1. Foreword
In the power transmission system, most of the three-phase alternating current methods are used. So how does it work? How was it invented? Who invented the three-phase power transmission system? Let's listen to Teacher Kathy tell the complicated story and answer why some countries use 50Hz AC , some countries use 60Hz AC, and there is only one country in the world that uses half.
▲ Figure 1.1.1 Three-phase AC power transmission system
2. AC meter
In order to tell the story behind the three-phase power transmission system clearly, we need to take a moment to talk about the three-phase alternator and three-phase motor . For this reason, we also need to mention George Westinghouse and his two-phase alternator and motor .
▲ Figure 1.2.1 Westinghouse and his first alternator
Data shows that it all started in April 1888. At this time, Westinghouse had been using single-phase AC to power city lighting for two years, and Edison had been troubled by the AC power supply for more than four months. At this time, the Enterprise Federation is coordinating the copper market, and the cost of DC transmission has increased, because the metallic copper used in DC transmission is three times that of AC transmission. However, Westinghouse also has its own problems. These problems cannot be solved for the time being, but they are no longer a problem for Edison DC . For example, Westinghouse was unable to convert the alternating current flowing back and forth into the circular motion required by the meter and motor.
At first, Westinghouse was most worried about the electric meter problem. If there is no electricity meter that can be used, electricity bills will only be charged according to the unified access rate, which is equivalent to encouraging users to use as much electricity as possible. Fortunately, in April 1888, an employee, Shallenberger, placed a spring between two metal pieces of the equipment, and the spring actually rotated. A month later, Schallenberg had a working AC meter. In August, they had electric meters ready for sale on the market. Meters operating at 133 Hz were particularly popular, with a total of 120,000 units sold over a 10-year period.
▲ Figure 1.2.2 Schallenberg and his AC meter
3. AC motor
Now that Westinghouse has an AC meter, it also needs an AC motor, which can output industrial power when driven by AC. A few weeks after Schallenberg's discovery of the rotary spring, Westinghouse heard from another employee that a former Italian professor named Galileo Ferraris had designed a new alternator and corresponding AC motor. Ferraris' design requires a dedicated generator, which uses two coils to generate alternating current. Coils A and B are 90 degrees apart in space. The parameters of the two coils are the same. They use the same electromagnet to induce current, so they will induce alternating current of the same frequency, but the maximum voltage value is different in time, that is, the phase difference is 90 degrees. Since these two sets of coils have two different phases, they are called two-phase alternators.
▲ Figure 1.3.1 Ferraris’ two-phase generator
To make a two-phase AC motor, Ferraris connects two coils at the two-phase AC points. The two coils are also 90 degrees apart in space, thus generating a rotating magnetic field in the middle of the coils. The rotor is between the two coils, and the rotating magnetic field induces eddy currents in the rotor. This eddy current generates electromagnetic force between the currents of the two coils, causing the rotor to rotate.
▲ Figure 1.3.2 AC motor
Ferraris did not patent his idea because he believed that the solution would not generate the power needed by industry. Although Ferrari provided the solution to Westinghouse for free, Westinghouse paid Ferrari a $1,000 fee.
IV. Tesla's AC Motor
During the same period, in 1888, Westinghouse heard that a 32-year-old Serbian inventor named Nikola Tesla was demonstrating his two-phase AC motor and generator to the American Institute of Electrical Engineers. His AC motors are very powerful and can be used for industrial power.
▲ Figure 1.4.1 Tesla and his AC motor
According to Tesla's description, his two-phase motor and generator were the same design as Ferras's. He believed that Professor Ferraris not only independently arrived at the same theoretical results, but also in the same way down to the smallest details. But regardless, Nikola Tesla held U.S. patents on his AC motors and generators. But Westinghouse's lawyers believe Tesla's demands are unfair. But Westinghouse believed that Westinghouse Electric Company could not allow others to have a motor that could be made to work in an alternating current system.
So in October 1888, George Westinghouse paid Nikola Tesla and his company a huge sum of US$170,000 to purchase Tesla's AC motor patent, which is equivalent to US$5 million today. In addition, the company will also need to pay a permanent ownership fee of US$2.5 per horsepower for future motor sales. This was an incredible amount of money, and in 1900 Nikola Tesla said, If other companies and manufacturers were as fair and generous as Mr. Westinghouse, I would have many more applicable inventions than I do now.
▲ Figure 1.4.2 Westinghouse and Tesla
5. Westinghouse Electric Company
Although Westinghouse Electric invested another US$300,000 in research and development of Tesla motors so that they can output industrial power, the motor function has always been unable to meet the needs. Part of the reason was that Tesla's motor was designed to operate on 60 Hz AC, but Westinghouse wanted the motor to operate on 133 Hz AC so that it could fit Schallenberg's AC meter.
In April 1890, the Edison Company's commercial spies sent Edison a gloating message. Mr. Westinghouse only had one set of communication equipment for the experiment, but the experiment failed. Westinghouse is now at loggerheads with Tesla, who invented the AC motor.
Although it failed to obtain an AC motor that could be used for industrial applications and launched a public relations war with Edison, the Westinghouse Company was operating very well. For example, between 1886 and 1890, Westinghouse Electric Company's sales increased from $150,000 per year to $4 million per year.
▲ Figure 1.5.1 Description of Westinghouse Electric’s profit income
On November 15, 1890, a British bank collapsed, and the economies of both the United Kingdom and the United States were related to it. In order to fulfill the order, Westinghouse Electric Company borrowed a large amount of loans from the bank, and now his company is on the verge of bankruptcy. The bank wanted to finance the company, although their respective managers had different opinions. The bank manager believed that Mr. Westinghouse wasted a lot of money on experiments and paid generously for the services and patents he hoped to obtain. Later, Westinghouse also gave a lot of support to the bank that helped them and kept the original bank manager's position, so he decided that more business interests must be obtained. He decided to stop all research on Tesla motors.
▲ Figure 1.5.2 Westinghouse Electric no longer continues motor research
6. Mikhail Dolliver Dobrovolsky
Although Westinghouse's research work on polyphase motors and generators stopped. But others continue to work on it. According to the information available, the most important person is a 26-year-old Russian-Polish named Mikhail Doliv Dobrovolski. He works for a German AEG company.
▲ Figure 1.6.1 Mikhail Dolliver Dobrovsky
Later in 1888, a few months after Tesla became famous for his two-phase motor, Dolliver Dobrovolsky believed that Tesla's two-phase motor, which used two completely independent alternating currents 90 degrees out of phase, had no particular advantages. The magnetic field generated around the rotor fluctuates by approximately 40%. Dolliver Dobrovolsky proved through mathematical calculations that the use of three-phase alternating current can reduce magnetic field fluctuations to 15%. So he began building three-phase electric generators and motors, with three sets of coil windings in the system.
▲ Figure 1.6.2 Dolliver Dobrowski’s three-phase motor
It was also during this period that Dolliver Dobrovsky realized that three-phase electricity was not only beneficial to motors, but also a new way of power transmission, using three wires instead of six. This advantage is only possible when using three-phase alternating current. The sum of the currents of the three-phase current in is equal to 0 at any time. This requires the three-phase electricity to be in a balanced state, with the same amplitude and a phase difference of 120 degrees. At this time, you can connect one end of the three coils together as ground wire , and the other three wires as live wires to transmit power. This is very critical for power transmission, because the biggest problem in power transmission is how to reduce costs. In the final analysis, it is to reduce the use of metallic copper in transmission lines. Using three-phase power cuts the wires used to transmit power in half, while still using three items to drive a high-voltage three-phase motor.
▲ Figure 1.6.3 Three-phase electrical output
Not only that, in August 1889, Dolliver Dobrovolsky also applied for a patent for two three-phase transformers , which were called delta transformers, star or Y-type transformers according to their connection shapes. Using these transformers, three-phase alternating current can be boosted and transmitted over long distances using small currents, and the corresponding line losses are very small. At the user end, a transformer is used to reduce the voltage to ensure the safety of electricity.
▲ Figure 1.6.4 Three-phase power transmission system
But then again, how to light a light bulb using a single live wire? He didn't actually use a single live wire to light the lamp. Instead, a single live wire and a return to neutral wire are used to light the lamp. The neutral line is considered to be added. If the three-phase electrical load is balanced and no current flows through the neutral line, each circuit can still work.
In addition, Dolliver Dobrovolsky also found that relying on the vortex on the rotor to push the rotor is actually not efficient. In order to reduce eddy currents on the rotor, Dolliver Dobrovolsky added parallel ribs to the rotor and applied for a patent in 1889. The ribbed rotor looks a lot like a cage. In 1894, British scientist Sylvanus Thompson said that the rotor resembled a squirrel cage and was large enough to hold a squirrel inside. Squirrel cage motors are now the mainstream AC motors in electrical engineering. It was recorded in a 2017 textbook that the squirrel cage motor designed by Dolliver Dobrovolsky was so perfect that it had been used almost unchanged for more than a hundred years.
▲ Figure 1.6.5 Squirrel cage motor
7. Actual three-phase power transmission system
Back in 1890, Dolliver Dobrovolsky’s three-phase motor and power transmission system impressed a serious-looking man. His name was Oscar von Miller, who was the technical director of the Frankfurt Electrical Exhibition at the time. Maitreya began to plan to use high-voltage direct current driven by waterfalls to generate electrical energy. This requires finding a waterfall nearby that provides the cement plant needed to install the hydraulic turbine unit . The nearest dam that meets the conditions is in Laufen, Germany, which is a full 175 kilometers away from Frankfurt.
▲ Figure 1.7.1 Oskar von Miller and Frankfurt Fair
At first, Miller was looking for a Swiss engineer named Charles Brown. At that time, their company was testing high-voltage direct current transmission for hydroelectric power stations. After much consideration, Maitreya decided to use an exciting new three-phase transmission system. So he coordinated with Brown Company, Dolliver Dombrowski Company, the German government and cement plants to promote the development of this technology.
Dolliver Dobrovolsky used a three-phase generator driven by the Laufen Falls to generate three-phase electricity, using a star transformer to step up the 55 volt alternating current to an astonishing 8500 volt alternating current. Three wires were then used to carry electricity to Frankfurt. Such high voltages are required in order to use the thinnest wires possible. The final diameter of the wire was only 5 millimeters, and the transmission line consumed 60 tons of copper.
▲ Figure 1.7.2 Laufen to Frankfurt transmission system
They then use another star transformer to reduce the high voltage to 65 volts. In addition to lighting some lamps, they also drive a 100-horsepower three-phase motor to drive an artificial waterfall.
They used a real waterfall to drive a generator to generate three-phase electricity, and then after 175 kilometers of power transmission, they finally drove a motor to create an artificial waterfall. The system seemed cool at the time.
▲ Figure 1.7.3 Three-phase motor and driven artificial waterfall
Many scientists believe that this long-distance power transmission system is impossible to implement, but the result is that after such long-distance transmission, 74% of the power is finally transmitted to the user. The project was described by newspapers as "simply spectacular". A record article in the Journal of Electrical Engineering commented on this, saying that it is no exaggeration to say that the Laufen to Franklin power transmission system is the most difficult and significant experiment done by mankind in electrical technology since the mysterious force of nature can serve mankind.
This was the first transmission system, and in many ways it was the same as today's transmission system, where we still use the same three-phase delta transformers, star transformers.
But don’t be confused by the fact that most indoor electrical plugs have three plugs, thinking that they are three-phase electricity. In fact, most indoor appliance plugs have only one live wire, and the other two are the neutral wire and the protective ground wire. The ground wire is often connected to a nearby metal plate underground.
▲ Figure 1.7.4 Household appliance plug
8. Honor is underestimated
But Dolliver Dobrovolsky was not very good at expressing himself and did not promote the advantages of his system enough. Many people are also confused about two phases and three phases. Both of these were called polyphase alternating current, another name given by Sylvanus Thompson that we still use today.
Perhaps Dolliver Dobrovolsky did not realize that his partner in the transmission system, Charles Brown, was jealous of the attention he was getting, and the attention that three-phase electricity was getting. In a magazine column in October 1891, the author wrote that there were many difficulties associated with using three-phase electricity, but that thanks to Dolliver Dobrovolsky the construction improvements during the Laufen-Frankfurt demonstration project were made without any glitches. In this regard, Brown claimed that the three-phase electric technology used in Frankfurt came from the fruits of Tesla's labor and was clearly and specifically described in the patent he applied for.
▲ Figure 1.8.1 Tesla’s three-phase generator
Maybe you think there is no final note in Brown’s words, which is explained below. In 1888, Tesla not only applied for a 2-phase alternator, but also a three-phase alternator. If Dolliver Dobrovolsky knew about Tesla three-phase motors, he should have emphasized that Tesla uses six transmission lines instead of three, reflecting the advantages of the three-phase three-wire transmission system. But he didn't mention any of this. It just emphasizes the advantages and disadvantages between two-phase motors and three-phase motors.
Since Dolliver Dobrovolsky did not speak English, but Brown could speak the application, and the system was so complex, many people believed that Tesla invented all three-phase power transmission systems, and the influence of Dolliver Dobrovolsky was ignored. These can gradually be clarified as time goes by.
9. World's Fair
On May 21, 1891, about a week after the opening of the World's Fair in Chicago, Nikolai's patrons pushed him to make the first demonstration of his latest device, the Tesla coil .
▲ Figure 1.9.1 Nikola Tesla display
The Tesla coil was an immediate success on a global scale. Although the three-phase power transmission system can save 50% of wires, the Tesla coil can light up the light bulb without using any wires, as long as the light bulb is close to the Tesla coil. The entire world has pretty much become Tesla fanatics. In a report in the Electronic Engineer magazine, it was said that no one in our time has been able to gain such a wide range of scientific and technological reputation through one event as Tesla, a talented young electrical engineer.
▲ Figure 1.9.2 A magazine that praised Tesla
It was during this critical period that Westinghouse decided to reinvest in making two-phase motors suitable for industrial drives. The reason why he is so convinced is because one of his engineers believes that 60 Hz AC can be transmitted over long distances with less line loss than 133 Hz. Another engineer, Benjamin Lamy, claimed that the Tesla motor windings could be modified for industrial use. With the consent of Tesla and his backers, who owned 54% of the patent rights, Westinghouse could waive the patent fee of $2.50 per horsepower on the motor.
Later in 1891, Benjamin Lamy was allowed to build his two-phase AC motor. An industrially available two-phase motor was available in early 1892. According to Lamy, this was the first working AC motor produced by the Westinghouse Electric Company and had all the characteristics of a modern AC motor.
As the 1893 World's Fair in Chicago approached, the Westinghouse Electric Company met to discuss how to commercially market the Tesla motor. Benjamin Lamy suggested that they needed to make multiphase alternators fashionable so that everyone would buy them, and the problem of promoting the electric motor would be solved. A year later Lamy recalled that company instructions to build a standard production line for multi-phase alternators were immediately made and promoted at all times and on any occasion.
▲ Figure 1.9.3 Using two single-phase motors to form a multi-phase generator
Then, Westinghouse realized that he was in trouble at the expo. The company did not yet have any high-power two-phase generator, and there was not enough time to develop it, let alone a three-phase generator. Lamy recalled that Westinghouse suggested using two single-phase alternators, staggered to create a spatial phase difference of 90 degrees. This is a small step forward towards polyphase power supply systems.
Based on this little trick, he even posted a sign at the expo saying that the expo was powered by a Tesla polyphase power supply system. Westinghouse also invited Tesla to the Westinghouse Electric Company Expo branch for a demonstration, mainly to show the connection between Westinghouse Electric and Tesla in all aspects.
▲ Figure 1.9.4 Notices posted by Westinghouse Electric at the Expo
10. General Electric and Westinghouse Electric
In 1892, the year before the Expo, Edison General Electric merged with other companies. Edison was fired from the company, and Edison was removed from the company name, leaving only General Electric. Setting aside Edison's prejudice against alternating current, General Electric rose from a direct current company to a leader in three-phase alternating current. Lamy, who by this time was Westinghouse's chief engineer, recalled back. There are two sets of polyphase alternating current systems, one is a two-phase system and the other is a three-phase system.Westinghouse Electric is considered to be the company engaged in promoting two-phase alternating current, and General Electric is the company engaged in promoting three-phase alternating current. Although both companies are promoting the use of two polyphase AC systems at the same time.
▲ Figure 1.10.1 General Electric
After the expo, Westinghouse spent a lot of money to sue Tesla for two-phase and three-phase infringement. In April 1896, Westinghouse paid Tesla $216,600 for a contract to share technology with General Electric, an agreement that virtually allowed both companies to pursue their own ideas for multiphase electrical applications. The electrical market is basically monopolized by these two companies.
During this period they talked a lot about Tesla's invention, but suppressed Dolliver Dombrowski. Dolliver Dombrowski was still working for AEG at this time and became the company's chief engineer, helping the company become a leader in the power transmission industry in Europe, Asia and Africa.
11. Alternating current frequency
Since Dolliver Dobrovolsky proved through experiments that high-frequency AC points will cause more power transmission losses, he initially used 40 Hz alternating current because the flickering of light bulbs was uncomfortable, so he increased the alternating current frequency to 50 Hz and has maintained it to this day. Tesla insists on using 60 Hz AC power, so the AC power used in the United States is 60 Hz. Countries that use the power supply system provided by General Electric or Westinghouse Electric also use 60 Hz AC power.
The only weird one among them is Japan, Dolliver Dobrovolsky Company AEG provided power transmission technology in Tokyo in 1895, using 50 Hz alternating current. General Electric provided the power transmission system for Osaka in 1896, using 60 Hz alternating current. Therefore, Japan is divided into two parts, one part uses 50 Hz AC power, and the other part uses 60 Hz AC power.
▲ Figure 1.11.1 Japan AC frequency distribution
In 1914 World War I began, Dolliver Dobrovolsky wisely believed that Germany was not a safe place for Russians , so he moved most of his work to Switzerland and changed his Russian nationality to Swiss nationality. In 1918, Russia withdrew from the First World War, and Dolliver Dobrovolsky returned to Germany and was once again busy the Russian Revolution . At that time Dolliver Dobrovolsky suffered from heart disease and died of a heart attack in November 1919.
▲ Figure 1.11.2 Dolliver Dobrowski in his old age
When Germany was defeated in the middle of the First World War, people liked to discuss the achievements of the Russian Poles who abandoned them when they were needed most. Russia was busy with domestic revolution at this time, and various honors were given to those who had achieved success in Germany, which aroused their identification with Russian citizens, but these people did not participate in their revolution.
12. Postscript
Americans all believe that Tesla invented alternating current and transferred the corresponding patents to General Electric and Westinghouse Electric. People are very sad about the death of Dolliver Dobrovolsky, who also made outstanding contributions to alternating current. But it's unfair to him that his contributions are not recognized.
As a conclusion, if you ask who first invented the three-phase AC motor and generator, the answer is very clear, it was Nikola Tesla. He applied for a patent for a three-phase motor and generator in 1888. If you ask who first demonstrated the transmission system of three-phase electricity, along with the squirrel cage motor and more, the answer is different. It should be Mikhail Dolliver Domrovsky.
In 1891 Dolliver Dobrovolsky wrote, The scientific value of the discoveries of Professor Ferraris and Mr. Tesla cannot be underestimated, but the first actually constructed and practical rotating three-phase current system undoubtedly deserves this honor because we have brought the entire system to a height of perfection.
▲ Figure 1.12.1 Dolliver Dombrowski's Contributions to Alternating Current
If you're wondering about the scientist who discovered that high-frequency alternating current caused greater transmission losses, and who moved General Electric from a direct current system to a three-phase alternating current system, it's another scientist who doesn't get the fame he deserves. He's Charles Steinmetz, the charismatic and eccentric man known as the Schenectady Wizard. We will talk about his legendary story next time.
References
[1]
The Tamer of Lightning: The History of Electricity: https://blog.csdn.net/zhuoqingjoking97298/article/details/128426612?csdn_share_tail=%7B%22type%22%3A%22blog%22%2C%22rType%22%3A%22a article%22%2C%22rId%22%3A%22128426612%22%2C%22source%22%3A%22zhuoqingjoking97298%22%7D
[2]
History of 3-phase Electricity & Distribution: https://www.youtube.com/watch?v=NEkegQanD2I&list=PLepnjl2hm9tF-CxhyRFZi3Pujkq_V4pKP&index=33
