Copyright 2013 Princeton University Press.

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1 o part of this book may be distributed, 84 Four tubes would be demagnetized and the changing magnetic field would induce a current in the coils. ext, the valve was opened, and steam (which was 100 C) would circulate inside the tubes and lower their temperature. This cooling process permitted the magnetic field to be restored in the iron tubes, and again, the changing magnetic field would induce another current in the coils. ince heating and cooling would induce currents moving in opposite directions, Tesla s pyromagnetic generator produced alternating current. Tesla regarded this pyromagnetic generator as a great invention and energetically worked on it from the fall of 1886 to the late summer of In all likelihood, he encountered problems in getting a sufficient temperature differential between heating and cooling. In order to generate a significant amount of electricity, the temperature of the core would have to rise and fall dramatically; if the core retained its latent heat, then little electricity would have been generated. Tesla did apply for a patent for this invention, but it was not granted. Distressed that he was not able to perfect this invention, Tesla feared that Peck and Brown might abandon him just as Vail and Lane had done in Rahway. However, Peck had ample confidence in Tesla and instead encouraged him to keep inventing. As it became clear that the pyromagnetic generator was not going to work, Tesla recalled, I met Mr. Peck just at the door of the building in which he had his office, and he spoke to me in a very kind way and said, ow do not be discouraged that this great invention of yours is not panning out right; you may bring it to a success after all. Perhaps it would be good if you would switch to some other of your ideas and drop this for a while. I have had an experience that this is a very good plan. I came back encouraged. 22 Learning to Use Two Out- of- phase Currents Taking Peck s advice, Tesla shifted his attention from the pyromagnetic generator to electric motors. He now returned to the ideal that had come to him in Budapest five years earlier: a motor with a rotating magnetic field (see Chapter 2). As a first step toward achieving this ideal, Tesla had to test his hunch that several alternating currents could produce a rotating magnetic field. He had thought a great deal Carlson_FIAL.indd 84

2 o part of this book may be distributed, Mastering Alternating Current 85 about how several alternating currents might be combined, but he had never tried them in practice. Tesla began by modifying the Weston DC dynamo in the lab so that it could produce two, three, or four separate alternating currents. 23 For his first experiments, he used a large laminated ring for the stator, similar to the one in his trasbourg motor. Rather than have a single winding around the ring as he did at trasbourg, Tesla now divided the winding into four separate coils, one in each quadrant. Tesla had the AC generator deliver two separate currents to coils on opposite sides of the ring (Figure 4.3). For the motor s rotor, he balanced a shoe polish tin on a pin in the center of the ring. To Tesla s delight, the rotating magnetic field caused the tin can to spin. 24 With this motor, Tesla had finally figured out how to combine alternating currents to create a rotating magnetic field in the motor s stator. To do so, the currents delivered to each pair of coils had to be out of phase with one another. In the case of two currents, while one current was at its maximum positive value, the other was at its maximum negative value. If one thinks of the alternating currents as sine waves, then one can say that these two currents are said to be out of phase by 90. ow understanding the importance of having the currents out of phase, Tesla could build a full- scale electric motor using the rotating magnetic field that he had envisioned in Budapest. The Rise of Alternating Current in the Late 1880s Thrilled with this breakthrough motor, Tesla invited Brown, his technically minded patron, to come and see a demonstration in the late summer of But as Brown watched the tin can spin in this prototype, Tesla now faced the challenge of convincing his patrons that his rotating magnetic field could be used as the basis of a practical, commercial AC motor. Why should they put money into a spinning tin can? While it may seem obvious to us to develop an AC motor, it was not so to electrical experts in To understand why this was the case, we need to discuss the situation in the electrical industry in the mid-1880s. Carlson_FIAL.indd 85

3 o part of this book may be distributed, 86 Four (a) Motor X 1 lip Rings Generator B X 2 A A B X 3 X 4 ide view of generator (b) Maximum Positive Current Flow I Zero Current II Maximum egative Current Flow Figure 4.3. Tesla s AC motor in Like most electrical engineers, Tesla used a combination of stationary electromagnetic coils (called the stator) and rotating electromagnetic coils (called the rotor) to convert motion into electric current and vice versa in his generator and motor. Diagram (a) shows how Tesla used four wires (X 1, X 2, X 3, X 4 ) to connect his motor to an AC generator. As shown in the side view, the generator s stator consisted of two coils (, ) and its rotor consisted of two coils mounted at right angles to each other. This generator produced two separate alternating currents that were delivered to the motor via two pairs of slips rings. The two currents traveled to the motor over the four wires and each current energized one pair of coils in the motor s stator (either AA or BB). The rotor in the motor is grey rectangle inside the four coils, but in his 1887 experiments, he used a round shoe-polish tin. Diagram (b) shows how the two separate alternating currents (I, II) were 90 degrees out of phase with each other, meaning that when one was at its maximum, the other was at zero. The images below the current graph show how the magnetic field in the motor s stator rotated as the currents rose and fell over time, with the arrow marked turning in a clockwise direction. As the magnetic field rotated in the motor, it induced an opposing magnetic force in the rotor, causing the rotor to turn. ote that the rotor is shown in the motor in diagram (a) but is not included in the smaller images in diagram (b), since it would be hard to show both the rotor and the rotating magnetic field. Carlson_FIAL.indd 86

4 o part of this book may be distributed, Mastering Alternating Current 87 On the one hand, Peck and Brown were probably comfortable with Tesla investigating motors because of the growing discussion in electrical circles about using motors in central stations. In the mid- 1880s, as the number of central stations grew and the utility industry became more competitive, central station operators became interested in expanding their customer base by adding motor service. While they would continue to provide electricity for lighting at night, central station operators saw motors as the means by which they could now sell power to factories and streetcar lines during the day. In response, electrical manufacturing firms added motors to their product lines, and by 1887 there were fifteen firms in the field with a combined output of ten thousand motors. 25 And if central stations could use motors to distribute power to factories, then perhaps a new efficient motor would allow Peck and Brown to distribute power from their ambitious ocean-steam scheme. 26 On the other hand, Peck and Brown were highly suspicious of Tesla s ideas about developing an AC motor since nearly all of the central stations in the United tates in the mid- 1880s were using DC, not AC. 27 In the late 1870s, a few electrical inventors in France as well as Elihu Thomson in America had experimented with using AC in their arc- lighting systems. Alternating current was attractive to these inventors since it permitted them to use a rudimentary transformer in order to solve the basic problem of how to get a single dynamo to power several arc lights at once; this was what electricians in the 1870s called the subdivision of the electric light. However, once Charles Brush of Cleveland introduced his DC arc- lighting system with an improved dynamo and regulator, American electricians switched to developing DC systems. Using DC, entrepreneurs were able to establish central stations for arc and incandescent lighting in dozens of American cities. 28 In Europe, though, AC was not forgotten, and inventors there improved the transformer; by winding two different coils on a single iron core, they found they could raise or lower the voltage of alternating current, and they quickly started using this new device in a variety of ways. For instance, in London in 1883, Lucien Gaulard and John Gibbs used one of the first transformers to connect both arc and different incandescent lights in series to a single large generator. 29 About the same time in Budapest, the engineers Tesla had met at Ganz and Carlson_FIAL.indd 87

5 o part of this book may be distributed, 88 Four Company Zipernowski, Bláthy, and Déri (ZBD) saw AC as a way of developing an incandescent lighting system that could serve a wider area. By having their generator produce high- voltage AC, they found they could distribute power over longer distances using small copper wires. To protect customers from the high voltage, they used a transformer to step down the voltage before the current came into homes and shops. Within a few years, the ZBD system was being used to light several European cities. Both the Gaulard and Gibbs and ZBD systems employed single- phase AC since that was all that was needed to secure the desired voltage change. 30 The work in Europe on AC transformers was quickly appreciated by astute American electrical entrepreneurs. During a trip abroad in 1885, Charles Coffin of Thomson- Houston learned about the ZBD system and, upon his return, urged Thomson to resume his work on AC. In 1886, Edison agents in Europe warned that they were competing against Ganz and Company for lighting contracts, and they convinced the Edison organization to secure an option on the American patent rights for the ZBD system. 31 But the American entrepreneur most intrigued by the AC transformer was George Westinghouse ( ). Educated in his father s machine shop in chenectady, ew York, Westinghouse possessed a unique mix of technical genius and business acumen. ot only was Westinghouse able to develop air brakes and improved signal systems for the railroads, he was equally skilled at running the companies needed to manufacture and market these innovations on a large scale. In 1884, Westinghouse became interested in electric lighting, initially as a way of diversifying his Union witch and ignal Company. As a first step, Westinghouse hired William tanley Jr., who had patented an incandescent lamp and self- regulating dynamo. At first, Westinghouse simply intended to develop a DC system similar to that of Edison, but in the spring of 1885 he became intrigued by Gaulard and Gibbs s AC transformer system after reading about it in the journal Engineering. 32 ensing that there would be limited returns from developing one more DC system, Westinghouse decided to strike out in an entirely new direction. In particular, he suspected that AC could be used to establish central stations in municipalities that the Edison organization could not serve. Because of the high costs of its generators and copper distribution network, the Edison organization Carlson_FIAL.indd 88

6 o part of this book may be distributed, Mastering Alternating Current 89 could sell systems only to towns and cities in which there was a densely populated downtown; for an Edison central station to be profitable, it needed to be located where it could serve dozens of homes and businesses. Westinghouse believed that with AC, one could achieve economies of scale; by employing transformers, one could step up the voltage, distribute power across a wider region, and hence serve more customers. His AC system would be designed to be profitable in towns and cities in which the population was dispersed. Once he saw the potential for AC, Westinghouse moved decisively. He dispatched an associate, Guido Pantaleoni, to Europe to secure an option on the Gaulard and Gibbs system. In the summer of 1885, Westinghouse ordered several Gaulard and Gibbs transformers shipped to his factory in Pittsburgh, and he asked tanley to design an AC incandescent lighting system. 33 Working in a small laboratory in Great Barrington, Massachusetts, tanley developed a practical design for a transformer and confirmed the idea that transformers should be connected to the generator in parallel, not in series as Gaulard and Gibbs had done. To demonstrate the value of his transformer, tanley strung wires in trees along the streets of Great Barrington to deliver AC to homes and businesses in March Building on tanley s demonstration system, Westinghouse installed its first commercial AC system in Buffalo, ew York, the following ovember. Determined to keep up with Westinghouse, Thomson- Houston installed an AC system at the Lynn Electric Light Company in May 1887, and by year s end, Thomson- Houston had installed another twenty- two systems. 35 The electrical engineering community followed with interest the rapid development of AC lighting systems during While AC transformers had received only passing mention in Electrical World s annual review of the state of the art in January 1887, the journal regarded the development of lighting systems using transformers as one of the most important breakthroughs in January The electrical fraternity was fascinated with AC, not because they were certain that it was the technology of the future but because they saw a serious gap between the ideal and the real. Yes, ideally, AC should permit central stations to distribute power to a larger number of customers, but realistically this had yet to be achieved. As things stood by the end of 1887, AC presented both a commercial opportunity and significant technical problems and risks. Although Carlson_FIAL.indd 89

7 o part of this book may be distributed, 90 Four transformers could step the voltage up and down, engineers at Westinghouse and Thomson- Houston found it difficult to design an efficient transformer. Other critics were concerned about the costs of large AC power stations. Westinghouse claimed that a major advantage of AC was that one could erect a large plant on the outskirts of a city that could generate electricity cheaply. Familiar with the difficulties of raising capital to build stations, both Edison and many central station operators believed that large AC plants would cost too much money to build and the interest charges on the investment would eliminate any operating profits. 37 Yet another worry was safety. Edison and his associates had spent a great deal of time trying to identify better insulating materials for their low- voltage system, and they simply did not believe that Westinghouse could safely protect people from high- voltage shocks. 38 And finally, several commentators pointed out that the AC systems put forward by Westinghouse and Thomson- Houston were not as convenient or versatile as the DC systems; both companies lacked a meter for measuring how much electricity was used by each individual consumer as well as a motor for providing power to factories and streetcars. After completing a thorough study of the pros and cons of AC, Edison summed up the problems with AC by remarking that it was simply not worth the attention of practical men. 39 The Egg of Columbus Peck and Brown were well aware of these trends in the electrical industry. They knew that while there was growing interest in electric motors, no one was sure that the future belonged to AC. Hence, while Peck and Brown encouraged Tesla to investigate electric motors, they were not keen to have him work on an AC motor. AC, for all they knew, might just be a passing fad interesting, yes, but too difficult to perfect. Perhaps it would be better if Tesla focused on a DC motor for which there was a ready market. After several discouraging conferences with Peck and Brown to discuss his plans for an AC motor, Tesla realized that he needed a dramatic demonstration. It was not enough to show Brown a shoe Carlson_FIAL.indd 90