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Re: [TCML] Terry filters (speaker/motor load modeling)
In a message dated 1/2/08 10:12:59 A.M. Eastern Standard Time,
>A superconducting motor under a 1 HP load, even though it measures 0 DC
Ohms and some
>significant inductance under static (no load) conditions, must be modeled
as predominantly resistive
>to reflect the 1 HP load. The resistor value would change depending on the
magnitude of the
>mechanical load. If there were no load, after the rotor accelerates, the
resistive component would go
A superconducting motor would be modeled as predominately *inductance*.
A typical squirrel-cage AC induction motor has a "magnetizing current"
that it will always carry, at absolutely no load. This current is
significantly lower than the DC resistance of the windings would allow, since a
lightly-loaded motor is an inductive load. As the load on the motor increases, the
current in the rotor increases because the load torque is causing an increase in
"slip" between the rotating magnetic field from the stator windings and the
actual speed of the rotor. Hence, the magnetic lines of force cut across the
rotor faster and more frequently, thus increasing rotor current. This is
reflected in the stator current (motors are like transformers!).
Also like transformers, motors have a high inrush current, especially
I suspect motors might behave even more inductively than expected, since
the physical gap between the rotor and stator might cause a large "leakage"
One way to increase the power factor in a facility is to make sure all
the motors are running near peak load...
FWIW, I'd consider a woofer more of a permanent-magnet DC motor. And I
forgot to mention that another factor in woofer design involves keeping the
coil over the magnet core. Not only does the coil need to be over the magnet to
shed heat to it, but it acts like a "slide-choke" as it moves off the core.
Fidelity suffers as this occurs, but you need to move the voice coil a longer
distance as frequency lowers to put out the same amount of sound power.
What could be more Tesla-topical than AC induction motors?
Center for the Advanced Study of Ballistic Improbabilities
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