VFD or VSD - Which is Better?

I do know that VFD are very good, and they will minimise your energy consumption, and control the flow very well.

Sorry, but I've never heard of "variable speed eddy current type drive?"

A variable frequency drive is much more efficient than an eddy current drive.An eddy current drive takes a fixed speed motor, and magnetically couples it to the load. the torque is constant, but the speed is reduced. Since power is the product of speed and torque, at 50% speed 50% of the power is dissipated as heat loss by the clutch.Typically, the annual operating costs for a premium efficiency motor in the mid-west, where electricity is cheap, is about $500/hp yr, so an 800 hp motor would consume about $400,000 of electricity each year if running continuously.If an eddy current drive is used to run this at half speed, $200,000 of waste energy would be used.Belden VFD Drive cable is an essential part of any reliable and robust drive system, and on a system this large, downtime costs would be enormous as well. Belden VFD cables have the potential to reduce reflected wave voltages, and motor insulation stresses, and unlike THHN which can weaken and fail (due to Corona) when wet, are dielectrically strong enough to have very long life, even when used in a wet locations for many years.

Of course, an 800HP drive is going to pull about 1000 amps, so at least quad runs of 4/0 VFD would be required, and potentially even more due to potential de-rating factors.

Omni Cable's got it!

You are probably not old enough. This is very old technology. 60 years plus.

Hi

As you've posted in a mechanical section, asking an electrical question, I'm going to assume, until corrected that you are of a mechanical background.

VSD or VFD.... Variable Speed Drive... Variable Frequency Drive.

Two different acronyms for what is basically the same thing.

Lets take the VFD.. Variable Frequency Drive. for a motor powered by an AC power supply at a frequency of 60Hz, it will rotate (RPM) at 3600 RPM, if you change that frequency, you will change the motor RPM. That is basically what a VFD does, it changes the frequency.

A VSD, Variable Speed Drive..... same thing, it changes the frequency.. and the RPM of the motor.

As for which is better.. there is no fundamental difference in the principal function.. however there is a HUGE difference between the manufacturers and what they offer.

I could bore the pants off you and list all the different types of drives & how they function... but I won't!

But note... I've never in 20 years, found a "variable speed eddy current type drive".

I suggest you study the yellow pages, or google "variable frequency/speed drive manufacturers" and ask them.. ABB, Hitachi to name a few

They will help, and give them ALL the information required for them to give you what you want. Make sure that they also can provide harmonic mitigation as the downside of VSD's is harmonics.. but it can be corrected and... there are drives out there that are compliant with IEEE 519 that generate less that 5% THD.. thats what you need!

I'm told eddy current is a type of vfd but don't know much about it. Thank you for your insights.

you are welcome and I hope your project is up and running soon

He said it was an eddy current drive. They were also know as "Eddy Current Couplings". An eddy current drive is an obsolete method of speed control. It has two armatures, connected only by an electrical field. One armature is connected to a motor running at full speed all the time. The other armature is connected to the load. A field current is used to create the magnetic field between the two armatures. If the field current is weak, the load spins slowly. As the strength of the field current is increased, the load speeds up. When the field current reaches its maximum value, the load is spinning at nearly 100% of the motor speed. Most eddy current drives have a water jacket to cool the drive. An enormous amount of energy is lost as heat. Efficiencies typically run from 10 to 40%. Back in the 1950s, these drives were common, as the DC drive and the Variable Frequency Drive had not yet been invented.

Since a typical VFD has efficiencies in the 90% range, it is a much better choice for speed control.

Yes I've heard and worked on those, its all in the description.. we had VERY large forerunners of today's VFD's for the "Eddy current couplings" in the steel works where I training all those years ago, they had SCR's the size of dinner plates that could cook at chicken at 20 paces with the heat they generated.

The good old days!! :)

The original Eddy Current Couplings predate SCR's by 20 years or more.

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Thank you, this helps much. Trying to figure out which is better from a long term cost point of view.

Thank you!

I forgot to say that... GA from me

Good day,

In my opinion both are good depending on the application. And I have found that many people are not familiar with the "variable speed eddy current type drive". I work at a shop that specializes in fluid drives and together we have well over 70 years experience(there is only 5 people working here) with designing these and building them and we are still trying to spread the knowledge of how fluid drives work. To start with they are not overly complicated and work off of the principles fluid dynamics with hydraulic oil. If you follow this link http://ecbiz60.inmotionhosting.com/~sutton7/page9.php it will take you a short video with info about the fluid drives. In a lot of cases, if you are looking for longevity and durability, I feel the fluid eddy current drive is the way to go. Because I have seen fluid drives last ,with proper maintenance, for 40 years and after that you just need to replace seals and bearings. But like I said it all depends on the application and what you are starting with. Another good thing about the fluid drive is that you can use a smaller motor than you could with a VFDs because of the soft start features of the fluid drive. And this means increased efficiency so less power and less ware. But i have already talked a lot. If you have any questions or need more info please just let me know. Take it easy :)

Thank you for your help!

Dear Mr.imbarney,

The eddy current drive has almost vanished from the industry, as it is not that efficient as compared to VFD.

DHAYANANDHAN.S