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

Tankless water heaters save energy because they are always off and they modulate their firing rate to 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. This restricted the distance between generating plant and loads. The most efficient plants could be used to supply varying loads during the day. Wind speeds as low as 23 knots (43 km/h) can permit conductors to encroach operating clearances, resulting in a flashover and loss of supply. If demand exceeds supply, the imbalance can cause generation plant(s) and transmission equipment to automatically disconnect or shut down to prevent damage. Underground power transmission has a significantly higher installation cost and greater operational limitations, but lowers maintenance costs. This extends the repair period and increases costs. Copper was sometimes used for overhead transmission, but aluminum is lighter, reduces yields only marginally and costs much less. For large conductors (more than a few centimetres in diameter), much of the current flow is concentrated near the surface due to the skin effect.

The lossless line approximation is the least accurate; it is typically used on short lines where the inductance is much greater than the resistance. One notable difference between these and their WE/NE counterparts, is that the switchhooks on AE models were designed in a such a way that it was virtually impossible to hang them up improperly, leaving the phone line open. HVDC links stabilize power distribution networks where sudden new loads, or blackouts, what is electric cable in one part of a network might otherwise result in synchronization problems and cascading failures. Widespread use of such motors were delayed many years by development problems and the scarcity of polyphase power systems needed to power them. In what became a universal system, these technological differences were temporarily bridged via the rotary converters and motor-generators that allowed the legacy systems to connect to the AC grid. The combined transmission and distribution network is part of electricity delivery, known as the electrical grid.

One grid connects most of continental Europe. A wide area synchronous grid, known as an interconnection in North America, directly connects generators delivering AC power with the same relative frequency to many consumers. Thus, generators were sited near their loads, a practice that later became known as distributed generation using large numbers of small generators. Thus, multiple parallel cables (called bundle conductors) are used for higher capacity. DC cables are not limited in length by their capacitance. Underground lines are limited by their thermal capacity, which permits less overload or re-rating lines. Underground cables take up no right-of-way, have lower visibility, and are less affected by weather. Typical communications cables include: Telephone: telephone cables supported by steel strand. It was powered by two Siemens & Halske alternators rated 30 hp (22 kW), 2 kV at 120 Hz and used 19 km of cables and 200 parallel-connected 2 kV to 20 V step-down transformers provided with a closed magnetic circuit, one for each lamp. It was powered by a 2 kV, 130 Hz Siemens & Halske alternator and featured several Gaulard transformers with primary windings connected in series, which fed incandescent lamps.

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. Neutral is usually at or very near to earth potential, being earthed either at the substation or at the service entrance (neutral-to-earth bonding is not permitted in the distribution board/consumer unit). Rewireable plugs must be designed so that they can be wired in a manner which prevents strain to the earth connection before the line and neutral connection in the event of failure of the cord anchorage. Rewirable plugs for hand-wiring with a screwdriver are commonly available and must be provided with instructions. BS 4573 British Standard Specification for two-pin reversible plugs and shaver socket-outlets defines a plug for use with electric shavers. The isolation transformer often includes a 115 V output that supplies a two-pin US Type A socket. The plug and socket replaced the BS 546 plug and socket, which are still found in old installations or in special applications.