Mitigation of common mode failures at multi-circuit line configurations by application of line arresters against back-flashovers

Due to the limited number of corridors multi circuit line configurations are often applied. These overhead lines frequently consist of high towers that are subject to lightning strokes. In case of higher current amplitudes and higher footing resistances due to bad earthing conditions back-flashovers are caused leading to common mode failures and to severe outages. The paper describes investigations performed by means of computer simulations to identify the towers of a multi-circuit line consisting of voltage levels 380 kV, 220 kV and 110 kV that are endangered by back-flashovers of the 110-kV double-circuit lines. The footing resistance of towers of the targeted line section has been measured by an instrument at high-frequency. Influence of various factors on the back-flashover over 110 kV insulator strings has been studied by means of EMTP-ATP simulations. Different current waveforms of the lightning stroke have been used to represent the first stroke and subsequent strokes. The towers are represented by the models described in [3], [8]. Available flashover analysis methods [7], [8], [12], [13] like leader development method by Pigini et al and by Motoyama, and voltage-time integration method by Kind have been applied. The towers at which back-flashover is more likely to occur than at other towers are identified by the time integral of voltage according to Kind. Various factors like tower footing impedance, tower surge impedance and tower height are considered. Application of line a surge arrester is shown to be a successful mitigation technique to reduce the back-flashover rate of those 110 kV lines. The lightning overvoltage performance of surge arresters has been analyzed by means of digital simulations. Based on the results of investigations line arresters were installed on the towers in question. Since the installation no further common mode failure has been observed

Nachbildung des Schaltlichtbogens bei der Berechnung elektromagnetischer Ausgleichsvorgaenge

SIGLETIB: AC 9120+MF / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Review of Arc Models in Distribution Networks

The incipient fault in underground cable is recognized as arc fault. Then the arc model selection is very important for the incipient fault detection. The arc features and some typical models have been introduced in detail, including traditional thermal based models, arc models in low voltage and models of arc in long free air. At last, the Kizilcay’s model is recommended to analyze the incipient fault in underground cable for its accuracy and widely utilized. Finally, some conclusions are summarized

Analytical method development and validation of mucopolysaccharide polysulfate in topical formulations by size exclusion chromatography

In this study, a new size exclusion chromatographic method has been developed and validated for the analysis of mucopolysaccharide polysulfate used as an anti-inflammatory and antithrombotic agent in topical formulations. Mucopolysaccharide polysulfate was analyzed in Repromer OH-4000 (10 mu m, 8.0 x 300 mm) and Repromer OH-5000 (10 mu m, 8.0 x 300 mm) columns using a 0.05 M sodium sulfate isocratic elution mobile phase system at 40 degrees C with a flow rate of 1 mL min(-1) and detected by using refractive index detection. The method was validated by means of the limit of quantification, limit of detection, linearity, robustness, recovery, precision and accuracy using the Bioanalytical Method Validation Guidance. The calibration curve showed linearity in the 0.090-1.575 mg mL(-1) range. The limits of detection and quantification were found to be 45.000 and 90.000 mu g mL(-1), respectively. Assay recovery and precision of mucopolysaccharide polysulfate from topical formulations at 0.450, 0.900 and 1.350 mg mL(-1) concentrations were evaluated. Intra-day and inter-day relative standard deviation values were calculated to be less than 2.46%. The mean recovery was calculated as 96.64%. The validated method was successfully applied to the determination of mucopolysaccharide polysulfate in cream and gel formulations

Determination of levofloxacin by HPLC with fluorescence detection in human breast milk

Aim: A new HPLC method with fluorescence detection has been developed and validated for the determination of levofloxacin, one of the fluoroquinolone class antibiotics, in breast milk. Materials & methods: Chromatographic separation was carried out on a reversed phase C18 column with acetonitrile and 10 mM o-phosphoric acid (25:75,v/v) mobile phase composition. Moxifloxacin was used as internal standard and the peaks were detected by fluorescence detection. Results & conclusion: Calibration graph was found linearly within the range of 2.5-500 ng/ml. Limit of detection and limit of quantification were found to be 0.63 and 2.11 ng/ml, respectively. Mean absolute recovery was 96.18%. The developed method has been successfully applied to the determination of levofloxacin in human breast milk taken from two healthy volunteers