Showing papers in "Canadian Electrical Engineering Journal in 1986"

An automated signal processing system for the signature analysis of radar waveforms from bridge decks

Abstract: This paper describes the results of a project which employed impulse radar to detect faults existing beneath the surface of an asphalt-covered bridge deck at Papineau Creek, Ontario. A simple but enlightening mathematical analysis is provided which accurately predicts the waveforms actually observed. The methodology clearly demonstrates the usefulness of impulse radar as a diagnostic tool in remote sensing. Amongst the problems discussed and solved are: the identification of faults due to debonding, scaling, and delamination; the measurement of asphalt thickness at selected locations on the bridge deck and hence the determination of average thickness over the entire bridge deck; and the automated processing of the data using a computer. A comparison of the radar detected faults with those detected using conventional methods is provided. A set of parameters has been developed which permits data to be reduced to a simple set of measurements that can be plotted for visual inspection.

Silicone oil as replacement fluid for PCBs in transformers

Abstract: A brief critical review of the electrical, thermal and flammability properties of silicone oil for transformers is presented in comparison to the same properties for polychlorinated biphenyl fluids (PCB) and mineral oil It is deduced that silicone oil is an acceptable substitute for PCBs Despite a significantly lower fire resistance, silicone oil is not toxic and is compatible with traces of PCBs and mineral oil It is therefore perfectly suited for the retrofilling of PCB contaminated transformers

Steady-state analysis of nonlinear dynamic systems with periodic excitation based on linearization in harmonic space

Abstract: This paper considers a very general formulation of the differential equations of a dynamic system in periodic steady state. These are linearized around an operating point, in algebraic form in terms of incremental harmonic phasor components. The solution is iterative, either Newton-type with quadratic convergence in the neighbourhood of the solution, or it has linear convergence if the Jacobian is not updated at each iteration.

Instantaneously adaptive delta sigma modulator

Abstract: An instantaneously adaptive delta sigma modulator, where the pulse amplitude is increased or decreased by a constant value, is proposed. Its performances for sinusoidal signals and speech are studied. While an adaptive delta modulator operating at similar bit rates will perform better, the delta sigma modulator is useful in signal processing applications.

Real-time interpolation with cubic splines and polyphase networks

Abstract: Deals with the development of a new approach to the problem of real-time interpolation of digital signals. Whereas the traditional methods of performing this operation make use of digital filters (FIR or IIR), this approach utilizes local cubic polynomial interpolative routines known as cubic spline functions. By using cubic splines, an algorithm has been obtained which can be implemented in a simple and economical way, yielding the desired real-time interpolator. The properties of this system include conceptual and structural simplicity, local control, speed of operation, and versatility.

Emergency Locator Transmitter (ELT) signal models for SARSAT

Abstract: Three different models for emergency locator transmitter (ELT) signals are proposed. The first model, the ideal coherent model ELT, produces a highly idealized spectrum which does not exist in practice. The second model, the nonideal coherent model ELT, is capable of producing a wide range of spectra which can be closely related to actual ELT signals. Mathematical analysis identifies a design problem not previously recognized and provides the basis for a new design specification which should become mandatory. The third model, the noncoherent model ELT, represents a class of ELT signals having very poor spectral properties. This type of ELT design should be avoided.

Image segmentation: A comparative study

Abstract: Machine extraction of meaningful features from the digitized representation of an image (picture, scene etc.) is of great interest to investigators working in such diverse fields as robotic vision, scene analysis, pattern recognition, and automatic part identification in manufacturing processes. The authors describe in detail their algorithms for implementing different segmentation strategies. These are a label propagation segmentation scheme (using the region growing algorithm) and a linked pyramid segmentation scheme. The two techniques are analyzed and compared with respect to their ability to satisfactorily segment a wide class of images (scenes, radiographs, machine parts etc.); computational overheads; memory overheads; and sensitivity to additive noise (Gaussian). In addition to the critical analysis and evaluation of the two techniques, the authors introduce the following enhancements: new predicates (similarity criteria) that are applicable to a broad class of images; incorporation of impulse noise suppression; hierarchical two-level processing to refine segmentation by label propagation; and use of a weighting function to improve the segmentation process.

Bounds for byte-oriented error-correcting codes with application to teletext systems

Abstract: Codes formed bytes of known parity with one byte of check bits are considered. A lower bound on the number of weight four codewords is obtained. An application to the choice of error-correcting code for the North American Broadcast Teletext Specification is discussed.

Realization of a class of two-dimensional zero-phase recursive digital filters with variable cutoff boundary

Abstract: Digital realization of a class of two-dimensional, zero-phase filters with variable cutoff boundary is given The derivation of the 2-D transfer function is based on the transformation of a 1-D analog reference filter using a two-variable reactance function Digital realization of the resulting 2-D transfer function is derived by using the generalized delay unit concept and cascade connections of two-port networks represented by their scattering matrices

Nonlinear point operators for edge detection

Abstract: An edge detection scheme is proposed. This scheme employs a nonlinear point operator, followed by a usual edge detector, e.g. the Sobel edge detector. Three point operator functions are defined and their effects on edge detection are analyzed. The performance of the Sobel edge detector and the nonlinear point operators in the presence of noise is evaluated. Examples of simulated and actual images are given, and the results show that a suitable point operator can improve the edge detection process.

Microprocessor-based universal adaptive controllers

Abstract: For an adaptive controller to be effective in cases where the system dynamics are completely unknown and change with operating conditions, it is desirable that the control action be regulated by a single parameter. Two control algorithms which have this characteristic are presented. One is based on the linear quadratic control theory and the other is based on pole placement technique. The microcomputer implementation of these two control algorithms is presented. For such control algorithms to be successful, the on-line program should be user-interactive so that the user can influence the control action. The interactive features are explained. Experimental results are presented to show the successful operation of the controller.

Simulation study of a signalling protocol for cellular mobile radio systems with hybrid voice channel assignment and a blocked-calls-held service discipline

Abstract: Presented are computer simulation results of a signalling protocol included in the AMPS system of AT&T in Chicago. In addition to signaling, the authors consider a hybrid voice channel assignment scheme with a blocked-calls-held queueing discipline for the voice channels. The system performance in terms of various system measures is evaluated.

An efficient method of PWM waveform generation using a microprocessor

Abstract: A Z-80 microprocessor-based control for a three-phase PWM inverter employing thyristors is discussed This PWM inverter combines the advantages of hardware modules and software algorithms to improve the flexibility and accuracy of the operation A floating point arithmetic unit developed in software forms a vital link of the software structure that calculates the PWM pulsewidths from the basic equation of a regular sampled PWM During PWM waveform generation the inherent time delay involved in the execution of instructions in the interrupt subroutines results in shifting of the edges of the PWM pulses and thus introduces a certain degree of harmonic distortion The cumulative nature of this time delay will alter the frequency of the output waveform in a continuous way By employing a suitable hardware structure the time delay involved in the interrupt subroutine is minimized to a great extent and the cumulative effect of the time delay is nullified To handle the interrupts arising during PWM waveform generation a simple and novel interrupt controller that is capable of handling the interrupts effectively is built around conventional TTL ICs instead of using a standard integrated interrupt controller module like 8259

New analytical approach for long-term optimal operation of a parallel multireservoir power system based on functional analysis

Abstract: Functional analysis and the minimum norm formulation are applied to maximize the total benefits from a parallel multireservoir power system, which may contain run-of-river downstream reservoirs. The hydroelectric power generation is a highly nonlinear function of the storage and the discharge. The method takes into account the water head variation (conversion factor variation) and the stochasticity of the river flows. The proposed method is computationally efficient compared to previous techniques. Numerical results are presented for a real system in operation consisting of three rivers. The first river has two series controllable reservoirs; the second river has two series reservoirs, the upstream reservoir is a controllable reservoir and the downstream reservoir is a run-of-river reservoir; and the third river has two series controllable reservoirs.

A proposed fault-tolerant microcomputer system

Abstract: Past experience with fault-tolerant and other reliability techniques has focused on such specialized systems as spacecraft control computers and telephone switches. However, current technology trends strongly suggest that specific reliability techniques should be developed and implemented for a large number of low-cost systems such as microprocessor-based controllers, instruments, and other industrial devices. In this paper a fault-tolerant microcomputer architecture which is particularly designed for industrial control and manufacturing is proposed. For this system, voting has been considered as a very appropriate fault-tolerant technique. However, voting at the component level and at the bus-level have been ruled out due to the unreliability of the voters required and their high cost. System voting without an explicit voter is finally selected. Analysis shows that the system has a higher reliability than either a nonredundant system or a bus-level voting system. Its mission time has been increased by a factor of 2.5 over non-redundant systems.

Weekly peak load forecasting for fast-developing cities

Abstract: The fast pace of the development activities in the Kingdom of Saudi Arabia (KSA) has resulted in the pressing need for more dependable forecasts for expanding industrial and residential electrical demands. Rapid-developing countries like the KSA experience a large, varying load growth rate, which has dynamic rather than static characteristics. The authors present a method for developing adequate time series models for the dynamic characteristics of the electrical power demands of a typical rapid-developing electric utility from actual five-year load demand time series. Two models have been developed. The first uses a long-trend component modelled by a polynomial function and a seasonal-cyclic component modelled by Fourier expansion. The second uses an autoregressive time series model for the seasonal-cyclic component. These models have been used to generate weekly peak-load forecasts for one year ahead.

Design and implementation of TORNET — A slotted-ring local area network

Abstract: TORNET is a local area network whose basic design is a variation of the slotted ring where register insertion is used because of its operational advantages. The complete network consists of a number of local rings connected to a central ring. Small computers and the terminals that access them are the normal devices found on a local ring, while expensive shared components, such as large disk files or printers, are attached to the central ring. Two packet lengths are implemented at the ring level. A short packet (one data byte) facilitates communications between terminals and computers. The long packet format (129 data bytes) is used for efficiency in file transfer operations. Two types of units are used to attach devices to a ring. The simpler one, called a character station, is used for simple devices such as terminals, and can only handle short packets. A block station, which can handle both long and short packets, is configured to support multiple virtual connection, and is used for computers. Software is designed using the ISO layered protocol, and has been implemented in the high-level language Concurrent Euclid. A bridge has been implemented for connecting local rings to the central ring, and an initial prototype for an X.25 gateway has been built.

Unit models for capacity reliability studies using the Canadian Electrical Association data base

Abstract: The need for availability information has grown tremendously during the last decade. This has led to the development of various data collection and analysis systems by different organizations in North America. The Equipment Reliability Information System (ERIS) of the Canadian Electrical Association (CEA) was developed to satisfy the needs of Canadian utilities for a uniform of recording the performance of generation and transmission equipment and for the centralized processing of these data. The authors unit models for capacity reliability studies which are compatible with the data provided in the present CEA data collection system.

The application of time domain Prony's method to three basic radar targets

Abstract: Time-domain Prony's method has been used to extract the dominant complex natural resonances of three simple radar targets: a conducting sphere, a finite cone and a finite right circular cylinder. The sliding window technique has been used to locate the consensus pole set. The effects of sampling interval, noise and polarization on the extraction process have been studied. The SNR has been studied with standard deviation of additive white gaussian noise as a variable parameter. The extraction process is sensitive to sampling rate. A reasonable and acceptable sampling interval has been found for each of these cases.

Design aspects of logic control circuits for direct frequency changers

Abstract: Industrial trends towards full automation and the declining prices of power semiconductor devices have stimulated a considerable interest in the design and development of the compact `silicon-intensive' class of power converters known as direct frequency changers (DFCs). It is demonstrated that such converters have special logic-control requirements because of the complexities of associated power circuits and power conversion techniques. The authors focus on the design aspects of logic-control circuits for DFCs. These aspects include: the derivation of the appropriate switching functions for DFCs, the processing of the DFC gating signals from their respective functions, and the development of the circuitry required to implement these functions and signal processing.

Effects of currents on human beings: Physical pathology and limits

Abstract: The impedance of human beings varies between 500 and 4000 Ohms, with the average value being 1000 Ohms. The step and holding currents are of the order of 12 mA for men and 9 mA for women. The currents that cause the ventricular fibrillation follow, in general, a normal distribution whose mean value varies between 20 mA and 100 mA for a shock lasting from 0.3 ms to five seconds. Currents in the order 0.5 A and over can cause burns whose depths depend on the trajectory of the current and the applied voltage. The induced currents due to an electrical field are not dangerous (12 μA). However, their real effects on human organisms are not yet well known. It is, therefore, very important to conceive the protection procedures in relation to the inherent risks associated with each situation. For example, when medical instruments are connected to electrodes situated close to the heart, stringent criteria on electrical isolation must be observed in order to avoid ventricular fibrillation. In low voltage installations, such as domestic applications where 120 V and 220 V are used, North American rules require the ground to be connected to the water mains. In certain European countries, the use of differential circuit breakers ensures a better protection against ground faults.

An improved model for the anisotropic trapezoidal antenna

Abstract: An analytical model of the anisotropic trapezoidal antenna is developed by showing that this antenna can be treated as a modified compressed `dispersionless' log-periodic dipole array This model accounts for all resonant behaviour caused by element mutual coupling Theoretical and experimental results indicate that, although this array displays characteristic strong, narrow-band resonances, a useful operating band can be obtained by adjusting the feedline characteristic impedance and termination

A theoretical bound for the processing of SARSAT signals

Abstract: Search and rescue satellite-aided tracking (SARSAT) has been responsible for saving the lives of many victims of airplane crashes and boating accidents The system, in operation since 1982, employs satellites in low orbits which relay the emergency signals from distressed platforms to an Earth station where signal processing techniques are used to measure Doppler frequency shift The author provides a theoretical bound which can be used to evaluate the performance of SARSAT signal processors Results show that, for a processing duration of 125 ms, an emergency locator transmitter (ELT) signal can be detected within ±8 Hz when the carrier-to-noise density ratio is only 15 dB-Hz

Effect of temperature on burst phenomena in aged mineral oil under non-uniform fields

Abstract: Presents the experimental results of high field conduction current burst phenomena in aged transformer oil using point-plane configuration. The effect of temperature and field strength variations on burst parameters are emphasized. It was found that bursts can be classified according to their direction. Generally, the amplitude of bursts increases with the increase in temperature, up to a certain value, after which the trend reverses. The total number of bursts per minute peaks at about 60-70°C. This observation suggests that bursts may be attributed to the electrode-film-liquid interface and not to micro bubble mechanisms.

Analysis of six-pulse and twelve-pulse forced commutated HVDC converters

Abstract: This paper deals with steady-state analysis of six pulse and twelve pulse forced commutated HVDC converters with and without AC filters. To carry out these studies, a general computer program of fast steady state analysis of HVDC converters method has been developed. The effects of variation of system parameters on angle of overlap and AC/DC harmonics are studied.