Transmission of Electricity
Electricity transmission is the process by which large amounts of Electricity produced at power plants (such as hydro, geothermal, thermal and wind), is transported over long distances for eventual use by consumers. Due to the large amount of power involved, and the properties of Electricity, transmission normally takes place at high voltage (132-kilovolt or above) to reduce losses that occur over long distances.
Electricity is usually transmitted to a substation near a populated area. At the substation, the high voltage Electricity is converted to lower voltages suitable for consumer use, and then transmitted to end users through relatively low-voltage Electricity distribution lines that are owned and operated by the national Electricity utility.
The construction, operation, and maintenance of new high-voltage transmission lines and associated facilities create a range of environmental impacts. The type and magnitude of the impacts associated with transmission line construction, operation and maintenance varies depending on line type and size, as well as the length of the transmission line, and a variety of other site-specific factors.
The main components of high-voltage Electricity transmission lines and associated facilities include the following:
- Transmission Pylons (Towers)
- Conductors (Transmission lines)
- Right-of-Way (Way leaves)
- Access Roads
Transmission pylons are the most visible component of the Electricity transmission system. Pylons support high-voltage conductors (cables that transmit the electricity, otherwise known as lines) above the ground and separate them from other lines, buildings, and people. Pylons vary in design and dimensions. The transmission pylons are lattice steel between 33.5 and 46 metres tall. A minimum of 30-metre right-of-way is needed for the area around the pylons and the spans between the pylons.
Conductors are the cables on the transmission pylons that carry the Electricity to substations. KETRACO will have varying designs of pylons and lines depending mainly on the voltage being carried. Conductors are constructed primarily of twisted metal strands, but newer conductors may incorporate ceramic fibres in a matrix of aluminium for added strength with lighter weight.
The right-of-way for a transmission corridor includes the land set aside for the transmission line and associated facilities, and land set aside for a safety margin between the line and nearby structures and vegetation. Having the safety margin helps avoid the risk of fire and other accidents. The right-of-way width needed for transmission lines ranges from 30 metres to 65 metres. The right-of-way is also used for access roads.
Vegetation that could pose a danger to a transmission line or tower is removed inside the right-of-way and outside the right-of-way if it could come too close to lines and pylons. On the right-of-way, low-growing vegetation is allowed to grow after construction and subsequently maintained at an optimum level.
Access is needed to the transmission tower sites for both line construction and maintenance. Grading and clearing vegetation may be required for access road construction. Roads are usually murrum. Access roads can be permanent or temporary depending on the need during construction and land use. On most rights-of-way, permanent access roads provide a way to repair and maintain the pylons and line and are available for emergencies.
In farmland and other areas where the existing land use is not compatible with a permanent access road, KETRACO uses temporary access roads during construction, then removes the roads and replants or otherwise restores the original land use.
The high voltages used for Electricity transmission (e.g., 500 kV) are converted for consumer use to lower voltages (e.g., 11 kV) at substations. Substations vary in size and configuration but may cover several acres, and are cleared of vegetation and surfaced with gravel. Access is limited to authorized personnel and the substation is fenced and gated for safety and security. In general, substations include a variety of structures, conductors, fencing, lighting, and other features that result in an "industrial" appearance.