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What's the deal with VFD ratings?
4

What's the deal with VFD ratings?

What's the deal with VFD ratings?

(OP)
I have a motor with a nameplate rating of:

Delta
36.6A
18.5kW


I grab a drive rated at 57A.
It shows up and the nameplate states:
Input: 200~240V 57.0A
Output: 0~240V 48.0A
Motor Rating: 11.0kW

This misses the mark by 7.5kW. What am I missing?

Keith Cress
kcress - http://www.flaminsystems.com

RE: What's the deal with VFD ratings?

Motor rated for 400+ V, while the drive is only 200+ V? Sqrt 3 is the missing mystery?

Muthu
www.edison.co.in

RE: What's the deal with VFD ratings?

18.5 kW / 36.6 Amps / 1.73 = 292 Volts.
Possibly a 380 Volt motor with Efficiency x PF of about 77%??

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: What's the deal with VFD ratings?

(OP)
Finally got a picture. No sign of 400V operation.



Keith Cress
kcress - http://www.flaminsystems.com

RE: What's the deal with VFD ratings?

Crazy NP. pf x eff = 0.7?

32 dB ? Quieter than a library?

Muthu
www.edison.co.in

RE: What's the deal with VFD ratings?

(OP)

Quote:

Quieter than a library?

That must be important with regards to a circular SAW MILL.

Keith Cress
kcress - http://www.flaminsystems.com

RE: What's the deal with VFD ratings?

Obviously. bigsmile

Must be some top edge cutting technology. censored

Muthu
www.edison.co.in

RE: What's the deal with VFD ratings?

(OP)
Kerfless? Blade is 1 micron wide?

Really perplexed on this.

FLA = Watts / (√3 x V x pf x eff)
FLA = 18,650 / (1.732 x 208 x 0.8 x 0.9)
FLA = 71.9A

Why is the plate stating 35.9A??

This motor is Y-Δ started. These numbskulls didn't put down the Y current did they?

So, I need to ignore the plate current and get an 18kW VFD?

Keith Cress
kcress - http://www.flaminsystems.com

RE: What's the deal with VFD ratings?

Keith,

The problem is deciding which part of the erroneous nameplate to believe. Is it a 208V motor requiring >70A to run or is it a 36A motor requiring >400V to run? The amp rating is actually closer to what you expect from a 460V motor than the 380V rating that you would expect from a dual voltage wye/delta motor having 208V as the low voltage. Having said that, is it really an 18.5kW motor?

Also, I will point out that the rated speed of 1470 rpm is pretty low for a 60Hz motor. Is it a Design C or D motor having very high slip or is it a 50hz motor? This is the problem, once you decide the nameplate is erroneous, which part can you believe, if any?


RE: What's the deal with VFD ratings?

That is the crux of it, not knowing where the mistake is.

Looks as though the 18.5kW is correct though. The “Y180M...” comes up as a Chinese 18.5kW 380V 1470RPM motor, “or any voltage between 220 - 760V, 50/60 Hz”. Yeah...

https://m.made-in-china.com/product/Y180m4-18-5kw-...
Click on the “Show more” link.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: What's the deal with VFD ratings?

So to finish that thought;
If it were me, I would tell them that given the obvious error(s) on the nameplate, you are going to assume the 208V and 18.5kW are correct, and only the FLA is wrong. Then treat it as a 25HP 208V motor with the VFD sized accordingly.

But warn them that IF the FLA was correct and they mislabeled the kW (ie its a 7.5kW motor with really poor efficiency), the motor may burn up before the OL trips in the VFD, at which time they can replace that toy motor with a real one made by someone who knows what they are doing.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: What's the deal with VFD ratings?

The 180M frame tallies with it being a 4-pole 18.5kW 50Hz machine.

A 2-pole design in that frame would be a 22kW machine, an 18.5kW 2-pole would be on a 160L frame and a 6-pole would be on a 200L frame.

If you can start it, measure the magnetising current when it's running open shaft - should be around 40%-50% of FLC at rated voltage. If it's way below that value then the chances are it's a higher voltage machine.

RE: What's the deal with VFD ratings?

jraef, your link is a good find and it does give us some clues. It appears that the kW rating, current, and speed are based on the 380V, 50Hz power supply. It is the nameplate voltage and frequency that do not match. Interestingly enough, the voltage and frequency stamps are a smaller typeset, suggesting that perhaps the motor is custom designed for 208V/60hz. This suggests the practice of pre-stamping the nameplate with kW, amperage, and speed and leaving the voltage and frequency to be stamped based on the custom voltage and frequency values. This is, of course, a shoddy practice. However, if true, this suggests that the motor rating would actually be 208V, about 62-65A, and about 1780 rpm.

Scotty, your suggestion is worthy of a LPS although I would suggest that the NLA could be as low as 30% for a four pole motor.

I will add that if the machine that the motor is a part of has a control power transformer in the control panel that this may lend confirmation to the motor voltage since the CPT primary voltage is usually the same as the motors mounted on the machine.

Another clue will be the size of the motor leads. The 208V, 65A rating on a six lead delta connected motor would need individual lead wires capable of carrying about 38A each. This would be somewhere between #10-14 AWG depending on lead wire temperature rating.

RE: What's the deal with VFD ratings?

380 Volts-50 Hz Delta is close enough to 760 Volts-60Hz Wye
I am with Jeff.
Go with the kW rating. (Cover Your ASSets)grin
Consider FLA = 35.9 Amps x 1.73 = 62 Amps.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: What's the deal with VFD ratings?

(OP)
Thanks for the great thinking here folks. (rhatcher love the sleuthing!) I have to send back the VFD and do it again. I don't want to torture the poor guy further hence the effort to get it as right as possible this time.

Hot off the presses!

It's a bandsaw I thought it was a waross saw (circular).

Saw running not cutting:
L1-L2: 203V
L2-L3: 203V
L3-L1: 203V

L1: 19A
L2: 20A
L3: 19A

Big wire to breaker: AWG 6

Measured here: (Hey! That's a 60A breaker. Not equating well with a +70A requirement of a 208V 25hp motor..)




In this panel. Note the Star/Delta starter.




And just for you rhatcher:



Which makes me wonder what the 380V is being used for?


This is -of course- a Chinese saw. I asked him how it cut - did 'seem fine or gutless'? He said it slows a lot in thick redwood, more than he would expect. He makes due with a slower feed rate.

Keith Cress
kcress - http://www.flaminsystems.com

RE: What's the deal with VFD ratings?

(OP)
Magnetizing current percentage x FLA = Unloaded current

If we split the 40% 30% gustimates:

0.35 x FLA = NLA
FLA = 20A/0.35
FLA = 57A

Fits with the 60A breaker.

So is this a 20hp motor and not really a 25hp?

Keith Cress
kcress - http://www.flaminsystems.com

RE: What's the deal with VFD ratings?

Hi rhatcher / Keith,

Something I've noticed with IEC motors is that both the starting currents and the open shaft currents are creeping up from the old norms. I guess this is because the manufacturers are trying to be more economical with the stator iron, although whether it is as crude as simply running the core closer to saturation I'm not sure - perhaps there are differences in the airgap and the rotor design too. The IE3 high efficiency motors are definitely more aggressive on starting, the old 6x FLC rule of thumb seems to be drifting toward 8x FLC.

I'm not saying what you have there is an IE3 motor - it could be pretty much anything if it's made in China - it's just a more general observation from this side of the water. smile

RE: What's the deal with VFD ratings?

What is that OL relay set for? Whatever it says will be 57% of the motor FLA (or should be, but coming from a place that can’t label the motor correctly, who knows).


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: What's the deal with VFD ratings?

Keith,

This is pretty perplexing. I can't make sense of the markings on the CPT. I would have guessed it was meant for 380V/208V step-down service but who knows. Is it actually stepping the 208V up to 380V and, if so, what is the 380V feeding? You should put a meter on it, perhaps it is stepping the 208V down to 114V which is 'close enough' to run 120V contactor coils.

The NLA amps that you recorded suggest the FLA is in the ballpark of what is predicted for the 18.5kW motor running at 208V. Also, the label on the breaker states In = 160A, not 60A. Why the breaker is this large is a mystery but this explains why it has not tripped smile. Jeff's suggestion of checking the overload rating is s good one, LPS for him. However, if they selected the OL's the same way that they selected the breaker you won't gain any insight from this.

Finally, what is the operator's goal in using a VFD? If anything, he will have to slow the feed rate even further when the saw is running slower. Also, the motor is fan cooled so you need to be careful running it at reduced speed with full load which is what will happen with a CT load like a saw.



RE: What's the deal with VFD ratings?

(OP)
Jeff, a capital idea!

rhatcher; That is a 208 step-up to 380V to run part of the system. Just proving your point that the original system is indeed a 380V system. I also see your point about the 114Vac angle.

I saw the In-160 rating but the client states that the breaker is a 60A unit and we can't see the breaker handle in any picture. I'm guessing the In-160 is perhaps a model number or frame size?

He has no interest in running the saw slower, the VFD is simply to allow frequent starts. It was considerably less money than a soft starter that only allowed 5 starts an hour. He often has to stop the saw to make adjustments between each cut. The star-delta is dying and he hates it. As for the overload its setting should set the motor current with a stake-in-the-ground because it's never tripped at it's dial setting.


Isn't it wonderful how they feed the breaker AWG 6 THHN and then feed the delta contactor AWG 8 (55A @ 90C) for a so-called 18.5kW motor?

As for Jeff's idea:

I'm not clear on why the overloads would be set to 57% of FLA. So, for the moment, if I don't know why, I'm gonna bet the Chinese sure don't.



32A-20A = 12A
Estimating that the dial is about 70% of that 12A = 8A
20A + 8A = 28A

Remember 208V.

Well if that don't beat all..



A 28A 208V motor is less than 10HP!! What a rip-off.
Explains why the AWG 8 hasn't charred black.



It's looking like the VFD we have will actually work since a 10HP motor is a 7.5kW motor and the drive we have is an 11kW Drive. (I'll throttle back the overload setting.)



So if the 57% doesn't come back and bite us the uncharred wire and the (100%) overload setting all make this look like a 10hp motor regardless of its 18kW frame.

I'll put in the drive-in-hand and run it. With it working a load I'll read out the amperage the VFD is supplying. We'll go from there.

Keith Cress
kcress - http://www.flaminsystems.com

RE: What's the deal with VFD ratings?

Keith,

Your first picture from the previous post that shows the incoming power leads also shows a label on the breaker stating In = 160A and the breaker model number also indicates a 160A rating.

Jeff's suggestion that the OL would be set to 57% of the motor rating is based on the fact that it is a six lead motor and the OL only monitors three leads of the six. 1/1.73 = 0.578. I would call it 58% but Keith was close enough.

With regard to your OL setting, I agree that it appears to be set at about 28A. This is interesting since you have not reported that the operator is having OL trips. Added to this, he also reports that the motor performance is less than expected. As I suspected, the OL appears to be set incorrectly, read on.

I had previously considered the motor to be a 'custom' version that is redesigned for 208V operation. However, I am now considering the idea that the motor is 'rerated' for 208V operation rather than 'redesigned'. Specifically, it may be the same winding as the 380V version. If this is true, the HP rating would be (208/380)^3 * 25 or 10HP/7.5kW.

This conclusion seems to be supported by all of the evidence at hand. If true, all I can say is wow, what a ripoff and what a deceptive way to nameplate a motor. It seems that your VFD will work and is, in fact, oversized. However, if you have it on hand I would run with it.

RE: What's the deal with VFD ratings?

Keith,

It just occurred to me, the panel, except for the OL, and the incoming power supply appear to be more than capable of handling a 25HP/18.5kW motor and I assume that the machine is also capable since the derated motor, operating well below it's capability, is mounted to it. If the motor feeder wires are capable of handling the load, the client may have the option of replacing the motor with one that is properly rated for 208V/25HP/18.5kW and, with the properly sized VFD, he could get the performance that he expects. This would allow a great increase in feed rate over what he has now.

RE: What's the deal with VFD ratings?

I ran into a couple of engineers who thought that it was acceptable to use a free air rating inside a panel. They eventually agreed to do it right.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: What's the deal with VFD ratings?

(OP)
I wanted to let you know what's transpired.

The drive-in-hand is an 11kW drive.
The Chinese motor was labeled 18.5kW.
The motor was mysteriously labeled 208V but is from 380V land.
Motor was originally installed with a now dying star-delta starter.

Yesterday we wired the motor in delta and dropped the leads onto to the possibly too small VFD that was in-hand. The manufacturer didn't bother running ANY grounds from the motor back to the control panel. Nor did they bother with providing a single ground point to the panel so none was brought by the 'electrician'. Cripes.

We tossed the drive on a piece of clean plywood on the floor and brought power from the YES 160A breaker in the panel, (Cripes3), to the drive. Unlanded everything related to the S/D starter. Rewired the motor cables in the control panel on an existing terminal block to assure a delta motor connection. Landed jumpers from this to the drive output. Ran a ground thru the plastic chain guide (the motor travels). Landed it on a drive ground screw.

Ran a ground on the floor, out the door from the fused disconnect, out to the control panel. Ran a ground wire from the control panel to another ground screw on the drive.

Turned on the dead 160A (??!?!?) Chint breaker. Turned on the service panel 60A breaker feeding the disconnect. Cautiously applied power to the 160 via the illegally around-the-corner disconnect and the drive lit up.

Checked the max freq parameter. Made sure it was completely in 'FrontPanel' mode. No jog available... (weird) Set the speed to 4Hz and pressed run at arms-length. The saw gently started up and ran at 4Hz. We changed the display to current and it vacillated between 20A and 35A randomly. With it still displaying amps we increased speed up to 60Hz. At 60Hz the display went to a solid 20A. Interesting.

Left it run for 20 minutes. Motor rise about 2C. Air fanning out of the drive about 2C.

Hit stop. The drive tripped on decel over voltage. Don't need a controlled stop so reconfigured to coast-to-stop.

On current display started the saw. Saw 40A for one blink.
Hit stop.

Dropped a 12x14 piece of redwood on the saw. Fired up the mill controls. And ran some cuts while monitoring the current. His normal feed rate is 30%, we cranked it up to 80%. The maximum current reached in steady-state was 28A... Drive temp went up to about 5C, motor temp went up to about 5C rise. The drive seems adequate (47A rating).

Now to tidy-up the whole mess.

Thanks again for your great guidance in helping me thru this lying-plate madness.

Keith Cress
kcress - http://www.flaminsystems.com

RE: What's the deal with VFD ratings?

And thanks to you! A happy ending, it seems. And your flamboyant writing makes it all the better.

But, as you know. After every sh*t work - there's also some paper work to do. Use soft tissue. It wipes best...

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

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