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Unformatted text preview: ROTATING MAGNETIC FIELD 1. Magnetic field in the machine with singlephase winding Twopole machine with single coil (phase) is shown in Fig.1. If supplied by dc. current the magnetic flux does not change in time. The mmf distribution along the machine airgap (angle ) is described by rectangular wave as shown in Fig.2. Its first harmonic is described by the function: F F m 1 1 af af = sin (1) The mmf is responsible for magnetic flux generation according to formulae: ( 29 ( 29 1 1 sin m m F R = (1.a) where R m is magnetic resistance (reluctance) of the magnetic circuit (along the flux ) (a) (b) X A 1 A 2 A Stator (armature) Rotor Coil (winding) in the slots 1 2 4 3 Magnetic flux lines Magnetic flux axis A 1 A 2 Coil Fig.1. Twopole machine (a) with single coil (b) If the coil is supplied with sinusoidal current the first harmonic of mmf is expressed by the function: F t F t m 1 1 , sin cos a f af af = (2) The magnetic flux generated in the machine changes in time sinusoidally. Applying the geometrical transformation to equation (2) we obtain: 1 F 1 2 3 4 1 (Pole pitch) (MMF) F 1 Fig.2 MMF distribution along airgap on the rotor circumference; pole pitch F t F t F t m m 1 1 1 1 2 1 2 , sin sin a f a f a f = + + (3) For the magnetic flux: ( 29 ( 29 ( 29 1 1 1 1 1 , sin sin 2 2 m m t t t =  + + (3.a) It means the alternating magnetic flux can be represented by two magnetic fluxes moving...
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 Fall '06
 Scalzo
 Flux

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