SOLUTION

Generation, Transmission, and Distribution systems are the main components of an electric power system. Generating stations and distribution systems are connected through transmission lines. Normally, transmission lines imply the bulk transfer of power by high-voltage links between main load centers. On the other hand, the distribution system is mainly responsible for the conveyance of this power to the consumers by means of lower voltage networks. Electric power is generated in the range of 11 kV to 25 kV, which is increased by stepped-up transformers to the main transmission voltage.

Electric Power can either be transmitted by means of AC or DC. Each system has its advantages and disadvantages. Therefore it is very crucial to have a comparative study of their merit and demerits and then decide which method should be adapted to transmit power.

ALTERNATING CURRENT (A.C.)

An alternating current is one that periodically changes in magnitude and direction. It increases from zero to a maximum value, then decreases to zero and reverses in direction, increases to a maximum in this direction, and then decreases to zero. The complete set of variations is known as a ‘cycle’. Thus during one-half of the cycle, the current flows in one direction, and in the following Cycle, it flows in the opposite direction.

DIRECT CURRENT (D.C.)

DC current is that current that may or may not change in magnitude but it does not change its direction.

A.C. VERSUS D.C.

It is worthwhile to give advantages of ac. and d.c. Advantages of a.c. over d.c.

ADVANTAGES OF A.C OVER DC

1. Alternating voltages can be stepped up or stepped down efficiently by a transformer. This permits the transmission of electric power at high voltages to achieve economy and distribute the power at utilization voltages.
2. A.C. motors are cheaper and simpler in construction than the d.c. motors.
3. The switchgear (e.g. switches, circuit breakers, etc.) for a.c. the system is cheaper than the d.c. system.
4. A.C. can be easily converted into d.c. by rectifiers.
5.  Alternating current can be regulated by using a choke coil without any significant wastage of electrical energy.
6. For long-distance transmission of power, a higher voltage is best. Higher voltage means a lower current for the same power, and the lower current means fewer losses due to resistance in the wires. AC has the advantage that simple, robust transformers can be used to easily and efficiently step the voltage up at one end, and down at the other end to the voltages used domestically. DC requires much more complex circuitry or inefficient motor/generator sets to convert the voltage.
7. We all know that we got A.C supply in our homes and we got this supply by transmitting ac over long distances. AC can be transmitted using step-up transformers but direct current or dc cannot be transmitted by this method.
8. The maintenance of a.c. sub-stations is easy and cheaper.
9. A wide range of voltage can be obtained by using the step-up or step-down transformer.
10. A.C. can be produced and transmitted more easily and cheaply than D.C.
11. A 3-phase A.C. Dynamo can produce more energy than a single-phase D.C. Dynamo of the same cost. A.C.
12. Dynamo (using slip rings) has less loss of energy and wear and tear than a D.C. Dynamo (using split-ring commutator).
13. Transmission of A.C. at ‘high-voltage’ and ‘low-voltage‘ reduces line losses.

Note:- There’s nothing inherently wrong with using DC for high-voltage long-distance power transmission, but there are some particular characteristics that sometimes make AC transmission more attractive. If the high cost of converter stations is excluded, the dc overhead lines and cables are less expensive than ac overhead lines and cables. Until the eighties, only AC was easy to step up or down as voltages, simply using transformers. Since then, advances in power semiconductors and microprocessor controllers have allowed DC to be easily converted to higher or lower voltages. But most high voltage power lines remain AC because it seems to be difficult to change the whole system