New feeder 2000+ feet

[nhee2]

I need to run (design) a new feeder to run approx. 2000 ft underground to a new pumping station on an existing site. Load is approx. 80 KVA.

I had assumed a MV feeder would be most economical (there is 13.2 KV on site but all existing site loads are fed by 480 VAC). However, looking at conductor pricing online and in RSMeans it does not appear there is much savings as the minimum 15 KV cable size looks to be #2. Even with increasing conductor sizes for a 480 VAC feeder the savings to go with 13.2KV do not seem that large, once a transformer, switch, terminations at the remote location are factored in.

- Does 15 KV cable come in sizes smaller than #2?
- Am I missing some other savings associated with the higher voltage feeder?

 

[zbang]

Can you kick up to 600v for the run? Not a great increase but it might help. (Or drop from 13kv to 4kv and send that over somewhat cheaper cable.) Don't know if either of those are actually rational. I take it a new PoCo service at the pump station is out of the question.

 

[electrofelon]

Can you kick up to 600v for the run? Not a great increase but it might help. (Or drop from 13kv to 4kv and send that over somewhat cheaper cable.) Don't know if either of those are actually rational. I take it a new PoCo service at the pump station is out of the question.

Right not a big increase but will help and keep you in "cheap" LV territory. Another advantage is if a neutral is required at the remote site, you wouldnt need to send it along.....

 

[zbang]

Another advantage is if a neutral is required at the remote site, you wouldn't need to send it along.....

Hadn't considered the neutral, sigh, but yes. Sometimes a separately-derived system is a good friend.

Another possibly hair-brained idea is to drop 13kv to 4kv, then send a corner-grounded delta to the far end- one fewer HV cable to run and terminate. (Is this even compliant? Haven't put much thought into that. I don't do HV stuff.)

 

[nhee2]

thanks for feedback.

will look at 4KV and associated costs of (2) xfmrs and cable vs. a 480 VAC run.

 

[kingpb]

80KVA load? So, you only need a 112.5KVa transformer. At 13.2KV that's 5 amps. At 4KV that's only 16 amps.

If you were to consider MV, you will be well over-sized at the MV swgr side, cable, and having to add a transformer, of which I don't know if you can get a 112.5KVA with a HV side of 13.2 or 4kV; then you need a MV switch at transformer.

Even accounting for voltage drop you only need 500KCMIL aluminum to get 100A (80KVA) at 480V, 2000ft; under 5% VD.

I wouldn't even consider MV, not a good application.

 

[RichB]

80KVA load? So, you only need a 112.5KVa transformer. At 13.2KV that's 5 amps. At 4KV that's only 16 amps.

If you were to consider MV, you will be well over-sized at the MV swgr side, cable, and having to add a transformer, of which I don't know if you can get a 112.5KVA with a HV side of 13.2 or 4kV; then you need a MV switch at transformer.

Even accounting for voltage drop you only need 500KCMIL aluminum to get 100A (80KVA) at 480V, 2000ft; under 5% VD.

I wouldn't even consider MV, not a good application.

++1 Stay with 480VAC

 

[steve66]

I agree with the 480V - also for ease of maintenance, and not having to add a transformer, and everything that goes with it.

Just be sure the voltage drop isn't too high for any motor starting currents.

 

[nhee2]

good feedback, I had come to this conclusion after initially assuming MV would be appropriate given the long distance. but wanted to throw it out there to make sure I was not missing something.

thanks for the help.

 

[Tony S]

If a new Tx has to be installed to meet the new load then a MV feed is surely more economical.

At LV volt drop is going to be the killer. At 2000ft a 150mm? cable will give 3.4% volt drop, 185mm? 2.6%. You can work out the equivalent AWG size.

I wouldn?t even consider LV over that distance.

 

[iwire]

If a new Tx has to be installed to meet the new load then a MV feed is surely more economical.

At LV volt drop is going to be the killer. At 2000ft a 150mm? cable will give 3.4% volt drop, 185mm? 2.6%. You can work out the equivalent AWG size.

I wouldn?t even consider LV over that distance.

I love it. Two knowledgeable members with entirely opposite opinions. You have to love this trade.

I cant speak for the metric world but here in the land of AWG it is a significant cost adder to go above 600 volts. It typically means different, more expensive contractors and the equipment is magnitudes more costly. Long term up keep will also be signifcantly more as well.

 

[Strathead]

If a new Tx has to be installed to meet the new load then a MV feed is surely more economical.

At LV volt drop is going to be the killer. At 2000ft a 150mm? cable will give 3.4% volt drop, 185mm? 2.6%. You can work out the equivalent AWG size.

I wouldn't even consider LV over that distance.

When the OP says, pump station, I think of a fairly constant load. Unless there are lights and such there, why not just run appropriate cable and install buck/boost transformers to account for voltage drop?

 

[electrofelon]

I love it. Two knowledgeable members with entirely opposite opinions. You have to love this trade.

I cant speak for the metric world but here in the land of AWG it is a significant cost adder to go above 600 volts. It typically means different, more expensive contractors and the equipment is magnitudes more costly. Long term up keep will also be signifcantly more as well.

I agree. I have calculated out quite a few long wire runs - none quite this "severe", but I always find that it takes A LOT of cheap aluminum conductor to add up to the cost of transformers and other expensive gear......

 

[nhee2]

Application is landfill. Pump operation is cyclical. As I said, I went in thinking MV would be 5 he way to go, but the cost savings are not much , if any when compared to big AL conductors

 

[Strathead]

Application is landfill. Pump operation is cyclical. As I said, I went in thinking MV would be 5 he way to go, but the cost savings are not much , if any when compared to big AL conductors

If the cyclical comment was in regards to my buck boost comment, that doesn't matter, the load would still be constant and buck boost would work. If there is a lead/lag pump set up that I didn't think about before, that on the other hand would preclude the buck boost because it wouldn't then be constant, at least when both pumps were running simultaneously.

 

[kwired]

Hadn't considered the neutral, sigh, but yes. Sometimes a separately-derived system is a good friend.

Another possibly hair-brained idea is to drop 13kv to 4kv, then send a corner-grounded delta to the far end- one fewer HV cable to run and terminate. (Is this even compliant? Haven't put much thought into that. I don't do HV stuff.)

Corner ground still requires a separate grounded and equipment grounding conductor - if the application is covered by NEC, and sounds like it likely is, if POCO were running a new service to that location they wouldn't use a separate EGC, even if they used their MGN as a current carrying circuit conductor.

 

[zbang]

Corner ground still requires a separate grounded and equipment grounding conductor

Sure. I was wondering if you could put the grounded phase on a LV cable, but then you'd have different sizes for the CCCs. Forget I mentioned it.