hysteresis in magnetism (electromagnetism)

This paper investigates the operation and protection issues on distribution systems with high penetration of residential PV systems. Residential PV systems represent small scale resources and therefore they have different impacts on a distribution circuit than larger scale resources. The paper considers a typical residential distribution system and shows that determining the fault current profile and voltage variations on such systems becomes more challenging. However, the impacts on system protection and voltage variation are not severe on such systems, and thus, high level penetration can be accommodated provided that proper revisions are made to the protection and voltage control schemes.

Accommodating High PV Penetration on Distribution Feeders

Photovoltaic power generation is growing at a rapid rate. Most new PV installations are grid-connected small-scale system. The impact of these installations on the grid operation need to be carefully studied to investigated. This paper presents the development of simulation tools required for such interconnection studies. The simulation tools were developed in the popular electromagnetic transient simulation program PSCAD/EMTDC and include a PV array model, maximum power point tracking controller model, and a grid connected inverter. An example of an interconnection study using the developed simulation tools is presented.

Simulation tools for photovoltaic system grid integration studies

The modeling of inrush currents that occur upon energization of a transformer is a challenge for Electromagnetic Transients Programs due to limitations in available transformer models and the ability to determine and specify initial flux. The estimation of transformer model parameters is also an issue. This paper presents a transformer model for low- and mid-frequency transient studies with a focus on the behavior in saturation and the estimation of residual fluxes. The comparison of the simulation results with analytical calculations and measurements proves the capability of the model to accurately represent energization and de-energization transients of a three-legged-core distribution transformer. A novel property is the ability of auto initialization after disconnection, made possible by the implementation of a hysteretic core model which properly simulates and remembers residual flux from the previous de-energization. Special attention is paid to parameter estimation. Detailed core and winding design data are not used as they are seldom available from the manufacturer. Sensitivity analysis is performed to verify the influence of each parameter on the inrush current envelope curve. It is observed that the parameter that most influences the current amplitude is the slope of the magnetization curve at extreme saturation.

Transformer Model for Inrush Current Calculations: Simulations, Measurements and Sensitivity Analysis

Although the adverse effects of using power electronic conversion on the insulation systems used in different apparatuses have been investigated, they are limited to low slew rates and repetitions. These results cannot be used for next-generation wide bandgap (WBG)-based conversion systems targeted to be fast (with a dv/dt up to 100 kV/ws) and operate at a high switching frequency up to 500 kHz. Frequency and slew rate are two of the most important factors of a voltage pulse, influencing the level of degradation of the insulation systems that are exposed to such voltage pulses. The paper reviews challenges concerning insulation degradation when benefitting from WBG-based conversion systems with the mentioned dv/dt and switching frequency values and identifies technical gaps and future research needs. The paper provides a framework for future research in dielectrics and electrical insulation design for systems under fast, repetitive voltage pluses originated by WBG-based conversion systems.

Accelerated insulation aging due to fast, repetitive voltages: A review identifying challenges and future research needs

In this paper, a three-phase transformer model is developed to be suitable for slow transient and power-quality studies. The proposed model takes into account the eddy currents, the magnetic core topology, and the nonlinear characteristics of the core material. In order to model the eddy currents effects in the magnetic core, Bertotti's work for the eddy currents is used and nonlinear resistors dependent on the magnetic core topology are proposed. A systematic procedure is developed for the determination of the incremental self and mutual inductances of the windings. The nonlinear characteristics of the core material are represented either by a magnetization curve or by a hysteresis loop. The hysteresis loop is introduced either by the mathematical model proposed by Tellinen or by the macroscopic model presented by Jiles-Atherton. Simulations results are compared to published measurements in order to verify the proposed model.

Three-Phase Transformer Model Including Magnetic Hysteresis and Eddy Currents Effects

In this paper, the prestrike and the restrike effects during switching a vacuum circuit breaker (VCB) connected to a dry-type foil-winding transformer are theoretically and experimentally analyzed. The analysis is conducted by performing a wide range of experimental three-phase switching on/off tests for a 3.75-MVA prototype test transformer connected to a VCB by a cable with different lengths and for different loading conditions. A refined transformer model is successfully applied for the computation of the voltage distribution along the transformer windings. In particular, the winding properties are separately investigated, for which the core influence for frequencies above some tens of kilohertz is studied, and the terminal impedance variation for a broad frequency range is accurately calculated. The simulated results are excellent. Based on these results, an analysis was performed to evaluate the severity of the switching operations by applying spectral analysis of the recorded signals. The statistical analysis of the overvoltages with respect to the cable length and the load value shows that long cables do not guarantee lower overvoltages because of the load and its interaction with the system that makes each case unique.

Analysis of Switching Effects of Vacuum Circuit Breaker on Dry-Type Foil-Winding Transformers Validated by Experiments

In this paper, a single-phase core-type and shell-type transformer model is proposed on the level of state equations. The magnetic hysteresis and the eddy currents effects are successfully included based on the analytical description of the magnetic core topology. Predicted values from simulations are in very good agreement with published measurements and hence, the developed transformer model is a powerful tool for transient and steady-state studies.

Single-phase transformer model including magnetic hysteresis and eddy currents

Social considerations for a sustainable future lead to market demands for electromobility. Hence, electrical power distribution operators are concerned about the real ongoing problem of the electrification of the transport sector. In this regard, the paper aims to investigate the large-scale integration of electric vehicles in a Swedish distribution network. To this end, the integration pattern is taken into consideration as appears in the literature for other countries and applies to the Swedish culture. Moreover, different charging power levels including smart charging techniques are examined for several percentages of electric vehicles penetration. Industrial simulation tools proven for their accuracy are used for the study. The results indicate that the grid can manage about 50% electric vehicles penetration at its current capacity. This percentage decreases when higher charging power levels apply, while the transformers appear overloaded in many cases. The investigation of alternatives to increase the grid’s capabilities reveal that smart techniques are comparable to the conventional re-dimension of the grid. At present, the increased integration of electric vehicles is manageable by implementing a combination of smart gird and upgrade investments in comparison to technically expensive alternatives based on grid digitalization and algorithms that need to be further confirmed for their reliability for power sharing and energy management.

Investigation of the Impact of Large-Scale Integration of Electric Vehicles for a Swedish Distribution Network

The goal of this work is to develop an efficient numerical model of foil-type windings. An equivalent lumped-parameter circuit model is presented, which is suitable for the computation of the terminal impedance within a broad frequency range and for internal voltage propagation studies. Owing to the special geometrical winding shape, particular attention has been paid to the calculation of the involved lumped parameters where efficient and accurate formulas for parameter determination are presented. The core influence is investigated for the broad frequency range by taking into account the frequency dependency of core material properties. Simulated results compared to measurements show that the proposed equivalent circuit in combination with the applied formulas for parameter determination can be used with full success for the computation of the terminal impedance and internal voltage distribution studies.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-epa.2014.0135

Andreas Theocharis

Papers

Three-Phase Transformer Model Including Magnetic Hysteresis and Eddy Currents Effects

Analysis of Switching Effects of Vacuum Circuit Breaker on Dry-Type Foil-Winding Transformers Validated by Experiments

Single-phase transformer model including magnetic hysteresis and eddy currents

Investigation of the Impact of Large-Scale Integration of Electric Vehicles for a Swedish Distribution Network

Modelling of foil-type transformer windings for computation of terminal impedance and internal voltage propagation