motor overheating question

winnie · Jun 2, 2008

weressl said:
155C is the rise over maximum ambient, so the actual temperature could be 195C. If you have a 20C ambient you are still OK with a higher rise of 175C as long as the actual temperature does not rise above 190C.

I stand partially corrected and partially in disagreement.

When I buy magnet wire for motor windings, it always has a temperature rating, not a temperature rise rating. The motor suppliers that I've worked with always rated in terms of maximum temperature.

However it appears that 'Class x' temperature rating can be used to describe both a maximum temperature and a temperature rise. See
http://www.engineeringtoolbox.com/nema-insulation-classes-d_734.html

'Class F' means either a maximum temperature of 155C _or_ a 105C rise in a 40C ambient.

Note that while the winding hotspot rating might be 311F, and the outer frame is at 200F, I'm still uncomfortable with the temperature level. The 'temperature rating' is the temperature at which the expected insulation life is 20000 hours, or about 2.5 years. If the outer frame is 200F, then the 'hot spot' will be close to or possibly exceed 311F.

-Jon

steveng · Jun 3, 2008

winnie said:
I stand partially corrected and partially in disagreement.

When I buy magnet wire for motor windings, it always has a temperature rating, not a temperature rise rating. The motor suppliers that I've worked with always rated in terms of maximum temperature.

However it appears that 'Class x' temperature rating can be used to describe both a maximum temperature and a temperature rise. See
http://www.engineeringtoolbox.com/nema-insulation-classes-d_734.html

'Class F' means either a maximum temperature of 155C _or_ a 105C rise in a 40C ambient.

Note that while the winding hotspot rating might be 311F, and the outer frame is at 200F, I'm still uncomfortable with the temperature level. The 'temperature rating' is the temperature at which the expected insulation life is 20000 hours, or about 2.5 years. If the outer frame is 200F, then the 'hot spot' will be close to or possibly exceed 311F.

-Jon

thanks jon, for the explanation of the temp rise versus the temp rating.
i understand it more now. this pump has been in service for several years,
it is operating at less than fla, the vent openings on the motor have little air
flowing thru them, i am going to try to close the suction valve some to see if the temp rise will decrease a little, the valve is old rusted in the open position.

thanks

ZZZ · Jun 4, 2008

You did not mention the ambient temperature. 40C rise is 104F above ambient. Digital thermometers are not accurate in many cases but if the room is 90F degrees 194F motor is o.k Too much grease will cause overheating faster than too little. We have many new High E motors that run at 205 F degrees. Call Baldor tech support for more info.

steveng · Jun 5, 2008

thanks z

thanks z

ZZZ said:
You did not mention the ambient temperature. 40C rise is 104F above ambient. Digital thermometers are not accurate in many cases but if the room is 90F degrees 194F motor is o.k Too much grease will cause overheating faster than too little. We have many new High E motors that run at 205 F degrees. Call Baldor tech support for more info.

thanks zzz, i appreciate the tip.
the ambient temp in the mech room ranges between 80-90
i have a new fluke ir thermo

coulter · Jun 6, 2008

Steve -

steveng said:
... i am going to try to close the suction valve some to see if the temp rise will decrease a little, ...

Missed that the first time I read it.

I'd try closing the discharge valve instead, pumps tend to get upset if you drop the suction pressure - puts them closer to cavitation.

carl

steveng · Jun 6, 2008

follow up

follow up

I checked the motor closer,

the motor windings megged 150 - 180 megohms from L-G

the insulation at the motor leads was broken and almost shorting, taped them up for now, the fla is 7.0 amps, my reading were 6.9 7.2 6.9

this motor is 8 yrs old,

when megging the motor windings from line to line, what readings should you get? i was using a fluke 1587,

i got a new motor on the way, its still running,
i was able to isolate the valves , so we can replace it this week.

thanks for suggestions and coomments

steveng · Jun 6, 2008

coulter said:
Steve -

Missed that the first time I read it.

I'd try closing the discharge valve instead, pumps tend to get upset if you drop the suction pressure - puts them closer to cavitation.

carl

i agreee, on smaller pumps,

but, i have tried that on some 40 hp pumps and the current increases , instead of decreasing.

cadpoint · Jun 6, 2008

Is the pump served from a magnetic starter disconnect, with internal thermal couples?
I just wired one of these today and had to have the chief mechanical man explain what this pump did.

The design has one pump per air handler, three trailor size AHU's, all wired to also talk to siemens control panel.

Are you sure the thermal coupling are the correct size?
If they are not, could be a aged and now worn, cause and effect problem...

But hey, I also got to read more about the pump : )

coulter · Jun 7, 2008

steveng said:
i agreee, on smaller pumps,

but, i have tried that on some 40 hp pumps and the current increases , instead of decreasing.

A couple of assumptions:
1. not-vertical axial flow, not propeller, not PD.
2. Discussion is on centrifugal radial flow impeller, within normal range of specific speeds - if not, cancel the rest.

I don't think hydraulic principles are horsepower dependent. What works on little ones like the one you have also works on bigger ones of the same style.

Consider the attached pump/system curve. It shows pretty standard pump characteristic/sytem curves. if you have something different, again cancel the rest. (reference: Gould pumps)

I can only think of two types of systems that apply here - and I wouldn't know which you have. If not like one of the two, CTR:-?

1. Closed loop,pressurized where the static system pressure is well above the NPSH, like a hot water boiler. Here the throttle valve can be anywhere in the system - suction, discharge, doesn't matter. The system curve moves to the left, flow goes down faster than the head goes up - so horsepower goes down.

2. Open loop, static suction head, like drawing from a tank. Putting a throttle valve on the suction side reduces the suction pressure, which will reduce the flow a bit and drop the required hp a bit. But that only works until the suction head drops below the NPSH. Now the flow and head drop quickly, because the pump is cavitating. Hard on pumps. Eats the impellers and casings right up.

Now if one puts the throttle valve on the discharge side, then the pump amd required hp react the same a case 1.

The only way I know for throttling the discharge to raise the hp is if the pump is operating off the end of the pump curve - high flow, low head, usually poor application caused by system changes. In this case, throttling the discharge can raise the head faster than the flow goes down - hp is up. Throttle it some more and get the pump back on its curve and the hp will go down.

I can't think of a single case where it is better to throttle the suction of a pump instead of the discharge. However, maybe today is the day to learn something new.

carl

chaterpilar · Jun 7, 2008

throttling deischarge has always yielded better results.

Now Steve...hope your voltage rating and connections were in line with your nameplate...any feedback on that..

steveng · Jun 10, 2008

thanks carl

thanks carl

coulter said:
A couple of assumptions:
1. not-vertical axial flow, not propeller, not PD.
2. Discussion is on centrifugal radial flow impeller, within normal range of specific speeds - if not, cancel the rest.

I don't think hydraulic principles are horsepower dependent. What works on little ones like the one you have also works on bigger ones of the same style.

Consider the attached pump/system curve. It shows pretty standard pump characteristic/sytem curves. if you have something different, again cancel the rest. (reference: Gould pumps)

I can only think of two types of systems that apply here - and I wouldn't know which you have. If not like one of the two, CTR:-?

1. Closed loop,pressurized where the static system pressure is well above the NPSH, like a hot water boiler. Here the throttle valve can be anywhere in the system - suction, discharge, doesn't matter. The system curve moves to the left, flow goes down faster than the head goes up - so horsepower goes down.

2. Open loop, static suction head, like drawing from a tank. Putting a throttle valve on the suction side reduces the suction pressure, which will reduce the flow a bit and drop the required hp a bit. But that only works until the suction head drops below the NPSH. Now the flow and head drop quickly, because the pump is cavitating. Hard on pumps. Eats the impellers and casings right up.

Now if one puts the throttle valve on the discharge side, then the pump amd required hp react the same a case 1.

The only way I know for throttling the discharge to raise the hp is if the pump is operating off the end of the pump curve - high flow, low head, usually poor application caused by system changes. In this case, throttling the discharge can raise the head faster than the flow goes down - hp is up. Throttle it some more and get the pump back on its curve and the hp will go down.

I can't think of a single case where it is better to throttle the suction of a pump instead of the discharge. However, maybe today is the day to learn something new.

carl

thanks carl, i defer to your wisdowm and experience, you convinced me,
maybe i misread what i read?:-? after reading your explanation i can see clearer now.

this appplication is the closed loop chill water, this pump is one of 5 pumping a 2 barrel closed loop in the return line back to the central plant, the primary loop pumps are 2, 4o hp, 525 gpm vertical mount motors, paco type splitcase pumps,

thanks for the time you took, to explain.

steve

steveng · Jun 10, 2008

chaterpilar said:
throttling deischarge has always yielded better results.

Now Steve...hope your voltage rating and connections were in line with your nameplate...any feedback on that..

yes, chat, the wiring was correct at 480volt 3ph , the insulation at the motor terminals was so bad , i thought it would short when i powerd back up, after throttling the discharge, i limited the amps to 7.0 or less, at the starter L3 was reading 7.5 and L1 and L2 were reading 6.9 to 7.0

this motor has lasted 8 yrs, the infra red temp reading on the housing hot spot was less than 190 after throttling dis valve to limit amps

thnaksalot

coulter · Jun 12, 2008

steveng said:
thanks carl, i defer to your wisdowm and experience, you convinced me,
maybe i misread what i read?:-? after reading your explanation i can see clearer now. ...

(Rippppp!!! Argggg!! I hate that when I strain a muscle patting myself on the back

)

Glad I could help.

carl

steveng · Jun 14, 2008

follow up, carl

follow up, carl

coulter said:
(Rippppp!!! Argggg!! I hate that when I strain a muscle patting myself on the back )

Glad I could help.

carl

carl, we installed the new motor today , motor data
motor fla 6.6 @480 3ph 1750 rpm 5 hp L1 475 L2 475 L3 472
class f insulation fr 184jm

when first started pump the amp load was 7.4 7.5 7.8
keep in mind this is a booster pump in line with main loop pumps supplying this pump, so in an off state the impellar still turns from the other pumps supplying the loop,

after throttling the discharge valve i got the amps within range of motor fla
L1- 6.5 L2 - 6.8 L3 - 6.6
my discharge valve is approx 50% closed, but the suction is wide open

the motor is running a lot cooler also , reading @ less than 150f

thanks carl ,
chat, and all you guys on this forum!

coulter · Jun 14, 2008

Steve -
That's great.

I'm still curious about the original motor - not enough to ask you to go look.

As I recall, early on you said the original motor "rla" was 8.1A. Assuming that means "fla", 8.1A is really high for a 480V, 5hp. 6.6A fla on the current motor is more what I would expect.

Maybe the original motor was a special. 8 years continuous is 70K hours. That's way longer (like twice) that most motor bearings are rated to last.

Just thinking out loud. You got it fixed.:smile: That's the important part.

carl

steveng · Jun 14, 2008

coulter said:
Steve -
That's great.

I'm still curious about the original motor - not enough to ask you to go look.

As I recall, early on you said the original motor "rla" was 8.1A. Assuming that means "fla", 8.1A is really high for a 480V, 5hp. 6.6A fla on the current motor is more what I would expect.

Maybe the original motor was a special. 8 years continuous is 70K hours. That's way longer (like twice) that most motor bearings are rated to last.

Just thinking out loud. You got it fixed.:smile: That's the important part.

carl

carl, i was wrong on that, the original motor fla was 7.0 and it was running at
7.5 7.6 7.8 when i first checked it.

steveng · Jun 14, 2008

carl, follow up on pumps!

carl, follow up on pumps!

coulter said:
A couple of assumptions:
1. not-vertical axial flow, not propeller, not PD.
2. Discussion is on centrifugal radial flow impeller, within normal range of specific speeds - if not, cancel the rest.

I don't think hydraulic principles are horsepower dependent. What works on little ones like the one you have also works on bigger ones of the same style.

Consider the attached pump/system curve. It shows pretty standard pump characteristic/sytem curves. if you have something different, again cancel the rest. (reference: Gould pumps)

I can only think of two types of systems that apply here - and I wouldn't know which you have. If not like one of the two, CTR:-?

1. Closed loop,pressurized where the static system pressure is well above the NPSH, like a hot water boiler. Here the throttle valve can be anywhere in the system - suction, discharge, doesn't matter. The system curve moves to the left, flow goes down faster than the head goes up - so horsepower goes down.

2. Open loop, static suction head, like drawing from a tank. Putting a throttle valve on the suction side reduces the suction pressure, which will reduce the flow a bit and drop the required hp a bit. But that only works until the suction head drops below the NPSH. Now the flow and head drop quickly, because the pump is cavitating. Hard on pumps. Eats the impellers and casings right up.

Now if one puts the throttle valve on the discharge side, then the pump amd required hp react the same a case 1.

The only way I know for throttling the discharge to raise the hp is if the pump is operating off the end of the pump curve - high flow, low head, usually poor application caused by system changes. In this case, throttling the discharge can raise the head faster than the flow goes down - hp is up. Throttle it some more and get the pump back on its curve and the hp will go down.

I can't think of a single case where it is better to throttle the suction of a pump instead of the discharge. However, maybe today is the day to learn something new.

carl

The only way I know for throttling the discharge to raise the hp is if the pump is operating off the end of the pump curve - high flow, low head, usually poor application caused by system changes. In this case, throttling the discharge can raise the head faster than the flow goes down - hp is up. Throttle it some more and get the pump back on its curve and the hp will go down.

carl, this is the system i have at work, maybe, you can help on this, i have 2- 40 hp split case paco type pumps that were engineered/changed a few yrs back from the original design and here is what i am describing,

i have 3 chillers in line on a common 2 pipe loop approx 2000 feet loop, each chiller has a 10 hp pump, we are setup to run only 2 chillers at a time, the chiller pumps feeds the 2-40 hp loop pumps via a common pipe 6 " from chiller to a 10 " pipe header then reduces back down to a 8 to 6 at the t configuration then to the suction of the 40 hp pumps, the suction side of the 40 hp pumps has been throttled, due to the piping design/poor design, it uses a saddle type t configuration at the suction which causes cavitation if the suction valve is wide open,

i think you described in your previous post what i a relating here about, the pump being beyond its curve,

the fla on my 40 hp is 51amps, i am about 46-48 on both pumps,
the primary pumps, which are the 10hp are being pumped to the suction of the 40 hp pumps,

the original design had only the 2- 40 hp pumps,
the design was changed in 1990 to the current setup.

any thoughts or suggestions,

coulter · Jun 15, 2008

steveng said:
... any thoughts or suggestions,

Yeah - but I don't know if they are valid. I know some about pumps, but am not an expert (major disclaimer - in case you missed that

)

steveng said:
... the design was changed in 1990 to the current setup. ...

My first thought is: It has been working for 18 years. It may not be perfect, but is perhaps close enough.

steveng said:
... the suction side of the 40 hp pumps has been throttled, due to the piping design/poor design, it uses a saddle type t configuration at the suction which causes cavitation if the suction valve is wide open, ...

Which ones cavitate, the 10hp or the 40hp? If it the 10hp that makes sense. Pumps in series add the head. If the 40hp is pulling too hard on the 10hp, it could be pulling the 10hp suction pressure down below the required NPSH. If not, see the comment about having been working for 18 years:smile:

You may wish to get the specific performance curves for your pumps (both the 10hp and the 40hp). I attached an example of a Paco split case 5x6x12, 1750rpm. Possibly it is similar to the 40hp you have.

Dig out your data sheets and get your impeller diameters. Find the specific gravity for the fluid you are pumping. And have at it. Should be kind of fun.

Two books I would recommend are, "Cameron Hydraulic Data" https://www55.ssldomain.com/fpdlit/Merchant2/merchant.mvc? ($50) and "Crane TP-410, Flow of Fluids" http://www.tp410.com/ ($50). I think there are free downloads for the Crane paper - but I kind of like the book in front of me.
A couple of things to remember:
Pump curves are in "head' not pressure. The ratio is the fluid specific gravity.

NPSH is what keeps a pump from cavitating. The pump suction has to be above the vapor pressure of the fluid - if not, the fluid boils, and that's cavitation.

Since I likely have told you more that I know - I'll stop.

Keep us informed - it's interesting.

carl

steveng · Jun 16, 2008

coulter said:
Yeah - but I don't know if they are valid. I know some about pumps, but am not an expert (major disclaimer - in case you missed that )

My first thought is: It has been working for 18 years. It may not be perfect, but is perhaps close enough.

HTML:

Which ones cavitate, the 10hp or the 40hp?

If it the 10hp that makes sense. Pumps in series add the head. If the 40hp is pulling too hard on the 10hp, it could be pulling the 10hp suction pressure down below the required NPSH. If not, see the comment about having been working for 18 years:smile:

You may wish to get the specific performance curves for your pumps (both the 10hp and the 40hp). I attached an example of a Paco split case 5x6x12, 1750rpm. Possibly it is similar to the 40hp you have.

Dig out your data sheets and get your impeller diameters. Find the specific gravity for the fluid you are pumping. And have at it. Should be kind of fun.

Two books I would recommend are, "Cameron Hydraulic Data" https://www55.ssldomain.com/fpdlit/Merchant2/merchant.mvc? ($50) and "Crane TP-410, Flow of Fluids" http://www.tp410.com/ ($50). I think there are free downloads for the Crane paper - but I kind of like the book in front of me.
A couple of things to remember:
Pump curves are in "head' not pressure. The ratio is the fluid specific gravity.

NPSH is what keeps a pump from cavitating. The pump suction has to be above the vapor pressure of the fluid - if not, the fluid boils, and that's cavitation.

Since I likely have told you more that I know - I'll stop.

Keep us informed - it's interesting.

carl

carl,
the 10 hp pump, pumps thru the chiller then to the suction of the 40hp pump, the piping is the problem, the suction piping is too close to the takeoff(not enough straight run to allow inlet flow) this creates turbulence at the impellar, so when i try to open the suction to full flow,(keep in mind i have 20hp of pump pumping into 2 common 40 hp pumps pumping from the same suction piping.) i overamp the 40hp pump motors.

what is npsh?

coulter · Jun 16, 2008

Net Positive Suction Head

When the fluid is sucked into the impeller eye, the pressure drops. If the pressure drops low enough and the local pressure in the pump is below the vapor pressure, then bubbles form. As I understand (that's code meaning I may not) when the bubbles collapse, the implosion erodes the impeller. The bubble formation and collapsing is called cavitation.

The NPSH listed on the pump curve tells you what the head must be above the vapor prressure at the pump inlet.

I mixed the terms "pressure" and "head". As I said they are related by the fluid specific gravity.

head is in feet, pressure is lb/in^2, sg is lb/in^3 or lb/ft^3.

"Head" was a difficult concept for me to get. The old guy at Northwest Pump explained it like this: Centrifugal pumps suck fluid in the impeller eye, then accelerate it out along the impeller vanes. The fluid leaves the impeller at some particular speed. If the pump discharge were pointed up, the fluid would rise to a heigth of (V^2)/g. That height is the pump head.

carl

motor overheating question

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