Estimating Motor Life time depreciation at SF
Estimating Motor Life time depreciation at SF
(OP)
Hi Guys,
Recession has hit us. So we are trying to run a 1000HP motor to its SF level. We are going to increase feed into the crusher and by pass the Multilin beyond the overload setting. Now,
We know that we are going to reduce the life time of that motor. Is there a way that i can predict how much life is that motor going to lose?
I read through a lot of stuff in this form about running motor at SF. Was very helpful but in my application where there is frequent spikes in the load pattern, i think i would be wrong to assume the average current and go ahead with my analysis.
Here is a short description of the system.
1. It is a 1000HP motor.
2. We currently run at an average power level of 625KW and the spikes go about 880KW sometimes.
3. We are going to increase the feed into the crusher so that it will be loaded 15% more.
4. The RTD in the stator never get hot. They are around 170-190F maximum. But the motor is a class F motor.
5. My boss says the motor would be good for 2-3 years. I strongly doubt that.
6. I said it depends on the frequency of the spikes.
7. We are thinking to bypass the multilin completely and just go with the RTD protection.
Is this a good idea?
How can i exactly predict how much time that motor is going to run.
Any suggestion of somehow improving the motor life when doign this??
What are your thoughts?
gokul
Recession has hit us. So we are trying to run a 1000HP motor to its SF level. We are going to increase feed into the crusher and by pass the Multilin beyond the overload setting. Now,
We know that we are going to reduce the life time of that motor. Is there a way that i can predict how much life is that motor going to lose?
I read through a lot of stuff in this form about running motor at SF. Was very helpful but in my application where there is frequent spikes in the load pattern, i think i would be wrong to assume the average current and go ahead with my analysis.
Here is a short description of the system.
1. It is a 1000HP motor.
2. We currently run at an average power level of 625KW and the spikes go about 880KW sometimes.
3. We are going to increase the feed into the crusher so that it will be loaded 15% more.
4. The RTD in the stator never get hot. They are around 170-190F maximum. But the motor is a class F motor.
5. My boss says the motor would be good for 2-3 years. I strongly doubt that.
6. I said it depends on the frequency of the spikes.
7. We are thinking to bypass the multilin completely and just go with the RTD protection.
Is this a good idea?
How can i exactly predict how much time that motor is going to run.
Any suggestion of somehow improving the motor life when doign this??
What are your thoughts?
gokul





RE: Estimating Motor Life time depreciation at SF
Bypassing the Multilin is not a good idea. RTDs are much too slow to provide adequate starting/locked rotor/short circuit protection.
"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg
RE: Estimating Motor Life time depreciation at SF
dpc's R.O.T. is the same one I have always used; 1/2 the life for each 10 deg. C rise over the rated temperature. But there is no hard rule, it actually depends upon the motor mfr. Some say that there is NO decrease in motor winding insulation life within the Service Factor; some say nothing about it, meaning there probably is. NEMA simply says that if you run into the SF, you can expect that the life will be decreased.
"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: Eng-Tips.com Forum Policies
RE: Estimating Motor Life time depreciation at SF
RE: Estimating Motor Life time depreciation at SF
RE: Estimating Motor Life time depreciation at SF
One more thing. I am going to predict the increase in degC the following manner. Can someone validate it?
My average current maximum for the current load is 110A
My average temperature maximum from the Stator RTD is 195F
I am assuming Linear relationship between current and temp
So i say for every additional amp we put in we increase the temp by 1.77F(195/110). Is it a rational way to do?
If it is right then i can assume the max life of the motor to be 10 years and then give them an approximate life expectancy of the motor at SF.
Please Guide.
gokul
RE: Estimating Motor Life time depreciation at SF
RE: Estimating Motor Life time depreciation at SF
Rated.
"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: Eng-Tips.com Forum Policies
RE: Estimating Motor Life time depreciation at SF
Another comment - The 10C rule is for aging of organic insulation. It is very relevant for oil filled transformers. It may have been relevant for older motor insulation. But I am pretty sure it is irrelevant for materials used in modern insulation systems (daglas enamel strand insulation, mica paper tape, epoxy and polyester resins). They do not have that type of thermal aging process. It is more of a threshhold temperature above which their mechanical properties change.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Estimating Motor Life time depreciation at SF
For a class F machine, operating below 120 deg C is "supposed" to ensure a 20 to 25 year life.
RE: Estimating Motor Life time depreciation at SF
The chart on the attached is one attempt at quantifying the effect of temperature on the "life" of a motor. One caveat. Although the article was written in 2003, the IEEE standards referenced, 117 & 101, were published in 1974 & 1987 respectively.
RE: Estimating Motor Life time depreciation at SF
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Estimating Motor Life time depreciation at SF
I agree with you. Interestingly, IEEE 117 (Standard Test Procedure for Evaluation of Systems of Insulating Materials for Random-Wound AC Electric Machinery) has actually been withdrawn.
RE: Estimating Motor Life time depreciation at SF
Class F insulation is 311F rated. You are measuring 195F at the stator RTD's. I personally would give myself a 20% safety margin, partly because the stator RTD's are likely not measuring the hottest spot in the stator. So, if the motor doesn't go over about 250F then it's life should not be reduced very much.
One thing to note. You will lose your re-start capability if you push the motor temperature to it's limits. So, plan on setting the proper re-start delay timers if you do this.
RE: Estimating Motor Life time depreciation at SF
RE: Estimating Motor Life time depreciation at SF
You might find this interesting.
RE: Estimating Motor Life time depreciation at SF
how do you keep finding these good articles ?
RE: Estimating Motor Life time depreciation at SF
RE: Estimating Motor Life time depreciation at SF
http:/
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Estimating Motor Life time depreciation at SF
I've been involved with the repair of industrial electric machines for over 30 years, but because I lack any formal education I have become adept at finding/storing/using a myriad of resources, a person can collect a lot of information over that many years. One of the best resources that I have found is this forum. I am amazed at the level of both technical and practical knowledge that the regular posters to this site possess. I'm learning a lot from you guys, thanks.
RE: Estimating Motor Life time depreciation at SF
RE: Estimating Motor Life time depreciation at SF
"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg
RE: Estimating Motor Life time depreciation at SF
epete - Thanks for that siemens link
RE: Estimating Motor Life time depreciation at SF