An easy way to visualize the difference between AC and DC currents is to plot their direction versus time. The first will look like a straight line, and the second will look like a wavy line. One cycle of this curve is the graphic basis of how alternating current is indicated on the circuits and pictograms (~), and the acronym AC (Alternating Current) has become a well-established term in texts.
Content
- DC and AC designations
- Edison's ideas
- Tesla's victory
- Renaissance of electrical warfare
DC and AC designations
All conductors have free electrons that can move in the presence of a potential difference. This flow of charged particles in a closed loop is called an electric current. If an electric charge moves in only one direction, then this phenomenon is called constant electric current, its designation "-» or DC (Direct Current).
The definition of alternating current can be derived from the opposite: it will be the movement of charges that change their direction on a periodic basis. Speaker vibrations can take a wide variety of forms, for example:
- sawtooth;
- square;
- triangular;
- sinusoidal.
Sinusoidal AC current is that type of energy, which is transported through modern power grids. Its huge advantage for power systems is that it makes it easy to change the transmitted voltage using transformers, and this waveform is easy to generate. These qualities allow you to save a huge amount of money and material resources in the production and transmission of electricity over long distances.
The following example can illustrate the benefits of using AC by power companies. Let us assume that there is a power plant as a generating capacity, which is capable of producing 1 million watts of energy.
For clarity, it will be convenient to consider 2 ways of transporting it:
- Transfer 1 million amperes with a voltage of 1 volt over the networks.
- Transportation of current with a force of 1 ampere and a voltage of 1 million volts.
The main difference is as follows: in the second case, a conductor of small thickness is required to transfer energy, while in the first case, one cannot do without a cable with a huge cross section. Therefore, energy companies convert the generated energy into very high voltage AC for transportation and then step down in close proximity to consumers.
Another benefit of AC for utilities is the superior reliability and simplicity of alternators over dynamos. In addition, AC has the following advantages:
- allows the operation of relatively more efficient, simple and reliable electrical machines;
- does not destroy switching devices.
All electronics and digital technology consumes DC. As a rule, direct current is generated using electrochemical and galvanic cells. These are relatively expensive ways to generate electricity, therefore, there are many device designs, converting AC to DC, based on preventing the flow of current in the opposite direction and rectifying the sinusoid using filters.
In combination with transformers, rectifiers allow obtaining the required parameters and high quality from the DC network.
Edison's ideas
Modern life cannot be imagined without electricity. In order for it to serve for civil and industrial purposes, it must not only be produced, but also delivered to the consumer. The first who decided to produce electricity in large quantities and transport it to factories, offices and households, was the American entrepreneur Thomas Edison - one of the most influential inventors the world.
To implement his idea, he designed and tested DC steam generators, electricity meters and elements of distribution networks. The first electrification of lighting was not easy at the time. Gas company owners saw Edison as a dangerous competitor who could put their businesses in jeopardy. But nothing could stop the inventor. Neither the colossal cost of laying cables in the sidewalks, nor accidents during testing prevented him in September 1882. launch the first lighting network of five thousand lamps.
In 5 years, more than 50 Edison power plants were in operation. Despite the great success, the inventor was unable to expand the geography of his electrical networks to the whole world. Residents of the areas in which the power plants were located complained of smoke and soot, and forced the closure of Edison's facilities. Thus, the first generation of coal-fired power plants eventually ceased operations, giving way to thousands of new, generating AC.
Tesla's victory
Most of the early electricity distributed was direct current, and there were no standards for consumers. For example, arc lamps needed several thousand volts, while Edison incandescent lamps required 110 volts. Siemens trams operated from 500 V, and industrial engines at factories could differ many times in stress.
Electric companies were forced to create and maintain several generating lines at the same time for different classes of loads. We can say that there were two major obstacles to the widespread use of DC networks:
- proximity of generators to loads;
- difficulties in providing a variety of voltages.
Croatian scientist Tesla, who worked with Edison, believed that using alternating current in electrical networks could solve these problems. Their disagreement over the prospects for alternating voltage ended with the AS researcher continuing his work with Edison's competitor, George Westinghouse. Tesla did not discover alternating current, but was the inventor of the synchronous generator and asynchronous motor, as well as the author of patents concerning the operation of polyphase devices.
The advantages of AC for generation and transportation were obvious, but Edison, instead of admitting it, remained firm in promoting DC and tried to discredit his competitors. He began to popularize the idea that AC is deadly to animals and humans. For example, Edison even became the inventor of the AC electric chair with the aim of gaining the foundation for a propaganda campaign on the dangers of AC.
Although the anti-advertising campaign was successful and yielded tangible results, Edison's joy of victory was short-lived. In 1892 the German physicist Pollack invented a mechanical rectifier with which it became possible to charge electric batteries, and the existence of DC transportation lost its last justification. Already in 1893, the Chicago World's Fair was lit from the AC network, which was the beginning of the triumph of alternating current in the 20th century, and the competitive events between inventors went down in history as the "war of currents".
Renaissance of electrical warfare
The growth in the use of renewable energy sources in the 21st century has led to the emergence of small-scale decentralized power grids with electricity consumption almost at the production site. For such power systems, the advantages of AC do not matter, therefore the use of direct current in them is justified.
Modern high-performance electronics have made progress in energy conversion and can transform direct current in voltage ranges up to 800 kV. volts with greater efficiency than AC electric cars. These innovations became the basis for the construction of high voltage direct current (HVDC) lines to transfer surplus solar or wind energy from one region to another. HVDC construction costs about twice as much as traditional ones, but due to the low losses and environmental friendliness of the entire system, such an investment is justified.
More and more electrical appliances require direct current. Computers, LED lighting and other electronic devices need to convert and rectify mains electricity. The number of electric vehicles is expected to increase in the coming years. Modern DC distribution systems are capable of eliminating converters in the home over time voltage and it is easy to integrate photovoltaic cells into household and industrial networks and storage batteries.
High voltage DC transmission is now a proven and proven technology in countries such as Germany and China. But for practical universal implementation, there are still many unresolved issues. How will both technologies coexist? What will be effective security measures? What technical and legal steps will be required to switch to DC? The benefits and scope of such changes are so significant that, apparently, we are talking about a paradigm shift.
