ECE 441 1
Interaction of Magnetic Fields(Motor Action)
• Look at adjacent current-carrying conductors– Currents in opposite directions– Flux “bunching” between the conductors– Force of repulsion acts to separate the conductors
ECE 441 2
Interaction of Magnetic Fields(Motor Action)
– Currents in the same direction– Flux in space between conductors in “opposite”
directions– Force of attraction acts to pull the conductors together
ECE 441 3
Elementary Two-Pole Motor
• Rotor core with 2 insulated conductors in “slots”• A stationary magnet – the “stator”
ECE 441 4
Current-Carrying Conductor in a Magnetic Field
ECE 441 5
Current-Carrying Conductor in a Magnetic Field
• Current-carrying conductor perpendicular to the B-field
ECE 441 6
Magnitude of the force on the conductor in a Magnetic Field
• Magnitude of the mechanical force on the conductor is
Where F = mechanical force (N)
B = flux density in the stator field (T)
= the effective length of the rotor conductor
I = current in the rotor conductor (A)
effectiveF Bl I
effectivel
ECE 441 7
Conductor “skewed” to the B-fieldby angle
= effective length of the rotor conductor (m)effectivel
(sin )effectivel l
ECE 441 8
Single-Loop Rotor CoilCarrying a Current
Situated in a Two-Pole Field
ECE 441 9
Torque produced by the 2-conductor couple
2D
T Fd 2D effective
T Bl Id
ECE 441 10
Elementary Two-Pole Generator
ECE 441 11
Voltage induced in the coil, e
• Flux through the coil window is sinusoidal
• Φ = Φmaxsin(ωt)
• Voltage induced in coil,e• e = N(dΦ/dt)
• e = NωΦmaxcos(ωt)
• Emax = ωNΦmax
• Emax = 2πfNΦmax
• Erms = 4.44fNΦmax
ECE 441 12
Directions of induced voltage and current
• Develop CCW counter-torque
• “Bunching” must occur at the top of coil side B and the bottom of coil side A
• Coil current is CCW as viewed from south pole