Effect of Windmilling on Motor Starting

[Besoeker]

Lee Bragg,

The method I proposed requires 3 diodes, a 2-pole DC contactor, and a zero-speed switch!

Phil Corso

Three diodes taking two lines and a flywheel diode across the inductive load?
No control of the current? And applying unregulated three hundred and some DC volts across an ac winding? So just the resistance to limit the current?
Don't try this at home.......

 

[mgookin]

It was the simpler; don't care which way it's turning. It's either turning or its not. If it's turning, stop it before you start it. You know you're starting from zero and we know how to do that!

 

[Besoeker]

It was the simpler;

Additional parts doesn't make it simpler.

 

[winnie]

http://forums.mikeholt.com/showthread.php?t=162470&page=4

The DOL starter with the right motor has to be about as uncomplicated as you can get.

By right motor, do you mean one that has sufficient rotor resistance to limit starting current, and is sized so that it can tolerate the requisite number of starts per hour when started from a 'windmilling' condition.

To the OP: given the requirements that other posters have described for tunnel ventilation, I wonder if there is a requirement for rapid reversal of the motors, eg. reversing a motor that is in operation at full speed, not simply windmilling. In this case, the acceleration time will be significantly longer than the acceleration time from stand-still. If this requirement exists then it might dominate motor sizing.

As a separate question: are the motors themselves already defined, and you are working on developing the control system...or are the motors part of what is being specified?

-Jon

 

[mgookin]

Additional parts doesn't make it simpler.

It was less parts. What was on the table before that was figure out which way it's turning to see if you want to stop it or not before you put the power on it. Less parts was to use a zero turn indicator to see if it's moving or not. If it's moving, brake it then start it. If not, just start it.

 

[hurk27]

Would the use of a 12 lead WYE start delta run motor help in a case like this? but if the air flow is strong enough it might just over come the ability of the WYE starting to reverse the windmilling motor?

 

[hurk27]

To bad you couldn't use DC motors but the cost would be too high, with a DC motor all you would need is to shunt the motor to keep it from windmilling, it would still turn but very slowly, to bad the windmilling couldn't be used to store energy for use by the system which could offset the cost of the DC motors? but then again it would get too complicated.

 

[Besoeker]

It was less parts. What was on the table before that was figure out which way it's turning to see if you want to stop it or not before you put the power on it. Less parts was to use a zero turn indicator to see if it's moving or not. If it's moving, brake it then start it. If not, just start it.

What was on the table from the OP was a DOL starter.

 

[Besoeker]

To bad you couldn't use DC motors but the cost would be too high, with a DC motor all you would need is to shunt the motor to keep it from windmilling, it would still turn but very slowly, to bad the windmilling couldn't be used to store energy for use by the system which could offset the cost of the DC motors? but then again it would get too complicated.

All possible. And all it would need is a regenerative (four quadrant) DC drive for the DC motor. It's a fairly standard item but, and there has to be some buts.....
It's still a lot more complex than a DOL starter with an AC motor.
And then there is that commutator which needs regular maintenance. That, in a tunnel, would be a real ballache.....

 

[Jraef]

Don't you think they just might carry a few spares in their inventory?

Yes, they do. That's the suspenders, using COTS motors is the belt.

 

[Besoeker]

Yes, they do. That's the suspenders, using COTS motors is the belt.

I'm not sure that many suppliers would keep 350hp motors on the shelf.
Expensive inventory.

 

[Phil Corso]

Ant-windmilling Circuit

Ant-windmilling Circuit

Besoeker... you are certainly the consummate 'PtP' (no, it's not an expletive!) I've ever encountered.

o Yes 3, or 6 if you prefer.

o Actually in my application, I wasn't concerned about windmiling direction, so I didn't use a commercial Zero-Speed switch. Instead I used a Hall-switch to detect that unit was rotating by counting "bolts" on a coupling!

Lee... let me know if addditional detail is required!

Phil Corso (cepsicon@aol.com)

 

[kwired]

I'm not sure that many suppliers would keep 350hp motors on the shelf.
Expensive inventory.

But the owner of the tunnel that potentially already has several of these blowers, may find it to be a good idea to have a spare or two on their own shelf.

 

[Besoeker]

Besoeker... you are certainly the consummate 'PtP' (no, it's not an expletive!) I've ever encountered.

Maybe not an expletive but neither do I imagine that it's a compliment. Perhaps you'd be kind enough to explain.

Yes 3, or 6 if you prefer.

With a six diodes in B6U configuration you'd get about 650Vdc from a 480Vac supply.
Would you really apply that to an AC motor winding? And live to tell the tale?

Actually in my application,

But in this case it isn't your application. It's a 350 hp motor.

 

[Besoeker]

But the owner of the tunnel that potentially already has several of these blowers, may find it to be a good idea to have a spare or two on their own shelf.

Quite.
See post #37.

 

[Phil Corso]

Besoeker... I've already given PtP definition to several members including moderators.

Phil

 

[Besoeker]

Besoeker... I've already given PtP definition to several members including moderators.

Phil

I'm not several members and I'm not a moderator.

 

[mivey]

I'm not several members and I'm not a moderator.

The expansion of the acronym and the surface definition is not really as revealing as is the underlying definition and intent. The acronym is used to caste distain upon those, who in the eyes of the user, "don't get it" and can't rise up to the user's perceived level of enlightenment.

Rather than interacting on an intellectual level the user labels the target and avoids engaging in something they consider to be beneath them. This allows the user to maintain their perceived level of enlightenment without actually having to test or improve said level. Its frequent use makes one prone to intellectual and social blindness to some degree.

 

[mivey]

The expansion of the acronym and the surface definition is not really as revealing as is the underlying definition and intent. The acronym is used to caste distain upon those, who in the eyes of the user, "don't get it" and can't rise up to the user's perceived level of enlightenment.

Rather than interacting on an intellectual level the user labels the target and avoids engaging in something they consider to be beneath them. This allows the user to maintain their perceived level of enlightenment without actually having to test or improve said level. Its frequent use makes one prone to intellectual and social blindness to some degree.

I forgot to mention that if I cast labels it is completely legitimate and justifiable.

 

[Open Neutral]

I'm trying to visualize something in my head.

First pass, assume the motor has a reduced voltage starter that limits the current to something safe for long than half a gnatsbreath, while the motor gets going.

Second pass, it's really a VFD accomplishing same.

What's the downside of same re: the "We don't know the motor's RPM at power up [where it could be [-900 RPM<->0<->+900] at any instant" problem?

It's been a long time since Jr. year AC Machines, and there must be lots I'm forgetting.