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This paper presents practical methods for dc side steady state harmonic calculation to analyze harmonic performance along the dc transmission line for the VSC based HVDC system. First, a general dc side harmonic calculation method based on Thevenin's equivalent and IEC general summation law is introduced. The converter and corresponding dc transmission line on both sides are represented as a harmonic voltage source U h and the harmonic impedance Z h seen from each dc side. Different from traditional AC side harmonic calculation which uses the envelopes of harmonic impedance loci, the methods in this paper compute all possible combinations of harmonic impedances covering all operation scenarios, which could easily find out the worst scenario. Second, an improved calculating method for the considering the harmonic model with multi-section dc transmission line harmonic impedance is proposed to improve the computational efficiency. And then, an accommodated harmonic impedance measurement for the dc side application based on small signal injection method is described. Finally, the PSCAD/EMTDC simulation verifications have been carried out based on a ±500kV/2000MW VSC HVDC system to verify the effectiveness of the proposed method.

As the insulating medium, sulfur hexafluoride (SF 6 ) is widely applied in gas insulation equipment. Over longterm operation, the solid insulation of the equipment is damaged by PD, causing it to react with SF 6 to generate COS and CF 4 which are critical SF 6 decomposition products inside the equipment. The detection of these two SF 6 decomposition products can help in assessment of the type and severity of insulation defects. Compared to the absorption spectroscopy and photoacoustic spectroscopy, FERS can using a single wavelength laser to simultaneously achieve the high sensitivity detection of mixture gases. In this paper, a highly sensitive SF 6 decomposition based on fiber-enhanced Raman spectroscopy is built up. The Raman spectroscopy of COS and CF 4 was acquired. The characteristic peak of COS at 859 cm−1 and that of CF 4 at 909 cm−1 were observed respectively. We study the relationship between laser power, pressure of fiber core and Raman scattering intensity, experimentally. The Raman scattering intensity is linear related to laser power and pressure. The response time of FERS which includes the filling time and evacuating time. was also examined. The filling time of the fiber is defined as the point when the intensity of the Raman peak does not change. FERS is promising to achieve the online monitoring technique to detect the SF 6 decomposition components with highly selective and sensitive.

As an important and widely used electrical equipment, GIS (gas insulated switchgear) greatly affects the stability and safety of the entire power grid. By detecting the concentration of SF 6 decomposed component gases in GIS, we can judge the faults existing in the GIS, and prevent the corrosive decomposed gases from damaging the insulation. However, existing SF 6 decomposition component detection methods can are difficult to achieve relatively accurate simultaneous detection of multi-component gases. In this paper, a method using cavity enhanced Raman spectroscopy was developed to simultaneously detect SO 2 and CF 4 under high concentration SF 6 . Based on frequency-locking cavity enhancement technology, we coupled laser light with a wavelength of 642 nm and a power of about 50 mW into a V-shaped resonant cavity, and realized three orders of power enhancement. Due to the special V-shaped structure of the resonant cavity, the direct reflected light from the cavity mirror will not feedback to the laser, thereby avoiding false locking. Under 1 atmosphere pressure, Raman spectroscopy of CF 4 and SO 2 with a concentration of 1% was obtained. The characteristic Raman spectral lines of CF 4 and SO 2 were determined as 909 cm−1 and 1151 cm−1, respectively. responding to their v1 transition. And the Raman spectrum of CF 4 and SO 2 under the pressure of gradient distribution was obtained, it was found that the Raman characteristic peak intensity of CF 4 and SO 2 was highly linear between pressure relationship. Besides, the mixed gas of CF 4 and SO 2 under high concentration SF 6 was detected simultaneously without any interference. This study laid the foundation for Raman spectroscopy for the detection and quantitative analysis of SF 6 decomposed gas components, indicating that Raman spectroscopy has great potential in the field of SF 6 decomposed gas component detection.

This paper presents a reactive power optimization method considering seasonal load changing based on a two-year project. Data of lines, transformers and seasonal load were taken into account to create a simulation model. By taking the moment when the load is maximum in each season, flow of the distribution network was calculated. The calculation results were closer to the actual measurement results. Based on Genetic algorithm, four reactive compensation plan along with seasons were got. The paper got a best project Considerating the line losses, Voltage qualification rate and bus voltage Security. The best reactive power optimization result can significantly reduce the distribution network losses and improve voltage qualification rate.