Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations TugboatEng on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
selecting a dream motor
- Thread starter Tmoose
- Start date
The 3 - 4X FLT is going to be problematic. What is the purpose of this requirement? Better yet, described yur specific application in more detail. No need to divulge anything ropietary, but gibe is an idea of what you are trying to accomplish, i.e. load, inertia, shock loading etc.
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more." Nikola Tesla
Read the Eng-Tips Site Policies at faq731-376
![[pirate]](/data/assets/smilies/pirate.gif "[pirate] [pirate]")
Member, [blue]P3[/blue]
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more." Nikola Tesla
Read the Eng-Tips Site Policies at faq731-376
Member, [blue]P3[/blue]![[rofl3]](/data/assets/smilies/rofl3.gif "[rofl3] [rofl3]")
OK here is some to work with
Will handle abuse
1. start immense overloads
2. keep immense overloads
3. Will always run in the direction I want regardless of how I connect (foolproof connections no reverse any 2 phase stuff)
4. Will always stay cool - no burnouts
5. Absolutely immune to water will run flooded
6. Does not care about ambient temp
7. Never needs maintenance
8. WIll tolerate low voltage
9. Will tolerate VFDs
LAST BUT NOT LEAST
One size fits all
AND costs only 5 bucks
AND fits in back pocket??
Dan Bentler
Will handle abuse
1. start immense overloads
2. keep immense overloads
3. Will always run in the direction I want regardless of how I connect (foolproof connections no reverse any 2 phase stuff)
4. Will always stay cool - no burnouts
5. Absolutely immune to water will run flooded
6. Does not care about ambient temp
7. Never needs maintenance
8. WIll tolerate low voltage
9. Will tolerate VFDs
LAST BUT NOT LEAST
One size fits all
AND costs only 5 bucks
AND fits in back pocket??
Dan Bentler
electricpete
Electrical
A standard NEMA design B induction motor has a minimum requirement for starting torque somewhere in the neighborhood 200% of FLT (I think there is a table which gives minimum starting torque as function of horsepower and speed). A 300hp motor then would have the starting torque you need. Probably not the least-cost option.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
electricpete
Electrical
Whoops. I think maybe that was breakdown torque, not locked rotor torque. I'll double check tomorrow.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
E-pete,
Design B can have 275% LRT, but only for small motor sizes (undefined). Usually 160% for most sizes. Design D provides 275% LRT, but is high slip/ medium efficiency, so you will pay for it constantly. A Design C motor could give you 220% starting torque, but I have never seen one off-the-shelf above 75HP.
Tmoose.
To provide that kind of starting torque you need to go with a Design B motor, oversized to 300HP to get starting torque (Locked Rotor Torque) of 320% of your 150HP running torque without having to sacrifice long term running eficiency. Don't worry about the oversizing, the motor will only draw as much power as it needs for the load.
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more." Nikola Tesla
Read the Eng-Tips Site Policies at faq731-376
Member, [blue]P3[/blue]
Design B can have 275% LRT, but only for small motor sizes (undefined). Usually 160% for most sizes. Design D provides 275% LRT, but is high slip/ medium efficiency, so you will pay for it constantly. A Design C motor could give you 220% starting torque, but I have never seen one off-the-shelf above 75HP.
Tmoose.
To provide that kind of starting torque you need to go with a Design B motor, oversized to 300HP to get starting torque (Locked Rotor Torque) of 320% of your 150HP running torque without having to sacrifice long term running eficiency. Don't worry about the oversizing, the motor will only draw as much power as it needs for the load.
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more." Nikola Tesla
Read the Eng-Tips Site Policies at faq731-376
Member, [blue]P3[/blue]A series, or maybe compound, DC machine would give you the starting torque you want, and the power and speed are right in the ballpark for this kind of motor. You must consider the downsides of increased maintenance because of the brushgear, and that the wound rotor is inherently less durable than the squirrel cage rotor from an induction machine. The cost of a DC machine and controlgear will probably exceed the cost of an oversized induction machine plus its control gear. The DC machine will almost certainly be a custom design; the induction machine will be pretty much of the the shelf.
One for the old-timers (who I am catching up!): does anyone still make wound rotor induction machines? This starting torque should be achievable with a WRIM, should it not?
----------------------------------
One day my ship will come in.
But with my luck, I'll be at the airport!
One for the old-timers (who I am catching up!): does anyone still make wound rotor induction machines? This starting torque should be achievable with a WRIM, should it not?
----------------------------------
One day my ship will come in.
But with my luck, I'll be at the airport!
ScottyUK,
Yes, and yes, and bravo for keeping the concept alive, I should have mentioned it. My only problem with WRIMs is that breakdown torque can be low, but then again, he didn't mention that as an issue. Efficiency is low on them as well, but again he didn't say that it was going to run a long time, only that it was only going to start very occasionally. I still wish we had more info.
I hate DC now, can you tell from the fact that I never mention it? You are right though. It's just that every DC motor I've had to have worked on lately has become a hassle. I can't find a decent motor shop that knows what they are doing with them. All the good guys that knew anything about them are retiring, and the young guys are not taught about them any more.
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more." Nikola Tesla
Read the Eng-Tips Site Policies at faq731-376
Member, [blue]P3[/blue]
Yes, and yes, and bravo for keeping the concept alive, I should have mentioned it. My only problem with WRIMs is that breakdown torque can be low, but then again, he didn't mention that as an issue. Efficiency is low on them as well, but again he didn't say that it was going to run a long time, only that it was only going to start very occasionally. I still wish we had more info.
I hate DC now, can you tell from the fact that I never mention it? You are right though. It's just that every DC motor I've had to have worked on lately has become a hassle. I can't find a decent motor shop that knows what they are doing with them. All the good guys that knew anything about them are retiring, and the young guys are not taught about them any more.
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more." Nikola Tesla
Read the Eng-Tips Site Policies at faq731-376
Member, [blue]P3[/blue]I love DC! It forces you to do the design right because it is so damned unforgiving of sloppy design and poor manufacture. It is becoming a minority interest to the controlgear suppliers, so components are getting expensive and hard to find. DC is hard to beat for the emergency run-down systems fed from the turbine battery - simple and very reliable, if rather crude and brutal. We're lucky that this region has a long history of steelmaking and mining - there are still a lot of motor shops with experience of maintaining DC machines who can do a first-class job.
----------------------------------
One day my ship will come in.
But with my luck, I'll be at the airport!
----------------------------------
One day my ship will come in.
But with my luck, I'll be at the airport!
- Thread starter
- #13
Thanks for the help guys.
Its a pony motor for start-up and occasional modest speed adjustment around 1800 rpm.
The big starting torque requirement is based on the break-away torque of the driven apparatus which currently uses basic hydrodynamic sleeve bearings.
Most of the time the pony is just spinnin'.
Its a pony motor for start-up and occasional modest speed adjustment around 1800 rpm.
The big starting torque requirement is based on the break-away torque of the driven apparatus which currently uses basic hydrodynamic sleeve bearings.
Most of the time the pony is just spinnin'.
I hope you are starting a turbine or another mechanically driven system. If it is another larger electric motor you will not really be able to occasionally add-in a motor on a common shaft for "modest speed adjustment" because in all likelyhood, it would just look like another load to your big motor.
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more." Nikola Tesla
Read the Eng-Tips Site Policies at faq731-376
Member, [blue]P3[/blue]
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more." Nikola Tesla
Read the Eng-Tips Site Policies at faq731-376
Member, [blue]P3[/blue]
raisinbran
Electrical
Tmoose,
Another option would be to use an induction motor with a fluid (hydro-dynamic) coupling. This allows the motor to be started at almost no load, so it comes up to speed rapidly. If the coupler is sized and filled properly, the use of a fluid coupler allows you to have full breakdown torque at zero speed (load speed, not motor speed).
Another advantage is they they serve as somewhat of a shock absorber clutch to isolate the motor from jam situation. As with anything hydraulic, there is more maintenance, but if sized properly and cooled properly, it might not be too bad.
They slip between 2 and they percent, so you are giving up some system efficiency.
Good luck,
Raisinbran
Another option would be to use an induction motor with a fluid (hydro-dynamic) coupling. This allows the motor to be started at almost no load, so it comes up to speed rapidly. If the coupler is sized and filled properly, the use of a fluid coupler allows you to have full breakdown torque at zero speed (load speed, not motor speed).
Another advantage is they they serve as somewhat of a shock absorber clutch to isolate the motor from jam situation. As with anything hydraulic, there is more maintenance, but if sized properly and cooled properly, it might not be too bad.
They slip between 2 and they percent, so you are giving up some system efficiency.
Good luck,
Raisinbran
LionelHutz
Electrical
I'd talk to a motor manufactor about a custom motor. Since it's a starting motor they can trade off full speed characteristics to get a higher starting torque.
Probably design D then, but I'm still curious about your statement of "... occasional modest speed adjustment around 1800 rpm." What did you mean by this?
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more." Nikola Tesla
Read the Eng-Tips Site Policies at faq731-376
Member, [blue]P3[/blue]
"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more." Nikola Tesla
Read the Eng-Tips Site Policies at faq731-376
Member, [blue]P3[/blue]
DAVIDSTECKER
Mechanical
Design "D" is the way to go.
Locked Rotor and Break Down Torque are a minium 270%
I use them them on almost all of our machines.
A simple contactor style starter works fine.
I believe ours come with class "H" insulation with is compatable with VFD's.
Your mileage may vary.
Check all this out to you own satisfaction.
Locked Rotor and Break Down Torque are a minium 270%
I use them them on almost all of our machines.
A simple contactor style starter works fine.
I believe ours come with class "H" insulation with is compatable with VFD's.
Your mileage may vary.
Check all this out to you own satisfaction.
- Thread starter
- #19
"I hope you are starting a turbine or another mechanically driven system. If it is another larger electric motor you will not really be able to occasionally add-in a motor on a common shaft for "modest speed adjustment" because in all likelyhood, it would just look like another load to your big motor"
"but I'm still curious about your statement of "... occasional modest speed adjustment around 1800 rpm." What did you mean by this? "
------------------------
This will be a pony motor for an Illudiom Pew36 Explosive Space Modulator Synchonous Condenser
"but I'm still curious about your statement of "... occasional modest speed adjustment around 1800 rpm." What did you mean by this? "
------------------------
This will be a pony motor for an Illudiom Pew36 Explosive Space Modulator Synchonous Condenser
LOL, Marvin the Martian. Funny. I guess I deserved that.Tmoose said:
I wasn't trying to pry, I was genuinely concerned that you were trying to do something with an electric motor without realizing that you can't. It happens all the time with you ME's. EE's get stuck trying to sort out your messes because we don't get to see the project until after you are done. I won't ask again, sorry.
And you left the 'r' out of synchronous.
- Status
Similar threads
- Question
- Question