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In determining the screw systems associated with incompletely specified displacements, the displacement of a line was known to be an exceptional case. Recent research has concluded that all possible screws for the finite displacement of a line do not form a screw system. This paper utilizes Dimentberg's definition of pitch to demonstrate that all possible screws for displacing a line from one position to another can indeed form a screw system of the third order. Two different approaches are taken: one uses the concept of a screw triangle, and the other is based on analytical geometry. A set of three linearly independent screws of the screw system is shown to be perpendicularly intersecting the external bisector of the initial and final positions of the line. [DOI: 10.1115/1.1539510]

Explicit formulas for determining system loss, current flows and voltages in terms of system and network data are developed for large-scale unbalanced distribution systems. The three-phase formulas consider multi-phase grounded or ungrounded loads and lines, cogenerators, multi-phase shunt elements and transformers of different connections all of which exist in large-scale unbalanced distribution systems. Test results on a number of distribution systems, including an actual 394-bus distribution network, are included to illustrate the accuracy and speed of the proposed formula for real-time analysis and control of distribution systems. It is shown numerically that the results given by these closed-form formulas are very close to those obtained by rigorous three-phase power flow methods. Applications of the explicit expressions to real-time control of distribution systems are also identified. Also, some features of the explicit formulas which are not possible with traditional power flow studies are discussed.

A novel solution algorithm for capacitor placement and real-time control in real large-scale unbalanced distribution systems is evaluated and implemented to determine the number, locations, sizes, types and control schemes of capacitors to be placed on large-scale unbalanced distribution systems. A detailed numerical study regarding the solution algorithm in large scale unbalanced distribution systems is undertaken. Promising numerical results on both 292 bus and 394 bus real unbalanced distribution systems containing unbalanced loads and phasing and various types of transformers are presented. The computational performance for the capacitor control problem under load variations is encouraging. Key Words: VAR/Volt Control, Capacitor Placement, Loss Formula, Quadratic Integer Programming, Unbalanced Distribution Systems, Large-Scale Systems.

A comprehensive study of capacitor placements and real-time control in general unbalanced distribution systems is undertaken. New developments in a loss reduction formula, problem formulations, solution methodology and mathematical justification are presented. The problem is decoupled into two subproblems: the capacitor placement subproblem and the real-time control subproblem. An effective solution algorithm for placing capacitors and determining their real-time control schemes for general unbalanced distribution systems is proposed. To meet the need for efficient implementation in real-time environments, a fast pseudo gradient type mechanism for deriving capacitor control settings is incorporated into the solution algorithms. A quadratic integer programming based approach is proposed to determine the number, locations and sizing of capacitors to be placed in the distribution systems. The subproblem of determining capacitor control settings under varying loading conditions is formulated as another quadratic integer programming problem. Mathematical justification is provided to show that the proposed algorithms are guaranteed to yield local optimal solutions. Numerical studies on the determination of capacitor number, size, location and real-time control schemes on large-scale unbalanced distribution systems under nonlinear load variations are presented in great detail in the companion paper [17]. Key Words: VAR/Volt Control, Capacitor Placement, Real-time Control, Loss Formula, Quadratic Integer Programming, Unbalanced Distribution Systems, Large-Scale Systems.

Real-time applications demand fast computation, this paper proposes an efficient algorithm for real-time network reconfiguration on large unbalanced distribution networks. A novel formulation of the network reconfiguration to achieve loss minimization and load balancing is given. To reduce computational requirements for the solution algorithm, well justified power flow and loss reduction formulas in terms of the on/off status of network switches are proposed for efficient system updating. The algorithm relies only on a few full power flow studies based on system states attained by explicit expressions using backward-forward sweeps for efficient computation of system's states at the critical system operating points. The solution algorithm runs in an amount of time linearly proportional to the number of tie switches and the number of sectionalizing switches in the system. The solution algorithm has been implemented into a software package and tested on unbalanced distribution systems including a system with 292-buses, 76-laterals, 7 transformers, 45 switches and 255 line sections under diverse system conditions. Key Words: Network Reconfiguration, Real-Time Applications, Loss Formula, Nonlinear Integer Programming, Unbalanced Distribution Systems, Large Scale Systems.

In control and stability studies, load models should realistically represent th aggregate load behavior of all kinds of individual components. In this paper, the development of a composite load model, where the load is represented as a combination of an RC circuit in parallel with an induction motor equivalent circuit, is presented. A procedure is developed for identifying a frequency-dependent composite load model using digital measurements from an on-line transient recording system, taking account of system frequency variation. A nonlinear model parameter estimation technique is described to derive the frequency-dependent load model. A computer program called LMSP has been developed. The program consists of five major phases: user-interface, data manipulation, load model identification, model conversion and system model response evaluation. A case study is presented to illustrate, in particular, th accuracy of the developed model for the representation of dynamic load behavior of an actual power system.

A comprehensive approach to strategic planning of LC compensators in a nonsinusoidal distribution system is presented. Different from most existing approaches, this approach can handle practical (discrete) instead of continuous LC compensator values and determine fixed or switchable compensators corresponding to different load levels. The problem is formulated as a non-differentiable, combinatorial optimization problem. A solution algorithm based on simulated annealing is employed to determine the 'optimal' locations, types and sizes, and settings of these LC compensators. The 'optimality' of the solution is from minimizing the system costs while meeting different operational constraints and harmonic limits.

In this paper, a sixth-order synchronous generator model identification technique from on-line measurement is considered. An algorithm is devised to identify the generator model. A constrained conjugate gradient method is incorporated into the algorithm to guarantee rapid convergence to the final solution. Using the algorithm, a complete generator model is derived from on-line measurements recorded by a plant transient recording system during a system disturbance. In addition, the algorithm does not greatly rely upon the accuracy of the initial estimates, allowing the initial estimates to deviate reasonably far from the true parameters. Detailed numerical studies of the Taipower system using raw and filtered data are included.

Accurate generator modeling allows for more precise calculations of power system control and stability limits. In this paper, a procedure using a set of measured data from an on-line plant transient recording and analysis (PTRA) system to develop the synchronous generator model for the Taipower system is described. A continuous-time transfer-function matrix is derived for a popular sixth-order synchronous generator model. In order to accommodate the nature of on-line digital measurements, the transfer-function matrix is transformed into a simple discrete-time linear regression model. A measure of discrepancy between the generator model outputs and the on-line measurements from generators is employed. A modified conjugate gradient method suitable for identifying generator parameters is developed to minimize the measure of discrepancy, from which a set of accurate generator parameter values can be obtained. The merits of the modified conjugate gradient method include its computational efficiency and numerical reliability. The proposed procedure allows simultaneous estimation of all generator parameter values. A detailed algorithm and numerical studies are reported in a companion paper [7].

Accurate dynamic load models allow more precise calculations of power system controls and stability limits, which are critical in the planning and operation of power systems. This paper describes the development of dynamic load models using the measurement approach for the Taipower system. Two dynamic load model structures are developed. A procedure for applying a set of measured data from an on-line transient recording system to develop dynamic load models for the Taipower system is described. A technique based on the concept of confidance interval is used to validate the developed high-order load model structure. Case studies are also presented.

Grain boundary directed spinodal decomposition has a substantial effect on the microstructure evolution and properties of polycrystalline alloys. The morphological selection mechanism of spinodal decomposition at grain boundaries is a major challenge to reveal, and remains elusive so far. In this work, the effect of grain boundaries on spinodal decomposition is investigated by using the phase-field model. The simulation results indicate that the spinodal morphology at the grain boundary is anisotropic bicontinuous microstructures different from the isotropic continuous microstructures of spinodal decomposition in the bulk phase. Moreover, at grain boundaries with higher energy, the decomposed phases are alternating α/β layers that are parallel to the grain boundary. On the contrary, alternating α/β layers are perpendicular to the grain boundary. [ABSTRACT FROM AUTHOR]