Search results

The axial magnetic field occurs in the end-region of large turbo-generators is known to induce hot points or voltages between laminations, that may cause insulation breakdown and thus stator faults.

It is important to dispose of simple methods for estimating the axial flux rapidly with regard to the operating point of the machine.

The authors provide a practical model of the axial magnetic field based on a simplified vector diagram. The parameters required to build the vector composition of the flux densities are assessed with a limited number of finite element method simulations of the whole end-region of the machine. These simulations were validated by an experimental test on a real turbo-generator. Then the axial flux density was simply estimated for various operating points.

The originality of the paper concerns the practical model of the axial magnetic field based on a simplified vector diagram.

Problems caused by end winding vibrations in power plant generators have become increasingly evident in recent years and reveal a need for monitoring and diagnostic systems. An increasing number of operational outages are caused by failures of the winding insulation or the conductor itself due to end winding vibrations. Meanwhile, it is clear that the condition of the end winding must be continuously monitored during operation to detect ineffective end winding support in time and to plan the repair.

In this paper, the complex and nonlinear excitation mechanisms in large machines are presented and modern methods for vibration monitoring are described. Through a consistent use of vibration monitoring in the end winding area as well as the vibration diagnosis done by experts, damage mechanisms can be detected at an early stage, repair measures can be planned and serious damage owing to a weakened main insulation can be avoided.

By combining modal analysis and trend monitoring in relation to the learned vibration behaviour, the end winding condition can be assessed in a differentiated manner and changes in the end winding structure can be detected early.

Finally, an assessment for a two-pole, air-cooled turbo generator is proposed.

The purpose of this paper is to present a numerical approach for the computation of 3D magnetic fields in rotating electrical machines. The technique is suitable for the computation of flux densities and forces in the end windings of large synchronous turbo generators (TG).

The magnetostatic FEM model of the generator end windings is carried out for different displacements of the rotor axis to the stator magnetomotive force (MMF) axis. The method is based on a parallel integral formulation allowing to substantially reduce the computational effort.

The computational model requires only the discretization of magnetic materials and conductors and is fast enough for carrying out 3D analyses on a time scale fast enough for the needs of the designer. As far as the present application is concerned, the analysis of a synchronous generator in the class of 300‐400 MVA has shown that the most stressed elements of the armature conductors are those closer to the stator ends. The study demonstrates that the maximum stress component on the end windings is axial and is achieved when the MMF is aligned to the direct axis.

The present approach combining an efficient integral formulation, the sparsification of the relevant matrices and the parallel implementation of the related algorithms gives rise to an original computational tool that allows a more accurate description of the machine in comparison to other numerical simulations that can be found in the literature.

Interlaminar short circuits in turbo generator stators can lead to local damage of the iron core. The purpose of this paper is to model an interlaminar short circuit diagnosis test on an existing structure.

This work presents the modeling of short‐circuited laminations in a stator yoke of a turbo‐generator. A 3D finite element model, associated to a homogenization technique, is used to calculate the short‐circuit current. The diagnosis test known as El Cid has been modelled as well.

Calculation results are compared with the experiment. The same tendency has been observed both in experimental and numerical results.

Additional calculations may be performed (parametric studies) in order to investigate El Cid measuring under different conditions (different material properties, fault position, size), which may lead to a better interpretation of the results.

Modelling of short circuit diagnosis tests under different conditions may help with the interpretation of measuring results, predicting the fault size/seriousness and location. So, only the concerned parts of the stator have to be disassembled and repaired/rebuilt.

It is not easy to model numerically a structure with a short circuit inside, since different dimensions are involved: the fault and the varnish between laminations are much smaller than the stator itself. Thus, homogenization techniques have been used to model the lamination stack region. The combination of this technique with the modelling of the El Cid test constitutes a tool to study this kind of fault and calculate its severity and location in a stator.

BRITISH‐designed and manufactured, a new oil injector has the potential of at least doubling the life of a turbo‐charger unit. So claim Trans‐Europe Sales & Service Ltd, whose new TEP 3000 injector is readily fitted to all turbo engines, whether installed in a vehicle, a boat of part of a turbo‐generator standby unit.

FLUSHING (that is cleaning with a copious flow of liquid, usually lubricating oil) is a successful method of clearing circulating systems, such as those of steam turbo‐generators, of impurities; those associated with new installations or those which accumulate in service. This is because as a general rule only relatively light bodied oils are used as lubricants for this type of industrial machinery and again because the contaminants themselves are only loosely bound to the metal surfaces of the system components.

A major step forward in cathodic protection has been achieved at Blyth ‘B’ Power Station, Northumberland, where new equipment giving even and positive distribution of current has been installed on two 350‐MW turbo‐generators for the first time on a commercial basis. The equipment gives increased operating efficiency of heat exchangers, saves maintenance costs because of a reduction of ‘down time’ due to corrosion, reduces power costs, and the possibility of mechanical damage is minimised.

The purpose of this paper is to elucidate on specific risk mitigation approach which is known as “scenario approach”. Description of stepwise process of their elaboration, which is worth considering for managers, offers feasible tool not only for company risk management improvement but also for significant enhancement of the quality of company strategic planning. Authors also draw attention to advantages and disadvantages of investment and strategic scenario planning. Theoretical implications of using scenario approaches are exemplified both by the set of investment projects and company strategic planning process where method in question was applied.

As for methods applied which fulfilled research strategies, it is worth mentioning following items: analysis which explores particular parts of methodology of scenario elaboration and application, the way of obtaining information, impact on strategy, working with risks and organizational support of outcomes in company environment; synthesis observing context and natural relation of problems solved which supports research hypotheses formulation; induction generalizing facts acquired from results in companies; deduction to be grounds on which conclusion of this paper was drawn up; abstraction used upon evaluation of case studies; comparison assessing consistency and inconsistency of phenomena and objects; description inevitable for characterization of companies and environment in which they operate; interview collecting information inevitable for the evaluation of the way of working with scenarios and company knowledge standards; modelling was used upon consideration about possible future development of factors observed.

The paper arrived at conclusion, that scenario approach, when used appropriately, may significantly mitigate risk exposure of the company. Conclusions which have been made on selected industrial companies can be extended to other industrial branches. Practical application of scenario planning method confirmed that this approach was superior to deterministic single scenario model. Scenario technique thus compensates for deficiencies and omissions which are inherent in simplistic deterministic model. In cases where an investment scenario planning process proved to be insufficient, the paper refers to more advanced techniques like simulation methods or real options.

Over past ten years practical test of proposed stepwise process of scenarios elaboration was repeatedly tested on approx ten industrial companies during the tenure of Mr Soucek and Mr Špaček in top managerial positions.

This paper offers flexible and feasible toll for scenario elaboration and their further development. Such an approach contributes significantly to the enhancement of company risk management process. Proceedures described were successfully tested in managerial practice by two of authors while holding CEO positions in oil prcessing and pharma business.

This paper does not have direct social implication. But scenario approach as a powerful tool of risk management process may significantly contribute to company survival and thus impact social status all stakeholders concerned. Therefore social implications should be identified rather on the background of the problem.

Notwithstanding some general notion about scenario concept, there is still little evidence that scenario approach is applied in larger extent. It is prevalently due to lack of expertise of respective managers who are obviously puzzled with numerous outcomes to be obtained by this approach. Clearly define procedure of scenarios formation may be conducive to larger exploitation of this approach. Design of the elaboration and application of scenario approach which was proven to be functioning in the practice brings new benefits to risk management exploration.

This paper aims to go deeper on the analysis of the shaft voltage of large turbogenerators. The main interest of this study is the investigation process developed.

The analysis of the shaft voltage because of several defects is based on a two-dimensional (2D) finite element modeling. This 2D finite element model is used to determine the shaft voltage because of eccentricities or rotor short-circuit.

Dynamic eccentricities and rotor short circuit do not have an inherent impact on the shaft voltage. Circulating currents in the stator winding because of defects impact the shaft voltage.

The original value of this paper is the investigation process developed. This study proposes to quantify the impact of a smooth stator and then to explore the contribution of the real stator winding on the shaft voltage.

The purpose of this paper is to present study of thermal creep stresses and strain rates in a circular disc with shaft having variable density by using Seth’s transition theory.

Seth’s transition theory is applied to the problem of thermal creep transition stresses and strain rates in a thin rotating disc with shaft having variable density by finite deformation. Neither the yield criterion nor the associated flow rule is assumed here. The results obtained here are applicable to compressible materials. If the additional condition of incompressibility is imposed, then the expression for stresses corresponds to those arising from Tresca yield condition.

Thermal effect increased value of radial stress at the internal surface of the rotating disc made of incompressible material as compared to tangential stress and this value of radial stress further much increases with the increase in angular speed as compared to without thermal effect. Strain rates have maximum values at the internal surface for compressible material.

The model proposed in this paper is used in mechanical and electronic devices. They have extensive practical engineering application such as in steam and gas turbines, turbo generators, flywheel of internal combustion engines, turbojet engines, reciprocating engines, centrifugal compressors and brake disks.