220 kV 20 km transmission line

[radug]

Hello,

I would like to know which electrical studies should be done for designing a 220 kV 20 km transmission line: about 19 km overhead and the last km underground.

I have considered the thermal rating of the overhead conductor and the cable, as well as steady state voltage drop and short-circuit withstand capability.

What other studies should be performed during design stage? I heard something about putting reactances but I did not understand what for.

Any recommended references for performing the studies?


Thanks.

 

[davidbeach]

Fault studies?

 

[radug]

Thank you,

I was referring specifically to the overhead+underground line. It will be for solar power transmission, so it will be in a no-load state during night.

We will of course perform a short-circuit study of the whole system (power plants + transmission infrastructures).

 

[magoo2]

radug,

I think I now understand your initial comment. Your putting reactances means installing shunt reactors.

You need to look at the voltage rise (Ferranti rise) under no load conditions. If the voltage is too high, you may need the reactors. I suspect for the distances involved at 200 kV you probably don't need reactors. You're dealing with a fairly short line.

 

[bacon4life]

Any limits where you are for electromagnetic fields at the edges of the right-of-way?

 

[QBplanner]

30 km 230kV lines normally does't require reactors.

Normally, to solve the power frequency O/V you have three options:
high voltage reactors, high energy arrestor or dealying tripping.

You may have to proform a hand calculation to see how high the power frequency O/V will be and more detaield will be an EMTP type of study.

EMF is a good recommendation!

 

[rcw retired EE]

If the solar power facility owner owns the line, the revenue metering and interconnection point may be at the far end of the line, making the owner responsible for line losses, both kW and kVAR. Power plant developers are usually more sensitive to line losses than the utility.

In my experience, losses on a line designed to utility standards can be much higher than the developer realizes. This led to cancelling one project and redesign of the transmission lines on another, after the poles and hardware were purchased. A third project ended up paying severe power factor penalties to cover line losses. (In all those projects, the transmission line design was not in our scope.)

You may need to study the voltage profiles, and line losses for various operating conditions to optimize the design.

Galloping conductor analysis during windy icing conditions was another study that was done. But isn’t that analysis included in most line design programs now?

 

[radug]

Hello,

We have limited experience with transmission lines, that is why it will be done by others by means of a turn key contract. However, we have to specify, review and approve the documentation of the turn key proyect provider. That is why I need to know what studies are usually required, so that we do not miss any of them.

We are also concerned about the reveneu metering and we have already taken it into account so that reveneus are maximized.

 

[odlanor]

the other problem is ressonance, If you have a transformer
connected directly to the transmission line with CB at the terminal line.
I guess for 230kV, feeder transformer with line length close to 75 meters you get it.

 

[m3ntosan]

I guess you will need some reactances for the OHL, to provide for protection settings.. maybe, and also you may have to provide R, X ,B [%]100 MVA for the TSO who will operate the OHL.

If single phase high speed automatic reclosure will be available on the OHL, have you considered CTs at underground cable's ends for AR lock-out?