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Unformatted text preview: ROTATING MAGNETIC FIELD 1. Magnetic field in the machine with single-phase winding Two-pole 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 air-gap (angle Θ ) is described by rectangular wave as shown in Fig.2. Its first harmonic is described by the function: F F m 1 1 Θ Θ af af = sin (1) The mmf is responsible for magnetic flux generation according to formulae: ( 29 ( 29 1 1 sin m m F R Θ Φ Θ = (1.a) where R m – is magnetic resistance (reluctance) of the magnetic circuit (along the flux Φ ) (a) (b) X A 1 A 2 A Stator (armature) Rotor Coil (winding) in the slots 1 2 4 3 Magnetic flux lines Φ Magnetic flux axis A 1 A 2 Coil Fig.1. Two-pole 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 Θ Θ , sin cos a f af af = ϖ (2) The magnetic flux generated in the machine changes in time sinusoidally. Applying the geometrical transformation to equation (2) we obtain: 1 F Θ τ 1 2 3 4 1 (Pole pitch) (MMF) F 1 Fig.2 MMF distribution along air-gap on the rotor circumference; τ – pole pitch F t F t F t m m 1 1 1 1 2 1 2 Θ Θ Θ , sin sin a f a f a f =- + + ϖ ϖ (3) For the magnetic flux: ( 29 ( 29 ( 29 1 1 1 1 1 , sin sin 2 2 m m t t t ϖ ϖ Φ Θ = Φ Θ - + Φ Θ + (3.a) It means the alternating magnetic flux can be represented by two magnetic fluxes moving...
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This note was uploaded on 02/06/2012 for the course EE 4002 taught by Professor Scalzo during the Fall '06 term at LSU.
- Fall '06