POWER TRANSMISSION AND DISTRIBUTION
The voltage of large generators usually is in the range of 13.8 kV to 24kV. Large modern generators, however, are built for voltages ranging from 18-24kV. No standard for generator voltages has been adopted.
Electric power transmission or "high voltage electric transmission" is the bulk transfer of electrical energy, from generating plants (historically hydroelectric, nuclear or coal fired but now also wind, solar, geothermal and other forms of renewable energy) to substations located near to population centers. This is distinct from the local wiring between high voltage substations and customers, which is typically referred to as electricity distribution.
Transmission lines, when interconnected with each other, become high voltage transmission networks. In the US, these are typically referred to as "power grids" or sometimes simply as "the grid". North America has three major grids: The Western Interconnect; The Eastern Interconnect and the Electric Reliability Council of Texas (or ERCOT) grid.
Historically, transmission and distribution lines were owned by the same company, but over the last decade or so many countries have introduced market reforms that have led to the separation of the electricity transmission business from the distribution business.
Transmission lines mostly use three phase alternating current (AC), although single phase AC is sometimes used in railway electrification systems. High-voltage direct current (HVDC) technology is used only for very long distances (typically greater than 400 miles); undersea cables (typically longer than 30 miles); or for connecting two AC networks that are not synchronized.
Electricity is transmitted at high voltages (110 kV or above) to reduce the energy lost in long distance transmission. Power is usually transmitted through overhead power lines. Underground power transmission has a significantly higher cost and greater operational limitations but is sometimes used in urban areas or sensitive locations.
A key limitation in the distribution of electricity is the difficulty in storing significant quantities of electrical energy. A sophisticated system of control is therefore required, to ensure electric generation very closely matches the demand. If supply and demand are not in balance, generation plants and transmission equipment can shut down which, in the worst cases, can lead to a major regional blackout, such as occurred in Cal ifornia and the US Northwest in 1996 and in the US Northeast in 1965, 1977 and 2003. To reduce the risk of such failures, electric transmission networks are interconnected into regional, national or continental wide networks thereby providing multiple redundant alternate routes for power to flow should (weather or equipment) failures occur. Much analysis is done by transmission companies to determine the maximum reliable capacity of each line which is mostly less than its physical or thermal limit, to ensure spare capacity is available should there by any such failure in another part of the network.
It includes all land conversion, structures and equipment at a primary source of supply,
line switching and conversion stations between generating or receiving point and the
entrance to a distribution center or wholesale point. All lines equipment whose primary
purpose is to augment, integrate or tie together sources of power supply.
Diagram of an electrical system.
Electric power transmission or "high voltage electric transmission" is the bulk transfer of electrical energy, from generating plants (historically hydroelectric, nuclear or coal fired but now also wind, solar, geothermal and other forms of renewable energy) to substations located near to population centers. This is distinct from the local wiring between high voltage substations and customers, which is typically referred to as electricity distribution.
Transmission lines, when interconnected with each other, become high voltage transmission networks. In the US, these are typically referred to as "power grids" or sometimes simply as "the grid". North America has three major grids: The Western Interconnect; The Eastern Interconnect and the Electric Reliability Council of Texas (or ERCOT) grid.
Historically, transmission and distribution lines were owned by the same company, but over the last decade or so many countries have introduced market reforms that have led to the separation of the electricity transmission business from the distribution business.
Transmission lines mostly use three phase alternating current (AC), although single phase AC is sometimes used in railway electrification systems. High-voltage direct current (HVDC) technology is used only for very long distances (typically greater than 400 miles); undersea cables (typically longer than 30 miles); or for connecting two AC networks that are not synchronized.
Electricity is transmitted at high voltages (110 kV or above) to reduce the energy lost in long distance transmission. Power is usually transmitted through overhead power lines. Underground power transmission has a significantly higher cost and greater operational limitations but is sometimes used in urban areas or sensitive locations.
A key limitation in the distribution of electricity is the difficulty in storing significant quantities of electrical energy. A sophisticated system of control is therefore required, to ensure electric generation very closely matches the demand. If supply and demand are not in balance, generation plants and transmission equipment can shut down which, in the worst cases, can lead to a major regional blackout, such as occurred in Cal ifornia and the US Northwest in 1996 and in the US Northeast in 1965, 1977 and 2003. To reduce the risk of such failures, electric transmission networks are interconnected into regional, national or continental wide networks thereby providing multiple redundant alternate routes for power to flow should (weather or equipment) failures occur. Much analysis is done by transmission companies to determine the maximum reliable capacity of each line which is mostly less than its physical or thermal limit, to ensure spare capacity is available should there by any such failure in another part of the network.
Transmission lines
TRANSMISSION SYSTEM
It includes all land conversion, structures and equipment at a primary source of supply,
line switching and conversion stations between generating or receiving point and the
entrance to a distribution center or wholesale point. All lines equipment whose primary
purpose is to augment, integrate or tie together sources of power supply.
DISTRIBUTION SYSTEM
It connects all individual loads to the transmission line at a substation which performs
voltage transmission and switching function.
voltage transmission and switching function.
Purpose of transmission
1. To transmit power from water power site to a market. These may be very long justified because of subsidy aspect connected with a project. 2. For bulk power to a load center from outlying steam station these are likely to be relatively short. 3. For interconnection purposes, transfer of energy from one system to another in case of emergency or in response to diversity in system peaks. | |
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