Search

The objective of the research was to determine the effect of different tillage methods on some soil physicochemical properties in Niger Delta University Teaching and Research Farms. The land was divided into plots measuring 5 x 5 m with three replicates per treatment. Five tillage treatments considered were: No Till, hoeing, digging, hoeing + digging once, and hoeing + digging twice. Two samples were collected per plot at 0-15 cm and 15-30 cm depth. A total number of thirty (30) samples were collected from the field. The research was laid out using the Randomized Complete Block Design. Results showed that the tillage methods had no significant effect on the soil's chemical properties but influenced the physical. Mean pH across all plots ranged from 4.42 - 4.49 indicating strongly acidic state, electrical conductivity ranged 65.67-82 dS m-1 indicating no salinity stress, detrimental to crops; organic carbon and organic matter were moderate with a range of 18.52-21.55 g kg-1 and 37.03-43.10 g kg-1 respectively. Total nitrogen was at its moderate range of 7.88-12.17 g kg-1. Exchangeable acidity was low with a range of 1.52-1.71 cmol kg-1. The tillage methods influenced soil bulk density and porosity; the highest bulk density was recorded in the NT zone (1.18 g cm-3) which decreased steadily with an increase in tillage intensity. With the hoe+digging (twice) recording the lowest value of 0.94 g cm-3. Similarly, the highest porosity value was found in the tillage method with the lowest bulk density value (0.94 g cm-3: 64.7%), while the lowest was observed in the tillage method with the highest bulk density value (1.18 g cm-3: 55.7%). pH had positive correlation (P<0.05) with electrical conductivity (r=0.62), organic carbon (r=0.94), organic matter (r=0.90), and negative correlation with exchangeable acidity (r=-0.52). Organic carbon had strong positive correlation with organic matter (r=0.99), effective cation exchange capacity (r=0.69), clay (r=0.50), and total nitrogen (r=0.61). Silt (r=0.74) and clay (r=0.70) showed positive relationship with bulk density, while bulk density (r= -0.99) showed strong negative correlation with porosity. It is therefore recommended that crude tillage methods be used for sustainable and conservative agriculture. [ABSTRACT FROM AUTHOR]

In transient stability simulators such as PSS/E, the bus frequency is estimated using a window of (positive-sequence) phasor angle measurements. A digital filter is often used to account for the filtering effect in actual measurement devices and to eliminate sudden changes during frequency computations. Although transient stability simulators label the filtered angle derivative as the “frequency,” the frequency provided by such programs does not match actual measurements reported by phasor measurement units (PMUs), which makes it difficult to gauge the validity of studies (e.g., wide-area event detection and control applications) that are based on such simulations. In this paper, we implement a frequency computation method directly using positive phasor angles provided by simulators. The proposed method is tested on two systems extensively and validated against the measurements of an actual PMU. The improved frequency measurements closely match PMU responses. Cross-validation results also suggest the method may be used for other systems without conducting full time-domain simulations. [ABSTRACT FROM AUTHOR]

An identification algorithm is proposed for generator outages in external systems given tie-line flow measurements and pre-outage linear sensitivity factors. The problem is challenging due to limited information available to operators in interconnected systems. To overcome the underdetermined nature of the problem (the number of tie-line measurements is smaller than the number of generators), a clustering method based on pivoted QR decomposition is implemented so that the outage location can be identified to the area of origination. Two test systems, the 68-bus New England system and the 500-bus synthetic system, were used for validation. The results demonstrate that with limited knowledge of the external system, the algorithm is able to identify the correct generator cluster in all cases. Another advantage of the proposed algorithm is its high efficiency, which enables detection within sub-milliseconds. In addition, an estimation of the cluster injection change is also provided by the algorithm. [ABSTRACT FROM AUTHOR]

This paper proposes and evaluates a systematic method of scheduling energy storage and conventional generation capacities in a day-ahead frequency regulation market, based on compliance to control performance standard 1 (CPS1), during each hour of the following day. The salient feature of this method is the development of two simple piecewise linear curves that represent the relationship between first, conventional generation and energy storage power capacities, and second, energy storage power and energy capacities, to satisfy CPS1 compliance in the presence of stochastic load variations. These curves are then modeled inside a mixed integer linear program to solve for resource allocations by minimizing total capacity cost. As such, the formulation avoids complex algorithms that are otherwise required to model frequency dynamics inside the optimization problem. To reduce computation time, a scenario reduction algorithm is used to obtain a small set of scenarios to represent the stochastic load. The proposed method is evaluated using comprehensive dynamic simulations of the two-area IEEE reliability test system implemented in PSS/E. The results prove that the proposed method is effective for scheduling capacities to meet CPS1 compliance with minimum cost. [ABSTRACT FROM AUTHOR]

In this paper, we propose a data-driven load fluctuation model, based on high-resolution historical demand data from multi-regional systems, that can be used for research such as power system generation control studies and probabilistic load flow studies. As in previous studies, the random load fluctuations are modeled as independent Gaussian random variables; however, unlike in previous studies, we do not assume the relationship between the standard deviation and the base demand in each region is known a priori. Instead, we propose a framework for determining the relationship between the base demand level and short-term demand uncertainty. The developed framework has been tested using actual 5-minute demand data from the New York and New Zealand power systems. The results demonstrate that the proposed models outperform those used in previous work. Coefficients of the example cases are included, the parameters of which can be applied to similar multi-region systems. [ABSTRACT FROM AUTHOR]

This paper proposes and evaluates a systematic method for controlling an energy storage system for preventing load shedding due to transient declines in frequency. The proposed controller works on local measurements and uses an extended Kalman filter to perform online identification of system parameters. These results are then used to implement a model predictive controller for the safe withdrawal of support and energy recovery, both without incurring transient load shedding. The formulation accounts for single generator outages and includes power system parameters such as inertia, damping, and droop. The proposed method is evaluated using the nonlinear simulations of 6-bus and 24-bus test systems known as Roy Billinton Test System (RBTS) and IEEE Reliability Test System. The results show that the proposed controller is effective in preventing transient load shedding. [ABSTRACT FROM PUBLISHER]

The kinetics of the addition of phenol to diisopropylcarbodiimide, and reaction of the resulting N, N′-diisopropyl- O-phenylisourea with hydroxide, are reported. The isourea is generated by a slow overall termolecular equilibrium process, inhibited by isourea-phenol salt generation. In contrast to an earlier report, reaction of the isourea with hydroxide does not induce a synthetically useful 1,3-O-N (Chapman) rearrangement. Instead, deprotonation results in solvolysis by carbodiimide elimination. [ABSTRACT FROM AUTHOR]

Phasor measurement units (PMUs) are being increasingly deployed to improve monitoring and control of the power grid due to their improved data synchronization and reporting rates in comparison with legacy metering devices. However, one drawback of their higher data rates is the associated increase in bandwidth (for transmission) and storage requirements (for data archives). Fortunately, typical grid behavior can lead to significant compression opportunities for phasor angle measurements. For example, operation of the grid at near-nominal frequency results in small changes in phase angles between frames, and the similarity in frequencies throughout the system results in a high level of correlation between phasor angles of different PMUs. This paper presents several methods for preprocessing of phasor angles that take advantage of these system characteristics, including a new method—frequency compensated difference encoding—that is able to significantly reduce angle data entropy. After the preprocessor stage, the signal is input to an entropy encoder, based on Golomb–Rice codes, that is ideal for high-throughput signal compression. The ability of the proposed methods to compress phase angles is demonstrated using a large corpus of data—over 1 billion phasor angles from 25 data sets—captured during typical and atypical grid conditions. [ABSTRACT FROM PUBLISHER]

One role of grid operators is to identify potential problems before they occur and, if necessary, take preemptive actions. As wind generation becomes increasingly widespread, there is the potential for credible, simultaneous fluctuations of output at different locations to result in limit violations. Existing analysis methods that consider forecast errors either inadequately model the control responses available to system operators (e.g., using participation factors) or ignore network constraints, which limits their utility in identifying situations that would require operator action. An alternative method of handling forecast errors, utilizing bilevel programming, is proposed here to identify situations that may result in branch overloads. What distinguishes this method from prior approaches is that it only identifies overloads that can occur despite optimal operator reaction to forecast errors--i.e., when the overload is unavoidable, given current control capabilities. Studies conducted on 37- and 118-bus test systems demonstrate both the utility and feasibility of using this method for online operations. [ABSTRACT FROM PUBLISHER]

This paper proposes and investigates a new line-commutated current-sourced converter (LCC)-high voltage dc current (HVDC) global supplementary control (GSC) strategy for stabilizing and enhancing the dynamic performance of a large ac system that is segmented by LCC-HVDC links. The GSC is designed based on a linear quadratic Gaussian (LQG) method and enables coordinated supplementary control action of multiple HVDC links that participate in segmentation. The GSC can stabilize the ac system while either minimizing the propagation of oscillatory dynamics from one segment to other segments (GSC1) or enabling their controlled transfer from a disturbed segment to other segments (GSC2). The study results show that in a fully-dc-segmented system: 1) GSC1 and GSC2 are able to stabilize the system; 2) under GSC1, each segment can experience major disturbances without causing adjacent segments to experience the disturbances with the same degree of severity; and 3) GSC2 enables controlled transfer of the oscillations among the segments and, depending on the system configuration, can further reduce the magnitude and duration of oscillatory dynamics. The studies are conducted on a three-segment ac system including three interconnecting LCC-HVDC links. [ABSTRACT FROM AUTHOR]

Hopf bifurcation phenomenon of a power system results in oscillatory dynamics which can lead to instabilities in the system. Therefore, it is desirable to operate the system such that a sufficient margin to Hopf bifurcation is ensured. This paper presents a methodology based on the adjustment of the setpoint values of the HVDC link controllers, to prevent instability or increase the stability margin of the system subject to Hopf bifurcation. In this paper, the first-order sensitivities of the Hopf stability margin to the setpoint values of the HVDC links are presented. These sensitivities identify the optimum direction to change the HVDC setpoints to steer the system away from instability, increase the stability margin, and improve the damping of oscillatory modes. The proposed method is evaluated on various system configurations subject to Hopf bifurcation phenomena caused by a variety of events, such as load and line impedance variations. Simulation results show that at the optimum operating point, for a variety of Hopf bifurcations, the stability margin and damping of the oscillatory modes improve. [ABSTRACT FROM AUTHOR]

Using direct stimulation in patients undergoing awake mapping of gliomas, Tate et al. report a bilateral probabilistic map of cortical epicentres of brain functions, including sensorimotor and language. The data challenge classical theories, especially of Broca's area as a speech output region, and provide a distributed framework of neural networks.The organization of basic functions of the human brain, particularly in the right hemisphere, remains poorly understood. Recent advances in functional neuroimaging have improved our understanding of cortical organization but do not allow for direct interrogation or determination of essential (versus participatory) cortical regions. Direct cortical stimulation represents a unique opportunity to provide novel insights into the functional distribution of critical epicentres. Direct cortical stimulation (bipolar, 60 Hz, 1-ms pulse) was performed in 165 consecutive patients undergoing awake mapping for resection of low-grade gliomas. Tasks included motor, sensory, counting, and picture naming. Stimulation sites eliciting positive (sensory/motor) or negative (speech arrest, dysarthria, anomia, phonological and semantic paraphasias) findings were recorded and mapped onto a standard Montreal Neurological Institute brain atlas. Montreal Neurological Institute-space functional data were subjected to cluster analysis algorithms (K-means, partition around medioids, hierarchical Ward) to elucidate crucial network epicentres. Sensorimotor function was observed in the pre/post-central gyri as expected. Articulation epicentres were also found within the pre/post-central gyri. However, speech arrest localized to ventral premotor cortex, not the classical Broca’s area. Anomia/paraphasia data demonstrated foci not only within classical Wernicke’s area but also within the middle and inferior frontal gyri. We report the first bilateral probabilistic map for crucial cortical epicentres of human brain functions in the right and left hemispheres, including sensory, motor, and language (speech, articulation, phonology and semantics). These data challenge classical theories of brain organization (e.g. Broca’s area as speech output region) and provide a distributed framework for future studies of neural networks. [ABSTRACT FROM PUBLISHER]

Although phasor measurement units (PMUs) have become increasingly widespread throughout power networks, the buses monitored by PMUs still constitute a very small percentage of the total number of system buses. Our research explores methods to derive useful information from PMU data in spite of this limited coverage. In particular, we have developed an algorithm which uses known system topology information, together with PMU phasor angle measurements, to detect system line outages. In addition to determining the outaged line, the algorithm also provides an estimate of the pre-outage flow on the outaged line. To demonstrate the effectiveness of our approach, the algorithm is demonstrated using simulated and real PMU data from two systems—a 37-bus study case and the TVA control area. [ABSTRACT FROM AUTHOR]

A key need facing the electric power industry is the ongoing requirement to develop its future workforce. While university education is a crucial step in this process, studies have shown that many promising students are unaware of possible careers in the power industry. Many also lose interest in math and science during their high school and even middle school years. This paper presents lesson plans and associated applets designed to help address these needs,. developed as a collaboration between electric power researchers and education specialists. Thus far, two units have been developed to engage pre-university students in the power area. The first unit, Power and Energy in the Home, serves as an introduction to the concepts of power and energy and provides many sample loads to illustrate the impacts of running different appliances. Special attention is paid to environmental issues by the inclusion of Energy Star appliances along with incandescent and compact fluorescent lighting. The second unit, titled The Power Grid, aims to inform students about the macroscopic picture of how energy gets from generators to loads. Many different generation technologies are included, along with external system connections to demonstrate how power is imported and exported. Discussion of line overloading, and how networks can be both beneficial and detrimental depending on circumstances, are facilitated by features built into the applet and provided in the lesson plans. The materials have been distributed to students and educators, many of whom have provided valuable feedback. [ABSTRACT FROM AUTHOR]

Studies of the optimal multiplier (or optimal step size) modification to the standard Newton-Raphson (NR) load flow have mainly focused on highly stressed and unsolvable systems. This paper extends these previous studies by comparing performance of the NR load flow with and without optimal multipliers for a variety of unstressed, stressed, and unsolvable systems. Also, the impact of coordinate system choice in representing the voltage phasor at each bus is considered. In total, four solution methods are compared: the NR algorithm with and without optimal multipliers using polar and rectangular coordinates. This comparison is carried out by combining analysis of the optimal multiplier technique with empirical results for two-bus, 118-bus, and 10 274-bus test cases. These results indicate that the polar NR load flow with optimal multipliers is the best method of solution for both solvable and unsolvable cases. [ABSTRACT FROM AUTHOR]