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

In hot and cold climates home air conditioning and heating loads affect the overall load. This is an everyday occurrence in AC systems, but one that can become disrupted when AC system components fail and place unexpected loads on the grid. Voltage-based regulation is complex to use in mesh networks, since the individual components and setpoints would need to be reconfigured every time a new generator is added to the mesh. 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. As an example, to adjust the flow of AC power on a hypothetical line between Seattle and Boston would require adjustment of the relative phase of the two regional electrical grids. The ratio of real power transmitted to the load to apparent power (the product of a circuit's voltage and current, without reference to phase angle) is the power factor. HVDC lines are restricted only by thermal and voltage drop limits, since the phase angle is not material. It is undesirable for the angle to approach 90 degrees, as the power flowing decreases while resistive losses remain.

For transmission systems with low power factor, losses are higher than for systems with high power factor. It is uneconomical to connect all distribution substations to the high main transmission voltage, what is electric cable because that equipment is larger and more expensive. The voltage, power, frequency, load factor, and reliability capabilities of the transmission system are designed to provide cost effective performance. Transmission (sometimes called sub-transmission to distinguish it from transmission lines supported by steel structures): three uninsulated conductors which carry 3-phase high voltage (typically 69 to 200 kilovolts) circuits among substations. The French TGV (High Speed Train) formation has a power car at each end of the train but only runs with one pantograph raised under the high speed 25 kV AC lines. Every single one of these programs, however, owes its existence to America’s first television program, which was called The Queen’s Messenger. Transmission lines can be used to carry data: this is called power-line carrier, or power-line communication (PLC). Rarely, and for short distances, pilot-wires are strung along the transmission line path. The lossless line approximation is the least accurate; it is typically used on short lines where the inductance is much greater than the resistance.

The conductors' mutual inductance is partially dependent on the physical orientation of the lines with respect to each other. Current flowing through transmission lines induces a magnetic field that surrounds the lines of each phase and affects the inductance of the surrounding conductors of other phases. As of 1980, the longest cost-effective distance for DC transmission was 7,000 kilometres (4,300 miles). A reconductoring project in southeastern Texas upgraded 240 miles of transmission lines at a cost of $900,000 per mile, versus a 3,600-mile greenfield project that averaged $1.9 million per mile. For AC it was 4,000 kilometres (2,500 miles), though US transmission lines are substantially shorter. As power systems evolved, voltages formerly used for transmission were used for subtransmission, and subtransmission voltages became distribution voltages. Voltages of 69 kV, 115 kV, and 138 kV are often used for subtransmission in North America. Like transmission, subtransmission moves relatively large amounts of power, and like distribution, subtransmission covers an area instead of just point-to-point. As new internet technologies like fiber and 5G have proliferated, consumers have far more options for home internet than they did a few years ago. Learn more about the whole field of electrical insulation on our page here.

See how motor wire is packed and wound into modern induction motors in our video here. Single-phase AC is used only for distribution to end users since it is not usable for large polyphase induction motors. SIL, the voltage drops from sending end and the line consumes VARs. Brownouts occur when power supplied drops below the demand. While the price of generating capacity is high, energy demand is variable, making it often cheaper to import needed power than to generate it locally. Additionally, there are finite limits to the capacity and other performance characteristics of UTP, regardless of the inventiveness of technologists. There is no static wire. BS 546:1934 clause 2 specifies interchangeability with BS 372 Part II which includes the same four plug and socket sizes. January 1957: BS 1363:1947 Amendment 5, added clause permitting operation of shutters by simultaneous insertion of two or more pins (in addition to original method using only earth pin). Without them maximum current was typically set as a compromise between understanding of operation conditions and risk minimization.