This bugged me a lot when I was studying Electrical Engineering and took a lot of time to clear up this doubt.First a little bit of History. Initially Power Distribution happened through DC. It was not until 1950's when people started converting to AC. In India, I am one of the few rare ones to have seen and used DC supplies in early 1980 at Howrah, WB.Lets look at what we want as features from the power supply:Low / Negligible drop over long distancesNon-LethalEfficient Power transfer i.e. Low power wastageAbility to connect Sources and Sinks arbitrarilyAbility to Step-up or Step-down as per requirement with simple equipmentLets see how DC fares:Very high voltage drop over distances. Needs Power Supply sources at regular intervals to maintain Voltage.Extremely LETHAL! You might get permanent muscle contraction/expansion injuries as our body works on milli-volts of DC , whereas supplies are typically 100's of volts.Power wastage is pretty high owing to being associated with the voltage drop.

for Example, if a 10MW, 200V DC plant see's a 10% voltage drop the power wasted is also 10% [ 1MW ] based on a simplistic model. In reality it is much greater.You cannot connect sources arbitrarily. There is always a chance of equipment being damaged due to voltage difference. You have to put in a current limiting resistance which causes associated power loss and voltage drop.DC-DC converters are typically electronic and did not come along the time when DC supplies were used. So there was NO way to convert voltage levels. And now for AC:Voltage Drop [ or even rise !! ] is a function of source and load and transmission line impedences. It requires a pretty complex Network Simulation to figure out these drops. Further these drops are not static, they are dynamic that i.e they change every instant. This makes AC capital expensive , as expensive are required to control the plant and distribution centers.Lethality is a function of Volatge. At 110V, 60Hz [ US ] or 220V,50Hz [ INDIA ] the voltages will cause a tingle but no permanent damage or death.

Power is wasted on the resistive elements of the transmission lines, not due to the capacitive and inductive effects. Thus unless there are faults , power wastage can be controlled greatly.ac service houston texasSources and Sinks can be connected arbitrarily as long they are in-phase. do window ac units work without a windowThere is a particular mechanism to sync a Source to a Live line and connect it as a source.  cost of an ac unitPage on iitkgp.ernet.in With the help of Transformers, Voltage can be stepped-up or down pretty easily as per requirement.Thus , AC scores better than DC almost on all aspects. The next question is what waveform of AC is better , i.e. Why a Sinusoidal wave ?Written Because we found a way to change the AC voltage levels from one to another before knowing how to do the same with the DC (i.e: the invention of the transformers ) and I can arguably say, if the nowadays technology of the power electronics and high power semiconductor devices had been reached in the late of 19th century, the DC would dominate over the AC.

Back to 1882, the first commercial distribution was DC, it was commissioned by Edison, a 24 km long cable at 110V to light Pearl Street Station. Transmitting power over a long distance at such a low voltage would inevitably lead to unacceptable losses. In 1885, the voltage transformers were invented, allowing stepping up the AC voltage before transmission (i.e, current is reduced and the losses can be highly reduced) and stepping it down to a voltage level appropriate to the distribution level. Thus, Edison lost the war of current against Westinghouse who was backed by Nicola Tesla.Nowadays, the renewable energy sources like photovoltaics and wind turbines produce DC and in the same time most of our loads are battery based systems such as: electric vehicles, phones, laptops, .. Other loads like LED lighting systems, TV, .. It makes no sense to convert DC to AC and transmit it (for a very short distance in many cases) then convert it back to DC.Quitting the dependence -only- on AC in our homes is just a matter of time and, I claim that DC is coming back, ..

Written Thanks for A2A.At the moment you have no choice but to go with the crowd and use AC as even if you generate your own DC supply (or AC having wave shape other than sinusoidal) you will find it difficult to get common electrical equipment which can be directly connected without modifications. Many answers given takes one through the historical developments that happened around 140 years ago. How when it was needed to increase the DC voltage to transmit power over even few miles was not possible because DC generators could not generate more than 400 V-500 V because of commutation problem. The actual turn around happened with the development and use of Transformers and poly-phase Induction Motors and every thing connected with them. So the development of AC was natural. Now a days HVDC is a competitor to EHV or UHV AC, but it is only for transmission - still the generation and utilization are in AC.​More Than Power to You ​ON Semiconductor has acquired Fairchild. Together, we deliver a more

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