Q: If the cost of transmission upgrades passed on to consumers is so low, but the cost of congestion is so high, why are we not doing more to improve the efficiency, capacity and reliability of the grid using modern conductors such as ACCC and ACCR?
A: The question asked why not use “modern” transmission conductors to improve grid “efficiency, capacity and reliability”. First thing to note is that these conductors don’t significantly impact efficiency or reliability. Efficiency or losses = I2R. Guess which term goes up with high capacity conductors? Yep, it is the one that is squared! If efficiency is a big priority and it is to be significantly impacted, a larger cross section conductor is needed. But, the calculation of the system-wide impact on efficiency is left to the interested participant. Capacity has an interesting relationship with reliability in that line capacity usually is only an issue after a failure, i.e. at the N-1 or N-2 state. So, planning tries to have adequate capacity for those states.
The “modern” grid is being required to deliver power from locations that didn’t exist when the grid was designed. It is just inconvenient that renewable sources are usually not at the plants where the grid’s lines terminated. Because grid configuration isn’t as variable as when the wind blows (or not) and when the sun shines (or not), the “modern” grid, planners are needing to get power from places that the grid just wasn’t designed for. So, this makes capacity and congestion more of an issue.
My take is that the “modern” conductors enable line capacity uprating, which can (mostly) use the structures and rights-of-way that are already in place. For new line construction conductors represent much less than 10% of overall line cost and the incentive in the new line case is to install as much capacity as circumstances will allow. An aside is that line voltage-uprating is an under-utilized option to really increase a corridor’s capacity, if the original line configuration will allow it. But, that is a whole other topic.
Transmission & Distribution World
A: ACCR (aluminum conductor composite reinforced) and other high-temperature, low-sag conductors such as ACSS (aluminum conductor steel supported) can increase transmission capacity for a given aluminum conductor cross sectional area. They can do this without adding additional weight to the transmission structure and supporting insulators as would use of larger conventional ACSR (aluminum conductor steel reinforced) conductor(s). Therefore such conductors are very suitable for increasing transmission capacity without having to make substantial structural changes.
Operation at higher conductor temperatures, however, increases resistance and decreases transmission efficiency. This may not be much of an issue if the additional capacity is used primarily for short term emergency operation following contingencies. Such conductors are more expensive, but there could be some offsetting savings in the insulators and structures. Because of their minimal impact on the existing structures, they are an excellent choice for upgrades to existing transmission lines.
HVDC Business Development
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