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RE: (ET) AC motor theory, dynamic braking, and regeneration

Steve wrote;

From:   Steven Naugler[SMTP:snaugler earthlink net]
Sent:   Tuesday, January 12, 1999 9:27 PM
To:     Larry Elie; elec-trak discussion list; Max Hall
Subject:        Re: (ET) AC motor theory, dynamic braking, and regeneration

;    In an AC circuit, having a low power factor does not theoretically
;increase power wasted, it only increases the current needed to deliver 
;power.  Where you waste power when power factor is low is due to your I
;squared R (resistive) losses.  If your current is needlessly higher, all 
;your voltage drops are higher and you have greater unwanted electric
;resistance heating.
;    If Dan's power factor is 0.8 (80%), a reasonable number for even a 
;inverter at high loads, the current through the AC parts of the circuit 
;be 1.25  (1 / 0.8 = 1.25) times higher than theoretically needed.  On the 
;side of the inverter you will have some DC current with probably some 
;ugly AC waveform superimposed on top of it.  All of this increases the I

Actually Steve, almost ALL inverters have really ugly waveforms....

;squared R losses, but as they are quite low to start, Dan probably won't 
;them in his application.  If I is 1.25 times theoretical, I squared is 
;times theoretical.  If, for example, Dan's resistive losses were 5% of 
;power delivered if his power factor were 1 (100%), then with a power 
;of 0.8 (80%) his resistive losses would be 1.56 times higher, or 7.81%  
(5 %
;x 1.56 = 7.81%).

I think I said 5 to 15%, which you quoted below.  The reason I gave a 
range is that 
the inverter waveform may look more like a square-wave than a sine-wave, 
on how well it was made.  Yes, they can indeed be that bad.  I'm not sure 
how to do 
the calculation without looking at both the current and voltage waveforms.

;    When we in industry are penalized for low power factor it is generally
;for three reasons:
;1.  We are subsidizing the power company's purchases of larger than
;theoretically needed transformers and other power delivery equipment.
;2.  Where installed equipment is at maximum capacity and not easily 
;(all of New York City) they make it very expensive to waste capacity.  If
;power factor in their transmission lines is 100% they can sell 25% more
;electricity than if their power factor is 80%.
;3.  Of the three,this is frequently of the lowest concern.  They don't 
;to waste electricity due to I squared R losses.
;    One last note to those of you who don't understand power factor.  I 
;not be giving an unsolicited lecture on power factor.  The GE stuff is DC
;where power factor has no significant effect.  My wife already thinks I
;spend to much time on this discussion group.  I'll pass for now.

;Steve Naugler

Sure, DC is negledgeable.  The WORST AC case is not the inductive loads, 
but the 
capacitve ones (large switching power supplies), at least as far as the 
ones I have 
seen.  You can't add a cheap capacitor to re-set the phase; you have to do 
correction in order to make a power supply that will work on normal 

-----Original Message-----
From: Larry Elie <lelie ford com>
To: elec-trak discussion list <elec-trak cosmos5 phy tufts edu>; Max Hall
<maxo iname com>
Date: Tuesday, January 12, 1999 10:55 AM
Subject: RE: (ET) AC motor theory, dynamic braking, and regeneration

>Steven Naugler replied to Dan in accurate detail about using AC with an
inverter for a battery vehicle.  Yes, it
>can be done, but I suspect there is one more thing to worry about;
power-factor.  An AC motor is not a
>pure resistive load.  It costs you extra power because of a phase angle.
There are 3 ways to deal with the
>problem:  1.) Ignore it, and have 5 to 15% of your batteries energy go out
without doing any work (actually,
>with most inverters, you already loose that much so you might not care).
2.)  Add a capacitor to delay
>things so the power factor is right under SOME load.  The down side is 
you will be varying the load
>and the power factor some.  This difference may be small.  3.)  Active
power factor (Nola or equiv.) correction.
>These are all doable.  BTW, for CONTROL reasons, the Ranger EV uses a AC
traction motor/generator, and
>yes, you can do regenerative breaking.  The circuit is complex and
patented.  The GE is fun, but you can do
>things a lot better today than when it was designed.
>Larry Elie