Inrush Currents In Power Transformers Research Articles

Discrimination between internal faults and inrush currents in power transformers based on the discriminative-feature-focused CNN

Overcoming the drawback of the incorrect action of differential protection induced by the inrush current is a crucial issue for transformer protection. This paper proposes a deep learning protection scheme based on a discriminative-feature-focused convolutional neural network to improve the protection accuracy. Considering that internal faults and inrush currents can be reliably distinguished based on the unsaturated part of the differential current, the three-module network and specialized loss function are designed to guide the proposed network to extract the discriminative features of the unsaturated part of the differential current. By focusing on discriminative features with invariance and robustness, the proposed method presents high accuracy and remedies the problem of the limited generalization ability of artificial-intelligence-based protection in engineering applications. Test results on various datasets show that the proposed scheme can accurately identify transformer states with good robustness to noise and generalization to complex scenes, such as CT saturation, overexcitation, and field data. A time-consuming test deployed on hardware shows that this algorithm meets the protection time requirements. The comparison with previous methods confirms the superior reliability and generalization ability of the proposed scheme.

Comparison and Analysis of Magnetizing Inrush and Fault Condition for Power Transformer

This paper presents the second harmonics present in the primary current of a power transformer at different conditions using Fast Fourier Transform and Total Harmonic Distortion techniques to analyze the inrush condition and to distinguish it with fault condition of a power transformer. Result shows that the 2nd harmonic content is pre-dominant in inrush condition of primary current of the power transformer. It is observed that there are significant differences amongst the parameters found during inrush condition, normal condition and internal fault condition which are useful in the identification of magnetizing inrush current of power transformer. The simulation is done in MATLAB/SIMULINK.

Identification of inrush currents in power transformers based on higher-order statistics

This paper presents a novel method based on higher-order statistics for discrimination between magnetizing inrush and internal fault in power transformers. The distribution characteristics of the sample points of differential currents, under various operation conditions, are firstly investigated and quantified using higher-order statistics. Based on these characteristics, three kurtosis-based indices are defined for distinguishing inrush current from internal fault current. The final discrimination criterion combines these three indices to improve the performance of inrush current identification. Extensive simulation studies and experimental tests verify the effectiveness of the proposed method and its advantages over the conventional second harmonic restraint method.

An Experimental Implementation of the <inline-formula> <tex-math notation="TeX">$dq$</tex-math></inline-formula>-Axis Wavelet Packet Transform Hybrid Technique for Three-Phase Power Transformer Protection

A successful development and implementation of the dq-axis components and the wavelet packet transform (WPT)-based hybrid technique for power transformer protection is introduced in this paper. In this approach, the high-frequency subband contents of the dq-axis components of the differential current is extracted using the WPT. This characterization helps to provide enough information to efficiently detect and discriminate internal faults from inrush currents in power transformers. This hybrid method provides accurate information with only one level of the WPT of the dq-axis components of the differential current for power transformer protection. A real-time experiment is carried out for different normal and abnormal operating conditions, such as inrush and internal faults for different cases of loading, to test the efficacy of the proposed algorithm. The experimental results show fast, accurate, and reliable responses to all different types of disturbances that may occur in power transformers.

Power Transformer Differential Protection Through Gradient of the Differential Current

This paper presents a new methodology for identifying internal faults and inrush currents in power transformers based on the gradient of the differential current. The technique is to calculate the angle of the gradient vector along the curve of the differential current in the data window and through waveforms recognition techniques to identify the type of occurrence. The gradient vector of a function corresponds to a vector tangent to the curve at the point under consideration. The gradient vector, to move along the curve of the differential current, changes its angle to the horizontal reference. The behavior of the gradient vector angle, through statistical calculations will be used to identify the occurrence of internal faults or the presence of inrush currents. The method was tested by simulating various types of internal and external faults and also several cases of inrush currents in a power transformer which is modeled by the EMTP/ATP software and also by implementing the algorithm in MATLAB\(^{\textregistered }\), presenting highly satisfactory results.

A runs test‐based method for discrimination between internal faults and inrush currents in power transformers

AbstractA new method based on runs test is proposed to distinguish the inrush currents from the internal faults in power transformers, which is derived from the inherent differences between these waveforms. First, two statistical hypotheses that represent these differences are defined. Then by testing these hypotheses using runs test and by comparing the outputs of the hypotheses, a criterion to identify the internal fault is obtained. A total of 200 experimental cases are used to test the performance of the technique. In all of the tests, the proposed method accurately distinguished between fault and inrush currents without any errors. Also the suitable performance of the method is demonstrated by simulation of different faults and switching conditions on a power transformer. For this purpose, a small part of Iran power system involving a power transformer and the transmission lines on both sides of the transformer has been considered. To include effective factors on differential current components, the elements of this power system have been precisely modeled in PSCAD/EMTDC. Copyright © 2010 John Wiley & Sons, Ltd.

Wavelet and ANN Based Relaying for Power Transformer Protection

This paper presents an efficient wavelet and neural network (WNN) based algorithm for distinguishing magnetizing inrush currents from internal fault currents in three phase power transformers. The wavelet transform is applied first to decompose the current signals of the power transformer into a series of detailed wavelet components. The values of the detailed coefficients obtained can accurately discriminate between an internal fault and magnetizing inrush currents in power transformers. The detailed coefficients are further used to train an Artificial Neural Network (ANN). The trained ANN clearly distinguishes an internal fault current from magnetizing inrush current. A typical 750 MVA, 27/420KV, ∆/Y power transformer connected between a 27KV source at the sending end and a 420KV transmission line connected to an infinite bus power system at the receiving end were simulated using PSCAD/EMTDC software. The generated data were used by the MATLAB software to test the performance of the proposed technique. The simulation results obtained show that the new algorithm is more reliable and accurate. It provides a high operating sensitivity for internal faults and remains stable for inrush currents of the power transformers.

A Novel Wavelet-Based Algorithm for Discrimination of Internal Faults From Magnetizing Inrush Currents in Power Transformers

In this paper, a new algorithm based on processing differential current is proposed for digital differential protection of power transformers by considering different behaviors of the differential currents under fault and inrush current conditions. In this method, a criterion function is defined in terms of difference of amplitude of wavelet coefficients over a specific frequency band. The criterion function is then used for three phases, and internal faults are precisely discriminated from inrush current less than a quarter a cycle after the disturbance; this is one advantage of the method. Another advantage of the proposed method is that the fault detection algorithm does not depend on the selection of thresholds. The merit of this method is demonstrated by simulation of different faults and switching conditions on a power transformer using PSCAD/EMTDC software. Also the proposed algorithm is tested offline using data collected from a prototype laboratory three-phase power transformer. The test results show that the new algorithm is very quick and accurate

Novel approach to reducing the inrush current of a power transformer

An inrush current is a transient current that results from a sudden change in the exciting voltage across a transformer's windings. It may cause inadvertent operation of the protective relay system and necessitate strengthening of the transformer's mechanical structure. A novel approach to reducing the inrush current of power transformer, by increasing the transient inductance of the primary coil by changing the distribution of the coil winding is presented. During the period of this study, 30 patterns of 220 V/110–220 V 5 kVA-power transformers with three-layer and four-layer winding structures were developed as demonstrations of the approach. According to field tests and theory, the proposed method successfully limits the inrush current.

A wavelet transform based decision making logic method for discrimination between internal faults and inrush currents in power transformers

This paper describes a decision making logic method for discrimination between internal faults and inrush currents in power transformers using the wavelet transform based feature extraction technique. It is shown that the features extracted by the wavelet transform have a more distinctive property than those extracted by the fast Fourier transform due to the good time and frequency localisation characteristics of the wavelet transform. As a result, by quantifying the extracted features, the decision for distinguishing an internal fault from an inrush current in different power transformer systems can be accurately made. The extensive simulation studies have verified that the proposed method is more reliable and simpler, and is suitable for different power transformer systems.

Investigation of magnetizing inrush current in transformers. I. Numerical simulation

A simple method for simulating magnetizing inrush currents in power transformers using real-time measurements is proposed. The method is based on a simplified model for representing the inrush current under different loading conditions. A digital simulation method using a PC-AT microcomputer is also proposed. Transformer operating conditions, including transformer loading power factors, switching-on angles, and remanent flux, are included. The simulation result show very good agreement with experiment results. >

Computation of Transients in EHV Systems (with Reference to High Speed Protective Systems)

EHV systems, being characterised by high degree of interconnections, increased fault levels and large X/R ratios, insist on fast clearance of faults with high discriminating ability. When studying the shortest times in which reliable protection measurements have to be made, it is necessary to take into account the interaction between the primary system transients transmitted by transducers, the transients induced by these transducers themselves and their effects on the decision processes of the protection schemes. Digital computer simulation can give a degree of representation that goes well beyond that feasible with laboratory analogue modelling. The purpose of the present paper is to present the results of analysis of fault transients, current and potential transducer transients and inrush currents in power transformers for a typical 400 kV system,using direct integration technique based on Dommel’s method. The computed dynamic performances of a mho and a quadrilateral type distance relays are also presented.

Determination of Transient Inrush Currents in Power Transformers Due to Out-of-Phase Switching Occurrences

This paper describes a basic method to determine the crest value of the transient inrush currents flowing in power transformer windings resulting either from imperfect synchronizing procedures or from erroneous switching operations. The currents which flow under these unusual conditions are similar in magnitude and envelope to through-short circuit faults and may, in some cases, exceed the currents which flow through transformer windings during three-phase faults on their terminals.