Using 33kV line for 11kV distribution 1

[Cerkit]

Hi,

Does anyone know what the main issues (if any) are associated with using higher voltage (such as 33kV) lines or cables for 11kV power distribution?

Thanks

 

[cuky2000]

The cost of line and cable rated for 33 kV will impose a heavy penalty to use in an 11 kV system.
If this is a private project will be a challenger to justify this to the owner. For the public project, this will bring a red flag to the approver.

 

[Cerkit]

To clarify, this is from the point of view that the 33kV assets are existing already. I am referring to technical issues not financial.

 

[cuky2000]

For existing asset, I do not see any issue to operate a 33 kV OH line at 11 kV. Just check if there is any PT or surge arrester that need to be replaced for the 11 kV.
If the asset is UG, in addition to the above, check if the extra capacitance of the cable will impact any issue associated with charging current and capacitance switching.

 

[xnuke]

If the 33 kV line was sized for the expected load, and the load remains the same, the line will be too small to carry the larger current needed at 11 kV.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[edison123]

The load carrying capscity will be 1/3rd. Lesz chance of electrical failures.

Muthu

http://www.edison.co.in

 

[cranky108]

I've seen this done in the US, where a 34kV line was used for 13kV. In the cases I saw there was an intention to convert the line in the future to the higher voltage, or the one large customer went out of business, so the tap was converted to the lower voltage.

I have also seen a 3 phase line used as a V phase line.

Things like this happen.

 

[Mbrooke]

Or where a 230kv line is used for 34kv

 

[itsmoked]

Bizarre looking Mbrooke!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[crshears]

Bizarre-looking only at first blush; we have numerous instances where we use retired 115 kV circuits as 28 kV feeders.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[Mbrooke]

It is, but gets the job done.

 

[wroggent]

34.5kV on a line built for 138kV

 

[Overvoltage]

Yep, happens all the time. Benefits: better clearance, better isolation between phases, and reusing existing infrastructure (less cost).

Can't say I'm not impressed by the 230kV line with the 35kV pole next to the structure, though!

Typically, we'll operate a 35kV line that has been retired (and is nearing the end of its life) at 12kV before it is rebuilt or moved UG at 12kV. At one time we had a 115kV line energized at 12kV, but that was an odd situation.

 

[bacon4life]

Higher voltage lines have conductors further apart, so will have a slightly larger impedance and higher voltage drop than a line insulated for the intended voltage. As others said, it is routinely done. During our system wide voltage conversion from 4 kV to 12 kV, individual sections would be reinsulated for the higher voltage using hot line techniques. Some of the reinsulated sections operated for long periods until each entire substation are was ready for the higher voltage.

 

[waross]

Our little island system in Central America had a problem with salt spray building up on the insulators in hot dry but windy weather.
In the autumn, when the rains started the salt started to conduct and we would have a period of numerous flashovers.
We changed out our 15 kV class insulators (system voltage, 13,200 Volts) with 35 kV class insulators. Our flashovers became rare.

Bill
--------------------
"Why not the best?"
Jimmy Carter