Satish J. Ranade

Interharmonics: Theory and Modeling

Some of the most remarkable issues related to interharmonic theory and modeling are presented. Starting from the basic definitions and concepts, attention is first devoted to interharmonic sources. Then, the interharmonic assessment is considered with particular attention to the problem of the frequency resolution and of the computational burden associated with the analysis of periodic steady-state waveforms. Finally, modeling of different kinds of interharmonic sources and the extension of the classical models developed for power system harmonic analysis to include interharmonics are discussed. Numerical results for the issues presented are given with references to case studies constituted by popular schemes of adjustable speed drives.

Modeling devices with nonlinear Voltage-current Characteristics for harmonic studies

This paper documents the modeling of harmonic sources with nonlinear voltage-current characteristics such as transformers, iron-core reactors, rotating machines, arc furnaces, energy efficient lightings, and some household electronic appliances. The harmonic generating characteristics of these apparatus are reviewed. Different modeling techniques are summarized and suggestions for the use of different models are also provided whenever possible.

A study of islanding in utility-connected residential photovoltaic systems

Islanding is the continued operation of a group of utility-connected photovoltaic systems even after loss of the utility source. Such operation can be hazardous to both utility personnel as well as to components in the system. Models and methods for the analysis of this phenomenon are presented in this paper. The methods are used in a companion paper to explore the possibility of islanding in practical systems. Although all such systems have a natural propensity to island, it is shown that the controls used in many commercially available units make islanding a rather unlikely phenomenon.

Effects of pulsed-power loads upon an electric power grid

Certain proposed particle-accelerator and laser experiments, and other devices related to fusion research, require multi-megawatt, repetitive power pulses, often at low (subsynchronous) frequency. While some power-delivery technologies call for a certain degree of buffering of the utility demand using capacitive, inductive, or inertial energy storage, considerations have also been made for serving such loads directly from the line. In either case, such pulsed loads represent non-traditional applications from the utilitys perspective which, in certain cases, can have significant design and operational implications. This paper outlines an approach to the analysis of the effects of such loads upon the electric power grid using existing analysis techniques. The impacts studied include busvoltage flicker, transient and dynamic stability, and torsional excitation. The impact of a particular pulsed load is examined and illustrated for the power network serving the Los Alamos National Laboratory. 19 refs., 13 figs.

The development of power system load models from measurements

This paper examines the use of least-squares (regression) techniques in developing static polynomial(ZIP) models from voltage change tests. It is demonstrated that test conducted at the distribution feeder level can yield unreliable models. Reasons for the poor quality of results are explored through examples. Preliminary experience with using fuzzy regression to identify dynamic and ZIP models through a physically-based model estimation approach is provided.

Capacity Discovery in customer-driven micro-grids

A completely decentralized system to discover the capacity of a micro-grid in a distribution feeder is presented. It is shown that in a multi-agent system with only neighbor-neighbor communication between agents in a radial feeder, each agent can determine the total generation capacity available at its node. Properties of the algorithm suggest convergence in a finite number of iterations. A Matlab/Simulink implementation is used to illustrate the algorithm for a seven-bus distribution system.

Characterizing and quantifying noise in PMU data

Data recorded by Phasor Measurement Units (PMUs) contains noise. This paper characterizes and quantifies this noise for voltage, current and frequency data recorded at three different voltage levels. The probability distribution of the measurement noise and its typical power are identified. The PMU noise quantification can help in generation of experimental PMU data in close conformity with field PMU data, bad data removal, missing data prediction, and effective design of statistical filters for noise rejection.

Design of an under voltage load shedding scheme

This work describes the design and development of a controlled under voltage load shedding scheme (UVLS) for protection against fast and slow voltage collapse of the Public Service Company of New Mexico (PNM) transmission system. This UVLS was designed as a technically-effective and economically-viable control-based countermeasure to prevent voltage instability and collapse for low probability events involving the loss of multiple transmission elements. This work also discusses the effects of load modeling assumptions and summarizes PNMs load modeling and monitoring efforts at the distribution feeder level.

Harmonic Characteristics and Impact of Utility-Interactive Photovoltaic Prototypes on the NMSU Distribution Feeder

Nonsimultaneous measurements of voltage and current harmonics associated with the distribution and utility-interactive photovoltaic systems at the Southwest Residential Experiment Station are summarized in this paper. A qualitative analysis of the data is presented. The harmonic impacts of the prototypes-on the distribution system appear to be minimal. Needs in the area of measurement and analysis of harmonic propagation in general systems are identified.

Identification of chains of events leading to catastrophic failures of power systems

Catastrophic failures have been traditionally treated as rare events. However, in view of the manner in which power systems have been evolving over the past decade, and the frequency with which catastrophic failures have occurred in this period, it is imperative that systematic approaches be devised to identify the likely chains of events that lead to these failures, so that appropriate countermeasures - strategic and tactical - may be designed and implemented. The paper discusses the recent body of work on structural issues, such as hidden failures and failure sequences, and identifies the need to explore further how chains conspire to form, and how the transition rates of the dependent events might change as the chain evolves. The paper then proceeds to develop a genetic algorithm based method that searches through the state space to identify likely event trees that connect healthy system states to catastrophic failure states. The method is illustrated via a small test system. The simplicity of the system enables an intuitive understanding of the mechanics of the method.