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Electrical Machine Design

Study 103 Electrical Engineering MCQs with correct answers and explanations.

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51Electrical EngineeringMedium

For large power transformers, self oil cooled type or air blast type which of the following values of current density may be used?

A1.0 to 1.2 A/mm2

B2.2 to 3.2 A/mm2

C1.5 to 2.0 A/mm2

D3.2 to 4.2 A/mm2

Correct answer

B. 2.2 to 3.2 A/mm2

Explanation

The correct answer is 2.2 to 3.2 A/mm2.

52Electrical EngineeringMedium

The change in flux linkages can be caused in which of the following ways?

AThe coil is stationary with respect to flux and the flux varies in magnitude with respect to time

BThe flux is constant with respect to time and is stationary and the coil moves through it

CBoth the changes mentioned above occur together, i.e., the coil moves through a time varying field

DAll of the above

Correct answer

D. All of the above

Explanation

The correct answer is All of the above.

53Electrical EngineeringMedium

The forced oil and air circulation method is usual one for transformers of capacities________?

A30 MVA upwards

Bupto 10 MVA

Cupto 20 MVA

Dupto 5 MVA

Correct answer

A. 30 MVA upwards

Explanation

The correct answer is 30 MVA upwards.

54Electrical EngineeringMedium

In a D.C. machine the current per brush arm should not be more than________?

A100 A

B300 A

C200 A

D400 A

Correct answer

D. 400 A

Explanation

The correct answer is 400 A.

55Electrical EngineeringMedium

In D.C. machines, the ________ in field mmf results in increase in size and cost of machines?

Aeither of the above

Bnone of the above

Cdecrease

Dincrease

Correct answer

D. increase

Explanation

The correct answer is increase.

56Electrical EngineeringMedium

Materials exhibiting zero value of resistivity are known as ________?

Ainsulators

Bconductors

Csuperconductors

Dsemiconductors

Correct answer

C. superconductors

Explanation

The correct answer is superconductors.

57Electrical EngineeringMedium

D.C. servomotors are used in________?

Apurely D.C. control systems

Bboth D.C. and AC. control systems

Cpurely AC. control systems

Dnone of the above

Correct answer

A. purely D.C. control systems

Explanation

The correct answer is purely D.C. control systems.

58Electrical EngineeringMedium

On which of the following variables heat convected depends?

AGravitational constant

BPower density

CTemperature difference between heated surface and coolant

DThermal resistivity, density, specific heat

EAll of the above

Correct answer

E. All of the above

Explanation

The correct answer is All of the above.

59Electrical EngineeringMedium

Transformers with a capacity of up to ________ have a cooling radiator system with natural cooling?

A2 MVA

B10 MVA

C7.5 MVA

D5 MVA

Correct answer

B. 10 MVA

Explanation

The correct answer is 10 MVA.

60Electrical EngineeringMedium

The heated parts of an electrical machine dissipate heat into their surroundings by which of the following modes of heat dissipation?

AConvection

BAll of the above

CRadiation

DConduction

Correct answer

B. All of the above

Explanation

The correct answer is All of the above.

The change in flux linkages can be caused in which of the following ways?

AThe coil is stationary with respect to flux and the flux varies in magnitude with respect to time

BThe flux is constant with respect to time and is stationary and the coil moves through it

CBoth the changes mentioned above occur together, i.e., the coil moves through a time varying field

DAll of the above

Correct answer

D. All of the above

Explanation

The correct answer is All of the above.