Estimating Motor Life time depreciation at SF 5

[gokulkrish2]

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

 

[LionelHutz]

The motor likely has a breakdown torque that is over 200% of rated. The slip at this breakdown torque will likely be around twice it's rated slip. So, you should be able to load the motor to over twice it's rating without it stalling. It will just run a little slower. However, the thermal limits of the motor will basically dictate how much load you can actually apply, unless you go and break something.

 

[dpc]

Since stating the obvious is one of my specialties: At some point the overload capacity becomes a moot point because the NEC (in the US) requires overload protection based on the motor's nameplate amp rating. So the overload protection will be (eventually) shutting down the motor once you exceed the service factor amps.

"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg

 

[edison123]

starkopete - A h/t from a fellow repairer. May our tribe grow.

epete - Thanks for that siemens link

 

[gokulkrish2]

Now tat is why i like this forum so much. Thanks a lot electricpete