Motor vs transformer

[Hrushaabh]

What are the differences between motors and trasformers?
which one has higher efficiency?

 

[augie47]

here are a few of sites that will help explain each.

http://www.copper.org/applications/electrical/energy/trans_losses.html

http://www.engineeringtoolbox.com/electrical-motor-efficiency-d_655.html

http://www.copper.org/applications/electrical/energy/trans_efficiency.html

I think you will see that, as a rule, transformers are more efficient.

 

[coulter]

What are the differences between motors and trasformers? ...

I need some more data On what you are asking. I'm pretty sure your not looking for, "motors turn - xfm change voltage levels"

One could consider a motor a rotary transformer. The physics principles are similar.

...which one has higher efficiency?

Well you don't get much torque out of a transformer

Assuming you mean eff = Pout/Pin:
Some data I have seen rate motors at 93% and xfm at 97%. Generally speaking, to have that high an efficiency, both are at rated load.

edit spelling
carl

 

[augie47]

"Well you don't get much torque out of a transformer:wink: "

saw a 150 kva hooked up with "hv" to "lv" by mistake... it almost had torgue when energized.

 

[Lxnxjxhx]

"Economy of scale" also dictates that large things are more efficient than small things. One large 10 hp motor will be more efficient than 10 ea. 1 hp motors. Same rule for one of these little wall transformers that came in at 65% efficient.

Car ~ 100 hp/ton of payload
Truck ~ 10 hp/ton
Train ~ 1 hp/ton

 

[LarryFine]

Car ~ 100 hp/ton of payload
Truck ~ 10 hp/ton
Train ~ 1 hp/ton

So that's why we never see train drag-racing.

 

[Lxnxjxhx]

train drag-racing

train drag-racing

With some of the videos I've seen on TV, you may not have to wait long for this particular one.

Hmmmm. . . I think I'll go figure how many GE jet engines it would take to accelerate a train enough to have a respectable showing in a drag race. F=ma. Or is it e=ir? No, e=mc^2. Help me out here. . .

 

[RHJohnson]

Augie47 - Where did you see that - ! Color me scared - I don't want to ever go near that place or those electricians! I'm afraid to ask - but what was the high voltage level, and what were that former transformer ratings.

 

[mivey]

train help

train help

Help me out here. . .

The following probably is completely false since I know squat about jet engines but, since we are having fun, a = F/m. Let's call a 10 second quarter mile acceptable for a train.

Now let's pick a train, say a SD90MAC-H at 6000HP, 425000lbs (192777_kg), 83:16 gear, top speed of 75MPH. Assume we can fix the gearing, traction, constant acceleration, etc, and have perfect conditions.

With rough physics, a=(2*D-2*V0*t)/t^2 = (2*1320-2*0*10)/(10^2) = 26.4_ft/s^2. The final velocity is V = V0 + a*t = 0 + 26.4_ft/s^2*10_s = 264_ft/2 = 180_mph = 80.4672_m/s.

The energy change is 0.5*m*V^2 = 0.5*192777_kg*(80.4672_m/s)^2 = 624111887_kg*m^2/s^2(J) = 591544_Btu. This expended over 10 seconds yields a power of 83,695_HP

Since we have 6,000_HP already, we need an additional 77,695_HP. So, we need 92.831% of 62411887_N*m or a thrust of 34,873_lbf for 1320 feet.

One engine from an F-15 can produce 25-29000 pounds of thrust while an F-22 engine can produce 35000 lbs of thrust (1/2 of a 747 engine). A dragster jet engine might run 5-10000 lbs of thrust.

So, we could make a decent showing with one or two fighter jet engines, or about three to seven smaller jet engines.

If I completely messed this math up, feel free to run it again as I only went through it once and am too tired to do it again.

 

[spsnyder]

If you think of a transformer as an induction motor with a locked rotor, than it's easy to see that the transformer is more "efficient" as far as Pout/Pin. Look at the power-flow diagrams for induction motors and transformers. They both have core losses, resistance losses, air gap losses, "misc" losses. However the transformer doesn't have friction or windage losses since nothing is moving.

However if you base efficiency on actual work or torque, I would like to revise my answer....

Regards,

 

[Lxnxjxhx]

train

train

I pursued that for a while. Here's what I think.
A CrotchRocket (a.k.a. murdercycle) can pull 1 G at the handlebars.
A jet engine has a thrust/weight ratio of 2, therefore it can pull 2 G's, so if you have enough of them you could null out the weight of the thing that you are accelerating. A ratio of 1 for application would be useless if you want the dragster performance.

Somewhat related: If you weigh 150 pounds and can run up several flights of stairs (say, 60 vertical feet) in 15 seconds, you have put out 1.1 hp for that interval. It helps if you are 20 years old, like I was, once.