Electric transmission and distribution (T&D) technologies include components used to transmit and distribute electricity (including electricity from renewable sources) from generation sites to end users (customers). T&D lines may be located above or below ground. The primary components of above-ground transmission lines include transmission structures (lattice steel towers or tubular steel poles), conductors (wires), insulators (connect wires to structures), and ground wires (lightning strike protection wires).
In general, transmission lines carry a higher voltage of electricity while distribution lines are primarily lower-voltage. Transmission lines are connected to substations that "step-down" the power to a lower-voltage so that it can be delivered to customers through distribution lines, although some large industrial customers receive their electricity at transmission or sub-transmission (primary) voltage. The type of towers, number and width of conducting wires, and therefore visibility of the system is determined by the current and voltage of the electricity being transmitted.
Transmission and related infrastructure through parks requires a Special Use Permit. Authority for permitting is limited to findings by the NPS that no impairment to park resources and "not incompatible with the public interest" (16 USC 5 & 79, and Director's Order #53).
For more information on electric transmission and distribution technologies, please visit the Department of Energy's Office of Electricity Delivery and Energy Reliability website.
Technology-Specific Impacts
The electric transmission and distribution lines associated with utility-scale renewable energy projects may impact NPS natural, cultural, and historical resources differently depending on location, whether the lines are above or below ground, and whether they are used for transmission or distribution. Key impacts for above-ground lines include bird death through collision and electrocution, disruption of bird migratory paths, and visual concerns.
Collision and Electrocution: Electrocution occurs when a bird attempts to perch on conduction wires with insufficient clearance and touches two conductors of different phases, or a conductor and ground wire at the same time. Direct collision can also cause mortality and occurs most often with ground wires, which are thinner and less visible to birds.
Disruption of Migratory Bird Paths: Above ground power lines as well as construction and trenching for below-ground lines can disrupt migratory paths and lead to population decline.
Visual Impacts: Electric transmission lines and towers have the ability to affect national park views of natural, cultural, and historic beauty even from a distance. For example, construction and vegetation clearing for related infrastructure may affect park visuals. Aesthetics and visitor experience should be balanced with environmental impacts when determining size, location, and other system features.
Impacts will vary by location and therefore may include, but are not limited to those listed above. For more information on potential environmental, cultural, and historic resource impacts of electric transmission and distribution technologies, please see the "Office of Electricity Delivery and Energy Reliability," or visit the links below.
Related Resources
Last updated: September 21, 2016