Actual Transformer Winding Research Articles

Research on new method of transformer winding deformation detection

As one of the most important electrical equipment in power system, the stable operation of transformer is the key factor to ensure the safety of power grid system. Winding deformation is the most common fault of transformer, which will seriously affect the reliable operation of the whole power system. Therefore, the detection of transformer winding deformation is of great significance to prevent transformer accidents. In order to further improve the reliability of transformer winding deformation detection, this paper proposes a transformer winding deformation detection method based on oscillation wave method. Firstly, the equivalent circuit model of transformer winding is established, and the transformer winding fault is simulated by changing the inductance and capacitance parameters in the model, and the law between the change of oscillation wave curve and the change of related performance indexes and equivalent parameters is obtained. Finally, the field test verification is carried out on a 10 kV transformer in the laboratory. The results show that the oscillation wave method can diagnose the transformer winding deformation and can be used for the actual transformer winding deformation detection.

A novel estimation methodology for multi-resonance equivalent inductance of transformer winding for inter-turn short-circuit fault detection

A novel, indirect measurement technique for estimating equivalent inductance associated with multi-resonance behavior of an isolated transformer winding is reported for both healthy and inter-turn short-circuit fault-condition. For healthy winding, the authors proposed measuring two unique admittance magnitude responses of the winding followed by utilizing their natural frequencies for estimating the said inductance. Here, the one response is for line-end excitation with neutral-end grounded and the other one is for two equal and opposite polarity excitations from two ends of the winding. For inter-turn shorting, driving-point admittance magnitude response with neutral-end open is also utilized. This inductance seems to be one important parameter for verifying the design constraint mainly for impulse behavior as well as for identifying inter-turn shorting of the winding. The proposed method was also verified by experimental measurements on two actual transformer windings; one of which incorporated an iron core within it. All pertinent analytical derivations and the associated results are also included in the paper.

A Robust Approach for Locating and Assessing Mechanical Faults in an Actual Transformer Winding Using the State Space of Its Lumped Equivalent Model

A Robust Approach for Locating and Assessing Mechanical Faults in an Actual Transformer Winding Using the State Space of Its Lumped Equivalent Model

Analytical Expressions to Link SCNF and OCNF of Transformer Windings to Their Inductances and Capacitances for 1-$\Phi$, 3-$\Phi$ Y and $\Delta$ Configurations

Recently, the present authors’ research group derived an analytical expression to link the harmonic sum of the squares of short circuit natural frequencies (SCNFs) of a single, isolated winding to its elementary inductances and capacitances. Also, it was demonstrated how this expression could be practically used for locating radial and axial displacements, along with assessing its severity on a single, isolated, actual transformer winding. The next logical task was to extend the derived expression to multi-phase windings, viz., star/delta connections and for any terminal condition of the neutral. Actually, it would be desirable to have a similar expression for open circuit natural frequency (OCNF) as well. A major highlight of this paper is that it presents a single, unified approach (using salient features of coefficients of the numerator and denominator polynomial of driving-point impedance) by which compact analytical expressions can be simultaneously derived for both SCNF and OCNF, for any multi-phase transformer configuration, and for any condition of the neutral terminal. Complete derivation details of the proposed method are presented, and then, the expressions for SCNF and OCNF are derived for 1- $\Phi$ isolated windings as well as 3- $\Phi$ (Y, $\Delta$ ) configurations. Finally, simulation results for all the cases are reported.

Determination of transformer HV winding axial displacement extent using hyperbolic method – a feasibility study

In recent years, ultra-wideband (UWB) systems have been proposed for online monitoring of power transformers. This study aims at a new UWB-based method to determine the axial displacement (AD) extent in the transformer high-voltage (HV) winding. In the proposed design, two receiving antennas and one transmitting antenna are used. Two receiving antennas receive signals at two different positions due to axial displacement occurrence, and the displacement extent is determined using an analytical method known as hyperbolic method, which is based on signals time difference of arrival. The proposed method is initially studied by simulations using computer simulation technology software. Finally, the experimental results show the effectiveness of the proposed method to detect the AD extent in an actual transformer winding.

Determination of transformer HV winding axial displacement occurrence, direction, and extent using time‐domain analysis of UWB signals

In this study, a new method is proposed to monitor axial displacement (AD) of transformer high-voltage (HV) winding using electromagnetic waves. The proposed method employed two receiving antennas and one transmitting antenna to exchange ultra-wideband (UWB) signals with the winding. The magnitude Euclidean distance (MED) index is used to compare the received signals when winding is sound or defective. Two receiving antennas receive signals at two different positions upon ADs in winding which causes different values in the amplitude of the received signals as well as the MED index of two receiving antennas. Hence, taking advantage of this feature, the occurrence, direction, and extent of AD can be identified. The proposed method is assessed using a simulation model. Then, experiments are conducted on an actual transformer winding using an experimental setup.

Diagnosing axial displacement in an actual, single, isolated transformer winding: Experimental results

Localization and severity assessment of an axial displacement occurring in an actual transformer winding is reported. Axial displacements considered in this paper are still in their initial or incipient stages of development and so assumed to be physically confined between two consecutive double-disks. It is needless to emphasize that early detection of such a winding condition is crucial. In a recent paper, authors derived a generalized analytical formula that linked the harmonic sum of squares of short-circuit natural frequencies of the winding to the basic winding parameters, viz., capacitances and inductances (taken on a per double-disk basis). This formula was successfully used to localize a radial displacement. Proceeding further, it is now shown, how the same expression can be used to localize and assess severity of an actual axial displacement. A procedure is developed for this purpose. Its philosophy is explained, and thereafter, it is verified by experiments on a single, actual, isolated, continuous-disk transformer winding. The results seem to be promising.

Improved Power Transformer Winding Deformation Fault Diagnosis Method

according to analysing the generation principle of transformer winding deformation and its impact on the vibration signal, and make a large number of trial, it can be found in addition to the fundamental frequency component that can reflect the failure, the new characteristic frequency which conclude 50Hz frequency component and some of its harmonic components, the harmonic components of the fundamental frequency can also reflect the failure. Transformer winding deformation fault diagnosis method is proposed based on the relationship between the characteristic frequency, it can not only diagnose whether the failure inside the transformer windings, but also determine the type of fault. In order to verify the proposed method, deformation fault is set to the actual transformer winding. After de-noising, discounted processing, the acquisition monitoring points of vibration signal is used by the proposed method, and the actual transformer is diagnosed, The diagnostic result is same with actual failure. It is shown that the proposed diagnostic method is accurate and feasible.

Study on Mechanical State Diagnosis of Power Transformer Winding Based on Vibration Method

This paper uses the vibration method to diagnose the mechanical state of transformer winding,directed against the fact that the accuracy of the mechanical fault diagnosis in transformer winding is not high. It collects the load test vibration signal of transformer winding in normal and abnormal state, analyzes the vibration signals in different states, and use the vibration frequency and load current matching to judge the winding condition. By setting the different faults to the actual transformer winding of S11-M-500/35 type, it uses the vibration method to do the diagnosis analysis. And the research content is of great significance for the promotion and application of vibration analysis method.

Interleaved winding and suppression of natural frequencies

Ideally, it is desirable to design and manufacture a transformer winding that can render all its internal resonances non-excitable. This study examines the effectiveness of an interleaved winding in achieving this goal. While investigating its effectiveness, it led to the establishment of a much desired theoretical basis that reinforces the reasons put forward in the literature to explain internal insulation failures observed in interleaved windings used in extra high voltage (EHV) transformers. Numerical calculations along with experimental verification on actual transformer windings are presented. This study reveals that most of the natural frequencies that are normally non-excitable in the line and neutral current responses of an interleaved winding have been rendered excitable in the disk-to-disk voltages, thus, providing favourable conditions for insulation overstress because of resonant overvoltages. Prevalence of such a condition is an inherent characteristic of interleaved windings.

Localisation of discrete change in a transformer winding: a network-function-loci approach

An entirely different approach for localisation of winding deformation based on terminal measurements is presented. Within the context of this study, winding deformation means, a discrete and specific change externally imposed at a particular position on the winding. The proposed method is based on pre-computing and plotting the complex network-function loci [e.g. driving-point impedance (DPI)] at a selected frequency, for a meaningful range of values for each element (increasing and decreasing) of the ladder network which represents the winding. This loci diagram is called the nomogram. After introducing a discrete change, amplitude and phase of DPI are measured. By plotting this single measurement on the nomogram, it is possible to estimate the location and identify the extent of change. In contrast to the existing approach, the proposed method is fast, non-iterative and yields reasonably good localisation. Experimental results for actual transformer windings (interleaved and continuous disc) are presented.

Construction of Physically Realizable Driving-Point Function From Measured Frequency Response Data on a Model Winding

A simple method is described for constructing physically realizable driving-point impedance function from measured frequency response data (i.e., magnitude and phase) on a model winding and a transformer. A unique feature of the proposed method is that it ensures the constructed rational function is always positive-real, thereby guaranteeing synthesis of a physically realizable network every time. This feature could not always be guaranteed by earlier methods. Hence, it was a limitation. The proposed method is demonstrated on a single-layer model winding and the measured terminal characteristics is converted to a lumped parameter ladder network, since this representation is naturally suited to establish a physical mapping between the actual winding and synthesized circuit. So, the need to guarantee physical realizability is evident. Proceeding further, the terminal characteristics of a 315-kVA, 11/6.9-kV transformer is measured and a rational function representation is obtained. However, its realization as a coupled ladder network requires some more work to be done. In summary, it is believed that this proposal is a step towards providing a solution for localization of deformation in actual transformer windings.

Localization of Changes in a Model Winding Based on Terminal Measurements: Experimental Study

By using some properties of driving-point functions and adopting an iterative circuit synthesis approach, the location, extent, and type of change introduced in a model winding could be identified, based on terminal measurements. In this study, a model winding was used. From knowledge of its measured short-circuit and open-circuit natural frequencies, and pertinent winding data, an equivalent circuit was synthesized (called reference circuit). Next, changes were introduced at different locations in the model winding and its natural frequencies were measured. Corresponding to every new set of measured natural frequencies, a new circuit was synthesized (with topology remaining unchanged). A comparison of these circuits with the reference circuit revealed that a mapping could be established between changes introduced in the model winding and those predicted by the synthesized circuits. Many case studies are presented by considering continuous-disc and interleaved winding representations. Reasonably good results were obtained. Thus, localization of changes, based on terminal measurements, is shown to be a possibility. So, it is believed that these findings could be of some assistance in addressing the ultimate task of locating mechanical deformations in actual transformer windings.