Evaluation of Lightning Impulse Test by Frequency Response Analysis

In this work are presented the basis for improving the interpretation of transformer lightning impulse test and the development of a graphical user interface system, which allows comparisons of time domain data and frequency response. The frequency response is obtained from deconvolution of voltage and neutral current records. A quantitative comparison of frequency response is performed using the techniques applied to displacement detection through Frequency Response Analysis, such as correlation and spectral deviation. The system is implemented using 8 bit digitizers to acquire the voltage and neutral current records. The quantization error and reliability of the frequency response obtained is handled through the use of the coherence function and tolerance bands. The system is thoroughly tested applying a lightning impulse test to a dry type distribution transformer, simulating an interdisc fault with a spark gap. Failure detection is confirmed

Deconvolution techniques with applications in cardiovascular systems analysis

System characterization by means of Impulse and Frequency Response Functions are well known in classical linear systems analysis. Impulse Response Function is a time domain description of a linear system where as the Frequency Response Function represents the frequency domain counterpart. Linear systems are often characterized in frequency domain. In many biological research applications, it becomes necessary to examine the impulse response function in order to understand the behavior of the system under investigation. One such application is the arterial system in cardiovascular dynamics. It has been shown that although both representations are identical, some aspects of the arterial system are better emphasized by one description than by the other. In order to obtain accurate estimates of the impulse response function it is desirable to solve the convolution integral in the time domain by deconvolving the system input and output time histories. Solution of the convolution integral is however extremely complex and requires the use of numerical approximation methods. This work is primarily focused on developing these numerical approximation procedures with particular application emphasis on the arterial system

Comparison of several methods for obtaining the time response of linear systems to either a unit impulse or arbitrary input from frequency-response data

Several methods of obtaining the time response of Linear systems to either a unit impulse or an arbitrary input from frequency-response data are described and compared. Comparisons indicate that all the methods give good accuracy when applied to a second-order system; the main difference is the required computing time. The methods generally classified as inverse Laplace transform methods were found to be most effective in determining the response to a unit impulse from frequency-response data of higher order systems. Some discussion and examples are given of the use of such methods as flight-data-analysis techniques in predicting loads and motions of a flexible aircraft on the basis of simple calculations when the aircraft frequency response is known

On Frequency-Domain Implementation of Digital FIR Filters Using Overlap-Add and Overlap-Save Techniques

In this paper, new insights in frequency-domain implementations of digital finite-length impulse response filtering (linear convolution) using overlap-add and overlap-save techniques are provided. It is shown that, in practical finite-wordlength implementations, the overall system corresponds to a time-varying system that can be represented in essentially two different ways. One way is to represent the system with a distortion function and aliasing functions, which in this paper is derived from multirate filter bank representations. The other way is to use a periodically time-varying impulse-response representation or, equivalently, a set of time-invariant impulse responses and the corresponding frequency responses. The paper provides systematic derivations and analyses of these representations along with filter impulse response properties and design examples. The representations are particularly useful when analyzing the effect of coefficient quantizations as well as the use of shorter DFT lengths than theoretically required. A comprehensive computational-complexity analysis is also provided, and accurate formulas for estimating the optimal DFT lengths for given filter lengths are derived. Using optimal DFT lengths, it is shown that the frequency-domain implementations have lower computational complexities (multiplication rates) than the corresponding time-domain implementations for filter lengths that are shorter than those reported earlier in the literature. In particular, for general (unsymmetric) filters, the frequency-domain implementations are shown to be more efficient for all filter lengths. This opens up for new considerations when comparing complexities of different filter implementations.Comment: 13 pages, 26 figure

Tradeoffs in manipulator structure and control. Part 4: Flexible manipulator analysis program

The Flexible Manipulator Analysis Program (FMAP) is a collection of FORTRAN coding to allow easy analysis of the flexible dynamics of mechanical arms. The user specifies the arm configuration and parameters and any or all of several frequency domain analyses to be performed, while the time domain impulse response is obtained by inverse Fourier transformation of the frequency response. A detailed explanation of how to use FMAP is provided

Electromagnetic forces acting between the stator and eccentric cage rotor

Electromagnetic forces act between the rotor and stator when the rotor is performing eccentric motions with respect to the stator. The aim of this research was to study the charactarestics of the forces and develop the tools to calculate these forces accurately and as quickly as possible. A new method, called the impulse method, is developed into the finite element analysis of the electromagnetic field to calculate the forces for a wide whirling frequency range by one simulation. The idea of the impulse method is to move the rotor from its central position for a short period of time. This displacement excitation disturbs the magnetic field and, by doing this, produces forces between the rotor and stator. Using spectral analysis techniques, the frequency response function of the forces is calculated using the excitation and response signals. The impulse method is based on the assumption of the spatial linearity of the force. The impulse method is utilised in the analysis of the rotor eccentricity. The spatial linearity of the force and the effects of the circulating currents and saturation on the forces are studied herein. The field of investigation is enlarged from the cylindrical whirling motion to the conical motions of the rotor. The modelling of the conical motion requires that the axial variations of the magnetic field be taken into account. This is done by multislice finite element analysis.reviewe

Finite-Impulse- Response Modeling of Voltage Instrument Transformers Applicable for Fast Front Transients Simulations

This paper presents a method for Finite-Impulse-Response (FIR) modeling of voltage instrument transformers. The method is based on Wiener filtering and measurement of the transformer response in the frequency domain using a low frequency network analyzer. The proposed method allows, through digital filtering operation, an accurate simulation of the transformer response to transient excitation. Furthermore, the proposed approach to the modeling of the system function allows unequal spacing of the frequency samples. The linearity of the transformer is analyzed applying the Fourier analysis and different waveforms of the primary voltage, and methods for the model order selection, based on the generalized information criterion, are discussed and applied. The theoretical analysis is confirmed with measurements in time domain, using the recurrent surge generator

Finite-Impulse- Response Modeling of Voltage Instrument Transformers Applicable for Fast Front Transients Simulations

This paper presents a method for Finite-Impulse-Response (FIR) modeling of voltage instrument transformers. The method is based on Wiener filtering and measurement of the transformer response in the frequency domain using a low frequency network analyzer. The proposed method allows, through digital filtering operation, an accurate simulation of the transformer response to transient excitation. Furthermore, the proposed approach to the modeling of the system function allows unequal spacing of the frequency samples. The linearity of the transformer is analyzed applying the Fourier analysis and different waveforms of the primary voltage, and methods for the model order selection, based on the generalized information criterion, are discussed and applied. The theoretical analysis is confirmed with measurements in time domain, using the recurrent surge generator

Real-time Auto Tuning of a Closed Loop Second Order System with Internal Time Delay Using Pseudo Random Binary Sequences

This research yielded a real-time auto tuning algorithm to adaptively tune a proportional integral and derivative (PID) controller for a first or second-order system with internal time-delay. The method uses a 15-bit pseudo-random binary sequence as an input to obtain the closed-loop system impulse response while the system is operating. Time-delay is assessed by analysis of the estimated closed-loop impulse response and is used in the system model for closed-loop pole assessment. The fast fourier transform of the estimated impulse response produces an estimate of the frequency response data, and a non-linear regression optimization technique, utilizing MATLAB, identifies the closed-loop system transfer function based on assumed form. Closed-loop poles are then placed, based on an iterative tuning study, automatically by the algorithm to achieve a user-defined overshoot and ensure stability of the system with time-delay. This is accomplished by adjusting the PID compensator gains. The algorithm is capable of tuning the system from an initially stable set of PID gains to within 5% of the user-defined overshoot. The research demonstrates that the auto tuning method is feasible for time-delays on the order of the plant time constant but is extendable to larger time-delays