Graham,

As you know there have been many comparisons on VFD power vs. FC. They come in many flavors where VFD does show significant benefits:

1. Full speed savings in power and power factor that reduces the loss within the VFD and motor (totaling < 1%) compared to the ~3% loss in the fluid coupling and motor under full load. Then there are those that claim the control room cooling and airconditioning take another 1% or more plus the capital cost. However, then we can also claim the FC has its achilles heal in bearings, seals and fluid related controls. Bla bla Bla. Then others claim the VFD motors cannot take the heat without auxilliary cooling for long starting ramps - > 100 seconds.

2. Variable speed VFD matched to demand tonnage - case in point 20 km Curragh North where automatic speed changes are set between receiving multi-compartment 500 t hopper and similar feeding hopper - conveyor speed algorithm set on hopper levels and material demand between various receiving secondary coal processes and storage piles. Using variable speed to match tonnage and speed to provide more-or-less constant belt cross-sectional loading can produce substantial power savings, depending on the frequencies of operating speeds - Curragh North is rated for 7.5 m/s, in the past in mostly operated at 6 m/s or 4.5 m/s ( best speeds to avoid amplified belt vibrations). Setting the values and savings are also dependent on the belt rubber compound. Some belts are much better over the operating strain range. This is part of the CDI expertise.

3. Ability to inspect and positon belt for various damages, wear and repair

4. Ability to identify belt critical vibration modes and enable programming the belt speed to avoid modal frequencies and operating in their bands.

5. VFD does not change with changes in temperature, with one FC drive exposed to sun while other is in the shade resulting in imbalanced demand power.

6. VFD can be designed to eliminate its operation (switched out of power path) when belt is at full speed - improving the mean-time-to-fail and mean-time-to-repair.

7. VFD can have an on-line backup power module while FC cannot thereby improving availability of larger systems

8. VFD offers better control of belt tensions and safety factor thereby improving splice life - among the techniques are special starting curves that also include using inverter frequency to monintor the health of the starting curve.

9. VFD can be set to control on speed or torque which comes in handy with multiple drives on overland conveyors

10. and above are reserved for Mr. Spriggs.

Are you trying to set a trap? You always/already know the answer, so why the question? To ensnare the uninitiated? Trophy hunting? ■

Forgot some points:

10. VFD shows belt wear improves when operating below highest speed

11. VFD shows better dust emissions when operating below maximum design speed.

12. Mr. Spriggs?? ■

Yet more,

12. VFD willl show benefits in tuning our critical vibrations on overland or long belts by minimizing the belt edge flap that are instrumental in reducing idler life, in causing end disk failure in rollers, in failure of idler bracket weldments,....

13. VFD can minimize belt noise by tuning out high belt edge flap rythmic air pulsations that neighbors object to.

14. Graham ???? ■

In conclusion,

Power savings can be substantial. We have made such analysis accounting for much of the above and concluded the savings can be a high percentage of the conveyor system capital cost when applying modern Net Present Value techniques together with cost of kW-hours and their escallations. To be fair, there can be many factors or few to make the arguement for VFD or FC.

Some just argue they are not interested in the training required to implement and maintain an electronic gadget. Some argue, local support for VFD is poor and the possibility of a mistake by ill trained VFD personnel, that don't know the mechanics of belt conveyors and their complications, make the FC a favorite, outweighing the VFD benefits.

We are not arguing the length of a string, but, unless you have a specific design of interest and apriori knowledge of the client, the answer is futile. ■

Dear Friend Graham,

Your Ryan dreamfest must be controlled. I think it is beginning to taint your other sense and should be examined by a specialist.

We have taken many measurements of fluid couplings to study the accurate slip between drive and driven halves, by applying our extra fancy company designed speed sensors that can accurately measure the speed difference between drive and driven coupling halves to within small fractions of a percent (< 0.1%). As such, we could see the speed slip factors. Voith has measured the same in their factory with a special dynamometer. CDI also has very accurate torques measurement tools (>99% accuracy as validated by motor speed torque curves and VFD internal monitoring, load cells under the high tension pillow blocks, ..) as well as our speed sensor tools. More than 100 field measurements have been taken on VFD and Fluid couplings during commissioning and forensic studies. They have validated the theories in use many times over.

Now that your senses are heighened, its time for you to again engage Meg. Forget what I said about a specialist. ■

Yes, there are many fluid couplings that have been replaced by VFD's and measurements taken. There are also a few VFD's that have been replaced by fluid couplings. Why, well the purveyor edicted it to be so. You know when something fails, replace it, and all things like it, but do not necessarily fix it. People invent new wife's tails or new Meg Ryan images every time they close their eyes.

It seems, at every response, there is a Meg Ryan heard in Mr Sprigg's pitter patter. Go, and may the force be with you Graham. ■

I wonder if Larry and Graham are friends?

Because only friends can relate like you guys do in this forum.

I'm also like you Mr Spriggs would like to know if there are any actual measured figures, because everyone seems to be talking about what VSD's "CAN" do not what they have done.

Regards,

Bonginkosi ■

Dear Bonginkosi /Graham,

My friend Graham is seeking an answer to a small bit of data. Replacing a fluid coupling with an inverter comes more from other reasons than power savings.

Usually, the size of drive we are talking about is below 300 kW. A client's cost to change to an inverter will not include the high priority of power savings.

I offer in defense of chasing down the noted project date, is a bit of work. For the installations we are aware of, you must include some portion of the air conditioning system and pressurized room operating and capital cost besides the raw power cost at the shaft. Graham is aware of all these nuances and will later say where are these added cost to be fair. CDI has a large suite of garages full of project information that can be retrieved at a cost. Then add the incidentals I note above to make A/B comparisons. Since we are not in the business of inventing a day or two of free services, I take my time to see when we can do it without fanfare and without pressure to deliver.

CDI is not the only firm who has had such experience, I hoped a fresher face could take up Graham's call.

Back to the reasons for going from fluid coupling to inverter, and some have also gone the other way to fluid couplings from inverter installations. The reasons are sometimes unbelievable and need to be set aside from this conversation. So I ask for patience. the answer will come.

I did offer notice that we have tested FC and inverters on sites to validation their performance. I am sure Graham has done the same and can tell how close he is to the theory. The only rub here is, for the fluid coupling, you need to see what is fed to the motor and what is fed to the drive pulley shaft. In between we have a reducer and fc. On the inverter, you need to see what is fed to the inverter drive and then what is fed to the drive pulley shaft. This is a little more tricky to factor all electrical hocus-pocus. Then you need to see what portion of the electric house demand is only associated with Inverter.

A bigger item separates Inverters from Fluid Couplings is reliability and maintainability. Another thread is required to do this justice.

Even thought we spat at each other from time to time, Graham is a very positive addition to this forum and to our material handling society. Tell him to keep up his energy for the next big job. Dont look back at the trivial. ■

Dear Graham,

This is a topic of a paper we are writing. You recall Curragh North, the 20 km overland we did with Laing O'Rourke and Goodyear in 2007? The conveyor is programmed to change speed when the receiving bin, at the coal process plant, begins to fill, or the loading bin level is lowered due to infrequent truck arrivals.

It has 4 fixed speed ranges that are safe to operate at that minimize the effects of belt resonance and idler spin coupling. The operator allows this to automatically adjust according to a generalize algorithm. Thus, we can see the effect of the differences using the 4250 kW driven inverter system (4 x1000 kW plus 1 x 250 kw)

In principle, you save belt wear and tear, idler life, noise and power. THe power can be deduced from both idler drag and lubicant theory, and by looking at any rubber Master Curve E';E" curve. Speed is = temperature. Higher speed = lower temperature for most modern rubbers.

I will send you an early edition as we complete the ordeal. We also have good data from Newcastle Univ and their idler test stand and our joint effort on the rolling resistance rig that measures rubber indentions losses. Add to that flexure and trampling losses that are also speed dependent. The big $$$ question on your mind is how much?

This varies with the rubber properties and idler lubricants. And dont forget reducer churning losses.

Not checked for spelling.

Hoping your wife is recovery from you flirtatious dalliance.

As the wise old man said, if there is a fresh carrot, the bunning can hop faster. ■

Hi Graham,

I share your frustration only in that there are no responses from the VFD suppliers.

For my part I was a longtime fluid coupling user but always loved the VFDs. Their downside was, they cost too much. That has changed. For most uses they no longer cost too much. My VFD applications have utilized the frequency variation at starting and stopping, and for load sharing and target tension control. Thus I can assume that during loaded running I have about a 3.5% energy advantage over the continuously running fluid coupling connected drive.

VFDs are now more prevalent then fluid couplings for our conveyors.

Joe Dos Santos ■

Potentially slightly off topic, though I seem to recall a paper (brochure?) from (or regarding) ABB at Worsley for the (last?) cable belt upgrade.

I have not been able to recall where I saw it or locate it in my records, so I hope I am not dreaming and it wasn’t privileged, though I seem to recall it cited a “total” drive efficiency (VSD and motor and maybe reducer etc), which was a Contract performance requirement and was demonstrated, inter alia I assume, for the purpose of being issued a Practical Completion certificate.

Although in this case, the situation was a DC drive being replaced with a VSD / AC synchronous motor (cf fluid coupling being replaced with VSD / AC motor) it may provide some practical “confidence” (given it was approved by a Principal for the purpose of PC, although there are obviously various other issues which may affect this conclusion in this application in particular and others in general) in the efficiency of the VSD drive as a unit, rather than evaluating components as elements (and hence potentially without appreciating the impact on each other – i.e. reduction in motor efficiency due to operation via a VSD etc).

Furthermore I seem to recall this is a “constant” speed application, so it would not include all of the potential benefits associated with a VSD.

Hopefully this jogs the memory of others who can recall seeing it, to see if it provides any value for this discussion (or confirm I have lost my mind).

Regards,

Lyle ■

You mention that you are describing a constant speed application. In such a case, under continuous running, using the exact same motors, with a direct connect you get the advantage of not suffering the fluid coupling continuous slip losses about 3.5%. This is true with any direct connect during running.

Joe Dos Santos ■

Joe,

The 3.5% is quite high. There are some cases, but much less frequent that 2.5% for a fluid coupling with proper filling. ■

Larry,

Indeed the desired start-up characteristics may be accomplished by controlling the rate of fluid entering the circuit, either by scoop-tube control, in the case of the vari-fill type coupling, or by multiple delay chambers in the case of an advanced fixed fill type fluid coupling. In any case, the point is that, whatever the slip, that is the least that the energy disadvantage can be.

Joe Dos Santos ■

Originally Posted by Lyle Brown

Potentially slightly off topic, though I seem to recall a paper (brochure?) from (or regarding) ABB at Worsley for the (last?) cable belt upgrade.

I have not been able to recall where I saw it or locate it in my records, so I hope I am not dreaming and it wasn’t privileged, though I seem to recall it cited a “total” drive efficiency (VSD and motor and maybe reducer etc), which was a Contract performance requirement and was demonstrated, inter alia I assume, for the purpose of being issued a Practical Completion certificate.

Although in this case, the situation was a DC drive being replaced with a VSD / AC synchronous motor (cf fluid coupling being replaced with VSD / AC motor) it may provide some practical “confidence” (given it was approved by a Principal for the purpose of PC, although there are obviously various other issues which may affect this conclusion in this application in particular and others in general) in the efficiency of the VSD drive as a unit, rather than evaluating components as elements (and hence potentially without appreciating the impact on each other – i.e. reduction in motor efficiency due to operation via a VSD etc).

Furthermore I seem to recall this is a “constant” speed application, so it would not include all of the potential benefits associated with a VSD.

Hopefully this jogs the memory of others who can recall seeing it, to see if it provides any value for this discussion (or confirm I have lost my mind).

Regards,

Lyle

Both VSD and Fluid couplings have it sown advantage and disadvantages.

Normally VSD was used in installations which needs smooth start and acceleration and speed control like equipments traveling,slewing etc

For cooling of motor when it runs in low speed higher size frame is selected or external cooling system is adopted.

In conveyor system where start up only is necessary,VSD is adopted in case of large conveyors also.The accelerating time can be large,but less than the maximum stalling time of the motors.Once the speed is achieved, the VSD is by-passed and the motor run in the rated speed.

VSD needs a lot of special care,such as the panel should be near to the drive,higher frame size of motor,additional harmonic filters etc.

A properly designed and executed VSD can run the conveyor in 2 speeds to enable conveying of materials of different characteristic.

A lot of coordination is necessary if the motor and VSD are of different make.

Rgds,

Narayanan Nalinashan. ■

Originally Posted by NarayananNalinakshan

Both VSD and Fluid couplings have it sown advantage and disadvantages.

Normally VSD was used in installations which needs smooth start and acceleration and speed control like equipments traveling,slewing etc

For cooling of motor when it runs in low speed higher size frame is selected or external cooling system is adopted.

In conveyor system where start up only is necessary,VSD is adopted in case of large conveyors also.The accelerating time can be large,but less than the maximum stalling time of the motors.Once the speed is achieved, the VSD is by-passed and the motor run in the rated speed. VSD needs a lot of special care,such as the panel should be near to the drive,higher frame size of motor,additional harmonic filters etc. NOT NECESSARY. WE DESIGNED SYSTEMS WHERE THE VFD DRIVES WERE FAR (~1km ) FROM THE MOTORS. LA CARIDAD, Mexico in 1977 four inverters started 20 conveyor motors as published in 1977 SME Journal

A properly designed and executed VSD can run the conveyor in 2 speeds to enable conveying of materials of different characteristic. IT CAN DO MORE.

A lot of coordination is necessary if the motor and VSD are of different make.

Rgds,

Narayanan Nalinashan.

I am sure you have your experience with VFD drives. However, yours is not the only experience. I suggest you be a little less emphatic with words and leave the audience follow reasoning over facts that are not the only facts. ■

Good Day to you ALL. It has been a long while since I have had a few minutes to share my thoughts and experiences on subjects as I have had the past 10 months developing my patented stub axle idler rolls factory which I have had to basically develop the proprietary equipment from scratch. I will keep you in touch with this progress but this digresses from this Thread line.

I have been reading the comments and I know that Graham has raised a question that we would all love to read but I suspect that this comparison will never happen due to the complexities to get identical side by side conveyors doing the same task in a single site for monitoring purposes.

If the Dodge Controlled Start Transmission can be classed as a Fluid Coupling, I make a few of my thoughts on the system I prefer. FC's work well for many applications and are a common usage worldwide, however they have their limitations. Again, 'Horses for Courses'.

I make a comment here that I love the Dodge CST( Controlled Start Transmission ) for the coverage of requirements for all belt speeds and loadings. A BHP mine had CST's in one conveyor in the Longwall Mine and Dodge VFD and DC Drives on other conveyors. Unfortunately, they were all differing lengths and impossible to correlate data into a comparison format.

I will say that the cost of the DC Drives in comparison was very large compared to the CSTs & VFDs which ranged closely to each other at a much reduced value.

The DC Drives were a massive installation and removal nightmare as everything was ridiculously heavy to handle especially in confined spaces and manpower injuries were an ongoing headache to try to overcome. The volume of space also required to excavate was another issue to deal with as underground vertical excavation is expensive and hazardous to complete.

The VFD's also had to have larger vertical caverns to get the cooling towers in and presented their own issues here. The PLC controls and logic required caused headaches for the setup group and plagued the running when the conveyor speed was reduced and trip outs due to overheating issues were never ending. These days they are getting better but the issues still exist.

The Dodge CST from my own experience of installing most of them in Queensland & New South Wales in Australia, Philippines and Mongolia were the easiest to setup and run faultlessly and which met most of the clients requests of protection for the whole conveyor system but the belt damage was where the most saving existed in less belt stretch and splice damages. The CST can run as long a start ramp-up time or can jog happily all day if necessary, as in block heading development work, without heating issues. At running speed the system goes into a full lockup on the primary drive/s (or if dual drives per pulley) and the others run with <0.1% approximately slip to cater for belt stretch between the drive pulleys so each drive is delivering the same pulling effect.

Between the DCs and CSTs, which were on adjacent longwall blocks maingate belt systems, it turned out the DCs were more power hungry than the CST according to what I was told by the electrical engineer at the time and he said he could not understand why and he was the DC's main instigator for use. This was only hearsay and I do not have written documentation to confirm his figures.

I know the installation costs of the two systems and the CST was about 1/2 and installation time was 1/3 for the period to commissioning. The DC's also had a large maintenance down time due to electrical control issues with the system. ■