An 875kVA transformer isn't big enough for a 1,000 hp motor. If you were in the business of designing drive systems you would have no difficulty in understanding that.
There is no ad absurdum about it.
you're wrong. no you're stupid. well you're stupider so there.
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There is no ad absurdum about it.
let's agree to disagree
imho it is sufficient
especially if the 840 was measured at the drive output, then motor load is only ~750 kva (90 kva for the filter/xfmr consumption) on a 875 kva xfmr
need more info from the op
If it was, it wouldn't run over temp.
qcroanoke
Sometimes I don't know if I'm the boxer or the bag
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A concept
it did not run over temp
he said that is what he expected to see ('usually') but did not, but rather the output was clamped at 840 which surprised him (and imo impossible)
that is why we need more info
but on the surface, if measured at the drive out, the most convenient point, the xfmr only operated at 750 or 85%
electrofelon
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Wouldn't it depend on how much the motor was loaded? Perhaps the motor was oversized, or the calculated size was just over the next size down?
Quite right. Possibly a number of things. But if the transformer got too hot that's one problem right there.
Fulthrotl
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1HP = 746 watts.
1,000 HP = 746,000 watts.
that's not allowing for any losses whatsoever.
no heat, transformer loss, zip.
125% would be 932,500 watts.
failure not = burned up, damaged or over temp
he was told the output was clamped at 840 kva, not possible
it started and ran the motor fine
he did not know how they ascertained that
increase load gradually until output plateaued?
we do know where the 840 was measured, makes a big difference
filter takes 50-60 kva
xfmr consumes 40 or so
For all you know, we have a similar setup that works fine in the plant. Our's is an 850kVA transformer driving a 665kW motor for a reciprocating pump! If you compare with the OP's setup, 875kVA for a 746kW (1,00hp) motor against our 850kVA for 665kW. The OPs setup is loading their transformer about 9.4 times greater than ours.
electrofelon
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I am having trouble with that math! Your transformer to motor ratio is only slightly higher than the OP (1.17 vs 1.28).
I dont think it ever went over temp. Here is what the OP said:
The way I read that, if you take into account the previous and next few sentences, he wasnt saying that his transformer went over temp. He was saying, in general overtemp is what he sees on an overloaded transformer versus the "current limit" phenomenon he thinks he is seeing now.
Agreed. The transformer simply isn't big enough regardless of any other problems that there may be.
The OP question is 840KVA limitation of 875KVA transformer. My proof is no evidence other than OP statement existed for it.
???
665/850 = 0.78
746/875 = 0.85
1.09 or 9% more
moot
when converted to kva for eff/pf for this motor range
BOTH are ok
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so?
the xfmr is rated in mva
the motor depending on measuring point
is between 740-840 kva both < 875
filter loss 60 kva
xfmr 40 kva
calcs http://forums.mikeholt.com/showthread.php?t=187812&page=5&p=1871852#post1871852
drive mfgs (link previously posted) state xfmr kva >= motor kva
which it is
and the filter reduces stress on the xfmr
no one can say the xfmr is too small
the data indicates otherwise
From the OP:
"usually it just runs over temp."
I don't know why you continue to ignore that.
why do you misrepresent it?
he said 'usually', but not in this case, in this case output was clamped at 840 kva
impossible
I'm not the only one
imo it was NOT over temp
only output limited (impossible in this case)
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