Rated voltage - current its value on the circuit.
We sincerely thank James King for a story about the history of galvanic voltage sources.
In RF line voltage used with an average effective value of 220 V and frequency 50 Hz. This means that the voltage amplitude is variable, but is allowed to replace constant at 220 in calculating the power consumption and other parameters.
In everyday life, common bulb on 12 V AC, which according to the rules (GOST 50571.11) are applied in the territory of bathrooms and toilets. A constant 12 V prevail among automotive batteries. Note that the battery with the nominal value of the time has come to give to the dump. Operating the battery is charged to 14 V.
In the literature, often deal with the concepts of line and phase voltages. This denomination. Measured between the first two phases, the second between each phase and neutral. For 220 V figures are respectively 380 and 220 V. This is the average current value of the amplitude at the root of two times more.
Under the new standards, the country is now entering a voltage of 230 V. Neither 380 nor 220 in the socket can no longer be detected. It is illegal, according to state standards, the supplier is responsible for the quality of energy supplied. Steps taken by the government to operate smoothly import equipment. In the 10 years of the XXI century began to prohibit the use of incandescent light bulbs. Increasing the voltage by only 10% reduces their lifespan by about half. Violators, quietly use the device, will now pay more often.
Go to LED lighting! At the same time pay for the light to fall ten times.
The standard voltage
July 14, 1729 was a great event: Steven Gray guessed to conduct the static electricity on the silk threads and other materials, creating the first chain. Prior to the introduction of electricity companies had to be located directly on the banks of rivers. Which is inconvenient. It is much easier to build factories near the resources.
It is difficult to lead the development of natural resources away from energy sources. Human strength is no substitute for electricity. The first attempt to transfer energy to a distance became a commercial telegraph in 1837, the line length of 20 km. This proves that it is possible to transmit energy over long distances and to perform there with the help of her work. Five years earlier, Sir Joseph Henry showed a device with wires bay a mile. Electromagnet raised very respectable even by the load current times.
All was done using the voltaic pile - a set of circles of copper and zinc, separated by a layer of wet tissue impregnated with salt water. The first major design appeared in 1836. It was the first standard of the rated voltage, as measured by other sources, such as thermoelectric generators. John Daniel Frederick tried to solve the difficulty of gas evolution (hydrogen) galvanic source during operation. This led him to the idea of using two electrolytes instead of one.
Daniel was based on a report by Professor Davey for 1801 on the chemical nature of the voltaic pile, as a result of oxidation of the metal. Later, the theme was addressed by Becquerel. Daniel decided to test the electrochemical experiments of Faraday and was looking for a suitable source. As a result, a new type of electrochemical cell:
- The original design:
- In the center of the bowl was a zinc rod, surrounded by bovine esophagus. Inside poured weak acid solution of zinc.
- esophagus Vkrug went hollow copper cylinder 3.5 inches in diameter, filled with a weak solution of copper sulphate. The cylinder is covered with a perforated plate through which pass the center of the bull's esophagus and a zinc rod.
- On the bottom face of the copper disk are large crystals of copper sulfate, not give a solution to go out of saturation.
- Reconstruction (see. Figure).:
- Copper hollow cylinder is located in the center of the bowl (see. Fig.) immersed in a copper sulfate solution.
- The design can fit within the membrane of the esophagus bovine.
- Zinc located outside the hollow cylinder covered with amalgam and slightly smaller height, surrounded by a weak solution of sulfuric acid.
It is not known what led scientists to such an exotic design, but it worked great. A hundred years before the events of the scientist exactly would be accused of witchcraft. In 1881, at the International Conference decided electricians that the voltage output by one unit of Daniel, will be known as 1 V. This quantity is now used to measure the rated voltage. Subject: real potential Daniel cell at a temperature of 25 degrees Celsius is 1.1 V.
Designer noted that bovine esophagus may replace faience, but the performance of the cell becomes worse. Later John Gaso suggested using bisque as a porous membrane. High internal resistance of the cell causes a small current, but constancy of potential (1.1 V) was quickly noticed, and the electrochemical cell was used as a reference to the official recognition of those in 1881 year. From this time talking about the nominal voltage.
Already in 1843 Louis Deleui using Bunsen cells and electric arc lit up Place de la Concorde in Paris. This is an important point, as seen below, on the French show equal to other prominent figures of the time.
It is believed that the first magneto Pixie built in 1832, but the massive use of the current is not found. In 1844, a pair of hand-made generators Woolrich for galvanizing metals, and this is the first industrial designs. In the mid 50s energy steel used to obtain it from the vapor and converting the crankshaft and using such widgets into electricity. It was already known engines Page, the perpetrators of the opposite, pushing the train composition.
Two-ton engine at 600 rpm, designed by Blackwell first attempt is considered a fully automatic steam generator current. In tandem with them to use a mechanical switch for the rectification of the variable component. In 1858, these generators were being used as a device of British lighthouses. The result is not exceeded expectations, but made the first step to energy supplies for the needs of mankind.
Parallel demonstrations were electric lighting in France. There's a novelty rather served to entertain the audience. By the early 70s isolated lighthouses firmly switched to electricity, including Odessa. Germans on the scene, before remaining in the shadow of the British and French experiments. Organizer and inventor Oskar von Miller wanted to beat foreigners. He was ordered to organize the transfer of electrical energy to a distance of 35 miles. What was the first high-voltage network in the world.
Denomination always marked
Why increase the nominal voltage
In the section of the two-pole machines, a brief excursion into the transmission chain development. It is shown that the voltage is constantly striving to improve. This is required to provide an acceptable efficiency, which now does not fall below 90%. This is explained by Ohm's law for subcircuit:
- When current flows through the energy is lost.
- This happens according to the law of Joule.
- The value is determined by current losses.
According to Ohm's law, these quantities, including pressure, are associated. The higher the voltage, the less current at the same transmitted power. Consequently, the lower and loss. So, when power transmission over long distances is required to increase the wire cross-section as the rated voltage. Already in 1923 passed 220 kV line. All of the 20 German company RWE AG to build such a line. One crosses the Rhine, thrown over the two pylon height of 138 meters in the area of Forde. Since the 20s the need for positioning the company close to power disappeared completely.
In parallel, the US went electrification process. The first hydroelectric power station at Niagara was built back in the 90-ies of the XIX century, not three-phase. Nikola Tesla system consisted of a 4-wire, and could easily be converted. During the events described voltage rating of transmission lines grew:
- German line in Rommerskirhene was the first for a rated voltage of 380 kV. At the same time a similar path, paved through the Strait of Messina, was commissioned in Italy.
- The United States, USSR and Canada at the same time put into operation the line rated voltage of 750 kV in 1967.
- In 1982, the most high-voltage line is inserted between the Elektrostal and Ekibastuz. Three-phase AC rated voltage of 1.2 MV.
- In 1999, Japan is building China-Iwaki nominal voltage 1 MV line.
Since the beginning of the XXI century for the construction of high-voltage lines come from China.
Known stress denominations
All long-haul transmission lines operating today operate at nominal voltages of 115 - 1200 kW three-phase current. A further increase in the voltage is ineffective, leading to the appearance of heavy corona discharges, is a tendency to develop into an arc. The biggest losses arise on the low-voltage side. For example, in France, the annual losses estimated at 325 GW hours, which is 2.5%, they achieve 7.5% in the USA. This is due to the difference of the nominal voltage - 220 against 110.
At the 1980 cost-effective line length is 7000 km, but the real-life much shorter than the stated figure. At considerable distances begin to play the role of capacitive and inductive reactance. Together they form a reactive impedance which does not provide power supply users. This wandering to and fro currents, which are entirely parasitic effect. This factor is determined by the power line, not too big.
Today proved that it is cheaper in the long distances to supply a constant current does not flow in the induction of resistance - capacitance formed by a wire and earth, and inductive. There is no concept of reactive power. It proved by the fact that Nikola Tesla led the struggle for the AC mainly for damage to Edison.
Given saved, it is advantageous to construct the ends of lines powerful converter station for transfer currents. At the same time leave the radiation losses, seepage through the screen into the ground, reduces the level of corona discharge. Even today, the cables to recharge submarine batteries are powered by direct current, alternating transmit them impractical at a distance of 30 km. Today's lines have a 20 times greater extent, successfully operated. For AC transmission constraints depend on the distance:
- At short lines - the heat loss, designed not to destroy the wire insulation.
- At medium distances is taken into account the voltage drop, it is impossible to take too high.
- At long distances come into force factors of reactive power, determining the stability of the system.