Power Transformer System Research Articles

Overvoltages on power filters under energizing industrial power system transformer

The practice of operating industrial power supply systems containing filter circuits has shown that filter tuning can have a significant impact on filter performance. On the basis of simulations of a real power supply system carried out by the Matlab / Simulink package, the results of a study of the impact of filter manufacturing tolerances on the filter transients under transformer energizing are presented. The most severe transients are observed for filter circuits in the power supply systems of electric arc furnaces due to frequently repeated operating energizing furnace transformers. This article summarizes the analysis of overvoltages on capacitors and reactors for various configurations of the filter circuit, arising during energizing the arc furnace transformer, taking into account the possible detuning of the filters.

Sizing power transformers in power systems planning using thermal rating

It has already been shown in the literature that power transformers may be more accurately sized by their thermal limits than by their rated power limit. In practice however, thermal limits are usually considered only in operations; but not at planning stage, where the more usual notion of rated power is used. This paper proposes a novel method to take into account (and benefit from) thermal limits directly at planning stage. This is made possible by quantifying separately the impact of each generator and load on the temperature of the distribution transformer. Decoupling the effect of individual generators and loads is achieved by linearizing and rewriting the analytical expression of the hot-spot transformer temperature. The practical value of the method is assessed using a real-world dataset, by estimating the increase in the hosting capacity of the considered transformer for additional generators and loads. Significant gains are obtained when the transformer is sized by generation, in particular when photovoltaic (PV) generators are involved.

Comparison study between SVPWM and FSVPWM strategy in fuzzy second order sliding mode control of a DFIG-based wind turbine

AbstractIn this work, we present a new fuzzy second-order sliding mode controller (FSOSMC) for wind power transformation system based on a doubly-fed induction generator (DFIG) using intelligent space vector pulse width modulation (SVPWM). The proposed command strategy combines a fuzzy logic and a second order sliding mode control (SOSMC) for the DFIG command. This strategy presents attractive features such as chattering-free, compared to the conventional first and second order sliding mode techniques. The use of this method provides very satisfactory performance for the DFIG command. The effectiveness of this command strategy is proven through the simulation results.

Mitigation of Inrush Current in Three Phase Power Transformer by Prefluxing Technique

Transformers are major component for electrical energy transfer in power system. Sta¬bility and security of the transformer protection are important to system operation. At the time of transformer energization, a high current will be drawn by the transformer. The mentioned current is called transient inrush current and it may rise to ten times the nominal full load current of transformer during operation. Energization transients can produce me-chanical stress to the transformer, cause protection system malfunction and it often affects the power system quality and may disrupt the operation of sensitive electrical loads such as computers and medical equipment connected to the system. Re¬duction and the way to control of energization transient currents have become im-portant concerns to the power industry for engineers. One of the methods to reduce inrush current is use of point on wave switching at the time transformer is initially connected to supply. It is called controlled switching or point-on-wave switching. In the point on wave switching, the energization of three phases is controlled ac-cording to the residual flux which remains in the transformer. Conven¬tionally, controlled switching or point on wave switching was the method being used to counter this problem, but this method required the knowledge of residual fluxes of transformer before energization which is quite tedious to get. So a technique has been pro-posed to mitigate inrush current in three phase transformer, by a process called pre-fluxing. After setting the in-itial fluxes of transformer it is energized by conventional controlled switching. A system of power transformer of specified rating is simulated in MATLAB simulink and results were obtained. This Paper describes the mod-eling of inrush current of 3- phase, 300 MVA, 11/400 KV, 50 Hz transformer, and mitigation of inrush current with both techniques using point on wave switching and prefluxing. The simulation is done in MATLAB..

Determination of maximum level of EV penetration with consideration of EV charging load and harmonic currents

In order to accommodate Electric Vehicles (EVs) charging demand which is expected to rise steeply in the coming years due to environmental concerns on global warming, it is important to determine the maximum EV penetration can be allowed without network upgrading and avoid overloading of Medium Voltage (MV) cables and distribution transformers in residential distribution power systems. Previous work on modelling and analysis of relationship between the temperature of MV cables and transformer with EV penetration level failed to consider the contribution of harmonic distortion in the demand. In this paper, a methodology is proposed to model the EV penetration and their effects on operational temperature of MV cables and transformers, with charging scenarios and harmonic currents taken into consideration. The method is simulated in a typical urban residential distribution system. The results show that EV penetration above 27.25 % with 6.6 kW EV chargers charging in uncontrolled domestic scenario will lead to 10 kV 400 mm2 three core cable overloading in the simulation with harmonic current taken into consideration. The result is 30.74 % if harmonic currents are ignored. The maximum allowable EV penetration of 35/10 kV 16 MVA and 10 kV 1250 kVA transformer is 50.22% and 26.19% respectively. If EVs charge in off-peak time, the cable and transformer can avoid overloading and the charging cost is lower.

Vulnerability Assessment of Korean Electric Power Systems to Late-Time (E3) High-Altitude Electromagnetic Pulses

High-altitude electromagnetic pulses (HEMPs) are bursts of electromagnetic energy that result from nuclear weapon detonations at altitudes at or above 30 km. A HEMP is comprised of three components: E1, E2, and E3. E1 and E2 are instantaneous emissions that can damage electronic components, whereas E3 generates low-frequency, geomagnetically-induced currents in transmission lines and power transformers. These currents can lead to the half-cycle saturation of power transformers and increased reactive power consumption. This study assessed the impact of the E3 HEMP on Korean electric power systems. For this assessment, two publicly available E3 HEMP environments were identified. A Direct Current (DC)equivalent model of Korean power systems was developed to calculate the geomagnetically-induced currents and increased the reactive power absorption of transformers in power systems. The vulnerability assessment involved two types of analysis: Static power flow analysis and dynamic transient stability analysis. The maximum electric field limit was determined by performing a steady-state analysis. The capability of the Korean electric power systems to maintain synchronism and acceptable voltages in the transient stability time frame following an E3 HEMP event was evaluated. Furthermore, the effects of detonations at five target locations were compared. It was concluded that Korean electric power systems cannot maintain their stability when affected by an E3 HEMP.

Investigation of The DGs Effect on The Coordination Between Protective Elements in Distribution Network

Addition of Distributed Generators (DGs) to the electric network have more advantages to the network. It improves the voltage profile and the power flow in the network. In the last decade, DGs is used in power system, especially the distribution system. Coordination study for protective devices must be performed on the distribution network with DGs to reach selectivity with minimum clearance time of fault. Due to DG insertion to the electric system, the short circuit level is changed and coordination between protective elements should be done. This paper presents a technique to avoid the miscoordination problem between protective devices due to the impact of DG units insertion without any additional costs. The proposed technique depend on activating and updating the setting of network relays to achieve correct coordination. Also, it doesn't need any additional costs or any additional equipement to be installed in the electric network. This paper make studies on a real radial system of power transformer with its feeders of a 66kV utility substation before and after adding DGs. ETAP software is used to simulate the network under study.

Effects of Moisture on Furfural Partitioning in Oil-Paper Insulation System and Aging Assessment of Power Transformers

The furfural concentration in oil is a well-accepted chemical marker indicating the aging condition of power transformers. However, recent researches suggest that the furfural concentration in oil is affected by moisture, because moisture influences the furfural partitioning ratio in oil-paper insulation system. In this study, the correlation of moisture and furfural partitioning ratio was investigated. The accelerated thermal aging test and moisture absorption test were conducted to prepare oil-paper samples with different furfural and moisture concentrations. For samples with different moisture concentrations, the furfural partitioning ratios between oil and paper were compared. Results showed that samples with high humidity exhibited a high furfural mass fraction in oil. This finding implied that high humidity promoted the furfural diffusion from paper to oil. Further, the interference of moisture on aging assessment of insulation paper was analyzed. Results showed that the increase of moisture concentration in oil-paper system would significantly affect the accuracy of insulation paper aging assessment. A corrected equation for aging assessment of insulation paper with different moisture concentrations was established. Verification result showed that the equation could effectively correct the interference of moisture and enhance the accuracy of the aging assessment of insulation paper.

Damage assessment of transformer Kraft paper insulation aged in mineral and vegetable oils

Most high-voltage transformers are fluid filled machines whose insulation system is constituted of dielectric oil–solid combination. The insulation oil generally used is mineral oil, however, this fluid has started to be substituted by natural and synthetic esters due to their higher biodegradability and flash point in comparison with mineral oil. The introduction of a new fluid in the insulation system of power transformers requires kinetic models which can estimate the degradation rate of insulation solids, taking into account the properties of the new materials. The aim of this work is to go further in demonstrating that a kinetic model based on damage parameter can be used as a cellulose degradation model for Kraft paper, which is one of the solid materials used in the insulation system of oil-filled transformers. The ageing study has been extended to Kraft specimens immersed in two different oils (mineral and natural ester). The kinetic model that best tracks the ageing patterns was shown to be a function of damage parameter estimated through the energy consumed per unit volume of the failure zone (ER) in comparison with other mechanical properties such as rupture strength (σR) or strain under ultimate strength (ecm). Finally, an assessment of the effect of end-of-life criteria on correlation coefficient was carried out, providing further evidence that this criteria established until now (25% retained tensile strength) should be discussed in order to obtain more accurate kinetic models.

Study on Characteristic Parameters of Short-Circuit Impedance for a Four-Winding Inductive Filtering Transformer in Power System Supplying Nonlinear Loads

Different from a three-winding transformer and ac passive filtering method, this paper proposes an inductive filtering (IF) method with a four-winding inductive filtering transformer (FW-IFT) for power system supplying nonlinear loads. Based on this, the characteristic parameters of the short-circuit impedance for the FW-IFT are studied in detail by theoretical analysis and experimental verification. According to the single-phase equivalent circuit, the voltage equations of the FW-IFT are established at the fundamental and harmonic frequencies. By short-circuit test, the constraint condition of the inductive filtering is obtained, which can satisfy the demand of nonlinear loads in power system. Then, the influences of the filter impedance on characteristic parameter of the short-circuit impedance are analyzed and calculated. The detailed theoretical calculation and the experimental results verified the feasibility and correctness of the aforementioned theoretical analysis and calculation.

Stakeholder Management: An Approach in CCS Projects

Currently, a prime position in the global emission mitigation and power transformation system is taken up by CCS technology (carbon capture and storage), proven by the successful realization of a number of CCS projects around the world, not only for CO2 storage, but also for its deployment in industry. CO2-utilizing technologies are circular business models connected with the usage of emissions to provide added benefits throughout the value chain, with their value being part of a response to end the era of cheap mineral resources and materials, as well as their ability to contribute to the transition to a low carbon economy. At the same time, one of the main problems they face lies in the engagement and interaction of stakeholders, as well as public perception of these projects. The purpose of this research is to explore the main stakeholder groups in CCS projects and offer an approach for their management. The methodology of this study is based on case studies, stakeholder management tools, and a checklist method, which were adapted to the specific area of CCS projects. The results of this study amounted to the identification of stakeholder groups with interests and respective roles in CCS projects, as well as proposing a new approach for their assessment through the created checklist method.

Fibre Bragg Grating sensing based temperature monitoring system of power transformer

Fibre Bragg Grating sensing based temperature monitoring system of power transformer

Detection of moisture content in transformer oil using platinum coated on D-shaped optical fiber

The presence of moistures in transformer deteriorates transformer insulation. These effects decrease both electrical and mechanical strength of the transformer. Water in transformer oil also brings the risk of bubble formation when desorption of water increases the local concentration of gases in the oil. The water content in the insulating oil (or transformer oil) needs to be less than 10 ppm at normal temperature or contradictory, it will affect the efficiency of the power transformer system. Here, we report a D-shaped optical fiber sensor coated with a platinum thin layer with a thickness of 25 nm was designed to detect the response of transverse electric field (TE) power towards the content of moisture in the insulating oil. A Simulative based investigation using COMSOL Multiphysics has also been carried out to study the relation between analyte on the materials at different refractive index and the simulation study follows the finite element method (FEM). Four samples of aged oil were tested from actual transformer oil with different values of water contents of 15 ppm, 16 ppm, 18 ppm, and 21 ppm. The oil samples were dropped on the sensing region of the fiber and resulting in the drop of TE power from the initial value. It was observed that higher values of water percentages in the oil caused large fluctuations in TE power. On top of that, the changes in TE power show that the sensor is having fast response and good sensitivity.

Effectiveness of Superconducting Fault Current Limiting Transformers in Power Systems

Superconducting devices have emerged in many applications during the last few decades. They offer many advantages, including high efficiency, compact size, and superior performance. However, the main drawback of these devices is the high cost. An option to reduce the high cost and improve the cost-benefit ratio is to integrate two functions into one device. This paper presents the superconducting fault current limiting transformer (SFCLT) as a superior alternative to normal power transformers. The transformer has superconducting windings and also provides fault current limiting capability to reduce high fault currents. The SFCLT is tested in two power system models: a 7 bus wind farm-based model simulated in PSCAD and on the 80 bus simplified Australian power system model simulated in real-time digital simulator. Various conditions were studied to investigate the effectiveness of the fault current limiting transformer.

New Identification Method for Power Transformer and Phase in Distribution Systems

In city, identification for 3 phase-4 wires power distribution lines is difficult due to compound installation of overhead and underground lines, transposition, bad view caused by trees or big buildings. It is necessary that the correct and fast identification method is required for load balancing among distribution lines. Tracing off-line method with high power impulse signal injection has been used recently. Our proposed method uses to identify live lines with very small power high frequency signal injection based on data communication technology. Two end communication terminals are required to be synchronized between them for determination on electrically same phases. Challenging issue is to achieve synchronization without GPS providing synchronizing time. A novel power transformer and phase identification system is designed and implemented. The system consists of a transmitter and a receiver with power-line communication module. Some experiments are conducted to verify the theoretical concepts in a big commercial building.

Обеспечение безопасных условий эксплуатации силовых трансформаторов при тепловых воздействиях токов коротких замыканий

Introduction. Power transformers are the basic equipment of the industrial power systems. One of the key indicators of determining the service lifetime of the transformer including its performance characteristics is the condition and residual life of its isolation. Aging and f insulation deprecation are directly related to the operating temperature of the transformer in use, as well as to the reliable operation of the cooling system. This research direction is up-to-date, especially when it comes to fully rated power transformers. Materials and Methods . Power transformers of the district substations that feed the industrial and transport enterprises are considered. Modes of power transformers, which are caused by the uneven workload of the phases and short-circuiting, are studied. All these factors lead to the thermal deformation of the power transformer insulation and, as a rule, to the outage of power transformers. Research Results. The forced cooling system of power transformers, which allows increasing their cooling capacity and the cooling fluid volume, is developed by the authors and described in the paper. Thermal calculations of heating design elements of the power transformers are carried out both in the conventional cooling system and the new one. The comparative analysis and calculations have shown the feasibility of the developed cooling system of power transformers, which allows extending the insulation lifetime. The developed cooling system is forced. The authors used a reserve power transformer tank as an additional expander. This design solution can be implemented for transformers operating at low temperatures, as well as under long-term limit loads. Discussion and Conclusions . The developed cooling system eliminates the requirement for purchase costs on extra equipment and maintenance support. It can be used at the enterprise power facilities and in the rail transportation.

Increasing Certainty of Fault Identification in Power Transformers of Power Plants by Setting Parameters for Fuzzy Model

Проблематика. В умовах об’єктивно існуючого зростання аварійності в сучасних електроенергетичних системах унаслідок відмов потужного силового електрообладнання загострюється проблема забезпечення надійності та безпеки функціонування теплових, атомних і гідроелектростанцій. Тому задача розробки адекватних математичних моделей оцінки технічного стану та визначення ризику відмови силових трансформаторів потужних енергоблоків електростанцій є актуальною. Мета дослідження. Метою роботи є удосконалення нечіткої моделі діагностування технічного стану силового трансформатора настроюванням параметрів та визначення ризику відмови за наявності дефекту. Методика реалізації. При розробці математичної моделі силового трансформатора використовувались підходи, що ґрунтуються на теорії нечітких множин, нечіткої логіки, та методи нелінійної оптимізації. Задача визначення ризику відмови силового трансформатора за наявності дефекту розв’язувалась на основі сформованої ієрархії факторів і параметрів впливу на інтегральний показник ризику відмови силового трансформатора. Результати дослідження. Обґрунтовано необхідність комплексного моделювання технічного стану силового трансформатора і режимів електроенергетичної системи. Удосконалено розроблену нечітку модель оцінки технічного стану силового трансформатора завдяки параметричній ідентифікації оптимальних значень функцій належності нечітких термів лінгвістичних змінних параметрів та визначенню ризику відмови силового трансформатора. Висновки. Для оцінки ризику виникнення аварійних ситуацій в електроенергетичних системах при відмовах електрообладнання запропоновано математичну модель визначення ризику відмови силового трансформатора за наявності дефекту.

Gradient Search Technique Applied to Dual-Optimal Design of a 3-Phase Core Type Transformer

Most of the power and distribution transformers in power system are 3-phase core type transformers. They are extensively used- as such their cost is a sizable proportion of the total system cost. Therefore they are to be designed cost-optimally. The optimality is with reference to an objective function, generally in presence of constraints. The design variables are to be varied within their given bounds and the optimal solution is to be reached in finite number of steps, satisfying the given constraints. The paper presents a method for optimizing the design, in presence of constraints specified by the customer and the regulatory authorities, through gradient search technique. The objective function is a weighted combination of the cost of the transformer and the running losses which is not a mathematically framed but obtained from the transformer design sub-routine through computer programme. The objective of this paper is to find out above objective function without mathematically framed function which leads to inaccuracy for approximation due to magnetic saturation and nonlinearity present in the system.Most of the objective function is framed by taking few terms from a polynomial to avoid complicacy of the function, such as core loss expression obtained from curve with the variation of flux densities. The starting point has been chosen within the allowable parameter space- the steepest decent path has been followed for convergence. The step length has been judiciously chosen. The hyper surface has been found to be concave. As such no local minima problem is faced. The method is best as it its convergence is quickest.

Static Headspace GC/MS Method for Determination of Methanol and Ethanol Contents, as the Degradation Markers of Solid Insulation Systems of Power Transformers

Methanol in insulating oil has been proposed as a new marker for condition assessment of the solid insulation system of power transformers. In the current work, as a first step of using the new marker, an analytical static headspace gas chromatography/mass spectrometry method has been developed, optimized, and validated to measure methanol and ethanol contents in the insulating mineral oil. The analyzing setup consists of a 6890 N gas chromatograph equipped with a 5973 network mass spectrometer (MS) in the absence of a costly headspace autosampler, and the chromatography separation was performed on a 60 m × 320 µm × 0.5 µm VF-WAXms GC column. Calibration curves have been provided using several concentrations of the alcohols, and also limit of detection (LOD), limit of quantification (LOQ), and relative standard deviation percentage (RSD%) have been determined.

Outlook on South-East European power system until 2050: Least-cost decarbonization pathway meeting EU mitigation targets

Climate change forces humankind to strong reduction measures for greenhouse gas (GHG) emissions. Following this scientific consensus the European Union obliged it's member states to achieve high reduction targets to almost zero emissions – especially in the power generation sector – until 2050. Evidence-based strategies to implement cost-effective reduction pathways are necessary to achieve these targets. We developed a multi-regional power system model – elesplan-m – to analyze a least-cost decarbonization pathway for Europe with special focus on South-East-Europe (SEE). The analysis seeks for optimal strategies in the power sector while it neglects cross-sectoral demand shifts coming up with the electrification of transport and the use of heat pumps. Results underline both, the possibility and the enormous efforts required to achieve the intended decarbonization. SEE needs to increase its photovoltaic capacity to 120.7 GW, wind power capacity to 92.4 GW and transmission capacities to neighboring countries to 32.7 GW until 2050 to achieve the GHG emission reduction targets. The power system transformation requires annual average investments of almost one billion EUR in SEE. Resulting levelized cost of power supply of this region adds up to 12.1 ctEUR/kWh.