Derating of Pump Motors at Higher Altitude 4

[vecnaj1978]

Hello Everbody

I need a suggestion on the installation of pumps at Higher altitude

I need to install a Chilled water pump at an altitude of 2200 Meters above sea Level, The motor i am using is an TEFC AC Induction motor. The motor Manufacturer recomends to derate the mtore if the installation is above 1000 Above sea Level
Since this is all about the avialablilty of air at Higher Altitude and the motors needs to be derated

My question is if i install these pump in an airconditioned space,Do i still need to derate the Motors

If yes then please let me know the reasons and if no the wat is the reason

Thanks in advance for our Sugessions

Vec

 

[bimr]

That concern is for operating motors at ambient conditions, not in conditioned space. Motors with Class B or F insulation operate satisfactorily at altitudes above 1,000 meters if the ambient temperature is lower than 104 Degrees F. So you will be ok.

"Standard motors are suitable for operation up to 3300 feet; motors with service factor may be used at altitudes up to 9900 feet at 1.0 service factor."

"Operated at less load (a motor with service factor rating of
1.15 or higher can be operated at altitudes up to 9000 feet with a
1.0 service factor)"

http://www.dreisilker.com/Documents/Ctrl_Hyperlink/8_uid121420091225102.pdf

See the linked page:

 

[vecnaj1978]

Thanks Bimr

The reply is bit confusing me
i was told that at higher altitude the motors does not get enough air for cooling and hence the Out put of motors is reduced, and to get the required power we need to derate the motor

if cooling is the only criteria at higher altitude then can i install these motors in airconditioned room and by doing this i do not derate the motor

can you please help me in answering this is brief

Thank you

 

[bimr]

You only need to be concerned if you are operating outdoors in ambient conditions (hot weather). There is no problem if you are operating in conditioned space. See the attached page.

 

[bimr]

The rating of standard motors assumes operation at sea level in a
40°C ambient. For purposes of standardization it is considered that
there is no difference in motor operating temperature between sea
level and 3300 feet altitude.

The cooling effect of ventilating air is a function of its density. The
atmospheric pressure and density at higher altitudes is reduced and
the air cannot remove as much motor heat, causing the motor to run
hotter. As a general guide, motor temperature rise increases 1% for
every 330 feet above 3300 feet. To keep motor heating within safe
limits at altitudes above 3300 feet, there are the following
alternatives:

A. Supply a motor designed for standard sea level operation which
can either be:
(1) Operated at less load (a motor with service factor rating of
1.15 or higher can be operated at altitudes up to 9000 feet with a
1.0 service factor), or

(2) Operated in a lower ambient temperature per the following
table:
If Ambient Max. Altitude with
Temperature is: Same Service Factor is:
30° C 6600 ft.
20° C 9900 ft.

It should be remembered that, although the outdoor ambient tem-
perature at higher altitudes is low, motors probably will be
installed indoors in higher ambient temperatures. Motors applied per A(1) or A(2) above, will have no special altitude or temperature data on the nameplate.
B. Supply a special motor designed for the required high altitude
operation, with appropriate data stamped on the nameplate.

 

[BigInch]

First, Assume you want the same service factor at all altitudes. Why would that change?

Cooling is a function of density, as bimers article says, which is a function of absolute pressure and absolute temperature. However a small change in pressure has a much more pronounced effect on air density than does a large change in temperature.

Air density at 10,000 feet is 10.1 psia/14.7 psia = 69% of sea level, a 31% REDUCTION, and that's keeping the same, say 60[°] F temperature at sea level and at 10,000 ft altitude.

60 F (15.5 C) = 520 R
Now drop the temperature all the way down to 0 F (-18 C) = 460 R
Density is increased at that very low operating temperature by ONLY 460/520 = 13%
SO A NET REDUCTION OF 18%, IF OPERATED AT -18C

Operated inside a heated building, or perhaps simply an unventilated building, (not that many places need AC at 10,000 ft elev), its back to the 31% DECREASE



"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[Pumpsonly]

By Ambient temp it means the air temp surrounding the motor. The standard motor rating are based on 40C ambient temp.

If you have high altitude and at the same time also ambient temp lower that 40C you also can apply the up-rate factor.

see attached page extracted from a Technical Guide book published by a motor manufacturer.

 

[bimr]

Most electric motors are designed to run at 50% to 100% of rated load. Maximum efficiency is usually near 75% of rated load. Thus, a 10-horsepower (hp) motor has an acceptable load range of 5 to 10 hp; peak efficiency is at 7.5 hp.

Service factor is a multiplier that indicates how much a motor can be overloaded. For example, a 10-hp motor with a 1.15 service factor can handle an 11.5-hp load for short periods of time without incurring significant damage. Although many motors have service factors of 1.15, running the motor continuously above rated load reduces efficiency and motor life.

You say that you have a TEFC motor which usually has a 1.15 service factor. If you had a TENV motor, then the service factor is commonly 1.0. So in effect, you have already upgraded the motor by going to a TEFC motor.

The question is, what percentage of rated load will you be operating. If you will be at 85-100% operating continuously, then you should will have to evaluate this further.

 

[BigInch]

So, if it's somewhere around 60F at 10,000 ft, then it might actually be a gain of 3% or so.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[BigInch]

That also assumes that a 1% better cooling rate translates into a 1% increase in motor efficiency. I wouldn't think that is 100% valid assumption either, is it?

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[BigInch]

Hey. Say the motor is running at 90% efficiency, then only a max of 10% of its power is being rejected as heat, so a 1% improvement in that 10% heat dissipation rate is only 0.1 % better in terms of motor efficiency. In that case you'd have to improve the cooling rate by 100% to get 10% of motor efficiency back. Does that make sense?

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[ElSid1]

As previously noted, it is a density issue for cooling the load. TEFC motors (if MG-1) at elevation typically go up in insulation class for that reason. 2200M elevation, on a motor with a service factor does NOT require a de-rate

http://ufgscriteria.tpub.com/ufc_3-520-01/ufc_3-520-010077.htm

Always consult the manufacturer to verify. See this thread

http://www.eng-tips.com/viewthread.cfm?qid=24254

Did you do a search before posting? Also, this is a motor de-rate issue ... would have been better in the electrical section

 

[BigInch]

"with a service factor"
Again. Service factors are part of the service specification. If you require a service factor, how is it possible to eliminate that requirement by installing it at 2000 m? This "Not necessary to derate a motor with a service factor logic", makes no sense whatsoever.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[Pumpsonly]

Increase or decrease in cooling efficiency do not change the motor electrical and mechanical efficiency. With lower ambient temp ( assume same altitude) the stator will run cooler if the same load/current is applied. The power output of a motor is limited by the allowable operating temp of the insulation material. The current you put through the winding generate heat in the stator due to the resistance of the winding. If the heat generated is higher than the cooling effect, the temp.of the stator temp. will keep increasing until it exceed the limit of the insulation material and burnt out.
When you operate a motor into the service factor load you are actually running the motor much hotter than when you run below the 1.0 SF rating.
Most industrial motors are built with Class F insulation material but operate at class B temp. rise at 1.0 service factory.
You will find the motor maker will state that the 1.10 or 1.15 service factor rating will be operating at Class F temp. rise.

 

[nfinit]

I've learned this lesson the hard way, and at only 6600ft. If you maintain your service factor, you derate the motor. So to that extent, I agree with BigInch.

 

[ElSid1]

how is it possible to eliminate that requirement by installing it at 2000 m

You don't eliminte the SF requirement. The motor is adjusted for dielectric and current parameters

http://www.eng-tips.com/viewthread.cfm?qid=24254

Most industrial motors are built with Class F insulation material but operate at class B temp. rise at 1.0 service factory.

I agree. However, there is a NEMA MG1 motor derate chart given to me yrs ago. For the life of me, I cannot find it The closest I came was my link to

http://ufgscriteria.tpub.com/ufc_3-520-01/ufc_3-520-010077.htm.

In short, at 2200M, a motor specified with a SF, does NOT require a de-rate

 

[BigInch]

Does not require a derate. I'll go along with that. I've proven that already to my satisfaction at least, but apparently true only if operated at 60 F instead of 40 C, where the 31% loss of cooling capacity due to reduced air density is compensated by a 34% increase in cooling capacity by the lower ambient temperature.

PumpsOnly,
OK. I can understand that the power output will be the same; it has to be as the pump only draws the power it needs to do its work and the motor supplies that quantity; so no change on the demand side. BUT.. any energy balance suggests that excess heat generated must be subtracted from somewhere, so if excess heat is being generated by the windings and output power is the same, then input power must have been increased in order not to result in a lesser output.

ElCid,
Charts are nice, but don't explain a thing. The increased insulation, from reduced air density, explains how the voltage holds up, but not what's going on with the heat. My understanding, or lack thereof, concerning service factors has always been in relation to how much relative operating time a motor can spend over design load, where excess heat is generated and winding temperatures run hotter than normal. The only resoning that even comes close to explaining why a derate is not made is the possible cooling capacity increase from lower ambient temperatures. I have proven (to my satisfaction) how cooling does not require a rerate, so therefore the SF would also not require a reduction. Now my question is, why was SF mentioned as a condition when discussing the potential rerating of a motor brought to altitude.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[ElSid1]

why was SF mentioned as a condition when discussing the potential derating of a motor brought to altitude

An electrical may be better at explaining this, but here is how I learned it:
As mentioned above, most motors operate at class B insulation and have class F. The SF "forces" the manufacturer to "add a little more" of the class F insulation into the motor. This allows a motor, with an SF, to operate without derating up to 3000 ft (different than chart I linked to, but I was always told 3000 was the break even point. Probably a rule of thumb). Links to some papers ... and I always default to my electrical or manufacturer to verify operation

http://www.neiengineering.com/wp-co...f-Electrical-Power-Systems-and-Components.pdf

http://www.industry.usa.siemens.com/drives/us/en/electric-motor/anema-motors/specification/Documents/nema-application-guide.pdf[/URL]]Other factors affecting temperature rise,
such as duty cycle, high ambient temperatures, and high altitude operation may also influence the decision to derate the motor.

In short, altitude beyond 3000 feet above sea level, thinner air negatively impacts the ability of the insulation to adequately cool. Specifying a motor with a SF adds insulation which allows for the derate to start at a higher elevation (~9000 ft or 3000 m). Always consult the manufacturer. This is a synopsis of how it was taught/explained to me.

 

[BigInch]

ElSid1, Thanks for those links. The first, on page 409, seems to agree with my analysis above. They confirm that it requires a 1.15 SF motor to operate at unity at high altitudes. Unfortunately a decrease in SF is in effect a derate. If I wanted to have the same service factor at altitude as at sea level, then I would have no choice but to chose a better motor. If that's not a derate, I don't know what is.

PumpsOnly, Table II of that reference suggests that the temperature is allowed to decrease from 40 to 20 C when moving to 3000 m altitude, suggesting that ambient temp is correlated to output, not winding temperature. That temperature reduction I believe tends to confirm my analysis above, as I assumed close to the same 20 C at altitude.

While my simple air density and temperature does not consider SF, or indicates that it would not require a reduction from 1.15 to 1, the above link does. I suspect that the reduction in SF is necessary due to a tendency of an overloaded motor to generate even more heat than usual, which won't be as easily disipated at altitude.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[bimr]

BigInch

In your statement above, you left off "at an ambient temperature of 40 C".

It may be semantics, I don't believe that operating at a reduced temperature is considered to be a derate on the motor. It is a limit on the design operating conditions. See the attachment.

"A motor with a higher insulation class may not require derating in these conditions."

http://www.wermac.com/acm_2.pdf

In addition, "It should be noted that any motor operating continuously at a service factor greater than 1 will have a reduced life expectancy compared to operating it at it’s rated horsepower."

http://www.wermac.com/acm_2.pdf

jraef (Electrical) posted this comment on service factor:

"Service Factor (SF) is a concept uniquie to NEMA design motors and is defined as a percentage by which the motor can withstand an increased load while still maintaining rated torque and speed within an accepted tolerance, even though current is expected to rise. Some believe this to be a short time rating, however you will never find an AMOUNT of time discussed, mostly because it is nebulous. What is said is that when using a motor's SF, an increased temperature rise is to be expected and therefore the motor life will not be the same as if the SF was not used. Many OEMs choose to use SF as if it represented an increased HP at the shaft, mostly in order to avoid stepping up to the next size motor if their application calls for just a little more than a standard motor design allows. Those OEMs are generally not concerned that the motor will last 5 years instead of 20 years, because either way it is out of their warranty by the time it fails."

http://www.eng-tips.com/viewthread.cfm?qid=161272