VSD, VFD, VVVF drive, Soft Starter - Definitions 2

[RRaghunath]

VSD, VFD, VVVF drive as well as Soft starter - all are solid state motor controllers based on the principle of varying the frequency / voltage of the power supply applied to the motor to achieve smooth start / speed variation.

If true, why so many different terms and when to apply what?

May be, some one can help.

Thanks in anticipation.

raghunath_n00@rediffmail.com

 

[Skogsgurra]

"Why so many different terms?"

Actually, you introduced a new one for me, the VVVF, and I haven't the faintest idea what it is. I have done quite well in the - shall we say VSD - business without the FLA VVVF. So let us leave that one out and make believe we never heard it.

That leaves us with VSD, VFD and Soft-stater.

VSD is actually a generic TLA for Variable Speed Drive. And it doesn't even imply a frequency inverter, even if it usually is one.

VFD, the Variable Frequency Drive, usually means a PWM frequency inverter. But not necessarily. It can also mean a CSI inverter a Venturini (matrix), a ZVC or a PAM inverter. There are many more, actually.

Soft-starters are another breed. They mostly do their thing when you start the motor and then takes the rest of the day off. Most soft starters work by slowly (within seconds) increase the stator voltage. And most do it using Triacs or thyristors. Not many use IGBTs - if they do, they should be f-ing close to a VFD.

Having said that. I must add that I always use "VFD" for frequency inverters. Sometimes I use the terms "scalar drive" or "vector drive" to differentiate between the two common types of VFDs that are in use.

Compared to how many words there are to describe an interesting woman, I think that we have very few words for frequency inverters. And if we do not introduce more (what IS a VVVF?) we can keep it managble.

 

[ScottyUK]

Hi Skogsgurra,

VVVF is, I think, variable voltage, variable frequency drive. Which isn't any different from a normal VFD, since these are forced to vary their voltage to avoid iron saturation. Perhaps it is a marketing man's way of making his drive 'different' from the competition!





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If we learn from our mistakes,
I'm getting a great education!

 

[Skogsgurra]

Thanks Scotty!

Always there when needed...

 

[UKpete]

I can't help noticing that in machines and drives, most of the TLAs (three-letter acronyms) are associated with the drive electronics, not with motors and generators.

Incidentally the other attractive feature of motors from my point of view is also that the technology doesn't keep changing. Compare our situation with say engineers in digital electronics - those fellows hardly dare go on holiday.

 

[Skogsgurra]

That may be why I feel being on an eternal holiday ;-)

 

[electricpete]

skogs and UKPete - good answers. Those distinctions make good sense and something I was never aware of.

I can't pass up the opportunity to comment wrt skogs' first post. FLA is a TLA which thoroughly cornfused me. I was wondering what Full Load Amps had to do with the question. Then I saw the one that just flew over my head. Made for a good laugh.

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[sreid]

The place where the term VVVF is seen is in the technical literature (drive/motor theory-research).

 

[macmil]

I am a mere mechanical guy who visits in this forum in awe, mainly for interest and educational purposes. I have learned most of the acronyms over the years, but then TLA floored me. So thanks to you for clearing that one up, and yes I was able to deduce the FLA. I suppose FLW will be the next creation for bad language ! Keep up the good work !

 

[DickDV]

I've seen VFD, ASD, AFD, inverter, drive, and freq drive all refer to the same thing, right or wrong.

The only thing that bothers me is the last one. I'm not sure, when I hear it spoken, whether the intended spelling is "freq" drive or "freak" drive.

Having lived and worked around these things for 15 years, that last spelling is a bit bothersome!!!

One other note for the original poster. An electronic soft start or reduced voltage starter is significantly different from inverter-based variable frequency drives in that the soft starter is not variable frequency. It is only manipulating the incoming sine wave, either 50 or 60Hz, to reduce the inrush current or the starting torque or both by reducing the voltage to the motor. This makes the start completely dis-synchronous as far as the motor is concerned. Variable frequency drives, on the other hand, start the motor in its normal near-synchronous mode resulting in much higher torque per amp performance.

If your object in softstarting is reduced torque, the difference is small. But if your object is to reduce inrush current, the difference is significant. An inverter will always beat a softstart on reducing inrush currents for the same output torque. Of course, over 10hp, an inverter is more expensive too.

 

[jraef]

Here are some more alternates (these are all real BTW);

VFD = Voluteer Fire Department, the people you call when you forget to properly set the FLA setting.

ASD = Autistic Spectrum Disorder, the kind of narrow mental focus capability one must have to be in this industry.

AFD = Anticipatory Failure Determination, a method of predicting failure, as in applying a soft starter and expecting it to change the speed, or using a non-vector drive to run a 2 pole motor at 3RPM.

VSD = Vetricullar Septal Defect, a heart malady that is the likely result of applying an AFD to a single phase motor because you didn't read the instructions properly, and seeing both devices let the smoke out.


"Venditori de oleum-vipera non vigere excordis populi"

 

[Marke]

Just my two cents worth,
I have seen the term VVVF used particularly by the Japanese manufacturers for around twenty years. It is as correcty stated above, Variable Voltage Variabel Frequency.
A soft starter is Variable Voltage Constant Frequency (VVCF).
Add VSD as another common TLA to describe a variable speed drive.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[Skogsgurra]

Ain't this business just fun? If one only could make some money out of it too. Or at least a decent living...

BTW, there are also TLAs that are 33 percent shorter than the common TLA.

 

[jraef]

You mean the dreaded Two Letter Acronym? I thought those had been outlawed by the TAC (Thrialphic Acronym Committee) of the IARC (International Acronym Regualtory Commission)? At the last meeting of the AFLUB (Acronym Forum and Legislation Unifying Body) there was a move to have Two Letter Acronyms be refered to as 2LA in order to avoid confusion with TLA, but the AAO (Alphbetic Acronymn Only) wing caused a filibuster and the movement was tabled until the next meeting at Reykjavik in 2010.

OK, it's a weekend and I have no life it seems...

 

[Skogsgurra]

At last! A reason to go to Reykjavik!

BTW, did you know that OLA is an Icelandic name? It is the TLA for Olafviuhr*. The OLA for Olafviuhr is O. The process leading to such linguistic quantum leaps is known as "reductio ad absurbum" or "KISS" which is the FLA for - well, you know that already.


* Local spelling variations exist.

 

[UKpete]

For those having trouble with some of the above acronyms:

http://www.acronymfinder.com/

(it's actually quite good - it even has VVVF)

 

[RRaghunath]

This is really interesting apart from being informative.

Skogsgurra,
VVVF is truly Variable Voltage Variable Frequency drive as many have already clarified.

DickDV,
Thanks for explaining nicely the difference between soft starter and VFD (or Inverter drive).

At the end of it, I think Skogsgurra's words
"Compared to how many words there are to describe an interesting woman, I think that we have very few words for frequency inverters"
clarify the subject abundantly.
Thanks Skogsgurra.

raghunath_n00@rediffmail.com

 

[bentov]

I read somewhere that ASD (which could presumably apply to AC VFD's, DC SCR's, eddy current units (ECD's?), disc tracs, ring cones, PIV's, CVT's, etc., etc.) is more accurate than "V" anything, using a climate analogy: the weather outside is "variable", while the weather inside (where engineers rule) is "adjustable" . . .

 

[jraef]

Back to the serious side of this, add into the mix the acronyms for different types of inverter topologies as well. I have been around long enough to have seen most of them, but I am increasingly finding younger engineers who are unaware of the different TLAs that were once common. CSI inverters is the most recent case in point. I used the term in a presentation and got vacant stares from my audience, perhapse thinking I was refering to something on a popular US TV show! VSI is another term no longer used much, probably because they are almost all VSIs now. LCIs are becomming rare except in the largest of applications as well. I had to submit CSI and LCI to the acronym website. BTW, thanks for that link UKpete, I love stuff like that.

"Venditori de oleum-vipera non vigere excordis populi"