HISTORY

Early Three-Phase Power

Winner in the development of polyphase ac
Gerhard Neidhöfer

 
Early alternating current (ac) systems were the response to the supply limitations of Thomas Alva Edison's direct current (dc) power system, unsuitable for service areas with radii above a few hundred meters (up to about 1,000 ft), later about 3 km (2 mi). Transformers, invented in 1885, made it possible to raise the electric transmission voltage and to reduce the line current in the same proportion. The transmission I2R loss decreased considerably, so that supply distances became almost unlimited.

What followed was "the battle of the currents," beginning in about 1888 and extending into the first decade of the 20th century. In North America, the main competitors were Thomas Edison and George Westinghouse. The latter, a firm advocate of ac, was assisted by the brilliant inventor Nikola Tesla. This genuinely exciting period is depicted in "triumph of ac" (see "For Further Reading"), outlining the events in North America, in particular. On the other side of the Atlantic Ocean, the most prominent advocate of dc was the German engineer Werner Siemens, whereas ac developments were performed by pioneers and companies in a number of countries. Siemens was named an honorary member of the American Institute of Electrical Engineers (AIEE) in 1892.
The early decades of what became known as the "Electric Age" were marked by the efforts of outstanding engineers, inventors, and entrepreneurs on both sides of the Atlantic Ocean to develop a power supply system to best meet electrical generation, transmission, distribution, and customer utilization requirements. This article, authored by Prof. Dr. Gerhard Neidhöfer, is a fascinating account of the development and evolution of alternating current (ac) and polyphase systems with special emphasis on the development of three-phase ac power, the prevailing system that today enjoys worldwide use.

Gerhard, born in Germany, earned the Dipl.-Ing. degree in electrical engineering from the Technische Hochschule, Darmstadt, Germany, and the doctor of science degree in applied mathematics from the Université de Grenoble, France. He joined Brown Boveri Company (BBC) in Baden, Switzerland, before graduation and enjoyed a 39-year career working there in the large generator and motor business. Since retiring in 1996 from Asea Brown Boveri (ABB), the successor to BBC, he has served as an expert consultant to the company and subsequently to Alstom, which took over the power generation business from ABB. He resides in Hausen b. Brugg, Switzerland.

He has lectured widely on various aspects of electric machines and has been a frequent contributor at international conferences, having authored nearly 40 technical papers and coauthored two books on electric power engineering. Of particular interest to readers of this article, he published his latest book in 2004, Michael von Dolivo-Dobrowolsky and the Three-Phase Alternating Current. This book covers the life and accomplishments of this brilliant inventor and early promoter of three-phase technology.

He has been an active IEEE PES member since 1984 and was named an IEEE Fellow in 1999 "for contributions to the development of electrical machines and to the international harmonization of electric machinery standards." We are honored to have Prof. Dr. Neidhöfer as our guest history author for this issue of IEEE Power & Energy Magazine.

—Carl Sulzberger
Associate Editor, History

First Commercial ac Power Systems

The first ac systems were achieved in the late 1880s. Most of them served to convert remote water power into electricity that was then transmitted by a high-voltage line to the users, mostly with commercial and residential electrical loads. All systems, of course, operated with single-phase ac.

One of the first industrial high-voltage ac power systems was erected in the mining district of Telluride, Colorado, with power transmission from two waterfalls over a distance of about 4 km (2.5 mi) to the Gold King Ore Mill, 610 m (2,000 ft) higher up. George Westinghouse, the winner of an intense competition, installed one generator and one motor, both of the synchronous type and each rated at 100 hp, to be connected across two bare copper wires on crossarms and insulators, operating at 3 kV. The mill motor had to be brought up to synchronous speed by a single-phase induction starting motor, a "Tesla motor," which itself had to be started by hand. The commercial operation began in 1891. The Ames hydroelectric plant became an achievement of historical significance and was named an IEEE Milestone in Electrical Engineering in July 1988.

Polyphase ac Systems and the Inventors

As spectacular as the first use of ac may have appeared, one basic problem remained: single-phase motors are not able to start by themselves. The reason for this is that the magnetic field of a coil, fed by ac, is alternating in time, but, related to space, the field remains fixed to the coil axis. Consequently, a single-phase motor does not produce any torque at standstill. What the motors need for self-starting is a spatially rotating field forming a traveling wave in the airgap. To accomplish this, much intuition and imagination were required. The the most prominent inventors in this field are Galileo Ferraris, Charles Schenk Bradley, Friedrich August Haselwander, Nikola Tesla, Michael Dolivo-Dobrowolsky, and Jonas Wenström.

Galileo Ferraris (1847–1897)

This Italian professor from Turin recognized in 1885 that two coils, arranged perpendicular to each other and fed by two alternating currents of the same amplitude and frequency but with a phase displacement of 1/4 period, produced a steadily revolving magnetic field. A copper cylinder positioned in the center would then be caused to revolve as well. Ferraris demonstrated this effect in a simple model conforming to Figure 1. He made the idea public in March 1888 in a paper and lecture to the Royal Academy of Sciences of Turin titled "Electrodynamic Rotation Produced by Means of Alternating Currents." The message spread like wildfire but, at the 1889 World Exposition in Paris, France, Ferraris had to recognize that other researchers, Nikola Tesla in particular, had similar ideas.

Charles Schenk Bradley (1853–1929)

This American inventor had conducted experiments on polyphase motors and current systems, apparently before Ferraris's disclosure. But he seems not to have recognized the importance of his observations. In 1887, Bradley was the first to apply for a patent concerning two-phase ac power transmission with four wires. In 1888, he was close to discovering the three-phase ac principle when specifying terminal connections on a ring winding at three symmetrical outer points. Another patent issued in 1888 referred to a two-phase induction motor, actually the first one with a secondary armature completely short-circuited (cage stator).

Friedrich August Haselwander (1859–1932)

This German technician was inspired while meditating on a dc dynamo he had in his workshop for repair. The electric-arc dynamo had a Thomson-Houston armature, including three coils with a common internal connection and a three-segment commutator. For experimental purposes, he replaced the commutator by three sliprings to which he carried the outer coil ends. This, indeed, was the birth of the three-phase dynamo. Haselwander is also credited with having built the first three-phase synchronous generator with salient poles in 1887. See Figure 2. Furthermore, he recognized the principle of three-phase power transmission with two synchronous machines and three transmission wires, a system he presented in 1888 as a world premiere.

Nikola Tesla (1856–1943)

This Croatian-born Serbian inventor appears as the most active contributor to the development of polyphase systems. Following his early emigration to the United States, he had a varied career with his own enterprise, as a short-time employee of Thomas Edison, and as an advisor to the Westinghouse Electric Company. Above all, he was a gifted inventor.

It was in late 1887 when Tesla filed for several U.S. patents in the field of polyphase ac generators, power transmission, transformers, motors, and lighting. In May 1888, he gave a lecture to the AIEE titled "A New System of Alternate Current Motors and Transformers." Tesla explained a rotating magnetic field as being "a progressing shifting of the magnetism produced by progressive movement of the magnetic poles." This peculiar wording reflects Tesla's way of thinking and may prove that he did not know Ferraris's specific notations.

One of the many figures in Tesla's basic patent, shown as Figure 3, is representative of the invention and symbolizes a two-phase generator and motor connected together. In the same patent, Tesla mentioned a generator with three coils, the ends of which are led to six insulated contact rings with collecting brushes connected to those of a motor by six wires, thus forming three independent circuits. This, indeed, was very close to the proper three-phase system but without the final step of having the three independent circuits integrated in a system of interlinked circuits with a common neutral point, needing three terminals only. In another patent shortly after this, Tesla states the same as Haselwander, with reference to the Thomson-Houston armature, that the three coil ends could be led to three continuous rings for taking off the alternating currents that operate the motor, the latter also being provided with three symmetrically arranged coils. This statement is another of Tesla's few comments on three-phase arrangements.

Among polyphase systems, Tesla strongly preferred two-phase configurations as is evident from his many statements in this regard. This fact greatly influenced Americans of his generation.

Michael Dolivo-Dobrowolsky (1862–1919)

This Russian-born outstanding engineer is closely associated with the development of three-phase ac. The son of a noble St. Petersburg family, Dolivo-Dobrowolsky emigrated as a student to Darmstadt, Germany, to complete his education in electrical engineering. In 1887, he joined the Allgemeine Electricitäts-Gesellschaft (AEG) in Berlin where he spent a long, successful career which extended until after World War I. From 1903 to 1907, he took a sabbatical, moving to Lausanne, Switzerland, where he and his family acquired Swiss citizenship.

He was only in his second professional year, in 1888, when he heard about Ferraris's experiments on rotating magnetic fields, and his misinterpretation that such motors would not attain efficiencies better than 50%. Dolivo-Dobrowolsky noted in a 1916 survey: "The error was that he searched for the maximum output, produced at the slip of 50%.I kissed Ferraris's hand from afar for the nice idea and decided to investigate the matter intensively and to build a small test motor as soon as possible.Early in 1889, the motor was ready for trial and revealed surprising properties. The motor immediately ran up to full speed, was completely noiseless and could not be brought to a stop by hand!." The test model was conceived as a three-phase induction motor, needing no more than three terminals, with a squirrel-cage rotor. A mock-up of the test motor is shown in Figure 4.

This episode may stand for the whole of the ingenious work which Dolivo-Dobrowolsky accomplished in creating appropriate machines, apparatus, and systems for three-phase ac.

Jonas Wenström (1855–1893)

This very talented Swedish engineer filed for several patents in 1890 related to a complete system for distributing electric power comprising a synchronous generator with star- or delta-connections, as well as transformers, synchronous motors, and induction motors, all of them designed to operate with three phases. In the same year, the Swedish company ASEA, for which Wenström served as a consultant, built and successfully tested the first prototype. As to the invention of three-phase ac systems, Wenström would be mentioned first if the other inventors had not preceded him by one or two years.

Three-Phase ac: Main Features

The most striking feature of ac was the fact that ac motors were eventually able to start by themselves, needing no outside help. And there are many other properties which made three-phase ac so special and attractive, including the following:
  • As the three individual currents are displaced by 120° in time from each another, at any moment the sum of the instantaneous values amounts to zero. Thus, no return line is necessary, with each line current finding its way back in one or both of the other lines. The inner ends of the three lines can be interconnected, forming the star point.
  • A balanced three-phase load takes power that, over the three phases together, is constant with respect to time. Consequently, the torque of a three-phase motor or generator does not pulsate, a great difference compared to single-phase ac machines.
  • What is valid for the currents must also be true for the magnetic fluxes. Indeed, in a three-phase transformer, the three leg fluxes also sum to zero. This enables transformers to comprise three magnetic legs interlinked within a closed core. The basic structure as shown in Figure 5 is taken from a U.S. patent issued in early 1890.
  • Three-phase ac systems are also suited for single-phase loads when adding a fourth line, the neutral conductor. There had previously been doubts from skeptics, saying that lighting, for instance, would only need a single-phase supply, three-phase systems being unnecessarily expensive for such applications.

The Great Challenge in 1891

The year 1891 became key for the first high-voltage, long-distance transmission of power combined with the use of three-phase ac. The scene was the International Electrical Exposition at Frankfurt am Main (Frankfurt on the Main River), Germany. The organizers wished to bring forward all decisive materials and arguments concerning "the unpleasant battle of the currents."

High-Voltage Power Transmission, Lauffen–Frankfurt

A spectacular contribution to the Frankfurt Exposition was the experiment with power transmission from a hydroelectric plant at Lauffen am Neckar (Lauffen on the Neckar River), 175 km (about 110 mi) away, by means of high-voltage transmission. An early illustration (Figure 6) shows the 300 hp hydroelectric dynamo and switchboard, provided with three phases. Figure 7 shows the 100 hp, three-phase induction motor that, at the other end of the transmission line, served to drive a pump for an artificial waterfall. The power transmission was effected by three bare wires suspended from poles, first operating at 15 kV and later at 25 kV. Included were three-phase transformers at both ends of the line. Most equipment was manufactured in joint cooperation of the Oerlikon Company MFO, Switzerland, and AEG, Berlin. Their respective engineers were Charles E.L. Brown, expert in high-voltage technology and large machinery construction, and Michael Dolivo-Dobrowolsky, expert in three-phase machinery and transformers. Each company built a certain share of the transformers, based on Dolivo-Dobrowolsky's three-leg design and oil-immersed according to Brown's proposal. The dynamo came from MFO in Zurich, the motor from AEG in Berlin. The transmission experiment was a great success that drew worldwide attention and acclaim.

The United States was represented at the Frankfurt Exposition by a delegation of eight experts led by Carl Hering, vice-president of the AIEE. He also acted as a special correspondent for Electrical World magazine, writing a series of reports. Carl Hering merits another comment. During 1884, he had been the first assistant to the new electrotechnical chair installed at the Polytechnic School of Darmstadt, Germany. The School's annual report 1883/1884 mentions him as "engineer C. Hering from Philadelphia." His successor was then "Michael von Dolivo-Dobrowolsky from Saint Petersburg" who also took over Hering's private accommodations at Blumenstrasse 12.

Discussion on Polyphase Current in Frankfurt

The International Exposition ended with a one-week Electrical Congress. It provided the platform for both advocates and skeptics to discuss polyphase currents. Dolivo-Dobrowolsky read the paper "Electrical Transmission of Power by Alternating Currents." In particular, he mentioned other inventors in the field by saying: "With reference to the unsynchronous, especially the so-called rotary current (drehstrom) motors which were first suggested and used by Tesla and Ferraris, I believe, I am able to state that I have succeeded in making them very economical and practical." As can be seen, Dolivo-Dobrowolsky created publicity for three-phase ac that, in German, he named "Drehstrom" in recognition of the rotating field involved. As for a term in English, he and Carl Hering had chosen the expression "rotary current" but which obviously failed to be accepted. While the term "Drehstrom" continued to spread throughout German-speaking countries, "three-phase ac" became the standard English term.

Another paper at the Electrical Congress is informative. The speaker, Ludwig Gutmann from Pittsburgh, Pennsylvania, was skeptical about the benefit of three-phase ac, "as such motors need very special stations and lines without distributing electric light." He outlined that in the United States there were at that time more than 500 stations existing which operate with common, single-phase ac. He also gave to understand that "new types of motors, unknown up to now, are progressing in development, requiring not more than the common two-line system." This statement illustrates in some way the expectations of a good many experts of that time. Lauffen–Frankfurt 1891 in Historical Perspective The great event in 1891 went down in history as the birth of long-distance, three-phase power transmission. It has its place in countless surveys and addresses. Unfortunately, the silver jubilee of this accomplishment fell in 1916 during World War I. The same is true of the celebration of Nikola Tesla when he was awarded the Edison Medal by AIEE in 1917. In his address, Prof. Bernhard Arthur Behrend from Boston, Massachusetts, first reminded the audience of Tesla's famous lecture to the AIEE in 1888 and continued: "Three years later, in 1891, there was given the first great demonstration, by Swiss engineers, of the transmission of power at 30,000 volts from Lauffen to Frankfort [Frankfurt] by means of Mr. Tesla's system...." The wording is far from being accurate or complete, but may perhaps be explained by the spirit of that time. Surprisingly, it seems that Prof. Behrend's statement has remained largely unquestioned up to this day.

The Breakthrough of Three-Phase Power

A Continuing Battle

The main purpose of Lauffen–Frankfurt 1891 was to have demonstrated that high-voltage power transmission by overhead lines is practicable and economical. The experiment had also proved the suitability of three-phase ac; however, without claiming its exclusiveness. Thus, the question was still open as to under which conditions three-phase or single-phase currents would best apply. Here are some highlights of what happened, mainly in Germany, during the showdown of the current systems, with a glance at the course taken in North America.

Single-Phase Plants in the 1880s: An Interlude

As to Frankfurt, the story took an unexpected course. In 1893, two years after the outstanding demonstration of three-phase transmission from Lauffen to Frankfurt, the decision for the municipal power station was surprisingly taken in favor of single-phase ac. The town council apparently preferred to stimulate the development of the city in its urban life (with common single-phase ac for lighting), whereas industrial works (with a greater need for three-phase power) should settle in suburban districts.

The 1890s became the decade of ascent and decline of single-phase ac, with a boom in the middle of the decade. Not a few experts of the time considered three-phase current to be merely a transitional stage in the development of the ac system until reliable self-starting, single-phase motors might become available. The reality, however, made them change their minds during the 1890s. The Frankfurt power station turned out to be inadequate, costly, and isolated in an expanding three-phase environment.

First Three-Phase Supplies

The Lauffen hydroelectric generating station had to serve partly for the town of Heilbronn, some 10 km (6.2 mi) away. As the dynamos were of three-phase design, Heilbronn achieved the distinction, in 1892, of being the first town with three-phase supply.

In Sweden, the first power transmission to be based on three-phase ac was put into operation in 1893, over a distance of 13 km (8.1 mi) from the Hellsjön hydroelectric plant to Grängesberg. Jonas Wenström, the promoter, witnessed the event in the last year of his life.

Advance of Three-Phase Plants

A regular line of business with three-phase technology was first established by AEG in Germany. Beginning in 1894, the company built power stations based on three-phase technique in increasing numbers for the home market and for export. In the same year, AEG and Swiss partners founded the Power Transmission Company Rheinfelden. In 1898, the giant hydroelectric plant, placed on the Rhine River at the Swiss-German border, went into operation, with 20 hydroelectric units of 12,000 kW capacity in total. This plant is shown in Figure 8. Ten units produced dc power for adjoining electro-chemical plants, and the other ten generated three-phase power which, for the most part, was transmitted to other industrial plants and distant towns. The Rheinfelden three-phase installation expanded and gradually became the nucleus of the European interconnected network.

Key Events in North America

During the same period, there was, in North America, similar progress with single-phase and polyphase ac, the latter mainly in Tesla's preferred two-phase version. Some of the highlights can be reviewed by reading "triumph of ac, from Pearl Street to Niagara" (see "For Further Reading"). Indeed, Niagara was the key place where George Westinghouse was crowned with success. In 1893, the Niagara Falls Power Company decided on the adoption of polyphase (two-phase) ac and ordered three hydrogenerator units with remarkable ratings of 5,000 hp each. Late in August 1895, the power system went into operation, including a high-voltage transmission line to Buffalo, New York, about 32 km (20 mi) away. This early Niagara project was named an IEEE Milestone in Electrical Engineering in June 1990.

This great event also stands for the zenith of the two-phase system, which later became virtually obsolete. The article "the first polyphase system" (see "For Further Reading") looks back at two-phase power for ac distribution in North America. In 1903, when the next Niagara plant extension took place, the new ac generators were built with three phases, as were all the following plant additions.

Breakthrough of Three-Phase Power

The transition from two-phase to three-phase current was not, as it may appear, solely the addition of one phase in all of the equipment. It meant a change to a special and widely superior class of equipment offering many advantages. Thus, generators, motors, and transformers could be designed better, with higher utilization of volume and material, and better efficiency.

The first use of three-phase ac, mainly in industrial enterprises and workshops, took place with some hesitation; often the primary costs were considered more than the benefits. The adoption of the new technique was also accompanied with problems of patent rights and partially handicapped by litigation for years. Thus, the breakthrough had its own particular course in the countries concerned. Germany may serve as an example. Figure 9 illustrates two trends. In the second half of the 1890s, single-phase plants were continuously rising in number. However, soon after the beginning of the 20th century, single-phase plants suffered from stagnation. On the other hand, three-phase plants expanded steadily from the very beginning and increasingly dominated the scene.

Epilogue

The battle of the currents, in its last period, was a showdown of various classes of ac, from single-phase ac up to polyphase variants. Depending on the circumstances in the leading countries, initial progress was first made by two-phase systems or directly by the three-phase system which definitively won the competition. From approximately 1900, it was clear that three-phase power was going to become the leader in electricity supply throughout the world.

For Further Reading

C.L. Sulzberger, "Triumph of ac," IEEE Power Energy Mag., vol. 1, no. 3, pp. 64–67, May/June 2003, and no. 4, pp. 70–73, July/Aug. 2003.

T.J. Blalock, "The first polyphase system," IEEE Power Energy Mag., vol. 2, no. 2, pp. 63–66, Mar./Apr. 2004.

C. Hering, "The Frankfort [Frankfurt] Electrical Congress—Description of the Lauffen-Frankfort [Lauffen-Frankfurt] Plant for the transmission of power—Electrical practice in Europe as Seen by an American—Lauffen-Frankfort [Lauffen-Frankfurt] transmission of power—Results of test," Elec. World, vol. 18, no. 13, pp. 232, 232–234, 234–235, 1891; vol. 19, no. 2, pp. 20–21, 1892.

M. von Dolivo-Dobrowolsky, "Electrical transmission of power by alternating currents," Elec. World, vol. 18, no. 13, pp. 268–269, 1891.

C.E.L. Brown, "Reasons for the use of the three-phase current in the Lauffen–Frankfort [Lauffen-Frankfurt] transmission," Elec. World, vol. 18, no. 19, p. 346, 1891.

C. Hering, "Comments on Mr. Brown's letter," Elec. World, vol. 18, no. 19, p. 346, 1891.

"Niagara to-day," Elec. Eng., vol. XIX, no. 350, pp. 127–128, Jan. 1895.

B.A. Behrend, "Tribute [to Tesla] of B.A. Behrend," Elec. World, vol. 69, no. 20, p. 981, 1917.

E.D. Adams, Niagara Power. History of the Niagara Falls Power Company 1886–1918. Evolution of its Central Power Station and Alternating Current System, Volume II Construction and Operation. Niagara Falls, N.Y. Privately printed for The Niagara Falls Power Company, MCMXVIII, 1927.

F. Hillebrand, "Zur Geschichte des Drehstroms," (Beginnings of three-phase alternating current), ETZ-A Elektrotechnische Zeitschrift Ausgabe A vol. 80, no. 13, pp. 409–421 and no. 14, pp. 453–461, 1959.

C.R. Wright, "100 Years of ac transmission, 1891 to 1991: Taming the West—With ac power," IEEE Power Eng. Rev., vol. 11, no. 3, pp. 7–9, Mar. 1991. Discussion in vol. 11, no. 6, pp. 32–34, June 1991.

J.R. Stewart, "History of electrical power, Cohoes and Niagara: Mills, canals, and hydropower," IEEE Power Eng. Rev, vol. 11, no. 6, pp. 30–31, June 1991.

G. Neidhöfer, "The evolution of the synchronous machine," ABB Rev., Supplement 1, Zurich. ABB Marketing Services LTD., pp. 1–11, 1992.

G. Neidhöfer, Michael von Dolivo-Dobrowolsky und der Drehstrom - Anfänge der modernen Antriebstechnik und Stromversorgung (Michael Von Dolivo-Dobrowolsky and the Three-Phase Alternating Current—At the Roots of Modern Drive Technology and Power Supply). Berlin: VDE Verlag, 2004.