ELECTRIC ENERGY GENERATION, UTILISATION AND CONSERVATION TWO MARKS
UNIT-IV
TWO MARKS
1. What are
the applications of dc series motor?
The series
DC motor is an industry workhorse for high and low power, fixed
and variable
speed electric drives. Applications range from cheap toys to automotive
applications.
They are
inexpensive to manufacture and are used in variable speed household
appliances such
as sewing machines and power tools.
Its high
starting torque makes it particularly suitable for a wide range of traction
applications.
2. Name the
sub system of solar power plant.
Solar
energy collection system
Thermal
energy transfer system Thermal energy storage system
Energy
conversion system
3. Indicate
the difficulties in using geo thermal energy
Overall
efficiency of power production is low
Drilling
operation is noisy
Large areas
are needed for exploitation of geo thermal energy
4. State
the advantages of interconnected operation of power system
Increased
reliability of supply: in the event of power failure at one station the
supply can
be fed from other station Reduction in total installed capacity
Spinning
reserve is reduced
5. What is
tariff?
Different methods of charging consumers are known as
tariff or rates of payment
for the consumption of electricity.
6. How can
we calculate the cost of electricity?
Sum all the
operating expenses for each year of operation - fuel, O&M, consumables,
etc.
Add the
carrying cost of capital - Total capacity x Fixed Charge Rate
Divide by
Kwh's produced in the year
Yields
average annual cost of electricity THB/Kwh
7. What is
two part tariff?
When the rate of electrical energy is changed on the
basis of maximum demand on
the consumer and the units consumed, then it is called
two part tariff.
8. What is
energy efficient drive?
The concept of energy efficient design has develops to
challenge the efficiency of
induction motor especially for the rating of 37 Kw.
9.
State the advantage of core less induction furnace Time
taken to reach the melting temp is less
There
is no smoke and noise
10.
What is induction heating?
Induction heating is a method of providing fast &
consistent heating for
manufacturing
applications which involved bonding or changing properties of metlal for
electrically conducting materials.
11.
What is plane angle?
A plane angle is subtended at a point and
is enclosed by two straight lines lying in the same plane. A plane angle is
expressed in terms of degrees or radian.A radian is the angle subtended by an
arc of a circle whose length equals the radius of the circle.
12. Define
illumination.
Illuminance is the total
luminous flux incident on a surface, per unit area. It is a
measure of
the intensity of the incident light,
wavelength-weighted by the luminosity function to correlate with human
brightness perception. Similarly, luminous emittance
is the
luminous flux per unit area emitted from a surface. Luminous emittance is also
known as
luminous exitance
13. What
are the several strategies available to minimize energy requirements in any
building?
Specification
of illumination requirements for each
given use area. Analysis of
lighting
quality to insure that adverse components of lighting (for example, glare or incorrectcolor spectrum) are not biasing
the design.
Integration
of space planning and interior architecture (including choice of interior surfaces
and room geometries) to lighting design.
Design of
time of day use that does not expend unnecessary energy. Selection of
fixture and lamp
types that reflect best available technology
forenergy conservation.
Training of
building occupants to utilize lighting equipment in most efficient manner.
14. State
illumination law.
Frechner's Law states that the same percentage change in
stimulus calculated
from the
least amount perceptible gives the same change in sensation. Inverse Square
Law states
that the intensity of illumination produced by a point source varies
inversely as square of the distance from the source.
15. Define
solid angle.
A concept which frequently is used for illumination
calculation is the solid
angle.
Solid angle
subtended by area = area of inter section at sphere surface / (radius of
sphere)^2
16. Define
luminous flux.
It is the rate of energy radiation in the form of light
waves and is denoted by F =
Q / t. where Q is the radiant energy. Its unit is lumen.
17. Define
lumen.
One lumen is defined as the luminous flux emitted by a
source of one candle
power in a solid angle.
Lumen = candle power of source * solid angle 18. Define
candle power.
It is defined as the no. of lumens emitted by that source
per unit solid angle in a
given direction. The term candle power is used
interchangeably with intensity.
19. What
are the classifications of lighting?
Lighting is
classified by intended use as general, localized, or task lighting, depending
largely on the distribution of the light produced by the fixture.
Task
lighting Is mainly functional and is usually the most
concentrated, for
purposes
such as reading or inspection of materials. For example, reading
poor-
quality
reproductions may require task lighting levels up to 1500 lux (150
footcandles), and some
inspection tasks or surgical procedures require even higher levels.
Accent
lighting is mainly decorative, intended to highlight pictures,
plants, or other elements of interior design or landscaping.
General
lighting fills in between the two and is intended for general illumination of
an area. Indoors, this would be a basic lamp on a table or floor, or a
fixture on
the
ceiling. Outdoors, general lighting for a parking lot may be as low
as 10-20
lux (1-2
footcandles) since pedestrians and motorists already used to the
dark will need little light for crossing the area.
20. What
are the several factor caused by Over-illumination
Not using
timers, occupancy sensors or other controls to extinguish lighting
w he n not
ne e de d
Improper
design, especially of workplace spaces, by specifying higher levels of
light than
needed for a given task
Incorrect
choice of fixtures or light bulbs, which do not direct light into
areas as
needed
Improper
selection of hardware to utilize more energy than needed to accomplish
the lighting
task
UNIT - V
TWO MARKS
1. Classify
an electric drive.
Group drive
Individual
drive
Multi motor
drive
2. What are
the factors affecting selection of motor?
Electrical
characteristics
Size of
motor
Mechanical
factors
Cost
3. What are
the factors to be considered in size of motor?
Continuous
rating
Variable
load rating Over load capacity
Pull out
torque
4. What are
the mechanical factors?
Type of
enclosure
Rearings
Transmission
of drive
Noise level
5. Write
the nature of mechanical load.
Constant
load torque
Load torque a speed
Load torque a speed ^2 Load torque a 1/speed
6. Classify
the load torque depending upon the time.
Continuous
and constant load Continuous but vaiable loads
Pulsating
loads
Impact loads
Short time
intermittent
7. What are
the essential requirements of a satisfactory braking?
It should
be fast , reliable and controllable
The stored
energy of rotating parts should be dissipated through suitable means. A failure
of any part of the braking system should result in braking only.
8. What are
the three methods of electrical braking?
Plugging or
counter current braking
Rheostatic
braking
Regenerative
braking
9. What is
mechanical or friction braking?
It is the braking in which the stored energy of the
rotating parts is dissipated as
heat by a brake shoe or band rubbing on a wheel or brake
drum.
10. State
the working of dynamic or rheostatic braking.
In this method the motor is disconnected from the supply
and is used as a
generator,
driven by the momentum of the equipment to be broken, the electric energy
so generated
is dissipated as in external resistors. This method can be used for dc, induction
and synchronous motors.
11. State
the two advantages of electric drive.
Electric drives are adaptable to any type of load
requirement
There is a wider
variety of electric motors, which can be designed exactly according to
load requirements.
12. What is
an individual drive?
A single electric motor is used to drive one individual
machine though its cost is
more than
group drive but each operator has complete control of his machine which will enable.
13. Define
continuous rating of motor.
It is that output which a motor can give continuously for
long time without
exceeding the given temperature riseand motor should be
20% overload for 2 hours.
14. Write
the torque equation of a dc motor.
Equation: T = FR
Where: T = Torque, lb-ft
F = Force,
lb
R = Radius, or distance which force is applied from pivot
location, ft
15. Write
the formula to determine a fan or blowers horsepower.
Equation:
Where T = Required Torque, lb-ft
WK2 = Inertia of load to be accelerated = Change of
speed,
rpm
t = Time to accelerate the load, seconds
16. What
are the four important functions in a hybrid vehicle application?
It enables
the "start-stop" function, turning off the engine when the vehicle is
stationary
saving fuel.
It generates
the electrical energy to power all the electrical ancillaries.
It provides
a power boost to assist the engine when required, permitting smaller engines for
similar performance.
In some
configurations it recuperates energy from regenerative braking.
17. What is
reluctance torque?
Torque is created due to the reaction between magnetic
fields. Consider a
small bar
magnet in the field of another larger magnet such as the gap between the
poles of a
horse shoe magnet or one of the pole pairs of an electric motor. When the bar
magnet is aligned with the poles of the large magnet its field will be in line
with the external field. This is an equilibrium position and the bar will not
experience any
force to
move it. However if the bar is misaligned with the poles, either rotated or
displaced,
it will experience a force pulling it back into line with the external field.
In the case of a lateral displacement, the force diminishes as the distance
increases, but in
the case of
a rotation, the force will increase reaching a maximum when the bar is at
right angles
to the external field. In other words the torque on the magnet is at a maximum
when the fields are orthogonal and zero when the field are aligned.
18. Define
torque angle.
Even in synchronous motors in which the rotor turns at
the same speed as the
flux wave,
because of the losses noted above the rotor poles will never reach complete
alignment
with the peaks in the flux wave, and there will still be a displacement
between the
rotating flux wave and the rotating field. Otherwise there would be no
torque. This
displacement is called the "torque angle". The motor torque is zero
when the torque angle is zero and is at its maximum when the torque angle is 90
degrees. If the torque angle exceeds 90 degrees the rotor will pull out of
synchronism and stop.
19. Write
the characteristics of motor.
Torque generally speaking the torque produced by a
motor is proportional to the
current it
consumes and also proportional to the flux in the air gap.
T = K 1I B
Speed
o In DC motors the rotational speed is proportional to the
applied voltage. The
speed is however inversely proportional to the flux in
the air gap.
In AC motors
the speed is proportional to the frequency of the applied voltage and inversely
proportional to the number of magnetic poles.
20. What is
cogging?
Cogging is the jerky, non uniform angular velocity of a
machine rotor particularly
apparent at
low speeds in motors with a small number of poles. It occurs because the rotor
tends to speed up as it approaches the stator poles and to slow down as it
leaves the poles. It is also noticeable when pulsed DC is used if the frequency
of the supply waveform is too low. The problem can be reduced by using skewed
rotor windings as well as increasing the number of poles in the motor.
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