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WorksheetsEE8002_DEA_QUIZ-I (02.06.2020)
Total questions: 30
Worksheet time: 15mins
Which of the following is the major consideration to evolve a good design ?
Cost
Durability
Compliance with performance criteria as laid down in specifications
All of the above
The efficiency of a machine should be as (a) as possible to reduce the operating cost.
If an insulating material is operated beyond the maximum allowable temperature, its life is
drastically increased
drastically reduced
unaffected
none of the above
Materials exhibiting zero value of resistivity are known as ______
conductors
semiconductors
insulators
superconductors
________ has a low relative permeability and is used principally in field frames when cost is of primary importance and extra weight is not objectionable
Cast steel
Aluminium
Soft steel
Cast iron
______is extensively used for those portions of magnetic circuit which carry steady flux and need superior mechanical properties ?
Grey cast-iron
Cast steel
High carbon steel
Stainless steel
The heated parts of an electrical machine dissipate heat into their surroundings by which of the following modes of heat dissipation ?
Conduction
Convection
Radiation
All of the above
Which of the following is an advantage of hydrogen cooling ?
Increase in efficiency
Increase in ratings
Increase in life
Smaller size of coolers
All of the above
----------are used for construction of core of electromagnets.
Soft magnetic materials
Hard magnetic materials
Either (a) or (b)
None of the above
The distance between the starts of two consecutive coils measured in terms of coil sides is called..................
front pitch
winding pitch
commutator pitch
back pitch
Which of the following is the basic consideration in the design of insulation ?
Electrical considerations
Mechanical considerations
Thermal considerations
All of the above
Which of the following gives materials in order of decreasing values of permeability ?
Cobalt, Nickel, Aluminium, Iron
Permalloy, Nickel, Air, Water
Silver, Copper, Aluminium, Iron
Pure iron, Silicon iron. Aluminium, Bismuth.
In electrical machines the material preferred for pole shoes of electro-magnets is
Pure iron
Aluminium
Copper
Lead.
Diamagnetic : Paramagnetic::
Water: Air
Iron: Steel
Permalloy: Super-alloy
Nickel: Cobalt.
If the permeability of a material is 0.999991. it can be classified as
Diamagnetic material
Paramagnetic material
Ferro-magnetic material
Ferrite.
If yb is the back pitch and u is the no. of coil sides per slot, then split coils can be avoided if the following quantity is an integer
(yb + 1)/ μ
(yb + 1 )
(yb - 1)/ μ
(yb - 1)
For simplex wave and lap windings, the back pitch yb and front pitch yf are as follows:
yb is odd, yf is even
yb is even, yf is odd
both yb and yf are odd
both yb and yf are even.
An ideal insulating material should have low
insulation resistance
dielectric strength
dielectric loss angle
mechanic strength.
The class of insulation used for large rating HV alternators
Y
A
B
C
Fibre glass insulation can be used up to temperature of
60°C
80°C
130°C
180°C
Class H insulation is normally used in
traction motors
submersible pump motors
single phase motor
dc motors.
In case of ball bearings, the ball are made of
cast iron
mild steel
carbon chrome steel
none of the above
What is the basic property of electrical conducting materials?
allows the passage of current through the materials
blocks the passage of current through the materials
leaks the current through the materials
reverses the direction of current in the materials
What is the correct classification of the conducting materials?
low resistivity, low conductivity
low resistivity, high conductivity
high resistivity, high conductivity
medium resistivity, medium conductivity
What are the conditions of the conducting materials with respect to melting point and resistance to corrosion?
high melting point, low resistance to corrosion
low melting point, low resistance to corrosion
high melting point, high resistance to corrosion
low melting point, high resistance to corrosion
What is the representation of permeability?
coercivity/retentivity
flux/flux density
magnetic force/magnetic flux density
magnetic flux density/magnetic force
High Reluctance affects the performance of magnetic materials.
True
False
If the power ratings are crossed, machine breakdown occurs?
True
False
Insulation Resistance should be high in insulators.
True
False
How many classifications of overhead line insulators are there?
3
4
5
6
