Introduction 2.A network can be defined as a group of computers and other devices connected in some ways so as to be able to exchange data.Each of the devices on the network can be thought of as a node; each node has a unique address. 1.5 Transmission Line Design Specifications. Line loading increased, and transmission lines were. Fundamental Concepts of Electrical Power Transmission.
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The three-phase system has three phase conductors. The system voltage is defined as the RMS voltage between the conductors, also called line-to-line voltage. The voltage between the phase conductor and ground, called line-to-ground voltage, is equal to the line-to-line voltage divided by the square root of three.The generating station produces the electric energy. The generator voltage is usually around 15 to 25 kV. This relatively low voltage is not appropriate for the transmission of energy over long distances. At the generating station a transformer is used to increase the voltage and reduce the current.In Figure 1 the voltage is increased to 500 kV and an extra-high voltage (EHV) line transmits the generator-produced energy to a distant substation.
Energy generation, transmission and distribution concept (click to expand)The voltage is reduced at the 500 kV/220 kV EHV substation to the high voltage level and high voltage lines transmit the energy to high voltage substations located within cities.At the high voltage substation the voltage is reduced to 69 kV. Sub-transmission lines connect the high voltage substation to many local distribution stations located within cities. Sub-transmission lines are frequently located along major streets.Electricity distribution conceptThe voltage is reduced to 12 kV at the distribution substation.
Several distribution lines emanate from each distribution substation as overhead or underground lines. Distribution lines distribute the energy along streets and alleys.
NOTE: as the article begins with “Some times ago the Electric power transmission was in DC” I assume it was written regarding power transmission technology that existed in most XX century.“Two conductors in DC transmission while three required in AC”.The author is talking about 3-phase. In AC this is done because when computing overall cost it is cheaper to use 3 conductors.“There are no Inductance and Surges (High Voltage waves for very short time) in DC transmission”.Wrong. Inductance is always present regardless of the conductors being used for AC or DC. A sudden current change in a DC line may generate dangerous voltage spikes. Example: in a 12V car you can find surges of up to +200 and -200V when switching loads.“There is no concept of Skin effect in DC transmission. Therefore, small cross sectional area conductor required”.Right, but AC can be easily stepped up in voltage and cross section will be lower for the same transmitted power.“In DC System, the speed control range is greater than AC System”.Wrong.
Variable frequency drives can slow a motor down to turtle speeds.“In AC Lines, there is Capacitance, so continuously power loss when no load on lines or Line is open. Other line losses are due to inductance”.Wrong. Capacitive and inductive reactances do not generate energy loss, only create reactive energy.Regrettably, the reason why I was interested to read the note was about very high voltage DC transmission, a topic I couldn’t find enough information, but there is just a mere mention to choppers and boosters.One thing in favour to DC is: DC motors are more compact and lightweight than AC ones for the same power, and can reach much higher RPMs, and the hassle of brushes can be overcome by brushless electronic designs.