Frequency Response Analysis

The sweep frequency response analysis (SFRA) is an analysis technique for detecting winding displacement and deformation (among other mechanical and electrical failures) on power and distribution transformers. Nowadays, there is an increasing interest in SFRA method because of its sensibility in detecting mechanical faults without opening the unit. SFRA as a diagnostic technique must integrate both the off-line measurements and the interpretation of the data in order to provide an assessment of the condition of the windings. However, guidelines for the measurement and record interpretation are not available. The evaluation is presently done by experts in the topic through the visual inspection or with the help of statistical parameters such as the correlation coefficient and the standard deviation. However, criteria like the limits of normal variation of the parameters, and the features observed in the records in the presence of a determined type of fault could not to coincide. Although, there are some proposals for making the interpretation more objective, neither of them integrate human expertise along with the different kind of parameters obtained from the evaluation of the records in a diagnostic model. This paper presents a survey on the alternatives in the measurement techniques and interpretation of SFRA measurements, describing some sources of uncertainty in applying this methodology.

A new digital control solution to motion control problems is proposed. It is based on a unique active disturbance rejection concept, where the disturbances are estimated using an extended state observer (ESO) and compensated in each sampling period. The dynamic compensation reduces the motion system to approximately a double integrator which can be easily controlled using a nonlinear proportional-derivative controller. The proposed Active Disturbance-Rejection Controller (ADRC) consists of the ESO and the nonlinear PD controller and is designed without an explicit mathematical model of the plant. Hence the controller is inherently robust against plant variations. Through simulation, frequency response analysis, and hardware tests, it is shown that the proposed approach is superior to the current PID based technology. It stands out especially in handling set point change, large inertia and friction variations, and external torque disturbance, all of which is seen as "disturbance" by ADRC and is actively compensated. The improvement in transient response and steady state error is also quite evident.

For past few decades the study about phononic crystals are getting more popular. Understanding and controlling the phononic properties of the phononic crystals provides opportunities to reduce environmental noise. In this thesis there is a brief introduction to phononic crystals.
My research topic of the thesis is about vibration reduction of beams connected to spring resonators with one degree of freedom, with the ultimate purpose to find bandgaps. In the bandgaps of the frequency ranges, flexural wave cannot propagate in the structures. I have done two analysis to find bandgaps. The first one is finding flexural bandgaps through Eigenfrequencies. And the second one is finding band gaps through frequency response analysis. Two methods also shows us the range of band gaps.
All the simulation works have been done in COMSOL Multiphysics. COMSOL Multiphysics is a very suitable tool for analysis of wave propagation in phononic crystals. In the thesis, I give the steps for two kind of simulations in COMSOL Multiphysics.

KEY WORDS：Phononic Crystals, FEM, Eigenfrequencies, Frequency Response Analysis, Band Gap, Euler-Bernoulli Beam, Spring Resonator.

Any failures in these equipments directly reduce network reliability and increase maintenance costs. Consequently, the preventive maintenance techniques are increasingly developed. In this regard, frequency response analysis is an appropriate method in order to diagnose any change which occurs in transformer physical construction.

This paper presents a simplified distributed parameter model for minor winding deformation fault analysis of power transformers on the basis of frequency response analysis (FRA). The FRA data of an experimental transformer is employed as a reference trace, which are compared with the simulations of the simplified distributed parameter model concerning minor winding deformation faults. In order to perform quantitative analysis when a deformation fault occurs, three statistical indicators are used to analyze the FRA simulation data. It is suggested in the results that minor winding deformation faults can be detected at the frequency range above 1 MHz.

The paper presents the description for diagnostic methods of induction motor's stator windings fault. The presented methods use Frequency Response Analysis (FRA) technique for detection of Winding Faults in Induction Motor. This method is previously reliable method for faults diagnosis and detection in many parts of transformers including transformer windings. In this paper, this method was used for motor windings faults detection. This paper presents the FRA response interpretation on internal short circuit (SC) fault at stator winding on three cases studies of different three-phase induction motors (TPIM), were analysed according to two status: healthy induction motor at normal winding status and same motor with windings shorted of main windings. A conclusion of this paper provides the interpretation of and validation the FRA response due to internal SC fault case by using NCEPRI algorithm, which is considered as one of certified statistical indicators. The proposed method in this paper had a useful result for detect and diagnosis of stator windings faults of TPIM. The applications of developed method can be used to detece the other machines types faults.

An electrochemical impedance spectroscopy (EIS) study of electrodes in a phosphoric acid loaded polybenzimidazole (PBI) membrane fuel cell is reported. Using EIS, the effect of electrode parameters such as Pt catalyst wt%, acid doping in PBI and PTFE baesd electrodes and catalyst heat treatment on kinetic and mass transport characteristics is characterised. The influence of cell parameters of current load, temperature and oxidant gas on response is demonstrated and interpreted using an equivalent circuit model. For polarisable electrodes under small to medium steady-state current operation, the model was capable of identifying electrodes with the best kinetic or mass transport behaviour and classifying behaviour in terms of relative performance.

Monitoring and diagnosis of power transformer in power systems have been examined and debated significantly in last few decades. Recently, more researchers have expressed their interest in these issues as the utilities and network operators operating under a rising cost-effecting pressure. Especially, in studying to monitor winding faults which is found to be the most common fault within transformers. This paper addresses the issue of the effect of inter-windings short circuit fault in a Dyn11 connected transformer. The specific aim is to study the effect of fault at winding of other phases to the response of measured phase. Frequency Response Analysis (FRA) which is discovered to be a powerful and sensitive method to examine and evaluate the condition, including the mechanical reliability of the transformer windings is used.

This paper describes the finite element (FE) analysis technique to predict fatigue life using the narrow band frequency response approach. The life prediction results are useful for improving the component design methodology at the very early development stage. The approach is found to be suitable for a periodic loading but requires very large time records to accurately describe random loading processes. This paper is aimed at investigating the effects of surface treatments on the fatigue life of the free piston linear engine's components. Finite element modelling and frequency response analysis were conducted using computer aided design and finite element analysis commercial codes, respectively. In addition, the fatigue life prediction was carried out using finite element based fatigue analysis commercial code. Narrow band approach was specially applied to predict the fatigue life of the free piston linear engine cylinder block. Significant variation was observed between the surface treatments and untreated cylinder block of free piston engine. The obtained results indicated that nitrided treatment yielded the longest life. This approach can determine premature products failure phenomena, and therefore can reduce time to market, improve product reliability and customer confidence.

One of the most important methods for transformers fault diagnosis (especially mechanical defects) is the frequency response analysis (FRA). The most important step in the FRA diagnostic process is to differentiate the faults and classify them in different classes. This paper uses the intelligent support vector machine (SVM) method to classify transformer faults. To this end, two groups of transformers were tested and necessary measurements were obtained; the transformers with healthy conditions and the ones with various fault conditions (axial displacement, radial deformation, disc space variation, short-circuits, and core deformation). Then, by dividing the frequency intervals of the measurements, a new feature based on the cross-correlation technique was proposed for SVM training and validation. After the training process, by applying the data obtained from actual transformers, the performance of SVM in different conditions was evaluated and compared. Finally, the most appropriate feature was presented.

Study and analysis the effect of variable applied voltage on SCIM performances based on FEA is presented. Three phase squirrel cage induction motor SCIM has been investigated and numerically simulated using finite element method (FEM) with the aid of ANSYS software (RMxprt and Maxwell 2D/3D). This research presents study and analysis of the effects of the voltage variation on performance and efficiency of the three-phase induction motor of the squirrel cage type. The Finite Elements Analysis Method FEA is used as one of the best methods for analysis and simulation of electrical motors in addition to the possibility of dealing with nonlinear equations, Since the induction motor is a complex electromagnetic reaction, the researchers used the ANSYS program to represent and analyze the performance of the motor under variable supply voltage. The case studied in this research is three phases, 380V, 50Hz, 2.2kW, induction motor that widely use in industrial application. The aim of this research is to study the effect of voltage variation on efficiency, current value, power factor and torque of SCIM. The RMxprt software has been used for modeling and simulating the induction motor and calculating the values of phases currents, input and output power in additional of overall efficiency at steady state condition. The next stage of the research is creating Maxwell 2-D design from the base model of RMxprt software, Maxwell 2-D model has the ability to computing the distribution of magnetic field and explaining the performance under steady-state operation. The obtained results show significant reduction of motor performance due to the effect of variation of apply voltage.

We present a 3-D model for calculating magnetic fields in a power transformer and the effective parameters (inductance and resistance) of its windings. The transformer is representative of large transformers with power ratings ranging from hundreds of kilovolt amperes to hundreds of megavolt amperes. The model accounts for anisotropic frequency-dependent properties of the laminated transformer core and eddy currents in the steel sheets. We discuss the results of the calculations performed in the frequency range 10 Hz-10 MHz, and show that the largest variations of both the magnetic field and parameters of the windings take place at frequencies below 10 kHz and, at frequencies higher than 1 MHz, the magnetic core does not significantly affect the variation of the effective parameters.

This paper presents an embedded frequency response analyzer (EFRA) for fuel cells (FC) based on a low-cost digital signal processor (DSP). Frequency response analysis technique provides valuable information of different electrochemical processes that occur inside the FC. The small size and low power consumption allows this special device to be embedded into the FC controller or the power conditioning stage. The system is capable of measuring automatically the frequency response of the FC at different operating points, even when the FC is operating with load. These measurements can be used to characterize the FC at design stage and to perform on-line monitoring of the FC state during continuous operation. The proposed instrument uses the lock-in amplification technique, which allows very accurate and precise measurements even in the presence of high noise levels. The proposed hardware and signal processing technique are described in this paper including experimental result of a 1.2 kW proton exchange membrane fuel cell (PEMFC) system

As an early part of a large design and fabrication-oriented project FasdHTS funded by the GROWTH programme of the European Commission, an exotic concept ship was designed in very high tensile steel (EHS690) with the purpose of finding out consequences for design and production. The project has already produced a considerable bank of knowledge for design and shipyard production in this material. This paper presents analysis and discussions on static and dynamic behaviour of a high tensile steel deck designed with trapezoidal stiffeners. First, a finite element model of the deck structure is created. The influence of support condition for the longitudinal girders, and the contact area between the vehicle tyre and panel were analysed. The results from modal analysis of the structure under different load conditions are presented. The different load conditions comprise the unloaded and loaded deck, and the load type, i.e. cargo loads or vehicle loads (car loads or truck loads). From the frequency response analysis under harmonic excitation, it shows how the locations and numbers of cars parked on the deck influence the dynamic response of the structure. Furthermore, by studying the car-deck interaction, it is found that the effects of normal cargo loads are quite different from the vehicle loads due to the spring/damping effects of the vehicles. It is suggested that the carloads have a similar mechanism to that of tuned mass dampers. Finally, two transient analyses of the structure due to excitations transferred from deck supports and lorry braking-induced loading are performed.

The major amount of worldwide transportation is done by using automobiles. In automotive industries truck chassis are designed as per the design standards but the bodies manufactured by various manufacturers are designed without standard design considerations. In India there is huge market of these manufacturers. These bodies are manufactured as per their loading capacity, there is no standardization of design considering engine vibrations and dynamic performance. Truck bodies manufactured without design standards are unsafe for dynamic performance. The body is excited by dynamic force induced by the engine. Under such dynamic excitations, the body tends to vibrate at some frequency, as truck engine operating rpm range is between 900rpm to 3000rpm. Because of engine, truck body undergoes vibration range between 15Hz to 50Hz. Whenever the natural frequency of vibration of a truck body structure coincides with the frequency of the external excitation induced by engine, there occurs a phenomenon known as resonance, at resonance drastic increase in deflection occurs which leads to excessive deflections and failure of the truck body structure. Hence there exists a need for the industry sector to modify the design of dump truck body structure which allows dump truck body to withstand safe between engine excitation frequencies and simultaneously improvising the strength, reducing weight, and prolonged operational life.

Figure 1. (a) Stanford Bunny model with 35.947 vertices. (b) Corrupted with zero mean Gaussian noise with standard deviation σ = 0.4 of mean edge length. (c) Denoised with our method. Notice that no oversmoothing occurs along the surface and that, despite huge noise level, sharp details were well recovered in the eyes and also enhanced in the ears.

In many industrial activities, the assessment of the good condition of the devices involved in these activities is an important issue. The condition assessment is usually carried out taking some measurements of the device and postprocessing them somehow. One approach about taking measurements is in either the frequency or the time domain (which are mathematically equivalent through the Fourier Transform). This approach is very appreciated in cases such as electrical transformers in order to check whether some winding have been displaced or not after a high current (caused for instance by a shortcircuit or by a lighting). The Frequency Response Analysis (FRA) for transformer advanced maintenance is very usefull in this case due to this fault is dillicult to detect by means of any other procedure and its consequences could be serious. A procedure to model the frequency response is presented in this paper. It has been oriented to implement a modeling aided analysis for electrical transformers maintenance. However, this approach can be extended to different cases in which the frequency response modeling is required, adapting both the model and the algorithms to each particular case.

Transformers are one of the main devices in the utility grids. Reliability, power quality, economic cost and even the company image are influenced by the transformers health. For this reason, advanced techniques have been developed in recent years in order to improve the transformer life assessment. FRA (Frequency Response Analysis) Techniques are nowadays widely used by the electric utilities as one of these advanced techniques. They are specially appreciated to detect winding displacements inside the transformer. The main problem about FRA Techniques is to interpret the observed evolution of the frequency response in order to identify both failures and failures tendencies in the transformer. In order to solve this problem, a Modeling Tool is proposed in this work using the frequency response measured at the transformer.

As an early part of a large design and fabrication-oriented project FasdHTS funded by the GROWTH programme of the European Commission, an exotic concept ship was designed in very high tensile steel (EHS690) with the purpose of finding out consequences for design and production. The project has already produced a considerable bank of knowledge for design and shipyard production in this material. This paper presents analysis and discussions on static and dynamic behaviour of a high tensile steel deck designed with trapezoidal stiffeners. First, a finite element model of the deck structure is created. The influence of support condition for the longitudinal girders, and the contact area between the vehicle tyre and panel were analysed. The results from modal analysis of the structure under different load conditions are presented. The different load conditions comprise the unloaded and loaded deck, and the load type, i.e. cargo loads or vehicle loads (car loads or truck loads). From the frequency response analysis under harmonic excitation, it shows how the locations and numbers of cars parked on the deck influence the dynamic response of the structure. Furthermore, by studying the car-deck interaction, it is found that the effects of normal cargo loads are quite different from the vehicle loads due to the spring/damping effects of the vehicles. It is suggested that the carloads have a similar mechanism to that of tuned mass dampers. Finally, two transient analyses of the structure due to excitations transferred from deck supports and lorry braking-induced loading are performed.

ABSTRACT Interturn winding faults are one of the most prevalent and potentially destructive electrical faults in power transformers. This contribution is an initiative to explore the potential of the sweep frequency response analysis (SFRA) method in detecting interturn winding faults and also identifying the most appropriate measurement configuration for making sensitive frequency response measurements. This application enables timely warning of the rising failure and so is of particular importance, as these kinds of defects, if left undetected, can propagate and lead to catastrophic phase–ground or phase–phase faults which can finally cause the breakdown of the whole transformer. In this paper contribution is made to a better understanding of the transformer performance and modification of the transformer winding frequency response in the presence of interturn faults. The paper includes a full description of the details of the SFRA method and measuring procedure, along with principal experiments conducted on a 100 kVA distribution transformer. A large number of measurements with different transfer functions, various terminal configurations and three categories of measurement types was conducted to identify the most appropriate configuration for making SFRA measurements. The experimental results proved that the identified measurement configuration is sensitive to detect unambiguously interturn faults even down to 0.2% shorted turns along the winding.