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Checking different weather cases on Primary & Neutral of same circuit - OH line design in PLSCAD

Checking different weather cases on Primary & Neutral of same circuit - OH line design in PLSCAD

Checking different weather cases on Primary & Neutral of same circuit - OH line design in PLSCAD

(OP)
Hi all,

I've been working on designing a new 3-phase OH distribution line and going through NESC book to find what are the different weather cases to check for on OH primary and neutral conductors.

I recently found that if primary and neutral being used are different conductors, then the top one has to be checked for worst case condition (in most cases - max operating condition which is 120F temp) and the bottom conductor has to be checked for ambient temps (usually 60F) so that we can see if the clearances are being maintained. But does anyone know if we need to check for 120F on top conductor and NESC Rule 250C (Extreme wind case) on bottom conductor - because in most cases this would drive to worst case scenario where it is hard to maintain clearances in such conditions.

Also, is that case actually possible in real world? which if not, I do not see any point in checking for that combination of weather case.

Thanks everyone,

RE: Checking different weather cases on Primary & Neutral of same circuit - OH line design in PLSCAD

I don't see getting a significant wind difference between phase and neutral at normal spacing, but the amount of ice can vary. Did you consider an ice coated phase with a bare neutral below?

RE: Checking different weather cases on Primary & Neutral of same circuit - OH line design in PLSCAD

During high wind load cases, the phase conductors will operate much closer to ambient. For example for one of our conductors, going from 2 ft/s wind to 20ft/s wind will reduce the operating temperature from 100C to 50C per the IEEE 738 formula.

Take a look at figure 233-2.

RE: Checking different weather cases on Primary & Neutral of same circuit - OH line design in PLSCAD

(OP)
@stevenal: Yes, I did consider the ice coated cable with bare neutral and it did pass the required clearance. Like bacon4life said, with the extreme wind case, I didn't know that the temp of OH conductor can be calculated by IEEE 738, and it varies with wind speed. Good to know that...

Thanks,

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