What do you understand by electric heating? State its advantages over other methods of heating.

Electric heating:

Electric heat is provided by use of a high temperature wire, which is resistant to electric flow with more heat being produced by more electric current being fed into the heating element, creating more resistance and more heat. This method of producing heat is called electric heating. 

Advantage of electric heating: 

1. Cleanliness 
2. Absence of flue gases, soot. …etc
3. Accurate control of temperature. 
4. Low maintenance cost 
5. Quicker operation 
6. Higher efficiency 
7. Uniform and economic heating capability 

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Discuss the criterion for choice of voltage for transmission and distribution.

Criterion For Choice Of Voltage For Transmission And Distribution:

We know that the power  P =VI, so for the same power if voltage is increased then current will decrease. If suppose power required is 500 W and voltage is 250V then current I will be equal to 500/250 =2A. 

Now if voltage is increased from 250V to 500V and the power required is same then I = 500/500 =1 A 

Now, if the voltage is still increased to say 1000V for the same power 

then I = 500/1000 =0.5 A 

From the above examples, we see that if the voltage is doubled, the current will be halved and when it is quadrupled then current is reduced to 1/4th of its initial value.

Thus we conclude that if voltage is increased to n times then the current will be  reduced to 1/nth times for the same power.With the reduction of the current to 1/nth times, the conductor area will also be reduced to 1/nth times  of its original area for the same current density, Hence less material is required when the voltage is increased.

We also know that when the current passes through any conductor, there is loss of power in that particular conductor according to the relation, I^2R. As the loss is proportional to the square of the current. So if the current is reduced to ½ value , then the loss will be reduced to 1/4th its original value. Hence the efficiency of the transmission line and all others equipments associated with  the line will increase and more power will be available for use. 

When current is passing through a conductor there will be a voltage drop according to the relation V=IR. So, when the current is reduced the drop of the voltage is less in the line, of course with the same cross sectional area of the conductor. 

With the reduction of cross sectional area, considered the main advantage of transmitting electrical energy at very high voltage viz 132kV , 220kV or even 400kV.  But in case of distribution system such high voltage is dangerous, so distribution voltage is generally 400/230V. 

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List out the advantages of nuclear power plants over conventional thermal power plants.

Advantage of Nuclear Power Plants:

1. Nuclear Power station reduces the demand for oil coal and gases.

2. Weight of nuclear fuel required for a given station capacity is negligible compared to that required for a conventional thermal power station. As a result the problems of transport and resulting costs are avoided. 

3. The area and volume need for a nuclear power station is less in comparison to a conventional power plant of equal capacity. 

4. In addition to producing large amount of power, a nuclear power plant produces valuable fissile material, which is extracted when the fuel is renewed.

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Compare the induction motor with a transformer.

Comparison of induction motor with a transformer:

Figure: Sketch showing similarity between transformer and induction motor

The transfer of energy from stator to the rotor of an induction motor takes place entirely inductively with the help of flux mutually linking the two. Hence an induction motor is essentially a transformer with stator forming the primary and rotor forming the rotating secondary.

Transformer	Induction Motor
(1) Secondary is stationary	(1) Secondary winding is rotating
(2) Secondary is not short circuited	(2) Secondary is always short circuited
(3) No-load current is about 1% of full load	(3) No-load current is approximately 30 to 50% current (due to low reluctance path   of full current (due to high reluctance of steel core)  of air gap)
(4) emf induced in secondary depends on   K (turns ratio)	(4) Depends on K and slip also
(5) Frequency of primary and secondary currents  are same	(5) Frequency of stator current (f) and rotor current (sf) are not the same.

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List out the important advantages of HVDC transmission.

Important advantages of HVDC transmission : 

• Economical in long distance high power transmission.
• HVDC transmission line has only two conductors.
• Reactive power losses do not occur in HVDC. 

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