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