Maximum Radial MVA 5

[Mbrooke]

For all practical purposes, what is the maximum MVA you would design/load anyone line serving radial load? Say you had a radial load pocket of 600MVA-800MVA. Would you use two circuits? Four? Six? Right-of-Way width not an issue.

 

[Mbrooke]

Regarding this symbol:

(δ)

Do you mean phi? Or are you referring to delta lower case?

 

[cuky2000]

This letter represent the angular difference between the sending-end voltage a the receiving end voltage.
Could be called as any later. Notice that the Sin(δ) or Sin(Φ) control the power flow while the cos()=PF.

 

[Mbrooke]

I'm confused... you're saying Sin(δ) is the same as Sin(Φ)?

 

[cuky2000]

For the power transfer across a radial transmission line P=(V_r.V_s/X).Sin(δ)

Where δ=angular difference between the sending-end voltage a the receiving end voltage.

For additional reference, see page 2 of this link

 

[Mbrooke]

Alright, thanks for clearing this up.

 

[Mbrooke]

Can anyone shed light on a 230kv tower cost vs a 138kv tower cost? A tower holding cardinals vs blue birds on each side?

 

[7anoter4]

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/raw/upload/v1598624312/tips/Tramsmission_Line_Excel_Forum_wkexox.xlsx[/url]

 

[7anoter4]

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/raw/upload/v1598635451/tips/Transmission_Line_Forum_xefcca.xlsx[/url]

 

[Mbrooke]

Thanks, looking at them now.

 

[Mbrooke]

Alright. 110-220MVA per circuit is respectable.

But lets say I'm dealing with shorter lengths- or even the lengths involved- what is the maximum amount of load that a grid engineer would consider to much for a trip and reclose where the receiving end is not run paralleled (normally open)?

Engineering books are coming up dry and real world examples appear to be all over the place but typically not more than 120MVA average.

 

[bacon4life]

There are several transmission estimating guides available such as

https://cdn.misoenergy.org/20190212...ion Guide for MTEP 2019_for review317692.pdf.

220 MVA @ 138 kV with a 70 mile exposure would be very low reliability for the USA. In risk based assessment, one can look at the product of line miles and load served to come up with MW*Miles risk to compare various options.

 

[Mbrooke]

Does the exposure your thinking considering lightning a trip and reclose event?

https://www.youtube.com/watch?v=cNjUckDvfug

To me this would the biggest factor IMO.

 

[bacon4life]

Many other risks besides lightning are roughly proportional to length. Even though I live in an area with extremely low lightning risk, we still have outages from from trees, wind/weather, fires, birds, vandalism, equipment failure, car-vs-pole, etc.

 

[Mbrooke]

Understood- though a dedicated right of way does help.

 

[davidbeach]

Tell the dedicated right of way story to the City of Palo Alto, about 12 or 13 years ago. One small air plane, three 115kV lines, complete black-out.

 

[Mbrooke]

I'd love to hear more about this. Any links, papers or anecdotes?

Though to be fair there are plenty of cases where a right of way failure in the US would result in more than 1,200MW of lost load or even broader voltage collapse. Ie losing 2-3 structures (4-6 circuits) in the Westchester Right-Of-Way results in extensive load shedding or voltage collapse in and around the 5 boroughs. Worse case over 16,000MW of load could be lost.

https://files.engineering.com/getfi...&file=Millwood_to_Sprainbrook_contingency.pdf

 

[bacon4life]

The San Francisco peninsula used to be powered by 6 transmission lines sharing a ROW at the end of the SFO airport runway. Although they have not had plane crash take out all the lines, they did loose all the lines in 1998 when a crew left grounds on the bus in the substation where all the lines terminate. The Trans Bay cable now provides an alternate supply path to San Francisco.

 

[Mbrooke]

I know of that incident about the grounds being left in place! Read about it several times. Its one I use for reference of busbar protection and work practices.