Baldor Motors/SFA 1

[tmo42]

We need to tabulate Service Factor Amps for various motors we are considering matching with drive. Can't find the SFA published in any materials either in Baldor Motors catalog or on their website. Does anyone know if this information is published anywhere? I'm still waiting for Baldor Motors to contact me back.

 

[GusD]

Hi Tmo42

I have just finish load tetsing 4 - Baldor motors and the 4 VFDs that will eventually drive it.The unit has a Single front end and 4 inverters.One of the Inverters is water cooled ,the other 3 are air blower cooled.
We ordered these motors from Baldor for a specially project.1- 200 hp for a VIB Screen,1-600 for an Impactor /crusher and 2 -600 hp for Slurry Pumps.
The windings are Inverter duty of course,with Class F
insulation with Class B Temp rise.
I am somewhat confused by the talk of SFAs and what it suppose to mean.
The motor nameplate shows the motor FLAs.It does not care if the S. factor is 1/1.15/1.25 or whathave you.
Overloads are set normally at a max of 1.25 of motor full load current(FLC).Service Factors are related to H.P not to nameplate FLAmps.
I don't know how large your motors are,but regardless of the size,electric motors should not be operated at their service factors on a continuous bases.The Factor is in place to allow for momentary process changes,voltage variations,or amb.temp changes.If you operate your motors at SFactor you lost the ability to deal with these variations and run the chance of severelly overheating your motor.For every 10 Dec inc. above TRise your motor life is reduced by a half.(I guess you all know that)
TMO42-I don't know where you are located,but I do know the name and PH # of a Baldor Rep in our area that was most helpful with all the info we needed during the tests.If it Ok with him I'll give you the Ph #.
I asked this fellow to get me the Data sheets for the windings,showing Stator slots /Rotor slots and I had it in my hands the following day.I don't recall many of our Suppliers being that forthcoming.

Hope it does not confuse the issue even more.

GusD

 

[tmo42]

Hmm. The nameplate for Baldor Catalog #VM3550 lists FLA as 2.3 and SFA 2.5 with a SF of 1.15...

As I was explained it, SFA was the maximum continuous amps without damaging the motor. Looked at as sort of a 'danger' value. But it's desired to know just how much we can squeeze out of the motor. I suppose it's more likely the penny pinchers up higher that cause this to be a concern, but even still.

The formula listed earlier... while it does seem to be accurate in about half the cases I tested.. in others it seems to be a bit... wildly high. Especially in low horse motors with high service factors.

 

[jOmega]

tmo42 & ElectricPete,

Appreciate the data on the Baldor motor. That's why in my original post to EP I cautioned about using the SF as a multiplier of the motor N/P FLA.... and yes, EP, I did read your May 02 post and did note your comment about the "first approximation" and "SFA" ... However, years of experience teach us that the uninitiated will see that and think it acceptable to go with SF x FLA ...mostly because they don't know any better or haven't experienced motors burning up or failing prematurely as a consequence of such action.

I think that as the data tmo42 just provided shows, that such approximation only leads to trouble... and should not be considered as you cannot operate the motor long term at the value of SF x FLA.... without overloading the motor.

In fact, the data shows that 2.5/2.3 is a 1.08695 multiplier of the motors FLA.... and is 94.5% or the current you'd be running at if you used the 1.15 x FLA = 2.645 amps ... or another way of seeing this would be to say thatif you operated at SF x FLA, you'd be operating at almost a 6% current overload.

So, I would ask.... what's the benefit of even considering it.... as it has no useful purpose and cannot be used. May be fine for esoteric discussions and limited thereto; but for general comsumtion, I find that sticking to the facts based in reality (as opposed to generalizations) and playing to the conservative side keeps ya out of trouble.

"Ini facilius facias quam feras."

 

[electricpete]

j[ignore]&Omega[/ignore];

The original poster expressed interest in calculating SFA from FLA and I proposed a method based on the equivalent circuit. All equations were identified as approximations. I see no problem with that.

I have a quiz for you: What happens to power factor when load component increases but magnetizing current does not increase? Now, re-read my 5/2 message and your 5/3 response.

 

[jOmega]

EP :

Excellent Question.

Need some time to research/model/analyze/and respond.

jÙ

 

[electricpete]

I don't know exactly what the explanation is for the small motors. It may be that the error of neglecting series leakage reactance is more pronounced. One other thing is that Baldor only provides this info to one decimal point.... the rounding error might make a difference for small motors.

What if fla = 2.6A actually represented FLA = 2.251 rounded ot nearest 0.1A?

FLA:=2.251;:
FLA := 2.251

> NLA:=0.2*FLA; # For 2-pole motor
NLA := .4502

> LA:=sqrt(FLA^2-NLA^2);
LA := 2.205

> SF:=1.15:
> SFA:=sqrt(NLA^2+SF^2*LA^2);
SFA := 2.576
Actual SFA reported as 2.5 could have been as high as 2.549
Now only 1% error. Just a thought. If the small motors are CONSISTENTLY off, there is probably something else going on.

 

[electricpete]

Small motors have higher leakage reactances and lower magnetizing reactances on per-unit basis than comparable speed large motors. So not only does the error in neglecting leakage reactance increase, but the NLA is likely a larger fraction of FLA. Higher NLA estimate will bring the SFA estimate down slightly.

 

[tmo42]

Hmm.. my comments about the low horse, high SF motors was based on me testing the data for some of the Franklin Motors... it seems that for the Balder motors, the SFA calculation is pretty close; in many cases, if I round down to the nearest .1A it's almost dead on.

 

[tmo42]

I also want to note that I actually have the NLA data for the Balder motors, wheras I was estimating for the Franklins. I suspect that, as you just said, I was using an estimate for NLA that was too small, and that's where my error was originating.

 

[jbartos]

Suggestion: Visit

http://www.pupman.com/listarchives/2000/August/msg00166.html

for a sample of SFA