• Document: Low Frequency AC Transmission System
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International Journal of Signal Processing, Image Processing and Pattern Recognition Vol. 8, No. 5 (2015), pp. 315-326 http://dx.doi.org/10.14257/ijsip.2015.8.5.32 Low Frequency AC Transmission System G. Sirisha Kumari 1 and K.Veerendranath 2 1 M. Tech student in EEE Department 2 Asst. Professor in EEE Department 1 sirishakumari.28@gmail.com, 2 veerendra.nath1@gmail.com Abstract Presently, High Voltage AC transmission and High Voltage DC transmission systems are well established technologies for transmission of power. A new Low Frequency AC transmission system employs transmission at an intermediate frequency and thus, establishes itself in between these two alternatives. Low Frequency AC transmission system can transmit bulk power over long distance with low investment cost. This system is based on generation at low frequency and AC to AC conversion from nominal to low frequency using power electronic devices. This technology is more reliable and provides a cost effective solution for power transmission. This paper presents the feasibility of applying low frequency AC transmission technology to interface the wind farm to grid, which is a major issue. The wind power plant collection is DC based and connects transmission line with 12-pulse converter. This system is interfaced with main power grid with cycloconverter. Low Frequency AC transmission system is implemented with a suitable controller. The system design and control strategies are discussed. System performances are verified using MATLAB/SIMULINK. Keywords: power transmission, wind energy, thyristor converters, low frequency AC (LFAC), cycloconverter 1. Introduction The electrical power system consists of generation, transmission and distribution system. Remote electrical power generation and interconnection of system lead to invention of transmission system at different power levels. Electrical power generated is transmitted over long distance to substations by using transmission cables. Conventionally, High Voltage AC (HVAC) and High Voltage DC (HVDC) are well established technologies for transmission [1]. HVAC system can able to design the protection system and change voltage levels using transformers. However, the high capacitance of submarine AC power cables lead to significant charging current, which reduces the active power transmission capacity and limits the transmission distance. It is used for short distance transmission for 50-70km. To overcome the disadvantage of HVAC system, High Voltage DC transmission system is developed. Depending on types of power electronic devices used, HVDC system are classified in to two classes. There are Line Commutated Converter HVDC (LCC-HVDC) using thyristor and Voltage Source Converter HVDC (VSC-HVDC) using self commutated devices like insulated gate bipolar transistors (IGBT). The main advantage of HVDC technology is that it imposes no limit on transmission distance due to absence of reactive current in transmission line. LCC-HVDC systems are capable to transmit high power up to 1GW with high reliability but it consumes reactive power from the grid and introduces lower order harmonics, which results in the requirement for auxiliary equipment such as capacitor banks, ac filters and static synchronous compensators. On the other hand, VSC-HVDC systems are able to regulate active and reactive power exchange with onshore grid and offshore ac collection grid. Also, space charge accumulation is caused by the DC currents. The ISSN: 2005-4254 IJSIP Copyright ⓒ 2015 SERSC International Journal of Signal Processing, Image Processing and Pattern Recognition Vol. 8, No. 5 (2015) reduced efficiency and cost of the converters are drawbacks of VSC-HVDC systems. HVDC is used for transmission of power for the distance greater than 100km. Due to the limitations of both HVAC and AVDC transmission system, a High Voltage Low Frequency AC (LFAC) transmission has been proposed as anew alternative technology for transmission of power [2-5]. The low frequency AC transmission system utilizes an intermediate frequency for transmission of power. The main advantage of LFAC transmission technology is increase in power transmission capacity over long distance for a given submarine power cable. This lead to considerable cost saving due to reduction in cabling requirement, decline in cable charging current and also losses are reduced compared to traditional transmission systems. Thus, investment cost and maintenance cost is reduced as well, since the frequency converter that synchronizes the frequency between LFAC system and power grid. Other benefits of LFAC system include improved voltage stability and no space charge accumulation due to the use of lower frequency range. . 2.

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