early electric motors
Faraday's electromagnetic experiments, 1821 The first electric motors were simple electrostatic devices, described in experiments by Scottish monk Andrew Gordon and American experimenter Benjamin Franklin in the 1740s. The theoretical principle behind it, Coulomb's law, was discovered by Henry Cavendish in 1771, but has not yet been published. The law was discovered independently in 1785 by Charles-Augustin de Coulomb, who published it and is now widely known and his name. [4] The electrochemical cell [5] invented by Alessandro Volta in 1799 made it possible to generate a continuous current. After the discovery of this interaction between currents and magnetic fields, known as the electromagnetic interaction by Hans Christianrsted in 1820, much progress was soon made. It took André-Marie Ampère just a few weeks to develop the first formula for electromagnetic interaction and to propose Ampère's force law, which describes the interaction of electric current and magnetic field. mechanical force. In 1821, Michael Faraday demonstrated the effects of rotational motion for the first time. A free-hanging wire was dipped into a mercury bath where a permanent magnet (PM) was placed. When current is passed through the wire, the wire rotates around the magnet, indicating that the current creates a tight circular magnetic field around the wire. [7] Such motors are usually demonstrated in physical experiments, substituting salt water for (toxic) mercury. Barlow's wheels were an early improvement on that Faraday demonstration, although these and similar homopolar motors were not suitable for practical use until the end of the century.
"Electromagnetic Self-Rotor" by Jedlik, 1827 (Museum of Applied Arts, Budapest). Historic motors still work well today.
James Joule showing Kelvin an electric motor at the Hunterian Museum in Glasgow in 1842
In 1827, the Hungarian physicist nyos Jedlik began experimenting with electromagnetic coils. After Jedlik solved the technical problem of continuous rotation with the invention of the commutator, he called his early device an "electromagnetic self-rotor." Although they were only used for teaching, in 1828 Jedrick demonstrated the first device containing the three main components of a practical DC motor: the stator, rotor and commutator. The device does not use permanent magnets because the magnetic fields of the stationary and rotating components are generated only by the current flowing through their windings.
DC motor
British scientist William Sturgeon invented the first commutator DC motor capable of rotating machinery in 1832. Following the Sturgeon's work, American inventor Thomas Davenport built a commutator-type DC motor, which he patented in 1837. The motor runs at 600 revolutions per minute and powers the power tool and printing press. Due to the high cost of primary batteries, the electric motor was not a commercial success, and Davenport went bankrupt. Several inventors followed Sturgeon to develop DC motors, but they all ran into the same battery cost issue. With no power distribution system available at the time, there was no actual commercial market for these motors.
After many other more or less successful attempts with relatively weak rotating and reciprocating devices, the Prussian Moritz von Jacobi created the first real rotating electric motor in May 1834. It produces an extraordinary mechanical output. His motorcycle set a world record, which Jacobi improved four years later in September 1838. His second moto was powerful enough to drive a 14-person boat on a wide river. Also in 1839/40, other developers managed to make motors of similar, then higher performance.
In 1855, Jedlik built a device capable of doing useful work using principles similar to those used by his electromagnetic spin-wing. That same year, he built an electric car model.
A major turning point came in 1864, when Antonio Pacinotti first described the toroidal armature (although it was originally conceived in a DC generator (ie, generator)). This feature has symmetrically grouped coils that are closed to each other and connected to the bars of a commutator whose brushes provide a nearly unfluctuating current. The first commercially successful DC motors followed the development of Zénobe Gramme, who in 1871 reinvented Pacinotti's design and adopted some of Werner Siemens' solutions.
The benefits to the DC motor derive from the reversibility of the motor, which was announced by Siemens in 1867 and discovered through Pacinotti's observations came to 1869 when Graham accidentally proved it, at the Vienna World's Fair of 1873, when he put the two Each of these DC devices is within 2 km of each other, using one of them as a generator and the other as an electric motor.
The drum rotor was introduced in 1872 by Friedrich von Hefner-Alteneck of Siemens and Halske to replace Pacinotti's ring armature, thereby increasing machine efficiency. [6] Laminated rotors were introduced the following year by Siemens & Halske, resulting in reduced iron losses and higher induced voltages. In 1880, Jonas Wenstrm provided the rotor with slots to accommodate the windings, further improving efficiency.
In 1886, Frank Julian Sprague invented the first practical DC motor, a sparkless device that maintained a relatively constant speed under variable loads. Around this time, Sprague's other electrical inventions greatly improved the power distribution performance of the grid (work done prior to Thomas Edison's tenure), allowing power from electric motors to return to the grid, via overhead Wires and trolley poles power the trolleys and provide the control system for electrical operation. This led Sprague to invent the first electric trolley system using electric motors in Richmond, Virginia in 1887–88, an electric elevator and control system in 1892, and an electric subway with independently powered centrally controlled cars. The latter was first installed in Chicago in 1892 by the South Side Elevated Railroad, where it was colloquially known as the "L". Sprague's electric motor and its related inventions generated interest and found widespread use in industrial electric motors. The development of electric motors with acceptable efficiency has been delayed for decades due to a failure to recognize the critical importance of the air gap between the rotor and stator. Efficient designs have relatively small air gaps. For the same reason, the St. Louis car, long used in classrooms to illustrate the principles of motion, is extremely inefficient and doesn't look like a modern car.
Electric motors have revolutionized the industry. Industrial processes are no longer limited by power transmission using shafts, belts, compressed air or hydraulics. Instead, each machine can be equipped with its own power source, which can be easily controlled while in use and improve power transfer efficiency. Electric motors used in agriculture remove human and animal muscle power from tasks like handling grain or pumping water. The use of electric motors in the home reduces heavy labor in the home and enables higher standards of convenience, comfort and safety. Today, electric motors consume more than half of the electricity produced in the United States.
AC motor
In 1824, French physicist Franois Arago proposed the existence of a rotating magnetic field, known as the Arago rotation, by manually opening and closing a switch, which Walter Baily demonstrated in 1879 as the first primitive induction motor. During the 1880s, many inventors attempted to develop viable AC motors [31], as the advantages of AC motors in high voltage transmission over long distances were offset by the inability to run on AC motors.
In 1885, Galileo Ferraris invented the first AC commutatorless induction motor. Ferraris improved on his first designs by producing more advanced units in 1886. In 1888, the Royal Academy of Sciences in Turin published Ferraris' detailed study of the basis for the operation of electric motors, but at the time concluded that "a device based on this principle cannot be of any commercial significance as an electric motor."
The possible industrial development was conceived by Nikola Tesla, who invented his self-contained induction motor in 1887 and patented it in May 1888. That same year, Tesla presented his paper on the AIEE of a new system for AC motors and transformers as described in three patents of two-phase four-stator pole motor types: one with a four-pole rotor forming a non-self-starting reluctance motor, and the other with The wound rotor constitutes a self-starting induction motor, and the third type is a true synchronous motor, which respectively provides excitation DC power to the rotor windings. However, a patent filed by Tesla in 1887 also described a short-circuit rotor induction motor. George Westinghouse had acquired the rights from Ferraris ($1,000) and immediately bought Tesla's patents ($60,000, plus $2.50 per horsepower car sold until 1897 paid in 2010),[32] hired Tesla to develop the electric motor, and commissioned CF Scott to help Tesla; however, Tesla left elsewhere in 1889. [Excessive citations] It was found that the constant speed AC induction motor was not suitable for streetcars,[31] but Westinghouse engineers successfully retrofitted it to power a mining operation in Telluride, Colorado in 1891. [53][54][55] Westinghouse realized its first practical induction motor in 1892 and developed a family of polyphase 60 Hz induction motors in 1893, but these early Westinghouse motors were built with wound rotors two-phase motor. BG Lamme subsequently developed the spinning rod wound rotor. [45]
In staunchly promoting the development of three-phase, Mikhail Dolivo-Dobrovolsky invented the three-phase induction motor in 1889, which is both a squirrel rotor and a wound rotor type with a starting varistor, and in 1890 invented the three-arm transformer. Between AEG and Maschinenfabrik Oerlikon, Doliwo-Dobrowolski and Charles Eugene Lancelot Brown developed larger models, a 20 hp squirrel cage and a 100 hp wound rotor with a starting varistor. These were the first three-phase asynchronous motors suitable for practical operation. Winstrom has been developing similar three-phase machines since 1889. At the International Electrotechnical Exhibition in Frankfurt in 1891, the first long-distance three-phase system was successfully demonstrated. It is rated at 15 kV and stretches 175 km from Laufen Falls on the Neckar. The Lauffen power station consists of a 240 kW 86 V 40 Hz alternator and a step-up transformer, while at the exhibition a step-down transformer powers a 100 hp three-phase induction motor that powers an artificial waterfall, representing the original transformer's transfer. energy source. ] Three-phase induction is now used in the vast majority of commercial applications. However, he claimed that Tesla's electric motors were impractical due to two-phase pulsations, prompting him to stick to his three-phase work.
In 1891, GE began to develop the three-phase asynchronous motor [45] by 1896, GE and Westinghouse signed a cross-licensing agreement for the design of the bar-winding rotor, later known as the cage rotor. Improvements to the induction motor stemmed from these inventions and innovations, so that the 100-horsepower induction motor now has the same installed dimensions as the 7.5-horsepower motor of 1897.
components
Motor rotor (left) and stator (right)
Rotor[edit]
Main article: Rotor (electric)
In an electric motor, the moving part is the rotor, which rotates the shaft to transmit mechanical power. The rotor typically contains conductors that carry currents that interact with the stator's magnetic field to create a force that rotates the shaft. Alternatively, some rotors carry permanent magnets, while the stators hold the conductors.
bearing
The rotor is supported by bearings that allow the rotor to rotate about its axis. The bearings are in turn supported by the motor housing. The motor shaft extends through the bearing to the outside of the motor, where the load is applied. Because the force of the load is applied outside the outermost bearing, the load is suspended. [59]
stator
Main article: Stator
The stator is the fixed part of the electromagnetic circuit of the motor and usually consists of windings or permanent magnets. The stator core consists of many thin metal sheets called laminations. Laminations are used to reduce the energy losses that would result if a solid core were used.
air gap
The distance between the rotor and stator is called the air gap. Air gaps have a significant impact and are usually as small as possible, as large air gaps can have a strong negative impact on performance. It is the main source of low power factor for motor operation. The excitation current increases as the air gap increases. Therefore, the air gap should be minimized. In addition to noise and losses, small gaps can also cause mechanical problems.
Salient pole rotor
Winding[edit]
Main article: Winding
A winding is a wire placed in a coil, usually wrapped around a laminated soft ferromagnetic core, to form poles when energized.
Motors come in two basic field pole configurations: salient and non-salient. In a salient-pole machine, the magnetic field of the poles is created by windings wound on the poles below the pole faces. In non-salient pole or distributed field or circular rotor machines, the windings are distributed in pole face slots. [60] A shaded-pole motor has a coiled portion of a pole that retards the phase of the magnetic field of that pole.
The conductors of some electric motors consist of thicker metal, such as metal strips or sheets, usually copper, or aluminum. These are usually driven by electromagnetic induction.
commutator
Main article: Commutator (electric)
Small DC motor for toys and its commutator
A commutator is a mechanism used to switch the input of most DC motors and some AC motors. It consists of slip ring segments insulated from each other and from the shaft. The armature current of the motor is supplied through stationary brushes in contact with the rotating commutator, which causes the required current reversal and as the rotor rotates from pole to polePower the motor in the best possible way. [61][62] In the absence of this current reversal, the motor will brake to a stop. Externally commutated induction and permanent magnet motors are replacing electromechanical commutated motors, given the improved technology in the fields of electronic controllers, sensorless control, induction motors, and permanent magnet motors.
Motor Supply and Control
Motor power
As mentioned above, DC motors are usually supplied by slip ring commutators. The commutation of the AC motor can be achieved using a slip ring commutator or external commutation, and it can be of a fixed-speed or variable-speed control type, and it can also be a synchronous or asynchronous type. General purpose electric motors can run either AC or DC.
motor control
By adjusting the DC voltage applied to the terminals, DC motors can run at variable speeds.
AC motors, usually running at fixed speed, are powered either directly from the grid or through a motor soft starter.
AC motors operating at variable speed are powered by various power inverters, variable frequency drives or electronic commutator technologies.
The term electronic commutator is often associated with self-commutated brushless DC motor and switched reluctance motor applications.
