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ELECTRIC ENERGY GENERATION, UTILISATION AND CONSERVATION TWO MARKS

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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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