Transmission Line Basics

All power flows into and through the same grid, but it loses strength as it travels long distances. Substations are needed to change voltage (like 500kV to 230kV) and to maintain voltage levels to avoid “voltage drop” which will interrupt power.

Transmission lines are needed to:

Connect large loads (data centers!) to the grid (typically 230 kV, a few miles)

Distribute large amounts of power around a concentrated area of large loads (e.g., the Aspen-Golden-Mars-Wishing Star 500 kV loop, up to about 50 miles)

Bring power from generation sources outside the load area (typically 500, or 765 kV in our region; 50-150 miles for 500 kV, up to 300 miles or so for 765 kV, up to 2,000 miles or so for HVDC).

Transformers are used to lower the voltage as the lines get closer and branch out to the various loads. This can all be viewed as similar to what occurs with highways going from Interstates, to state highways, to local roads.

Local transmission lines and substations are coordinated by the energy companies with the regional transmission operator (PJM in the case of Virginia) through a Supplemental Need Request. Regional lines are coordinated through a Regional Transmission Expansion Plan (RTEP), such as the 2022-RTEP-W3 project approved by PJM in December 2023. Once approved by PJM, transmission lines must be approved by state regulators, who can override local zoning considerations.

Unlike for transmission lines, counties must approve zoning exceptions where required for substations.

What can we do when the transmission lines are coming for us?

So, can’t we just bury them?

Many people’s first reaction is to want to bury the transmission line. This is MUCH more expensive, but has been done on at least two occasions in Virginia with 230 kV lines, including the two-mile section of the Leesburg Bypass line. This has only been done once before in the United States at 500 kV, and the Virginia SCC hearing examiner recently rejected a proposal to bury the Aspen-Gold line along route 7. In addition to the cost, power companies claim the time to build and difficulty where rock or other utilities are underground, or significant highways or waterways are in the path makes it too hard.

Just Say No

Stopping a transmission line requires demonstrating that the need identified by PJM is not valid (this is hard for citizens or even outside experts to do) or by showing that the harm that would be done (environmental, historical, cultural, etc.) by the line overrides the need. In the latter case, power companies try to demonstrate that they can reduce the harm enough by altering the path or the method of construction. If the regulator grants eminent domain powers to the utility, which is the ability to take private land, then the landowner can try to argue a case in the circuit court (hard). Frederick County MD over the period 2010-2012 was able to block the PATH transmission line by denying the zoning permit for the final substation and then prevailed in subsequent court hearings and appeals.

Move Them Somewhere Else

In addition to arguing for a change of route to mitigate harms, it can be effective to argue that a line should use existing rights of way, when available. This deference is a matter of law at both state and federal levels. This was done in the regulator case for the Leesburg Bypass 230 kV line and was used to help persuade NextEra to abandon the 500 kV line through western Loudoun in favor of having FirstEnergy build the line in its existing right of way through northern Loudoun. The obvious downside to this is the harm to neighbors near the existing right of way. While it may be much less overall harm, it has a real effect on those landowners.

The strong opposition to the Maryland Piedmont Reliability Project has sought use of existing rights of way to the 70-mile greenfield line approved by PJM in December 2023; however, the power company has argued that the area around the existing right of way is already too congested with housing and other development. The energy company has shown no willingness to give up the work to another company that might be able to combine the new line with an existing lower-voltage line on double-circuit towers (as FirstEnergy is doing after NextEra gave up the work).

Reduce the Need for Lines: Put Load and Generation together (Collocate)

One alternative to building new transmission is on-site generation at the data center itself, but this often means gas-fired power and its own local pollution concerns.

Data centers are exploring options to build next to either existing or new power generation plants. This would avoid the need to build transmission lines beyond that location. This option has been controversial in the case of data centers going “behind the meter” of existing power generation plants because the data centers appear to be avoiding contributions to the cost of the overall grid and are essentially taking generation capacity from the existing customer base. A related option is for the data center to build its own power generation on site, for example taking advantage of a nearby natural gas line as one data center in Loudoun has done. Even building data centers next to power plants does not come close to solving the problem of not enough power plants!

Do More With Existing Right of Ways

New Federal regulations (Order 1920) require consideration of measures to “right size” (make best use of) existing rights of way prior to building new rights of way. Approaches to do this include:

Monopoles vs Lattice Towers: Using monopoles instead of lattice towers can reduce the required width to about two thirds of the lattice tower right of way. This is accomplished by stacking the three phases of the transmission line vertically instead of horizontally and thus requires a taller tower and higher construction costs. This can be used to place three monopole towers in place of two lattice towers, as Dominion will be doing as part of 2022-RTEP-W3 north and south of Leesburg.

Double Circuit Towers: At voltages of 230 kV and below, the power companies will put two transmission lines on one “double-circuit” tower; however, at higher voltages the companies try to avoid the risk of a tower failure (e.g., lightning) taking out two lines together (power companies overseas will do this regardless). Dominion, for example, prefers to have two separate 500 kV lines next to each other (these days, using monopoles to reduce width of the right of way).

Different and newer types of wires! – see next section: HVDC and other conductors.