This paper proposes a method for optimal placement of phasor measurement units (PMUs) for complete observability of a power system for normal operating conditions, as well as for single branch ...outages. A binary search algorithm is used to determine the minimum number of PMUs needed to make the system observable. In case of more than one solution, a strategy is proposed to select the solution resulting in the most preferred pattern of measurement redundancy. The proposed method is used to benchmark the optimal PMU placement solutions for the IEEE 14-bus, IEEE 24-bus, IEEE 30-bus and New England 39-bus test systems. The proposed method is applied on a 298-bus system to determine the optimal placement of PMUs when conventional measurements are available.
This paper proposes an application of the cubature Kalman filter (CKF) to the power system dynamic state estimation (PSDSE) utilizing the measurements from the remote terminal units as well as the ...phasor measurement units. The CKF process utilizes the spherical cubature and Gaussian quadrature rules to estimate the probability density functions of the state space and the measurement space. This helps in linearization of the nonlinear measurement function without loss of accuracy. The CKF does not require formation of the Jacobian and Hessian matrices to execute the PSDSE, which saves the execution time. A state forecasting technique is utilized to forecast the states during the interval between two time instants of receiving the measurement sets from the field. This helps in estimating the states of the power system during the period when the field measurements are not available. The effectiveness of the application of the CKF to the PSDSE has been demonstrated on IEEE 30 bus system and 246 bus Northern Regional Power Grid Indian system.
Context. The Galactic transient black hole candidate (BHC) GX 339-4 exhibited several outbursts at regular intervals of about two to three years in the Rossi X-ray Timing Explorer (RXTE) era. After ...remaining in an almost quiescent state for three long years, it again became X-ray active in January, 2010, continuing to be so over the next ~14 months. Aims. We study the timing and spectral properties of the BHC during its recent outburst and understand the behavioral change in the accretion flow dynamics associated with the evolution of the various X-ray features. Methods. The detailed analysis of the temporal and spectral properties of the source during this outburst are carried out using archival data of the RXTE PCA instrument. We analyze a total of 236 observational intervals consisting of 419 days of data observed by RXTE, from 2010 January 12 to 2011 March 6. Results. Our study provides a comprehensive understanding of the mass accretion processes and properties of the accretion disk of the BHC. The PCA spectra of 2.5–25 keV are mainly fitted with a combination of two components, namely, a disk black body and a power-law. The entire outburst as observed by RXTE, is divided into four spectral states, namely, hard, hard-intermediate, soft-intermediate, and soft. Quasi-periodic oscillations (QPOs) were found in three out of the four states, namely hard, hard-intermediate, and soft-intermediate states. The QPO frequencies increase monotonically from 0.102 Hz to 5.692 Hz in the rising phase of the outburst, while during the declining phase QPO frequencies decrease monotonically from 6.420 to 1.149 Hz. The evolution pattern, i.e. the hardness-intensity diagram, of the present outburst can be reproduced by two different components of the flow of accreting material. Conclusions. The recent outburst of GX 339-4 gives us an opportunity to understand the evolution of the two-component accretion rates starting from the onset to the end of the outburst phase. We found that the QPO frequency variation could be explained by the propagating oscillatory shock model (POS) and the hardness versus intensity variation can be reproduced if we assume that higher viscosity causes the conversion of a low angular momentum disk component into a Keplerian component during the outburst phase. The decline phase starts because of the reduction in the viscosity.
This paper presents a method for the use of synchronized measurements for complete observability of a power system. The placement of phasor measurement units (PMUs), utilizing time-synchronized ...measurements of voltage and current phasors, is studied in this paper. An integer quadratic programming approach is used to minimize the total number of PMUs required, and to maximize the measurement redundancy at the power system buses. Existing conventional measurements can also be accommodated in the proposed PMU placement method. Complete observability of the system is ensured under normal operating conditions as well as under the outage of a single transmission line or a single PMU. Simulation results on the IEEE 14-bus, 30-bus, 57-bus, and 118-bus test systems as well as on a 298-bus test system are presented in this paper.
This Letter presents the development of a dual linearly polarised microstrip antenna for S- and C-band with improved isolation and bandwidth. The antenna is dual linearly polarised at each of the ...bands. The S-band patch is proximity coupled to two orthogonal feed lines, whereas the C-band patches are aperture coupled to other two mutually orthogonal feed lines. The antenna results in an impedance bandwidth ≥ 3.65% with an isolation ≥ 26 dB at the S-band ports. At the C-band ports, it also displays an isolation ≥ 45 dB over the entire operating bandwidth of ≥ 21%. All these results are improved compared to the earlier reported investigations.
Aims. We study the formation of water and methanol in the dense cloud conditions to find the dependence of its production rate on the binding energies, reaction mechanisms, temperatures, and grain ...site number. We wish to find the effective grain surface area available for chemical reaction and the effective recombination timescales as functions of grain and gas parameters. Methods. We used a Monte Carlo simulation to follow the chemical processes occurring on the grain surface. We carried out the simulations on the Olivine grains of different sizes, temperatures, gas phase abundances and different reaction mechanisms. We consider H, O, and CO as the accreting species from the gas phase and allow ten chemical reactions among them on the grains. Results. We find that the formation rate of various molecules is strongly dependent on the binding energies. When the binding energies are high, it is very difficult to produce significant amounts of the molecular species. Instead, the grain is found to be full of atomic species. The production rates are found to depend on the number density in the gas phase. When the density is high, the production of various molecules on the grains is small as grain sites are quickly filled up by atomic species. If both the Eley-Rideal and Langmuir-Hinselwood mechanisms are considered, then the production rates are maximum and the grains are filled up relatively faster. Thus, if allowed, the Eley-Rideal mechanism can also play a major role and more so when the grain is full of immobile species. We show that the concept of the effective grain surface area, which we introduced in our earlier work, plays a significant role in grain chemistry. Conclusions. We compute the abundance of water and methanol and show that the results strongly depend on the density and composition in the gas phase, as well as various grain parameters. In the rate equation, it is generally assumed that the recombination efficiencies are independent of the grain parameters, and the surface coverage. Presently, our computed parameter α for each product is found to depend on the accretion rate, the grain parameters and the surface coverage of the grain. We compare our results obtained from the rate equation and the one from the effective rate equation, which includes α. A comparison of our results with the observed abundance shows very good agreement.
Solar power forecasting is important for the reliable and economic operation of power systems with high penetration of solar energy. The solar power forecasts for the day-ahead time horizon are more ...erroneous than the hour-ahead time horizon. Numerical weather prediction (NWP) variables such as irradiance, cloud cover, precipitation etc. are used as input to day-ahead forecasting models. The uncertainty in NWP varies with weather conditions. Different forecasting algorithms based on a single method are available in the literature. Combination of individual forecasting algorithms increases the accuracy of the forecasts. However, the combined-forecast has yet not been analysed much in the area of day-ahead solar power forecasting. This paper thus explores different combined-forecast methods such as mean, median, linear regression and non-linear regressions using supervised machine learning algorithms. The number of models required for day-ahead solar power forecasts is studied. One for all hour (same) or separate models for each hour of the day are possible. The effects of retraining frequency on the performance of the forecasting models, which is important for the computational burden of the system, are also studied. Forecasting algorithms are applied to three solar plants in Australia.
•Different combined-forecasts for day-ahead solar power forecasting were explored.•The number of forecasting models required for solar power forecasting was analysed.•The effect of different retraining frequencies for day-ahead solar power forecasting models was examined.•Several machine-learning based forecasting models were implemented.
Reverse-transcription loop-mediated isothermal amplification (RT-LAMP) assay was developed for detection of groundnut bud necrosis virus (GBNV) causing potato stem necrosis disease. The isothermal ...temperatures, reaction periods and concentrations of reaction mixture were optimized where, the assay worked well at 65 °C for 50 min, 6 U of WarmStart Bst 2.0 DNA polymerase, 1.4 mM dNTPs and 2.0 mM MgSO4. The optimized assay proved to be specific to GBNV with no cross reactivity to other viruses infecting potato in India. The specificity of RT-LAMP assay was found to be 100 fold more sensitive than that of RT-PCR. The developed assay was applied for the detection of GBNV from 80 potato leaf samples where 24 samples were found infected which was confirmed by RT-PCR. It was concluded that the RT-LAMP assay developed for detection of GBNV was specific, sensitive and suitable for its use in virus indexing under potato seed production programme.
•Developed RT-LAMP assay for specific and sensitive detection of GBNV infecting potato.•The assay was proved to be highly specificity without any cross-reactivity.•The developed RT-LAMP assay proved to be 100 fold more sensitive as compared to RT-PCR.•Developed assay was applied for detection of GBNV from unknown potato leaf samples.
The development of a dual polarised microstrip antenna for S- and C-band with improved characteristics is presented. It is dual linearly polarised at S-band and dual circularly polarised at C-band. ...Two orthogonal feeds have been conceived for proximity coupling at S-band. The other two composite feeds are aperture coupled at C-band. These generate left-hand and right-hand circular polarisations exclusively. The antenna reveals 3.5% or more impedance bandwidth at the S-band ports with an isolation better than 22 dB (the best isolation is ≈31.5 dB at the band-centre). It yields >21.2% impedance bandwidth and about 10.2% axial-ratio bandwidth at each of the C-band ports, both being improved compared to the earlier reports. Achieved isolation between the C-band ports is better than 18.5 dB (≈23.5 dB at the centre of the working band).
•The perturbation of inertia and reactance factors are analyzed to investigate their impact on the output power and frequency of the VSG.•The output power oscillations of a VSG unit can be suppressed ...by increasing the value of line reactance virtually.•A self-regulated virtual impedance (SRVI) VSG technique is proposed to limit fault current and to improve system damping.•It provides a regulated value of virtual impedance as a function of the rate of change of RMS value of DG current during the transient condition.
In this paper, a self-regulated virtual impedance (SRVI) control of virtual synchronous generator (VSG) is proposed. In the modern power system, large penetration of inverter-interfaced distributed generator (DG) decreases the equivalent inertia of the grid. The system, therefore, becomes more prone to frequency instability, and the fault current limits are reduced due to inverter power ratings. The VSG control of the inverter is used to maintain and enhance the transient stability of the system by introducing virtual inertia in it. In the proposed control, the SRVI control block is added in VSG control to further improve the damping and to limit the fault current during overloads and/or faults. The virtual impedance in the SRVI block is regulated as a function of the rate of change of root mean square (RMS) value of DG current during the transient case. The design of virtual impedance for the proposed control is also discussed in this paper. To see the effectiveness of the proposed technique, electromagnetic transient (EMT) simulation is performed using a real-time digital simulator (RTDS) for disturbances that result in large frequency deviations. The simulation results show that the proposed scheme outperforms the conventional VSG control.
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