Calculation Of Transient Electromagnetic Fields Research Articles

Influence of different underexcited operations on thermal field in the turbogenerator end region with magnetic shield structure

The losses and temperatures of end parts will increase obviously in the turbogenerator end region under underexcited operation. In order to study the influence of different underexcited operations on temperature of end parts in the turbogenerator end region with magnetic shield structure, a turbogenerator is considered as an example in this paper. Three-dimensional transient electromagnetic field of turbogenerator end region is given. The magnetic density distribution of clamping plate and magnetic shield is researched. The losses of end parts and stator end cores from three-dimensional transient electromagnetic field calculation are applied to end region as heat sources under different underexcited operations. Pressure value of fan outlet and velocity values of different inlets from flow network calculations are applied to end region as boundary conditions in the 3-D fluid and thermal coupling analysis model. Further, fluid field and thermal field are calculated under different underexcited operations. The distribution laws of fluid velocity and fluid temperature in the turbogenerator end region are determined. The temperature distribution laws of the stator-end copper windings, press finger, clamping plate, screen plate, magnetic shield, and stator end cores are studied under different underexcited operations. The accuracy of numerical calculation is validated by measured values.

Numerical analysis of end part temperature in the turbogenerator end region with magnetic shield structure under the different operation conditions

Due to the serious overheating problem of end parts in the large turbogenerator end region, accurate calculation of end-part temperature has become a key design factor. In this paper, 3-D fluid and thermal coupling model in the end region of 1250 MW turbogenerator are given. The loss values gained from 3-D transient electromagnetic field calculation are applied to the solving end region as heat sources. Pressure value of fan outlet and fluid velocities of end region inlets from flow network calculation are applied to the solving end region as boundary conditions in the 3-D fluid and thermal coupling analysis model. The fluid flow and temperature distribution of end parts in the end region of large turbogenerator with magnetic shield structure are studied under the different operation conditions. The distribution of fluid velocity in the ventilation duct of stator end core is obtained. The temperature distribution laws of stator-end copper coils, screen plate, finger plate, press plate, and magnetic shield are researched under the different operation conditions. The location of the highest temperature point in the turbogenerator end region with magnetic shield structure is determined. The accuracy of numerical calculation is validated by experimental measured values.

Numerical calculation of CHTC on end metal parts and flow in end region of a turbogenerator

The convection heat transfer coefficient (CHTC) distribution of surfaces of end metal parts directly affects the temperature distribution of end metal parts. In this study, a large turbogenerator is analysed. To study the CHTC distribution of surfaces of end metal parts in detail, a three-dimensional (3D) fluid and thermal analysis model of whole turbogenerator end region is established. The losses of end metal parts from 3D transient electromagnetic field calculation are provided to end metal parts as heat sources. Pressure values of end-region outlets and fluid velocity of fan outlet from flow network calculation are provided to end region as boundary conditions in the 3D fluid and thermal analysis model. CHTC distribution laws of the surfaces of the clamping plate, finger plate, and copper screen are studied in detail by the finite volume method. The fluid flow and temperature distribution of end metal parts are determined in the end region of the turbogenerator. The calculated results are compared with measured data.

Calculation of Temperature Distribution in End Region of Large Turbogenerator Under Different Cooling Mediums

In order to study the influence of different cooling mediums on the fluid velocity and the temperature distribution of end parts in the turbogenerator end region, a 330-MW turbogenerator is analyzed. Three-dimensional fluid-thermal coupling analysis model of the turbogenerator end region is given. When the different cooling mediums are used, fluid velocity of fan inlet and pressure values of end-region outlet from the flow network calculation are applied to the end region as boundary conditions, and the losses from 3-D transient electromagnetic field calculation are applied to the end parts as heat sources in the fluid-thermal coupling field. The fluid field and temperature field in the turbogenerator end region are calculated using the hydrogen and air as cooling medium, respectively. Fluid velocity and temperature of end parts in the turbogenerator end region are compared when the different cooling mediums are used. When the hydrogen is used as the cooling medium, comparing the calculated temperature results with the test values, the calculated temperature results match well with test values. These will provide a reference for the ventilation cooling design of large turbogenerator.

Multiphysical Field Collaborative Optimization of Premium Induction Motor Based on GA

The premium induction motor has received worldwide attention in recent years due to its high efficiency. However, the high efficiency benefits from the high cost. In the paper, a multiphysical field collaborative optimization method of the premium induction motor based on the genetic algorithm (GA) is presented to improve the utilization of the materials and reduce the cost. First, the cost and efficiency are taken as bi-objective; the magnetic circuit optimization based on GA is established to get the initial electromagnetic scheme. Then, the parameters of the premium induction motor are automatically transferred to a 2-D transient electromagnetic field calculation model so that the operation performances of the premium motor can be determined. The results will be sent to the magnetic circuit optimization to compare with the optimization objectives. The electromagnetic scheme will adjust until the errors between the transient operation performances and optimization objectives are within the convergence errors. Based on the results above, the transient results will be transferred to the 2-D temperature field calculation model to determine the thermal distributions of the premium induction motor. The structures of the premium induction motor will also adjust until the thermal distributions meet the requirements. The presented multiphysical field collaborative optimization method is applied to optimize several premium motors, and the accuracy is validated by the experimental data.

Research on the Temperature Field of High-Voltage High Power Line Start Permanent Magnet Synchronous Machines with Different Rotor Cage Structure

For line start permanent magnet synchronous machines (LSPMSMs), the eddy current loss in the rotor, which has of significant effects on rotor working temperature, may cause thermal demagnetization to permanent magnet. Therefore, this paper addresses an investigation on the temperature distribution in LSPMSM based on a 6 kV, 315 kW prototype with solid starting cage bar. Firstly, the loss distributions, obtained from a 2-D transient electromagnetic field calculation, are determined as the distributed heat source in thermal analyses. Then, the fluid-thermal coupled analyses are performed, by which the temperature distributions in the machine are determined. Meanwhile, the calculated motor performance is verified via comparison with the measured results. The calculation results show that the temperatures in the rotor core and permanent magnets are relatively high. To find the solution for reducing the rotor working temperature, a rotor air slot structure was proposed in this analysis. The theoretical calculation indicates that the rotor working temperature reduction is obvious with the rotor air slot in the machine. Therefore, the operating situation of solid rotor LSPMSM could be improved effectively with the proposed rotor thermal solution, which also benefits the machine reliability and safety.

A study on the discrete image method for calculation of transient electromagnetic fields in geological media

We conducted a study on the numerical calculation and response analysis of a transient electromagnetic field generated by a ground source in geological media. One solution method, the traditional discrete image method, involves complex operation, and its digital filtering algorithm requires a large number of calculations. To solve these problems, we proposed an improved discrete image method, where the following are realized: the real number of the electromagnetic field solution based on the Gaver–Stehfest algorithm for approximate inversion, the exponential approximation of the objective kernel function using the Prony method, the transient electromagnetic field according to discrete image theory, and closed-form solution of the approximate coefficients. To verify the method, we tentatively calculated the transient electromagnetic field in a homogeneous model and compared it with the results obtained from the Hankel transform digital filtering method. The results show that the method has considerable accuracy and good applicability. We then used this method to calculate the transient electromagnetic field generated by a ground magnetic dipole source in a typical geoelectric model and analyzed the horizontal component response of the induced magnetic field obtained from the “ground excitation–stratum measurement” method. We reached the conclusion that the horizontal component response of a transient field is related to the geoelectric structure, observation time, spatial location, and others. The horizontal component response of the induced magnetic field reflects the eddy current field distribution and its vertical gradient variation. During the detection of abnormal objects, positions with a zero or comparatively large offset were selected for the drillhole measurements or a comparatively long observation delay was adopted to reduce the influence of the ambient field on the survey results. The discrete image method and forward calculation results in this paper can be used as references for relevant research.

FDTD Calculation of Transient Electromagnetic Fields in the Grounding System of Wind Towers Due to Direct Lightning Strikes

Lightning protection system (LPS) for wind power generation has become an important public issue due to greatly increasing installations of wind turbines (WTs) worldwide. Grounding system is one of the most important components required for appropriate LPS for WTs. Although the finite-difference time-domain (FDTD) method for solving Maxwells equations is difficult for computing earth potential rise (EPR) and transient grounding resistance (TGR), this method is used in this paper to compute EPR and TGR for different configurations of the grounding system of WTs because FDTD method can efficiently deal with the three-dimensional geometrical configurations of an investigated structure unlike electromagnetic transient programs (EMTP).

An Optimized Method for Transient Electromagnetic Field-Wave Field Conversion

In the forward transformation of wave-field, in order to decrease the number of integral coefficients and the sampling number of dispersed digital integral, as well as ensure the transient electromagnetic field calculation precision, a two-step optimized method has been proposed. This method can deal well with the ill-posed question caused by large amount of integral coefficients and depress the ill-posed problem of the first-kind calculator function. In the wave-field inverse transformation, the normalized method has been adopted, optimized and normalized parameters have been selected by the deviation theory and the Newton iterative form, to make the transformed wave field stable and reliable. The comparison between numerical results and known wave-field function values shows that the method put forward in this paper is effective and useful.

Conservation of energy of the transient electromagnetic field in solid conductors

The calculation of transient electromagnetic fields in solid conductors becomes more important in the future because of the increasing demands on system design under EMC-constraints. The switching of currents in a system of conductors is especially crucial because a transient wave is stimulated in the non-conducting environment. The energy balance for the switching of an exciting current shows that the integration of the dissipated power over the infinite time interval is equal to the energy stored in the magnetic field in the conducting space before switching plus the energy that flows through the conductor's surface during the transient process. The energy difference between the initial field before and immediately after the switching is radiated into the free space by a transient wave that is excited at the moment of switching. This relation is proved for the switching of a continuous current in an elementary coaxial line and the shielding of the transient field of a magnetic dipole of arbitrary orientation by a conducting and permeable hollow sphere.

A method of calculation of transient electromagnetic field in non-linear ferromagnetic medium

The paper presents a method of calculation the transient electromagnetic field in ferromagnetic material, taking into account the real characteristics of magnetization. Using the difference method, the spatial-temporal distributions of electromagnetic field have been calculated in result of solving the non-linear partial differential equation for electric field E (in space Ω(x, t)). For the difference diagram assumed for approximation of the differential equation, the conditions of stability and convergence, and the condition of obtaining the minimum error of approximation, have been determined.