Online assessment of winding deformation based on optimised excitation
25 Oct 2010-pp 84-89
TL;DR: On line assessment of winding deformation in a power transformer can be performed via a bushing tap excitation with optimized high frequency excitation through a benchmark layer winding to validate the suitability of the technique.
Abstract: On line assessment of winding deformation in a power transformer can be performed via a bushing tap excitation with optimized high frequency excitation. A benchmark layer winding is used to validate the use of the specific high frequency excitation. Axial displacement, compression and buckling of the winding are simulated and the changes identified. Measurements are performed on a voltage transformer to verify the suitability of the technique. The procedure will result in a considerably shorter time for measurement.
Citations
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01 Aug 2014
TL;DR: In this paper, a Simulink-based toolbox was developed for studying the problems associated with online frequency response analysis of power transformers, including various transformer circuit models and proposed online test configurations found in existing literature.
Abstract: Power transformers are among the most critical and valuable assets in an electric utility. Their failure can compromise system security, reliability and result in load shedding. These factors coupled with the long lead times involved in replacement mean that condition based monitoring is fast becoming the norm for minimization of down time. Among the gamut of available test methods, Frequency Response Analysis (FRA) has become a cornerstone method in the appraisal of winding health. FRA is predominantly an offline test, requiring the transformer to be taken out of service, but the move toward a smarter grid continues to drive research into online testing. This paper details the development of a Simulink based toolbox for studying the problems associated with online FRA of power transformers. The toolbox includes various transformer circuit models and proposed online test configurations found in existing literature.
1 citations
Dissertation•
01 Jan 2013
TL;DR: In this paper, a winding is modeled using finite element method (FEM) based software and parameters such as capacitance and inductance are calculated for 10 section healthy coil using these parameter values, SFRA plots are obtained which are a set of reference for deformation analysis.
Abstract: The winding is modeled using finite element method (FEM) based software and parameters such as capacitance and inductance are calculated for 10 section healthy coil Using these parameter values, SFRA plots are obtained which are a set of reference for deformation analysis The winding is modeled as radially and axially deformed coils using FEM software The parameters change with deformation in the winding The deformation is carried at five consecutive sections, and affected parameters are calculated for the same The main purpose of doing so is to find the location of deformation corresponding to a similar deformation in an actual transformer The main advantage of the FEM modeling is we can deform the sections as desired unlike in an actual case and obtain the fingerprint graphs from the modified parameter values The SFRA plots are obtained for the deformations at five sections for axial and radial deformations A comparison is carried between the SFRA plots for deformed cases with the reference set The deviations observed are in resonant frequencies, peak current magnitude and bandwidth From the observations, the type and location of deformation can be found corresponding to a similar deformation in an actual transformer
References
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TL;DR: The properties of ten different excitation signals are studied to analyze their suitability as excitation signal for fast Fourier transform (FFT)-based signal and network analyzers and the flexibility to create a customized amplitude spectrum is investigated.
Abstract: The properties of ten different excitation signals are studied to analyze their suitability as excitation signals for fast Fourier transform (FFT)-based signal and network analyzers. Their influence on the measurement time, accuracy, and sensitivity to nonlinear distortions is described. The flexibility to create a customized amplitude spectrum is investigated. With this information it becomes possible to select the best excitation signal for many applications. >
167 citations
TL;DR: In this article, three different ways of using the transfer function method for detecting mechanical winding displacements in power transformers are investigated, and the most reliable approach is time-based comparison, which requires finger print data from a previous measurement.
Abstract: The paper investigates three different ways of using the transfer function method for detecting mechanical winding displacements in power transformers. The most reliable approach is time-based comparison , which requires finger print data from a previous measurement. Such information is, however, usually not available. For multilegged transformers without zigzag-connected windings the results of separately tested legs can be used as mutual references (construction-based comparison ). A third approach is to compare the transfer functions with those obtained from an identically constructed transformer ( type-based comparison). However, for a transformer with given nominal specification data, the winding design may over time undergo changes which causes changes to the transfer function. It is proposed to solve this problem by calculating tolerance bands using transfer functions from a big group of the same-type transformers. A novel statistical algorithm for this purpose is presented. The approach is demonstrated for a set of 28 specified identically 200-MVA power transformers.
164 citations
"Online assessment of winding deform..." refers background in this paper
...INTRODUCTION Methods for assessing winding deformation in power transformers have received sufficient attention in the recent years [1], [2]....
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TL;DR: In this article, the authors present a method for calculating terminal and internal impedance versus frequency for a lumped parameter model of a transformer, where the transformer's total frequency response can be accurately determined from this impedance data directly, i.e., the terminal resonance and anti-resonance and internal amplification factor characteristic can be calculated for a single or three-phase transformer model.
Abstract: This paper presents a method for calculating terminal and internal impedance versus frequency for a lumped parameter model of a transformer The transformer's total frequency response can be accurately determined from this impedance data directly, ie, the terminal resonance and anti-resonance and internal amplification factor characteristic can be calculated for a single or three-phase transformer model Since most equipment associated with power system operation can be accurately modeled with lumped parameter networks, this method also provides an accurate, straightforward method for determining the resonance characteristic of those systems An additional significance of this method is that the accuracy of the calculation is limited only by the user's ability to represent the equipment or system Heretofore, the accuracy of this calculation was limited by the simplifying assumptions required of the network model by each solution method This paper presents the definitions and mathematical theory underlying the method Two examples are presented in which comparisons are made between measured and calculated values for a helical air core coil and a 200 MVA single-phase autotransformer The agreement is excellent
149 citations
TL;DR: In this paper, the authors discuss numerical-criteria-based evaluation techniques for frequency response analysis (FRA) for verifying the mechanical integrity of power transformers and conclude that if original fingerprints are available, the method gives very reliable indication for diagnosing the faulty winding.
Abstract: Frequency response analysis (FRA) is an emerging, powerful non-intrusive condition monitoring and diagnostic tool for verifying the mechanical integrity of power transformers. FRA results are graphical in nature and require trained experts to interpret test results. The work reported discusses numerical-criteria-based evaluation techniques. Persons not familiar with interpreting the FRA results can apply the evaluation criteria. The various criteria help in deriving proper conclusions. By evaluating correlation coefficient (CC), standard deviation and absolute sum of logarithmic error (ASLE) techniques, it is possible to discriminate between defective and non-defective windings. Experimental studies were conducted on two test transformers for axial and radial displacements, and additionally two sets of identical substation transformers. The techniques mentioned above are useful for interpreting frequency responses even in situations when a reference fingerprint was not available. However, it was concluded that if original fingerprints are available, the method gives very reliable indication for diagnosing the faulty winding. In addition, the severity of displacement/deformation can also be concluded from the amount of variation of the parameters from the suggested critical values.
108 citations
"Online assessment of winding deform..." refers background in this paper
...Similarly, a case study is conducted in [12] on a 31....
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TL;DR: In this paper, a custom high-power signal generator that injects high-frequency signals on the bushing tap of the transformer under investigation, as well as a circuit to replace the short bushing-tap short and allow online operation of the system is demonstrated on a 650 kV transformer.
Abstract: Online transformer condition monitoring techniques based on transfer function methods, such as transmission-line diagnostics and swept frequency-response analysis, require the injection of a known test signal into the transformer On larger power transformers, a practical method is to use the available bushing tap connection In this paper, we will discuss a custom high-power signal generator that injects high-frequency signals on the bushing tap of the transformer under investigation, as well as a circuit to replace the bushing tap short and allow online operation of the system Finally, the system is demonstrated on a 650 kV transformer
95 citations
"Online assessment of winding deform..." refers background or methods in this paper
...The excitation voltage is applied across the bushing tap [2] as shown in Fig 18....
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...An online method was also proposed for measurement of deformation based on excitation from a bushing tap [2]....
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...INTRODUCTION Methods for assessing winding deformation in power transformers have received sufficient attention in the recent years [1], [2]....
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