Peter Sokolowski

Identifying vulnerable lines in a power network using complex network theory

The latest developments in complex network theory have provided a new direction to power system research. Based on this theory a power system can be modelled as a graph with nodes and vertices and further analysis can help in identifying the important lines. This paper proposes a new betweenness index using the reactance of the transmission lines as the weight and criteria to measure of vulnerability of a power network. The reactance is a simplified measure of power flow in a lossless transmission line based on the power flow analysis equations. The weighted line index is defined as the reactance of the electric path taken to reach from one node to another node. More power is transmitted along the lines with less reactance, to reach from the source node to destination node, which gives the edges with less reactance a higher weight in the analysis. The analyzes have been carried out on the IEEE 39 bus system and IEEE 118 Bus System. The new betweenness index can identify the critical lines of the system, either due to their position in the network or by the power they transmit along the network.

Analyzing power network vulnerability with maximum flow based centrality approach

Complex network theory has been studied extensively in solving large scale practical problems and the recent developments have given a new direction to power system research. This theory allows modeling a power system as a network and the latest developments incorporate more and more electrical properties as opposed to the topological analysis in the past. In the past, such networks have been analyzed based on shortest path travel and betweenness index. In a power system, the power might not necessarily flow only through the shortest path so this paper proposes a centrality index based on the maximum power flow through the edges. The links which carry more portion of power from the source (generator) to sink (load) are given a higher weight in this analysis. Few simple cases have been explained and then the algorithm has been demonstrated on the IEEE 39 bus system.

Systematic Modeling and Symbolically Assisted Simulation of Power Systems

Large disturbance behavior of power systems often involves complex interactions between continuous dynamics and discrete events. Such behavior can be captured in a systematic way by a model that consists of differential, switched algebraic, and state-reset (DSAR) equations. The paper presents a practical object-oriented approach to implementing the DSAR model. Each component of a system can be modeled autonomously. Connections between components are established by simple algebraic equations. Simulation of the model using numerically robust implicit integration requires the generation of partial derivatives. The object-oriented model structure allows this differentiation to be achieved symbolically without sacrificing simulation speed.

Human Uterine Wall Tension Trajectories and the Onset of Parturition

Uterine wall tension is thought to be an important determinant of the onset of labor in pregnant women. We characterize human uterine wall tension using ultrasound from the second trimester of pregnancy until parturition and compare preterm, term and twin pregnancies. A total of 320 pregnant women were followed from first antenatal visit to delivery during the period 2000–2004 at the John Hunter Hospital, NSW, Australia. The uterine wall thickness, length, anterior-posterior diameter and transverse diameter were determined by serial ultrasounds. Subjects were divided into three groups: women with singleton pregnancies and spontaneous labor onset, either preterm or term and women with twin pregnancies. Intrauterine pressure results from the literature were combined with our data to form trajectories for uterine wall thickness, volume and tension for each woman using the prolate ellipsoid method and the groups were compared at 20, 25 and 30 weeks gestation. Uterine wall tension followed an exponential curve, with results increasing throughout pregnancy with the site of maximum tension on the anterior wall. For those delivering preterm, uterine wall thickness was increased compared with term. For twin pregnancies intrauterine volume was increased compared to singletons (), but wall thickness was not. There was no evidence for increased tension in those delivering preterm or those with twin gestations. These data are not consistent with a role for high uterine wall tension as a causal factor in preterm spontaneous labor in singleton or twin gestations. It seems likely that hormonal differences in multiple gestations are responsible for increased rates of preterm birth in this group rather than increased tension.

On complex network approach for fault detection in power grids

The latest developments in complex network theory have provided a new direction for power system research. Based on this theory a power system can be modeled as a graph with nodes and vertices and further analysis can help in addressing typical problems such as identifying the vulnerable lines and pole fires, and locating faults. This paper reports some of our recent research in this area and discusses some potential areas in power grids where the complex network theory can be used.

Fault location in power networks using graph theory

This paper proposes a method for analyzing the vulnerability of a power system using network theory. It locates fault by combining the travelling waves methodology with the network topology to isolate the faulty link first and then locate the fault distance. The algorithm is verified on a test power network using Alternate Transients Program/Electromagnetic Transients Program (ATP/EMTP) and Matlab. The time stamps recorded are combined with the network topology to isolate the faulty link and calculate the fault distance.

A multi-agent simulation framework for distributed generation with battery storage

Distributed Generation (DG) is a sustainable alternative energy paradigm that allows flexible customer-participated demand response management, high penetration of renewable sources and reduction of greenhouse gas emission. This paper proposes a multi-agent simulation framework that captures emerging complex responses that originate from individual household behaviors. These behaviors have been unattainable with traditional top-down simulation frameworks. The simulation results demonstrate a suboptimal policy choice may lead to unwanted energy profile responses on the distribution network.

Analysis of the leakage current on polluted insulators using correlation coefficient

Flashover is damaging to the power transmission and distribution system. In this paper, correlation coefficient as a measure of nonlinearity is employed to analyze the leakage current signals generated from heavily polluted insulators for flashover prediction purpose. Data is generated with dry and wet conditions together with various supply voltages. By calculating the correlation coefficients between the supply voltages and the leakage currents, some patterns are found which may help identify the status of insulators.

Characterizing impedance profiles for leakage currents from HV insulators on wooden poles

In this paper, the impedance characteristic profiles of wooden power poles altering the leakage current from high voltage (HV) insulators are investigated to better understand the role of wood in leakage current signatures. A comparison with past research shows the capacitive components of a poles impedance have previously been ignored, however, has little effect on using an impedance value for effective resistance. Examining the impedance properties of typical Copper Chromium Arsenate (CCA) impregnated wood for 66 kV distribution poles shows dangerous conductance properties of wood at this voltage, providing an explanation for these poles catching fire at triple the rate of 22 kV distribution poles. After a systematic investigation of wood used for poles, a preliminary impedance characteristic of wooden poles in Victoria, Australia is established for the first time, where the pole is weathered, CCA impregnated and operating at 22 kV under both dry and wet weather conditions.