There is much more to putting transmission lines underground than just burying them. Overhead and underground lines make use of very different technologies.

Underground lines typically cost more, but can more easily be routed through highly developed urban areas, ideally within tunnels beneath city streets. They also offer aesthetic or other environmental advantages to overhead transmission lines, especially to those who live along the planned overhead transmission route. But a disadvantage to underground installations is that their construction requirements, unlike an overhead line, necessitate access to every foot of the route, increasing construction impacts on roadways, traffic, wetlands, and wildlife habitats. Also, some types of transmission cables are contained in pipes filled with a mineral oil under pressure that can leak if the pipe is ruptured. Unlike an overhead system, these pressurized oil cable systems often require new substations with equipment to pressurize the oil, contain any spills, and manage the electricity flows.

Electric power system engineers recognize that when it comes to working with higher transmission voltages, underground lines have important differences from overhead lines. For instance, because the heat created by resistive losses moves more slowly away from underground cables, underground transmission lines commonly require more or bigger conductors to deliver the same amount of power. Because of the thick insulation around underground cables, installed cable lengths are shorter and many more splices (made in large underground vaults) are necessary. While a failure may happen less frequently on an underground line, when it does its location and repair typically take a couple of weeks to complete, during which time the remaining transmission system must operate reliably without the cable. Also, the substations at the ends of an underground cable will often need to have large shunt reactors installed to compensate for the high charging currents associated with these cables.

Right of Way Acquisition

Rights of way sometimes need to be expanded along sections of a transmission route and it is not always possible to avoid having an impact on some people living near the corridor. When balancing the electric needs of many with property issues, it is not possible to avoid all abutting homes.

Two key philosophies guide Connecticut Light & Power (CL&P) in routing the proposed 345-kV power lines:

1. The routes should cause the least amount of disturbance to people and the environment, which includes minimizing the number of homes in the corridor.



2. Property owners should be fairly compensated for any land that must be acquired.

On sections of the right of way where the width needs to be expanded, CL&P will pursue a plan that intrudes least of all on abutting property owners and environmentally sensitive areas.

In acquiring property rights from private owners, CL&P pays the Fair Market Value of the necessary rights. Fair Market Value is typically determined by retaining local independent real estate appraisers to estimate the value of the applicable property rights.

CL&P will make a good faith offer representing the Fair Market Value of the property rights sought. The focus and energy of CL&P's negotiations will be to reach a mutually acceptable real estate transaction with the property owner.