Core Loss Distribution Research Articles

A Novel Excitation Approach for Power Transformer Simulation Based on Finite Element Analysis

Power transformers play an indispensable component in AC transmission systems. If the operating condition of a power transformer can be accurately predicted before the equipment is operated, it will help transformer manufacturers to design optimized power transformers. In the optimal design of the power transformer, the design value of the magnetic flux density in the core is important, and it affects the efficiency, cost, and life cycle. Therefore, this paper uses the software of ANSYS Maxwell to solve the instantaneous magnetic flux density distribution, core loss distribution, and total iron loss of the iron core based on the finite element method in the time domain. In addition, a new external excitation equation is proposed. The new external excitation equation can improve the accuracy of the simulation results and reduce the simulation time. Finally, the three-phase five-limb transformer is developed, and actually measures the local magnetic flux density and total core loss to verify the feasibility of the proposed finite element method of model and simulation parameters.

Core Loss Calculation of Anode Saturable Reactor in Damping Oscillation State Based on J-A Theory

Anode saturable reactor (ASR) is an important part of the HVDC converter valve. Due to the surge current during the transient processes of thyristors, a sharp increase will occur in core losses and over temperature-rising of the reactor, which may cause premature failure and is difficult to estimate in the design optimization of the reactors. To investigate the single core loss of anode saturable reactor, during such operating conditions, this paper proposes an approach to calculate the core loss from the Jiles-Atherton (J-A) dynamic hysteresis model, which can be applied for various operating conditions with good accuracy. Finally, the model is incorporated into the finite element method (FEM) to investigate the core loss distribution of the iron core during the oscillation process at off-state.

Thermal Design, Optimization, and Packaging of Planar Magnetic Components

This article is focused on the thermal design and three-dimensional (3-D) package optimization of planar magnetic components (PMCs), including transformers and inductors for application in an electric vehicle composite boost dc-dc converter. Each PMC comprises electrical windings in printed circuit board (PCB) form in combination with a ferrite core. Multiple features of each PMC package are thermally optimized for the proposed device configurations with given core size, core loss distribution, number of turns in the PCB winding, winding copper thickness, and winding loss distribution. These heuristically optimized features include a lower level cold plate structure with a conformal base for enhanced convective heat transfer, an upper level PMC cap structure for doubled-sided cooling through conductive heat flow to the cold plate, the implementation of functionally distributed copper thermal and electrothermal vias in the PCB winding for improved cross-plane thermal conductance, and judicious implementation of select materials at various locations and interfaces within the package. Detailed numerical modeling reveals the combined effect of this 3-D packaging strategy with a 79.3 °C and 48.5 °C maximum temperature reduction in the core and PCB winding, respectively, relative to a baseline device configuration. Select PMC experimental validation confirms the expected thermal performance of an optimized PCB design. The thermal design approach is relevant for a range of high-power-density electronics PMC packaging applications.

Magnetic-Thermal Coupling Analysis of Saturable Reactor

As the vital equipment of ultra-high voltage direct current (UHVDC) transmission, the anodic saturable reactor is crucial to the safe operation of converter valve. Based on dynamic core loss model, the eddy current analysis and core loss calculation on saturable reactor are carried out by finite-element method (FEM) simulation software Maxwell. Through the fast-mapping interpolation method between heterogeneous meshes, the core loss is mapped from electromagnetic field to the fluid field by Fluent user-defined functions (UDFs), which makes the distribution of heat source more realistic. The distributions of temperature and velocity of the anodic saturable reactor are obtained by computational fluid dynamics (CFD) simulation software Fluent. The temperature simulation results show that the hottest spots inside the core and on the reactor inner toroidal surface are 117.4 °C and 80.5 °C, respectively. The experimental results demonstrate the validity of the calculation methods of core loss and temperature distribution.

A thermographic camera method for measuring the core loss distribution

Motor core losses are usually evaluated as the total loss minus known losses, including copper and mechanical losses. However, it is difficult to identify the main cause of core losses based on this evaluation method. In our previous study, we proposed a method for directly evaluating core loss distribution based on heat measurements using a thermographic camera. In this paper, we examine the reliability of thermal measurements using a device that can simultaneously measure core loss both by the general magnetic method and by the thermal measurement method. In the comparison method, the magnetic loss and thermal measurements are conducted simultaneously using an open magnetic path single sheet tester that permits simultaneous direct imaging of a sample with a thermographic camera, and the core loss values are compared and examined. We demonstrate a good agreement between the thermal and magnetic measurement below 10% difference for flux densities higher than 1T.

An adjustable degrees-of-freedom numerical method for computing the temperature distribution of electrical devices

A novel adjustable degrees-of-freedom numerical method for computing the temperature distribution of electrical devices is presented. The proposed method provides a convenient, accurate and efficient approach to increase/reduce variables and couple/decouple variables. In traditional finite element method (FEM), the electromagnetic field and thermal field need different FEM meshes, which reduce the efficiency and accuracy of the field coupling. Also, the traditional method introduces the inevitable error when the power loss is plotted from Maxwell to Fluent as the different meshes are employed. In this paper, the greatest advantage is that the electromagnetic field and thermal field can be computed using a single mesh with the proposed technology of exploiting different constrained degrees-of-freedom, which decreases the computation time and system complexity. The global domain divided into several sub-domains were utilizing various corresponding functions and also employed to reduce the computational burden when calculating the core loss, copper loss, stray loss and temperature distribution. Numerical examples are reported to showcase the accuracy and effectiveness of the proposed method.

Core Loss Calculation Based on Finite-Element Method With Jiles–Atherton Dynamic Hysteresis Model

For accurate computation of core losses, the Jiles–Atherton ( $J$ – $A$ ) dynamic hysteresis model accounting for hysteresis, eddy current and excess losses is incorporated into the finite-element method (FEM). The $J$ – $A$ dynamic hysteresis model is constructed by combining the traditional $J$ – $A$ hysteresis model with the models of instantaneous eddy current and excess losses. The $J$ – $A$ model parameters and dynamic loss coefficients are determined by fitting the models to the measurement data of a single sheet tester (SST 500) and Epstein frame tester. To find the robust best fit, the particle swarm optimization algorithm is employed. By using the proposed $J$ – $A$ dynamic hysteresis model and FEM, the magnetic characteristics of a magnetic core is simulated and the core loss distribution within the core obtained. The calculated and measured results are compared to show the accuracy and effectiveness of the proposed model.

Comparison of core loss and magnetic flux distribution in amorphous and silicon steel core transformers

No-load losses are caused by the magnetizing current that needed to energize the transformers core. These losses are constant and occur 24 h a day, regardless of the load. So, the customers should pay the fixed monthly cost for these losses. In recent years, amorphous alloy has been used to improve distribution transformers performance with the decrease in No-load losses and the increase in the efficiency of transformers. This paper outlines the 2605SA1 amorphous core as a new development of the amorphous alloy with a higher saturation induction. This paper presents a comparison between traditional distribution transformers and amorphous distribution transformers. Distribution of flux density in two different transformers with amorphous core and M5-type silicon steel core has been simulated using 3-D finite element modelling. The simulation and modelling results have been compared with the tests results of 630 kVA, 34.5/0.4 kV prototypes manufactured in the TEK TRANSFORMER factory in Turkey. A good agreement has been obtained between the simulation and experimental results. The simulation and test results show that amorphous core considerably (about 63%) reduces the no-load power losses as well as efficiency of transformers.

300 MW汽轮发电机电磁性能的有限元仿真计算

本文利用Ansoft Maxwell有限元软件对一台300 MW汽轮发电机的空载特性、短路特性以及气隙磁密、感应电势、电磁转矩和铁耗等电磁参数进行了计算分析，采用精度较高的Bertotti铁耗模型得到定子轭部铁耗沿径向分布状况，为发电机温度场计算以及降耗措施提供理论依据，同时为进一步研究汽轮发电机单机运行、并网运行及各种故障状态提供参考依据。 In this paper, no-load characteristic, short-circuit characteristic and air-gap flux density, EMF, electromagnetic torque and core losses of a 300 MW turbogenerator are calculated and presented by using the Ansoft Maxwell finite element software. The coreloss distributions in stator yoke along radial are simulated by using the accurate Bertotti model. All the results can provide theoretical foundation for temperature field calculation and reducing consumption measures, and at the same time provide some references for the further study of unit operation and parallel operation as well as various fault diagnosis of the turbogenerator.

Magnetic Anisotropic Properties Measurement and Analysis of the Soft Magnetic Composite Materials

Soft magnetic composite (SMC) material produced by powder metallurgical techniques is assumed to be an isotropic material. It is applied in the core with special structure of rotating electrical machines, in which, the local magnetic flux density varies with time depend on both magnitude and orientation. Magnetic anisotropic feature may be shown in the material and influences the core operational performance. By using the designed 3-D magnetic properties tester, this paper presents the alternating and rotational magnetic properties of the SMC materials. Slightly anisotropic properties are found in hysteresis features and core loss distributions along different magnetization directions or planes. Experimental results show that some direction of the testing specimen seems harder to be magnetized than other directions. Milling and pressing process of the bulk specimen may cause changing of the grain size, micro-strain and pinning. These can influence the coercivity and remanence of the material and cause magnetic anisotropy, which may also be enhanced by increasing frequency and magnetization.

Electromagnetic Design of a New Electromagnetic Planetary-Gear Machine

A novel brushless compound-structure permanent-magnet synchronous machine (CS-PMSM) based on the magnetic field modulation principle is proposed for hybrid electric vehicles. As the key part of the brushless CS-PMSM, the operation principle of the electromagnetic planetary-gear machine (EPGM) is investigated by analytical method. The magnetic-field distribution and torque performance of the EPGM are studied by finite-element method (FEM). To obtain the optimal design scheme, the influence of the span ratio and thickness of the magnetic block and the slot-opening on the electromagnetic performance is investigated. Finally, the core loss distribution of the EPGM is investigated and the performance of this machine is fully evaluated.

Characteristic Performance Analysis of Squirrel Cage Induction Motor With Broken Bars

This paper presents the results of an investigation of the effects of broken squirrel-cage bars. In the investigation, a comprehensive time-stepping coupled finite element approach was fully used to compute stator current waveforms, torque, magnetic flux density waveform, the rotor bar currents, and end-ring currents for three cases: no broken bars, one broken bar, and two adjacent broken bars. The iron core loss distributions in the stator are computed, and the harmonic component of air gap flux density is analyzed. This paper also gives the computed rotor parameters and the vector diagram of the rotor current in cages with and without broken bars. From these data, the faulty signatures are extracted. Experimental results derived from a two-pole 1.1 kW induction motor confirm the validity of the proposed method. Furthermore, this method, which could help to develop diagnostics of broken bars and performance evaluation of induction motor, has great potential in future applications.

Finite-Element Analysis of Field Distribution and Characteristic Performance of Squirrel-Cage Induction Motor With Broken Bars

This paper develops the foundations of a technique for diagnosis and characterization of effects of broken bars in squirrel-cage induction motors based on the time-stepping coupled finite-element approach. These studies are performed by using the model to compute healthy case, one-broken-bar fault, and two adjacent broken bars fault performance data, which contains stator starting current waveforms, the current density on the bars, the magnetic force distribution on the rotor bars, and the distribution of magnetic field. Meanwhile, the iron core loss distributions on the rotor tooth adjacent to broken bars are computed, and the harmonic component of air-gap flux density is analyzed. From this data, the faulty signatures are extracted. Theoretical approach together with experimental results derived from a two-pole 1.1 kW induction motor confirms the validity of the proposed method. Furthermore, this method, which could help to develop diagnostics of broken bars and performance evaluation of induction motors, has great potential in future applications

Effects of broken bars/end-ring connectors and airgap eccentricities on ohmic and core losses of induction motors in ASDs using a coupled finite element-state space method

In this paper, effects of rotor abnormalities such as broken squirrel-cage bars, broken cage connectors and airgap eccentricity on ohmic and core losses of induction motors are presented. In this investigation, a comprehensive time-stepping coupled finite element-state space (TSCFE-SS) model was fully utilized to compute the time-domain elemental flux density waveforms and various time-domain waveforms of motor winding currents useful for core loss and ohmic loss computations. Such investigation is feasible by use of the TSCFE-SS model due to its intrinsic nature and characteristics. The results obtained from the simulations of an example 1.2-hp induction motor clearly indicate that faults due to broken squirrel-cage bars/end-connectors can increase motor core losses in comparison to the healthy case. The results also give the effect of saturation on the core loss distributions within the cross-section of the motor, and indicate the potential for possible excessive loss concentrations and consequent hot spots near zones of bar and connector breakages in the rotor.

Diagnosis and characterization of effects of broken bars and connectors in squirrel-cage induction motors by a time-stepping coupled finite element-state space modeling approach

In this paper, a comprehensive presentation of a time-stepping coupled finite element-state space modeling approach for diagnosis and characterization of effects of rotor (cage) broken bars and connectors in squirrel-cage induction motors is given. The model is used to compute/predict the characteristic frequency components which are indicative of rotor bar and connector breakages in the armature current waveforms and developed torque profiles, respectively. It was found that failures due to rotor connector breakages tend to degrade the developed torque of the machine considerably more than failures due to rotor bar breakages. Also, the effects and implications of rotor breakages on core loss distributions are quantified and described. Furthermore, this model has great potential in future applications to generate databases for use in overall noninvasive diagnostics of faults or troubleshooting in relation to quality assessments of the state of the motor and the overall drive.

A method of measuring loss distribution in electrical machines

The paper discusses the need for new measurement techniques for the investigation and evaluation of machine behaviour. The disadvantages of former methods of core-loss measurement are dealt with, and an improved thermal method is described, based on the principle that the initial rate of rise of temperature at any point is proportional to the loss generated at that point. It is shown theoretically that, to achieve sufficient accuracy, measurements must be made over a short period of time, and this requirement is met by the use of a chopper-type d.c. amplifier and recorder to measure the e.m.f. generated in thermocouples. The measuring equipment is described and the effects of stray a.c. pick-up are discussed. Examples of applications are given which show that not only can the core-loss distribution be measured but also the effects of changes of geometry or materials can be studied by tests on a single production machine.