Running power 4000 feet

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With so many ideas being thrown around, have you mentioned to the customer how much all of this may cost before spending a ton of time figuring out all the details? I haven't been estimating for as long as some on here, but I have learned the hard way a time or two. It seems that sometimes you work up some grand plan, all the details ironed out, and then when you present it to the customer, they almost fall over and then scrap the project in the blink of an eye.

I had one last year where a customer wanted me to quote retrofitting a 600 amp 480v transfer switch into an existing service. I hashed out all the details, cam-locks for the cords, a phase rotation monitor, etc and came back with a price around 17k. The customer quickly informed me they thought it would only be around $1700 or so.

Now most times I ballpark the price up front and if they are still serious, I tell them I will give them a hard number.
 
Cow said:
With so many ideas being thrown around, have you mentioned to the customer how much all of this may cost before spending a ton of time figuring out all the details? I haven't been estimating for as long as some on here, but I have learned the hard way a time or two. It seems that sometimes you work up some grand plan, all the details ironed out, and then when you present it to the customer, they almost fall over and then scrap the project in the blink of an eye.

I had one last year where a customer wanted me to quote retrofitting a 600 amp 480v transfer switch into an existing service. I hashed out all the details, cam-locks for the cords, a phase rotation monitor, etc and came back with a price around 17k. The customer quickly informed me they thought it would only be around $1700 or so.

Now most times I ballpark the price up front and if they are still serious, I tell them I will give them a hard number.
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They know it will be in the ten thousands and are willing to pay, the thing is they want it as cheap as possible considering the already steep price. But I do understand your concern, this is one of those 'should be cheap' scenarios (and it normally is), but voltage drop is throwing me for a loop.

Going over 480 volts is the only economical solution crunching the numbers.
 
This all sounds like some bogus story drummed up to spark the conversation the op wanted


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Post the mV drop per unit length of your proposed cable and I’ll do the number crunching. I would normally use “mV per metre” but can transpose the calculation to any values you work to.

960V using two 10KVA 120/240/480V transformers each end of the run is quite easy, the crunch will come with NEC compliance. You could consider having the two transformers in the same unit if that gets around some of the problems.
 
Tony S said:
Post the mV drop per unit length of your proposed cable and I’ll do the number crunching. I would normally use “mV per metre” but can transpose the calculation to any values you work to.

960V using two 10KVA 120/240/480V transformers each end of the run is quite easy, the crunch will come with NEC compliance. You could consider having the two transformers in the same unit if that gets around some of the problems.
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Question. If I put to transformers in series, will this still be within dielectric stress limits?
 
mbrooke said:
Question. If I put to transformers in series, will this still be within dielectric stress limits?
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In the UK yes, but I know the design tolerances used over here. For something like this I would specify the use and the manufacture will give a Yay or Ney to the suitability of the units.

I’d guarantee they will say Yay even for off the shelf units and will give the warranties. The important thing is let them know the intended use.
 
Tony S said:
In the UK yes, but I know the design tolerances used over here. For something like this I would specify the use and the manufacture will give a Yay or Ney to the suitability of the units.

I’d guarantee they will say Yay even for off the shelf units and will give the warranties. The important thing is let them know the intended use.
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I think, that when the center is grounded, the voltage stress will never been 480 volts when two units are paralleled to give 960 volts?
 
kwired said:
From art 100:

Structure.
That which is built or constructed.

Unless you picked that transformer from a tree, I think it fits the definition.;)
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Ok, that is now worth considering. Only issue is I need to find the cost of URD by the foot.


Tony S said:
http://cablesizer.com/

It’s easy to see what raising the voltage has on current and therefore the required cable CSA/cost.
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That is eye opening :eek:


Not only does less current mean less voltage drop, but as the voltage goes up voltage drop goes down even if the current stays the same. That means that doubling the voltage leads to 4x less voltage drop.
 
*Percentage* voltage drop, that is.
So if you have oversized the wires far enough beyond the minimum ampacity for voltage drop reasons at the lower voltage it is possible that doubling the voltage will allow you to cut the size by a factor of four.
 
GoldDigger said:
*Percentage* voltage drop, that is.
So if you have oversized the wires far enough beyond the minimum ampacity for voltage drop reasons at the lower voltage it is possible that doubling the voltage will allow you to cut the size by a factor of four.
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Hence why 1000 volts will trump 600 volts. The amperage reduction is further complimented by that slight increase in voltage.
 
4 off 480/240V transformers.
Top drawing 20KVA 4 off 10KVA
Bottom drawing 15KVA 4 off 7.5KVA
They should be off the shelf.

Have two units mounted in the same enclosure and order a spare unit for stock.

American-3_zpszlthyk8r.jpg
 
mbrooke said:
Hence why 1000 volts will trump 600 volts. The amperage reduction is further complimented by that slight increase in voltage.
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Yet we have the problem with needing a different design of insulation for circuits over 600 volts, which depending on load levels involved can still become somewhat of a wash between using 600 volts or going higher.
 
kwired said:
Yet we have the problem with needing a different design of insulation for circuits over 600 volts, which depending on load levels involved can still become somewhat of a wash between using 600 volts or going higher.
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For sure.

1,000 volts might trump 600 volts but you cant just assume so by looking only at a reduced conductor size.


There is still this to consider
  • More expensive labor
  • More expensive switches
  • More expensive overcurrent protection
  • Repairs more difficult (Unless the facility already handles this voltage level)
 
iwire said:
For sure.

1,000 volts might trump 600 volts but you cant just assume so by looking only at a reduced conductor size.


There is still this to consider
  • More expensive labor
  • More expensive switches
  • More expensive overcurrent protection
  • Repairs more difficult (Unless the facility already handles this voltage level)
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Correct, but coming from a hypothetical (theoretical) place. If conductors and switches can legally handle a 600 volt corner grounded system, why can't they handle a center grounded 1kv system where the phase to ground voltage is only 500 volts?
 
mbrooke said:
Ok, that is now worth considering. Only issue is I need to find the cost of URD by the foot.




That is eye opening :eek:


Not only does less current mean less voltage drop, but as the voltage goes up voltage drop goes down even if the current stays the same. That means that doubling the voltage leads to 4x less voltage drop.
Click to expand...

P = E2/R, if memory serves.
the squared thing helps out a lot.

double the voltage, quadruple the power, the resistance stays the same,
but the percentage of voltage drop is quartered, and so that magic 2%
voltage drop that makes my electrical engineer wake up crying in the night
isn't as hard to reach in the calculations.
 
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