How would I provide a 480 +10% voltage system.

[stuartdmc]

I am designing a new project and one of the general electrical requirements are to provide 480 ? 10% Volts, 3 phase, 3 wire, 60 Hz, high-resistance grounded system.

This is a first for me, How would I provide 480 + 10% volts?, should I oversize the conductors to insure 0% VD? and the something for the grounding system?

 

[Smart $]

I am designing a new project and one of the general electrical requirements are to provide 480 ? 10% Volts, 3 phase, 3 wire, 60 Hz, high-resistance grounded system.

This is a first for me, How would I provide 480 + 10% volts?, should I oversize the conductors to insure 0% VD? and the something for the grounding system?

The devil is in the details

Nominal voltages specified to ? 10% Volts is typical across the board. You generally don't have to do anything beyond the norm to meet the requirement unless you have abnormal circumstances, which you didn't elaborate on...

And FWIW, it's impossible to oversize conductors to ensure 0% VD

 

[GoldDigger]

And FWIW, it's impossible to oversize conductors to ensure 0% VD

+1
Give me any VD greater than 0% and I can meet it, if POCO plays along. But 0% is beyond the limits of physics without using superconductors (including all connections. )
So you can have 0% for all practical purposes, which is good enough for most EEs.

 

[broadgage]

Almost certainly what is required is a standard system with a nominal voltage of 480, and with a plus or minus tolerance of 10% either way.

It is possible that what is wanted is a supply that can be adjusted, perhaps for testing equipment, but that would be a most unlikely requirement.

Almost certainly a standard 480 volt system.

 

[beanland]

POCO Variation

POCO Variation

The POCO will have a +/-% allowance and drift during the day; best to assume ?5%. Design for 480V and keep the voltage drop from service to load below 5%. Beyond that, you cannot control.

BTW: if you have a transformer, you can raise the voltage by using capacitors on the secondary of the transformer. A leading (capacitive) current passing through a reactance will create a voltage rise.

 

[iceworm]

... provide 480 ? 10% Volts, 3 phase, 3 wire, 60 Hz, high-resistance grounded system. ... How would I provide 480 + 10% volts? ...

I worked one close tolerance system. They took the service at 69kv, had two 14MVA xfm with on-load tap changers. The secondary voltage stayed within 2.5% of nominal. So, it is not hard to do. But it was not 100%. If the utility went black, so did the plant.

So, "How would I provide 480 + 10% volts?" Well, that depends on if the customer is missle defense or if it is irrigation. Perfect opportunity to talk to the customer and understand their motives. What are they looking for and why. Narrow down the spec to what they actually need. What can they stand for outages, sags/swells out of voltage spec, switching transients.

Another way to describe is do they want 480 ? 10% come hell, highwater, or hurricane; or are they satisified with whatever the utility can be bothered to provide? Could be a cost factor of 10x to 100X between the two.

ice

 

[iceworm]

... provide 480 ? 10% Volts, 3 phase, 3 wire, 60 Hz, high-resistance grounded system. ... and the something for the grounding system?

Impedance grounding is pretty simple and it is my favorite - so easy to do.

The customer will likely have to own the transformers. Utilities generally loath to provide anything other than grounded systems.

You will need a grounding resistor usually 27 or 54 ohms, ground detector, pulser, and a ground current clamp on ammeter.

Look at IEEE 141 (Red book) and IEEE 242(Buff book)

ice