Likun Wang

Influence of Metal Screen Materials on 3-D Electromagnetic Field and Eddy Current Loss in the End Region of Turbogenerator

Since the structure of a large capacity turbogenerator is complex in the end region, accurate calculation about the leakage magnetic field becomes a key factor in the design. In this paper, a 330-MW level turbogenerator is electromagnetically analyzed and investigated with different metal screens in the end region. Its nonlinear transient electromagnetic field and eddy current loss were calculated by using the time step finite-element method (FEM). The influences of metal screen materials on the electromagnetic field and eddy current loss were compared and analyzed. All of these will contribute to the turbogenerator engineering design. Using the loss gained by the magnetic field calculation as a heat source, the thermal field of the end region with a copper screen was calculated. Compared with the test data, the calculated temperature results match well with the measured data.

Research on Flow Rule and Thermal Dissipation Between the Rotor Poles of a Fully Air-Cooled Hydrogenerator

Aiming at providing a theoretical basis for the 1000-MW giant fully air-cooled hydrogenerator, which is being studied and developed currently, this paper established a coupling calculation model of 3-D fluid and temperature field based on the actual structure and size of a 250-MW fully air-cooled fanless hydrogenerator. Fluid dynamics control equations, and corresponding boundary conditions in the solved region were given. The additional losses from electromagnetic field calculation were applied to the coupling model as heat sources. Using a computational fluid dynamics approach, the flow distribution of cooling air and the temperature distribution of rotor structures were obtained. It focused on the axial and radial variation rules of the flow condition of cooling air between adjacent poles. Meanwhile, it conducted a detailed research study on the variation rule of the heat-transfer coefficients of pole shoes and damping bars. Temperature calculated value of exciting windings was coincident well with the measured value. The calculated error between the two values meets the engineering requirement, thus verifying both applicability and accuracy of the solution method this paper presents.

Calculation and Analysis of the Surface Heat-Transfer Coefficient and Temperature Fields on the Three-Dimensional Complex End Windings of a Large Turbogenerator

With increased turbogenerator capacity and electromagnetic load, overheating of the complex end parts has become one of the main problems affecting safe and stable turbogenerator operation. In this research, a flow network was built representing the structural and ventilation characteristics of a 330-MW turbogenerator. The fan inlet velocity and pressures (boundary conditions) of each end-region outlet were obtained by the flow network method. The 3-D transient electromagnetic field in the turbogenerator end was calculated, and the eddy current losses (heat sources) of the end parts were obtained by the finite-element method. To study the surface heat-transfer coefficient distribution on the stator-end winding surface, fluid and thermal mathematical and geometric models of the whole turbogenerator end region were given. Using the finite-volume method, the surface heat-transfer coefficient distribution on the complex 3-D stator-end winding surface, fluid-flow distribution, and temperature distribution of the end parts were investigated under rated-load conditions. The calculated temperature results match well with measured data. This research can provide a theoretical basis for calculating the heat-transfer coefficients of the outer surfaces of large turbogenerators.

Influence of Underexcitation Operation on Electromagnetic Loss in the End Metal Parts and Stator Step Packets of a Turbogenerator

The leading operation of large generators is an effective method to adjust the electric reactive power surplus, and the leading-power factor was restricted by the temperature rise of the end parts. In this paper, a three-dimensional (3-D) electromagnetic field of a 330-MW water-hydrogen-hydrogen-cooled turbogenerator in the end region was investigated, and the effect of end leakage magnetic flux on stator step packets was considered in the calculation process. The magnetic flux density distribution was analyzed, and the eddy current losses of metal parts in the end region and core losses of stator step packets were calculated under lagging and leading operations. The influences of the leading-power factor on the losses of end components were analyzed, which could provide a theoretical basis for the safety of the leading operation.

A New Approach to Evaluate Influence of Transverse Edge Effect of a Single-Sided HTS Linear Induction Motor Used for Linear Metro

A new approach has been proposed to evaluate the influence of the transverse edge effect of high-temperature superconducting (HTS) linear induction motor (LIM) in this paper. Taking a 3.5 kW single-sided HTS LIM for an example, the cross-flux density distributions were analyzed by analytical method. Based on results mentioned above, a new transverse coefficient was proposed to evaluate the influence of the transverse edge effect on the cross-flux density distribution. The influences of the motor configurations and parameters on the transverse coefficient were also investigated. The 3-D finite-element method was adopted to verify the accuracy of the presented analytical method.

Numerical Calculation and Analysis of Three-Dimensional Transient Electromagnetic Field in the End Region of Large Water–Hydrogen–Hydrogen Cooled Turbogenerator

Due to the complexity of the structures and magnetic field distribution in the end region of large turbogenerators, using a 330-MW water-hydrogen-hydrogen cooled turbogenerator as an example, the 3-D mathematical and geometry models of the nonlinear transient eddy current field were given. Taking the nonlinearity of the core material and the influences of noncontact between the copper screen and the clamping plate, as well as the shape of stator end windings into consideration, the 3-D transient electromagnetic field was calculated, and the losses of different metal parts were obtained by the finite-element method. The calculated power losses were applied to the thermal field as heat sources. Temperatures of the copper screen were gained. The calculated results of copper screen were well coincident with the test data. Hence, the calculated results are accurate, and the method of calculation is effective.

Research on the Impact of Screen Properties on Eddy Current and Flux in End Region of a Large Air-Cooled Turbo-Generator

Large turbo-generators are an important energy conversion device in power stations. Once a failure occurs in the turbo-generator, it not only affects the reliability of the power system but also causes enormous economic losses. Nowadays, large air-cooled turbo-generators have developed. The safe and steady operation of turbo-generator is important for the electric power system. Leakage magnetic field is a potential hazard in end region of a turbo-generator. Leakage magnetic flux could cause eddy current to be induced in the metal component of end region, which leads to heat generation. In this paper, aiming at the complex end structure of turbo-generator, a three dimensional (3-D) mathematic model used for electromagnetic field calculation in end region of a 150-MW air-cooled turbo-generator is established. Finite element method is used to calculate the 3-D magnetic field in end region of a turbo-generator. Magnetic flux leakage testing is conducted under no-load condition. It shows that there is a good agreement between the theoretical simulation and the experimental results. Eddy current loss of end parts is gained based on the electromagnetic induction theory.

Influence of Stator Parameter Variation and Phase-Shift Under Synchronizing Out of Phase on Turbine Generator Electromagnetic Field

Synchronizing out of phase may sometimes occur to a turbine generator due to the misoperation or failure of a synchronizing controller. There could be a large impulse current in stator windings during out of phase synchronizing. The impulse current could seriously damage the windings insulation, and the magnetic flux density might be easily supersaturated at the rotor pole surface, leading to stronger stress on the rotor tooth and damage the turbine generator. Aiming at studying the electromagnetic field when synchronizing out of phase occurs, a mathematical model of the transient electromagnetic field with field-circuit-grid coupled is established by taking a 150 MW air-cooled turbine generator for consideration. Impulse current in stator winding and supersaturation at the rotor pole surface are calculated respectively in different angles between the vector of the turbine generator electromotive force and voltage vector of power grid. According to the largest impulse current in stator windings at the 180° out-of-phase synchronization, the influence on the magnetic field distribution and saturation at the rotor pole surface of turbine generator stator resistance and the end region leakage inductances that vary in a certain range is studied. The results could provide theoretical basis for researching of electromagnetic field at out-of-phase synchronization of large turbine generator in the end zone.

Influences of turbo-generator end winding dimensions on electromagnetic loss in the end core and metal parts

For the complex structure of the large capacity turbo-generator in end region, the accurate calculation of the leakage magnetic field became key factor in large generator design. Affected by the leakage magnetic field, there is a problem that the end stator ladder packets, copper screen, press plate has a local high temperature. The three-dimensional electromagnetic field of a 330 MW water-hydrogen-hydrogen turbo-generator in the end region was investigated, and the effect of 4 stator ladder packets was considered in the calculation process. The influences of the end extension of stator and rotor end windings beyond the stator or rotor end 10cm on the losses of the end stator ladder packets, copper screen, and press plate were compared and analyzed. All of these will be help for the turbo-generator engineering design.

Assessment of the Stray Flux, Losses, and Temperature Rise in the End Region of a High-Power Turbogenerator Based on a Novel Frequency-Domain Model

The electromagnetic and heat issue is the core of the key problems for large synchronous generators. This paper presents a new method to account for the rotary excitation field of a large synchronous generator using a new 3-D static frequency-domain finite element to solve the end magnetic field and electromagnetic losses via phase transformation. The solution time is significantly reduced. Both magnetic flux leakage and temperature testing of the end structures are conducted. There is good consistency between the theoretical simulation and the experimental results for both magnetic and thermal fields. The regularity of the magnetic and thermal field distributions is studied drawing on the electromagnetic and heat transfer theories.