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प्रश्न
Give the advantage of AC in long distance power transmission with an illustration.
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उत्तर
- When power is transmitting for long-distance a fraction of power is lost due to joule heating (I2R).
- This power loss can be tackled either by reducing current i or by reducing resistance R of a transmission line.
- At the transmitting point, voltage is increased and the current is decreased by a step-up transformer.
- This reduced current at high voltage reaches the destination without applicable loss.
- At the receiving point, voltage is decreased and current is increased by step down transformer.
- Example 1:
2MW power is transmitted at 40Ω with 10 kV voltage
I = `"P"/"V" = (2 xx 10^6)/(10 xx 10^3)` = 200 A
Power loss = I2 R = (200)2 × 40 = 1.6 × 106 W
% of Power loss = `(1.6 xx 10^6)/(2 xx 10^6) xx 100 % = 80%` - Example 2:
When 2MW power at 40 Q is transmitted with 100 kV voltage.
I = `"P"/"V" = (2 xx 10^3)/(100 xx 10^3)` = 20 A
Power loss = I2 R = (200)2 × 40 = 0.016 × 106 W
% of power loss = `(0.016 xx 10^6)/(2 xx 10^6) xx 100%`
= 0.8 × 100% = 80%
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संबंधित प्रश्न
A group of students while coming from the school noticed a box marked "Danger H.T. 2200 V" at a substation in the main street. They did not understand the utility of a such a high voltage, while they argued, the supply was only 220 V. They asked their teacher this question the next day. The teacher thought it to be an important question and therefore explained to the whole class.
Answer the following questions:
(i) What device is used to bring the high voltage down to low voltage of a.c. current and what is the principle of its working ?
(ii) Is it possible to use this device for bringing down the high dc voltage to the low voltage? Explain
(iii) Write the values displayed by the students and the teacher.
You are required to make an electromagnet from a soft iron bar by using a cell, an insulated coil of copper wire and a switch. (a) Draw a circuit diagram to represent the process. (b) label the poles of the electromagnet.
State two ways through which the strength of an electromagnet can be increased.
The primary coil of a transformed has 800 urns and the secondary coil has 8 turns. It is connected to a 220 V a.c. supply. What will be the output voltage?
Mention the two characteristic properties of the material suitable for making core of a transformer.
Draw a labeled diagram of a full wave rectifier circuit. State its working principle. Show the input-output waveforms ?
A power transmission line feeds input power at 2300 V to a stepdown transformer with its primary windings having 4000 turns. What should be the number of turns in the secondary in order to get output power at 230 V?
1 MW power is to be delivered from a power station to a town 10 km away. One uses a pair of Cu wires of radius 0.5 cm for this purpose. Calculate the fraction of ohmic losses to power transmitted if
- power is transmitted at 220 V. Comment on the feasibility of doing this.
- a step-up transformer is used to boost the voltage to 11000 V, power transmitted, then a step-down transfomer is used to bring voltage to 220 V. (ρCu = 1.7 × 10–8 SI unit)
The primary coil of a transformer has 60 turns whereas its secondary coil has 3000 turns.
If a current of 5A flows in the primary coil, how much current will flow in a load in the secondary coil? State the assumption you have made regarding the transformer, in this calculation.
