Theaim of this is to present a fair comparison between two systems, Direct Current(DC) and Alternating Current (AC) efficiency in the residential homes.
AC andDC clashed with each other in the early days of the electric power systems.Apparently, it was the ability to transform voltage levels, which would causeone side to win or the other. If DC systems could have developed this ability,the power system might have been DC today. The electromagnetic transformersallowed AC to transform its voltage level and thus AC. won the battle of thecurrents. It became the medium for electric power generation, transmission,distribution and utilization in the form of residential loads.Alluseful generators of electricity come in two basic forms, alternating currentand direct current.
Direct current (dc) comes from generators that do notchange in polarity, always producing a positive charge. In alternating current(ac) the polarity of the terminals is always changing from positive tonegative. Thus, alternating current flow is left.Directcurrent only flows in one direction in a circuit.
Because the polarity of adirect current voltage source is always the same, the flow of current neverchanges direction. Batteries are one of the more common direct current voltagesources. Batteries are good because their voltage is fixed as well as theirpolarity. Direct current does not always need to a constant voltage but it mustalways stay traveling in the same direction. There are such direct currentscalled varying and pulsating that change value but not direction. DC had towait for a long time until the development of High Voltage Direct Current(HVDC) transmission re-introduced DC in the power system. Heavy electriccurrents due to line charging/discharging and reactive power losses wereavoided and HVDC transmission became a success. Then DC appeared on thegeneration side of the power system in the form of the economically andenvironmentally motivated power generation sources namely the renewable energysources.
AChad shown that it was much better for transmitting electricity over longdistances. Championed in the last 2 decades of the 19th century by inventorsand theoreticians such as Nikola Tesla and Charles Steinmetz and theentrepreneur George Westinghouse, AC won out as the dominant power supplymedium.Alternatingcurrent was chosen early in the 20th century as the North American standardbecause it presented fewer risks and promised higher reliability than competingDC systems of the day. DC is the European standard. Many of DC’s deficiencies werelater corrected, but not until a substantial North American infrastructure hadalready been developed.Usuallyrepresented as two wires leading to a device that uses electricity, electricpower distribution requires a circuit. One wire is negative and the other iseither is positive or neutral (ground) in AC current.
The two wires take turnsat sending electricity. AC current uses a standard “rhythm” in whicheach side gets its turn 60 times each second, thus the 60Hz designation givento standard AC current in North America. This switching of polarity takes theform of a rhythmic pulse in the electrical current that occurs within thenormal audible range.
This is why you can actually hear this rhythm in circuitssuch as fluorescent lighting ballasts and audio equipment as a low buzzingtone. This buzz is referred to as “sixty cycle hum”. Two AC powerschemes were used in North America prior to the 1970s. One offered energy at45-50Hz, the other at 60Hz. “Fifty-cycle power”, occasionallyreferred to as “rural power”, is now obsolete and the 60Hz standardis now used throughout North America.Theelectricity is always the same polarity, which means that in a two-wirecircuit, one “wire”, or side of the circuit, is always negative, andthe negative side is always the one that sends the electricity in DC circuits.
There is no hum because there is no cyclic change in current flow. The cost ofconverting DC current to AC is relatively high, so DC is typicallycost-effective only for long-distance transmission but DC current is moreeffective for long-distance, high-voltage transmission because it results inless energy lost in transmission.Electricaldevices that convert electricity directly into other forms of energy canoperate just as effectively from AC current as from DC. Light bulbs and heatingelements don’t care whether their energy is supplied by AC or DC current.Nearly all modern electronic devices require direct current for theiroperation, however. Alternating current is still used to deliver electricity tothe device, and usually at much, lower than the supplied voltage so thatelectronic devices can use it a transformer is included with these devices toconvert AC power to DC power.Currentthat constantly changes in amplitude, and which reverses direction at regularintervals is alternating current. You learned previously that direct currentflows only in one direction, and that the amplitude of current is determined bythe number of electrons flowing past a point in a circuit in one second.
Theamplitude of direct current in the wire is one ampere if, for example, acoulomb of electrons moves past a point in a wire in one second and all of theelectrons are moving in the same direction. If half a coulomb of electronsmoves in one direction past a point in the wire in half a second, then reversesdirection and moves past the same point in the opposite direction during thenext half-second, a total of one coulomb of electrons passes the point in onesecond, similarly. The amplitude of the alternating current is one ampere.
Certaindisadvantages in using direct current in the home became apparent whencommercial use of electricity became widespread in the United States. Thevoltage must be generated at the level (amplitude or value) required by theload if a commercial direct-current system is used. The dc generator mustdeliver 240 volts to properly light a 240-volt lamp, for example. A resistor oranother 120-volt lamp must be placed in series with the 120-volt lamp to dropthe extra 120 volts if a 120-volt lamp is to be supplied power from the240-volt generator. An amount of power equal to that consumed by the lamp iswasted when the resistor is used to reduce the voltage.Whenthe direct current (I) from the generating station must be transmitted, a longdistance over wires to the consumer another disadvantage of the direct-currentsystem becomes evident.
A large amount of power is lost due to the resistance(R) of the wire when this happens. The power loss is equal to I2R. However,this loss can be greatly reduced if the power is transmitted over the lines ata very high voltage level and a low current level. This is not a practicalsolution to the power loss in the dc system since the load would then have tobe operated at a dangerously high voltage. Practically all modern commercialelectric power companies generate and distribute alternating current (ac)because of the disadvantages related to transmitting and using direct current.
Alternatingvoltages can be stepped up or down in amplitude by a device called aTRANSFORMER, unlike direct voltages. Useof the transformer permits efficient transmission of electrical power overlong-distance lines. The transformer output power is at high voltage and lowcurrent level at the electrical power station. The voltage is stepped down by atransformer to the value required by the load at the consumer end of thetransmission lines. Alternating current has replaced direct current in all buta few commercial power distribution systems due to its inherent advantages andversatility.Younow know that there are two types of current and voltage, that is, directcurrent and voltage and alternating current and voltage. The dc voltage has constantamplitude. Some voltages go through periodic changes in amplitude.
The pattern,which results when these changes in amplitude with respect to time, is known asa WAVEFORM.Alternatingcurrent is more superior to direct current. The main reason for this is that itcan be controlled in terms of voltage by the use of a transformer. As we haveseen, alternating current is more common and useful, in electromagnets, as wellas home appliances.Efficiencyhas been one of the major factors used to judge if DC is better than AC.
to presenta comparative efficiency study of AC and DC residential power distributionsystems. The DC power transfer, although, given up a long time ago; iswitnessing a comeback in the system and for the particular case of residentialpower distribution, its efficiency was found comparable to that of AC. However,if AC power has to be given up in favor of DC, then DC should not only matchthe feasibility of AC, it should exceed this to provide a strong reasoning formaking this huge change in the power system. At the present, this doesn’tappear to be the case as far as system efficiency is concerned.
Even theincrease of DC power demand in buildings via the use of air-conditioning wasfound to make a small contribution to the overall system performance. From thepoint of view of efficiency, an increase in demand of DC power may not be ajustification/suggestion for opting DC power distribution as long as energy hasto flow through power electronic converters.Onthe residential side, the tremendous increase of modern electronic loads hascreated a significant demand for DC power. Besides the usual householdelectronic loads, the modern concept of Light Emitting Diodes (LED) lighting iscreating yet another consumer of DC electric energy. Apart from these, the VariableSpeed Drives based air-conditioning (cooling and heating) leads to theconversion of the input AC power to DC, which is then again converted to AC andsupplied to the compressor motor. If these loads are also included as loadsdemanding DC power, then the overall demand of DC power may exceed the demandof AC power for the modern residential buildings.
Thebest current is to use is both AC and DC current. Some devices perform betterand have better efficiency with AC current and other devices perform betterwith DC current then AC current would. Nevertheless, for right now, AC current isin the Lead and DC current is catching up. ReferencesThe War of the Currents: AC vs. DC Power. (n.d.).
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