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66-475: As Stuyvesant Barry reports in his biography of Laurens Hammond, Hammond himself acknowledged that his invention of the clock that was to bear his name was inspired by the success of Henry Warren's Telechron clocks. Upon discovering the Telechron technology, Hammond designed a motor that was synchronous, like Warren's, that is to say, it rotated at a speed that was tied to the frequency of the current supplied by

132-408: A shaded-pole type. Costs are an important parameter for starters. Rotor excitation is a possible way to resolve the issue. In addition, starting methods for large synchronous machines include repetitive polarity inversion of the rotor poles during startup. By varying the excitation of a synchronous motor, it can be made to operate at lagging, leading and unity power factor . Excitation at which

198-498: A belt operation by unskilled laborers. In addition, Hammond licensed his invention to other clock makers such as Waterbury, Sessions, and Ingraham. In 1932, the economic troubles of the Great Depression threatened the clock-making industry; about 150 clock companies went out of business. To make matters worse, Hammond's licensees discovered that Hammond's patent on his motor was invalid, due to an earlier German invention of

264-508: A brand: "Telechron" is the name used by a manufacturer of electric timers in Leland, North Carolina. Moreover, a company that spun off from one of Telechron's research labs in 1928 is still flourishing: Electric Time Company manufactures custom tower and post clocks in Medfield, Massachusetts. Electric Time is the only such company in the U.S. that still makes its own clock movements. From

330-411: A commercial point of view, it was the increased durability of batteries as well as the invention of the quartz movement that proved fatal to Telechron. From the point of view of the history of technology, however, another problem is more crucial: if the electric power grid is used as a system for the "distribution of time," as Warren himself wrote, then, in the case of a power failure, the clocks stop, and

396-401: A drive system can operate at exactly the same speed. The power supply frequency determines motor operating speed. Hysteresis motors have a solid, smooth, cylindrical rotor, cast of a high coercivity magnetically "hard" cobalt steel. This material has a wide hysteresis loop (high coercivity ), meaning once it is magnetized in a given direction, it requires a high magnetic field to reverse

462-410: A net lagging power factor, the presence of overexcited synchronous motors moves the system's net power factor closer to unity, improving efficiency. Such power-factor correction is usually a side effect of motors already present in the system to provide mechanical work, although motors can be run without mechanical load simply to provide power-factor correction. In large industrial plants such as factories

528-486: A rate locked to the line frequency since they do not rely on induction to produce the rotor's magnetic field. Induction motors require slip : the rotor must rotate at a frequency slightly slower than the AC alternations in order to induce current in the rotor. Small synchronous motors are used in timing applications such as in synchronous clocks , timers in appliances, tape recorders and precision servomechanisms in which

594-451: A reduction in their use, and the bell housing was eliminated, with only the metal strip above the coil remaining. This in itself, however, provided a loud buzz when the alarm was tripped (and was the basis of the alarm in all brands of alarm clocks for many years after the war). Post-war, very few Telechrons had bell alarms, and the bell had disappeared completely by 1960. Telechron was one of the first companies to introduce what became known as

660-448: A separate source or from a generator directly connected to the motor shaft. A permanent magnet synchronous motor and reluctance motor requires a control system for operating ( VFD or servo drive ). There is a large number of control methods for synchronous machines, selected depending on the construction of the electric motor and the scope. Control methods can be divided into: The PMSMs can also operate on open-loop control, which

726-413: A solid steel cast rotor with projecting (salient) toothed poles. Typically there are fewer rotor than stator poles to minimize torque ripple and to prevent the poles from all aligning simultaneously—a position that cannot generate torque. The size of the air gap in the magnetic circuit and thus the reluctance is minimum when the poles align with the stator's (rotating) magnetic field, and increases with

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792-436: A squirrel cage in the rotor for starting—these are known as line-start or self-starting. These are typically used as higher-efficiency replacements for induction motors (owing to the lack of slip), but must ensure that synchronous speed is reached and that the system can withstand torque ripple during starting. PMSMs are typically controlled using direct torque control and field oriented control . Reluctance motors have

858-447: A stationary armature and rotating field winding. This type of construction has an advantage over DC motor type where the armature used is of rotating type. Electric motors generate power due to the interaction of the magnetic fields of the stator and the rotor. In synchronous motors, the stator carries 3 phase currents and produces 3 phase rotating magnetic flux (and therefore a rotating magnetic field). The rotor eventually locks in with

924-457: A synchronous machine shows armature current as a function of field current. With increasing field current armature current at first decreases, then reaches a minimum, then increases. The minimum point is also the point at which power factor is unity. This ability to selectively control power factor can be exploited for power factor correction of the power system to which the motor is connected. Since most power systems of any significant size have

990-473: A synchronous motor connected to the current produced by the power plant, the other driven by a traditional spring and pendulum. The pendulum was adjusted twice a day in accordance with time signals received from the Naval Observatory. As long as the hands of the electric clock, powered by a 60 Hz synchronous motor, moved along perfectly with those of the "traditional" clock, the power produced by

1056-557: Is derived from the Greek words tele , meaning "far off," and chronos , "time," thus referring to the transmission of time over long distances. Founded by Henry Ellis Warren, Telechron introduced the synchronous electric clock , which keeps time by the oscillations of the alternating current electricity that powers it from the electric power grid . Telechron had its heyday between 1925 and 1955, when it sold millions of electric clocks to American consumers. Henry E. Warren established

1122-498: Is in operation, the speed of the motor is dependent only on the supply frequency. When the motor load is increased beyond the breakdown load, the motor falls out of synchronization and the rotor no longer follows the rotating magnetic field. Since the motor cannot produce torque if it falls out of synchronization, practical synchronous motors have a partial or complete squirrel-cage damper called an amortisseur winding to stabilize operation and facilitate starting. Because this winding

1188-417: Is operating at an AC supply frequency of 60 Hz. The number of pole-pairs is 6, so the synchronous speed is: The number of magnetic poles, p {\displaystyle p} , is equal to the number of coil groups per phase. To determine the number of coil groups per phase in a 3-phase motor, count the number of coils, divide by the number of phases, which is 3. The coils may span several slots in

1254-453: Is plugged in. Telechron motors are easily quieted and revived by carefully drilling 2 small holes that just puncture the surface, one on the large section, and one on the small section. A very light oil is injected, and then the small holes are carefully soldered shut. If a heavy oil is used, the clock may fail to keep accurate time until the motor becomes warm. Telechron alarm clocks are particularly popular with collectors. Until about 1940,

1320-408: Is similar to that of a synchronous alternator . The stator frame contains wrapper plate (except for wound-rotor synchronous doubly fed electric machines ). Circumferential ribs and keybars are attached to the wrapper plate. To carry the weight of the machine, frame mounts and footings are required. The synchronous stator winding consists of a 3 phase winding. It is provided with a 3 phase supply, and

1386-420: Is smaller than that of an equivalent induction motor and can overheat on long operation, and because large slip-frequency voltages are induced in the rotor excitation winding, synchronous motor protection devices sense this condition and interrupt the power supply (out of step protection). Above a certain size, synchronous motors cannot self-start. This property is due to rotor inertia; it cannot instantly follow

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1452-465: Is sometimes used for start-up thus enabling the position sensing operation. The synchronous speed of a synchronous motor is given: in RPM , by: and in rad·s , by: where: A single-phase , 4-pole (2-pole-pair) synchronous motor is operating at an AC supply frequency of 50 Hz. The number of pole-pairs is 2, so the synchronous speed is: A three-phase , 12-pole (6-pole-pair) synchronous motor

1518-421: The magnetic circuit of these machines needs to be able to concentrate the magnetic flux, typically leading to the use of spoke type rotors. Machines that use ferrite magnets have lower power density and torque density when compared with neodymium machines. PMSMs have been used as gearless elevator motors since 2000. Most PMSMs require a variable-frequency drive to start them. However, some incorporate

1584-441: The "snooze" alarm in the early 1950s. Synchronous motor A synchronous electric motor is an AC electric motor in which, at steady state , the rotation of the shaft is synchronized with the frequency of the supply current ; the rotation period is exactly equal to an integer number of AC cycles. Synchronous motors use electromagnets as the stator of the motor which create a magnetic field that rotates in time with

1650-644: The 1920s into the 1950s was not solely due to the technical advantages of their clocks, although all Telechron clocks were powered by successive versions of Henry Warren's synchronous motor. Rather, the Telechron company sought to produce clocks whose designs reflected one of the fundamental principles of the Art Deco movement: to combine modern engineering (including mass-production) with the beauty of simple geometric shapes. Thus, Telechron clocks are often considered genuine pieces of art—but art affordable by all, as thousands of them were made. The company employed some of

1716-539: The 1950s battery-operated clocks that weren't dependent on the power grid took market share, and in the 1960s the quartz clock replaced synchronous clocks. The problem of how to keep clocks synchronized with primary standards was solved with the radio clock , which receives time signals not through the electric grid, but from government time radio stations. There is a growing community of hobbyists who collect Telechron clocks. An antique Telechron clock will usually come to life immediately (though sometimes noisily) when it

1782-437: The angle between them. This creates torque that pulls the rotor into alignment with the nearest pole of the stator field. At synchronous speed the rotor is thus "locked" to the rotating stator field. This cannot start the motor, so the rotor poles usually have squirrel-cage windings embedded in them, to provide torque below synchronous speed. The machine thus starts as an induction motor until it approaches synchronous speed, when

1848-457: The company in 1912 in Ashland, Massachusetts . Initially, it was called "The Warren Clock Company," producing battery-powered clocks. These proved unreliable, however, since batteries weakened quickly, which resulted in inaccurate time-keeping. Warren saw electric motors as the solution to this problem. In 1915, he invented a self-starting synchronous motor consisting of a rotor and a coil, which

1914-625: The company was his invention of the Hammond organ . His first model, the Model A Console organ was released in 1935, year in which his company was renamed "The Hammond Organ Company" to reflect the new emphasis. The production of clocks was discontinued entirely in 1941. There is less literature on the Hammond clocks than on the Telechrons . Apart from some websites, such as the ones referred to in

1980-411: The dial whenever the power failed. This red dot alerted the consumer to the need to reset the clock (by obtaining the accurate time through the telephone, for example, or from a radio). Setting the clock would reset the indicator. The electric clock market grew rapidly in the 1930s, and Telechron's patented power interruption indicator gave his clocks an advantage over competing synchronous clocks, but by

2046-490: The economic potential of Warren's invention. When Warren retired in 1943, General Electric gradually absorbed Telechron into its operations. The clocks labeled "Telechron" on the dial, as well as those labeled "General Electric" (or both "General Electric" and "Telechron" on the dials) were both made in the Ashland, Massachusetts, factory. GE clocks had their own case, dial and hand designs, as well as model names and numbers, but

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2112-651: The electric company was uniform. In Electrifying Time , Jim Linz writes that "in 1947, Warren Master Clocks regulated over 95 percent of the electric lines in the United States." It is interesting to note, then, that the uniformity of alternating current in the United States, which was necessary in order to build large power grids, was initially ensured by a very traditional clock system. Furthermore, Henry Warren invented his master clock at first simply in order to guarantee that his synchronous clock motor would provide accurate time. The Telechron company's success from

2178-430: The finest designers of the time, such as Leo Ivan Bruce (1911–1973) and John P. Rainbault. In the evolution of their designs, Telechron clocks were a faithful mirror of their own time. Just as a clock like the "Administrator" (designed by Leo Ivan Bruce) reflected thirties aesthetics, so the "Dimension" had 1950s lines. Telechrons were relatively expensive compared to other clocks. In 1941, their most inexpensive alarm clock

2244-474: The frequency of the alternating current led not only to inaccurate time-keeping but, more seriously, to incompatible power grids in the United States, as power could not readily be transferred from one grid to another. In order to overcome these problems, Warren invented a "master clock," which he installed at the Boston Edison Company in 1916. This master clock had two movements, one driven by

2310-468: The individual consumers' Telechrons lose their connection with the master clock (and, by implication, with the time provided by the Naval Observatory). If there is a temporary power outage while the owner is out, the running clock will display the incorrect time when he returns. Warren, foreseeing this difficulty, provided his clocks with an "indicating device": a red dot that would appear on

2376-528: The interaction between synchronous motors and other, lagging, loads may be an explicit consideration in the plant's electrical design. where, here, When load is applied, torque angle δ {\displaystyle \delta } increases. When δ {\displaystyle \delta } = 90° the torque will be maximum. If load is applied further then the motor will lose its synchronism, since motor torque will be less than load torque. The maximum load torque that can be applied to

2442-469: The internal workings of both brands of clock were always the same Telechron type of movement. In addition to its association with GE, Telechron cooperated closely with one of America's most famous makers of traditional clocks, the Herschede company. Walter Herschede became interested in synchronous clocks in the 1920s, but did not want to risk the good name of his company by associating it too quickly with

2508-426: The magnetization. The rotating stator field causes each small volume of the rotor to experience a reversing magnetic field. Because of hysteresis the phase of the magnetization lags behind the phase of the applied field. Thus the axis of the magnetic field induced in the rotor lags behind the axis of the stator field by a constant angle δ, producing torque as the rotor tries to "catch up" with the stator field. As long as

2574-479: The material for the cases; glass crystals were phased out in favor of plastic ones; and the much less durable S rotor took the place of the H rotor. Nevertheless, the decline of the synchronous clock could not be stopped. GE sold the last of its former Telechron plants in 1979. After successive attempts to revive the business remained fruitless, it closed permanently in 1992. Nonetheless, even if Telechron's original operations have ceased, Telechron continues to exist as

2640-462: The motor must operate at a precise speed; accuracy depends on the power line frequency , which is carefully controlled in large interconnected grid systems. Synchronous motors are available in self-excited, fractional to industrial sizes. In the fractional power range, most synchronous motors are used to provide precise constant speed. These machines are commonly used in analog electric clocks, timers and related devices. In typical industrial sizes,

2706-558: The new technology. Thus, he founded the Revere Clock Company as a division of Herschede that would market clocks driven by Telechron motors. These motors, however, were housed in the elegant cases of mantel and grandfather clocks for which Herschede was known; moreover, these clocks were equipped with chimes. Telechron—now the "Clock and Timer Division" of GE—declined in the 1950s, mainly because batteries had become much more long-lived and reliable. Battery-powered clocks have

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2772-526: The notes, one may consult Spin to Start , the newsletter of the Synchronous Society, which was devoted to the collection of Hammond clocks. Only two issues have appeared, however: vol. 1, no. 1 (October 1996) and vol. 1, no. 2 (February 1998). [REDACTED] Media related to Hammond Clock Company at Wikimedia Commons Telechron Telechron was an American company that manufactured electric clocks between 1912 and 1992. "Telechron"

2838-410: The obvious advantage of not depending on the proximity of a power outlet, and do not require the often somewhat unattractive electric cable. Furthermore, the accuracy of the quartz clock superseded the principles of the synchronous motor. GE tried to respond to the declining market for Warren's technology by producing cheaper, less solidly manufactured clocks. Thus, plastic replaced bakelite or wood as

2904-428: The oscillations of the current. The rotor with permanent magnets or electromagnets turns in step with the stator field at the same rate and as a result, provides the second synchronized rotating magnet field. Doubly fed synchronous motors use independently-excited multiphase AC electromagnets for both rotor and stator. Synchronous and induction motors are the most widely used AC motors. Synchronous motors rotate at

2970-418: The overwhelming majority of Telechron alarm clocks had bell alarms. The entire mechanism was enclosed in a bell housing of steel. Atop the clock's coil was a metal strip that vibrated at 60 cycles per second when the alarm was tripped. This strip had a V-shaped arm attached to it, ending in a striker, which vibrated in turn against the bell housing. With the approach of war, restrictions on various metals required

3036-453: The power factor is unity is termed normal excitation voltage . The magnitude of current at this excitation is minimum. Excitation voltage more than normal excitation is called over excitation voltage, excitation voltage less than normal excitation is called under excitation. When the motor is over excited, the back emf will be greater than the motor terminal voltage. This causes a demagnetizing effect due to armature reaction. The V curve of

3102-488: The power grid. In this way, any clock operated by such a motor would run with great precision as long as the operators of the power grid kept the current's frequency constant. This had become possible since the introduction of the Warren master clock, an innovation of which Hammond took full advantage with his own invention. Hammond's motor, however, differed from Warren's in a number of respects: above all, it ran more slowly and

3168-459: The power line frequency to run the gear mechanism at the correct speed. Such small synchronous motors are able to start without assistance if the moment of inertia of the rotor and its mechanical load are sufficiently small. The motor accelerates from slip speed to synchronous speed during an accelerating half cycle of the reluctance torque. Single-phase synchronous motors such as in electric wall clocks can freely rotate in either direction, unlike

3234-413: The reluctance type, hysteresis motors are used where precise constant speed is required. Usually made in larger sizes (larger than about 1 horsepower or 1 kilowatt) these motors require direct current (DC) to excite (magnetize) the rotor. This is most straightforwardly supplied through slip rings . A brushless AC induction and rectifier arrangement can also be used. The power may be supplied from

3300-418: The resultant air-gap flux by the forward motion of the prime mover ". Motor action occurs if the field poles are "dragged behind the resultant air-gap flux by the retarding torque of a shaft load ". The two major types of synchronous motors are distinguished by how the rotor is magnetized: non-excited and direct-current excited. In non-excited motors, the rotor is made of steel. It rotates in step with

3366-405: The rotating magnetic field and rotates along with it. Once the rotor field locks in with the rotating magnetic field, the motor is said to be synched. A single-phase (or two-phase derived from single phase) stator is possible, but in this case the direction of rotation is not defined and the machine may start in either direction unless prevented from doing so by startup arrangements. Once the motor

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3432-538: The rotating stator field. A major advantage of the hysteresis motor is that since the lag angle δ is independent of speed, it develops constant torque from startup to synchronous speed. Therefore, it is self-starting and doesn't need an induction winding to start it, although many designs embed a squirrel-cage conductive winding structure in the rotor to provide extra torque at start-up. Hysteresis motors are manufactured in sub-fractional horsepower ratings, primarily as servomotors and timing motors. More expensive than

3498-406: The rotation of the stator's magnetic field. Since a synchronous motor produces no inherent average torque at standstill, it cannot accelerate to synchronous speed without a supplemental mechanism. Large motors operating on commercial power include a squirrel-cage induction winding that provides sufficient torque for acceleration and also serves to damp motor speed oscillations. Once the rotor nears

3564-422: The rotor "pulls in" and locks to the stator field. Reluctance motor designs have ratings that range from fractional horsepower (a few watts) to about 22 kW . Small reluctance motors have low torque , and are generally used for instrumentation applications. Moderate torque, multi-horsepower motors use squirrel cage construction with toothed rotors. When used with an adjustable frequency power supply, all motors in

3630-420: The rotor is below synchronous speed, each particle of the rotor experiences a reversing magnetic field at the "slip" frequency that drives it around its hysteresis loop, causing the rotor field to lag and create torque. The rotor has a 2-pole low reluctance bar structure. As the rotor approaches synchronous speed and slip goes to zero, this magnetizes and aligns with the stator field, causing the rotor to "lock" to

3696-422: The rotor is provided with a DC supply. DC excited motors require brushes and slip rings to connect to the excitation supply. The field winding can be excited by a brushless exciter. Cylindrical, round rotors, (also known as non-salient pole rotor) are used for up to six poles. In some machines or when a large number of poles are needed, a salient pole rotor is used. Most synchronous motor construction uses

3762-491: The rotor to create a constant magnetic field. The stator carries windings connected to an AC electricity supply to produce a rotating magnetic field (as in an asynchronous motor ). At synchronous speed the rotor poles lock to the rotating magnetic field. PMSMs are similar to brushless DC motors . Neodymium magnets are the most common, although rapid fluctuation of neodymium magnet prices triggered research in ferrite magnets . Due to inherent characteristics of ferrite magnets ,

3828-531: The same technology. In this situation, Hammond attempted to save his factory by starting the production of an electric bridge table . This proved to be nothing but a fleeting success. Hammond did finally manage to save his company in 1931 with a $ 75,000.00 contract from the Postal Telegraph Company, for putting their company name on large electric wall clocks. These clocks were to replace old key-wind clocks in railroad stations. What further saved

3894-479: The stator core, making it tedious to count them. For a 3-phase motor, if you count a total of 12 coil groups, it has 4 magnetic poles. For a 12-pole 3-phase machine, there will be 36 coils. The number of magnetic poles in the rotor is equal to the number of magnetic poles in the stator. The principal components of electric motors are the stator and the rotor. Synchronous motor and induction motor stators are similar in construction. The construction of synchronous motor

3960-429: The stator's rotating magnetic field, so it has an almost-constant magnetic field through it. The external stator field magnetizes the rotor, inducing the magnetic poles needed to turn it. The rotor is made of a high- retentivity steel such as cobalt steel. These are manufactured in permanent magnet , reluctance and hysteresis designs: A permanent-magnet synchronous motor (PMSM) uses permanent magnets embedded in

4026-425: The synchronous motor provides an efficient means of converting AC energy to work ( electrical efficiency above 95% is normal for larger sizes) and it can operate at leading or unity power factor and thereby provide power-factor correction. Synchronous motors fall under the category of synchronous machines that also includes synchronous generators. Generator action occurs if the field poles are "driven ahead of

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4092-451: The synchronous speed, the field winding becomes excited and the motor pulls into synchronization. Very large motor systems may include a "pony" motor that accelerates the unloaded synchronous machine before load is applied. Electronically controlled motors can be accelerated from zero speed by changing the frequency of the stator current. Small synchronous motors are commonly used in line-powered electric mechanical clocks or timers that use

4158-409: Was founded in 1928 to produce and market clocks that were equipped with Hammond's new motor. The Hammond clock factory manufactured more than 100 different clock models, some simple and cheap, others made from expensive materials such as marble and onyx. Hammond employed well-paid toolmakers who created sophisticated tools to stamp out the various components of his clocks, which could then be assembled in

4224-425: Was not self-starting. (Warren had patented his self-starting technology.) The latter Hammond did not consider to be a disadvantage; he believed that people would be misled by their clocks if they restarted automatically after a power outage. As Hammond's new clock motor was not self-starting, his clocks possessed a characteristic little knob on the back that one had to spin to start the motor. The Hammond Clock Company

4290-519: Was patented in 1918. A synchronous motor spins at the same rate as the cycle of the alternating current driving it. Synchronous electric clocks had been available previously, but had to be started manually. In later years, Telechron would advertise its clocks as "bringing true time," because power plants had begun to maintain frequency of the alternating current very close to an average of 60 Hz. But such constancy did not yet exist when Warren first experimented with his synchronous motors. Irregularities in

4356-438: Was the model 7H117 "Reporter," and it sold for $ 2.95, the equivalent of $ 30.00 in 2008 funds. But their beautiful design and amazing reliability assured a brisk market for them throughout the company's most prosperous years. As noted above, Henry Warren initially named his company "The Warren Clock Company." It became "Warren Telechron" in 1926. As early as 1917, General Electric acquired a strong interest in Telechron, realizing

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