Pleasant View-Hamilton 230kV Line

Project Details

Construction Updates

Check here for updates to the schedule for traffic stops. This schedule is not complete, and is subject to change.  Motorists can expect delays at these times and locations:

• Mid-September:  Crews will be pulling wires along Route 7 Bypass from the Sycolin Road area north to the interchange at Leesburg Outlet Mall
• September - October:  Work will take place along East Market Street

Project Schedule

2009

• Construction notification letters were mailed to residents along the route
• Right-of-way areas were prepared for construction, foundations have been installed along almost 50% of the route.

2010

• January - W&OD Trail Detour route opens to the public.
• January - Underground construction begins along W&OD Trail. 
• Spring - Construction of the Hamilton Substation scheduled to begin. 
• Spring/Summer - Poles installed along Rt. 7 from Hamilton area to Crosstrail Blvd.  Poles have started going up on the western end of the project, near the new Hamilton substation. The crews will continue in a west-to-east direction. 
• Spring - Construction begins at both transition stations: Breezy Knoll off of the Colonial Highway at Rt. 9, and the Dry Mill South location near the intersection of Dry Mill and Woodburn Rd. 
• May-Sept. - Multiple brief traffic stops along Route 7 will be necessary as we string conductors between the poles
• Fall - New transmission line and substation scheduled to be in service.
  

Need For The Project

The Purcellville load area is presently served by four long distribution lines (34.5 kV); two from Lovettesville Substation, one from Millville Substation in West Virginia, and one from Middleburg Substation. The new 230 kV transmission line and substation will provide a new, local energy source to the area.

Specifications and Dimensions

• Approximate total line length: 12 miles 
• Approximate overhead right-of-way width: 80 feet 
• Approximate underground line length: 2 miles 
• Approximate underground right-of-way width: 40 feet 
• Typical pole description: single pole, galvanized steel 
• Typical pole height: 120 feet 
• Typical pole spacing: 700 feet

SCC Approval Process -- Case No. PUE-2005-00018

On February 15, 2008 the Virginia State Corporation Commission (SCC) issued a Final Order approving the Pleasant View-Hamilton 230 kV Transmission Line and 230 kV-34.5 kV Hamilton Substation.

Five alternative routes were evaluated ranging from approximately 12.0 miles to 15.3 miles in length. Both full length and partial length underground options were examined during the course of the SCC proceeding.

SCC Findings Highlights

• Need - "…we find that additional transmission facilities and the Hamilton Substation are needed to serve the Purcellville Load Area. …additional facilities will provide substantial reliability improvements to such area."
• Route - "We find that the new transmission line should follow the Modified D route …No route can eliminate all adverse impacts."
• Underground – "…recommendation against underground construction due to both the physical, and the cost to ratepayers, impacts that would result therefrom."
• Structures – "…the transmission line will be constructed on single-shaft pole structures. …which will reduce substantially the visual impact of the line as compared to a lattice-type structure."
• Electric and/or Magnetic Fields (EMF) – "…there is insufficient evidence in this proceeding for us to conclude that electric and/or magnetic fields pose a risk or hazard to human health."

House Bill 1319

On March 6, 2008 the General Assembly established a pilot program (House Bill 1319 ) to underground certain high voltage transmission lines within the Commonwealth. This bill passed both houses of the General Assembly and was approved by Governor Timothy M. Kaine on April 2, 2008.  The first project to be part of this pilot program is a portion of the Pleasant View to Hamilton 230 kV line.

On May 21, 2008, Dominion filed a "Modified Request" with the Virginia State Corporation Commission for approval to underground a portion of the Pleasant View to Hamilton 230 kV line project as a pilot, under 2.A of HB 1319 (>> View this filing: Modified Request). On May 28, 2008, Dominion received approval for this request (>> View this order: Case No. PUE-2008-00042 ).

The portion of the Pleasant View-Hamilton line to be installed underground will be approximately  2 miles long and will be located just west of Leesburg in the vicinity of Dry Mill Road and placed within W&OD Trail property. This section of the route is identified as Segment Trail B (see Approved Route Map).
 

Maps

• View a route map featuring enlarged aerial views of the route and approximate pole locations. (When viewing this PDF, use the scroll bar on the right-hand side to return to the main map at the top, or use the "bookmarks" or "pages" features in Acrobat.)
• See environmental study area and the route approved by the Virginia State Corporation Commission. (A legend of topographical features is provided in the lower right corner of the map.)  
• This route is referred to as the Modified D alternative route, recommended by the SCC Hearing Examiner Howard P. Anderson, Jr.

Details on Underground Lines

Overhead (OH) lines have proven to be the best choice for providing safe, reliable and economical power to our customers. Dominion operates a high-voltage network of approximately 6,100 miles of transmission lines. Of this total, less than 1% (52 miles) is comprised of underground (UG) cables. At 230 kV, there are approximately 2400 miles of OH lines and 34 miles of UG cables. These installations are primarily for large water crossings, dense metro areas, or other areas that are not suitable for overhead lines.

When considering whether or not to install underground transmission facilities, the following issues need to be evaluated:

Outage Considerations

In comparing the reliability of overhead (OH) lines and underground (UG) cables, reliability needs to be examined from both short and long timeframes. Short term considerations favor UG cables since they tend to be somewhat immune from most weather-related outage initiators such as weather, trees and lightning. However, UG cables fall short of the performance of OH lines in long term views. This is mainly due to their inherently long outage times once problems do occur.

Most problems with OH lines can be restored in terms of hours. A damaged structure can usually be replaced in the same day of the damage. Dominion maintains a staff of trained line workers and a fleet of construction equipment that can facilitate OH line repairs. In contrast, UG cables can take up to two weeks to complete repairs even under ideal conditions.

Construction Impacts

The environmental impacts associated with UG cable installation are significantly greater than those of OH line construction. Excavation of a continuous trench approximately 5 -8 feet wide and 5 feet deep is much more disruptive than digging a typical 4 -6 foot diameter hole, 20 feet deep for each pole foundation located every 700 feet along the route.  In some suburban or rural areas, significant clearing and grading may be required to facilitate access for construction of underground facilities.

Impacts to the local community include mainly construction equipment noise and dust from the excavation and back-filling activities. The duration of construction for an UG line is roughly three to six times that for an OH line depending on subsurface conditions encountered.

Easement Requirement for UG Lines

The easement width for underground lines can vary depending on the number of circuits, the design and whether or not it is a network circuit.  The width is typically less than that needed for an equivalent overhead line, except in areas where significant grading activities are required to enable the underground line to be installed.

Costs

In general, the construction and installation of underground transmission lines cost 8-10 times more than an equivalent overhead line.  This is mainly due to the time, materials, process, and skilled labor involved.  The duration of construction for an UG line is roughly three to six times that for an OH line depending on subsurface conditions encountered.  XLPE cables are placed in individual conduit (PVC pipe) for ease of replacement and maintenance.  The conduit is incased in a concrete mixture, sometimes a specialized design known as FTB (Fluidized Thermal Backfill) to help dissipate heat and to protect the lines from potential damage and the public from injury.

The entire process of underground cable systems installation requires specialized contractors to perform this skilled work.  Skilled labor is specifically needed when connecting (splicing) sections of cable together.

Life Expectancy

When using XLPE (Crossed-linked Polyethylene) underground cable, the life expectancy is roughly half of a typical overhead line.  In both cases the company would maintain the lines to extend the useful life in perpetuity.  Such maintenance activities would likely include complete replacement of XLPE cables before age-related failures occur.

System "Network" Considerations

In the system network, UG cables that are configured in parallel with OH lines present additional technical challenges. Due to the inability to operate UG cables at the high conductor temperatures that OH lines are designed to run, the typical UG installation requires multiple cables to meet the same capacity as the OH line. This adds significantly to the cost and complexity of the UG installation. The electrical characteristics (lower impedance) of these multi-cable circuits will cause them to carry significantly more than a parallel OH line. This severely reduces the ability of the OH line to carry load. There are additional electrical components that can be utilized to help overcome this undesirable effect; however, these units further complicate the system, add significantly to the cost and can potentially reduce the overall system reliability.

Line Length Challenges

Long UG cables can have detrimental impacts on the transmission system. UG cables have a significantly higher capacitance in comparison to OH lines. This capacitance causes system voltages to rise in periods of light loading. In some cases the voltages rise to levels that require intervention such as removing the cables from the system. Installing additional electrical equipment to compensate for the capacitance can also mitigate this effect.

This capacitance is a function of the circuit length and the number of cables. There are losses (dielectric) associated with this capacitance that are present whenever the cable is energized. Current must flow in the cable to "charge" this capacitance. As the length of cable increases the amount of current that flows in the source end must also increase.  In theory a cable can be of a critical length of which the current flowing in it uses up the available capacity just to supply these losses. In practice long cable circuits are equipped with additional components that help compensate for these capacitive losses and will reduce this overall impact of lengthy cables. These components are not required for equivalent length OH lines. There is a significant cost to install this compensation equipment on the cables.

Multiple Cables & Forced Cooling Options

In the detailed design phase of underground projects two options are typically investigated, i.e., circuits with forced cooled cables and circuits of multiple cables. UG cable systems can utilize forced-cooling equipment to help remove heat from the cable systems increasing the capacity of the circuit. Forced cooling equipment can be as simple as fluid-to-air heat exchangers (radiators) or as complex as large refrigeration units.
The cooling requirements dictate what equipment must be utilized. Forced-cooling equipment located in the substations along the UG circuit route would increase noise levels as a result of dielectric fluid pumping equipment and fans cooling the fluid passing through heat exchangers.

Forced cooling is typically operated only during peak load periods each day. This approach to increase capacity for short duration might also be employed to enable an UG cable circuit to meet demand in a network contingency situation involving an outage of a line elsewhere in the system. Availability of this equipment when required to operate is critical to network reliability.

Solid dielectric cables systems that utilize cross-linked polyethylene (XLPE) insulation are not typically forced cooled.  Multiple cables are operated in parallel to achieve the higher capacities of overhead lines.
This decision as to which approach to use will be based on several factors such as initial cost, long-term operations and maintenance costs and suitability for the performance required for electric system conditions.
 

Electric and Magnetic Fields

Dominion is sensitive to public concern about possible health effects from exposure to electromagnetic fields. We continually monitor EMF research and speak to our customers and employees regularly to share the latest information available. The Virginia Department of Health, in its final report on EMF research said:

"Based on the review and analysis of the exhaustive literature review and other research projects completed under the EMF-RAPID program, the Virginia Department of Health is of the opinion that there is no conclusive and convincing evidence that exposure to extremely low frequency EMF emanated from nearby high voltage transmission lines is causally associated with an increased incidence of cancer or other detrimental health effects in humans. Even if it is assumed that there is an increased risk of cancer as implied in some epidemiologic studies, the empirical relative risk appears to be fairly small in magnitude and the observed association appears to be tenuous. The studies published in the literature lack clear demonstration of a cause and effect relationship as well as a definitive dose-response gradient."

• Review Dominion's latest EMF Update.
  

Powerline and Substation Visuals

1. View an example of an existing 230 kV transmission line pole. These poles can typically be either brown or gray in color. The poles along Rt. 7 in Loudoun will be a light gray, galvanized steel.
2. View two engineering exhibits of typical transmission structures. The exact dimensions described at the bottom of the exhibit will vary depending on final engineering.
3. View a visual simulation of the proposed Hamilton Substation.

Contact Us

Contact us if you have questions or concerns about the Pleasant View-Hamilton 230kV Line.