Lighting project - voltage drop problems

[kbsparky]

I am in the process of doing a design/build project for lighting up a couple of ballfields. We are looking at approx 80kVA of continuous load.

The problem we have is the utility transformer is 3 phase, 208Y/120 Volts, and is located 500 feet away. From the transformer to the panel, and then out to the poles and ultimately the fixtures, I calculated a voltage drop of about 20.3 Volts. On a 208 Volt supply, this represents a 10% drop.

Not acceptable in my opinion.

Upsizing the conductors to compensate for this is looking to be quite expensive, and I am considering installing a 112.5 kVA transformer to boost it up to a 480 Volt system.

Doing so would allow me to use smaller size wires, and put more fixtures on each branch circuit. The voltage drop calculations show I would be within 5% at the fixtures, an acceptable amount.

I have not installed many transformers "in reverse" as this would require.

I believe that using a standard "delta-wye" transformer would work, but there would be no neutral connection (X-0) for either the primary, or secondary.

A few questions come to mind for this:

• I would certainly install a fused disconnect for the primary side (208) of this transformer. Would I need an additional one on the secondary side before my main breaker in the 480 Volt panel?
• Even though it is 500 feet away?
• Since the secondary would be "delta" 480 Volts, and no neutral conductor would be present, how does one perform the bonding/grounding? Does "X-0" get used at all?
• I am planning to install a 10 kVA 480-120/240 single phase transformer at the ball field pavilion building for incidental lighting and receptacle loads, including scoreboard(s). This would be a separately derived system, and make its own neutral.

Comments or suggestions are welcome.

 

[yired29]

They do offer step up transformers.http://www.swgr.com/store/dry-type-low-transformer/product/11-4417.aspx

 

[LarryFine]

I agree with the 480v idea, for your reasons: less voltage drop and fewer lighting circuits.

• I would certainly install a fused disconnect for the primary side (208) of this transformer. Would I need an additional one on the secondary side before my main breaker in the 480 Volt panel?

• I say no, the panel main is fine. Its feeder would be a tap.

• Even though it is 500 feet away?

• Because it's 500' away. I'd want a local disconnect.

  [*] Since the secondary would be "delta" 480 Volts, and no neutral conductor would be present, how does one perform the bonding/grounding? Does "X-0" get used at all?

  Best would be a Y secondary with the X-0 bonded/electroded at the transformer, a conductor run with the feeders, and bonded/electroded again at the panel. A neutral also gives you the option of 277v as well as 480v lights.

  [*] I am planning to install a 10 kVA 480-120/240 single phase transformer at the ball field pavilion building for incidental lighting and receptacle loads, including scoreboard(s). This would be a separately derived system, and make its own neutral.

  You might make this one 3ph as well, partly in case there's an HVAC or other motor load, and partly because I just love electrical symmetry.

 

[winnie]

I agree that higher voltage is probably the better approach, but balance this against the particular aspects of the lighting hardware that you are using and the number of hours per year that the facility will be used.

If the lighting ballast compensates for reduced supply voltage, then voltage drop becomes an issue of supply efficiency, not system performance. The losses end up costing money long term, but depending upon the frequency of use it may be cheaper over-all to accept more voltage drop at the beginning.

A common '480V delta to 208/120V wye' transformer is generally intended to be used as a step down transformer. While most are permitted to be used 'in reverse', there are numerous problems with this approach. In addition to the grounding issues that you mention, you may also have problems with increased 'inrush' current, and problems with the fact that your voltage adjusting taps are now on the secondary side rather than the primary side.

If you do use the transformer 'in reverse' your grounding options include 'corner grounding', where one of the phases is intentionally grounded, or using a 'grounding transformer' (small zig-zag autotransformer) to derive a neutral for grounding.

If you have sufficient lead time, then the right way to go is to install the 'proper' 208V delta to 480/277V wye step up transformer. These are somewhat less common on the used market, but they are certainly available from the manufacturers.

Of course you should also consider the costs of having the utility supply 480V. With a customer owned transformer, you end up paying for idle loss all the time the transformer is energized. Unless you cut power upstream of the transformer except when it is being used, you can pay quite a bit over time simply to keep the transformer warm. And if you do cut the power to the transformer, you may have issues with the cold transformer picking up moisture and the like.

-Jon

 

[kbsparky]

Update -->

Update -->

Update on this project:

Once we got the cost estimate from the power company, it was determined to have them set a transformer, and a separate 277/480 Volt service/meter at the ballpark.

Voltage drop issues solved! :grin: And, we can use smaller circuit conductors, too!

 

[cschmid]

plus you can pay many years of service charges for the cost of an install like that.