Variable Freq. Drives

[Besoeker]

And I respectfully suggest your numbers are better than mine:smile:

I suppose being still in it after 40 years...well, you can't get it too much wrong to survive - particularly in the current economic climate.

For sure, I get concerned and sometimes even stressed.
I take technical and commercial responsibility and risk for many of our projects.
At what point do you decide the margin isn't enough? Could we have offerd a better solution? Do we want to take a hit on the basis of future business opportunities?
Did we miss some major cost?
Can the customer pay?

Amazing that I still have a full head of hair.
:wink:

 

[weressl]

That's the way I see it. Pump manufacturers have been designing pumps for 150? years, and do pretty well at it.

They take their closest pump, trim the impeller to match the specified process. That's where the pump affinity laws come from - and they work well. As you alluded, sometimes the simplest, cost effective solution is mechanical - not high tech electrical.

Not necessarily so. Look at where the pumping efficieny goes WITH the impeller and compare it to the ASD lifecycle cost, THEN make the decision. The pumps have not changed for 150 years. Are you suggesting that they are the perfect solution and there is no technological future for anything else or for improvement? The fact is that the pump manufacturers focus pretty little on energy efficeny. ASD has long passed the stage of being 'high-tech' electrical, it is a commodity item. Ir are you still playing 45's?:smile:

Yes. Wasn't there a thread a bit back talking about how all of the refrigeration vfd controls in a large store were generally turned off cause they couldn't get them to work right - or they would break and the repair costs weren't worth it? Makes one wonder about the life cycle costs.

The local folks could care less about MAKING them work. It seems like that Corporate influenced the design for efficieny, but they failed to introduce controls that would maintain their usage. You are making statements on insufficent information. But those staements - without insufficent data - does not have to be always negative, just like the weavers in Manchester destroyed the machines did NOT stop technological evolution.

I don't think so. Like everything else, one must do the engineering to get a cost effective, low maintenance, system that meets the customer's spec.

Absolutely. SO why didn't you use the same logic above?

cf[/quote]

 

[weressl]

VFD's reduce maintenance and prolong the life of the motor and pump?

Bes - Have you seen any evidence this is true?

cf

Absolutely, so do soft starts. Bearings' life and maintenance cycle depends on rpm*load; reduce either and you prolong both. Temperature reduction will prolong insulation and lubricant life. Reduced mechanical shock, during start, will prolong bearing life and insulation life. Reduced mechanical load also reduces material stress and consequent stress aging and failure.

Elementary my dear Watson.:smile:

 

[weressl]

Amazing that I still have a full head of hair.
:wink:

Can we give it a tug?:grin:

 

[Besoeker]

Can we give it a tug?:grin:

Paiinful.
But if that what floats your boat....

This what you will have to work with....

 

[weressl]

Paiinful.
But if that what floats your boat....

This what you will have to work with....

Yep, will be testing for a tupee:grin:

 

[Cold Fusion]

I---At what point do you decide the margin isn't enough? ---

I did the preliminary analysis on two prospective installations were I recommended not to do it - not enough payback, and these were both 24/7 process applications. Surprised me, i though I could make VFDs payoff.

1988, 4000V,900hp, 885rpm, through a hydraulic variable speed reducer to 720 - 780rpm, driving an ID fan. Best AB (Rockwell) could offer was a stepdown transformer to paralleled 480V drives, stepup xfm to 4000V. By the time we went through the two xfm and the drives, the efficiency was not a lot better than the hydraulic speed reducer. The existing control system was a hand wheel on the side of the speed reducer adjusted by the operating engineer (and that is what they wanted) - so there was not much to be gained by having a 4-20ma input. Electricity at this plant was cheap - they needed 150psi and 25psi process steam and they got it by running the 800psi steam through extraction turbines.

1998, 4000V, 3000hp, centrifigul pump, process required about a 10:1 turndown. We might have been able to do it, multiple pumps, VFD and control valves, but I couldn't convince management to give $1000K to try it out - one of them said show us your figures that shows the pay back time, we will want three years or less - go figure.

cf

 

[Besoeker]

Yep, will be testing for a tupee:grin:

Scotsman, red hair, engineer......
C'mon - what's not to believe?

 

[Besoeker]

I did the preliminary analysis on two prospective installations were I recommended not to do it - not enough payback, and these were both 24/7 process applications. Surprised me, i though I could make VFDs payoff.

1988, 4000V,900hp, 885rpm, through a hydraulic variable speed reducer to 720 - 780rpm, driving an ID fan. Best AB (Rockwell) could offer was a stepdown transformer to paralleled 480V drives, stepup xfm to 4000V.

You should have talked to me.
I could have given you a drive that needed neither step down nor step up transformers, low harmonics, and best efficiency.

 

[Cold Fusion]

---. The pumps have not changed for 150 years. Are you suggesting that they are the perfect solution and there is no technological future for anything else or for improvement? ---

No. But just because a technology is 100 years old does not mean it is bad or outmoded. It may have stuck around that long because it works really well.

Here's what I understod you to say:
One need not trim an impeller to match the process rather; pick an off the shelf pump closest to the process specs with the best efficiency and a VFD will do the matching for you.

If that is what you meant to say then I would have to say that is in error. It is extremely rare that an off the shelf pump matches the process specs. I don't think I have ever seen a process pump that doesn't have curves showing different sized impellers. Which is the same a trimming an impeller. And yes, a VFD may also be needed.

I recommend you get a copy of Cameron Hydraulic data, and Crane technical paper 410. A trip out to your rotating equipment shop would also be good. Maybe you don't get out enough.

---The fact is that the pump manufacturers focus pretty little on energy efficeny. ---

I didn't know that. And I suspect the pump manufacturers didn't know that either. As far as i know they do all they can to keen the hydraulic efficiency a hagh as they can. Although, you are right in one way - the technology is mature enough there is likely not much to gain any more -

---. ASD has long passed the stage of being 'high-tech' electrical, it is a commodity item. ---

I suspect there are a great number, right here on this site, that consider any power electronics as high tech as compared to a starter and control valve.

---. Ir are you still playing 45's?:smile: ---

Haven't got up there yet - can't get my gramaphome to slow down that far.

. ---You are making statements on insufficent information. ---

No, I'm making statements based on the insufficient information.

--- But those staements - without insufficent data - does not have to be always negative, just like the weavers in Manchester destroyed the machines did NOT stop technological evolution.---

That I wouldn't know. 100years before my time - maybe 200 years, my ancient history on this period is not real good. But if you say it happened that way I'll believe you.

---Absolutely. SO why didn't you use the same logic above? ---

I did. I tend to examine all available solutions, and pick the most cost effective. If a modern technique does not fit and a 100 year old one does, then the one that fits is the one I will pick. Bear in mind that a modern technique may not fit for a simple reason such as the customer management and crew have no interest in learning to handle it - as in the example of the refridgeration vfds.

cf

 

[Cold Fusion]

You should have talked to me.
I could have given you a drive that needed neither step down nor step up transformers, low harmonics, and best efficiency.

I'm sure you could have. But I don't recall you guys having in an office in Seattle or Anchorage. AB said they did not have high reliability MV semiconductors yet. They were still working on them.

cf

 

[Cold Fusion]

Absolutely, so do soft starts. Bearings' life and maintenance cycle depends on rpm*load; reduce either and you prolong both. Temperature reduction will prolong insulation and lubricant life. Reduced mechanical shock, during start, will prolong bearing life and insulation life. Reduced mechanical load also reduces material stress and consequent stress aging and failure.

Elementary my dear Watson.:smile:

For a 24/7 process pump with a few starts per month or year, little of that would apply and the high harmonic content of the drive output could just as easily raise the motor temperature. I'm not saying it is not true, I an just curious as to the physics on why a motor or a pump would last longer on a VFD.

Bes -
I'm thinking you have the answers on this.

cf

 

[Besoeker]

That I wouldn't know. 100years before my time - maybe 200 years, my ancient history on this period is not real good. But if you say it happened that way I'll believe you.cf

I think weressl was referring to the Luddites from the early eighteen hundreds.
They broke textile machines because they thought that labour-saving technology would increase unemployment.

 

[Besoeker]

I'm sure you could have. But I don't recall you guys having in an office in Seattle or Anchorage. AB said they did not have high reliability MV semiconductors yet. They were still working on them.

cf

Well, we have offices world-wide but I'm not about to advertise on someone else's forum.
With the right type of drive, you don't need particularly high voltage semiconductors.

 

[Besoeker]

For a 24/7 process pump with a few starts per month or year, little of that would apply and the high harmonic content of the drive output could just as easily raise the motor temperature. I'm not saying it is not true, I an just curious as to the physics on why a motor or a pump would last longer on a VFD.

Bes -
I'm thinking you have the answers on this.

cf

I'm in a bit of a hurry so I'll be brief.
A VFD will avoid the stress on motor, coupling, and driven load resulting from direct on line starting.
If the speed is turned down, the machine will rotate les often in a given period.

And, the output current from modern or even reasonably modern VFDs does not contain a high harmonic content.

 

[weressl]

For a 24/7 process pump with a few starts per month or year, little of that would apply and the high harmonic content of the drive output could just as easily raise the motor temperature. I'm not saying it is not true, I an just curious as to the physics on why a motor or a pump would last longer on a VFD.

cf

<<Bearings' life and maintenance cycle depends on rpm*load; reduce either and you prolong both.>>

<<Temperature reduction will prolong insulation and lubricant life.>>

<<Reduced mechanical shock, during start, will prolong bearing life and insulation life.>>

<<Reduced mechanical load also reduces material stress and consequent stress aging and failure.>>

So on which part of the above do you need further understanding or explanation of 'physics'?

These are kind of basics, have to do with the basic functionality of each of the systems.

Or do you not know what is the difference between an accross-the-line and soft starts?

 

[Cold Fusion]

<<Bearings' life and maintenance cycle depends on rpm*load; reduce either and you prolong both.>>

<<Temperature reduction will prolong insulation and lubricant life.>>

<<Reduced mechanical shock, during start, will prolong bearing life and insulation life.>>

<<Reduced mechanical load also reduces material stress and consequent stress aging and failure.>> ---

Most of your points have some truth but are not completely valid. I'll point out a couple: As long as one is inside of the bearing velocity, shock loading, continuous radial and axial loads, vibration, reducing the load or rpm won't help at all. In fact reduce the load and rpm too far and the bearing life gets less.

Here is another: As long as the temperature is a comfortable margin within the insulation/lubrication spec, reducing it further will not increase motor/ bearing life.

So if you are telling me that adding a vfd to reduce load, rpm, temperature to get an increase in life-cycle - I'm going to suggest that the system is really poorly designed.

---So on which part of the above do you need further understanding or explanation of 'physics'?---

I can't tell that as long as the design is within repetative shock loading limits, that a VFD does any thing to prolong life or reduce maintenance.

---Or do you not know what is the difference between an accross-the-line and soft starts?

I think so. But if you think one will fix all of the evils you listed, then I can't tell that you do.

As I have already said, I'm not against VFDs, they just are not a fix all for all the evils listed in this thread. Good design will fix all of these evils. And that good design sometimes includes a VFD

cf

 

[JWCELECTRIC]

CF,

Have you ever installed a control valve for a process instead of a VFD? and if so what were your results?

 

[weressl]

Most of your points have some truth but are not completely valid. I'll point out a couple: As long as one is inside of the bearing velocity, shock loading, continuous radial and axial loads, vibration, reducing the load or rpm won't help at all. In fact reduce the load and rpm too far and the bearing life gets less.

Reducing load and speed will increase the bearing life BEYOND it's rated speed/load design.

Please explain the physics how the reduction of load an rpm will shorten the bearing life.

Here is another: As long as the temperature is a comfortable margin within the insulation/lubrication spec, reducing it further will not increase motor/ bearing life.

You mixed up the bearing life relation with the insulation and lubrican service life. I made no such a claim.

Both insulation and lubrication will have longer service life at reduced temperatures. It is the elevated temperature that destroys both. Are you avare of how the service life is computed for those compounds from thermal testing in owens and using a mathematical formula to project end-of-service life?

So if you are telling me that adding a vfd to reduce load, rpm, temperature to get an increase in life-cycle - I'm going to suggest that the system is really poorly designed.

I can't tell that as long as the design is within repetative shock loading limits, that a VFD does any thing to prolong life or reduce maintenance.

I think so. But if you think one will fix all of the evils you listed, then I can't tell that you do.

As I have already said, I'm not against VFDs, they just are not a fix all for all the evils listed in this thread. Good design will fix all of these evils. And that good design sometimes includes a VFD

cf

So let me see; if I bend a wire 90 degrees and straighten it, it will withstand - say - 200 bends before breaking. If I don't bend it it will break on its own?

In the other parts you're building a strawmen argument. I NEVER claimed to put in and ASD to prolong insulation or mechanical service life or to reduce maintenance. What I claimed that those - incidental - benefits should also be taken into consideration when calculating lifecycle cost and payback.

Indeed I have put a SSRV starter into service for purely mechanical benefits, the frequent starts would destroy the chain drive prematurely, so it had to be replaced every 3 months. The SSRV reduced the werar and after 3.5 years the same chain was still in service. In that application varying the speed had no benefit.

In another application, production called for the installation of SSRV's on a cooling fan set installation as on startup the FVNR start would trip the vibration switch, so they had to bypass it. (The vibration switch is a safety feature to detect blade breakeage and prevent the 'rain' of 8' long blades and parts flying from 80' above.) Since the application would benefit from varying the speed both from the process flow and the air temperature changes, I installed a set of ASD's. Not only did the cost saving - calculated purely on the energy basis - paid for the cost difference within 3 months, but the entire installation was paid in 14 months. Belts have not been changed on those either as frequently as before.

 

[weressl]

Most of your points have some truth but are not completely valid. I'll point out a couple: As long as one is inside of the bearing velocity, shock loading, continuous radial and axial loads, vibration, reducing the load or rpm won't help at all. In fact reduce the load and rpm too far and the bearing life gets less.


cf

Bearing life formula:

L=(C/P)^p*(1,000,000/60n)

L - basic rating life, operating hours;
C - basic dynamic load rating;
P - equivalent dynamic bearing load;
n - operating speed;
p - life equation exponent:
?ball bearings use 3;
?roller bearings use 10/3.

Many factors affect the overall bearing life, with the major
ones being the following:
? proper installation;
? lubrication;
? operating temperature;
? operating alignment;
? shaft and housing fits;​

? material quality.

IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 39, NO. 5, SEPTEMBER/OCTOBER 2003