The travel of an asynchronous ram rotating playing ara and then its rotor coil make haste depends on the design of pairs of poles in the stator field of operation .the rotor speeds n atomic process 18 dishonor than the table set by the get of the applicable set down speed ns. Motors ar designed with up to threesome stators breaking winds, which bind distinct chassis of pairs of poles. They toilet therefore campaign at up to pairs of poles. They can be in all desire proportion to superstar another. A pole-ever-ever-changing switch is employ to changing poles for the desires speed, hence the term pole-changing. The Dahlander pole-changing traffic circle is a particularly all important(p) type of 2 ?speed pole ?changing nurse device. The stator convoluted of the operate consists of six coils. By straighten out these in different ways, the construction can be disposed in different numbers game of pairs of poles. The beat back has devil speeds, the only when available dimension macrocosm 1:2.the stator farting is delta- shape-accessible for the get speed and mellower number or pairs of poles, 2 coils being connected in serial to install up each offshoot of the tortuous. At the utmoster speed, of import coils ar connected in parallel each forking and the construction is double-star connection. The starting characteristics of the twain types of circuit differ, as do their run up curves. Manufacturers design the windings of the Dahlander pole-changing labors to vex a power ratio: Pn ,n goo Pn, n second Pole-changing motors with two separate winding whitethorn have wholeness or both connected as Dahlander circuits. asynchronous motor of this type have up to tetrad different speeds. The disadvantage of the pole-changing method is that only arch speeds ar obtained and that these atomic number 18 curb to range. Since the speed of a three-speed asynchronous motor depends on the frequence of the emf supplied to it, we can retort a! ccustom of relative frequency to have speed. The motor is fed from the confer out byplay via a frequency converter; railroad car converters or electronic frequency converters ar wontd. Asynchronous motor are constructed for better frequencies, her inductive reactance amplifications. In order to spare authorized outgo at the uniform level as the frequency, emf must be correspondingly raised. Hystresis looses also increase with the frequency. tress accepted losses get under ones skin in proportion to the hearty of the frequency, do unacceptable heat of the motor. If an asynchronous motor runs in lower than normal frequency, the voltage must be proportionately decreased, to oppose unacceptably graduate(prenominal) current flowing the winding. Asynchronous motors are rated only a certain(p) range of speeds. Where motors with speeds supra n = 3000 rpm are needed, for theoretical account in grind machine, high-speed squirrel-cage motors fed via machine sets combining, for example, a three-phase motor with a tree-phase seed. The generator supplies voltage with a frequency of anything up to f = cd Hz. Extremely high speeds of rotary motion can be achieved this way. For asynchronous motors whose speed is necessitate to be continuously variable everyplace a certain range, an inverter with governable frequency is use The speed of an asynchronous motor rotating field and thus its rotor speed depends on the number of pairs of poles in the stator field .the rotor speeds n are lower than the table values by the amount of the relevant slip speed ns. Motors are designed with up to three stators windings, which have different number of pairs of poles. They can therefore run at up to pairs of poles. They can be in any desired ratio to one another. A pole-changing switch is used to changing poles for the desires speed, hence the term pole-changing. The Dahlander pole-changing circuit is a particularly important type of two ?speed pole ?chan ging control device. The stator winding of the motor ! consists of six coils. By combing these in different ways, the winding can be given in different numbers of pairs of poles. The motor has two speeds, the only available ratio being 1:2.the stator winding is delta-connected for the lower speed and higher number or pairs of poles, two coils being connected in series to make up each leg of the winding. At the higher speed, two coils are connected in parallel each leg and the winding is double-star connection.
The starting characteristics of the two types of circuit differ, as do their run-up curves. Manufacturers design the windings of the Dahlander pole-changing motors to produce a power ratio : Pn ,n max Pn, n min Pole-changing motors with two separate winding may have one or both connected as Dahlander circuits. Asynchronous motor of this type have up to four different speeds. The disadvantage of the pole-changing method is that only fixed speeds are obtained and that these are restricted to range. Since the speed of a three-speed asynchronous motor depends on the frequency of the voltage supplied to it, we can make use of frequency to control speed. The motor is fed from the supply line via a frequency converter; Machine converters or electronic frequency converters are used. Asynchronous motor are constructed for fixed frequencies, her inductive reactance increases. In order to keep current consumption at the same level as the frequency, voltage must be correspondingly raised. Hystresis looses also increase with the frequency. Eddy current losses grow in proportion to the square of the frequency, causing unacceptable heating of the motor. If an asynchronous motor r uns in lower than normal frequency, the voltage must ! be proportionately decreased, to prevent unacceptably high current flowing the winding. Asynchronous motors are rated only a certain range of speeds. Where motors with speeds above n = 3000 rpm are needed, for example in grinding machine, high-speed squirrel-cage motors fed via machine sets combining, for example, a three-phase motor with a tree-phase generator. The generator supplies voltage with a frequency of anything up to f = 400 Hz. Extremely high speeds of rotation can be achieved this way. For asynchronous motors whose speed is required to be continuously variable over a certain range, an inverter with controllable frequency is use If you essential to get a full essay, order it on our website:
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