Induction motor Across the line - reduced torque

Status
Not open for further replies.
Wow so this site pretty much goes over the Primary Resistor, Primary Reactor, Autotransoformer, and Part winding starting methods:

I have to read a bunch more to feel comfortable enough to venture off to actually try it.

Thank you for pointing me in the right direction.
 
No electronics? Does that Include vacuum tubes?

I wounder what we could do to control a squirrel cage motor with a couple of amplidynes and some old school analog electronics :LOL:
 
Joethemechanic said:
No electronics? Does that Include vacuum tubes?

I wounder what we could do to control a squirrel cage motor with a couple of amplidynes and some old school analog electronics :LOL:
Click to expand...
Believe it or not, some of the systems I get involved with still have the old ward Leonard WW2 systems.
 
W@ttson said:
Believe it or not, some of the systems I get involved with still have the old ward Leonard WW2 systems.
Click to expand...
About 2 years ago I was talking to one of the Pagnottis (Jeddo Coal, a big time mining co here) and he was looking for an amplidyne. I can't remember what it was for. It might have been for this

ak.jpg
 
W@ttson said:
480V yes.

For this particular case, no I can’t get a custom motor, but for the next time, absolutely!
Click to expand...

If you were running at 240V, then an ordinary dual voltage motor could be switched to the 480V configuration with contactors, effectively halving the applied voltage.

But this wouldn't work for 480V unless you use a non-standard motor.

Sorry, just throwing out random ideas at this point.

-Jon
 
230516-1627 EDT

W@attson:

Can you provide a speed-torque curve for your motor?

When I took a course in AC Machinery the book we used was by Bailey and Gault. Bailey was one of the pioneers in AC machinery. He was still alive when I took the class in 1955. I never met him. Gault was younger but had died before I took the course. So I had a different, but excellent teacher, J. G. Tarboux.

In said book is a chapter on Induction Motors. Page 185 has a plot of how the speed-torque varies with different rotor resistances. This plot of various rotor resistances shows maximum torque at various levels being the same. The lower the resistance the greater is the foldback in the curve, and the lower speed where this peak torque occurs.

A high inertia load on a low resistance rotor motor will take a longer time to accelerate, F = M * A.

To keep zero backlash during deceleration you need a motor drive torqure trying to accelearte the load greater than the frictional losses in the drive train. But obviously this torque needs to be as low as possible so as to not be accelerating the load. So obviously the speed torque curve needs to be low enough that it provides enough torque to keep backlash at zero, but not so high as to prevent the load from going to zero speed.

.
 
Gar,
If you looked at a chart showing multiple torque speed curves based on the rotor resistance, that was from a Wound Rotor Induction Motor, not a Squirrel Cage Induction Motor. A WRIM has been suggested as an option for the OP to explore, but it’s not a solution he can implement on this existing unit. You can’t change the torque-speed curve of a SCIM.
 
gar said:
230516-1627 EDT

W@attson:

Can you provide a speed-torque curve for your motor?

When I took a course in AC Machinery the book we used was by Bailey and Gault. Bailey was one of the pioneers in AC machinery. He was still alive when I took the class in 1955. I never met him. Gault was younger but had died before I took the course. So I had a different, but excellent teacher, J. G. Tarboux.

In said book is a chapter on Induction Motors. Page 185 has a plot of how the speed-torque varies with different rotor resistances. This plot of various rotor resistances shows maximum torque at various levels being the same. The lower the resistance the greater is the foldback in the curve, and the lower speed where this peak torque occurs.

A high inertia load on a low resistance rotor motor will take a longer time to accelerate, F = M * A.

To keep zero backlash during deceleration you need a motor drive torqure trying to accelearte the load greater than the frictional losses in the drive train. But obviously this torque needs to be as low as possible so as to not be accelerating the load. So obviously the speed torque curve needs to be low enough that it provides enough torque to keep backlash at zero, but not so high as to prevent the load from going to zero speed.

.
Click to expand...

acm.jpg

Title: Alternating-Current Machinery

Publisher: McGraw-Hill

Publication Date: 1951

Looks like The Bible
 
winnie said:
Would this application warrant the use of a custom wound motor?

Jon
Click to expand...

winnie said:
For this particular case, no I can’t get a custom motor, but for the next time, absolutely!
Click to expand...

If the motor selection has not already been made, it seems to me that a 2-speed "constant-torque" single winding motor could offer some advantages in this application. With such a motor, before nearing the stop at the end of travel, the high inertia load could be decelerated to 1/2 speed by having contactors select the "low speed" mode. At 1/2 speed the kinetic energy of the load will be reduced by 75% and the momentum by 50%. This should reduce the likelihood of a significant rebound from the stop. When the low speed is selected, the motor will provide regenerative braking and deliver current into its power source until the motor gets close to its synchronous RPM in 1/2 speed mode.

An alternative to reduce the motor volts-per-turn and heating:

If a custom motor was an option, a 9-lead connection to a 2-speed motor would allow the addition of the low speed configuration used in 2-speed "variable torque" motors. This consists of a wye connection of the three pairs of series connected windings which are configured in a delta in the low speed mode of a "constant torque" motor. When this additional connection is selected by contactors, it will reduce the volts-per-turn on the windings down to 58% of that in the "constant torque" low speed configuration, with a consequent reduction in current and heating. This second low-speed mode will have a reduced torque and might be selected after any possibility of a rebound is over, or before that if the rebound is sufficiently controlled using this lower torque level. Of course, this current reduction could also be done with a standard 2-speed "constant torque" motor by using external means such as an autotransformer, series impedances, etc.
 
230517-1558 EDT

Jraef:

The curves I referred to apply to all induction motors. If you do not provide a means to adjust the rotor resistance during operation of the motor, then the motor just follows the single curve that occurs for whatever its rotor resistance provides.

A high resistance rotor will not allow as much continuous steady state output power in a given package size because that power dissipation is all in the rotor. By adding slip rings to the armature, then that power dissipation can be outside of the motor.

.
 
cascade-connection-of-motor-768x381.png

Or this, or add as many motors as you like (think traction systems). Fir even more fun mix motors of different syncroness speeds
 
gar said:
230516-1627 EDT

W@attson:

Can you provide a speed-torque curve for your motor?

When I took a course in AC Machinery the book we used was by Bailey and Gault. Bailey was one of the pioneers in AC machinery. He was still alive when I took the class in 1955. I never met him. Gault was younger but had died before I took the course. So I had a different, but excellent teacher, J. G. Tarboux.

In said book is a chapter on Induction Motors. Page 185 has a plot of how the speed-torque varies with different rotor resistances. This plot of various rotor resistances shows maximum torque at various levels being the same. The lower the resistance the greater is the foldback in the curve, and the lower speed where this peak torque occurs.

A high inertia load on a low resistance rotor motor will take a longer time to accelerate, F = M * A.

To keep zero backlash during deceleration you need a motor drive torqure trying to accelearte the load greater than the frictional losses in the drive train. But obviously this torque needs to be as low as possible so as to not be accelerating the load. So obviously the speed torque curve needs to be low enough that it provides enough torque to keep backlash at zero, but not so high as to prevent the load from going to zero speed.

.
Click to expand...
The rotor bar Design is what you are referring to. Here is a paper on the different geometries of rotor bars and how it changes the speed torque curve:

 
Besoeker3 said:
Actually we, my company, produced a number of those. Also known as Static Kramers. Mostly these were in the MW 11kV range although we did a few at 3.3kV. Our version was called the ISK - Improved Static Kramer for improved power factor.
Click to expand...
The only cascades I've ever seen in real life were ones I did on my bench with small bridge crane motors just for an experiment. I read about them in one of my textbooks and wanted to try it
 
The 'modern' version of those cascade systems are called 'doubly fed induction motors'. You have a wound rotor machine. The stator is fed direct off the line. The _rotor_ is fed with a VFD. Very roughly the VFD is sized for the rotor loss power, not the full electrical input power to the machine.

-Jon
 
winnie said:
The 'modern' version of those cascade systems are called 'doubly fed induction motors'. You have a wound rotor machine. The stator is fed direct off the line. The _rotor_ is fed with a VFD. Very roughly the VFD is sized for the rotor loss power, not the full electrical input power to the machine.

-Jon
Click to expand...
I was wondering about electronic control of the rotor circuit. It's probably been 20+ years since I've done any work with wound rotor motors. Everything then was just resistance
 
Status
Not open for further replies.
Top