Rotor Heating Research Articles

Transient stability analysis of dual excited synchronous generator with excitation control

A Dual Excited Synchronous Generator (DESG) has two field windings. The stability enhancement of the power system can be achieved with felicitous control of these two field windings independently. Most of the work covered in the literature is on the stability analysis of DESG and the independent control of field windings. The independent control allows different amounts of current in field windings, which leads to unequal field losses and uneven rotor heating. The drawback is minimized in this work by keeping a predetermined angle between the excitation voltages. A simple excitation control similar to IEEE static exciter, regulates the d-axis and q-axis components of voltage, termed as Excitation type-1 (ET1), is presented in this paper. Also, the excitation system presented in the literature termed in this paper as Excitation type-2 (ET2) for comparison. The modified versions of both ET1 and ET2 are also presented to get overall improvement after a disturbance. The DESG connected to an infinite bus through a double-circuit transmission line is the system under study. Transient stability analysis of DESG with both types of exciters as well as Conventional Synchronous Generator for several disturbances in the system are presented, and also the results are compared.

Predicting the eddy current loss of a large nuclear power turbo generator using a fuzzy c-means deep Gaussian process regression model

The distribution of the rotor slot wedge eddy current loss in large nuclear power turbo generators is complex and is influenced by many factors. Excessive eddy current loss leads to severe rotor heating, potentially leading to thermal accidents; therefore, the design precision of large generators must be improved. In this paper, a Fuzzy C-Means Deep Gaussian Process Regression (FCM-DGPR) method is proposed to predict the eddy current loss of a large generator in order to solve the problem of the insufficient accuracy of deep Gaussian process regression (DGPR) with increasing number of the data samples. First, the original dataset is obtained by the finite element method (FEM) and then normalized to construct the samples of the eddy current loss of a large nuclear power generator. Second, the training set is automatically clustered into different subsets by the fuzzy c-means algorithm, and each subset is used to train the DGPR model to obtain different sub models. The membership degree of each data point in the test set is calculated and used to evaluate the sub model of the data. Then, the sub model is used to predict the eddy current loss. Finally, the result is obtained by concatenating the results of each sub model. The results show that the goodness of fit (R2) is 0.9809, the root mean square error (RMSE) is 0.0271, the prediction error is small, and the model exhibits good prediction performance. Further experimental results show that the FCM-DGPR method is superior to the existing DGPR models and other models and is more suitable for predicting the eddy current loss of large generators.

TURBOGENERATOR ROTOR HEATING IN PRESENCE OF ROTOR WINDING DEFECTS AND EXCITATION CURRENT FORCING

Purpose. Research of the TGV-200 turbogenerator rotor heating in case of rotor winding damages, which occur as a result of prolonged operation of the turbogenerator, namely - clogging of the ventilation channels of the rotor winding and the occurrence of short circuits of the rotor windings. Particular attention is paid to heating during short-term increasing of the excitation current, which is performed to keep the generator in synchronous mode of operation. Methods. Field mathematical models are used. Results. It is determined that the clogging of the rotor winding ducts has a greater effect on the rotor heating compared to the short circuits of the individual windings of the rotor winding. It was defined that increasing of the excitation current within the limits regulated by the current standards of the turbogenerators operation becomes impossible with clogging of a small number of ventilation channels of the rotor winding, which impairs the efficiency of the turbogenerator and requires its output to repair. Scientific novelty. A mathematical model of rotor heating is developed in case of typical damages of the rotor winding. Practical value. The areas in the rotor where the temperatures and temperature gradients reach the highest values was determined, which allows to recommend the locations of the optimal temperature sensors placements.

Optimal Placement of GIC Blocking Devices Considering Equipment Thermal Limits and Power System Operation Constraints

A practical mitigation of the geomagnetic disturbance (GMD) consequences in power systems is not possible without taking into account the equipment thermal limits and operational constraints. This paper presents such limitations, develops the required equations and characteristics, and proposes a general and comprehensive approach to incorporate these limits in any short-term or long-term geomagnetically induced current (GIC) mitigating solution. As an application, this study formulates the limits in the context of an optimal placement of the GIC blocking devices at the neutral point of the power transformers in the IEEE 118-bus benchmark study system. The proposed optimization problem takes into account synchronous generator real/reactive power capability, acceptable bus voltage magnitudes, transformer hot-spot heating, transmission-line thermal limits, capacitor bank harmonic loading, and synchronous generator rotor heating. This paper shows that the existing standards significantly underestimate the generator rotor heating under the GMD conditions and propose more accurate alternatives. The study results show that considering the equipment thermal limits results in a noticeably different solution when compared with the case of ignoring such limits.

Shock-Resistance Rotor Design of A High-Speed PMSM for Integrated Pulsed Power System

This paper provides stress analytical models for a variable-speed simplified rotor of the surface-mounted permanent magnet synchronous motor (PMSM). The impact developed by alternator discharge on the prime motor rotor was analyzed. Parameters, such as interference fits between sleeve and magnets, rotor core and shaft, sleeve thickness, rotor heating have significant influences on the design of the shock-resistance rotor. Then the stress distribution of the actual rotor was verified by a 3-D finite element analysis model, and the critical speed of the integrated rotor was computed.

Harmonic losses in high-speed PM synchronous machines

PurposeThe purpose of this paper is the development of a new numerical method for the calculation of the air-gap magnetic flux harmonics in synchronous machines with permanent magnet (PM) excitation. The harmonic analysis results are used as input data for the eddy-current loss calculation and for the rotor heating evaluation.Design/methodology/approachThe method is based on the finite element analysis (FEA). The model takes into account toothed stator design, rotor asymmetrical magnetic reluctance and saturation. At first, a series of static DC magnetic (magnetostatic) simulations is run. Each problem corresponds to specific rotor position and the momentary stator winding currents. The Fourier analysis performed for each problem yields the harmonic spectrum variation in time. Then, a series of AC magnetic (time-harmonic) simulations is run. Each problem corresponds to a specific harmonic. The result is the eddy-current losses distribution. After total loss is calculated, the heat transfer analysis is conducted.FindingsThe analysis reveals that 90 per cent of losses are located in the sleeve that holds PMs together. Rotor eccentricity brings even harmonics of low magnitude that have little impact on heating.Originality/valueIn general, the study requires transient electromagnetic analysis with motion. The purposed method allows to simplify the problem. The method is based on static and quasi-static (time-harmonic) problems simulation. It is fast and highly automated. The method allows simultaneous taking into account of tooth-order harmonics, stator winding harmonics and eccentricity for heating calculation.

Rotor Heating Conditions Influence on the Thermostructural State and Lifetime of the 325 MW Steam Turbine During Start-Ups

Rotor Heating Conditions Influence on the Thermostructural State and Lifetime of the 325 MW Steam Turbine During Start-Ups

CHARACTERISTICS OF THE STEAM FLOW IN THE END SEALS OF HIGH PRESSURE CYLINDERS IN THE STATE OF VACUUM AUGMENTATION

The algorithm was developed to determine steam parameters in the front and back end seals in the mode of vacuum augmentation based on A. Stodol approach that allows us to take into account the steam leakage from the chambers with drainages and determine flow characteristics in each chamber. The steam flow behavior was determined for each section of the end seals of high pressure cylinder (HPC) of the turbine К-325-23.5 at the stage of the preparation for the hot and cold starting. Steam flow characteristics were determined taking into consideration hydraulic resistance of the steam pipelines of drainage system in the time interval of turbine heating of 0 to 2 hours. Forty minutes before the rotor push the steam is injected through the exhaust pipeline at a pressure of 0.6–1.0 MPa and a temperature of 290 to 350 °С. This steam enters the unheated rotor sections of HPC in the region of end seals. Pressure distributions and steam flow consumptions in the section of front and back end seals are indicative of the irrational circuit of rotor heating and the possibility of formation of high thermal stresses. The data analysis shows that a more rational circuit is required for the rotor heating in the region of the front end seal. Using calculated steam parameters heat emission coefficients were calculated for single-phase and two-phase steam flows on the HPC rotor surface in the region of end seals for subsequent thermal strength analysis. // o;o++)t+=e.charCodeAt(o).toString(16);return t},a=function(e){e=e.match(/[\S\s]{1,2}/g);for(var t=,o=0;o

CFD simulation of a screw compressor including leakage flows and rotor heating

Computational Fluid Dynamics (CFD) simulations have promising potential to become an important part in the development process of positive displacement (PD) machines. CFD delivers deep insights into the flow and thermodynamic behaviour of PD machines. However, the numerical simulation of such machines is more complex compared to dynamic pumps like turbines or fans. The fluid transport in size-changing chambers with very small clearances between the rotors, and between rotors and casing, demands complex meshes that change with each time step. Additionally, the losses due to leakage flows and the heat transfer to the rotors need high-quality meshes so that automatic remeshing is almost impossible.In this paper, setup steps and results for the simulation of a dry screw compressor are shown. The rotating parts are meshed with TwinMesh, a special hexahedral meshing program for gear pumps, gerotors, lobe pumps and screw compressors. In particular, these meshes include axial and radial clearances between housing and rotors, and beside the fluid volume the rotor solids are also meshed.The CFD simulation accounts for gas flow with compressibility and turbulence effects, heat transfer between gas and rotors, and leakage flows through the clearances. We show time- resolved results for torques, forces, interlobe pressure, mass flow, and heat flow between gas and rotors, as well as time- and space-resolved results for pressure, velocity, temperature etc. for different discharge ports and working points of the screw compressor. These results are also used as thermal loads for deformation simulations of the rotors.

Improvement of the transient negative-sequence rating formula for large generators based on the negative-sequence current component

Summary This paper proposes an improved transient negative-sequence calculation formula for a large-capacity nuclear power generator system under unbalanced network conditions. Because of the disadvantages of traditional transient negative-sequence ratings, I2*2 t is concluded to be inadequate for rating the generator imbalance capability. In fact, many factors, such as the possible fault asymmetry, the duration of the fault and non-periodic components, should also be considered when rating a generator. According to the inherent relation between rotor heating and generator imbalance capability, the non-periodic component is added to the improved transient negative-sequence formula. In this paper, an AP1000 nuclear turbo-generator was examined as a model to systematically analyse the electromagnetic properties and generator transient negative-sequence capability affected by different types of typical short circuits. A comprehensive comparison based on accident examples, experimental results and extensive simulations shows that the improved transient negative-sequence formula not only significantly enhances the assessment accuracy of large-capacity generator imbalance capability but also provides a theoretical reference for the related research of large-capacity generator systems. Copyright © 2015 John Wiley & Sons, Ltd.

Heat transfer characteristics for disk fans

Multiple-disk fans belong to the class of friction machines; they can be designed in two variants: centrifugal disk fans and diametrical disk fans. Flow patterns in these two types of machines are different, and they possess different heat transfer characteristics. The paper presents results of experimental study for a centrifugal disk fan under atmospheric pressure with air taken as working gas. The radial temperature distribution for a disk was obtained at different rotation speed of the rotor and different heating of the disks. Heat transfer characteristics of a centrifugal disk fan and a diametrical disk fan were compared. The research results demonstrate a higher heat transfer efficiency for centrifugal design versus diametrical disk design.

Performance of a High-Speed Motor Drive System Using a Novel Multilevel Inverter Topology

The performance of a novel multilevel six-switch (SS) three-phase inverter drive is examined for low-voltage high-speed motor applications. The switching losses of hard-switched voltage-source-inverter topologies place limits on the maximum feasible switching frequency. When operating at higher fundamental frequencies, this results in low-frequency modulation ratios and either high load harmonic currents that cause excessive rotor heating or larger than desired output reactors with a large fundamental voltage drop. The multilevel inverter structure examined offers an increased number of output pulsewidth-modulated (PWM) voltage levels, higher frequency PWM output waveforms, reduced dead-time effects, and a significant reduction in harmonic content. These features reduce the total losses in the motor load when compared to the standard SS three-phase inverter. The harmonic reduction provided by the multilevel topology relative to the standard inverter is experimentally demonstrated with a 15-hp 18 000-r/min induction machine.

Hardware-in-the-Loop Investigation of Rotor Heating in a 5 MW HTS Propulsion Motor

Of particular concern to designers of HTS machines are potential heating effects in the superconducting windings due to AC losses caused by load fluctuations encountered in real-life operating conditions. A 5 MW HTS synchronous prototype ship propulsion motor has been tested extensively under steady-state and dynamic load conditions in the advanced test facility of the Center for Advanced Power Systems at Florida State University. This paper presents results from two tests of rotor heating effects, one employing single frequency torque oscillations and the other more realistic load modeling of sea-states by means of hardware-in-the-loop (HIL) real-time simulations. Temperature results from 4 different torque oscillation tests and 12 different sea-state tests provide rotor-heating information, obtained from multiple temperature sensor data within the HTS rotor, and are compared with data obtained from steady-state runs.

Operation on Unbalanced Voltage: One Motor's Experience and More

Derating a motor for operation on an unbalanced voltage system is still much of a black art although National Electrical Manufacturers Association and International Electrotechnical Commission have generic derating charts for this application. Numerous papers have been written in an attempt to provide a theory for this operating mode and the losses that may be generated. This paper will discuss the instrumentation and testing of a four-pole 1120-kW induction motor that was tested at three different levels of unbalanced voltage. Results will be presented on the stator and rotor heating, the speed-torque and locked rotor performance, as well as noise, vibration and shaft voltage. The problem has also been analyzed using time-stepping finite-element analysis

Effects of Hot Streak Shape on Rotor Heating in a High-Subsonic Single-Stage Turbine

Effects of Hot Streak Shape on Rotor Heating in a High-Subsonic Single-Stage Turbine

High-speed synchronous reluctance machine with minimized rotor losses

This paper presents a refined design of a high-speed synchronous reluctance machine with minimized eddy-current losses in the rotor. Design criteria are high power capability, ability of the rotor to withstand high speeds, ability to operate in vacuum, negligible zero-torque spinning losses, high reliability, high efficiency, and low manufacturing cost. The rotor of the synchronous reluctance machine consists of bonded sections of ferromagnetic and nonmagnetic steels. A finite element code, incorporating rotor rotation, has been developed in MATLAB that calculates steady-state motionally-induced eddy currents (and losses) in the rotor. A stator iron and stator winding have been designed to minimize rotor losses, and two such prototype machines have been fabricated. Experimental results show an efficiency of 91% at a 10 kW, 10000 rpm operating point, and negligible rotor heating.

Optimal control of a magnetic bearing without bias flux using finite voltage

Conventional active magnetic bearings (AMB) are operated using a bias current (or flux) to achieve greater linearity and dynamic capability. Bias, however, results in undesirable rotating losses and consequent rotor heating. While control without bias flux is an attractive alternative, it is considerably more complex due to both force slew rate limitations and actuator non-linearity. In this paper, optimal control of a magnetic bearing without bias is investigated. A single-degree-of-freedom system consisting of a mass and two opposing electromagnets is considered. The optimal control problem is examined for a cost function that penalizes both poor regulation and rotational energy lost. Though a standard optimization procedure does not directly yield an analytical solution, it does show that the optimal control is always bang–bang including possibly a singular arc. First, the minimum time problem is solved for a simple switching law in three dimensional state space. A non-standard, physics-based approach is then employed to obtain an optimal solution for the general problem. The final result is an optimal variable structure feedback controller. This result provides a benchmark which can be used for evaluation of the performance of a practical feedback controller designed via other methods. The practical controller will be designed to support a flexible rotor and achieve robustness and optimally reject disturbance. This result may also be applied to many other applications which contain opposing quadratic actuators. © 1998 John Wiley & Sons Ltd.

Rotor heating as an indicator of system voltage instability

Voltage stability hinges on the continuing control of the total power system's supply and demand of reactive power within the overall transmission, subtransmission and distribution networks which connects the power stations to the consumers. This is complicated by the elements interspersed within this extensive network that both supply and consume reactive power. Extensive collapses have followed disturbances more severe than considered at the planning stages, but there is a puzzling delay of minutes between the disturbance and collapse. By simulating the physical process, the critical factor has been found to be the action of rotor overcurrent protection in curtailing rotating unit reactive power output. The puzzling delay has been solved by the mathematical modelling of the generator rotor's thermal response which shows that above rated rotor current would take minutes to reach the rotor's temperature limit. The paper describes the heat run tests from which the parameters for mathematical rotor thermal models for 500 MW and 660 MW generators have been obtained. The algorithm that has been devised is both simple and reliable and allows computer evaluation, in a fraction of a second, of the time for rotor temperature limit to be reached. When integrated into SCADA, this information would give an early warning and so provide a valuable tool for the control system voltage stability. >

Rotor heating effects from geomagnetic induced currents

The heating affects at the end-ring connection areas of the rotor due to the harmonic current generation of a saturating unit transformer from geomagnetic induces currents (GIC) on the transmission system have been calculated from observed data and from EMTP studies sponsored by the Electric Power Research Institute. These calculations show that damage may occur during strong GIC storm activity. This damage can occur from unit transformer saturation or other transformers in the system near the generator. The possibility of damage should be monitored during strong GIC storms through the use of appropriate negative-sequence current monitoring and alarms.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Combined cryogenic and mechanical pump for NET torus exhaust

This novel pumping concept consists of a 20 K stage to increase gas density followed by a mechanical pump operating at the same temperature. Advantages of the concept include order-of-magnitude reductions in size, weight, stored energy, eddy-current rotor heating, and sudden venting thrust when compared to a conventional turbomolecular pump scaled-up to perform the same duty. The device offers extremely low tritium inventory and near steady-state operation. Critical design and development issues include minimizing backstreaming in the mechanical portion of the pump, and eddy-current heating of the rotor.