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Self - Inductance. Faraday postulated that a magnetic field consists of lines of force surrounding the current-carrying conductor. Think of these lines as elastic bands that close on themselves. As the current increases and decreases, the bands expand and collapse about the conductor.
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Self - Inductance • Faraday postulated that a magnetic field consists of lines of force surrounding the current-carrying conductor. • Think of these lines as elastic bands that close on themselves. • As the current increases and decreases, the bands expand and collapse about the conductor. ECE 201 Circuit Theory I
Self – Inductance continued Compress for decreasing magnetic field (due to decreasing current). Faraday’s Law : the voltage induced into the conductor is proportional to the number of lines that cut the conductor. Expand for increasing magnetic field (due to increasing current). ECE 201 Circuit Theory I
Faraday’s Law λ is called the “flux linkage” and is measured in weber-turns ECE 201 Circuit Theory I
Magnetic field linking an N-turn coil ECE 201 Circuit Theory I
Permeance, P • Permeance describes the magnetic properties of the space occupied by the flux. • Linear for non-magnetic materials • Units are webers/ampere-turn. ECE 201 Circuit Theory I
Self - Inductance ECE 201 Circuit Theory I
Voltage Polarity • When i increases, di/dt is + and v is +. • Energy produces the magnetic field ECE 201 Circuit Theory I
Voltage Polarity • When i decreases, di/dt is - and v is -. • i is still + • Magnetic field collapses - + ECE 201 Circuit Theory I