Deck 1: Design Considerations and Materials for Electrical Machines

Question 1

Which of the following is the major consideration to evolve a good design ?

A)Cost
B)Durability
C)Compliance with performance criteria as laid down in specifications
D)All of the above

Answer 1

All of the above

Question 2

impose limitation on design.

A)Saturation
B)Temperature rise
C)Efficiency
D)All above

Answer 2

All above

Question 3

The efficiency of a machine should be as ______ as possible to reduce the operating cost.

A)high
B)low
C)either of the above
D)none of the above

Answer 3

high

Question 4

If an insulating material is operated beyond the maximum allowable temperature, its life is

A)drastically increased
B)drastically reduced
C)unaffected
D)none of the above

Question 5

The design of mechanical parts is particularly important in case of _____ speed machines.

A)low
B)medium
C)high
D)any of the above

Question 6

In induction motors, the length of air gap in kept as small as mechanically possible is order to have

A)low power factor
B)high power factor
C)high over load capacity
D)any of the above

Question 7

In ______ machines, the size of the shaft is decided by the critical speed which depends on the deflection of the shaft.

A)small
B)medium
C)large
D)any of the above.

Question 8

The length cf air gap to be provided in ______ is primarily determined by power factor consideration.

A)d.c. series motor .
B)d.c. shunt motor
C)induction motor
D)synchronous motor

Question 9

Electrical machines having a power output upto about 750 W may be called_______machines.

A)small size
B)medium size
C)large size
D)any of the above

Question 10

Electrical machines having power outputs ranging from a few kW upto approximately 250 kW may be classified as

A)small size machines
B)medium size machines
C)large size machines
D)any ofthe above

Question 11

Commercial available medium size machines have a speed range of ______ .

A)200 to 400 r.p.m.
B)600 to 1000 r.p.m.
C)1000 to 1500 r.p.m.
D)2000 to 2500 r.p.m.

Question 12

The action of electromagnetic machines can be related to which ofthe following basic principles ?

A)Induction
B)Interaction
C)Alignment
D)All of the above

Question 13

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

A)The flux is constant with respect to time and is stationary and the coil moves throughnit
B)The coil is stationary with respect to flux and the flux varies in magnitude with respect to time
C)Both the changes mentioned above occure together, i.e., the coil moves through a time varying field
D)All ofthe above

Question 14

is universally used for windings of electrical machines because it is easily workable without any possibility of fracture.

A)Silver
B)Steel
C)Aluminium
D)Copper

Question 15

Aluminium when adopted as a conductor material in ______ transformers, decreases the overall cost of the transformer

A)small size
B)medium size
C)large size
D)any of the above size

Question 16

Which ofthe following materials is used in the manufacture of resistance grids to be used in the starters of large motors ?

A)Copper
B)Aluminium
C)Steel
D)Cast-iron

Question 17

Materials exhibiting zero value of resistivity are known as ______ .

A)conductors
B)semiconductors
C)insulators
D)superconductors

Question 18

________ has a lowrelative permeability and is used principally in field frames when cost is of primary importance and extra weight is not objectionable.

A)Cast steel
B)Aluminium
C)Soft steel
D)Cast iron

Question 19

______is extensively used for those portions of magnetic circuit which carry steady flux and need superior mechanical properties ?

A)Grey cast-iron
B)Cast steel
C)High carbon steel
D)Stainless steel

Question 20

Hot rolled sheets have ______ value of permeability

A)zero
B)low
C)high
D)none ofthe above

Question 21

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

A)Conduction
B)Convection
C)Radiation
D)All ofthe above

Question 22

The heat dissipated by from a surface depends upon its temperature and its characteristics like colour, roughness etc.

A)conduction
B)convection
C)radiation
D)any ofthe above

Question 23

The mcrease in heat dissipation by air blasts is due to increase in

A)conduction
B)convection
C)radiation
D)any ofthe above

Question 24

On which of the following variables heat convected depends ?

A)Power density
B)Temperature difference between heated surface and coolant
C)Thermal resistivity, density, specific heat
D)All ofthe above

Question 25

Which ofthe following methods is used for air cooling of turbo-alternators ?

A)One sided axial ventilation
B)Two sided axial ventilation
C)Multiple inlet system
D)All ofthe above