EE6402 -TRANSMISSION AND DISTRIBUTION 2 Marks And 16 Marks-Question Bank Unit 1-Structure of Power System Two marks Q&A (original) (raw)
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Karady, George G. “Transmission System” The Electric Power Engineering Handbook
The purpose of the electric transmission system is the interconnection of the electric energy producing power plants or generating stations with the loads. A three-phase AC system is used for most transmission lines. The operating frequency is 60 Hz in the U.S. and 50 Hz in Europe, Australia, and part of Asia. 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. .1 shows a typical system.
Industrial-minded countries of the world require a vast amount of energy of which electrical energy forms a major fraction. There are other types of energy such as oil for transportation and industry, natural gas for domestic and industrial consumption, which form a considerable proportion of the total energy consumption. Thus, electrical energy does not represent the only form in which energy is consumed but an important part nevertheless. It is only 150 years since the invention of the dynamo by Faraday and 120 years since the installation of the first central station by Edison using dc. But the world has already consumed major portion of its natural resources in this short period and is looking for sources of energy other than hydro and thermal to cater for the rapid rate of consumption which is outpacing the discovery of new resources. This will not slow down with time and therefore there exists a need to reduce the rate of annual increase in energy consumption by any intelligent society if resources have to be preserved for posterity. After the end of the Second World War, countries all over the world have become independent and are showing a tremendous rate of industrial development, mostly on the lines of North-American and European countries, the U.S.S.R. and Japan. Therefore, the need for energy is very urgent in these developing countries, and national policies and their relation to other countries are sometimes based on energy requirements, chiefly nuclear. Hydro-electric and coal or oil-fired stations are located very far from load centres for various reasons which requires the transmission of the generated electric power over very long distances. This requires very high voltages for transmission. The very rapid strides taken by development of dc transmission since 1950 is playing a major role in extra-long-distance transmission, complementing or supplementing e.h.v. ac transmission. They have their roles to play and a country must make intelligent assessment of both in order to decide which is best suited for the country's economy. This book concerns itself with problems of e.h.v. ac transmission only.
a very important paper o distribution of power system and parameters
Electricity grid interconnections have played a key role in the history of electric power systems. Most national and regional power systems that exist today began many decades ago as isolated systems, often as a single generator in a large city. As power systems expanded out from their urban cores, interconnections among neighboring systems became increasingly common 8 . Groups of utilities began to form power pools, allowing them to trade electricity and share capacity reserves. he irst power pool in the United States was formed in the Connecticut Valley in 925 9 . As transmission technologies improved, long distance interconnections developed, sometimes crossing national borders. he irst international interconnections in Europe came in 906, when Switzerland built transmission links to France and Italy.
An electric power distribution system is the final stage in the delivery of electric power; it carries electricity from the transmission system to individual consumers. Distribution substations connect to the transmission system and lower the transmission voltage to medium voltage ranging between 11/33 kV and 0.415 kV with the use of transformers. Primary distribution lines carry this medium voltage power to distribution transformers located near the customer's premises. Distribution transformers again STEP DOWN the voltage to the utilization voltage of household appliances and typically feed several customers through secondary distribution lines at this voltage. Commercial and residential customers are connected to the secondary distribution lines through service network. Customers demanding a much larger amount of power may be connected directly to the primary distribution level or the sub transmission level.
Transmission and Distribution Networks: AC versus DC
The fast development of power electronics based on new and powerful semiconductor devices has led to innovative technologies, such as HVDC, which can be applied to transmission and distribution systems. The distribution voltage level is smaller than the transmission one, thus the power electronics are less expensive in distribution. The technical and economical benefits of this technology represent an alternative to the application in AC systems. Some aspects, such as deregulation in the power industry, opening of the market for delivery of cheaper energy to customers and increasing the capacity of transmission and distribution of the existing lines are creating additional requirements for the operation of power systems. HVDC offer major advantages in meeting these requirements.
Comparative study of HVAC and HVDC transmission systems
Renewable and Sustainable Energy Reviews, 2016
Transport of energy over long distances from remote natural sources to consumers in big cities requires technical, economic and environmental considerations. Uncertain wind flow, sunshine, faults and communication failures can compromise system safety, reliability, power quality during small signal and large scale power system oscillations. HVAC systems tackle power swing issue by electrical islanding protection schemes which would need to be revised for integrated AC/DC systems. Advent of DC transformers, CSC-HVDC, VSC-HVDC and MMC-HVDC technologies have enabled the enhancement of power delivery and integration of renewable energy sources under smart grid vision. HVDC transmission lines are recognized as an efficient alternative to HVAC lines. HVAC system power transfer capability is limited by reactance, whereas HVDC lines can be loaded up to the conductor thermal limit. This paper reviews power transfer capabilities of HVAC, HVDC and High Phase Order (HPO) HVAC lines to compare their relative performance under diverse conditions. Techno-economic analysis of converting existing AC lines into DC lines is presented. High voltage race has been analyzed in context of environmental concerns and HVDC transmission systems are concluded to be the right path to energy transition.