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Motor load 50%of nameplate data

Motor load 50%of nameplate data

Motor load 50%of nameplate data

(OP)
Hello guys,
i have a very strange fact.
i have 7 fan vertical motor-pulley-fan in a steam condensation field and for every motor i collected phase-phase voltage, phase-neutral voltage, and phase current.
All the motor are mechanically and electrically equal and have 380V, 88A, cosfi=0,82 data but during data acquisition i found some with very low cosfi (until 0,6) and very low load (until 53A).
In attachment you found data acquired. I don't know how many time this problem is present.

None have idea about this issue? or can instruct me to find the way to solve it?

PS: There are no problem on belt and the pitch angle for every blade is locked on the main shaft and with correct angle (from constructor)!!

RE: Motor load 50%of nameplate data

That is what you should expect. Unloaded motors have horrid pf. Load them and it drops right back down. A bigger question is why are the motors unloaded? That would likely be because something is restricting the flow thru the fans.

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

RE: Motor load 50%of nameplate data

What Keith said.
If you are NOT being charged a PF penalty, don't worry about the PF.
If you ARE being charged a PF penalty, add PF correction capacitors to the motors.
Load.
42 kW is a good number for a 45 kW rated motor.
32 kW and 22 kW. I suspect bad data or a different differential pressure across those fans.
Don't trust the contractor's data until you verify it independently. Quite possibly both bad data and different differential pressures.

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

RE: Motor load 50%of nameplate data

You might be equating the RATING of the motor with the LOAD on the motor, they are NOT the same thing. The rating is the MAXIMUM load that the motor manufacturer says it can handle safely. What the actual LOAD is on the motor is based upon the work it is performing in the machine it is connected to. So just because your motors are rated for 88A doesn't mean the WILL always pull 88A, it just means that if you pull MORE than 88A, you motor is going to suffer a premature death.

So your motors appear to be lightly loaded. There is nothing inherently wrong with that, in fact that's actually still within the "sweet spot" of the motor's peak efficiency. And as said by Keith and Bill, if the motor is less than fully loaded, the Power Factor will be low, but that's irrelevant unless you are penalized for having poor PF.


" 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: Motor load 50%of nameplate data

Some of the 45 kW motors are loaded to 42 kW
One of the 45 kW motors is loaded to 22 kW.
The others are in between.
The loads are supposedly identical, almost.

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

RE: Motor load 50%of nameplate data

(OP)
Thank you all for your response.
I want to clarify some things probably not detailed by me before.
  1. I know about PF concern. No load means more contribute percentually of magnetizing current that is 90 degree by Voltage and PF drops. All this is normal.
  1. This type of fan are made as in a picture attached so every fan suck same air because there is no ducts
  1. I made measurements by myself with calibrated Fluke 39 power meter
  1. I made today new measurement leaving all the rest in OFF position so all big charge possible for that fan but change a little bit in current (now 57,6) and in the angle (now 51°)
Why only one motor in same conditions is so little loaded? This is a real little load or could be present a problem in a motor/power-line?

thank you

RE: Motor load 50%of nameplate data

Did you attach the picture? I don't see one. I think we need one to help you further.


Remember you can use the Camera Image in the Reply window to directly post a picture into the thread. Hopefully it's smaller than 1000 pixels wide.

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

RE: Motor load 50%of nameplate data

(OP)
ITSMOKED i'm really sorry.... i forgot glasses

RE: Motor load 50%of nameplate data

Sophistioelevib,
Is "Vel" in your table the motor nameplate velocity (rpm)? I assume not measured as they are identical. It would be useful to know the measured speeds (tachometer).
John.

RE: Motor load 50%of nameplate data

(OP)
Aussiejohn2,
yes is the speed of the motor and is just a nameplate data not measured.
Could be useful but it is really difficult for me to measure.
1. there is no possibility to use optical tachometer (strobo light due to too much light)
2. No possibility to use contact tachometer for particular structural conformation

The measurement made today was because during my analysis i supposed the running of the motor would be running helped from the others but today only this fan worked during measurement

thank you

RE: Motor load 50%of nameplate data

Modern optical tacho's that look for the reflections (not the old-style stroboscopic ones) do surprisingly well even in sunlight, especially if you can mark the equipment (pen, paint, ideally reflective tape). From your photo I would say it is well worth a try if you haven't already. Otherwise...can someone on night shift take the readings? .

RE: Motor load 50%of nameplate data

(OP)
Aussiejohn2,
i think, wanted to know the real speed of the motor/fan, you have already your suggestion for my problem in your mind.
Could you please says what you want to find/demonstrate with real speed of the motor/fan?

RE: Motor load 50%of nameplate data

" Could you please says what you want to find/demonstrate with real speed of the motor/fan? "

A chart like this for "my" motor" would interest me if I were concerned about the load on an induction motor.

https://www.nidec.com/en-NA/technology/motor/basic...

Maybe the belts are properly tensioned, but if the pulley/sheaves were not the correct sizes then true motor and fan rpm would make it abundantly clear real quick.

RE: Motor load 50%of nameplate data

Pulley ratio is the ratio of the pitch diameters of the pulleys. While the geometry of the pulleys are fairly accurate, the true pitch diameter depends on how the belts fit in the V-groove. As belts wear they will fit deeper into the V-groove. The percent change in pitch diameter will be greater for smaller pulleys and thus the ratio changes. Fan power is proportional to the cube of the rpm so small rpm differences will result in large power differences.

One other factor I've learned to pay attention to with fan arrangements like this is that all the fan motors are turning in the right direction. It is very common for maintenance people to reconnect 3-phase motor wires motors so the motor reverses. It is surprisingly difficult to observe this when it happens when multiple fans are involved, without feeling the actual air flow.

RE: Motor load 50%of nameplate data

Bad data (Different CT ratios, bad CT's)

Wrong rotation direction

Lower fan speed

Muthu
www.edison.co.in

RE: Motor load 50%of nameplate data

Sofistioelevib,
Tmoose has it, different pulley ratio (or different belt or different pitch despite locking at construction or reverse rotation) will all show up in slight differences in speed. This lets us distinguish electrical from mechanical factors.
Muthu,
These are only small motors, I don't think there is a CT.

RE: Motor load 50%of nameplate data

(OP)
Thak you all guys,
your support is really helpfull.

Finally the only suggestion came up seems to be a problem in a speed (belt, pulley, pitch angle, ecc)
I'm going in these days to verify this problem.

Any other consideration/idea about this problem?

I have to consider this low power factor as a real problem? And considering energy saving how much these fans (normally under 0,8) can impact?

Very thanks to all

Regards

RE: Motor load 50%of nameplate data

Look at your power bill. How much are you being charged for low power factor?

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

RE: Motor load 50%of nameplate data

What's on the other side of those fans? Maybe a plugged heat exchanger is reducing the airflow on the spurious motor? Different fan blade, maybe a replacement?

RE: Motor load 50%of nameplate data

(OP)
@all
Hy guys, unforntunately i can't really have possibilities to check speed of the motor with or without contact so the speed will be unnkown.

@john2025
Right now i've no chance to evaluate pitch angle but could be an idea, but effectively this heat exchanger is more plugged respect other

BUT
could be loosing load to change so much the PF?

Regards

RE: Motor load 50%of nameplate data

A simple calculation shows that a motor running at 0.8 pF at 100% load will drop to a PF of 0.64 at 50% load.
The motor current will drop to about 78%.
The simple calculation ignores the change in magnetizing current with a change in load but it makes the point.

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

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