Rotating Magnetic Field

Rotating Magnetic Field - 1 EE 4420 Electric Machine...

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1 EE – 4420 Electric Machine Analysis Fall 2005 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: FF m 11 Θ a f a f = sin (1) (a) (b) X A 1 A 2 A stator (armature) rotor coil (winding) in the slot 1 2 4 3 magnetic flux magnetic flux represented by vector A 1 A 2 Coil Fig.1. Two-pole machine (a) with single coil (b) F Θ τ 12 3 4 1 (Pole pitch) (MMF) F 1 Fig.2 MMF distribution in the air-gap on the rotor circumference; τ – pole pitch
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2 If the coil is supplied with sinusoidal current the first harmonic of mmf is expressed by the function: () ( ) ( ) 11 ,s i n c o s m Ft F t ω Θ= Θ (2) The magnetic flux generated in the machine changes in time sinusoidally. Applying the geometrical transformation to equation (2) we get: 1 i n s i n 22 mm F t F t Θ + Θ + (3) It means, the alternating magnetic flux can be represented by two magnetic fluxes moving in opposite directions with the same speed and their amplitudes are half of alternating flux. Fig.3 shows the vector of alternating flux as the sum of two rotating fields drawn for two time instants t 1 and t 2 .
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This note was uploaded on 02/26/2012 for the course EE 4150 taught by Professor Wu during the Fall '10 term at LSU.

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Rotating Magnetic Field - 1 EE 4420 Electric Machine...

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