Large Turbine Generators Research Articles

Performance of HVDC Converters in Enhancing Transient Stability of Power Systems and in the Torsional Stressing of Generator Shafts Due to Balanced and Unbalanced Operation of the Rectifier

This paper examines performance of HVDC converters with respect to real and reactive power at the inverter or rectifier following a command for power injected into or taken from the AC system to enhance power system stability. It also considers the effect balanced and unbalanced operation of inverters in asynchronous links has on torsional stressing of large turbine-generator shafts. First a 6-pulse bridge is modeledto determine characteristics for reactive power at both the inverter and rectifier as a function of AC power at the inverter or rectifier. Responses for real and reactive power following transient commands for AC real power are determined for a range of commands for real power to enhance transient performance of the power system. The characteristics relate to a link with typical parameters rated at 200 MW ~ 1000 MW. Performance of a 12-pulse bridge configuration that was modeled is then summarized. Noncharacteristic harmonic currents injected by the inverter into the AC system due to balanced and unbalanced operation of the rectifier in an asynchronous link is then reviewed. Excitation of turbine-generator shaft torsional vibrations by noncharacteristic currents injected into the AC system on account of balanced and unbalanced operation of the rectifier is then discussed.

Calculation and Measurement of Torsional Vibrations in Large Steam Turbosets – New Technique

ABB has been carrying out torsional vibration test on steam turbine sets for many years, with sizes ranging from 350MW coal fired steam turbines to 1000MW nuclear steam turbines. Rated speeds have been 1,800 rpm and 3600 rpm. Torsional shaft vibrations are excited in large steam turbine generators sets by electrical disturbance torques occurring in the active part of the generators. Due to the low torsional damping of the shaft trains, resonance can cause high torsional vibration amplitudes. Some thermal power plant operators require experimental verification of the natural torsional shaft frequencies. ABB has developed a new measurement technique which allows torsional vibration to be measured in a selected measurement plane along the shaft. With today's highly sensitive sensors and modern measurement and data analysis equipment, the excitation due to normal random disturbances in the electrical grid provides sufficiently good results. All natural torsional frequencies in the range of interest are obtained with an accuracy of ± 0.2 Hz and identified using the calculated natural frequencies. The new measurement technique, places no restrictions on normal power plant operation.

Analysis of saturated synchronous reactances of large turbine generator by considering cross-magnetizing reactances using finite elements

This paper describes a method to calculate saturated reactances of synchronous machines at various loads under steady-state operation by considering influence of cross-magnetizing phenomenon between d- and q-axis circuits. In the method, mutual reactances x/sub dq/ due to the cross-magnetizing phenomenon can be calculated on the basis of two-dimensional magnetic field analysis. The validity of analysis is shown by good agreement between measured and calculated field current values of a 592 MVA turbine generator at various loads. It is clear that quantitative accuracy requires the magnetic coupling between d- and q-axis circuits be considered. Subsequently, steady-state reactances at various loads are analyzed by considering mutual reactances x/sub dq/ due to cross-magnetizing phenomenon. The relation between the load angle /spl delta/ and mutual reactance x/sub dq/ is clarified, and the difference between equivalent synchronous reactances that are obtained by considering x/sub dq/ and conventional defined synchronous reactances that do not consider x/sub dq/ is shown numerically.

Methods of stator winding on-line diagnostics for large turbine generator preventive maintenance

The introduction of on-line diagnostic methods is a mandatory condition for the transition from the existing maintenance system to a preventive maintenance system. This paper analyses the methods of early detection of the most common defects in stator windings of large turbine generators with water cooling. The detection of overheating and leaks in the winding is described. The examples are given in which the detection of these defects and their repair prevented failures with heavy consequences.

Analysis of shaft torsional phenomena in governing large steam turbine generators with non-linear valve stroking

The paper focuses on how shaft torsional problems can be initiated in some situations by the fast action of steam control valves. It demonstrates that shaft flexibility can exert a significant influence on steam turbine-generator response following severe supply system disturbances, particularly for large machines where the turbine has nonlinear valve stroking and fast valving. The effect can be minimised by careful location of the speed sensor on the turbine shaft and by filtering to reduce speed input or acceleration signals due to troublesome low-frequency torsional vibrations to an insignificant level. Digital implementation of steam-turbine control systems is described. Response for a range of control philosophies where digital control procedures are used are given. Two large machines where digital speed sensing and filtering techniques in steam valve control are implemented are examined.

A Monte Carlo simulation approach to the evaluation of maximum turbine-generator shaft torsional torques during faulty synchronization

In this paper a Monte Carlo based approach to the evaluation of the maximum electromagnetic and torsional torques induced in turbine-generator shafts during faulty synchronization is presented. In this context, investigations have been conducted on a large turbine-generator model taking into consideration the uncertainty of several factors associated with the practical operation of a power system. The effect of employing a more precise synchronization device on the expected maximum turbine-generator torques as well as the probability density function of such torques have also been investigated. The results of these investigations are presented in the form of probability distributions of the maximum torsional torques induced in the turbine-generator shaft sections.

Effect of adaptive single-pole reclosing on the stochastic behavior of turbine-generator shaft torsional torques

This paper presents a Monte Carlo based approach to evaluate of the maximum torsional torques induced in turbine-generator shafts during high-speed reclosing of system faults. Two reclosing schemes were considered, namely simultaneous and adaptive reclosing. In the case of a single line-to-ground fault, single-pole reclosing is considered in clearing such a fault. In this context, investigations have been conducted on a large turbine-generator model taking into consideration the uncertainty of several factors associated with the practical operation of a power system. The effect of employing adaptive single-pole reclosing on the expected maximum torsional torques as well as their variances have also been investigated. A risk index which reflects the likelihood that the torque induced in a turbine-generator shaft exceeds its design value is also presented.

Calculation of electromagnetic forces on large generator end-windings under fault conditions using a three-dimensional finite element method

Electromagnetic forces generate vibrations in the end-winding support structure of large turbine generators under fault conditions. To study this phenomenon, a 3D electromagnetic model for the computation of the forces on the conductor bars, is described. The model is then applied to the study of a 600 MW generator under short circuit conditions.

Order backlogs and strategic pricing: the case of the U.S. large turbine generator industry

This paper illustrates the usefulness of game theory for strategic management through theoretical and empirical analysis of price competition in the presence of production backlogs. Game-theoretic analysis predicts a different relationship between relative prices and backlog levels than does analysis that ignores the sorts of interactive considerations emphasized by game theory. Empirical analysis based on data for the U.S. market for large turbine generators between 1951 and 1963 corroborates the game-theoretic prediction. The paper concludes with a discussion of the sorts of situations in which game-theoretic reasoning is particularly likely to prove useful. © 1998 John Wiley & Sons, Ltd.

Order backlogs and strategic pricing: the case of the U.S. large turbine generator industry

Order backlogs and strategic pricing: the case of the U.S. large turbine generator industry

Prediction, Diagnosis and Control of Rotor Thermal Vibration For Turbine Generator.

A large capacity turbine generator has tertiary mode of rotor vibration. Then the thermal unbalance of rotor has a large effect on increasing its vibration. This study presents a method for prediction and diagnosis in order to distinguish the thermal unbalance causes by using rotor condition supervision equipment and rotor thermal vibration measuring equipment. Furthermore this paper deals a method for actual adjustment in order to decrease the thermal vibration stroke by using thermal vibration operator. By this method, a satisfactory vibration was achieved for a large capacity turbine generator.

Effect of HVDC converter station faults on turbine-generator shaft torsional torques

This paper explores the impact of HVDC converter station faults on the torsional torques induced in turbine-generator shafts. In this context, investigations have been conducted on a large turbine-generator unit connected to an HVDC system. Faults considered are firethrough, misfire and a short-circuit across a nonconducting valve. The effect of the fault incidence time on the maximum turbine-generator torsional torques is also investigated. The results of these investigations are presented in the form of typical time responses as well as parametric studies.

Stochastic evaluation of turbine-generator shaft torsional torques

This paper presents a probabilistic approach to the evaluation of the maximum torsional torques induced in turbine-generator shafts during high-speed reclosing of system faults. In this context, investigations have been conducted on a large turbine-generator model taking into consideration the uncertainty of several factors associated with the practical operation of a power system. The results of these investigations are presented in the form of discrete probability distributions of the maximum torsional torques induced in the turbine-generator shaft sections.

Design of a complete multi-microcontroller based protection system for large diesel turbine generator

This paper presents a multi-microcontroller based protection system, which includes three relaying modules and one master control module, to realize parallel processing and background management. The proposed protection system is suitable to be employed as the primary and backup protection for a large diesel turbine generator. Hardware and software redundancy techniques are used, and the bottleneck effects of the single processor system are eliminated. The hardware of the protection system is modularized with the same architecture with respect to relaying modules. The master control module is responsible for system monitoring, communications and man-machine interfacing, it can reassign the protection functions in case of one relaying module failure.

Damping torsional oscillations due to network faults using the dynamic flywheel damper

The technical feasibility of using a dynamic flywheel damper to damp shaft torsional oscillations in large turbine generators is investigated. Torsional damping is achieved using the slide friction force of the flywheel damper based on generator speed. A system is defined and the shaft torques following various electrical system disturbances are evaluated and analysed. It is shown that substantial damping can be implemented with a well designed flywheel damper, thus reducing the risk of significant shaft damage due to network disturbances. The equivalent models and designs for the flywheel dampers fitted into the shaft couplings of turbine mechanical systems are also described. This method can effectively damp the torsional oscillations due to the high reliability of the damper.

Estimation of reactive power export and import capability for non-utility generators

Non-utility generators (NUG's) are typically required by their electric power sales agreement to have the capability to supply power to the purchasing utility near unity power factor. With the advent of large combustion turbine generators, many NUG's are simple or combined cycle facilities with generating capacities in excess of 100 MW. Utilities are recognizing that these large NUG facilities can be significant contributors to the reactive power [megavars (MVArs)] flow needed to support system requirements and transmission level grid voltages. NUG's are now being dispatched for MVAr export and import activities to meet utility requirements. The ability of a NUG to export or import MVArs is highly dependent on the actual transmission intertie voltage level. Unless plant-specific studies are performed, this capacity can be difficult to ascertain for the NUG operating and engineering personnel. This paper presents a method, based on system load-flow studies, for estimating the capacity of a NUG to export or import MVArs at a given transmission intertie voltage level. It also explores other key variables which determine the ability of a NUG to export or import VArs. This methodology can be used to aid operating personnel at existing facilities or as a guide during the design of a new facility.

Computation of forces and stresses on generator end windings using a 3D finite element method

Electromagnetic forces generate vibrations in the end-winding support structure of large turbine generators. In order to study in detail this phenomenon, a 3D electromagnetic model which computes the forces an the conductor bars, is coupled with a 3D mechanical model which calculates the displacements using the electromagnetic forces as an input. The method is applied to the study of a 600MW generator endminding under rated steady-state conditions.

Deformation, Alignment, and Vibration in Large Turbine-Generator Set

Within the Industrial Alignment Project (1990–93) and the Dynamic Alignment Project (1993–96), collaborative research and development efforts involving the department of geomatics engineering at The University of Calgary, the Natural Sciences and Engineering Research Council of Canada, and a number of industrial partners in western Canada, many high-precision machinery surveys have been carried out. In a project for one of the industrial partners, a number of epochs of deformation, alignment, and vibration measurements were made on a large turbine-generator set. Measurements were made in order to identify the root cause of high vibration levels. Analysis of these measurements reveals that high vibration levels are a result of a “soft foot” condition caused by structural weakness in the reinforced concrete table that supports the turbine-generator set. It was recommended that the owner consider stiffening the table by making solid (i.e. moment resisting) connections between the table and all supporting columns.

Stochastic evaluation of turbine-generator shaft torsional torques during faulty synchronisation

A probabilistic approach to the evaluation of the maximum torsional torques induced in turbine-generator shafts during faulty synchronisation is presented. This approach is based on utilisation of the conditional probability theorem to assess these torques. In this context, investigations have been conducted on a large turbine-generator model taking into consideration the uncertainty of several factors associated with the practical operation of a power system. The results of these investigations are presented in the form of discrete probability distributions of the maximum torsional torques induced in the turbine-generator shaft sections.

Considerations on Large Turbine Generator Electromagnetic Characteristics for an SFC Start.

This paper describes large turbine generator electromagnetic characteristics, considering harmonic components of the armature current, for a static frequency converter (SFC) start. Namely, the magnetomotive force for an SFC start is calculated, and frequency characteristics of higher harmonic magnetic flux and currents in a field circuit and a damper circuit are considered. Then the pulsating torque is analyzed, and the effects of the damper circuit toward the pulsating torque are considered. The results are as follows.(1) When the fundamental frequency is more than about one hertz, the higher harmonic magnetic flux decrease, and vibration due to the electromagnetic force is insignificant.(2) The eddy currents in each damper bar differ with each slot position and each angle between the armature fundamental magnetomotive force and the field fundamental magnetomotive force.(3) The torque waveforms differ for each fundamental frequency.