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Reduce Power Transfer Loss in Transmission Line by Integrating AC & DC Transmission

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Author(s): Alok Kumar1 , Surya Prakash

Journal: International Journal of Engineering Trends and Technology
ISSN 2231-5381

Volume: 4;
Issue: 6;
Start page: 2490;
Date: 2013;
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Keywords: Flexible AC transmission system (FACTS) | Extra high voltage (EHV)transmission | MatLab | Simultaneous ac-dc power transmission

ABSTRACT
In this paper it is possible to load the transmission lines very close to their thermal limits by allowing the conductors to carry usual ac along with dc super imposed on it. The added dc power flow does not cause any transient instability. This project gives the feasibility of converting a double circuit ac line into composite ac–dc power transmission line to get the advantages of parallel ac–dc transmission to improve stability and damping out oscillations. Simulation and experimental studies are carried out for the coordinated control as well as independent control of ac and dc power transmissions. No alterations of conductors, insulator strings, and towers of the original line are needed. The present situation demands the review of traditional power transmission theory and practice, on the basis of new concepts that allow full utilization of existing transmission facilities without decreasing system availability and security. To achieve this is by simultaneous ac–dc power transmission in which the conductors are allowed to carry superimposed dc current along with ac current. Ac and dc power flow independently, and the added dc power flow does not cause any transient instability. Simultaneous ac–dc power transmission was first proposed through a single circuit ac transmission line. In these proposals Mono-polar dc transmission with ground as return path was used. There were certain limitations due to use of ground as return path. Moreover, the instantaneous value of each conductor voltage with respect to ground becomes higher by the amount of the dc voltage, and more discs are to be added in each insulator string to withstand this increased voltage. In this paper, the feasibility study of conversion of a double circuit ac line to composite ac–dc line without altering the original line conductors, tower structures, and insulator strings has been presented. In this scheme, the dc power flow is point-to point bipolar transmission system. The novelty of our proposed scheme is that the power transfer enhancement is achieved without any alteration in the existing EHV ac line. The main object is to gain the advantage of parallel ac–dc transmission and to load the line close to its thermal limit
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