Three-phase voltage is an electrical power system using three phase lines, with a phase shift of 120 degrees. This provides uniform conditions for many applications, increasing efficiency.
The emergence of the concept of three-phase voltage
The father of three-phase voltage is considered Dolivo-Dobrovolsky in Russia and Nikola Tesla in the rest of the world. Events relating to the era of the subject of the dispute occurred in the 80s of the XIX century. Nikola Tesla demonstrated the first two-phase motor, working for a company where he was building electrical installations for various purposes. The interest in the phenomenon of electrifying the hair of a domestic cat led the scientist to great discoveries. Strolling in the park with a friend, Nikola Tesla realized that he would be able to put into practice the Arago theory of a rotating magnetic field, moreover, they would need:
- Two phases.
- Shift between them at a 90 degree angle.
In order to show the great significance of the discovery, we note that Yablochkov’s transformer did not attain mass fame at the time indicated, and Faraday’s magnetic induction experiments were safely forgotten, having written down only the law formula. The world did not want to know about:
- reactive power.
Generators( alternators) and dynamos rectified the voltage using a mechanical switch. Likewise, the entire electricity industry at that time was scanty. Edison was just starting to invent, nobody really knew about the incandescent bulb yet. By the way, in the Russian Federation they consider that the device was invented by Lodygin.
The idea of Tesla looked revolutionary, it was unknown how to get two phases with a given phase-to-phase shift. The young scientist was not interested in the question. He read about the reversibility of electric cars and radiated confidence that he would easily build a generator, arranging the windings accordingly. There were no difficulties with the drive. At the beginning of the 80s, steam was actively used, the demonstration model was supposed to be powered by a dynamo.
Tesla was not asked by the need to obtain a certain frequency. Studies have not been carried out, it was required just to make the rotor turn. The idea was realized through slip rings. At that time, DC collector motors were supplied with similar contacts, Tesla's output is not surprising. It is more interesting to explain the choice of the number of phases.
The advantage of the three phases of the
experimenters voice say that the three phases over two, but an explanation is needed. Immediately, thoughts about efficiency, torque and so on go to your head. But Tesla drew in a notebook hundreds of designs, obviously, would be able to arrange the poles in order to achieve the desired parameters. Conclusion - it's not about the design of the devices.
Now the voltage of 380 V is transmitted only through three wires. This could not be achieved in the original version of Nikola Tesla. In 1883, Edison spent a lot of energy trying to use a three-core wire. Obviously, I heard about the demonstration, arranged by Nikola Tesla, and understood the danger of the situation. In the civilized world, the owner of the patent gets the main profit, why should a well-known inventor drag out a capable engineer to the world?
Edison's logic is simple: users will see that three-core cables are cheaper than four-core cables, and they will not use the new products of Nikola Tesla. It is easy to guess that the ingenious plan of the inventor of the base for the incandescent bulbs failed. And with a bang. And the blame was. .. Dolivo-Dobrovolsky. Nikola Tesla's system for creating two phases required the presence of four wires. At the same time, Dolivo-Dobrovolsky proposed to transfer more energy through three.
The point here is in symmetry. Line voltages of 380 V at each moment leave an alternative to choose. For example, the current from the first phase can leak to the second or third. Depending on the presence of suitable potential. The result is a balance. If you combine the two phases of the Nikola Tesla system, you get a vinaigrette. As a result, it is permissible to remove the neutral in the Dolivo-Dobrovolsky system, if the load is symmetrical - as often happens in practice.
As a result, a greater voltage is obtained between the wires, which reduces each passing current at the same power. And sometimes it is possible to use only three lines, this applies to most enterprises. There are obvious benefits when creating local substations: the neutral of the secondary winding is grounded right there, no need to pull extra wire from the hydroelectric station. These reasons have become the advantages of three-phase voltage networks, today dominant. Tesla wires are easily upgraded into three phases.
The reason for the loss of Edison
Often there is an opinion that the Tesla system was better, so Edison lost. It is difficult to say how many dollars the last one lost, but, according to modern standards, circled over 4.5 million dollars for Nicola. Inflation! The authors tend to believe that Edison got his. Nikola Tesla was able to prove the benefits of direct current. For example, the latter is less inclined to crown on wires, the amplitude does not contain sharp emissions.
Today it is proved that it is more profitable to transmit direct current over long distances. This excludes from consideration the reactance of the network - inductance and capacitance. Which significantly reduces unstable reactive power. The 21st century is capable of becoming the second birth of direct current for transmission over long distances. But laughter causes Edison's inability to transfer energy. Tesla was right to help, then DC devices today would be used on a par with consumers of alternating current. For collector engines, this is better - efficiency and torque increase.
leaves, it is profitable to transmit direct current. Edison simply could not find the right solution, tried to take the task in vain, not plunging into the rear. Edison was a pure practitioner and could not find such clever solutions as converters. But all the generators of the middle of the XIX century had a built-in switch for rectification. It remained only to connect to the line, and on the receiving side to carry out the conversion. And that's it! Nicola brilliantly punished Edison, proving that there is some power in the world that controls the course of history.
alternating current was chosen because of the availability of powerful means for transmission. Speech about the transformer. Designed for the first time in 1831( or earlier) by Michael Faraday, this indispensable element of modern technology was left without deserved attention. Interest in the device returned Heinrich Rumkorf fifteen years later, using a dynamo to obtain a discharge in the spark gap. Step-up transformer greatly enhanced the effect. This directly opened the way for scientists to conduct experiments, but the essence of the transformation did not receive the deserved attention.
Instead, scientists fought hard over DC.Creating for him engines, lighting devices and generators. Surprisingly, knowing about the reversibility of electric cars, they did not think up earlier how to create a unipolar motor that stands today in hand mixers and blenders. In fact, single-phase household motors. And only a small part of the work on direct current.
We indicate an implicit advantage. DC current has a higher safety limit. It seems possible to make industrial networks harmless to people. Consider the statement in more detail, the arguments are not obvious to the inexperienced reader.
Why direct current is safer than
Scorched electricians say that a 220 V electric shock is not too dangerous, the main thing is not to fall under three-phase linear voltage. It is higher by about a root of three times( within 1.7).Linear is the voltage between two phases. Due to the shift between them at 120 degrees, this curious effect is obtained. Ignorant people ask what the difference is with a 90 degree shift. The answer is given at the beginning - the three phases form a symmetrical system. With a shift of 90, it would take four.
As a result, each line voltage is fed across the pole, which greatly simplifies their reproduction when it is required to achieve high power. For example, in traction engines of steamships, where it is required to change the force extremely smoothly and it is necessary to use shaft speed regulators. It happens, three or even six poles is not enough. Only a vacuum cleaner collector motor is enough two.
So, between phases there are 308 V. It looks safe if you increase the frequency of the transmission line to 700 Hz. Tesla found that from the specified value the skin effect is clearly manifested, the current does not penetrate deep into the body. Therefore, does not cause significant damage to humans. The scientist demonstrated lightning tongues on the body at much higher voltages and said that it is good for health, cleanses the skin well.
Frequency 700 Hz( or higher) was not used in everyday life - at the same time, transformer losses increased significantly. At the time of the decision on the nominal values of the first AC hydroelectric station, there were no developments in the manufacture of electrical materials. We offer more details on the topic of electronic transformers. There is no need to duplicate information. Due to the absence of the necessary materials, the magnetization reversal loss increased strongly with increasing frequency. Today, this does not cause difficulties at the level of technology.
Get up complexity - shielding. During the first attempts to transfer energy, they did not know about radiation. Radio took the first steps in the 90s of the XIX century. In fact, the increase in frequency is accompanied by a sharp increase in the release of energy into space. And the wires needed to be shielded, it is expensive, requires the presence of powerful dielectrics. Not the fact that modern networks could solve the problem.
Tesla offered to transmit energy through the air. Why built the tower Vordenklif. But. .. industrialists were interested in selling copper for the manufacture of wires and on this basis refused to the scientist in financing. But the main thing is that the time is coming when the three-phase voltage goes into non-existence or will be obtained from the transducers, and Tesla himself will give the answer how to do it.
More precisely, the answer will be given by numerous patents and ideas of the inventor. No wonder the records were immediately taken after the death of the scientist and carefully classified. We recommend to undertake the study of cavitation engines. It is time to dream that the machines will begin to ride on vegetable oil without polluting the environment with disgusting smoke and stinging. Please note that all the secrets lie on the surface and are waiting for someone who wants to reveal them. Perhaps someone from the readers will be able to do it first?