What's the deal with VFD ratings? 4

[itsmoked]

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

 

[rhatcher]

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.

 

[rhatcher]

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.

 

[waross]

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

 

[itsmoked]

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, (Cripes[sup]3[/sup]), 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

 

[Skogsgurra]

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

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[itsmoked]

LOL. Thanks Gunnar.

Keith Cress
kcress -

http://www.flaminsystems.com