1,914 research outputs found
Design and Mitigation Techniques of MV Capacitor Bank Switching Transients on 132 KV Substation
No full textThis paper presents the techniques to mitigate transients caused by capacitor switching in the distribution system. It includes the theory of capacitive switching transients with different methods of mitigation. The paper uses MATLAB SIMULINK software package to simulate the specific mitigation devices. The mathematical calculations of different parameters such as transient voltages, current, and frequencies for each device are compared with obtained value from the simulations of each case study. Poonam Bhati | Mukesh Kumar Lodha "Design and Mitigation Techniques of MV- Capacitor Bank Switching Transients on 132 KV Substation" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-4 , June 2019, URL: https://www.ijtsrd.com/papers/ijtsrd25093.pd
Dielectric stresses on 800 kV HVDC: Converter Transformers and Thyristor Valves
No full textInvestigation of dielectric stresses on the insulation system of 800 kV HVDC converter transformers and thyrisor valves by means of performing and analyzing RTDS simulations. Reviewing of current IEC standards for dielectric testing of these two component and assess if they are applicable for 800 kV equipment.Electrical Engineering, Mathematics and Computer Scienc
Steady State and transient behavior of underground cables in 380 kV transmission grids
No full textThe extension of the Dutch 380 kV high voltage grid is necessary in order to guarantee security of electricity supply to the consumers. To achieve this extension, there are two new 380 kV connections under construction in the Randstad area, a densely populated area in the western part of the Netherlands. In these 380 kV connections, underground cables are applied. The work described in this thesis forms a part of a monitoring program that is managed by the Dutch transmission grid operator TenneT. In this program, the behavior of the two new underground cable connections in the Dutch 380 kV grid is being investigated and the work described in this thesis contributes to this program. Unlike the common overhead transmission line, which has an inductive behavior, a cable acts as a capacitance when it is in operation. This difference in electrical behavior makes research on the grid behavior necessary. One of the research goals is to evaluate whether the power flows and voltage levels in the 380 kV grid stay within the prescribed limits. Another goal of this work is investigating whether the peak of the transient voltages at the cable terminals after lightning currents will stay below the Basic Insulation Level. The research is divided into two parts: steady state behavior and transient behavior. For the steady state part, PI sections are used to model the underground cable and overhead line to perform load flow studies in order to investigate the power flows and voltage levels in the 380 kV grid. For the transient part, the widely applied Frequency Dependent Phase Model (FDPM), which is a transmission line model that takes into account the frequency dependency of cable and line parameters, is used to model the cable and overhead line sections. For the transient part, the focus is on the modeling work of the complete underground cable system. Field measurements are performed for both the 380 kV cross-bonded cable and the overhead line sections and the results are used for transient cable model verification. The scientific contribution of this work is the determination of the parameters for the 380 kV cross bonding system by using reflection measurements and the validation of the FDPM transmission line model by using field measurements on the actual cross bonded 380 kV cable system. Finally, based on the studies described in this thesis, one can conclude that no remarkable overvoltages occur during the studied steady state and transient situations for the given dimensions of the observed 380 kV system
Genome-wide transcrptome and proteome analyses of tobacco psaA and psbA mutants
No full textPhotosynthesis in higher land plants is a complex process involving several proteins encoded by both nuclear and chloroplast genomes that requires a highly coordinated gene expression. Significant changes in plastid differentiation and biochemical processes are associated with the deletion of chloroplast genes. In this study we report - genome-wide responses caused by the deletion of tobacco psaA and psbA genes coding for core components of PSI and PSII, respectively, generated through a chloroplast genetic engineering approach. Transcriptomic and quantitative proteomic analysis showed the down regulation of specific groups of nuclear and chloroplast genes involved in photosynthesis, energy metabolism and chloroplast biogenesis. Moreover, our data show simultaneous activation of several defense and stress responsive genes including those involved in reactive oxygen species (ROS) scavenging mechanisms-. A major finding is the differential transcription of the plastome of deletion mutants: genes known to be transcribed by the plastid encoded polymerase (PEP) were generally down regulated while those transcribed by the nuclear encoded polymerase (NEP) were up regulated, indicating simultaneous activation of multiple signaling pathways in response to disruption of PSI and PSII complexes. The genome wide transcriptomic and proteomic analysis of the ∆psaA and ∆psbA deletion mutants revealed a simultaneous up and down regulation of t specific groups of genes located in nucleus and chloroplasts suggesting a complex circuitry involving both retrograde and anterograde signaling mechanisms responsible for the coordinated expression of nuclear and chloroplast genomes
Comparison of Power Loss Due to Corona Phenomena Model with Peek's Formula in High Voltage 115 kV and 230 kV System
No full textAbstractThis paper studied the power loss due to corona phenomenon with Gary's model and Peek's formula using Matlab program for the power loss simulation in 115 kV and 230 kV system that the corona loss varies with transmission conductor radius and spacing. The corona phenomenon effects on leakage capacitance and inductance of transmission line. The leakage current would increase in the condition of the corona incepted. The power loss due to corona has an inverse variation with radius and spacing of conductor. The Gary‘s model is not suitable for 115 kV. Due to the operating point of power system, the model losses had the value 7.5% with difference from the formula for 115kV system and 14.5% for 230 kV system
La tombe de Maiherperi (KV 36)
No full textThis study of KV 36, the tomb of the 18th Dynasty foster-child of the court (Xrd n kAp) Maiherperi in the Valley of the Kings, is a revised version of part of the author's doctoral dissertation ("Les tombes KV 34, KV 35, KV 36, KV 37, KV 38 découvertes par Victor Loret dans la Vallée des Rois: 'state of the art' à la lumière de nouveaux documents", École Pratique des Hautes Études, Paris, 2013). The principal aim of the study is to examine the tomb on the basis of archival material left by Victor Loret, who discovered it in 1899. Most of this material is today housed at the Università degli Studi di Milano. The author discusses some major questions concerning the person Maiherperi, especially his role at the royal court and the date of his burial. Also, the placement of the different objects of the tomb equipment at the time of the discovery as well as the importance of KV 36 for the discussion about embalmers' chaches are addressed
Investigation of Statistical Distribution of Energization Overvoltages in 380 kV Hybrid OHL-Cable Systems
No full textSwitching operations in power systems can produce significant overvoltages under specific circumstances. With the increasing application of underground cables in transmission systems, the statistical distribution of energization overvoltages is expected to change substantially due to the different electrical characteristics of cables and OHLs. Therefore, it is crucial to perform an insulation coordination study by analysis of the statistical distribution of energization overvoltages. This paper presents a statistical switching analysis on a hybrid OHL-Cable circuit to investigate how such hybrid circuits can affect the distribution of overvoltages. The literature has addressed the distribution of energization overvoltages only for OHLs or cables, but such an study is not available for hybrid systems consisting of OHLs and cables combined. The study is carried out for different cable lengths in the case study to identify how an increasing cable share in the circuit influences the overvoltages distribution due to no-load energization. Moreover, the impact of symmetrical and asymmetrical circuit structures is also addressed. The study is carried out on a distributed frequency-dependent parameter model of the Dutch 380 kV grid in PSCAD/EMTDC.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Intelligent Electrical Power GridsEEMS - Genera
Tungsten anode spectral model using interpolating cubic splines: Unfiltered x‐ray spectra from 20 kV to 640 kV
No full textPURPOSE: Monte Carlo methods were used to generate lightly filtered high resolution x-ray spectra spanning from 20 kV to 640 kV.
METHODS: X-ray spectra were simulated for a conventional tungsten anode. The Monte Carlo N-Particle eXtended radiation transport code (MCNPX 2.6.0) was used to produce 35 spectra over the tube potential range from 20 kV to 640 kV, and cubic spline interpolation procedures were used to create piecewise polynomials characterizing the photon fluence per energy bin as a function of x-ray tube potential. Using these basis spectra and the cubic spline interpolation, 621 spectra were generated at 1 kV intervals from 20 to 640 kV. The tungsten anode spectral model using interpolating cubic splines (TASMICS) produces minimally filtered (0.8 mm Be) x-ray spectra with 1 keV energy resolution. The TASMICS spectra were compared mathematically with other, previously reported spectra.
RESULTS: Using pairedt-test analyses, no statistically significant difference (i.e., p > 0.05) was observed between compared spectra over energy bins above 1% of peak bremsstrahlung fluence. For all energy bins, the correlation of determination (R(2)) demonstrated good correlation for all spectral comparisons. The mean overall difference (MOD) and mean absolute difference (MAD) were computed over energy bins (above 1% of peak bremsstrahlung fluence) and over all the kV permutations compared. MOD and MAD comparisons with previously reported spectra were 2.7% and 9.7%, respectively (TASMIP), 0.1% and 12.0%, respectively [R. Birch and M. Marshall, "Computation of bremsstrahlung x-ray spectra and comparison with spectra measured with a Ge(Li) detector," Phys. Med. Biol. 24, 505-517 (1979)], 0.4% and 8.1%, respectively (Poludniowski), and 0.4% and 8.1%, respectively (AAPM TG 195). The effective energy of TASMICS spectra with 2.5 mm of added Al filtration ranged from 17 keV (at 20 kV) to 138 keV (at 640 kV); with 0.2 mm of added Cu filtration the effective energy was 9 keV at 20 kV and 169 keV at 640 kV.
CONCLUSIONS: Ranging from 20 kV to 640 kV, 621 x-ray spectra were produced and are available at 1 kV tube potential intervals. The spectra are tabulated at 1 keV intervals. TASMICS spectra were shown to be largely equivalent to published spectral models and are available in spreadsheet format for interested users by emailing the corresponding author (JMB)
Reduction of Power Loss from Corona Phenomena in High Voltage Transmission Line 115 and 230 kV
No full textAbstractThe Power Loss from Corona Phenomena in High Voltage Transmission Line 115 and 230 kV were studied the effects of various elements that affect the power loss from corona in high voltage transmission line between Khon Kaen and Nakhon Ratchasima and the method to reduce power loss due to corona. This paper clarifies Peek's and Peterson's formula by utilizing Matlab program with the effect from different variables including conductor spacing, conductor radius and a system voltage. The Peterson's formula was suitable for the two systems than that of Peek's formula under the condition of phase voltage to corona inception voltage ratio. In the 115 kV system uses 795 MCM ACSR conductor with 1.447 cm radius and the spacing was 320 cm could generate a less power loss, and the 230 kV system uses 1272 MCM ACSR conductor with 1.75 radius, the spacing was 500 cm could generate a less power loss. When simulated to solve the conductor radius and the spacing that would have the less power loss. In 115 kV system, the suitable was 1.36 cm radius and 266 cm spacing and in 230 kV system the suitable was 0.85 cm radius and 660 cm. It therefore could reduce power loss by selecting the conductor radius and the conductor space increasing or protecting the system from the lightning
Measurement of Imaging Dose in 2D kV Image Guided Radiotherapy Using Indigenously Developed Portable Free Air Ionization Chamber
No full textObjective:
The objective of this work is to measure the imaging dose in two-dimensional kilovoltage (kV) image guided radiotherapy using in-house developed free air ionization chamber (FAIC).
Materials and Methods:
In-house developed FAIC and a commercially available shadow-free diagnostic (SFD) detector were used in this work. Reference points of the dosimeters were positioned at 100 cm distance from the focal spot of the x-ray tube of an on-board imager. The blades of x-ray tube were opened to 26.6 cm × 20 cm. The FAIC was operated at 3800 V supplied by an indigenously developed external high-voltage power supply, whereas the SFD was operated at 300 V supplied by the electrometer. The dosimeters were irradiated using head (70 kV, 9.77 mAs), abdomen (100 kV, 25.39 mAs), pelvis (110 kV, 29.30 mAs), and extremity (65 kV, 6.84 mAs) protocols. The air kerma per unit mAs was determined using the collected charge and the values determined in this work were compared with the values reported in the literature.
Results:
The measured air kerma by FAIC and SFD were in good agreement with each other within the uncertainty of measurement. However, the FAIC and SFD measured values were approximately 42% lesser than the values of air kerma reported in the literature.
Conclusions:
The default imaging protocols are optimized for image quality and patient dose, further optimization of exposure parameters according to the patient anatomy may help in reducing the imaging dose further
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