Magnetic-Coupled Variable Speed Belt Drive

There is too little information here, and too many possible variations, to give one-size-fits-all advice.

VFDs can be interfaced with pressure or flow sensors so as to respond automatically to changing process conditions. I'm not sure how many mechanical devices can do this, though they may be manually adjusted from time to time if the process conditions do not fluctuate continuously.

Mechanical devices may have belts, friction cones or disks, etc.; any of which will be subject to wear, and which also have efficiency losses of a few per cent.

Out of a suite of pumps or fans, one might have variable speed, while the rest are either on or off.

Etc.

There's only two things to be considered to my mind the efficiency of a VFD as against some mechanical contrivance, I know which I'd put my money on!

What has any of this to do with "magnetic coupled" drives?

It is the thread title that tries to encompass all, but misses the crux of the biscuit. Like na former business associate who suggested that a mag-drive peristaltic pump might be a good idea!

Belt and suspenders?

Maybe less elegant!

It looks as though someone has been reading the sales literature for a Magnadrive (or another similar brand). For those unfamiliar, they are a magnetically coupled Variable Speed Drive that controls speed by varying the magnetic field force in a slip coupling, essentially allowing more or less of the motor speed to be slipped in the coupling as a way of controlling speed.

What their sales literature always leaves out is their main detractor, they are much less efficient than VFDs. So you can vary the speed without some of the problems that VFDs represent, but also without the main benefit, the additional energy savings. Mag Drives are useful for applications where you will not get the additional energy savings anyway, i.e. constant torque loads, but they are almost pointless on a variable torque (quadratic) load. Most of the truly successful applications are very large high torque applications, such as a disc refiner in the pulp making industry or centrifuges (where energy recovery raking is not used).

They are also more expensive than a VFD, and in many cases you STILL need to use a soft starter for the motor, another cost factor they almost always leave out of the sales literature.

While I have no dogs in this race (meaning I do not presently work in it), I much rather understand and work on a supposed bearing spalling issue in software. Sorry, it is quicker, better, more enduring solution, than mechanical hardware. Yes, it is requiring hardware solutions, sometimes, but not now.

He Said:...Does not cause electrically induced pitting of the motor bearings

You said:...New one on me.. but always wiling to learn.. could you explain please.

I think the OP is refering to STEEL bearings, that MIGHT be affected by induction! I've never seen it or heard of it, thats not saying it couldn't.. anyone??

Earlier we could buy Variable Speed Pulley drive which consisted of Pulley which could be expanded as its construction was split type and spring loaded. Motor with pulley was mounted on slide to control speed.

You can also try High Torque Magnetic Motor which can give variable speed but is quite expensive.

Yes, for decades machine tools were built with mechanical variable speed drives. The principle is simple, and they work reliably. You have two cones on the input, two cones on the output. A chain or belt connects them. When the input is moved apart, the output is moved together. Simple, effective, well working. If one cone works in a 1:5 range, the transmission is 1:25. Neat.

There was even a car with this drive, the Daffodil from Netherland. A neat simple car. Today, with modern belt materials it wold be a viable proposition, IMHO.

The reply you have got from Brich is very good one, just I would like to add the following:-

-Magnetic Coupling drives usually have heating problems, as it depends on the Eddy current phenomena, and the larger the coupling the more heat will be generated.

- Magnetic coupling drives are point to point assignment, which means you can't utilize one motor's coupling with other motor, while in VFDs you can use assignment switch to connect one VFD to different motors this will increase the reliability of your system.

- You can use one VFD to run 2 motors that are sharing a load, like Mud Pumps in drilling rigs, and can easily control the load sharing between them, the thing that you can't do it by using the Magnetic coupling drives.

- VFDs give smoother torque and speed control than Mag Drives, as in VFDs the speed feedback always tracking the speed reference at any time.

- By using HMI the troubleshooting of VFDs is very easy.

- THD can be reduced by using only suitable line reactors at the input of the converters , and L-C filters at the DC bus of the VFDs, and no need to use expensive Harmonics filters for that.

I recommend VFDs

Regards

Thanks to all my technical experts.I have passed on the Forum suggestions and guidence to the concerned plant technical manager.

follow this to a previous topic ref VSD's

http://cr4.globalspec.com/thread/70575#comment754304

and look for answer 3

If you are in the United States, another advantage to the VFD's is you also may be eligible to receive additional funding via the utility companies grant program (http://www.dsireusa.org/).

We are stationed in Pakistan,but thanks for the reply.

In the early days of the VFD technology the listed concerns were valid. The fix to avoid the transient currents problem is now easy and inexpensive. The power savings of VFDs that are correctly applied are very attractive and the payback is quick.

Lou Bindner