Principle of DC Generator . Principle of DC Generator. The same principle applies. Generator operation is based on the principle of electromagnetic induction. Electric motors and generators. Every motor is a generator. This is the principle of a dynamic microphone. Evaluating and applying myriad motor technologies. Understanding AC induction, permanent magnet and servo motor technologies: OPERATION, CAPABILITIES AND CAVEATS. 13.4 Reluctance motor.Induction motor - Wikipedia, the free encyclopedia. Three- phase totally enclosed fan- cooled (TEFC) induction motor with end cover on the left, and without end cover to show cooling fan. In TEFC motors, interior losses are dissipated indirectly through enclosure fins mostly by forced air convection. An asynchronous motor type of an induction motor is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding. An induction motor can therefore be made without electrical connections to the rotor as are found in universal, DC and synchronous motors. An asynchronous motor's rotor can be either wound type or squirrel- cage type. Three- phasesquirrel- cage asynchronous motors are widely used in industrial drives because they are rugged, reliable and economical. Single- phase induction motors are used extensively for smaller loads, such as household appliances like fans. Although traditionally used in fixed- speed service, induction motors are increasingly being used with variable- frequency drives (VFDs) in variable- speed service. VFDs offer especially important energy savings opportunities for existing and prospective induction motors in variable- torque centrifugal fan, pump and compressor load applications. Squirrel cage induction motors are very widely used in both fixed- speed and variable- frequency drive (VFD) applications. Variable voltage and variable frequency drives are also used in variable- speed service. Note rotor air circulation vanes. Many such motors have a symmetric armature, and the frame may be reversed to place the electrical connection box (not shown) on the opposite side. History. Tesla applied for U. S. In April 1. 88. Now to go into the details of the operating principle of DC motor its important that we have a. Commutation in DC Machine or Commutation in DC Generator or Motor. The Simple DC Motor: A Teacher’s Guide. 2 The Anatomy of the Motor. The basic principle behind the simple DC motor is that wires that carry Royal Academy of Science of Turin published Ferraris's research on his AC polyphase motor detailing the foundations of motor operation. George Westinghouse, who was developing an alternating current power system at that time, licensed Tesla. Westinghouse employee C. Scott was assigned to assist Tesla and later took over development of the induction motor at Westinghouse. Lamme developed a rotating bar winding rotor. Kennelly was the first to bring out full significance of the letter . Whereas a synchronous motor's rotor turns at the same rate as the stator field, an induction motor's rotor rotates at a slower speed than the stator field. The induction motor stator's magnetic field is therefore changing or rotating relative to the rotor. This induces an opposing current in the induction motor's rotor, in effect the motor's secondary winding, when the latter is short- circuited or closed through an external impedance. The currents in the rotor windings in turn create magnetic fields in the rotor that react against the stator field. Due to Lenz's Law, the direction of the magnetic field created will be such as to oppose the change in current through the rotor windings. The cause of induced current in the rotor windings is the rotating stator magnetic field, so to oppose the change in rotor- winding currents the rotor will start to rotate in the direction of the rotating stator magnetic field. The rotor accelerates until the magnitude of induced rotor current and torque balances the applied load. Since rotation at synchronous speed would result in no induced rotor current, an induction motor always operates slower than synchronous speed. As the speed of the rotor drops below synchronous speed, the rotation rate of the magnetic field in the rotor increases, inducing more current in the windings and creating more torque. The ratio between the rotation rate of the magnetic field induced in the rotor and the rotation rate of the stator's rotating field is called slip. Under load, the speed drops and the slip increases enough to create sufficient torque to turn the load. For this reason, induction motors are sometimes referred to as asynchronous motors. The simplest three- phase machine has three pole pairs (total 6 stator poles), each pair connected to one of the phases of the 3- phase supply (red, green, blue), and arranged evenly around the stator. In a 4- pole 3- phase machine (4 pole- pairs, so for three phases it is 4 x 3 = 1. This is illustrated above right. The illustration on the left is of a 2- pole machine (2 pole- pairs, so for three phases it is 2 x 3 = 6 poles). Since the short- circuited rotor windings have small resistance, a small slip induces a large current in the rotor and produces large torque. Suitable for most low performance loads such as centrifugal pumps and fans, Design B motors are constrained by the following typical torque ranges. As the load torque increases beyond breakdown torque the motor stalls. Starting. A single phase induction motor requires separate starting circuitry to provide a rotating field to the motor. The normal running windings within such a single- phase motor can cause the rotor to turn in either direction, so the starting circuit determines the operating direction. In certain smaller single- phase motors, starting is done by means of a shaded pole with a copper wire turn around part of the pole. The current induced in this turn lags behind the supply current, creating a delayed magnetic field around the shaded part of the pole face. This imparts sufficient rotational field energy to start the motor. These motors are typically used in applications such as desk fans and record players, as the required starting torque is low, and the low efficiency is tolerable relative to the reduced cost of the motor and starting method compared to other AC motor designs. Larger single phase motors are split- phase motors and have a second stator winding fed with out- of- phase current; such currents may be created by feeding the winding through a capacitor or having it receive different values of inductance and resistance from the main winding. In capacitor- start designs, the second winding is disconnected once the motor is up to speed, usually either by a centrifugal switch acting on weights on the motor shaft or a thermistor which heats up and increases its resistance, reducing the current through the second winding to an insignificant level. The capacitor- run designs keep the second winding on when running, improving torque. A resistance start design uses a starter inserted in series with the startup winding, creating reactance. Self- starting polyphase induction motors produce torque even at standstill. Available squirrel cage induction motor starting methods include direct- on- line starting, reduced- voltage reactor or auto- transformer starting, star- delta starting or, increasingly, new solid- state soft assemblies and, of course, VFDs. The current distribution within the rotor bars varies depending on the frequency of the induced current. At standstill, the rotor current is the same frequency as the stator current, and tends to travel at the outermost parts of the cage rotor bars (by skin effect). The different bar shapes can give usefully different speed- torque characteristics as well as some control over the inrush current at startup. In wound rotor motors, rotor circuit connection through slip rings to external resistances allows change of speed- torque characteristics for acceleration control and speed control purposes. Speed control. Applications such as electric overhead cranes used DC drives or wound rotor motors (WRIM) with slip rings for rotor circuit connection to variable external resistance allowing considerable range of speed control. However, resistor losses associated with low speed operation of WRIMs is a major cost disadvantage, especially for constant loads. In many industrial variable- speed applications, DC and WRIM drives are being displaced by VFD- fed cage induction motors. The most common efficient way to control asynchronous motor speed of many loads is with VFDs. Barriers to adoption of VFDs due to cost and reliability considerations have been reduced considerably over the past three decades such that it is estimated that drive technology is adopted in as many as 3. Note the interleaving of the pole windings and the resulting quadrupole field. The stator of an induction motor consists of poles carrying supply current to induce a magnetic field that penetrates the rotor. To optimize the distribution of the magnetic field, the windings are distributed in slots around the stator, with the magnetic field having the same number of north and south poles. Induction motors are most commonly run on single- phase or three- phase power, but two- phase motors exist; in theory, induction motors can have any number of phases. Many single- phase motors having two windings can be viewed as two- phase motors, since a capacitor is used to generate a second power phase 9. Single- phase motors require some mechanism to produce a rotating field on startup. Cage induction motor rotor's conductor bars are typically skewed to reduce noise. Rotation reversal. In the case of three phase, reversal is carried out by swapping connection of any two phase conductors. In a single- phase split- phase motor, it is achieved by changing the connection between the primary winding and the start circuit. Single- phase split- phase motors that are designed for specific applications may have the connection between the primary winding and the start circuit connected internally so that the rotation cannot be changed. Also, single- phase shaded- pole motors have a fixed rotation, and the direction cannot be changed. Power factor. For economic and other considerations, power systems are rarely power factor corrected to unity power factor. There is existing and forthcoming legislation regarding the future mandatory use of premium- efficiency induction- type motors in defined equipment. For more information, see: Premium efficiency and Copper in energy efficient motors. Steinmetz equivalent circuit.
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