William James Premerlani

An approach for reverse engineering of relational databases

The process of software re-engineering consists of a reverse engineering step followed by a forward engineering step. During reverse engineering, one takes a past design or an implementation that embodies a design and extracts the essential problem domain content while discarding design optimizations and implementation decisions. During forward engineering, this model of the essence of an application becomes the basis for reimplementation in a new medium. Object-oriented models facilitate the =-engineering process because the same modeling paradigm is adept at representing abstract conceptual models and models with implementation decisions. Based on our experience with several examples, we propose a process for reverse engineering of relational databases.

Relational database design using an object-oriented methodology

Of the many approaches to relational database design, the Object Modeling Technique (OMT) is particularly effective. A comprehensive explanation and two applications show the semantic improvement of OMT over other approaches.

A new approach to on-line turn fault detection in AC motors

Turn fault detection is based on the principal that symmetrical (unfaulted) motors powered by symmetrical multiphase voltage sources will have no negative sequence currents flowing in the leads. A turn-to-turn fault will break that symmetry and give rise to a negative sequence current which may then be used as a measure of fault severity or to initiate protective action such as a circuit breaker trip. A new way of looking at the effects of turn faults has been developed that improves sensitivity and speed while reducing the probability of misdetection, taking into account voltage balance, load or voltage variation and instrument errors. The method has been implemented on a PC and tested, in real time, on a specially prepared small motor. Reliable detection of one shorted turn out of 648 turns per phase (in a Y connected motor) was demonstrated with the fault indicator becoming fully developed in two cycles of line frequency after initiation of the fault.

Development and Implementation of a Synchrophasor Estimator Capable of Measurements Under Dynamic Conditions

The classical two-parameter Fourier algorithm for computing synchrophasors is appropriate when the underlying voltage and current waveforms are sinusoids with constant amplitude and phase angle and with a frequency equal to the assumed value. Synchrophasor measurements, however, are applied in power systems to track dynamic conditions where, by definition, currents and voltages, though resembling sine-waves, exhibit changes in their magnitudes and vectorial positions. This paper presents a novel algorithm for estimating synchrophasors under such dynamic conditions. In contrast to the classical Fourier algorithm, our model is a complex Taylor expansion, yielding several parameters in the model to be estimated. Four- and six-parameter models are presented corresponding to first and second order Taylor expansions. This paper derives a compensation method for canceling the error in the classical Fourier algorithm that arises under dynamic conditions, shows comparative simulation and test results and describes an efficient implementation. Application of the error cancellation method to other phasor algorithms and extending the technique to higher order Taylor expansions, are discussed. Implementation of synchrophasor measurements on protection and control intelligent electronic devices (IEDs) is discussed, and solutions are presented that allow for secure integration.

An object-oriented relational database

A relational DBMS and an object-oriented programming language can be combined to yield a surprisingly effective OO-DBMS for many applications.

Observed idiosyncracies of relational database designs

Several processes have been advanced in the literature for reverse engineering of relational databases. The inputs to these processes are relational tables and available contextual information. The output is a model of the underlying logical intent, apart from the implementation artifacts. Most of the existing processes for database reverse engineering are inadequate; they assume too high a quality of input information. The authors of these processes are skilled database designers and they are overly optimistic about the state-of-the-art, as practiced. This paper catalogs odd aspects of relational database designs that we have encountered over the past several years. Many of these database designs are from commercial software products.

Converting OO models into RDBMS schema

This approach combines OMTool, an object-model editor, with the Schemer compiler. Schemer converts the object model into SQL code, which can then be used to generate relational tables. The approach frees application experts from the details of database structure during early development and lets them customize tables to a particular RDBMS.<<ETX>>

A catalog of object model transformations

The process of software development is gradually achieving more rigor. Proficient developers now construct software indirectly through the abstraction of models. Models allow a developer to focus on the essential aspects of an application and defer details. Transformations extend the power of models, as the developer can substitute refinement and optimization of models for tedious manipulation of code. We catalog object modeling transformations that we have encountered in our application work.

An adaptive, on-line, statistical method for bearing fault detection using stator current

It is well-known that motor current is a nonstationary signal whose properties vary with respect to the time varying operating conditions of the motor. As a result Fourier analysis makes it difficult to recognize fault conditions from the normal operating conditions of the motor. Time-frequency analysis, on the other hand, unambiguously represents the motor current which makes signal properties related to fault detection more evident in the transform domain. In this paper, we present an adaptive, statistical, time-frequency method for the detection of bearing faults. Due to the time varying normal operating conditions of the motor and the effect of motor geometry on the current, we employ a training base approach in which the algorithm is trained to recognize the normal operating conditions of the motor before the actual testing starts. The experimental results from our study suggests that the proposed method provides a powerful, and a general approach to the motor current based fault detection.

Synchrophasors: A primer and practical applications

Although the concept and definition of Synchrophasors dates back to 1980, the combination of 2nd generation IED platforms and power system needs has brought the technology into high-visibility in the electric power industry. As synchrophasor technology has matured, nuances of the measurement of a synchronized phasor have been identified and the details of ldquohowrdquo a phasor is defined, synchronized to absolute time, reported, and communicated have subsequently been re-codified int he recently revised IEEE standard: Synchrophasors for Power Systems - C37.118. This paper reviews the concept of the synchronized phasor in light of the IEEE C37.118 standard. Specifically, details of an ldquoun-correctedrdquo Fourier based phasor during off-nominal frequency conditions are presented as well as techniques for correction to meet the Synchrophasor standard. The need for IED input transformer and filter characterization / correction is presented. Simulations of various system transients and their phasor response are presented - specifically, the response of synchrophasor calculation to dynamic system conditions. Finally, this paper reviews application of synchrophasors on the SRP system today as well as plans and needs in the future.