2 HP motor overheating? 1

[Ripcord13]

We have a 2 hp motor connected to a gearbox that drives a 5' shaft which had two blades on the shaft to stir liquid in a 500 gallon vessel. Management decided to have maintenance install a third "more agressive" blade on the shaft and now the motor is drawing 7.2 amps and running at a temp of 176 degrees F. This is in a hazardous location room. Am I right in being a bit "uncomfortable" with this?

 

[edison123]

Sad the "management" wimped out on the motor. What is the rated motor current and how & where are you measuring that temp ?

 

[Ripcord13]

I used a Fluke thermal imager to get the temp reading. Fluke amprobe to get the current 7.1 amps

S! Rip

 

[waross]

Voltage?

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

 

[edison123]

Actual winding temp will be higher and how much higher depends on type of motor. What is the nameplate current ?

 

[Ripcord13]

Dayton motor XPFC, C face mounted verticle,1725 RPM 230 V 3 phase supplied by our 208 volt system (I don't buy the equipment management does) max amb 40, C insulation class B,
FLA 6.3, nema nom eff 82.5%

S! Rip

 

[edison123]

It's being overloaded by about 12%. With a class B insulation, I would expect a very short life for this motor at this load.

 

[Ripcord13]

Thank you Edison123 Now I have enough "ammo" to state my case.

S! Rip

 

[jraef]

I love how people make decisions such as adding a blade without consulting an engineer to determine the efects of doing so.

I once got into an argument with a management type about his insisting that I increase the speed of a pump (above motor base speed) in order to make up for the fact that they had removed a 400HP pump and installed a 100HP replacement. They were shocked that the 100HP pump could not handle the peak flow conditions and were angry at me for insisting that running the pump faster would not solve their problem.

They just closed their doors last month I heard...


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[DickDV]

The agitator blades are going to have to be trimmed to get the amps to come down to the nameplate value when the highest viscosity liquid is being processed.

176 degrees F is not particularly hot. An Insulation Class B motor is good for 110 degrees C which is 230 degrees F. That is winding temp so the motor shell would have to be lower. I'm guessing here but I'd say around 205 degrees F would be a good place to quit.

Unless the motor is located in a freezing cold environment, you're going to have to reduce the amps anyway.

 

[jraef]

Dick,
If he used a thermal imager looking at the outside frame, the motor was a lot hotter on the inside...


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[DickDV]

jraef, I agree. But how much hotter? That's why I said I was guessing.

At full motor speed, I was guessing at 25 degrees F differential temp from inside to outside. At 176 degrees outside, that would be 54 F degrees differential.

How much is reasonable? Maybe one of these motor shop guys can tell us.

 

[edison123]

DickDV

I have seen anywhere from 20 deg C to 60 deg C temp difference between the motor body and the winding. Motor body temperature is not indicative of the winding temperature anyway (except may be in trending on a route check). That's why none of the standards speak about motor body temperatures.

 

[melghazaly]

this motor is overloaded and i wonder why u dont have overload protection?!! anyhow its critical case here to run the motor while its being overloaded

 

[Ripcord13]

Guys thanks for your response. I finally have convinced them that you either have to remove the third blade or pay to have it wired to 460 Volts which means piping and wiring to the 460 volt panel.

 

[edison123]

Changing the supply voltage to 460 V isn't going to cut it.

First of, this isn't a dual voltage 260/460 V motor, going by your earlier post. If you supply 460 V, to a 230 V motor, it will cook the motor within minutes.

Second of, even if it is a dual voltage motor, the HP of the motor does not increase by increasing the supply voltage. Your rated motor current will come down by 50% at 460 V and the percentage overload as before will still be there.

Either you ask the "management" to chip in for a new higher HP motor or remove the third blade.

 

[Ripcord13]

Sorry I forgot to mention that it is a dual voltage 230/460 volt motor. So you don't think it would be a step in the right direction changing to 460 volts?

 

[davidbeach]

It is a 2 HP motor, supply voltage doesn't enter into that consideration. You have more than 2 HP of load. You need to either reduce the load or supply a 3 HP motor. A 3 HP motor at 240V will do just fine, as will a 3 HP motor at 480V.

 

[Ripcord13]

I was just thinking that maybe just maybe it might lower the temp of the motor but as you stated Edison "2 HP is still 2 HP" no matter what the voltage.

 

[MotorVib]

That temp look vary low to me. DickDV & edison123 are righ. The big question is how much does the room temp change? If you are at a constent temp then this might not be much of a problem but if the room temp is going to be going up this could be a problem. That is what when motors are tested in labs they look at the changes in temp when compared to room temp.

Chris

"In this house, we obey the laws of thermodynamics." Homer Simpson