Search

Online transformer condition monitoring techniques based on transfer function methods, such as transmission-line diagnostics and swept frequency-response analysis, require the injection of a known test signal into the transformer. On larger power transformers, a practical method is to use the available bushing tap connection. In this paper, we will discuss a custom high-power signal generator that injects high-frequency signals on the bushing tap of the transformer under investigation, as well as a circuit to replace the bushing tap short and allow online operation of the system. Finally, the system is demonstrated on a 650 kV transformer. Index Terms--Bushing tap injection, frequency response, frequency-response analysis (FRA), online diagnostics, power transformers, swept frequency-response analysis (SFRA), transmission-line diagnostics (TLD), winding signature.

Electromagnetic transient program (EMTP) simulators are being widely used in power system dynamics studies. However, their capability in real-time simulation of power systems is compromised due to the small time step used and relatively slow simulation speed. The shifted frequency analysis (SFA) is then proposed to accelerate the EMTP simulations for power system dynamics. The objective of this paper is to extend the SFA method [7] to model the induction machines in EMTP. By analyzing the relationship between rotor and stator physical variables, a phase-coordinate model with lower number of equations is first derived. Based on this, an SFA model is proposed as a general purpose model capable of simulating both fast transients and slow dynamics. Case study results have confirmed the SFA induction machine model is a valuable component for real-time EMTP simulations. It is observed that the SFA model is in excess of 70 times faster than the standard EMTP model when simulating dynamics with frequency spectra close to the fundamental power frequency. Index Terms--Dynamic phasor, electromagnetic transient program (EMTP), induction machine, power system dynamics, shifted frequency analysis.

This paper describes a new synchronous machine model based on the shifted frequency analysis (SFA) method, which uses dynamic phasor variables rather than instantaneous time domain variables. Discrete-time SFA component models have a form that is similar to the EMTP component models. Dynamic phasors provide envelopes of the time-domain waveforms and can be accurately transformed back to instantaneous time values. When the frequency spectra of the signals are close to the fundamental power frequency, the SFA model allows the use of large time steps without sacrificing accuracy. This makes the SFA method particularly efficient for power system operational dynamics. Index Terms--EMTP simulation, power system dynamics, shifted frequency analysis (SFA), synchronous machine modeling.

Multirate simulation of electric networks exhibiting a wide variety of time constants decreases the simulation runtimes by exploiting the property of circuit latency. The fundamental idea is to use different integration steps for different network subsystems, according to the requirements of accuracy of each subsystem. Programs that exploit circuit latency are usually based on relaxation methods that require iterations among the different subsystems of the original networks. These methods lack the numerical robustness of direct implicit integration methods used in circuit simulators and are not adequate for real-time simulation due to their non-uniform solution times. This paper proposes circuit latency exploitation without iterations making use of the concept of interlinked Multi-Area Thevenin Equivalents (MATE). Results are presented showing the efficiency and accuracy of the method. Index Terms--Circuit latency exploitation, multirate simulation, multi-area Thevenin equivalents (MATEs), numerical integration rules.

This paper presents the solution approach for simulation of control systems and nonlinearities used in UBC's Object Virtual Network Integrator (OVNI) power system simulator. OVNI is aimed at simulation of full-size power system networks in real time using integrated software/hardware solutions. The software solution is based on the Multiarea Thevenin Equivalent (MATE) network partitioning framework. Multilevel MATE expands the concept of MATE to a subsystem level, allowing for the efficient inclusion of controllers' equations and nonlinearities. Index Terms--Controllers, diakoptics, EMTP solution, Multi-level Muitiarea Thevenin Equivalent (MATE), nonlinear elements.

This paper presents the techniques derived for an efficient and accurate latency exploitation of electric networks using time-domain transients simulation software, such as the 'Electromagnetic Transients Program' (EMTP). Latency exploitation is related to the capability of numerically solving the differential equations governing the behavior of electric networks with different integration steps. With this approach, the limitations of a single fixed size integration step, as required by EMTP-type programs, can be overcome, resulting in a decreased number of numerical operations for a given total simulation time. Using a network partitioning and recombination technique, latency exploitation is achieved using noniterative solutions. Results are shown for networks consisting exclusively of lumped elements and networks with transmission lines and are compared with those obtained from conventional EMTP simulations. Index Terms--Decoupling of systems, electromagnetic transients, integration rules, latency exploitation, Thevenin equivalents, transmission lines.

A major difficulty in multiphase cable modeling with traditional electromagnetic transient program like the EMTP is the synthesis of the frequency-dependent transformation matrix which relates modal and phase domain variables. This paper presents a new model (zCable) to represent the frequency-dependence of cable parameters directly in phase coordinates thus avoiding the problems related to frequency-dependent transformation matrices. The cable model is split into two parts: a constant ideal line section and a frequency-dependent loss section. A pi-correction is proposed to solve the problem of different traveling times in the ideal line section. The main advantage of the proposed model as compared to existing frequency-dependent transformation matrix models is the model's absolute numerical stability for strongly asymmetrical cable configurations and for arbitrary fault conditions. In addition, the model parameters are easy to obtain with robust algorithms and the model can be efficiently implemented in the context of a real-time PC-cluster simulator. Index Terms--EMTP simulation, frequency-dependent cable and line modeling.

In this paper, a new algorithm for the calculation of the frequency-dependent parameters of arbitrarily shaped power cable arrangements is presented. The algorithm uses digital images to discretize the cable geometry and partial subconductor equivalent circuit method to estimate the cable parameters. The proposed methodology adapts itself to the physical memory of the computer, allowing the program to partition the partial subconductor impedance matrices when their sizes exceed the available physical memory. Coaxial cables and sector-shaped cables are studied, and the results are compared with those obtained from analytical formulae and the finite-element method. Index Terms--Conductor, EMTP, frequency-dependent parameters, inductance, PEEC, power cables, proximity effect, PSEC, resistance, skin effect.

A new technique has been developed to accurately calculate frequency dependent underground cable parameters. The technique is based on the well-known concept of conductors' subdivision. As opposed to the traditional technique, current density is not assumed constant in the subconductors but linear with matching values at the boundaries between subconductors. This drastically reduces the number of subconductors needed for accurate calculations, especially at higher frequencies. Typical computer-time savings in a SUN SPARC workstation range from 80% to 95%, depending on the frequency at which the parameters are calculated. The application of the technique is illustrated for pipe-type cables. The results are compared with those of a finite element technique. Overall, the new technique was found to be accurate, efficient, and requires minimum user intervention. Key words: cable parameters, skin effect, resistance and inductance matrices.

Byline: Hafiz Abdur Rahman, Konstantin Beznosov, Jose R. Marti Understanding the origin of infrastructure failures and their propagation patterns in critical infrastructures can provide important information for secure and reliable infrastructure design. Among the critical infrastructures, the Communication and Information Technology Infrastructure (CITI) is crucial, as it provides the basic mechanism for sharing information among all infrastructures. Failures in CITI can disrupt the effective functionality of the other critical infrastructures. Conversely, failures in the other infrastructures can also propagate to CITI, and hence disrupt the operation of all systems. In this study, we used public domain failure reports to identify the origin of these failures and their propagation patterns. We analysed 347 infrastructure failure cases reported from 1994 to 2005 in the Association for Computing Machinery's (ACM) RISKS forum. We studied these reports to determine the causes of infrastructure failures and their impact on CITI and other critical infrastructures in a number of dimensions, such as the origin of failures, impacts of failures in spatial and temporal dimensions, their effect on public safety and how failures propagate from one infrastructure to another. The results obtained from the analysis of these real-life failure cases, which occurred over a considerable timespan, should be useful to researchers and practitioners. This paper also discusses the difficulties and limitations of using public domain data in academic research.

Byline: Jose R. Marti, Jorge A. Hollman, Carlos Ventura, Juri Jatskevich This paper takes a systems engineering approach to the problem of operations coordination among multiple infrastructures to minimise the impact of large disasters on human lives. Temporal coordination is essential to avoid bottlenecks in the simultaneous recovery of multiple infrastructures systems. A solution framework is presented in terms of multiple-delay difference equations which bring out the temporal interdependencies among infrastructures. The present work is part of an effort by the Government of Canada, through the Natural Sciences and Engineering Research Council (NSERC) and Public Safety and Emergency Preparedness Canada (PSEPC) to fund research to develop innovative ways to mitigate large disaster situations.

Byline: Jorge A. Hollman, Jose R. Marti, Juri Jatskevich, K.D. Srivastava This paper presents specific guidelines for policymakers with the objective to develop and enhance cooperation among critical infrastructures operators. The proposed actions are an effective means to increase the resiliency of the National Critical Infrastructures (NCIs) based on a dynamic islanding scheme, which depends on the considered emergency scenario. The present work emerges in response to the Public Safety and Emergency Preparedness of Canada Modernisation of the Emergency Preparedness Act consultation process (PSEPC, 2005) and is part of the Joint Infrastructure Interdependencies Research Project, sponsored by Public Safety and Emergency Preparedness of Canada (PSEPC).