We know that electricity can be divided into alternating current and direct current, so do you know which kind of electricity is needed for electrical appliances in your home?
Many people may think that it is alternating current, after all, Tesla's alternating current has defeated Edison's direct current more than 100 years ago. Unfortunately, this answer is wrong, and the vast majority of appliances we use now, including LED lights, all that are needed are direct current. Wait, isn't the transmission line at home delivering alternating current? Indeed, it is precisely because the electricity in the home is not the electricity we need, so it must be converted before use, so we will find that the plug of the home appliance is getting larger and larger, and the role of this "big plug" is to convert alternating current into direct current. Speaking of this, I can't help but want to spit on the plug board production enterprises, it is really not enough to keep pace with the times, calculate 5 electrical appliances, buy a 5-hole plug board, the result can only be inserted 3, it is really impossible to squeeze ah.
Since all the appliances in the home need are direct current, why is it alternating current that enters the home? Why not change it directly to DC power supply?
When people first used electricity, they did use direct current, because at that time there was only direct current, and the person who popularized direct current to thousands of households was Edison. As more and more people use electricity, a problem arises, that is, the transmission of electricity. Electricity in the transmission process will be due to the presence of resistance and loss, and these losses of electrical energy will also be released in the form of thermal energy, resulting in the melting of transmission lines. What to do? There is no other way but to build more power plants to bring the power generation end closer to the power consumption end.
At this time, there was an employee named "Tesla" in Edison's company, who left the company because of Edison's suppression, and soon after he invented a new power system, that is, alternating current.
The difference between alternating current and direct current is very obvious, the size and direction of direct current do not change with time, and the direction of alternating current is changing every moment, such as alternating current with a frequency of 50 hertz, and its current direction changes 100 times per second. What does this mean? This means that DC cannot change the voltage, but AC can. Being able to change the voltage means being able to transmit electricity over long distances. The total power of the transmission line is equal to the voltage multiplied by the current, so in the case of constant power, the greater the voltage, the smaller the current. Therefore, increasing the voltage can reduce the current.
The loss of the transmission line is equal to the square of the current multiplied by the resistance, which shows that as long as the current is reduced, the loss is reduced, so as long as the voltage is raised, the loss of the transmission line can be reduced, and long-distance transmission can be realized.
At this point, Edison panicked, if everyone uses alternating current, the power plants built all over the world will not be a blood loss, so he began to try to suppress and denigrate alternating current, but in the end it did not stop the wheel of history, and alternating current finally defeated direct current. Alternating current can win and its historical environment has a close relationship, when people did not have any electrical appliances in their homes, whether it is direct current or alternating current, there is no difference for the light bulbs used for lighting, but now it is different, home appliances need direct current, so will direct current make a comeback?
Although alternating current can achieve long-distance power transmission, it is not without disadvantages.
The reason why alternating current can achieve long-distance transmission is because it can change the voltage, and the reason why it can change the voltage is because it can produce electromagnetic induction, and it is precisely because of the existence of electromagnetic induction, so between the alternating current transmission lines and between the transmission lines and the earth will produce inductance and capacitance due to electromagnetic induction, resulting in inductive and capacitive reactance, resulting in a large amount of power loss. So you know why the AC transmission lines are all set up very high, not afraid of wires touching people, but only away from the ground can you minimize electromagnetic induction and reduce reactive power losses. Although alternating current has such shortcomings, it can still send electricity out after all, is it still stronger than direct current? It's different now.
In Edison's time, direct current really could not complete long-distance transmission, but now it is different, we already have a way, that is, at the power generation end of the AC boost, and then use the converter to convert it into direct current for transmission, after reaching the end of the electricity, and then use an inverter to convert the DC to alternating current, and finally you can step down the voltage.
There is no electromagnetic induction of direct current, so reactive power losses can be avoided during the transmission process, which greatly improves the transmission efficiency. In order to solve the problem of uneven distribution of energy and power loads, the mainland has implemented the "West-to-East Power Transmission" plan, and in this plan, long-distance UHVDC transmission is used. Since direct current can already be transmitted over long distances, and all the electrical appliances need is direct current, is it possible to replace alternating current in the future? We'll have to wait and see.