ISSN: 2277-3754 ISO 9001:2008 Certified International Journal of Engineering and Innovative Technology (IJEIT) Volume 5, Issue 2, August 2015 DOI:10.17605/OSF.IO/GJZEV Page 108 Improvement in Power Capacity by Simultaneous HVAC-HVDC Transmission System Karan Ahuja, Chintu Rza, Gagandeep Sharma Abstract – A Simulink model has been proposed to test power upgradation by converting a double circuited hvac transmission system into a simultaneous hvac-hvdc transmission system. Sending end power and receiving end power have been calculated for a conventional hvac line at eight different line lengths. The same parameters along with dc link current and inverter voltage have been calculated for a simultaneous hvac-hvdc system at eight different line lengths. Difference between two successive line lengths was 25km. Ac and dc losses have been computed by employing the above mentioned parameters. Power upgradation has been calculated at all the eight lines by comparing the receiving end powers in simultaneous hvac-hvdc system with the respective conventional hvac system. Simulation results have been calculated. Index Terms–AC and DC power transmission, HVDC, HVAC, Simulation, Power Up gradation. I. INTRODUCTION If not for Electric Power, our country‟s economy today would have been in jeopardy and future a conundrum. Ever since the advent of Electricity, mankind has been benefited in leaps and bounds. The development henceforth has been multidimensional in various countries across the 24 time zones, be it social, economic or cultural. The crux of urbanization lies in the growth of agricultural as well as industrial sector. The Planning commission hereby prioritizes research and development in Electric Power Generation, Transmission and Distribution. Contradictory to the obvious the demand for electricity has increased gradually but leaving behind footprints of erratic geographical growth. Power Generation is centered in remote areas due to economic and environmental factors while the load centers are close by cities and towns. It has been observed that one could transmit power through the installed high capacity AC voltage lines only up to a certain upper limit beyond which the system runs into transient instability. Consequently, the lines are never loaded upto their maximum thermal limit rather much less than that [1]. This is a roadblock as one is forced to wonder for ways and means to elevate the capacity of the existing EHVAC transmission line prototype. Recent developments have exhibited the fact that 765/800KV lines are being constructed between Anapara-Unnao and Tehri-Meerut in Uttar Pradesh along with Moga-Krishanpura in Punjab and Vindyachal in MP. HVDC i.e. High Voltage Direct Current Transmission has seen the light of day in India operating at 500KV transmission voltage. Environmental constraints have long since limited the very realization of brand new power corridors. Thereby the onus has passed onto enhancing power transfer without any significant structural changes [2]. Development in Power Electronics has led to the ultimate saving solution – FACTS. Control mechanism of SCR devices in FACTS devices is extremely quick and efficient. There are promptly many options to choose from be it the Static VAR System (SVS), Static Phase Shifter (SPS) or the Controlled Series Capacitor (CSC) [3]. Rectifier control could be made possible by using a Proportional Integral Controller which required adjusting the firing angle [4]. Enhanced stability and improved damped out oscillations are few of the perks offered by these systems. Not only it is possible to successfully increase the transmission capacity by converting an EHVAC circuit into HVDC circuit, one could even determine the increase in magnitude [5]. It is also noteworthy that conversion into DC considerably decreased the per unit losses, improved lightning performance and accentuated reliability of the line [6]. Upon comparing and contrasting the performances of HVDC and HVAC transmission systems it has been found out that despite greater cost of HVDC equipment; qualities such as cost efficiency, zero stability problem, environmental friendly and human safety weighed strongly in favour of HVDC transmission system [7]. Added perks of such an arrangement happen to be enhanced transient stability, dynamic stability as well as damp out oscillations [8]. In terms of structure, self-supporting towers have been found to be more reliable as compared to guyed towers. In terms of reliability double circuit lines stood out [9]. In ac-dc transmission the overall performance has been compensated by capacitive VAR against the lagging VAR of conductors [10]. Modified semiconductor coated insulators have appreciatively altered the behavior of corona inception and flash over voltage of suspension dc and ac insulators [11]. In spite of superimposing dc current onto ac in combined transmission, it has been observed that there was no need to alter conductor size, insulator strings and towers [12]. The superimposed dc current made it possible for the line to be loaded to its thermal limit [13][14]. Reliability is a crucial factor. A four state component model simplified with the method of combining components and dividing subzone for DC substation as given in [15] has been studied to evaluate reliability to evaluate reliability. System stability could be maintained with high values of pre fault power and fault clearance time [16]. It has also been demonstrated that a combined transmission lowered the fault current and improved the performance