takes power (reactive) from the a.c. line when

 
A. applied voltage decreases but current increases
B.
both applied voltage and current rise
C. both applied voltage and current decrease

D.
Both (b) & (c)

... Answer is (A)

 

 
 

34. With 100% series compensation of lines
A. the circuit is series resonant at power frequency
B. low transient voltage
C. high transient current
D. (a) and (b)

  ... Answer is (D)

 

 
 
35. In a pure LC parallel circuit under resonance condition, current drawn from the supply mains is
A. very large
B. infinite
C. V increase
D.Zero
 
  ...
Answer is (D)

 
 
 

36.  While rising and falling if a wave is not symmetrical, it contains

A. Odd harmonics in addition to fundamental
B. both odd and even harmonics in additions to fundamental

C.
even harmonics in addition to fundamental
D. none of the above

  ... Answer is (C)

 

 
 

37. The main reason for generation of harmonics in a transformer could be

 
A. mechanical vibrations
B. saturation of core
C. fluctuating load
D. poor insulation

... Answer is (B)

 
 

38. While rising and while falling, if a wave is symmetrical, it contains

A. odd harmonics in addition to fundamental
B. both odd and even harmonics in addition to fundamental

C.
even harmonics in addition to fundamental
D. None of The above

... Answer is (A)

 
 

39. The principal information obtained from load flow studies in a power system are 1. magnitude and phase angle of the voltage at each bus. 2. reactive and real power flows in each of lines. 3. total power loss in the network. 4. Transient stability limit of the system Select the correct answer from the codes given below

A. 1,2 and 3
B. 2 and 4
C. I and 2
B. 3 and 4
 
  ... Answer is (A)

 
 

40. Shunt compensation in an EHV line is used to improve

 
A. stability and fault level
B. fault level and voltage profile
C. voltage profile and stability
D. stability, fault level and voltage profile

  ... Answer is (B)

 

 

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Chapter 5 : Harmonics and Transients- Page 3

Chapter 5 : Harmonics and Transients

21. The positive sequency component of voltage at the point of fault is zero when it is a :
 

A. 3-phase fault
B. L-L fault
C. L-L-G fault
D. L-G fault


... Answer is (A)

 

 
 

22. A wave-trap is used at the termination of a HVAC overhead line to a station switchyard to
A. attenuate sub-harmonic oscillations
B. provide for carrier communication
C. prevent the transformer magnetising harritonics from reaching the overhead line
D. damp the incoming surge waves from the overhead lines

... Answer is (B)

 
 
 

23.  Transient current in electrical circuits are associated with

 
A. 9 × 108 metre/sec
B.
2 × 108 metre/sec
C. 3
× 108 metre/sec
D.
108 metre/sec

... Answer is (D)

 

 
 

24. Earth wire on EHV overhead transmission line is provided to protect the line against

A. excessive fault voltages
B. corona effect
C.
lightning surge
D. switching surge

  ... Answer is (C)

 

 
 
25. One current transformer (CT) is mounted over a 3-phase 3-core cable with its sheath and armour removed from the portion covered by the CT. An ammeter placed in the CT secondary would measure
A. the positive sequence current
B. the negative sequence current
C. the zero sequence current
D. three times the zero sequence
 
  ...
Answer is (D)

 
 
 

26.  Consider the following statements : The transient stability of the power system under unbalanced fault conditions can be effectively improved by 1. Excitation control 2. phase-shifting transformer 3. single-pole switching of circuit breakers 4. increasing the turbine input. Of these statements

A. 3 and 4 are correct
B. 1 and 3 are correct

C.
1 and 2 are correct
D. 2 and 3 are correct

  ... Answer is (A)

 

 
 

27. Lightning arresters are used in power systems to protect electrical equipments against

 
A. direct strokes of lightning
B. power frequency overvoltages
C. overvoltages due to indirect lightning stroke
D. overcurrents due to lightning stroke

... Answer is (A)

 
 

28. A lightning arrestor connected between the line and earth in a power system

A. suppresses high frequency oscillations in the line
B. reflects back the travelling wave approaching it

C.
protects the terminal equipment against travelling surges
D. protects the transmission line against lightning stroke

... Answer is (C)

 
 

29. Tick out the correct statement :

A. The negative and zero sequence voltages are minimum at the fault point and increase towards the neutral
B. The negative sequence is maximum and zero sequence minimum at the fault point and decrease and increase respectively towards the neutral.
C. The negative and zero sequence voltages are maximum at the fault point and decreases towards the neutral
D. None of the above
 
  ... Answer is (C)

 
 

30. The order of the lightning discharge current is :


A.
1 amp
B. 1 microampere

C.
10,000 amp
D. 100 amp

  ... Answer is (C)

 

 

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Chapter 5 : Harmonics and Transients - Page 2

Chapter 5 : Harmonics and Transients

11. In an R-L circuit connected to an alternating sinusoidal voltage, size of transient current primarily depends on

A. the circuit impedance
B. the voltage frequency
C. the instant in the voltage cycle at which circuit is closed
D. the peak value of the steady-state current


... Answer is (C)

 

 
 

12. The transients which are produced due to sudden but energetic changes from one steady state of a circuit to another are called transients.
A. initiation
B. transition
C. relaxation
D. subsidence

... Answer is (B)

 
 
 

13.  Transient current in electrical circuits are associated with

 
A. inductors
B. capacitors
C. resistors
D. both (a) and (b)

... Answer is (D)

 

 
 

14. There are no transients in pure resistive circuits because they

A. have no stored energy
B. are linear circuits

C.
offer high resistance
D. obey Ohm's law

  ... Answer is (A)

 

 
 
15. 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
 
  ...
Answer is (D)

 
 
 

16.  The most economic load on an underground cable is :  

A. Equal to the surge loading
B.
Greater than its surge loading
C. Less thart the surge loading

D. None of the above is necessary

  ... Answer is (C)

 

 
 

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

A. Active and reactive both equal
B. Reactive only

C.
Mostly reactive
D. Mostly active

... Answer is (A)

 
 

18. If cc is the angle of voltage wave at which an R-L circuit is switched in and 0 is the impedance angle of the R-L circuit, there will be no transient when the circuit is switched in, if:

A. a = 0
B.a = 90 
C. a = 90 + 10
D. None of the above

... Answer is (A)

 
 

19. An RLC series circuit remains predominantly inductive

A. Above resonance frequency
B. At the lower half power frequency
C. At resonance frequency
D. Below resonance frequency
 
  ... Answer is (A)

 
 

20. A generator is connected to a synchronous motor. From stability point of view it is preferable to have


A.
Generator and motor neutrals reactance grounded
B. Generator neutral resistance and motor neutral reactance grounded

C.
Generator neutral reactance grounded and motor neutral resistance grounded
D. Generator and motor neutrals resistance grounded

  ... Answer is (B)

 

 

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Chapter 5 : Harmonics and Transients - Page 1

Chapter 5 : Harmonics and Transients

1. Non-sinusoidal waveforms are made of

A. fundamental and odd harmonics
B. even and odd harmonics only
C. different sinusoidal waveforms
D. fundamental and even harmonics


... Answer is (C)

 

 
 

2. The positive and negative halves of a complex wave are symmetrical when

 
A. it contains odd harmonics
B. phase difference between even harmonics and fundamental is either n/2 or 3n/2
C. it contains even harmonics
D. phase difference between even harmonics and fundamentals is 0 or it

... Answer is (A)

 
 
 

3.  The rms value of the complex voltage given by v = 162 sinωt + 12 sin 3ωt is

 
A. 20 2
B.20
C.28
D.192

... Answer is (B)

 

 
 

4. In a 3-phase system,the harmonic has negative phase sequence of RBY. 

A. 9
B.13
C.5
D.15

  ... Answer is (C)

 

 
 
5. Two complex waves will have the same wave-shape if
A. they contain the same harmonics
B. ratio of corresponding harmonics to their respective fundamentals is the same
C. harmonics are similarly spaced with respect to their fundamental
D. they have all of the above
 
  ...
Answer is (D)

 
 
 

6.  The trigonometric Fourier series for a complex wave will contain positive cosine terms only when
A. it contains even harmonics
B. its two half-cycles are symmetrical
C. its value is zero at 0= n/2, 3n/2 etc.
D. its value is zero at 0= n, 2n etc.

  ... Answer is (C)

 

 
 

7. Transient current in an R-L-C circuit is oscillatory when

A. R=0
B. R>2√L/C

C.
R<2√L/C
D. R=2√L/C

... Answer is (C)

 
 

8. The transient current in a loss-free L-C circuit when excited from an ac source is a/an sine wave.

A. under-damped
B. critically damped
C.
Over-damped
D. undamped

... Answer is (C)

 
 

9. Double-energy transients are produced in circuits consisting of

A. resistance and capacitance
B. resistance, inductance and capacitance
C. two or more resistors
D. resistance and inductance
 
  ... Answer is (B)

 
 

10.Tansient disturbance is produced in a circuit whenever


A. it is suddenly connected or discon nected from the supply
B. it is shorted
C. its applied voltage is changed suddenly
D. all of the above

  ... Answer is (D)

 

 

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