Question 1

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

Accepted Answer

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 D

Question 2

impose limitation on design.

Accepted Answer

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

Question 3

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

Accepted Answer

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

Question 4

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

Accepted Answer

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

Question 5

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

Accepted Answer

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

Question 6

Materials exhibiting zero value of resistivity are known as ______ .

Accepted Answer

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

Question 7

On which of the following variables heat convected depends ?

Accepted Answer

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

Question 8

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

Accepted Answer

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

Question 9

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

Accepted Answer

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 10

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

Accepted Answer

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

Question 11

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

Accepted Answer

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

Question 12

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

Accepted Answer

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

Question 13

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

Accepted Answer

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

Question 14

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

Accepted Answer

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

Question 15

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

Accepted Answer

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

Question 16

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

Accepted Answer

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

Question 17

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

Accepted Answer

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

Question 18

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

Accepted Answer

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

Question 19

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

Accepted Answer

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

Question 20

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

Accepted Answer

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

Exam 1: Design Considerations and Materials for Electrical Machines