Internal Winding Faults Research Articles

New approach for accurate discrimination and location of power transformers with different internal winding faults.

Power transformers are essential elements in power systems and thus their protection schemes have critical importance. In this paper, a scheme is proposed for accurate discrimination and location of internal faults in power transformers using conventional measuring devices attached to the transformer. Different types of internal winding faults are intensely considered: partial discharge, inter-disk faults, series and shunt short circuit faults and axial displacement. Depending on the transformer measured output voltage, input voltage and the input current, the construction of a locus diagram (ΔV-Iin) serves as an indicator for any physical modification to the winding. Using five suggested features extracted from the developed locus, an artificial neural network (ANN) technique is applied to accurately distinguish any deviation from the transformer healthy condition. The exact location of each fault inside the windings of power transformer is then determined. The obtained results validate the usefulness of the proposed scheme for different internal faults. The superiority of the proposed scheme is extensively examined by comparing its results with some published schemes.

Application of the Analysis of Variance (ANOVA) in the Interpretation of Power Transformer Faults

Electrical power transformers are the most exorbitant and tactically prominent components of the South African electrical power grid. In contrast, they are burdened by internal winding faults predominantly on account of insulation system failure. It is essential that these faults must be swiftly and precisely uncovered and suitable measures should be adopted to separate the faulty unit from the entire system. The frequency response analysis (FRA) is a technique for tracking a transformer’s mechanical integrity. Nevertheless, classifying the category of the fault and its gravity by benchmarking measured FRA responses is still backbreaking and for the most part, anchored in personnel proficiency. This work presents a quantum leap to normalize the FRA interpretation procedure by suggesting an interpretation code criteria based on an empirical survey of transformers ranging from 315 kVA to 40 MVA. The study then proposes an analysis of variance (ANOVA) based interpretation tool for diagnosing the statistical significance of FRA fingerprint and measured profiles. The latter cannot be relied upon by an expert or by the naked eye. Additionally, descriptive FRA frequency sub-region data statistics are proposed to evaluate the shift in both the magnitude and measuring frequency characteristics to formulate the recommended interpretation code criteria. To corroborate the code criteria by incorporating ANOVA and descriptive statistics, the study presents various case studies with unknown FRA profiles for fault diagnosis. The results constitute proof of the reliability of the proposed code criteria and a proposed hybrid of ANOVA and descriptive statistics.

Application of Probabilistic Neural Networks Using High-Frequency Components’ Differential Current for Transformer Protection Schemes to Discriminate between External Faults and Internal Winding Faults in Power Transformers

Internal and external faults in a power transformer are discriminated in this paper using an algorithm based on a combination of a discrete wavelet transform (DWT) and a probabilistic neural network (PNN). DWT decomposes high-frequency fault components using the maximum coefficients of a ¼ cycle DWT as input patterns for the training process in a decision algorithm. A division algorithm between a zero sequence of post-fault differential current waveforms and the differential current coefficient in the ¼ cycle DWT is used to detect the maximum ratio and faults. The simulation system uses various study cases based on Thailand’s electricity transmission and distribution systems. The simulation results demonstrated that the PNN and BPNN are effectively implemented and perform fault detection with satisfactory accuracy. However, the PNN method is most suitable for detecting internal and external faults, and the maximum coefficient algorithm is the most effective in detecting the fault. This study will be useful in differential protection for power transformers.

The Transient Response and Frequency Characteristics of Power Transformers Having Internal Winding Faults

The Transient Response and Frequency Characteristics of Power Transformers Having Internal Winding Faults

Modeling, Analysis, and Detection of Internal Winding Faults in Power Transformers

The winding interturn fault is critical in power transformers since its effect is not easily comprehensible at lower magnitude in the signatures of terminal voltages and currents. This paper presents a new and efficient approach for diagnosing the occurrence of incipient turn-to-turn short circuits in the windings of power transformers. The transformer is modeled in steady state and no-load operation. The analysis shows that the phase difference between the input voltage and input current in the faulty primary winding is changed in a manner that makes it a good measure to find the fault. A set of laboratory experiments on a custom-built transformer under various levels of faults confirms our theoretical analysis and results.

Noninvasive method for online detection of internal winding faults of 750 kV EHV shunt reactors

Seven hundred fifty kilovolt extra-high voltage (EHV) shunt reactors are important power equipment that stabilize the normal operation of an entire 750 kV power grid. Internal winding faults of a reactor could be a difficult issue when the reactor is in service, and result in sudden equipment failure and significant economic losses. To prevent sudden catastrophic failure of equipment, online detection should be implemented to evaluate the state of the reactor properties when requested. In this paper, a noninvasive method based on online impulse frequency analysis was proposed and developed to detect internal winding faults of a 750 kV EHV shunt reactor. Initially, the safe implementation of the online detecting device was verified before field installation. Unlike in previous work, the online detecting device was modified and improved according to the specific situation of shunt reactors. Original fingerprints of 750 kV EHV shunt reactors were obtained and analyzed after site installation and normal operation of the detecting device. A fault simulation test was implemented to validate the method. This paper provides guidance on actual implementation of online impulse frequency response analysis on power equipment.

The Spectrum Comparison Technique of DWT for Discriminating between External Fault and Internal Fault in Power Transformer

Abstract – This paper proposes a technique for detecting and identifying internal winding fault of three-phase two-winding transformer. A spectrum component obtained from DWT of differential current is analyzed. A ratio between per unit differential current and per unit time is calculated and performed as comparison indicator in order to discriminate between internal fault condition and external fault condition. Various cases based on Thailand electricity transmission and distribution systems are studied to verify the validity of the proposed algorithm. Results show that the proposed technique has good accuracy to detect fault and to identify its position in the considered system. Keywords : Power transformer, External fault, Internal fault, Discrete wavelet transform 1. Introduction To guarantee safety and stability of power grid operating, a precise protection scheme is required. In the literature for fault detection, several decision algorithms have been developed to be employed in the protective relay [1-10]. Most of them have different solutions and techniques. An application of a finite impulse response ANN (FIRANN) as differential protection for a three-phase power transformer is proposed in [1]. In [2], the paper describes a new approach for transformer differential protection that ensures security for external faults, inrush, and over-excitation conditions and provides dependability for internal faults. A new relaying fuzzy logic algorithm to enhance the fault detection sensitivities of conventional techniques is proposed in [3]. The relaying algorithm consists of flux-differential current derivative curve, harmonic restraint, and percentage differential characteristic curve. In [4], a new algorithm based on processing differential current harmonics is proposed for digital differential protection of power transformers. This algorithm has been developed by considering different behavior of second harmonic components of the differential currents under fault and inrush current conditions. In [5], the paper describes a new approach for transformer differential protection that ensures security for external faults, inrush and over-excitation conditions and provides dependability for internal faults. In [6], a new algorithm based on processing differential current harmonics is proposed for digital differential protection of power transformers. This algorithm has been developed by considering different behaviors of second harmonic components of the differential currents under fault and inrush current conditions. In [7], a novel analysis of the currents arising during a turn-to-turn fault in transformer in which a winding is delta-connected is done, so that data acquisition pre- and post-fault conditions may lead to a correct diagnosis. The approach given in this paper is based on the analysis of current sequences which appear in the fault state, and mainly in the nature of a zero sequence current (ZSC) in a delta winding, which is thoroughly discussed. In [8], the paper addresses turn-to-turn faults in power transformer windings. A sensitive detection method for such faults is described. As a result, most research works are interested in only the effects from magnetizing inrush current and the discrimination between magnetizing inrush current and internal faults [1-8], and etc. In addition, wavelet transform has been reported in the literature [9]. The idea of application of wavelet transform to fault diagnosis is not new, and there is a number of research papers related to this idea [9-14]. The advantage of the wavelet transform is that the band of analysis can be fine adjusted so that high frequency components and low frequency components are detected precisely. Results from the wavelet transform are shown both in time domain and in frequency domain. In previous research works [12], an analysis of the spectrum of the transient current signal is performed in order to determine whether the current is a fault or a magnetizing inrush current. The approximated signal of DWT is then employed in the algorithm for a decision unit in the protection scheme.

A complete motor protection algorithm based on PCA and ann: A real time study

Protection of an induction motor (IM) against possible faults, such as a stator winding fault, due to thermal deterioration, rotor bar and bearing failures, is very important in environments in which it is used intensively, as in industry as an actuator. In this work, a real time digital protection algorithm based on principal component analysis (PCA) and neural network method is presented for induction motors. The proposed protection algorithm covers internal winding faults (also known as stator faults), broken rotor bar faults, and bearing faults. Many laboratory experiments have been performed on a specially designed induction motor to evaluate the performance of the suggested protection algorithm. The hybrid protection algorithm described in this paper uses is based on a three phase rms supply. These currents are first preprocessed by PCA to extract distinctive features called residuals. The calculated residuals are applied to a feed-forward back-propagation neural network as input vectors for decision making. Outputs of the network are signals denoting winding fault, rotor bar fault, bearing fault, and normal operation. The proposed algorithm is implemented by using Matlab^{TM} and C++ with a NI-DAQ data acquisition board.

변환행렬법을 이용한 케이블 권선형 배전용 변압기 귄선의 진동모드 해석

This paper proposes a simulation method of the internal winding fault to calculate the short-circuit current, electromagnetic force and vibration mode in a distribution power transformer by using FEM program(FLUX2D) and analytic algorithm. A usage of the Transfer matrix method is also presented for the vibration mode analysis of the cable-type winding of power transformer. The equations of the winding are approximated by the series expansions of the distributed mass mode and Timoshenko`s beam theory. The simulation examples are provided for the cable type winding of the transformer(22.9[kV]/220[V], 1,000[kVA]) to verify the method. The proposed Transfer Matrix Method is also verified by the ANSYS program for the vibration mode of the transformer winding. The method presented may serve as one of the useful tools in the electromagnetic force and vibration analysis of the transformer winding under the short circuit condition.

수치해석을 이용한 배전용 변압기 권선 고장시의 전자력 계산방법 연구

본 논문에서는 전력계통에서 발생되는 surge나 고장전류에 의해서 변압기의 고압측 권선에 선간단락이 발생할 경우 유도되는 전자력의 크기를 유한요소 전자계해석 프로그램을 이용하여 해석하는 방법을 제안하였다. 연구에서 사용된 배전용 변압기 model은 1[MVA], 22,900/220[V] 단상 외철형 Cable 권선형 변압기로서 권선간 단락을 모의하는 방법을 제안하고, FEM 프로그램(FLUX2D)을 이용하여 단락전류와 각방향의 전자력을 계산하고 분석하였다. 누설자속분포, 권선단락 시 전압 및 전류파형, 권선간에 작용하는 힘의 변화와 분포를 계산하였다. Simulation 방법의 타당성을 검증하기 위하여 이론치와 Pspice 프로그램을 이용하여 계산한 결과와 5(%) 이내의 오차율로 아주 잘 일치함을 확인하였다. 선간단락전류는 정격전류의 약 400배이며, 전자력도 20-200배 정도로 급증하였다. 본 연구의 결과는 배전용 변압기의 신뢰도 향상을 위하여 변압기 코일과 절연구조 설계에 유용한 정보를 제공하게 될 것이다.

Recognition and Location of Transformer Winding Faults Using the Input Impedance

The purpose of this article is to present a frequency domain technique for the recognition and location of internal winding faults in power transformers. Both turn to turn and turn to ground faults will be considered. Using a simple distributed parameter network, cascaded with other sections to simulate a generalized model, the frequency domain input impedance is used as the main criterion to conduct this investigation. The performance of both the magnitude and the phase angle of the input impedance are analyzed. The location of the fault, as well as the number of series shorted turns, will be investigated.

Zero-sequence-based relaying technique for protecting power transformers and its performance assessment using unsupervised learning ANN

In this paper a simple and robust new relaying technique for protecting transformers from internal winding faults is proposed. Based on the measurement of zero sequence current inside a delta winding, the technique greatly simplifies the conventional differential relaying arrangement when a delta winding is available. Despite the number of windings of the transformer and the location of the fault, only measurement of induced zero sequence current within the delta winding is needed. Since the proposed technique has been shown to be prone to generate false pick-up signals during inrush, a simple restraining criterion is proposed and analysed. Additionally, use of projection techniques based on self-organizing maps (SOM) is proposed in this paper as a valuable tool for analysing multivariable data which are generated from the huge number of possible combinations existing between switching instant and fault location. Finite element simulations and laboratory tests have been combined into SOM to validate the proposed relaying technique and the restraining criterion. Copyright © 2005 John Wiley & Sons, Ltd.

Transformer protection based on the increment of flux linkages

The ratio of the increments of the primary and secondary winding flux linkages (RIFL) is equal to the turns ratio during normal operating conditions, magnetising inrush and over-excitation. It differs from the turns ratio during an internal winding fault. A transformer protection algorithm based on the RIFL will be described in the paper. For a single-phase and a three-phase Y–Y transformer, the increments of the flux linkages (IFL) are calculated. For a transformer with a delta winding, the differences of the IFL between the two phases are calculated to use the line currents, because the delta winding currents are practically unavailable. The ratio of the matching IFL or the differences of the IFL is compared with the turns ratio for fault detection. Compared to a conventional harmonically restrained or blocking differential relay, the algorithm improves the operating time of a relay and is independent of core characteristic and system conditions. Test results indicate that the algorithm can successfully discriminate between internal winding faults and all other operating conditions including magnetising inrush and over-excitation.

Modeling transformers with internal incipient faults

Incipient fault detection in transformers can provide early warning of electrical failure and could prevent catastrophic losses. To develop transformer incipient fault detection technique, a transformer model to simulate internal incipient faults is required. This paper presents a methodology to model internal incipient winding faults in distribution transformers. These models were implemented by combining deteriorating insulation models with an internal short circuit fault model. The internal short circuit fault model was developed using finite element analysis. The deteriorating insulation model, including an aging model and an arcing model connected in parallel, was developed based on the physical behavior of aging insulation and the arcing phenomena occurring when the insulation was severely damaged. The characteristic of the incipient faults from the simulation were compared with those from some potential experimental incipient fault cases. The comparison showed the experimentally obtained characteristic's of terminal behavior of the faulted transformer were similar to the simulation results from the incipient fault models.

Modeling Transformers with Internal Incipient Faults

Incipient fault detection in transformers can provide early warning of electrical failure and could prevent catastrophic losses. To develop the transformer incipient fault detection technique, a transformer model is required, to simulate internal incipient faults. This paper presents a methodology to model internal incipient winding faults in distribution transformers. These models were implemented by combining deteriorating insulation models with an internal short-circuit fault model. The internal short-circuit fault model was developed using finite element analysis. The deteriorating insulation model, including an aging model and an arcing model connected in parallel, was developed based on the physical behavior of aging insulation and the arcing phenomena occurring when the insulation was severely damaged. The characteristics of the incipient faults from the simulation were compared with those from some potential experimental incipient fault cases. The comparison showed that the experimentally obtained characteristics of terminal behaviors of the faulted transformer were similar to the simulation results from the incipient fault models.

Transient behaviour of salient-pole synchronous machines with internal stator winding faults

Internal stator winding faults in salient-pole synchronous machines can cause serious damage to a machine and the system to which it is connected. Thus, it is highly desirable to be able to accurately model their transient behaviour and to predict the resulting currents and voltages in order to develop appropriate protection schemes, particularly for high power machines. Based on the Multi-loop Circuit Method, a general mathematical model for a salient-pole synchronous machine with internal faults is established, and subsequently employed to simulate both the steady-state and transient behaviour for three different types of internal fault. Predicted results are validated by experimental measurements.

Finite element analysis of internal winding faults in distribution transformers

With the appearance of deregulation, distribution transformer predictive maintenance is becoming more important for utilities to prevent forced outages with the consequential costs. To detect and diagnose a transformer internal fault requires a transformer model to simulate these faults. This paper presents finite element analysis of internal winding faults in a distribution transformer. The transformer with a turn-to-earth fault or a turn-to-turn fault is modeled using coupled electromagnetic and structural finite elements. The terminal behaviors of the transformer are studied by an indirect coupling of the finite element method and circuit simulation. The procedure was realized using a commercially available software. The normal case and various faulty cases were simulated and the terminal behaviors of the transformer were studied and compared with field experimental results. The comparison results validate the finite element model to simulate internal faults in a distribution transformer.

Finite Element Analysis of Internal Winding Faults in Distribution Transformers

With the appearance of deregulation, distribution transformer predictive maintenance is becoming more important for utilities to prevent forced outages with the consequential costs. To detect and diagnose a transformer internal fault requires a transformer model to simulate these faults. This paper presents finite element analysis of internal winding faults in a distribution transformer. The transformer with a turn-to-earth fault or a turn-to-turn fault is modeled using coupled electromagnetic and structural finite elements. The terminal behaviors of the transformer are studied by an indirect coupling of the finite element method and circuit simulation. The procedure was realized using a commercially available software. The normal case and various faulty cases were simulated and the terminal behaviors of the transformer were studied and compared with field experimental results. The comparison results validate the finite element model to simulate internal faults in a distribution transformer.

Detection of and protection for internal low-current winding faults in overhead distribution transformers

Changing protection practices for overhead power distribution transformers involves mounting the arrester on the transformer tank and using lightning-surge-tolerant fuses to provide protection. Concerns about protecting transformers against low-magnitude internal winding faults as a result of this practice are addressed in this paper. An analysis of a high-power test involving primary and secondary winding faults is presented. The magnitude, duration, and signature of the winding faults are determined and categorized. An analysis of the response of surge-tolerant fuses shows that they often will not detect low-current winding faults before they propagate to the available system fault current. Testing also demonstrated the performance of current-limiters to effectively reduce the available system fault current, thereby minimizing stress to the transformer. The use of current limiters is recommended with surge-tolerant fuses. The pressure rise in the tank for primary winding faults is mainly caused by low-fault current and, when protected with current limiters, the relief device easily vents the gases. The pressure rise for secondary winding faults is more rapid and can exceed the capability of the relief device to limit the overpressure.

A three-phase differential relay for transformer protection

Established harmonic restraint differential relay concepts have been enlarged upon to provide a new static multiple-winding transformer differential relay. The resulting design includes simplification of the frequency selective circuits and new techniques for rapidly determining the harmonic content of the applied currents. The relay is shown to have improved sensitivity, to be responsive to internal transformer winding faults in less than two cycles, and to the more severe type of fault in less than one cycle. Full security against inrush currents and overexcitation as well as to external faults is demonstrated. Poor performance of current transformers is shown not to adversely affect either the security or dependability of the relay. Heavy current test results are presented which confirm the relay principles.