Sympathetic Inrush Current Research Articles

Wavelet scattering and multiclass support vector machine (WS_MSVM) for effective fault classification in transformers: a real-time experimental approach

The dependable operation of the protective system is affected by residual magnetism and magnetic bias during the activation of the transformer. Challenges arise in distinguishing between inrush current and fault current when the transformer circuit breaker switching angle and remnant flux attain specific values. This situation can lead to a lack of sensitivity or failure in the operation of the transformer protection system. Thus, this paper proposes an effective approach for classifying different faults in transformers (internal and non-internal faults) using wavelet scattering and multiclass support vector machine (MSVM) technique (WS_MSVM). The wavelet scattering method begins by transmitting the data through a sequence of wavelet transforms, nonlinear operations, and averaging processes. This series of operations aims to generate low-variance representations of time series data. Wavelet time scattering produces signal representations that remain unaffected by shifts in the input signal, while still preserving the ability to distinguish between internal and non-internal faults. Internal faults are those occurring within the zones of the current transformer (CT) connected on both sides of the transformer. On the other hand, non-internal faults consist of magnetizing inrush current, sympathetic inrush current, and external faults (faults occurring outside the CT zones). The efficacy of the proposed WS_SVM is evaluated on the real-time experimental results obtained from the differential path of a laboratory transformer. The experimental data generated over one power frequency cycle under diverse operating conditions is employed in MATLAB to assess the effectiveness of the proposed WS_SVM algorithm.

Point on Wave Energization Strategy and Sequential Phase Shifting for Sympathetic Inrush Current Mitigation in Three-Phase Transformer - Measurement

Inrush currents generated when an electrical transformer is energized can achieve great values and cause abnormal difficulties in the power grid. The sympathetic inrush current phenomenon is resulted in the power system when a transformer is energized with the existence of other transformer already energized. The main objective of this article is the attenuation of sympathetic inrush current in a three-phase transformer. The control technique is carried out by the consideration of the residual flux value when de-energizing the transformer as well as respecting the three-phase shifting. Moreover, an experimental setup to measure the inrush current will be presented. Furthermore, a technique for controlling the circuit breaker to energize a 2 kVA three-phase transformer which allows the sympathetic inrush current to be attenuated was also applied and tested in the experimental. The contribution of this paper is that this technique is applied in measurements with an in-depth estimation of the residual flux. The proposed technique made it possible to completely eliminate the sympathetic inrush current.

Varying the energisation condition to mitigate sympathetic inrush current

Transformers are generally easy to access and can contribute significantly to entire power system. When a transformer is turned on for the first time, it produces a magnetising inrush current which acts as a starting current. Energisation of transformer has a substantial impact on inrush current and transformer that are connected in parallel. Sympathetic inrush current is a phenomenon that appears when a transformer is switched-on in network whereas the other transformers that was earlier energised. Besides, when sympathetic inrush phenomena occur, the peak and period fluctuate significantly. In this paper, the transformers will be energised in three different ways and each condition will be explored in depth. The operation time of the transformer’s energisation whether it is energised simultaneously or at different times are tested and analysed in terms of their characteristics. It is performed using power system computer aided design (PSCAD) software, starting with a develop model of the energisation and then generate the outcomes. The results of the simulation demonstrate that energising the transformer in different ways can give different effect on the sympathetic inrush current, as well as the variables that affect it and methods for reducing it.

Sympathetic Transformer Inrush Detection and Relay Blocking During Power System Restoration

A classic inrush current occurs during normal energization of reactive grid elements like transformers. It can simulate short-circuit currents. Hence inrush currents have to be detected and protection relays need to be blocked for avoiding their overfunction. Conventional detection criteria are the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$2^{\textrm {nd}}$</tex-math></inline-formula> harmonic content and some kind of current waveform analysis. A classic inrush can evolve into a sympathetic inrush event, if the energization of a single transformers drives other transformers into magnetic saturation. The risk of facing a sympathetic inrush current is particularly high during a power system restoration process. Its characteristic waveform differs from the classic inrush. While the classic inrush has unipolar current peaks, the sympathetic inrush is characterized by bipolar peaks. The conventional detection criteria tend to fail in this case. This paper proposes a new approach to detect sympathetic transformer inrush currents. The approach includes the detection of classic inrush currents as well as the distinction against short-circuit currents for ensuring the relay blocking. First it introduces the basic physical mechanism behind the evolution of a classic to a sympathetic inrush. The higher risk of facing a sympathetic inrush during the restoration process is shown by the physical mechanism as well. The proposed detection method is then introduced in detail. Three new differentiation criteria will be applied and merged together to a final decision. The paper closes with practical lab tests of the new approach on simulated sympathetic and measured classic inrush currents. All lab tests showed good results and promise a practical implementation in the grid.

Transformer power differential protection using real-time HIL test-based implementation of second-order transient-extracting transform

A novel Instantaneous Power-based Differential Protection (IPDP) for transformers is presented in this paper. The instantaneous power, gathering the voltage and current information, discriminates between internal fault and external fault, inrush current, sympathetic inrush current, overexcitation, and ultrasaturation with and without CT (Current Transformer) saturation. The proposed method relies on the waveshape properties of the instantaneous power signal. A high-resolution time–frequency analysis (TFA) technique, namely Second-Order Transient-Extracting transform (STET), is used for the discrimination purpose. Furthermore, the STET technique results are examined in a Hardware-in-the-Loop (HIL) test using Raspberry Pi (R-Pi) to evaluate the real-time speed of the proposed algorithm. This real-time manipulation results in the internal fault and other transient phenomena distinction time to be 14 ms. The proposed method does not require transformer parameters and various operating conditions of the power system and is entirely immune against noise. The usefulness of the proposed method is evaluated through numerous simulations as well as experimental implementation. Two experimental setups are considered for ensuring the practicality of the proposed method. The first one is a laboratory setup for capturing real-world transformer internal fault and inrush current waveforms. The second one includes a relay and CT tester, namely, Vebko Amirkabir AMT105 relay tester and a laboratory CT for determining the CT saturation test.

Predictive Formulas to Improve Transformer Protection During Inrush Current Using the Proposed DC Equivalent Circuit

Switching- on a power transformer creates energizing inrush current (EIC) which in turn leads to sympathetic inrush current (SIC) in adjacent in-service transformers (ITs). Sympathetic inrush current changes the waveform and prolongs the duration of its origin EIC. This makes the analysis and estimation of EIC complicated. Occasionally, the stress of EIC can cause internal short circuit in energizing transformer. Detecting short-circuit fault current during EIC is a challenge for transformer differential protection. On the other hand, SIC may mislead the earth-fault protection of in-service-transformer. This paper, first, proposes a new dc equivalent-circuit based on the dc-component of inrush current, which is efficient in analyzing concurrent EIC and SIC. Next, based on this equivalent circuit, new predictive formulas for EIC and SIC are derived. By employing these formulas, the transformer internal fault during inrush current can be detected based on the comparison between the predicted and measured waveforms, which prevents differential protection from fail-to-trip. Also, the predicted SIC waveform can be compared with the measured waveform to prevent IT earth-fault protection from mal-trip, during inrush current. Finally, the proposed equivalent circuit and formulas are verified using the EMTP simulation results of a real grid, under different system conditions.

Phenomenon of Transformer Sympathetic Inrush and Analysis of an Example

According to a mal-operation accident of differential protection which is caused by the effect of a switching-on transformer with no load on a parallel running transformer in a 35KV substation, the emergency and the development of transformer sympathetic inrush current was analysed from the aspect of the flux. And the three-phase differential current and their second harmonic component were obtained, which shows that the mal-operation wasn’t caused by the low second harmonic component in the differential current but by the changed transfer characteristics of the current transformer, which leads to an increase in the differential current.

Improvement of operation of power transformer protection system during sympathetic inrush current phenomena using fault current limiter

Power transformer protection has a high sensitivity due to its important role in power systems. Various factors such as inrush and sympathetic inrush currents may result in the inappropriate performance of protective relays and cause problems such as power outage or blocking of sensitive loads. Until now, several studies have been performed on the detection and reduction of inrush current, however, the effect of sympathetic inrush current on transformer protection has not been addressed. In this study, the operation of the protection system during the sympathetic inrush current is comprehensively analysed. Furthermore, the use of a fault current limiter is proposed to reduce the undesirable effects of the phenomena. The effects of the limiter on the saturation of power and current transformers are investigated. A real transmission station is simulated using DIgSILENT Power Factory Software to perform these studies by considering the resistive and impedance fault current limiter. Results show that protective relays do not have an improper operation during the phenomena with limiters. Moreover, with the resistive fault current limiter, sympathetic inrush and inrush currents are decreased by 5 and 15% more than the impedance fault current limiter, respectively. Saturation of power and current transformers is significantly reduced with limiters, especially with a resistive fault current limiter.

An Intelligent Hybrid Approach Using KNN-GA to Enhance the Performance of Digital Protection Transformer Scheme

This paper presents a novel hybrid K nearest neighbor-genetic algorithm (KNN-GA)-based digital protection transformer scheme, which effectively discriminates its internal faults with noninternal faults. The internal faults include the faults within the current transformer (CT) locations on two sides of the transformer. The noninternal fault includes magnetizing inrush current, sympathetic inrush current, recovery inrush current, external faults (faults outside the CT locations), and overfluxing. In conventional differential protection of a transformer, many maloperations of differential relay have been reported under certain working conditions. A new hybrid KNN-GA algorithm is put forward to improve the performance of the differential relay of a transformer. In this paper, real-time experimental results are presented for laboratory custom built differential relay model of a transformer. The generated experimental data for one power frequency cycle for various operating conditions is used by MATLAB to test the performance of a proposed algorithm. The proposed scheme has also been implemented on a digital signal processor TMS 320C6416T for a real-world application. The performance evaluation shows that compared with conventional methods, the proposed algorithm has a good reliability in terms of discrimination between internal and noninternal faults.

Sympathetic inrush current in a transformer and a method for its identification

This paper studies the sympathetic interaction between transformers. The influencing factors of the sympathetic inrush current, including the system impedance, closing angle and the initial remnant flux of the added transformer, the system voltage, and the neutral grounding mode of the transformers, are analyzed in detail through dynamic simulation. Based on this, a method for identifying the sympathetic inrush current is proposed based on the essential curve feature of the magnetizing currents of the transformers during the sympathetic interaction, taking advantage of the information sharing between substations. The results from dynamic simulation and field‐recorded data show the validity of the proposed method. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

Identification of Transformer Sympathetic Inrush Based on W-DHNN

A new method to identify sympathetic inrush and internal fault current of transformer based on W-DHNN is put forward. Wavelet analysis can detect the abrupt change of the current signal. And extract the feature vectors of the signal. The characteristic values as the input value of discrete Hopfield neural network. Then using discrete Hopfield neural network to discriminate sympathetic inrush and internal fault current. This paper uses PSCAD/EMTDC software to model and emulates different parameters of transformer and fault types. The results show that the method is feasible.

New Method to Identify Sympathetic Inrush in Transformer Based on Hilbert Huang Transform

Sympathetic inrush may cause the mal-operation of differential protection. Aiming at this problem, based on the characteristic that sympathetic inrush contains a lot of aperiodic component and high harmonics, this paper proposes to use Hilbert Huang transform to identify sympathetic inrush. Firstly, the mathematical model of sympathetic inrush is established to analyze its characteristic. Then Hilbert transform is used to obtain harmonic contents of sympathetic inrush and internal fault current. According to the proportion of fundamental to current, sympathetic current can be identified and differential protection can be blocked. The simulation results show that this method has better reliability and sensitivity than the second harmonic restraint scheme. Besides, it has a good ability against TA saturation.

Analysis of short circuit and inrush transients in a current transformer using a field-circuit coupled FE formulation

The existing models based on the lumped-circuit approach consider the constant leakage inductance during transient simulations. However, leakage inductance of the current transformer (CT) may not remain constant. In fact, it may vary with the degree of saturation of the core. During severe saturation conditions, leakage inductance variation in fact may result in significant difference between the calculated and the measured secondary currents. In this work, a nonlinear, field-circuit coupled finite element model of a current transformer (CT) is presented. The model considers the variation in leakage inductance during the simulation of transient conditions. Moreover, since geometry of the transformer was taken into account, it was possible to estimate forces associated with the short-circuit current. Hysteresis characteristic of the core was taken into account by using Jiles–Atherton model in conjunction with fixed-point iteration method. The formulation was realized using a code developed in MATLAB and implemented for a 69 kV, 200/5 A current transformer. The normal operation and other cases such as short-circuit, and transformer sympathetic inrush current through the primary of the CT are presented. These cases demonstrate modeling flexibility of the field-circuit coupled formulation.