Power System Apparatus Research Articles

Appropriate analysis on properties of various compositions on fluids with and without additives for liquid insulation in power system transformer applications

Transformer is a well-known power system apparatus utilized in conjunction with solid insulations such as paper and press board, as well as liquid insulations like mineral oil, a petroleum-based fluid. Despite the notable drawbacks associated with mineral oil, such as limited resources for future generations and its non-eco-friendly nature, its usage remains ubiquitous. There is a growing imperative to explore alternative fluids that surpass mineral oil in terms of environmental impact and performance. Amidst the global shift towards green energy, this study focuses on vegetable seed oils such as corn oil, soybean oil, mustard oil, and rice bran oil as potential substitutes. The research evaluates these oils based on key transformer properties including breakdown voltage, water content, interfacial tension, viscosity, acidity, flash point, and fire point. Interestingly, rice bran oil and soybean oil exhibit promising characteristics that suggest they could effectively replace petroleum-based fluids in transformers. Furthermore, the study extends to blending mineral oil with vegetable seed oils in various compositions, incorporating natural and synthetic antioxidant additives ranging from 0 to 1%. Comparative analyses between samples with and without additives reveal that the inclusion of 1% propyl gallate yields outstanding performance improvements. For instance, a blend comprising 25 ml of mineral oil and 25 ml of soybean oil, supplemented with 1% propyl gallate, demonstrates 90% higher effectiveness compared to other blends and additives tested. Moreover, the research employs statistical regression analysis to establish relationships between different parameter variables, providing deeper insights into the performance and compatibility of these blended oils in transformer applications. This comprehensive investigation underscores the potential of vegetable seed oils as viable alternatives to mineral oil, contributing to the advancement of eco-friendly solutions in power systems.

Partial Discharge Location Algorithm Based on Total Least-Squares With Matérn Kernel in Cable Systems

Partial discharge (PD) location techniques are a useful tool for condition monitoring of electrical apparatus in power systems. However, the noisy PD measurements may significantly degrade the performance of location algorithms. This article deals with the PD location problem by using adaptive filtering techniques. Heretofore, scarce literature focuses on addressing the PD location based on such method. A novel adaptive algorithm, termed as total least-squares (TLS)-Matérn kernel (TLS-MK), is proposed. Benefiting from the merits of the Matérn kernel, the TLS model can effectively suppress the noise from the direct and reflected waves of the PD source. Meanwhile, the TLS-MK algorithm is used to estimate the time difference, which is used in the PD location. Moreover, the convergence behavior of the TLS-MK algorithm is analyzed. Simulations and experiments show that the proposed algorithm can enhance the location accuracy as compared to state-of-the-art methods for various PD signals.

A review on transformer condition monitoring with critical investigation of mineral oil and alternate dielectric fluids

Transformers are very critical elements of modern power system network and have evolved in many ways over its long history. Transformers are most significant apparatus in interconnected power systems with consideration of several aspects like reliability, efficiency, economy, wide applications and operation. However mineral oil also called transformer oil is attracting more attention from researchers and transformer industry due to environmental concerns, limited stock, high price of petroleum resources and its disposal issues after getting contaminated. Above issues have motivated researchers to turn their attention to biodegradable and/or renewable insulating oil. Multiple facets, such as environmental requirements, safety and economic considerations, availability of technology and raw material governs the development of new insulating liquid materials. In addition, the increased equipment efficacy and the adoption of more environment friendly alternate dielectric fluids for power system solutions is gaining popularity towards steps to reduce the carbon footprint and achieving net zero cum decarbonisation global policy. This article provides the detailed review of transformer condition monitoring and the critical investigation about environment friendly dielectric fluids. They claim excellent lifecycle of the insulation, better working compatibility and improved performance compared to the traditional mineral oil base fluids in adherence of compliance, standards and graphical abstracts. These alternate dielectric fluids are getting proved as superior transformer fluids. The diverse investigational work carried out is incorporated, providing an overview of research. In addition, the future scopes, challenges and environment friendliness of various fluids are studied and deliberately articulated.

Two Legs Voltage Source Converter with DSTATCOM, T-Connected Transformer for Power Quality Improvement

The numerous loads can impact the working environment and performance of the source apparatus. Hence, the reimbursement of this current will help in enhancing the presentation of the power system apparatus. This paper presents the strategy and employment of a Distribution Static Compensator (DSTATCOM) with the T-Connected transformer for compensation of load neutral current in the presence of three-phase unbalanced linear load. There are different types of control strategy in that one of the best methods is the unit vector template method-based control algorithm has been implemented for the control of the proposed DSTATCOM. The proposed model has been simulated in a SIMULINK/ MATLAB environment. The simulation results show the effectiveness of the proposed algorithm.

Overvoltage Impact on Internal Insulation Systems of Transformers in Electrical Networks with Vacuum Circuit Breakers

Vacuum circuit breakers are increasingly used as switching apparatus in electric power systems. The vacuum circuit breakers (VCBs) have very good operating properties. VCBs are characterized by specific physical phenomena that affect overvoltage exposure of the insulation systems of other devices. The most important phenomena are the ability to chop the current before the natural zero crossing, the ability to switch off high-frequency currents, and the rapid increase in dielectric strength recovery. One of the devices connected directly to vacuum circuit breakers is the distribution transformer. Overvoltages generated in electrical systems during switching off the transformers are a source of internal overvoltages in the windings. The analysis of the exposure of transformers operating in electrical networks equipped with vacuum circuit breakers is of great importance because of the impact on the insulation systems of switching overvoltages (SO). These types of overvoltages can be characterized by high maximum values and atypical waveforms, depending on the phenomena in the circuit breaker chambers, system configuration, parameters of electrical devices, and overvoltage protection. Overvoltages that stress the internal insulation systems are the result of the windings response to overvoltages at transformer terminals. This article presents an analysis of overvoltages that stress the transformer insulation systems, which occur while switching off transformers in systems with vacuum circuit breakers. The analysis was based on the results of laboratory measurements of switching overvoltages at transformer terminals and inside the winding, in a model medium-voltage electrical network with a vacuum circuit breaker.

ANALYSIS OF GEOMAGNETICALLY INDUCED CURRENT IN POWER GRID DURING GEOMAGNETIC STORM

Solar storms are event that has a big range of averse outcome on technological system, power grid specifically. During extreme geomagnetic storms a GIC begin to travel between long transmission lines or conducting constructions. The possibility of solar storms features an approximately linear relation with the sun spot activity level that fluctuates in eleven years cycle. This paper could be threat examination of GIC in power system and describe the causes, the implications, each on power system apparatus level and on power system level. When GIC flow in neutral of transformer winding it start to causes the Half-cycle core saturation and produce high level of harmonics can sense bad fault situation to protective relays and mis-operation of circuit breakers. Also this paper mentioned potential risk mitigation ways

A novel segmented sampling numerical calculation method for grounding parameters in horizontally multilayered soil

The grounding devices guarantee the safe and stable operation of the power system and electrical apparatus. The accurate calculation of grounding parameters lays the theoretical basis for the design and maintenance of grounding devices. The existing calculation methods for grounding parameters in layered soils are mainly based on the complex image method with global sampling. On the one hand, the global sampling method cannot accurately approximate the integral kernel of Green’s function in complicated horizontally layered soils with many thick layers, which would cause large calculation errors or divergent results. On the other hand, the number of complex images is often twice the number of soil layers, which would cause the calculation amount blindly increases linearly with the number of soil layers. To solve the above disadvantages, this paper proposes a novel segmented sampling numerical calculation method (SSNCM) for grounding parameters in horizontally layered soils. The segmented sampling calculation method of Green’s function based on the extreme points of the integral kernel function of Green’s function in layered soils and the unequal potential calculation method for grounding devices in layered soils are studied to form the SSNCM. The cases study on 3 typical grounding devices are calculated by the SSNCM and the software CDEGS. The results show that the SSNCM has better calculation efficiency and adaptability for different layered soils, and can provide a theoretical foundation for grounding parameters analysis and grounding devices design.

Adaptive set point modulation to mitigate transients in power systems

This paper presents an adaptive control strategy to improve the transient response of a stressed power system apparatus. This strategy, based on the set point automatic adjustment with correction-enabled (SPAACE), is an auxiliary control method to enhance the set point tracking of an apparatus. SPAACE modifies the set point of the controllable apparatus using a feedback signal from its output to mitigate transients that can be caused by events such as faults, load variations, and large reference set point changes. In this work, an adaptive version of SPAACE (ASPAACE), which uses an adaptive dead-zone band, adaptive scaling factor, and exponential prediction is introduced. Moreover, this study investigates the relationship between the natural frequency of the system and the prediction horizon of the ASPAACE controller. To demonstrate the performance of ASPAACE, different case studies are presented.

The Study on a New Method for Measurement of Electric Fast Transient Voltage Based on Electric Induction of Metal Slice

Accurate measurement of electric fast transient (EFT) voltage is very important for insulation design and fault analysis of electric apparatus. In this article, a new simple method for EFT voltage measurement is proposed. Based on the linearity between EFT voltage and electric field intensity on the surface of electrode, the principle of the method is introduced and the corresponding equivalent circuit is built. By using finite-element method (FEM), the capacitances are computed and the relationship between output and input voltages is simulated when we apply Laplace transformation. Experiment model with coaxial structure for verification of the proposed method is built. Based on this model, experiment is conducted. According to the equivalent circuit, by using measured voltage, the parameters of capacitances is also calculated, and they are good coincident with those computed by FEM. The calibration for these capacitances is also done, and their validation is further verified. The proposed method can be used to measure very fast transient overvoltage in gas insulated switchgear and transformer or other apparatus. It can also be used in insulation design and fault location for electric apparatus in power system.

Temperature Measuring-Based Decision-Making Prognostic Approach in Electric Power Transformers Winding Failures

The electric power transformer is a vital apparatus in power systems, and failure prognostics is significant for the protection of this asset. In addition to the asset damage, its unexpected failure would interrupt power delivery and jeopardize the stability of the system. There are several fault diagnosis methods introduced for the detection of this kind of fault; however, their functionality is for the postfault condition when the asset is already damaged, and the operation of the system is interrupted. Electric insulation deteriorations make the transformers susceptive to faults due to thermal and electrical stresses. In this article, the impact of early stages insulation deteriorations on the temperature inside the transformer is studied using a finite-element electromagnetic–thermofluid method and based on the observations an online sensor-based decision-making predictive fault diagnosis approach is proposed. Finally, the results are experimentally verified.

Review of Wildfire Management Techniques—Part II: Urgent Call for Investment in Research and Development of Preventative Solutions

In this part of the paper (Part II), available technical solutions to minimize or prevent wildfires caused by power networks are reviewed in more detail. These methods include fundamental changes to power system equipment, periodic checkups and maintenance, identification of faults via voltage/current waveforms, changes to protection and relaying settings and coordination, and installation of new power system apparatus. The strengths and drawbacks of each method are discussed. The discussion section brainstorms some future possible solutions that smart-grid technologies can enable. The paper concludes that there has neither been enough research in universities nor enough investment by industry to develop viable preventive solutions for wildfires that initiate from the daily operation of electrical power grids. This, in the authors’ opinion, is the crucial time for investment in research and development to tackle the lethal wildfire problem while electric power networks offer “the lowest hanging fruits to pick.”

Application of high-temperature superconducting small current limiting against over-current in low-noise amplifier electronic circuit

High temperature superconducting (HTS) materials have been employed in fabricating the fault current limiters, and they are regarded as the ideal fault current limiting apparatus in power system to make up for the capacity deficiency of the circuit breaker. The grade of the fault current in power system is higher, so the HTS-fault current limiters are mainly manufactured by the HTS tapes. Meanwhile, HTS-thin film is also deployed as the current limiting devices, but the rated current of single piece is not enough to limit the fault current in power system. Thus such current grade of the thin film could suit for the protection of Low-noise amplifier (LNA) electronic circuit. Since LNA is the most vulnerable element of the radio frequency (RF) front end (the rated current of it is smaller), and the function of the RF front end will be destroyed after the LNA is damaged. The protection method based on HTS small current limiting (SCL) on the LNA electronic circuit against the over-current is proposed in this paper. A group of preliminary contrastive experiments carried out in our laboratory to test the protective effect of the proposed protection method on LNA electronic circuit. It is found that this protective method based on HTSSCL can operate as expected and the LNA electronic circuit can also be protected well.

A review of fault ride through of PV and wind renewable energies in grid codes

This paper presents a comprehensive review of fault ride through (FRT) in the grid code of 38 selected countries with an emphasis on renewable energy (REN) sources–related rules. Grid codes are the rules legislated usually by the transmission system operators (TSOs) to determine the grid integration requirements of electrical power generators. Each country establishes its grid code for satisfying the minimum required technical criteria and revises it frequently to cope with new modifications of the utility. Growing the penetration of REN sources have influenced many operational aspects of the power system such as protection, power quality, reliability, and stability. Thereupon, regulations must ensure the power system's secure and controllable operation of REN sources. FRT is one of the main parts of the grid code, and its characteristics affect the performance and rating of power system apparatus. FRT defines the performance of electric power generators during and in postfault conditions. FRT of solar photovoltaic (PV) and wind turbines (WTs) as the main REN sources of energy has great importance in the grid codes. In this paper, a comparison of FRTs in the grid code of 38 countries, including low-voltage ride through (LVRT), zero-voltage ride through (ZVRT), and high-voltage ride through (HVRT) are provided and surveyed.

Gas Sensing Performances of ZnO Hierarchical Structures for Detecting Dissolved Gases in Transformer Oil: A Mini Review.

Power transformer is one of the critical and expensive apparatus in high voltage power system. Hence, using highly efficient gas sensors to real-time monitor the fault characteristic gases dissolved in transformer oil is in pressing need to ensure the smooth functionalization of the power system. Till date, as a semiconductor metal oxide, zinc oxide (ZnO) is considered as the promising resistive-type gas sensing material. However, the elevated operating temperature, slow response, poor selectivity and stability limit its extensive applications in the field of dissolved gases monitoring. In this respect, rigorous efforts have been made to offset the above-mentioned shortcomings by multiple strategies. In this review, we first introduce the various ZnO hierarchical structures which possess high surface areas and less aggregation, as well as their corresponding gas sensing performances. Then, the primary parameters (sensitivity, selectivity and stability) which affect the performances of ZnO hierarchical structures based gas sensors are discussed in detail. Much more attention is particularly paid to the improvement strategies of enhancing these parameters, mainly including surface modification, additive doping and ultraviolet (UV) light activation. We finally review gas sensing mechanism of ZnO hierarchical structure based gas sensor. Such a detailed study may open up an avenue to fabricate sensor which achieve high sensitivity, good selectivity and long-term stability, making it a promising candidate for transformer oil monitor.

Applications of Digital-Physical Hybrid Real-Time Simulation Platform in Power Systems

Digital-physical hybrid real-time simulation (hybrid simulation) platform integrates the advantages of both digital simulation and physical simulation by combining the physical simulation laboratory and the real-time digital simulator. Based on a 400 V/50 kVA hybrid simulation platform with 500 kVA short-circuit capacity, the hybrid simulation methodology and a Hausdorff distance based accuracy evaluation method are proposed. The case validation of power system fault recurrence is performed through this platform, and the stability and accuracy are further validated by comparing the hybrid simulation waveform and field-recorded waveform and by evaluating the accuracy with the proposed error index. Two typical application scenarios in power systems are studied subsequently. The static var generator testing shows the hybrid simulation platform can provide system-level testing conditions for power electronics equipment conveniently. The low-voltage ride through standard testing of a photovoltaic inverter indicates that the hybrid simulation platform can be also used for voltage standard testing for various power system apparatus with low cost. With this hybrid simulation platform, the power system simulation and equipment testing can be implemented with many advantages, such as short period of modelling, flexible modification of parameter and network, low cost, and low risk. Based on this powerful tool platform, there will be more application scenarios in future power systems.

A New Leakage Flux-Based Technique for Turn-to-Turn Fault Protection and Faulty Region Identification in Transformers

Power transformer, as one of the most important apparatus in power system, must be protected against the turn-to-turn faults. Although the various methods based on the terminal currents and/or voltages have been presented for transformer protection, the flux-based methods can be used to achieve the more accurate, sensitive, and secure results. Since the symmetrical form of the magnetic flux distribution will be disturbed due to any fault occurrence in the transformer windings, it can be considered as an appropriate criterion to achieve a suitable protection algorithm, which can detect the fault occurrence and identify the faulty phase/region. In this paper, a new leakage flux sensor is introduced and then a flux-based technique is proposed to detect and identify the faulty phase in transformers to apply in online conditions. By using the proposed technique, the faulty region can be identified in offline conditions, as well. The experimental results (which are done on a distribution transformer) show that this technique is secure in the face of overfluxing and transformer energizing conditions and can detect turn-to-turn faults with high sensitivity. Moreover, tap changer operation, imbalanced loads, and/or unsymmetrical voltage sources cannot influence the proposed technique security.

Estimation of corona location from audible noise

Electrical discharges on electrical insulation, though they do not have an immediate effect, could be very hazardous in power systems over time. For that reason, before taking power system apparatus in use, the possible discharges should be identified. In this study, a neural network is configured to determine the exact location of corona discharges by using the sound recordings of audible corona discharge. For the experiment, corona was intentionally produced by placing an x-shaped string on a relatively smooth high-voltage line model. The x-shaped string generates a sharp point on the wire and that results in high stress concentration on this x-shaped string. Obtaining localized high stress on the x-shaped string ensures that a corona starts on the string before anywhere else on the wire and location of the corona can be controlled for data collection. Corona sound samples and corresponding x-shaped string coordinates are applied to a neural network in which sound information forms the input data and coordinates were the output data. Network was configured so that corona location can be estimated by using only 1 s of a recording per discharge. Results show that it is possible to use this method to estimate the location of corona with around 5% error.

Improved low‐frequency transformer model based on Jiles–Atherton hysteresis theory

Transformers are the most widely used apparatus in power systems to transfer electrical energy from one side to another. Despite remarkable achievements in transformer modelling over the past few years, three-phase transformer modelling techniques have not progressed to that of their single-phase counterparts, mainly because of topological correctness of core and coil structure, complicated interaction between fluxes of the three iron core legs, and non-linear saturation of ferromagnetic material. An improved three-phase transformer model with extended inverse Jiles-Atherton (JA) hysteresis theory is proposed in this study. The extended inverse JA model with anisotropic anhysteretic magnetisation function is addressed, and the classical eddy-current-loss term and anomalous-loss term are directly incorporated into the original energy balance equation to represent the non-linearity and iron core losses rather than representing them with a parallel combination of resistances and saturable inductances (R//L model) as most previous studies have done. The results of inrush current case indicate that the proposed transformer model can predict the residual flux, include eddy-current-loss and anomalous-loss, and predict the inrush current peak values with relative error less than 6%.

A new wavelet network based method to estimate the lightning-related risk of failure of power system apparatus

Abstract This paper proposes a new and fast wavelet network based method for estimating the risk of failure caused by lightning overvoltages in arrester protected networks. First, failure risks obtained by simulations are used as the training data for training the wavelet network. The trained wavelet network is then used for accurate and fast estimating of the lightning-related risk of failure of power system apparatus for all possible conditions. The accuracy of the proposed method has been tested and verified under various conditions in the 230 kV network of Sistan–Baluchestan. Performance of the new method has also been compared with several existing methods under same conditions, and the test results show better accuracy of the proposed method. The proposed method not only does not have the restriction of conventional methods, but also it does not have the limitations associated with traditional neural networks based algorithms such as convergence to local optimum points, over-fit and/or under-fit problems. The main contribution of the paper is an accurate (due to proper selection of the training data set based on the k-fold cross validation technique and using wavelet network for estimation), fast (mean calculation time for the network risk of failure computation is 54 s) and simple wavelet network-based algorithm (as compared to the conventional algorithms) for estimating the lightning-related risk of failure of power system apparatus.

Modeling method of fast transient for unsymmetrical stray capacitance to ground

Transient characteristic of power system apparatus in a high‐frequency region should be modeled with stray capacitors. Pi‐type circuit is commonly used to represent the stray capacitors between terminals and those to the ground. A modeling method for the pi‐type circuit with unsymmetrical stray capacitances to ground is proposed in this paper. To obtain the unsymmetrical stray capacitances to ground, a couple of differential‐mode measurements are interchangeably applied. The parameters of the pi‐type circuit can be determined by the measurements with a common‐mode measurement. A nonlinear least‐squares method is used to estimate the capacitances. The method is applied to compose an equivalent circuit of a miniature circuit breaker (MCB), which has unsymmetrical stray capacitances to ground. The application is not only for the MCB but also for a scaled model of a high‐voltage circuit breaker. A gas‐filled arrester is used as a voltage sensor for the test because the voltage across the stray capacitor cannot be directly measured due to the input capacitance of a voltage probe. A transient response of the MCB with the gas‐filled arresters is numerically simulated to show the usefulness of the equivalent circuit. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.