Single-phase Transformer Research Articles

Localization for Dual Partial Discharge Sources in Transformer Oil Using Pressure-Balanced Fiber-Optic Ultrasonic Sensor Array.

The power transformer is one of the most crucial pieces of high-voltage equipment in the power system, and its stable operation is crucial to the reliability of power transmission. Partial discharge (PD) is a key factor leading to the degradation and failure of the insulation performance of power transformers. Therefore, online monitoring of partial discharge can not only obtain real-time information on the operating status of the equipment but also effectively predict the remaining service life of the transformer. Meanwhile, accurate localization of partial discharge sources can assist maintenance personnel in developing more precise and efficient maintenance plans, ensuring the stable operation of the power system. Dual partial discharge sources in transformer oil represent a more complex fault type, and piezoelectric transducers installed outside the transformer oil tank often fail to accurately capture such discharge waveforms. Additionally, the sensitivity of the built-in F-P sensors can decrease when installed deep within the oil tank due to the influence of oil pressure on its sensing diaphragm, resulting in an inability to accurately detect dual partial discharge sources in transformer oil. To address the impact of oil pressure on sensor sensitivity and achieve the detection of dual partial discharge sources under high-voltage conditions in transformers, this paper proposes an optical fiber ultrasonic sensor with a pressure-balancing structure. This sensor can adapt to changes in oil pressure environments inside transformers, has strong electromagnetic interference resistance, and can be installed deep within the oil tank to detect dual partial discharge sources. In this study, a dual PD detection system based on this sensor array is developed, employing a cross-positioning algorithm to achieve detection and localization of dual partial discharge sources in transformer oil. When applied to a 35 kV single-phase transformer for dual partial discharge source detection in different regions, the sensor array exhibits good sensitivity under high oil pressure conditions, enabling the detection and localization of dual partial discharge sources in oil and winding interturn without obstruction. For fault regions with obstructions, such as within the oil channel of the transformer winding, the sensor exhibits the capability to detect the discharge waveform stemming from dual partial discharge sources. Overall, the sensor demonstrates good sensitivity and directional clarity, providing effective detection of dual PD sources generated inside transformers.

Application of saturated core transformer as inrush current limiter

An inrush current is a transient current that results from a sudden change in the exciting voltage across a transformer's windings. Reducing the inrush current of transformers is desirable due to mechanical stresses and negligent operation of protective relay systems such as differential relays. This paper investigates the application of a saturated-core transformer as an inrush current limiter (ICL). Analytical methods of inrush current and its electromagnetic forces on transformer windings with and without application of proposed ICL are presented. Also, the core saturation of the ICL and transformer, in addition to the voltage drop on the ICL in transient and steady states, are investigated. A single-phase transformer is modeled in two dimensions (2-D), and the forces due to inrush current are calculated by the finite element method (FEM) in Maxwell software. The radial and axial force distributions of transformer windings with and without the ICL are investigated. The results show the capability of ICL to limit the transformer inrush current and reduction of its electromagnetic forces. Our simulations demonstrate a significant reduction in inrush current (75 %) using the proposed Inrush Current Limiter (ICL). Additionally, the ICL effectively mitigates electromagnetic forces within the transformer. Compared to a scenario without ICL, the ICL reduces radial forces by 80 % and axial forces by a substantial 90 %. These findings suggest that the ICL offers a promising solution for mitigating both inrush current and the associated electromagnetic forces in power transformers.

Buildup of Fault Protection for High-Current Single-Phase Transformers in Ore Furnaces

Buildup of Fault Protection for High-Current Single-Phase Transformers in Ore Furnaces

I Design and Material Selection of Single-Phase Transformers

Transformers are indispensable appliances in our lives and play an essential role in the production, transport, and distribution of electricity for living and working purposes. An apparatus that uses electromagnetic induction to modify voltage is called a transformer. Therefore, this paper focuses on analyzing the basic working principle of a transformer, a detailed disassembly of the transformer, briefly analyzing the structure of the transformer, calculating the core parameters and coil parameters, selecting the appropriate model, and accounting for the results based on the rated power of the given conventional transformer. The goal is to successfully design a small single-phase transformer supplying power to resistive loads. Through a series of calibration calculations, it is finally determined that the selected iron core meets the operating standards and achieves the design purpose.

Localization of Dual Partial Discharge in Transformer Windings Using Fabry–Pérot Optical Fiber Sensor Array

The power transformer is one of the most critical core devices for energy exchange in power systems, and its safe and stable operation is directly related to the reliability of the power grid. Partial discharge is the main cause of insulation degradation and failure of high-voltage electrical equipment. Online monitoring and accurate localization of partial discharge can provide information on the aging of power equipment, which is of great value for improving the safe operation and maintenance of the power grid. Internal dual partial discharge in transformer windings is a more complex type of fault. Since it is located inside the windings, the signal is attenuated and distorted, making it difficult for traditional monitoring methods to capture such partial discharge signal The Fabry–Perot optical fiber sensor is an ultrasonic detection method that can be built into the transformer interior. This sensor has high sensitivity and a small size, enabling flexible placement at different locations inside the transformer for precise partial discharge detection. Especially for the narrow space inside the high and low voltage windings, F–P sensors can form an array, utilizing the array’s directivity to locate the fault points. In this study, an ultrasonic detection system based on the F–P optical fiber sensor array was developed. The system utilizes a directional cross-localization algorithm based on the multiple signal classification (MUSIC) algorithm to accurately locate dual partial discharge sources. This partial discharge detection system was applied to a 35 kV single-phase transformer, enabling the localization of dual partial discharge sources within the high and low voltage windings. Combined with experimental results, this method exhibits high localization accuracy and is particularly suitable for detecting partial discharge phenomena that occur within or between transformer windings.

Measurement of residual flux density in the single-phase transformer by applying DC voltage

The inrush current causes many adverse effects on electrical equipment. One of the reasons for inrush current is residual flux. When a no-load transformer is energized and the closing angle is inappropriate, the residual flux accelerates the core saturation, resulting in high-amplitude inrush current. It is necessary to measure the amplitude and direction of residual flux to reduce its harm. This paper proposes a novel strategy for measuring the residual flux of transformers based on externally applied DC voltages. Firstly, a relationship between residual flux and response current is established based on field-circuit coupling analysis. Then, the core-type transformer and shell-type transformer are modeled by the finite element method, and the fitted model for calculating residual flux is obtained. Finally, experiments are carried out on a square core and a 10 kV, 250 kVA single-phase transformer. The feasibility and accuracy of the proposed strategy are verified by the measurement results.

Experimental test results of an automatic voltage regulator with independent phase voltage controller

The growing number of distributed renewable energy sources and dynamic constant-power loads (e.g. electric vehicle charging stations) pose new challenges for network operators. These changes result in alterations to network load profiles and load flows, leading to greater voltage volatility. One effective solution to these problems can be the use of automatic voltage regulators (AVRs), which stabilize and symmetrize voltage output, whether at distribution transformers (DTs) or elsewhere in the distribution network. The device developed by the authors consists of two bidirectional power converters and three single-phase transformers connected in series to the low-voltage grid as a stabilizer. The proposed control system provides accurate and fast regulation of the AVR’s output voltage (within the range of ±10% of the nominal grid voltage), with each phase being independently adjusted, regardless of the type of power load. The article includes test results demonstrating selected functionalities of the developed AVR. The physical model of the device discussed in the article is a research component of the LINTE2 laboratory of the Gdansk University of Technology.

Power Flow Analysis Using Fuzzy for Single Phase Transformer Less PV System Connected with a Nine-Level Converter

Power electronics technology advancements and growing environmental concerns worldwide have made photovoltaic (PV) systems more visible in distributed generation systems. Photovoltaics, or solar PV, is an important component of solar energy for generating electricity. Grid-connected inverters must be able to regulate the amount of power they inject into the grid, track maximum power points, be highly efficient, and inject currents into the grid with minimal harmonic distortion. Two step-down converters were used to construct an inverter without a single-phase transformer. This study investigates two multi-sequence inverter types that use different voltages and are based on single-phase grid-connected photovoltaic (PV) technology. A new nine-level grid-connected transformer-less photovoltaic converter was proposed in this study. MATLAB was used to construct the complicated FFT simulation using fuzzy logic controls. Analyzing efficiency through simulation in order to enhance efficiency. This work aims to replace PI controllers with fuzzy controlled systems so that single-stage operation can be improved with reduced switches in an economic manner. An improvement of 10% over the existing system is achieved by implementing fuzzy computing.

Even‐Order Harmonic Distortion Observations During Multiple Geomagnetic Disturbances: Investigation From New Zealand

AbstractLarge geomagnetic storms are a space weather hazard to power transmission networks due to the effects of Geomagnetically Induced Currents (GICs). GIC can negatively impact power transmission systems through the generation of even‐order current and voltage harmonics due to half‐cycle transformer saturation. This study investigates a decade of even‐order voltage total harmonic distortion (hereon referred to as Even‐Order Total Harmonic Distortion (ETHD)) observations provided by Transpower New Zealand Ltd., the national system operator. We make use of ETHD measurements at 139 locations throughout New Zealand, monitored at 377 separate circuit breakers, focusing on 10 large geomagnetic disturbances during the period 2013–2023. Analysis identified 5 key substations, which appeared to act as sources of ETHD. The majority of these substations include single phase transformer banks, and evidence of significant GIC magnitudes. The ETHD from the source substations was found to propagate into the surrounding network, with the percentage distortion typically decaying away over distances of 150–200 km locally, that is, at a rate of −0.0043 %km−1. During the study period some significant changes occurred in the power network, that is, removal of the Halfway Bush (HWB) single phase bank transformer T4 in November 2017, and decommissioning of the New Plymouth substation in December 2019. Decommissioning of these two assets resulted in less ETHD occurring in the surrounding regions during subsequent geomagnetic storms. However, ETHD still increased at HWB with increasing levels of GIC, indicating that three phase transformer units were still susceptible to saturation, albeit with about 1/3 of the ETHD percentage exhibited by single phase transformers.

Single Phase Transformer Less Inverter for Grid Connected Photo Voltaic System

Sustainable power generation systems have been developed as a result of increased consumption of energy, the rapid depletion of fossil fuels, and environmental degradation worldwide. Thus, the demand for photovoltaic systems is increasing, owing to the increased need for renewable resources worldwide. Transformers are often used in photovoltaic systems to offer voltage ratio conversions between input and output along with galvanic isolation. The inverter, that may be a transformer-less or with a transformer, is the enabling technology in PV systems. But, the efficiency and power density of these traditional iron and copper-based transformers are decreased while the inverter's weight, size, and cost are increased. Thus, it is recommended to refrain from utilizing transformers within the inverter. For this reason, transformer-less inverters for grid-tied, low-voltage, single-phase photovoltaic (PV) systems have gained more attention thesedays. To comply with the safety requirements imposed by grid regulations, there are a few distinctive challenges, particularly with respect to leakage current problems, which need to be sufficiently handled. Owing to this In recent years, distributed solar grid-tied systems have made widespread use of single phase transformerless Voltage Source Inverters.
 This paper explores a novel transformer-less solar inverter for grid connected PV system and Results are investigated in MATLAB Simulink provided a significant reduction in distortion in voltage and current at load side.

Study of Problem and Effect Mitigation Technique of Unbalance Capacitance in 500 kV Single Phase Transformers

This article presents the study of the effect of unbalanced stray capacitance in single-phase 500 kV power transformers and establishes the mitigation technique. The power transformers were operated in Wang Noi Substation for transmitting the electrical power. There are 3 units of single-phase power transformer. Previously, a transformer of phase B failed after being serviced for several years. Thus, the new power transformer was ordered instead of the failed one. However, once the new system had been operated, the hotspots at the surge arrester of tertiary winding (22 kV) were found and the unbalance of phase voltages was observed, resulting in overvoltage as a root cause of the problem. Once a thorough investigation was done, it was found that there was an effect of unbalanced stray capacitance between tertiary winding and ground core since the new power transformer has some different designs compared with the remaining. Hence, the mitigation technique was performed by adding the capacitor parallel to the tertiary winding until the voltage balance was achieved. Simulation with the PSCAD program was performed to determine the optimum value for additional capacitors, i.e., voltage balance, using an iterative method. In this article, the capacitors used for additional were capacitor voltage transformers, which have been installed. As a result of the troubleshooting, the voltage at the 22 kV bus was more balanced as well as not causing overvoltage, and the hotspots at the surge arrester of tertiary winding were not detected resulting in gaining the stability and reliability of using these transformers.

Power transformer fault diagnosis using dynamic multiscale graph modeling and M2SGCN network based on statistical fusion

Power equipment fault diagnostics hold significant importance for the stability of power grid systems. In pursuit of this objective, this paper proposes a fault diagnosis method that utilizes dynamic multiscale graph (DMG) modeling and the multiscale multi-stream GCN(M2SGCN) network, incorporating statistical fusion. Specifically, a novel DMG modeling method is proposed to derive visibility graph data and horizontal visibility graph data from vibration signals across multiple scales. Next, a comprehensive neural network architecture named M2SGCN is established to learn global and local features simultaneously, providing a more precise representation. Subsequently, a Dempster Shafer evidence theory statistical fusion technique combined with an adaptive threshold model (DSTFusion) is utilized to integrate primary decision results for enhanced fault diagnosis accuracy. In addition, two datasets obtained from single-phase and three-phase power transformers are analyzed to demonstrate the evolution process. When compared to state-of-the-art indicators such as accuracy, precision, recall, and F1 scores, the method proposed excels in multiple aspects, successfully detecting fault states before their occurrence and achieving outstanding performance.

Numerical Model for Eddy-Current Loss of Wound Core in Single-Phase Transformer

Taking the wound core transformer widely used in the field of traction energy saving as the research object, considering its unique geometric structure, combined with the magnetic circuit theory and finite element calculation of Ansys Maxwell software, the phenomenon of the magnetic flux distortion of the wound core is revealed, and the influence degree of various factors is analyzed; based on the Maxwell equation system of the magnetic quasi-static field, the calculation model of the magnetic flux distortion considering joints is deduced, and then the numerical calculation model of the eddy-current loss of the wound core considering the magnetic flux distortion is presented, which is verified by no-load tests and can reflect the change of the eddy-current loss caused by the geometry of the core with different frequencies and magnetic flux densities, and it can be applied to large-capacity traction transformer with calculation error less than 3%. The numerical model can quickly calculate the eddy-current loss by core structure parameters and material properties without sample preparation and simulation in design stage, which greatly saves engineering cost and can be used for structural design and optimization of the wound core.

Transformer Core Fault Diagnosis via Current Signal Analysis with Pearson Correlation Feature Selection

The role of transformers in power distribution is crucial, as their reliable operation is essential for maintaining the electrical grid’s stability. Single-phase transformers are highly versatile, making them suitable for various applications requiring precise voltage control and isolation. In this study, we investigated the fault diagnosis of a 1 kVA single-phase transformer core subjected to induced faults. Our diagnostic approach involved using a combination of advanced signal processing techniques, such as the fast Fourier transform (FFT) and Hilbert transform (HT), to analyze the current signals. Our analysis aimed to differentiate and characterize the unique signatures associated with each fault type, utilizing statistical feature selection based on the Pearson correlation and a machine learning classifier. Our results showed significant improvements in all metrics for the classifier models, particularly the k-nearest neighbor (KNN) algorithm, with 83.89% accuracy and a computational cost of 0.2963 s. For future studies, our focus will be on using deep learning models to improve the effectiveness of the proposed method.

Field Programmable Gate Array-Based Smart Switch to Avoid Inrush Current in PV Installations.

This paper introduces an FPGA-based implementation of a smart switch designed to avoid inrush currents occurring during the connection of single-phase transformers utilized in grid-connected photovoltaic (PV) systems. The magnitude of inrush currents is notably impacted by the residual flux within the transformer core and the precise moment of energization relative to the wave cycle. Alternative methods frequently hinge on intricate procedures to estimate residual flux. This challenge is adeptly circumvented by the innovative smart control system proposed herein, rendering it a cost-effective solution for grid-connected PV systems. The proposed solution for mitigating inrush current remains effective, even in the face of challenges with current and voltage sensors. This resilience arises from the system's ability to learn and adapt by leveraging information acquired from the network.

Two-speed Synchronous Generator for Special Purposes

This paper deals with basic performances of a design of a two-pole three-phase 40MVA synchronous generator. The generator is designed to test three-phase and single-phase high power transformers aimed to work within 50 Hz and 60 Hz network frequency. This means that the generator will operate at two nominal speeds, at 3000 rpm and 3600 rpm, with nominal power of 40 Mvar induction load when rating with symmetrical three-phase load. The additional requirements relate to constant operation with two-phase 25 MVA load and single-phase 13.5 MVA load, since for testing single-phase and special transformers phase connection you like will be used. In the course of designing, special attention was paid to correct dimensioning of the damper rotor winding as well as to the geometry of stator windings, rotor and air gap, which in the end will produce minimum voltage wave distortion, i.e. generator voltage wave shape with harmonious content less than 1% (as it was demanded).

Online time series monitoring method of transformer based on seq2seq model

Abstract To monitor the operating conditions of transformers in real time and improve the monitoring accuracy of three-phase voltage, load current and power frequency of transformers, an online time series monitoring method of transformers based on the seq2seq model is proposed. The impedance, excitation current, secondary side voltage and excitation branch of the transformer are reduced to the primary side value, and the regulation coefficient of the transformer under no-load operation is calculated. By obtaining the short circuit impedance of the transformer, the short circuit impedance of the transformer is analysed. Using the coupling inductance model structure of single-phase double-winding and single-phase three-winding transformers, the parameter matrix of a single-phase double-winding transformer is established. According to the corresponding relationship between port electrical data and online monitoring information, the transformer coupling inductance model is constructed. The online time series monitoring process of the transformer is designed by using the seq2seq model, and the online time series monitoring of the transformer is realized. The experimental results show that when monitoring the three-phase voltage, load current and power frequency of the transformer, the monitoring errors are controlled below 0.5, 5 and 0.5%, respectively, which greatly improves the accuracy of online time series monitoring of the transformer.

An improved online minor turn-turn winding fault diagnosis in a single-phase transformer based on instantaneous induced voltages and primary current locus

Online detection of the minor turn-turn winding fault in a single-phase transformer under no load condition using current waveform analysis is very complicated. In this paper, a new online minor turn-turn winding fault diagnosis in a single-phase transformer is proposed. Using a correlation between the instantaneous primary and secondary induced voltages difference with the primary current as a geometry location, the minor winding faults is detected effectively. The healthy transformer locus is considered as a reference locus. The minor winding faults could be detected by graphical analysis of the faulty loci with the reference locus in every cycle. Incipient winding fault detection in a single-phase transformer using the proposed technique under no load condition is a significant of this paper. The proposed locus is changed in shape and dimension by the winding faults severity. Therefore, the minor winding faults severity determination is carried out by faulty locus area comparison with the healthy locus. The experimental results validate the simulation results completely.

Parameter estimation in single-phase transformers via the generalized normal distribution optimizer while considering voltage and current measurements

This research addresses, from a perspective of metaheuristic optimization, the problem regarding parametric estimation in single-phase transformers while considering voltage and current measures at the terminals of the transformer and weighing linear loads. Transformer parametric estimation is modeled as a nonlinear problem in order to minimize the mean square error between the calculated voltage and current variables and the measurements taken. The nonlinearities are associated with Kirchhoff's first and second laws applied to the equivalent electrical circuit of the single-phase transformer. The nonlinear optimization problem is solved by applying a metaheuristic optimization algorithm known as the generalized normal distribution optimizer (GNDO), which uses evolution rules that allow exploring and exploiting the solution space via the classical probability function based on normal distributions. Numerical results in three test transformers of 20, 45, and 112.5 kVA demonstrate the effectiveness and robustness of the proposed GNDO approach when compared to other optimizers reported in the literature, such as the crow search algorithm, the coyote optimization algorithm, and the exact solution of the nonlinear optimization model using the fmincon solver of the MATLAB software. All numerical simulations confirm the potential of the GNDO approach to deal with complex optimization problems in engineering and science with promising results and low computational effort.

An Experimental Set-up Involving Low-cost Digital Controller to Study the Magnetizing Inrush Current in a Transformer using Point-on-Wave Switching Technique

Abstract Generally in under-graduate studies, magnetizing inrush current (MIC) is discussed theoretically without giving much practical exposure. This paper presents the development of a low cost experimental set-up using a digital controller to study the MIC and the different parameters which can affect the same. This also helps to show how the inrush current can be minimized. This set-up also provides a hands-on experience of MIC and its control in under-graduate study, which can help an upcoming practitioner in industry as well as in further research. This paper presents a brief description of MIC, followed by a short analysis. Here, a pair of anti-parallel thyristors are connected in series with the primary winding of a single-phase power transformer. The turningon instant of this switch, with respect to the zero-crossing instant of the input supply voltage, may be adjusted through a firmware, in a PIC18F4620 from Microchip Technology microcontroller development board from Microchip Technology to control the transformer energisation instant. The firmware is developed in MPLABX-IDE from Microchip Technology, and the scheme is verified via simulations in Proteus simulation software. A suitable circuit to support the microcontroller development board to achieve the above function is designed and fabricated.