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Join Date: Nov 2011
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Changing Options of Underloaded 160kw Motor?

11/20/2011 6:51 AM

In our company there is 160 kw motor running with star delta starter. Running load is 90A Pf .85 Voltage 426v Can I change this vaccum pump motor with 110kw motor.. Please guide dear friends......

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Guru
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#1

Re: Changing Options of Underloaded 160kw Motor?

11/20/2011 8:17 AM

It would seem to be over rated, but does it have any peak loads it has to handle?

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#2
In reply to #1

Re: Changing Options of Underloaded 160kw Motor?

11/20/2011 9:15 AM

no peak loads. Main motive is energy saving by smaller rating motor.

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Guru

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#3
In reply to #2

Re: Changing Options of Underloaded 160kw Motor?

11/20/2011 10:00 AM

But then why did they select a 160kW motor? Cushioning?

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Guru
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#4

Re: Changing Options of Underloaded 160kw Motor?

11/20/2011 11:07 AM

Motors use only what they need to use, plus losses inside the motor. All you will save is the very slight difference in the losses, maybe a fraction of a percent of total consumption. The cost of the new motor must be compared to the energy savings in order to properly evaluate this. If it runs 24/7/365 it may be worth it, but if it runs intermittently, as vacuum pumps often do, the payback may be too long to be of immediate impact.

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#7
In reply to #4

Re: Changing Options of Underloaded 160kw Motor?

11/21/2011 3:37 AM

yes its running 24/7/365

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Guru

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#5

Re: Changing Options of Underloaded 160kw Motor?

11/20/2011 11:59 PM

The smaller motor will run hotter and not save any energy.

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Guru

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#6

Re: Changing Options of Underloaded 160kw Motor?

11/21/2011 2:34 AM

They say at about 80% of the rated load the efficiency is maximum,so select accordingly

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Anonymous Poster #1
#8

Re: Changing Options of Underloaded 160kw Motor?

11/21/2011 8:20 AM

In India at 415 V (how did you manage 426V?) 3 phase

The power consumption is sqrt(3)x415x90x0.85 = 55KW and even at 426V(?) is 56KW

At 165KW you are running the motor at approximately 33% Load. At this load though the efficiency could be a few percentage lower but I won't have expected a high 0.85 pf. A pf of 0.65 to 0.7 would have been more probable.

The basic question is still why this very highty overrated motor?

Though I am not much aware of the vacuum pump characteristic curves, may be under certain load conditions it might need that power.

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Anonymous Poster (1); electricalexpert65 (1); JRaef (1); panju (2); pnaban (1); TonyS (1); Wal (1)

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