Once again about the Steinmetz transformer model and the ongoing subdivision of its leakage inductance

Purpose Despite its well-founded criticism and lack of proper justification under core saturation conditions, the T-equivalent transformer model (Steinmetz scheme) is obviously championing in the literature. This educational paper aims to explain in a simple manner the limitations of the T-model of a low-frequency transformer and critically analyses some attempts to improve it. Design/methodology/approach Using a simplified examination of magnetic fluxes in the core and windings and using the modeling in ATPDraw, it is shown that transient transformer models with the indivisible leakage inductance allow circumventing the drawbacks of the T-model. Findings The authors show the absence of valid grounds for subdividing the leakage inductance of a transformer between its primary and secondary windings. The connection between the use of individual leakage inductances and inaccurate prediction of inrush current peaks is outlined as an important example. Practical implications The presented models can be used either as independent tools or serve as a reference for subsequent developments. Social implications Over generations, the habitual transformer T-equivalent is widely used by engineers and Electromagnetic Transients Program experts with no attention to its inadequacy under core saturation conditions. Having studied typical winding configurations, the authors have shown that neither of them has any relation to the T-equivalent. Originality/value This educational paper will contribute to the correct understanding of the transients occurring in a transformer under abnormal conditions such as inrush current or ferroresonance events, as well as during an out-of-phase synchronization of step-up generator transformers.

Uncertainty Quantification by Monte Carlo Simulation of Lab-Derived Saturation Data from Sponge Cores

Fluid saturation data obtained from core analysis are used as control points for log calibration, saturation modeling and sweep evaluation. These lab-derived data are often viewed as ground-truth values without fundamentally understanding the key limitations of experimental procedures or scrutinizing the accuracy of measured lab data. This paper presents a unique assessment of sponge core data through parameterization, uncertainty analysis and Monte-Carlo modeling of critical variables influencing lab-derived saturation results. This work examines typical lab data and reservoir information that could impact final saturation results in sponge coring. We dissected and analyzed ranges of standard raw data from Dean-Stark and spectrometric analysis (including, gravimetric weights, distilled water volumes, pore volumes and sponge's absorbance), input variables of fluid and rock properties (such as, water salinity, formation volume factors, plug's dimension and stress corrections), governing equations (including, salt correction factors, water density correlations and lab mass balance equations) and other factors (for instance, sources of water salinity, filtrate invasion, bleeding by gas liberation and water evaporation). Based on our investigation, we have identified and statistically parameterized 11 key variables to quantify the uncertainty in lab-derived fluid saturation data in sponge cores. The variables' uncertainties were mapped into continuous distributions and randomly sampled by Monte-Carlo simulation to generate probabilistic saturation models for sponge cores. Simulation results indicate the significance of the water salinity parameter in mixed salinity environments, ranging between 20,000 to 150,000 ppm. This varied range of water salinity produces a wide uncertainty spectrum of core oil saturation in the range of +/- 3 to 10% saturation unit. Consequently, we developed two unique salinity variance models to capture the water salinity effect and minimize the uncertainty in the calculation of core saturation. The first model uses a material balance to solve for the salinity given the distilled water volume and gravimetric weight difference of the sample before and after leaching. The second model iteratively estimates the salinity required to achieve 100% of total fluids saturation at reservoir condition after correcting for the bleeding, stress and water evaporation effects. Our work shows that these derived models of water salinity are consistent with water salinity data from surface and bottomhole samples. Despite the prominence of applications of core saturation data in many aspects of the industry, thorough investigation into its quality and accuracy is usually overlooked. To the best of our knowledge, this is the first paper to present a novel analysis of the uncertainty coupled with Monte-Carlo simulation of lab-derived saturation's data from sponge cores. The modeling approach and results highlighted in this work provide the fundamental framework for modern uncertainty assessment of core data.

Procedure for the Accurate Modelling of Ring Induction Motors

This paper proposes a procedure for the accurate modelling of the ring induction motors (RIMs), based on the Monte Carlo (MC) method and the relations presented in the relevant metrology guidelines. Modelling was carried out based on the measured data for the torque-slip characteristic (TSC) and using the equivalent circuit for the RIM. The parameters included an extended Kloss equation (EKE) and the associated uncertainties were determined using the MC method. The polynomial procedure was applied as a numerical tool to complement the MC method to determine the power losses in the stator iron and the relevant uncertainty. This is in line with international standards for the theory of uncertainty application in the field of engineering. The novelty of this paper refers to the accurate modelling of the RIMs obtained by determining the corresponding uncertainties. The procedure presented in this paper was developed based on the assumption that the parameters of the equivalent circuit are independent of the temperature, influence of core saturation, and the phenomenon of current displacement. Our procedure can be successfully used for both the theoretical calculations related to the modelling of the RIMs, and in practical applications involving detailed measurements and the corresponding uncertainties. The use of the MC method allowed for significant improvement in the modelling results, in terms of both the TSC and EKE.

Detection of the initial region of the current transformer core saturation

In the first part of the paper the detailed analysis of the existing current transformer (CT) saturation detection methods with their classification is presented. A new saturation detection method has been proposed in second part of the paper. Mathematical description of the method is given. In the next section of the paper a CT model with test scheme is presented. To identify the reliability of proposed method against nose and remanent flux density experiments have been produced in the fourth section. Comparative analysis between proposed and existing methods is also given. Finally, in conclusion a detailed description of the method is given regarding its behavior with respect to remanent flux and noise

Residual flux impact in controlled switching of HVDC converter transformer

Converter transformers are an interface point of HVDC frameworks and are basic hardware from activity and reliability view point. Converter transformers are turned off intentionally under planned support and un-deliberately during fault conditions. Random energization of HVDC Converter transformer delivers high inrush currents due to core saturation asymmetries and endanger equipment health. In this paper, charging approach has been proposed. By utilizing point on wave exchanging for moderation of charging drifters during charging of 888 MVA 400/325 kV Converter Transformer of ±800 kV HVDC Sub-station. The proposed procedure has been applied on HVAC electrical Circuit Breaker furnished with Pre-Insertion Resistor considering diverse degree of residual flux. Performance of proposed philosophy has been affirmed by field tests and reproduction in PSCAD programming package and is found very viable. Near investigation is done in this paper and shows that with the use of proposed system, the switching transient during stimulation and field tests of coupled three phase converter transformers is decreased to worthy level.

UNCERTAINTY QUANTIFICATION BY MONTE CARLO SIMULATION OF LAB-DERIVED SATURATION DATA FROM SPONGE CORES

Fluid saturation data obtained from core analysis are used as control points for log calibration, saturation modeling and sweep evaluation. These lab-derived data are often viewed as ground-truth values without fundamentally understanding the key limitations of experimental procedures or scrutinizing the accuracy of measured lab data. This paper presents a unique assessment of sponge core data through parameterization, uncertainty analysis and Monte-Carlo modeling of critical variables influencing lab-derived saturation results. This work examines typical lab data and reservoir information that could impact final saturation results in sponge coring. We dissected and analyzed ranges of standard raw data from Dean-Stark and spectrometric analysis (including, gravimetric weights, distilled water volumes, pore volumes and sponge’s absorbance), input variables of fluid and rock properties (such as, water salinity, formation volume factors, plug’s dimension and stress corrections), governing equations (including, salt correction factors, water density correlations and lab mass balance equations) and other factors (for instance, sources of water salinity, filtrate invasion, bleeding by gas liberation and water evaporation). Based on our investigation, we have identified and statistically parameterized 11 key variables to quantify the uncertainty in lab-derived fluid saturation data in sponge cores. The variables’ uncertainties were mapped into continuous distributions and randomly sampled by Monte-Carlo simulation to generate probabilistic saturation models for sponge cores. Simulation results indicate the significance of the water salinity parameter in mixed salinity environments, ranging between 20,000 to 150,000 ppm. This varied range of water salinity produces a wide uncertainty spectrum of core oil saturation in the range of +/- 3 to 10% saturation unit. Consequently, we developed two unique salinity variance models to capture the water salinity effect and minimize the uncertainty in the calculation of core saturation. The first model uses a material balance to solve for the salinity given the distilled water volume and gravimetric weight difference of the sample before and after leaching. The second model iteratively estimates the salinity required to achieve 100% of total fluids saturation at reservoir condition after correcting for the bleeding, stress and water evaporation effects. Our work shows that these derived models of water salinity are consistent with water salinity data from surface and bottom-hole samples. Despite the prominence of applications of core saturation data in many aspects of the industry, thorough investigation into its quality and accuracy is usually overlooked. To the best of our knowledge, this is the first paper to present a novel analysis of the uncertainty coupled with Monte-Carlo simulation of lab-derived saturation’s data from sponge cores. The modeling approach and results highlighted in this work provide the fundamental framework for modern uncertainty assessment of core data.

Power Efficiency Improvement of a Boost Converter Using a Coupled Inductor with a Fuzzy Logic Controller: Application to a Photovoltaic System

DC/DC converters are widely used in photovoltaic (PV) systems to track the maximum power points (MPP) of a photovoltaic generator (PVG). The variation of solar radiation (G) and PV cells temperature (T) affect the power efficiency of these DC/DC converters because they change the MPP, thus a sizing adaptation of the component values in these DC/DC converters is needed. Power loss in the inductor due to core saturation can severely degrade power efficiency. This paper proposes a new method that allows to adapt the inductor values according to the variable output power of the PV array in order to minimize losses and improve the converter power efficiency. The main idea is to replace the DC/DC inductor with a coupled inductor where the DC/DC inductor value is adjusted through an additional winding in the magnetic core that modulates the magnetic field inside it. Low current intensities from the PVG supply this winding through a circuit controlled by a fuzzy logic controller in order to regulate the second winding current intensity. Experimental results show a significant improvement of the power efficiency of the proposed solution as compared to a conventional converter.

Research of Parameters of Electric Power Systems Affecting Core Saturation of Current Transformers with a Closed Magnetic Circuit in Transitional Short Circuit Modes

The relevance of the study is due to the excess of the permissible errors of current transformers in transient short-circuit modes associated with saturation of the cores of current transformers. The latter leads to improper operation of relay protection devices, which can negatively affect the stability of electric power systems and the efficiency of industrial enterprises with a continuous technological cycle, the power failure of which leads to significant economic damage. The aim of this work is to study the parameters of electric power systems that affect the saturation of the cores of current transformers with a closed magnetic circuit in transient short-circuit modes. The object of research is electromagnetic current transformers of accuracy class 10P in electric power systems. The study was carried out using numerical methods for solving algebraic and differential equations, methods of computer modeling of electromagnetic transient processes and functional programming. As a result, the main parameters influencing the nature and intensity of electromagnetic transients in current transformers during a short circuit are noted; it is shown that in transient short-circuit modes, significant errors in the operation of current transformers associated with core saturation are possible; recommended for assessing the compliance of current transformers of accuracy classes 5P, 10P with the conditions for the correct functioning of relay protection devices in transient short-circuit modes, to calculate the time to saturation of current transformers, taking into account the real parameters of the electric power system at the place where current transformers are installed, in addition to the traditional design checking of current transformers by permissible er-rors for the steady state short circuit.