voltage drop to 100 hp motor

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ken nevers

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I have a customer who wants to feed a 100 HP 480 volt three phase crusher motor at a stone quarry, feeder needs to run overhead 1700'. Do I figure voltage drop differently using free air ? Any idea's on wire size.

Thanks
Ken
 
Ambient temperature is going to affect conductor resistance, but it's not a component of the standard calculation.

Is there any way you could step the voltage up to 4160 or something and then step it back down at the point of utilization ? Or could you get primary service ?

Just as a real quick calc, I come up with 350 kCMIL CU for a 3% drop.
 
It's nearly impossible to run 350 kcmil copper overhead. If you choose to run overhead, I encourage you to use some type of aluminum or ACSR messenger cable which will allow you to run some distance between poles.

There ought to be a better way than 1700' of overhead 480v circuit.

Jim T
 
bphgravity said:
The problem is that 350 kcmil can carry a lot more current in free air than it can in a raceway or underground. :?
Click to expand...

True. I guess you would have to extrapolate the numbers and come up with an equivalent size based on a free air application ?
 
I think the standard voltage drop table is for wire in conduit. If you have the wires separated by a few feet like the utility companies do (one phase on each side of a cross arm, one phase in the middle, and the neutral or ground above) I think the resistance in ohms/km might be different.

Steve
 
The free air ampacity does not change the voltage drop. There may be some changes as a result of the overhead configeration as pointed out by Steve.
Don
 
The NEC lists a 460 volt 100 hp at 124 amps. Information for Bare AL conductor for 1 mile, 25C is as follows:
#3 - 155 amps, R = 1.77, X = .134

#2 - 180 amps, R = 1.41, X = .138

#1 - 209 amps, R = 1.12, X = .127

For 50C
#3 R = 1.95

#2 R = 1.55

#1 R = 1.23
 
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