Use of Modal Representation for the Supporting Structure in Model Based Fault Identification of Large Rotating Machinery: Part 1 – Theoretical Remarks

Fault identification by means of model-based techniques, both in frequency and time domain, is often employed in diagnostics of rotating machines, when the main task is to locate and to evaluate the severity of the malfunction. The model of the fully assembled machine is composed by the submodels of the rotor, of the bearings and of the foundation, while the effect of the faults is modelled by means of equivalent force systems. Some identification techniques, such as the least squares identification in frequency domain, proposed by the authors, have proven to be quite robust even if the submodels are not fine-tuned. Anyhow, the use of a reliable model can increase the accuracy of the identification. Normally a supporting structure is represented by means of rigid foundation or by pedestals, i.e. 2 d.o.f. mass–spring–damper systems, but these kind of models are often not able to reproduce correctly the influence of the dynamical behaviour of the supporting structure on the shaft, especially in large machines where coupled modes are present. Therefore, peculiar aspect of this paper is the use of a modal foundation to model the supporting structure of the machine and the method is discussed in detail in this first part. The modal representation of the foundation is then introduced in the least squares identification technique in frequency domain

Studies in Electrical Machines & Wind Turbines associated with developing Reliable Power Generation

The publications listed in date order in this document are offered for the Degree of Doctor of Science in Durham University and have been selected from the author’s full publication list. The papers in this thesis constitute a continuum of original work in fundamental and applied electrical science, spanning 30 years, deployed on real industrial problems, making a significant contribution to conventional and renewable energy power generation. This is the basis of a claim of high distinction, constituting an original and substantial contribution to engineering science

The large amplitude vibration of multi-rotor systems supported upon oil-film bearings

Imperial Users onl

Prediction of Vibration in the Discharge Ring of a River Type Hydroelectric Power Plant with Bulb Turbine Using Artificial Neural Networks and Support Vector Machine

Cracks are formed around the manhole covers located in the discharge ring areas of the turbine units of a hydroelectric power plant with a river-type bulb turbine due to the vibration of the units. Determining the operating parameters for the low vibration zone of the units to reduce or eliminate these cracks is an important issue in terms of reducing plant operating efficiency and maintenance costs. To solve this problem and to determine the central operating parameters in the safe vibration zone, a vibration prediction model was created with artificial neural networks and support vector machine. Operating parameters of the hydroelectric power plant; artificial neural networks and support vector machine were created to predict vibrations for each turbine unit using the water inlet-outlet height, network pollution level, power of each unit, total unit power, and vibration data from the discharge rings of the units. Vibration estimates were made based on operating parameters and compared with actual vibration values. The results obtained showed that the operating parameters for reducing the vibration values of the turbine units of the hydroelectric power plant could be determined practically with the help of artificial neural networks and support vector machine

Electromagnetic and mechanical finite element analysis of end region of large-sized three-phase squirrel-cage induction machines

This piece of research is related to the design of large-sized radial flux electric machines. It aims at studying the end-region magnetic field under the steady-state operation in order for an analysis of some important electromagnetic and mechanical phenomena that require careful thought during the design of the end region. The research work is focused on the end region of two large-sized three-phase squirrel-cage induction machines. In addition to the end-region magnetic field, the stator end-winding leakage inductance, the eddy currents inside the end shield and the end frame, and the end-winding forces and vibrations are covered. The 3-D time-harmonic finite element analysis of the above aspects, carried out with a commercial software package, forms the main part of the research work. The corresponding measurement, as a complement to the finite element analysis, is mainly for validating the models and the numerical calculations. A 3-D time-harmonic finite element analysis of the end-region magnetic field with suitable boundary conditions can give an accurate distribution of the magnetic field. The stator end-winding leakage only affects the core ends; hence, the end-winding leakage inductance can be calculated from the corresponding magnetic energy separated from the total magnetic energy. The eddy currents inside the end shield and the end frame do not affect the end-region magnetic field seriously, and it is feasible to consider them as surface currents and to model them with the standard impedance boundary condition. The end-winding forces cause vibrations and deformation, but the amplitude of vibration and the degree of deformation are small because of the end-winding bracing system. With the bracing system, the natural frequency of the most excitable mode of the end winding and its bracing system is also greatly raised, so resonances may be avoided. Under the steady-state operation of large-sized induction machines, the end-region magnetic field does not bring about severely disadvantageous electromagnetic and mechanical phenomena in the end region. However, from the viewpoint of optimisation, the end frame can be shifted farther from the end winding for eliminating potential hot spots. In addition, fewer bracing parts can be fixed to the knuckle portion and the lower part of the involute portion of the end connections for improving the cooling of the end region

Thermomechanical loads of powerful turbogenerator stator winding insulation in the presence of water cooling defects

Introduction. An analysis of incidents linked to power units’ emergency disconnecting from network as a result of turbogenerators’ malfunction on the NPP of Ukraine is conducted. It is identified, that the reason of the majority of incidents is an insufficient reliability of the stator winding’s direct cooling system. Problem. The most problematic point in winding for today is the frontal parts, where, while cooling is reduced, there are not only thermal, but also thermomechanical loadings on an insulation appearing. The level of these loading depends on structural design of frontal parts and a character of violation of coolant agent circulation in a bar. In some cases they can exceed limit values. The spread and the quality of research on this issue for today are insufficient. Goal. The aim of the completed research is to determine the thermomechanical loading of insulation of stator winding bar in a powerful turbogenerator with a direct liquid cooling under condition when coolant circulation is malfunctioned. Methodology. A complex mathematical model of thermomechanical processes in an insulation of stator winding bar of a powerful turbogenerator is developed. It takes into account the real geometry of the winding bar, variable thermal loading of core elements in radial and axial directions, as well as ways of fixation of slot and frontal winding parts. Studies of thermomechanical processes in an insulation of stator winding bar of turbogenerator are conducted. Results. Values of mechanical displacement and stress for the different modes of malfunction are obtained. Areas of bar, where mechanical loading may exceed the boundaries of mechanical durability of material of insulation of stator winding are identified. With decline of coolant liquid consumption the radial displacement and stress in the winding insulation bar in the area, where the bar exits from the slot are increasing along with that the values of radial stress of insulation of the winding bar in places of frontal parts’ fixation exceed limit values. Practical significance. The offered mathematical models allow to realize calculation experiments and can be used in practice for development and validation of diagnostic systems, analysis, design and investigation of emergency situations during exploitation of turbogenerators on power stations of Ukraine

Research on spacecraft and powerplant integration problems Spacecraft analysis topical report

Nuclear-electric power generating requirements for unmanned scientific solar system probe

Health monitoring techniques for rotating machinery.

The present research is concerned with health monitoring techniques for rotating machinery, for example Turbogenerator (TG) sets in the power industry. Vibration based condition monitoring is widely accepted for rotating machinery and hence the vibration response of a machine is again utilized in the present research study. Experience shows that faults develop in rotating machines during normal operation and hence their quick identification and remedy are important from safety and plant productivity considerations. The vibration based fault identification procedures are well developed for rotating machinery. However the quantification part of the identified faults has still not matured, and is an ongoing research topic. Hence the remedial action is usually time consuming, even though the machine is known to have some known faults, due to lack of knowledge of their locations and the extent of the faults. In general such a quantification of the identified fault relies on the mathematical model of the complete system along with the measured vibration response of the system. Rotating machinery consists of three major parts - a rotor, fluid journal bearings and a foundation which is often flexible. Often a good model of the rotor (usually a finite element model) and an adequate model of the fluid bearings may be constructed. However, a reliable model for the foundation is difficult to construct due to a number of practical difficulties. Hence the present study has concentrated on two objectives - reliable modelling for the foundation and the quantification of faults using the measured vibration response at the bearing pedestals and the mathematical model of the rotor and the fluid bearings. For the foundation model, the theory which was developed to estimate the models for flexible foundation has been described in the thesis. The method uses measured vibration response at bearing pedestals during machine run-downs, a priori rotor and journal bearing models, and a knowledge of the rotor unbalance, to estimate the stiffness, damping and mass matrices of the foundation. The method was tested on both simulated and experimental examples. The prediction capability of the estimated foundation model was also demonstrated. For the fault estimation a different approach has been used. It has been assumed that the foundation mathematical model is not known, and it is demonstrated that the two faults - the state of rotor unbalance and the misalignment in the rotor can be estimated reliably. The theory of the proposed methods is discussed in the thesis. The method uses measured vibration response at bearing pedestals during a single machine run-down, and a priori rotor and journal bearing models, to estimate the rotor unbalance and the misalignment along with the foundation parameters, so that the dynamics of the foundation is also accounted for during the estimation. The methods were tested on simulated and experimental examples and the estimation accuracy was found to be excellent and generally robust to errors in the rotor and bearing models