FLA Nameplates vr's 1.15 SF - Whose right? 5

[Lovison]

Hey Guys,

1. I've been hearing this for along time. If the motor for example has 93FLA nameplated on it but it also has 1.15 service factor does that mean that the 93 x 1.15 = 106.95 available amps and if so why don't they just nameplate it for that?

2. I think it has something to do with the insulation or temperature rise? I'm sure you'll correct me if I'm wrong. Does it mean that you have a Class F rise @ 93 FLA and Class B rise at 106.95 amps.

Now these are things I've heard for many years so I want to get this right once and for all.

3. I've seen other's take the motor nameplate horsepower example a 75HP x 1.15 = 86.25 HP. Is this correct?

4. One last issue. If the motor is rated at 460V and you input lets say 480V. I know more voltage means less amps. But can you get in trouble with the misconception of available amps? Can you overheat at the higher voltage? Or am I just overly concerned?

5. Let's say this motor is sized for a condition that is 73 NBHP or very little wiggle room for system error. Any psi swings could be deteramental.

6. Another issue I have considered is the ambient temperature and the affects the motor overheating possibilities so I will hold off on that until I find out if some answers to the above.


Wayne E. Lovison
service-parts@naglepumps.com

 

[redtrumpet]

If you truly want to get it right, you should obtain a copy of NEMA MG 1, as this is the standard that defines most of what you have questions about. Some parts of this standard are open to interpretation as can be seen in many previous threads, but NEMA MG 1 is where it all begins.

After reading through MG 1, if you still have questions on specific items, post them on this forum. Otherwise people on this forum could spend hours repeating what is already easily available in MG 1.

 

[redtrumpet]

I should also add that there are many excellent materials available on the web. electricpete has posted the link to the Reliance motors web site many times in this forum. GE has an AC motor application guide available online in .pdf form. Show some initiative, search other threads in this forum, search a few motor manufacturers websites and acquire a basic knowledge of the topic instead of asking professionals whose time is limited and valuable to do your leg work for you.

 

[Lovison]

redtrumpet,

I'm sorry this request was too petty. I will know better next time. Wayne E. Lovison
service-parts@naglepumps.com

 

[buzzp]

1. I have done a lot of research into motor nameplate data and I know for sure that if the nameplate has SF vs SFA, then the SF (service factor) applies to the HP, at least by NEMA standards. Some mfg's put SFA (service factor amps) on the motor. This is why some mfg's put SFA on the motor to avoid confusion.
2. I don't believe that the temperature class has anything to do with the nameplate data (sure it does determine max amps,etc) but once the data has been determined then there is no need to modify the nameplate data based on temperature if the motor has the correct insulation class to begin with for the application.
3. This is the correct way, yes. Assuming the 1.15 is labeled SF. NEMA also specifies this SF based on temperature class and motor size. Again, once it is determined then there is no need to modify the nameplate data of a properly spec'd motor.
4. A motor is supposed to operate at +-10% of the nameplate voltage without any problems. If the motor is stamped 480, then it should operate at 432-524 volts. There are curves for derating the life of the motor and the HP based on variation of line voltage. Another misconception about operating a motor above nameplate voltage: the current will go down only slightly but then it will go up just like operating at below nameplate voltage. I can't recall how much above nameplate volts before the current draw goes up but it is only like 5% of nameplate volts. My rule is if your operating at anything other than nameplate volts (usually the case) then the motor is drawing more current to do the same work than if the line voltage was at nameplate volts. So yes you can definately overload a motor by operating at higher than nameplate voltage.

I need to post a short article in the FAQ's that would address some of your questions. Hopefully, I can do that today. Thanks

 

[redtrumpet]

No problem, Wayne. When I first joined this forum less than a year ago there were only about 30,000 members. Now there are over 50,000. The volume of posts has increased accordingly. I can't speak for others, but I have only a few minutes a day to spare for the forums. If the forums degenerate to the point where people are using Eng-Tips as their first point of reference, instead of reserving it until the end of their investigation when they are still unsure of an answer or solution to their problem, then you may see members alienated and simply stop using Eng-Tips.

 

[buzzp]

I believe he raises valid questions. Obviously, there are many electricians in this forum who would benefit from this discussion. After all, there are not many engineers that deal with motor controls who have a clue about installing or troubleshooting motors or controls. I speak from experience in working as a design engineer with a motor control OEM that has been around for three decades. Trust me, most of them would benefit from this discussion. I was fortunate enough to spend a year or two in the field installing and troubleshooting motors and controls as a field service engineer. It was definately a worthwhile experience.

 

[busbar]

Lovison, a short search of etips returns a bunch of hits by a wide variety of posters. Notably:

thread238-7626 posted by electricpete from MG-1: "A motor operating continuously at any service factor greater than 1 will have a reduced life expectancy compared to operating at its rated nameplate horsepower. Insulation life (and) bearing life are reduced by the service factor load."

Also thread237-5317 thread237-11535 thread237-10080

What I’ve learned is that “service factor” loading is permissible only when nameplate voltage, frequency and ambient temperature numbers (note zero voltage imbalance) are met. Anything else is playing games with motor life. Using “SF Amps” to select overload protection is a tactic akin to that of sleazy used-car salesmen.

 

[electricpete]

Try these links of for size.

thread407-9096
thread238-7626
thread237-5317

Good discussions above. NEMA is what defines it.

Good comments by Buzz. I wasn't aware there was a separate designation for SFA.

 

[Lovison]

To: byssp, busbar and electricpete

You gentlemen will go along way. I appreciate the direction and the time given to me. All your threads
have helped me on a current project.

Once more I thank you all. Wayne E. Lovison
service-parts@naglepumps.com

 

[buzzp]

Busbar, Your comment to set overload protection: "Using “SF Amps” to select overload protection is a tactic akin to that of sleazy used-car salesmen." is exactly how overload settings should be set up. The motor is designed to operate up to this current draw without significantly reducing the life. So if it is comparable to a sleazy used car salesman then so be it, hehe. Maybe I didn't get the meaning of that statement or something. Thanks.

 

[busbar]

buzzp-- Pardon me for not wording it better. I meant to say that nameplate full-load current must be used to size/set overload protection, and use of "service factor amps" instead is a misapplication and it's likely a cooked stator can be guaranteed. Sorry. I hope that makes a little better sense.

 

[dpc]

Long-term operation of a motor at its service factor rating will generally reduce the motor life and operating efficiency.

Motor performance data is based on nominal horsepower rating, not service factor rating.

Back when I was specifying motors, we specified that bhp could not exceed 87% of motor nameplate horsepower for motors with SF of 1.00 and could not exceed 100% of nameplate horsepower for motors with SF of 1.15. For a motor on a VFD, SF had to be 1.15 and bhp could not exceed 87% of nameplate horsepower.

 

[buzzp]

I disagree. I believe the OL settings should be set at the service factor amps of the motor. The motor is designed to operate at this current draw. Yes I agree it will reduce the life of the motor. If the application was constantly running at above FLA and not running into SFA then the motor is undersized and should be replaced with a larger motor. Question is: is the replacement costs higher than the motor? How much does it cost to change the motor out?
Most electronic overloads allow you to change the TC (trip class) or the trip time to define how long it can run in this condition. If the OL setting is to low, then voltage fluctuations will give you nuisance trips. Since voltage variations affect current draw (low V or high V gives high current). If the motor is pulling FLA then use SFA to set the OL setting. If you set it to the FLA then the motor is undersized for the application. People do not realize how much money they may be able to save a company if the motors were sized correctly. This is assuming the utility is monitoring for PF and penalizing you based on this. Also, if the motor were sized properly then the overall power consumed would be less than that of a undersized or oversized motor.

 

[dpc]

I'm happy if the electricians set the overloads anywhere close to the motor full load amps!

Seriously, I think the overload setting is a compromise between keeping the motor running to keep production going, or protecting the motor to prolong its life.

(Best idea is to use an embedded thermistor to monitor actual winding temp if the motor is important to you.)

 

[busbar]

buzzp— Can we agree to disagree? I think maybe we have different reasons for motor loading. The “every 10°C increase in operating temperature halving insulation life” is fairly powerful stimulus to ease off of any extra motor loading. Also, a lot of my time has been spent in a manufacturing and research environment where the cost of lost production in most cases far exceeded to cost of a motor.

When the effort for rigging and lifting a motor is estimated at $20K, it’s not hard to justify dedicated, very-high grade voltage- AND current-imbalance protection.

Applying IEEE guides and standards starts making {if only statistical} sense after a while. It gets to a point where you notice a pattern and start to realize that there are people [on IEEE working groups] that have formally reflected their experiences on paper, and may just have something. When the rubber meets the road, I don’t think that any motor or overload-relay manufacturer would honestly expect anyone to set an overload relay at anything other than the nameplate full-load current. {Now the actual inverse-time/current curve has been accounted for in setting that overload device based on FLC.} Some vendors are good at making promises about their space-age miracle products, but try to get them to take a phone call at 3:30AM [heck—5:02PM] to arrange for repairs or a replacement. They can be really good at forgotten, empty promises they made 3 months ago while giving you a nifty inkpen with their 9-to-5 phone number, and now, do little but plenty of finger pointing. Not all the time, but for many cases the cost of a motor and the energy to feed it gets dwarfed by loss of production and excessive use of repair budgets. Production managers like to scream a lot when their machinery and manpower is not usable on a minute-by-minute basis to meet some contrived projections on a pimple-faced junior assistant vice president’s computer display somewhere across the country. You’ve seen ‘em—the little spoogeheaded twits with their pathetic, “What have you done for me today?” demeanor.

Reliability aside, I don’t think that any published efficiency calculations are based on anything but a motor loaded to 100.0%; not 115%; not even 105%.

 

[buzzp]

I agree to disagree. I will agree that the application determines how the OL should be set up. I come from the oil and water industry. In the oil business, lost production is lost money (no brainer). The magnitude of the losses is what will determine whether the motor should run or not. Some oil wells I worked with were producing 20-$40000 worth of fluid (assuming 100% oil which was not the case since have water, etc mixed in) an hour. This versus a motor that costs $10000. But another factor is the work over rig that must be hired to pull the motor out of its 10000 foot well. These rigs typically get $500 an hour whether its working or not. This is the price and its charged 24 hours a day. One particular field had such low voltage that instead of fixing the field wide low voltage problems (no one knew what they were doing) they hired someone to go around and reset the OL's. When I was on site (~3hrs) at one location, it tripped three times. But again, they wanted the oil and didn't care how it got out of the ground. So I do agree the application will determine if the motor protection is bypassed or used as it was designed. I would still always set my OL relay to SFA's (had to throw that in there, hehe).
Another factor that would need to be considered is that if the motor is considered a minor cost, then if it fails every six months, then how much lost production in downtime and installation/removal costs will it take to pay for the downtime/installation/removal costs that we were originally trying to avoid? (hope that came out right)
Bottom line: there is no sure fire way to say set OL at FLA or SFA. Many applications would never run for more than a few minutes without tripping. The marketing for motor protection is just for that, motor protection. Not application protection. But sometimes this is more important than the motor. On the other hand, sometimes the motor is more important.