• 목록
• 답변
• 글쓰기
• 게시판 리스트 옵션
  • 수정
  • 삭제

A week-long blackout in New York City, calls for "voluntary" conservation, the shutting off of power to large industrial enterprises, and lowering of voltages across the nation, were all evidence of the wreckage that has been made of this most critical infrastructure. Single-wire earth return (SWER) or single-wire ground return is a single-wire transmission line for supplying single-phase electrical power to remote areas at low cost. A 15 kV transmission line, approximately 175 km long, what are electric cables connected Lauffen on the Neckar and Frankfurt. The first three-phase alternating current using high voltage took place in 1891 during the international electricity exhibition in Frankfurt. The reduced current reduces heating losses. For a given amount of power, a higher voltage reduces the current and thus the resistive losses. Transmitting electricity at high voltage reduces the fraction of energy lost to Joule heating, which varies by conductor type, the current, and the transmission distance. It oversees 56,070 miles of transmission lines, and plans regional transmission expansion to maintain grid reliability and relieve congestion.

A transmission grid is a network of power stations, transmission lines, and substations. Long-distance transmission is typically done with overhead lines at voltages of 115 to 1,200 kV. New power lines can take 10 years to plan, permit, and build. These networks use components such as power lines, cables, circuit breakers, switches and transformers. Interconnection of local generation plants and small distribution networks was spurred by World War I, when large electrical generating plants were built by governments to power munitions factories. The Western Interconnection has two primary interchange voltages: 500 kV AC at 60 Hz, and ±500 kV (1,000 kV net) DC from North to South (Columbia River to Southern California) and Northeast to Southwest (Utah to Southern California). To make things more confusing, it's not unusual for international telephone standards to either be based on older US practices that are now rare in the US, or to have standardized on "in practice" properties of the US system instead of nominal values, or to have mixed conventions from Western Electric with conventions from European telephone manufacturers like Ericsson. The world of local telephone loops is a dirty one, full of dirt and rain. Hydro and wind sources cannot be moved closer to big cities, and solar costs are lowest in remote areas where local power needs are nominal.

The remaining or peak power demand, is supplied by peaking power plants, which are typically smaller, faster-responding, and higher cost sources, such as combined cycle or combustion turbine plants typically fueled by natural gas. Interconnecting multiple generating plants over a wide area reduced costs. The most efficient plants could be used to supply varying loads during the day. Local sources (even if more expensive and infrequently used) can protect the power supply from weather and other disasters that can disconnect distant suppliers. Since power lines are designed for long-term use, Kelvin's law is used in conjunction with long-term estimates of the price of copper and aluminum as well as interest rates. At times of lower interest rates and low commodity costs, Kelvin's law indicates that thicker wires are optimal. The optimum size of a conductor for a given voltage and current can be estimated by Kelvin's law for conductor size, which states that size is optimal when the annual cost of energy wasted in resistance is equal to the annual capital charges of providing the conductor. Joule's first law states that energy losses are proportional to the square of the current. And since conductance is proportional to cross-sectional area, resistive power loss is only reduced proportionally with increasing cross-sectional area, providing a much smaller benefit than the squared reduction provided by multiplying the voltage.

While power loss can also be reduced by increasing the wire's conductance (by increasing its cross-sectional area), larger conductors are heavier and more expensive. 100, provided the same sized conductors are used in both cases. Obviously "electricity" cannot be several different things at the same time. Because of this phenomenon, conductors must be periodically transposed along the line so that each phase sees equal time in each relative position to balance out the mutual inductance seen by all three phases. Depending on the type of switch, the line card may perform ADC and DAC to convert your analog local loop to digital signaling for further handling by digital means. At power stations, power is produced at a relatively low voltage between about 2.3 kV and 30 kV, depending on the size of the unit. In the United States, power transmission is, variously, 230 kV to 500 kV, with less than 230 kV or more than 500 kV as exceptions. A major barrier to wider adoption of merchant transmission is the difficulty in identifying who benefits from the facility so that the beneficiaries pay the toll. Because of the economic benefits of load sharing, wide area transmission grids may span countries and even continents.