Application Of Frequency Response Analysis Research Articles

Application of Frequency Response Analysis for Parameters Estimation of Switched Reluctance Motors

Application of Frequency Response Analysis for Parameters Estimation of Switched Reluctance Motors

Detection of Failures in Metal Oxide Surge Arresters Using Frequency Response Analysis

This work presents an innovative application of Frequency Response Analysis (FRA) in order to detect early degradation of Metal Oxide Surge Arresters (MOSAs). This technique has been widely used in power transformers, but has never been applied to MOSAs. It consists in comparisons of spectra, measured at different instants of the lifetime of the arrester. Differences between these spectra are an indicator that some electrical properties of the arrester have changed. An incremental deterioration test has been performed on arrester samples (with controlled circulation of leakage current, which increases the energy dissipation over the device), and the FRA spectra correctly identified the progression of damage. Although preliminary, the FRA results seemed promising, and it is expected that this technology could be used as another diagnostic tool for arresters.

Application of Frequency Response Analysis in Diagnosis of Synchronous Power Generators: A Model-Based Feasibility Study

Application of Frequency Response Analysis in Diagnosis of Synchronous Power Generators: A Model-Based Feasibility Study

Online Frequency Response Analysis of Electric Machinery through an Active Coupling System Based on Power Electronics.

This paper presents an innovative concept for the online application of Frequency Response Analysis (FRA). FRA is a well known technique that is applied to detect damage in electric machinery. As an offline technique, the machine under testing has to be removed from service—which may cause loss of production. Experimental adaptations of FRA to online operation are usually based on the use of passive high pass coupling—which, ideally, should provide attenuation to the grid voltage, and at the same time, allow the high frequency FRA signals to be injected at the machine. In practice, however, the passive coupling results in a trade-off between the required attenuation and the useful area obtained at the FRA spectra. This paper proposes the use of an active coupling system, based on power electronics, in order to cancel the grid voltage at the terminals of FRA equipment and allow its safe connection to an energized machine. The paper presents the basic concepts of FRA and the issue of online measurements. It also presents basic concepts about power electronics converters and the operating principles of the Modular Multilevel Converter, which enables the generation of an output voltage with low THD, which is important for tracking the grid voltage with minimum error.

Equivalent Broadband Electrical Circuit of Synchronous Machine Winding for Frequency Response Analysis Based on Gray Box Model

Frequency response analysis (FRA) is a popular tool to detect transformer winding deformation faults. It has been recently used to diagnose the winding inter-turn short circuit fault of the electric machine. The application of FRA is based on the fact that the winding can be equivalent to an electrical circuit consisting of resistance, inductance, and capacitance. Therefore, to obtain an accurate broadband equivalent circuit model of synchronous machine and perform the fault analysis and diagnosis, this paper introduces the gray box model technique based on the state space and genetic algorithm. The electrical circuit of a form-wound coil of a 4 kW machine with known electrical parameters is used to verify the proposed method primarily. Besides, the equivalent circuit modeling is carried out and experimentally verified on an actual 5 kW synchronous machine. Finally, the fault simulation analyses of winding inter-turn short circuits are performed based on the proposed equivalent electrical circuit. The verification result shows that the circuit parameters identified by the proposed method are accurate. Moreover, the fault simulation results indicate that the inter-turn short circuit faults can cause apparent variations in the frequency response curves. It is feasible to detect the winding fault of the synchronous machine by the FRA method.

Detection of Power Transformer Winding Deformation Using Improved FRA Based on Binary Morphology and Extreme Point Variation

Frequency response analysis (FRA) has recently been developed as a widely accepted tool for power transformer winding mechanical deformation diagnosis, and has proven to be effective and powerful in many cases. However, there still exist problems regarding the application of FRA. FRA is a comparative method in which the measured FRA signature should be compared with its fingerprint. Small differences of FRA signatures in certain frequency bands might be produced by external disturbance, which hinders fault diagnosis. Additionally, the existing correlation coefficient indicator recommended by power industry standards cannot reflect key information of signatures, namely the extreme points. This paper proposes an improved FRA based on binary morphology and extreme point variation. Binary morphology is first introduced to extract the certain frequency bands of signatures with significant difference. A composite indicator of extreme point variation is adopted to realize the diagnosis of fault level. A ternary diagram is constructed by the area proportions of the binary image to identify winding faults, which has a potential to realize cluster analysis of fault types.

Application of Frequency Response Analysis for in-service power transformers


 
 
 CIGRE, IEC and IEEE have recently approved the technique of Frequency Response Analysis (FRA) as an application tool for diagnosis of mechanical failures in power transformer’s active part, i.e., windings, leads and the core. The diagnosis is based on the discrepancy between frequency responses measured on power transformers mainly at different time points. In Vietnam, utilities such as Power Transmission Companies and Power Corporations are investigating this technique for application on their power transformers. 
 Mechanical failures in power transformers cause changes on measured frequency responses starting from a medium frequency range, from several hundreds of Hz or tens of kHz depending on transformer/winding type and power. For a reliable diagnosis, the understanding of transformer/winding structure on measured frequency responses is of importance; thus, the international standards suggested the simulation approach with physical distributed transformer circuits should be exploited. 
 The development of physical distributed circuits of power transformers normally needs availability of internal transformer structure and material properties for an analytical approach. However, for in-service power transformers, this task is challenging since the required data are not available. 
 For a feasible application of the simulation based FRA interpretation, this paper introduces an investigation on the development of a distributed equivalent circuit of an in-service 6.5 MVA 47/27.2 kV Yd5 power transformer. The result of this investigation is a feasible approach in determining electrical parameters in a physical distributed circuit, which supports analysis of frequency responses measured at transformer terminals for real application on in-service power transformers of utilities. 
 
 

Methodology to locate and quantify radial winding deformation in power transformers

Frequency response analysis (FRA) is a tool that can be used to detect changes within the structural geometry of a transformer. One application of FRA is to detect winding displacement after the transformer experiences an overcurrent event. This paper proposes a methodology which will facilitate both locating and quantifying winding deformation. The procedure is based on the fitting of a Gray Box transformer model to FRA measurements which were recorded both before and after the fault. Subtle variation in key parameters of the model can then be used to quantify winding deformation severity. The research will demonstrate the applicability of this approach to a wide range of transformer applications by using FRA from a modified 1.3 MVA distribution transformer, and assessing the change in key parameters relative to the emulated buckling introduced to the windings. The authors propose that this approach is ideally suited for use within an automated diagnostic system which will locate, diagnose and quantify winding deformation within power transformers.

Early detection of insulation failures on electric generators through online Frequency Response Analysis

This work presents an application of Frequency Response Analysis (FRA) on the detection of insulation failures on electric generators. An equipment for FRA of electric machines has been developed and its online connection to an induction generator through a C–L–C T-type coupling is presented. It is shown that the coupling circuit implies in a design trade-off between the attenuation of the power signal at fundamental frequency (which may damage the electronics of the analyzer) and the useful area obtained in the FRA spectra. It is shown that a C–L–C coupling greatly improves the performance of a regular capacitive coupling, improving its attenuation at fundamental frequency while maintaining similar frequency response at high frequencies. Experimental results are presented to validate the proposed equipment.

Field-winding fault detection in synchronous machines with static excitation through frequency response analysis

Frequency Response Analysis is a well-known technique for the diagnosis of power transformers. Currently, this technique is under research for its application in rotary electrical machines. This paper presents significant results on the application of Frequency Response Analysis to fault detection in field winding of synchronous machines with static excitation. First, the influence of the rotor position on the frequency response is evaluated. Secondly, some relevant test results are shown regarding ground fault and inter-turn fault detection in field windings at standstill condition. The influence of the fault resistance value is also taken into account. This paper also studies the applicability of Frequency Response Analysis in fault detection in field windings while rotating. This represents an important feature because some defects only appear with the machine rated speed. Several laboratory test results show the applicability of this fault detection technique in field windings at full speed with no excitation current.

ANALYSIS ON DEGRADATION AND DEFORMATION OF TRANSFORMER INSULATION SYSTEM

Performance of insulation system of power transformer is essential to ensure better performance of power network. Most of the power and distribution transformers in service are aged and, have experienced several thermal and electrical stresses due to varying loading conditions, in addition to ageing. The rate of degradation and hence, the useful life of the insulation system mainly depends on the variation of operational stresses. Due to the progress in insulation degradation, the dielectric strength of the insulating oil and paper over transformer winding may reach to a point such that it could not withstand any small abnormal currents and voltages. In order to maintain the quality of system operation it is necessary to keep the transformer in good condition. This needs appropriate maintenance based on reliable diagnostics. In this paper experimental results on the application of frequency response analysis (FRA) for the diagnosis of power transformers. Frequency Response of Transformer, also serves for assessing the deformation process.

The Application of Frequency Response Analysis in Online Testing System of Transformer

Online testing system based on frequency response analysis is proposed for the deformation of transformer winding. The structure of testing system, the selection of sweep sequence and computer diagram of data acquisition system are developed in the course of design. In the process of analysis, the concept of correlation coefficient is introduced to judge the relationship between the deformation extent and correlation coefficient. With the proposed method, the location of deformation can be determined. The testing curves demonstrate the effectiveness of the presented system.

Influence of Rotor Position in FRA Response for Detection of Insulation Failures in Salient-Pole Synchronous Machines

Frequency response analysis (FRA) is a very common test for the diagnosis of power transformers. This paper presents some relevant results on the application of FRA to the diagnosis of rotating machines. First, a reference rotor position for obtaining the reference FRA response of a rotating machine is proposed. Then, FRA with the proposed rotor position is used to identify faults in the stator of the machine. This paper studies turn-to-turn and ground faults in the stator for different fault resistance values. Several laboratory tests demonstrate the applicability and value of the use of FRA in the diagnosis of rotating machines.

Transformer Diagnosis Based on Coupled Circuits Method Modelling

Diagnostic goal of transformers in service is to detect the winding or the core in fault. Transformers are valuable equipment which makes a major contribution to the supply security of a power system. Consequently, it is of great importance to minimize the frequency and duration of unwanted outages of power transformers. So, Frequency Response Analysis (FRA) is found to be a useful tool for reliable detection of incipient mechanical fault in a transformer, by finding winding or core defects. The authors propose as first part of this article, the coupled circuits method, because, it gives most possible exhaustive modelling of transformers. And as second part of this work, the application of FRA in low frequency in order to improve and simplify the response reading. This study can be useful as a base data for the other transformers of the same categories intended for distribution grid. Keywords—Diagnostic; Coupled Circuit Method; FRA; Transformer Faults.

An automated system for frequency response analysis with application to an undergraduate laboratory of electrical machines

This paper describes a LabVIEW-based automated system to carry out frequency response tests in electrical machines. The system is being used by undergraduate students in the laboratory of electrical machines, where they can experiment with the application of frequency response analysis and the characterization of mathematical models. An advantage of the system is its friendly user interface to a laboratory experiment. The system avoids the risky utilization of oscilloscopes for data acquisition and shortens the time taken to analyze the measured data. The Automated System for Frequency Analysis (ASFFA) can carry out tests within a bandwidth of 0.001-900 Hz. In addition, the ASFFA can estimate the transfer function parameters based on one- or two-port network theory. Design details of the interface, system structure, frequency response tests, electrical machine modeling, and signal processing are presented. Finally, ASFFA is applied to synchronous, induction, and direct-current machines.

Application of Frequency Response Analysis to the Determination of Cathodic Discharge Mechanism during Silver Electroplating

The ac impedance data generated from the frequency response analysis technique were used to establish the mechanism of silver electroplating from the industrial cyanide plating bath. The deposition process involves parallel and concurrent charge‐transfer reactions from more than one silver complex. Depending on the cyanide concentration in the silver plating bath, the electrode reaction seems to proceed mostly through one of the silver species/complexes: , , or , which are in equilibrium with each other. The discharge of complex appears the predominant process, especially for bath concentrations in the range of commercial silver cyanide plating systems. The complex plane ac impedance diagrams of the plating system, at steady state, consist of two capacitive loops at the lower frequencies, preceded by a high frequency spectrum which corresponds to the faradaic charge‐transfer process. The lower frequency features are a manifestation of the surface adsorption and coverage processes by specific intermediate species like cyanide and carbonate ions in the plating bath.

The Practical Application of Frequency Response Analysis to Automatic Process Control

The paper shows how the basic principles of frequency response analysis may be applied to automatic process control without the introduction of any of the mathematics which are used in the servomechanism field of study, and which have in the past discouraged its use in the process field. It is shown how the frequency response of any part of an automatic control system may be represented graphically, how the response of any simple element of a system may be calculated, and how the response of the individual elements thus obtained may easily be combined to give the characteristics of the whole plant. Alternatively, the frequency response of the plant may be plotted experimentally without interrupting its operation. By reference to a typical example, it is shown that all proprietary “three-term” controllers do not necessarily function as simple theoretical controllers, but that their performance may often be represented as that of an effective theoretical controller, and may, in any case, be shown as a frequency response diagram from which the necessary information is available to match the controller to any particular process. The method introduced is shown to give a convenient measure of plant controllability, and by means of plant analysis on this basis, it is suggested how automatic control may often be improved by better design of the process rather than of the controller. The design of automatic controllers is also treated, and it is shown how various design features may be compared in the light of their frequency response characteristics. It is suggested that future controllers should be designed to give a specified frequency response.