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#62941 - 03/03/06 11:22 AM Calculation Question
Dnkldorf Offline
Member

Registered: 12/12/04
Posts: 1091
Loc: nowhere usa
Givens:
Voltage 424V
Current 354A
Wiring used 500MCM copper
Length of wires 500'
Number of conductors 3
price per KWH $.15
Hours of operation 24Hrs/ day 30days/month

Question: How much will I save in line losses a month if I increase the voltage to 480V?

Non-resistive loads....

Any takers?

Dnk....

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#62942 - 03/03/06 12:26 PM Re: Calculation Question
Dave T Offline
Member

Registered: 01/22/05
Posts: 157
Loc: Waukesha, WI, USA
The "new truck" post is easier than this one.

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#62943 - 03/03/06 12:53 PM Re: Calculation Question
Radar Offline
Member

Registered: 04/30/04
Posts: 349
Loc: Los Angeles, CA
Dnk - Are we to presume 424V 3Ø 3W with 354 line amps for the initial condition?

And entirely motor loads so we can say total connected VA = 424V x 354A x 1.73, which would also = 480V x 313A x 1.73 for the new condition?

Radar
_________________________
There are 10 types of people. Those who know binary, and those who don't.

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#62944 - 03/03/06 01:08 PM Re: Calculation Question
Celtic Offline
Member

Registered: 02/26/05
Posts: 367
Loc: NJ
How much (% or $ wise) do we get for answering this?
_________________________
~~ CELTIC ~~
...-= NJ =-...

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#62945 - 03/03/06 01:27 PM Re: Calculation Question
Redsy Offline
Member

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
I humbly withdraw my reply.

[This message has been edited by Redsy (edited 03-03-2006).]

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#62946 - 03/03/06 02:11 PM Re: Calculation Question
Dnkldorf Offline
Member

Registered: 12/12/04
Posts: 1091
Loc: nowhere usa
Dave T, that was toooo funny

Celtic, you get nothing but a "atta boy"

Redsy, your way off..or I'm way off...

Radar, just assume 354A per wire, nothing more than that yet. Assume all electrons are oscillating clockwise if you want...

Dnk...

[This message has been edited by Dnkldorf (edited 03-03-2006).]

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#62947 - 03/03/06 02:39 PM Re: Calculation Question
Radar Offline
Member

Registered: 04/30/04
Posts: 349
Loc: Los Angeles, CA
 Quote:
Assume all electrons are oscillating clockwise if you want...

That would be incorrect, I believe they'd go ccw. eheheh

Seriously, my guess is approximately $117.55.

Radar
_________________________
There are 10 types of people. Those who know binary, and those who don't.

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#62948 - 03/03/06 04:16 PM Re: Calculation Question
Dnkldorf Offline
Member

Registered: 12/12/04
Posts: 1091
Loc: nowhere usa
Atta-boy Radar...

I got $118.05....

For my next one, I'll come up with something like:
If I have twice as many sp 20a breakers than sp 30's, but 1/2 as many 2 pole 20A than 50's?

Give me the load on each breaker?

You game?


Dnk..

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#62949 - 03/03/06 04:52 PM Re: Calculation Question
Radar Offline
Member

Registered: 04/30/04
Posts: 349
Loc: Los Angeles, CA
I'm game - maybe we shouldda let this thread develope a little more before giving away the asnwer tho . . .

Radar
_________________________
There are 10 types of people. Those who know binary, and those who don't.

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#62950 - 03/03/06 04:58 PM Re: Calculation Question
winnie Offline
Member

Registered: 09/15/03
Posts: 652
Loc: boston, ma
As the computer on 'Star Trek' says: "Insufficient Data for Meaningful Response".

The problem is that we don't know how the load will respond to the change in voltage. If these are a bunch of lightly loaded motors, or resistance heaters, then increasing the voltage might result in _increased_ current flow to the load. On the other hand, if these are heavily loaded motors, or thermostat controlled resistance heaters, or other _constant power_ loads, then increasing the voltage means an automatic reduction in current flow. If these are motors, then increasing the supply voltage will mean reducing the 'load current' but increasing the 'magnetizing current' (reducing the power factor).

For the purpose of calculation, we have to assume something, so I am going to assume a simple constant power load; increasing the voltage means reducing the current and the same total VA supplied to the load.

The resistance of 500 MCM conductor at 25C is 0.0129 ohm per 500 feet. The voltage drop in each conductor is 354A*0.0129 Ohm= 4.57V, and the voltage delivered to the load is 424-(root3 * 4.57) = 416V. The VA delivered to the load is 416*354*root3=255kVA. The power dissipated in the wires is 4.57*354*3 = 4850W

Now we change things so that we have 476V delivered to the load (I am guessing here, rather than solving the equation) so we get 255kVA/root3/476=309A. Check the voltage drop and we get 309 * 0.0129 = 3.98V The power dissipated in the wires is now 3700W. So you end up saving about 1150W. 8766 hours in a year, so you end up saving about 10000 kWh per year. So I guess a savings of about $1500 per year.

-Jon

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