USE OF TRANSFORMER FOR LONG DISTANCE
When electrical energy has to transmitted to a distant place , the resistance of line wire is considerable. (USE OF TRANSFORMER FOR LONG DISTANCE)Due to this , a good deal of electric power I²R is dissipated as heat , where I is current through line wires and R , the resistance of the line
wires . Also , a sufficient fall of potential I R occurs along line wires. Hence, the effective voltage at a distant place will be much smaller than the actual value of the voltage supplied by the transmitting station . In addition to it , a few more difficulties are encountered , if transmission of electrical energy is done at low voltage (220 v). However by the transmission of electrical energy at high voltage (say ,22,000V ), the difficulties encountered in the power transmission can be minimized. To understand the role of two factors which are important in power transmission, consider that 11,000 watt of electric power is transmitted first at 220 V and then at 22,000 V.
1 LOSS OF ELECTRIC ENERGY.
When transmission of electric energy is done at 220 V , a current equal to 11,000/220 i.e. 50 A flows through the line wires. If R is resistance of line wires, energy equal to 50×50 i.e 2,500R joule will be dissipated per second as heat energy. On the other hand , when transmission is done at 22,000V , a current equal to 11,000/22,000 i.e. 0.5 A flows through the line wires. In this case, the electric energy dissipated per second at heat will be 0.25 R joule per second only.
Therefore, we conclude that if transmission of electric energy is done at high VOLTAGE ,the dissipation of energy is much reduced.
USE OF TRANSFORMER FOR LONG DISTANCE..
2. COST OF TRANSMISSION.
If transmission of electric energy is done at ,220V then as discussed above, to transmit electric power of 11,000 W , the current capacity of line wires has to be 50 A and if transmission is done at 22,000 V , the current capacity of line wires has to only 0.5 A . Therefore, if transmission is done at low voltage thick wires have to be used Due to the use of the thick line wires, the cost of transmission will increase. Further stronger poles would be needed in order to support thicker line wires. It will further add to the cost of transmission. On the other hand , if the transmission is done at high voltage, the line wires required are of low current capacity I.e. thin wires and high poles may be used. Due to this , the cost of transmission will be low .
Therefore it may be calculated that if transmission is done at high voltage, the transmission is much economical from the point of view of the cost of the line wires and poles used to support the wires .
So the given two factors, the transmission of electric energy is done at high voltage and for this a step- up transformer is used . No doubt, there will be some loss of energy in transformer also , but the energy loss in a transformer is negligible as compared to the energy loss along the long line wires between the two stations .
USE OF TRANSFORMER FOR LONG DISTANCE
OTHER USES OF A TRANSFORMER
1. A step- down transformer is used for obtaining large current for electric welding.
2. A step- down transformer is used in induction furnace for melting the metals.
3. A step- down transformer is used for the production of X – rays.
4. Transformer are used in voltage regulators and stabilised power supplies.
5. Small transformers are used in radio , television, telephones, loud speakers, etc.
ADVANTAGE AND DISADVANTAGES OF A.C OVER D.C.
1. The generation of A.C is found to be economical than that of D.C .
2. The alternating currents can be easily stepped up or stepped down by using a transformer.
3. The alternating currents can be regulated by using a choke coil without any significant wastage of electrical energy.
4. The alternating voltages can be transmitted to display places at a very small loss of electric power.
5. Further A.C. can be easily converted into D.C. using rectifiers.
1. The A.C. supply is more fatal and dangerous than D.C. in terms of shock received due to them.
2. The alternating current always flows on the outer layer of the wire. It is called skin effect. Therefore for use in A.C. circuits; instead of a single thick wire, the wire for its use on A.C. supply is prepared by putting a number of thin wires together. As such, the alternating current flows through all the wires and the skin effect is avoided.
3. The alternating current can not be used in electrolytic process, such as electroplating, electroplating , etc.