Bypassing (eliminating) a voltage level

[Mbrooke]

Typically I see 345 > 115 > 34.5kv.


In the US I am aware of several projects in New Jersey which are now stepping 345kv directly down to 26.4kv. Two substations in neighboring New Hampshire taking 345kv down to 34.5kv distribution, having been in existence for some time.


What advantages if any would there be to eliminating 115kv? What technical challenges would it create?

 

[davidbeach]

In my case I'd like to start skipping the 115kV and going straight from 230kV to 13.2kV or 34.5kV. The sole reason for that is pockets of high load density require so much transformation from 230kV to 115kV that the 115kV fault currents climb and climb. It won't happen, right of ways for 230kV are very limited, and so there are areas of our system where we have to manage long term plans to ensure that our 63kA 115kV circuit breakers don't become overdutied. If we could use 230kV where we use 115kV, in that area at least, fault duties would be halved (and losses reduced) without compromising load capacity.

 

[Mbrooke]

No way you could stick 230kv in place of 115kv with compact monopoles? I've seen bits of your system on Google earth, and yahhh, lots of 230kv to 115kv stations in the order of hundreds of MWs. Found it strange no offense lol. But if it makes you feel better California does the same thing.


But I'm with you on that. Perhaps 500>230>33kv would be the most ideal solution.

The thing is you have 345/115kv en mass in many states to the point I'm debating if its easier to just tap at 345kv while reserving 115kv for small rural load pockets. Distribution substations now typically supply 150MWs and on average the trend is to have more customers per station.

 

[prc]

I think this change is coming because of the increased power demand + higher rating possible with MV circuit breakers. Some years back when a large oil refinery was set up in India, they went for 174 MVA 220/33 KV x10 numbers to meet the load, skipping intermediate voltages. Malaysia has standardized on 30 MVA 132/11 kV to meet domestic loads and 90 MVA 132/33 kV to meet industrial loads from the same sub station. Next voltages adopted by them are 275 & 500 kV connected to 132 kV by auto-transformers. Of course the future trend will be to reducing the number of transmission voltage levels. In India it is slowly happening with eliminating 66 kV, 22 kV & 110 KV.