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ASHISHYT

ASHISHYT

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1. To determine voltage regulation of an alternator the following experimental results are required:

A. Short circuit characteristic and open circuit characteristic

B. Open circuit characteristic and mature impedance

C. Armature impedance

D. Short circuit characteristic and open circuit characteristic and Armature impedance

2. The temperature coefficient of resistance of a material is given as:

A.𝐑𝐭−𝐑𝟎

𝐑𝟎(𝐭𝟐−𝐭𝟏)

B.𝐑𝟎− 𝐑𝐭

𝐑𝐭(𝐭𝟏−𝐭𝟐)

C.𝐑𝟏

𝐑𝟎 (𝐭𝟐−𝐭𝟏)

D.𝐑𝐭 –𝐑𝟎

𝐑𝟎 (𝐭𝟏−𝐭𝟐)

3. A coil having 90 turns is connected to a 120 V, 60 Hz source. If the effective value of the magnetizing current is 4 A, then calculate the value of inductance of the coil.

A. 79.6 mH

B. 121.2 mH

C. 32.2 mH

D. 83.16 mH

4. Consider the following statements:

1) Mutual inductance describes the voltage induced at the ends of a coils due to the magnetic field generated by a second coil.

2) The dot convention allows a sign to be assigned to the voltage induced due to mutual inductance term.

3) The coupling coefficient is given by k = 𝐌

𝐋𝟏+𝐋𝟐

Which of the above statements are correct?

(A) 1, 2 and 3

(B) 1 and 3 only

(C) 1 and 2 only

(D) 2 and 3 only

5. If diameter of each conductor of a transmission line is 'd', then the diameter of n-layer stranded conductor will be

A. (2n-1) d

B. (2n+1) d

C. (3n-1) d

D. (3n+1) d

6. The disruptive critical voltage will: -

A. Decrease with the increase of moisture content in air

B. Increase with the increase of moisture content in air

C. Increase with the decrease of moisture content in air

D. Decrease with decreases of moisture content in air

7. What is the main drawback of the underground transmission system compared to the overhead transmission system?

A. Exposure to lightning

B. Heavy initial cost

C. Exposure to atmospheric hazards such as smoke, ice, wind

D. Induction interference between power and communication circuits

8. The design of insulation for systems above 400 kV, is based upon

A. lightning over voltage

B. switching surges

C. system voltage level

D. system load level

9. An instrument transformer is used to extend the range of-

A. induction instrument

B. electrostatic instrument

C. moving coil instrument

D. PMMC instrument

10. Repeatability and Reproducibility are related to

A. Accuracy of the instrument

B. Precision of the instrument

C. Both accuracy of the instrument & precision of the instrument

D. None of these

11. In a balanced 3-phase system, the current coil of a wattmeter is inserted in line 1 and the potential coil across 2 and 3. If the wattmeter reads 100 W, the reactive power drawn by the 3-phase load is

A. 173.2 VAR

B. 50 VAR

C. 100 VAR

D. 141.4 VAR

12. A 150 KW electric motor has an efficiency of 90%, when it operates at full load. Calculate the losses in the machine.

A. 92 KW

B. 150 KW

C. 163 KW

D. 16.66 KW

13. The 25 KVA transformer has a voltage ratio 3300/400V. Find the primary current.

A. 6.25 A

B. 75.8 A

C. 62.5 A

D. 7.58 A

14. Efficiency of a power-transformer under no load condition is approximately:

A. 75

B. 50

C. 25

D. None of the above

15. If the secondary burden of a current transformer is 15 VA and secondary current is 5 A, then the impedance of the connected load will be:

A. 0.6 Ω

B. 5 Ω

C. 6 Ω

D. 10Ω

16. The voltage regulation of a transformer at full load 0.9 p.f. lagging is 5%. For a full load at 0.9 p.f leading, the efficiency of the transformer is:

A. Remain the same

B. Become negative

C. Reduce and may even become negative

D. Increases

17. It is given that the starting current of a 3ϕ induction motor is 3 times the rated current, while the rated slip is 6%. What would be the ratio of starting torque to full-load torque?

A. 0.6

B. 1.8

C. 0.54

D. 1

18. The magnetic field intensity in a material whose 1 relative permeability is 1 when the flux density is 0.005T is: -

A. 250 AT/m

B. 452 AT/m

C. 1775 AT/m

D. 3980 AT/m

19. A coil of resistance 10Ω and inductance 2H is connected to 100V DC supply through a switch. The initial rate of change of current at the instant of closing the switch is:

A. 5 V/Sec

B. 50 V/sec

C. 10 V/sec

D. 100 V/sec

20. Inductance affects the direct current flows:

A. only at the time of turning off coil is

B. only at the time of turning on

C. at the time of turning on and off

D. at all the time of operations

21. If a resistor is connected across the voltage source and the frequency of voltage and current wave form is 50Hz, then what is frequency of instantaneous power?

A. 0Hz

B. 100Hz

C. 50Hz

D. 150Hz

22. Voltage magnification will occur in which of the following case?

A. Series Resonance

B. Parallel Resonance

C. Both

D. None

23. At which of the following frequency voltage across capacitor has maximum value for series circuit?

A. Equal to resonance frequency

B. Less than resonance frequency

C. Greater than resonance frequency

D. Zero frequency

24. According to duality principle a series inductor (L) can be represented as?

A. Series L

B. Parallel L

C. Series C

D. Parallel C

25. The functions of inter poles are: -

A. nullify reactance voltage and improve the commutation.

B. reduce cross magnetization effect and improve commutation

C. Both 1 and 2

D. none of the above

26. In DC machines shape of net flux density is?

A. sine wave

B. Flat topped or trapezoidal

C. Saddle shape

D. Peaky in nature

27. If terminal voltage of one 1000 rpm shunt motor is reduced to half the speed of the motor will be

A. 500 rpm

B. 250 rpm

C. 1000 rpm

D. 2000 rpm

28. In a 100 kVA, 1100/220 V, 50 Hz single-phase transformer with 2000 turns on the high-voltage side, the open-circuit test result gives 220 V, 91 A, 5 kW on low-voltage side. The core-loss component of current is, approximately?

A. 9.1 A

B. 22.7 A

C. 45.0 A

D. 91 A

29. When one transformer is removed from a Δ–Δ bank of 30 kVA transformer, the capacity of the resulting 3-phase transformer corresponding input line voltages?

A. 11.5 kVA

B. 17.3 kVA

C. 20 kVA

D. 25.9 kVA

30. If the armature current is increased to double its previous value, and the time of commutation is halved, how will the reactance voltage vary?

A. It will be halved

B. It will remain the same

C. It will be doubled

D. It will become four times

31. In which portion of the transmission system faults occur most frequently?

A. underground cables

B. transformers

C. overhead lines

D. alternators

32. Two coupled coils, connected in series, have an equivalent inductance of 16 mH or 8 mH depending on the connection. The mutual inductance between the coils is

A. 12mH

B. 8√2mH

C. 4 mH

D. 2mH

33. Based on revolving field theory, the forward and backward frequencies of the rotor emf of a 4-pole, 50Hz, singe- phase induction motor when running at 13 rpm in the same direction of the forward field are respectively

A. 107.69 Hz 7.69Hz

B. 93.33 Hz, 6.67Hz

C. 7.69 Hz, 107.69Hz

D. 6.67Hz, 93.33 Hz

34. The motor having a smooth chrome-steel cylinder as its rotor with no rotor winding is

A. Universal motor

B. Hysteresis motor

C. Repulsion motor

D. Reluctance motor

35. Pony motor is the method of starting of-

A. Slip ring motors

B. Synchronous motors

C. Schrage motors

D. Squirrel cage motors

36. A 3 phase, 50 Hz induction motor draws 50kW from the mains. If the stator losses are 2 kW and rotor emf oscillates at 100 oscillations per minute the rotor copper losses will be:

A. 1.8 kW

B. 1.2 kW

C. 1.9 kW

D. 1.6 kW

37. Out of the following which machine is also known as a generalized transformer

A. DC motor

B. Induction motor

C. DC generator

D. Synchronous motor

38. What is the value of flux in the section of yoke, if the pole flux is ϕ weber?

A. 𝛟×𝛟

B. √𝛟

C.𝛟

𝟐

D. 𝛟

39. If two ends of rod are to be welded, the method of welding is: -

A. Spot welding

B. Projection welding

C. Seam welding

D. Butt welding

40. Total flux required in any lighting scheme depends inversely on: -

A. space height ratio

B. coefficient of utilization

C. surface area

D. illumination

41. For the same wattage which lamp will produce least radiant heat?

A. Mercury Vapour Lamp

B. Sodium Vapour lamp

C. Fluorescent lamp

D. Tungsten Filament Lamp

42. Illumination of one lumen per sq. feet is called: -

A. Foot candle

B. Candela

C. Lumen meter

D. Lux

43. Most commonly used insulating layer material for MOSFET is: -

A. 𝐆𝐞𝐎𝟐

B. 𝐀𝐥𝟐𝐎𝟑.

C. 𝐀𝐒𝟐𝐎𝟓

D. 𝐒𝐢𝐎𝟐

44. In differential protection of bus-bars the CT ratio: -

A. Based on total expected fault current

B. Equal and based on primary current of lowest current carrying feeder

C. Based on their respective feeder current

D. Equal and based on primary current of highest current carrying feeder

45. SCR is a _______layer _____junction device.

A. single, three

B. two, four

C. three, four

D. four, three

46. Which of the following is not a part of Steam Power Plant?

A. Switch Yard

B. Ash precipitators

C. Draught fan

D. Surge Chamber

47. Earth electrode used in Plate earthing is a ______.

A. plate

B. pipe

C. rod

D. grid

48. Which of the following is used to maintain constant voltage in the feeder circuit?

A. Induction regulator

B. Booster

C. Tap changer

D. Phase advancers

49. Three wires having conductances 2,3 and 6 mho respectively are connected in parallel in a circuit. The equivalent resistance in the circuit will be:

A. 11 ohms

B. 1 ohms

C. 1/11 ohms

D. 33 ohms

50. In GTO, gate circuit losses are_________.

A. more

B. less

C. moderate

D. same as others

Power BJT Power MOSFET IGBT

Bipolar device Majority carrier or unipolar device Bipolar device

Current controlled device Voltage controlled device Voltage controlled device

Low input impedance High input impedance High input impedance

Low ON state voltage drop and low conduction loss

Higher ON voltage drop and higher conduction loss

Low ON state voltage drop and low conduction loss

Higher switching power loss Lower switching power loss Lower switching power less

BJT has Negative temperaturecoefficient for ON state resistance therefore secondary occurs in BJT

MOSFET has positive temperature coefficient for ON state resistance

therefore secondary breakdown will not occur.

Positive temperature coefficient therefore secondary breakdown will

not occur.

BJTs are not advisable for parallel operation.

Parallel operation is possible Parallel operation is possible

Ratings: - 1200 V, 800 A, 10 kHz to 20 kHz

500 V, 140 A, 1 MHz and is used in SMPS

500 A, 1200 V, 50 kHz

Power System Engineering

• Electric power is generated at the power generating stations by synchronous alternators that are usually driven either by steam or hydro turbines.

• Most of the power generation takes place at generating stations that may contain more than one such alternator-turbine combination.

Power System

Generation Transmission Distribution

Water

Gen Exc

HPH LPHD

A

P

HESP

LPTIPTHPT

IPCV

BFPCEP

DM water

SE

Cooling tower

CWPcondenser

H/W

HPCV

DRUM

Coal fire Boiler

HTSH

ITSH

Mill

CH

PA

FD

ID fan

Chimney

<<<

<

Flue gasesFrom Boiler

<

<

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<

ECO

<

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< <

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== =

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1 kg/cm2

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16 kg/cm2

165 kg/cm2

180⁰ C,Steam

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150 kg/cm2

180⁰ C

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150 kg/cm2

350⁰ C

150 kg/cm2

540⁰ C

5 kg/cm2

150⁰ C

26 kg/cm2, 540⁰ C

28 kg/cm2, 340⁰ C

50⁰ C- 60⁰ C

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Electrical Engineering by ASHISH SIR

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Electrical Engineering by ASHISH SIR

Electrical Engineering by ASHISH SIR

Electrical Engineering by ASHISH SIR

Electrical Engineering by ASHISH SIR

Electrical Engineering by ASHISH SIR

Electrical Engineering by ASHISH SIR

Electrical Engineering by ASHISH SIR

(28) In a steam power plant…………heats the feed water on its way to the boiler by delivering heat from the flue gases: -

(A) Superheater (B) Economizer

(B) Preheater (D) Turbine

(29) Power generation of thermal power plants is based on: -

(A) Rankine cycle

(B) Otto cycle

(C) Diesel cycle

(D) Carnot cycle