Karen Miu

Fast service restoration for large-scale distribution systems with priority customers and constraints

A fast, effective service restoration method is designed for large-scale distribution systems with priority customers. The service restoration problem is formulated as a constrained multi-objective optimization problem. A ranking-based search method employing analytical information obtained from three-phase power flow simulations is designed to restore service to as many priority customers as possible while maximizing the amount of total load restored and minimizing the number of required switch operations. The proposed method is designed with consideration to networks which have predominantly manual switches. Comprehensive simulation results of the search method, including priority customers, single and multiple faults and multiple out-of-service areas are presented for a 416 bus distribution network.

Capacitor placement, replacement and control in large-scale distribution systems by a GA-based two-stage algorithm

This paper presents a two-stage algorithm tailored for capacitor placement, replacement and control of general, large-scale, unbalanced distribution systems. The first stage of the proposed algorithm consists of a GA followed by the second stage which consists of a sensitivity-based heuristic method tailored for the capacitor placement, replacement and control problem. The two-stage algorithm is designed to take advantage of the merits of each technique. The GA is employed to find neighborhoods of high quality solutions and to provide a good initial guess for the sensitivity-based heuristic. The heuristic uses the sensitivity of real power loss to reactive power to quickly and locally improve upon the solution provided by the GA with less computation than by allowing the GA to continue. The two-stage algorithm was implemented in the C programming language and tested for a 292 bus unbalanced system with single, two and three-phase branches and grounded and ungrounded portions of the network with promising results.

Switch placement to improve system reliability for radial distribution systems with distributed generation

To improve system reliability for radial distribution systems with distributed generation (DG) under fault conditions, switch placement schemes are proposed to form self-supported areas after fault isolation. Customer priority is also considered in this problem. The switch placement problem is formulated as a nondifferentiable, multiobjective optimization problem. Graph-based algorithms, which incorporate direct load control, are developed to locate switches. Their results enable DG to support customers continuously in the event of fault. The proposed algorithms can be applied to unbalanced distribution networks with single or multiple distributed generators. Simulation results on a 394-bus distribution system, including priority customers, and single or multiple distributed generators, were also provided.

Multi-tier service restoration through network reconfiguration and capacitor control for large-scale radial distribution networks

A fast and effective service restoration algorithm allowing multi-tier or system-wide switching and capacitor control actions is developed for large-scale, radial distribution networks. The service restoration problem is formulated as a constrained multiple-objective optimization problem. A solution algorithm designed to consider networks with predominately manual switches is developed which utilizes information calculated from three-phase power flow analysis to restore as much priority and total load as possible while requiring a minimal number of control actions and amount of geographic travel distance. Simulation results are presented for a 399 bus distribution network and compared to the service restoration algorithm which avoided multi-tier switching.

Capacitor placement and real time control in large-scale unbalanced distribution systems: loss reduction formula, problem formulation, solution methodology and mathematical justification

A comprehensive study of capacitor placement 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.

Electric distribution system load capability: problem formulation, solution algorithm, and numerical results

This paper undertakes the problem of determining the load capability of distribution networks, or, equivalently, the amount of load a feeder, specific area or circuit of a large-scale unbalanced distribution network can withstand before violating an operational constraint. A new formulation is given. A solution algorithm suitable for large-scale unbalanced distribution networks with capacitor control actions is developed and test results on a NYSEG 394-bus distribution network are included.

Improving Service Restoration of Power Distribution Systems Through Load Curtailment of In-Service Customers

Load curtailment programs including direct load control and demand response allow system operators to directly and/or indirectly reduce a portion of total customer demand. One system application which can be improved by implementation of load curtailment is service restoration. As such, this work presents a problem formulation, solution algorithm, and simulation results for service restoration of power distribution systems incorporating load curtailment of in-service customers via direct load control. It is shown that the addition of load curtailment allows for one or more of the following: a reduction of the total number of switch operations required, an increase to the number of customers served, and/or an increase to the total amount of load restored. These improvements are demonstrated through simulation results from a 416-bus multiphase distribution system.

A network-based distributed slack bus model for DGs in unbalanced power flow studies

This paper revisits the concept of a single slack bus in power flow solvers for distribution systems to accommodate the anticipated growth of distributed generators (DGs) in unbalanced distribution systems. It introduces a distributed slack bus model through scalar participation factors by applying the concept of generator domains. The participation factors are incorporated into the three-phase power flow equations, and a Newton-Raphson solver is discussed and implemented. Simulation results on systems with a different number of DGs and different levels of DG penetration are obtained and studied.

Weighted least squares methods for load estimation in distribution networks

This paper investigates two weighted least squares (WLS) approaches to the problem of load estimation (LE) in unbalanced power distribution networks: (1) the WLS load parameter method in is restated more rigorously; and (2) a constrained distribution state estimation (DSE)-based method is introduced to consider operating and loading constraints. Detailed simulation results on 394-bus radial and weakly meshed power distribution systems are evaluated through four error indices proposed by the authors previously (see Proc. IEEE Int. Symp. Circuits Syst., Pheonix, AZ, vol.5, p.697-700, 2002). The results of both methods are compared and discussed. Observability issues are also addressed.

Incorporating Temperature Variations Into Transmission-Line Models

This paper discusses a transmission-line modeling approach that incorporates available ambient temperature information. Several proposed line modeling techniques are studied and include distributed and lumped parameter models. In order to capture the nonuniformity of line parameters caused by temperature gradients, a model with multiple nonuniform segments is also proposed. An automated tool has been developed to obtain appropriate line model segmentation and parameter values of each segment, given a set of temperature measurements and their locations along the line.