FACTS Element Transmission Line Containing Harmonic Analysis

With the extensive use of FACTS devices in transmission system, it improves stability of the system and power transmission capacity by controlling the key parameters of the system such as voltage, phase angle, frequency, impedance, current and power flow etc. and meanwhile it also improves the reactive power distribution and voltage support, implementing the safe and economic operation of the power system. However, it will be companied with large amount of harmonics, affecting the power quality at the same time. Hence, the widen use of the FACTS devices makes the harmonic problem becomes the focus among scholars again.Comparing several classical types of signal processing methods, the windowed Fourier transform is selected finally as the harmonic analysis method in this paper.In order to study the harmonic character of the transmission line with FACTS devices, this paper analyzes the theory of the classical FACTS such as STATCOM and UPFC. STATCOM could be regarded as synchronous voltage compensation devices which improves the stability of power system through control its voltage amplitude and phases and UPFC device is seen as an STATCOM in parallel and an SSSC in series connection in system. These two devices form a back-to back mode through the public DC bus to fulfill the power flow control by the exchange between active and reactive power.A simulation model is built by PSCAD/EMTDC software and simulations are carried out to analyze and research the frequency spectrum character of harmonics. Analyze the voltage and current data obtained from different fault conditions in transmission line with FACTS devices by utilizing the windowed Fourier transform. The results show that the harmonics in voltage and current signals extracted from measuring end are mainly the3rd,5th,7th,29th,31st,33rd and35th harmonics. Besides, the3rd harmonic is often produced by the distortion of the voltage and current signals caused by unbalanced fault.This paper provides certain theory foundation of harmonic management by analyzing harmonic character and also makes a good basis for the expansion of ’Effects on protection of system with FACTS devices’.