Large Steam Turbine Research Articles

Fault Tolerant Control and Safety Systems for Large Steam Turbines

The stringent requirements regarding availability of large turbine generator sets have led to the development of control and safety systems capable of withstanding malfunctions without impairing the production of electricity. These fault tolerant systems are made up of modules from the Microrec range to equip French nuclear units of 1300 and 1500 MW, in order to avoid any loss of power production subsequently to a failure of such a system. Three Identical and separate channels ensure the basic control (turbine speed control and governing valves opening). Automatic operation functions, such as speed run up, load variations, remote control, are ensured by a calculator. In case of fault it is automatically disconnected. The unit is then operated in a manual mode through the basic controllers. The safety system consists of three fail safe electric safety channels actuating a control circuit common to all the steam admission valves and an automaton for supervision and routine tests. These channels operate on a two-out-of-three basis. This equipment whose technological characteristics are described, uses micro-processors except for the protection channels which feature a hard-wired logic system.

The method and equipment for induction surface hardening of the leading edges of turbine blades

Methodology and equipment for hardening the leading edges of blades for large nuclear reactor steam turbines was investigated using blades made of 15Kh11MF hardened and tempered steel. A machine was designed and built for hardening the blade leading edges with a vacuum-tube oscillator and 66,000 Hz frequency. The electrical parameters of the induction heating were recorded. Hardening of the actual blades made it possible to obtain a hardened case with a depth of 1-3 mm and up to 5 mm in the lower portion of the blade and increased erosion resistance.

Trends and future scope in the monitoring of large steam turbine generators

Current practices in the monitoring of large steam turbine generators are briefly discussed, consideration being given to the traditional range of turbine supervisory equipment, and the more extended facilities which are sometimes now associated with rotating machinery, such as vibration monitoring, together with the more generalised data logging systems now specified by some Utilities. Consideration is given to the possible range of parameters and equipment areas which may now be incorporated into a monitoring scheme, and attention is drawn to the advances in display technology and operator interfaces which are now possible at moderate cost. In a concluding section, a range of monitoring functions which could be of wide general application in the field of steam turbine generators is discussed.

High-integrity ferrous castings for steam turbines – aspects of their development and manufacture

The past twenty to twenty–five years has been a period of considerable change for the foundry industry during which established practices and ingrained attitudes have required critical re–appraisal and occasionally drastic revision. The energy related industries, demanding higher quality components of proven integrity as service conditions have become progressively more exacting, have played an important role over this period as castings specifications have been subject to frequent revision to reflect changing requirements. Founders have been required to respond, first in order to exploit the buoyant market of the 1960's and early 1970's, and second to survive in the depressed international market of the late 1970's and early 1980's. This paper reviews developments in ferrous castings for large steam turbines during this period, and outlines the manner in which specifications for this type of casting have become progressively more stringent. The impact of these changes on the foundry industry is reviewed, and an outline is given of the response of one UK castings manufacturer to the challenge of competing in the international marketplace of the 1980's.MST/164

High-integrity ferrous castings for steam turbines – aspects of their development and manufacture

AbstractThe past twenty to twenty–five years has been a period of considerable change for the foundry industry during which established practices and ingrained attitudes have required critical re–appraisal and occasionally drastic revision. The energy related industries, demanding higher quality components of proven integrity as service conditions have become progressively more exacting, have played an important role over this period as castings specifications have been subject to frequent revision to reflect changing requirements. Founders have been required to respond, first in order to exploit the buoyant market of the 1960's and early 1970's, and second to survive in the depressed international market of the late 1970's and early 1980's. This paper reviews developments in ferrous castings for large steam turbines during this period, and outlines the manner in which specifications for this type of casting have become progressively more stringent. The impact of these changes on the foundry industry is r...

Experience and Recent Development with Gas Directly Cooled Rotors for Large Steam Turbine Generators

Experience and Recent Development with Gas Directly Cooled Rotors for Large Steam Turbine Generators

Modern Display and Storage of Large Steam Turbine-Generator Data

Display and storage of large steam turbine generator operating data have traditionally been done in a segmented fashion for the turbine, generator and boiler feedpump system. The distributed, microcomputer-based turbine generator supervisory equipment described in, this paper presents a method of handling turbine, generator, and boiler feedpump system measurements with a single system. The result is a modern, reliable, and efficient means of measuring, displaying, and storing large amounts of information.

Inlet angle distribution of last stage moving blades for large steam turbines

A simplified analytical method is presented for use in preliminary design studies on the final stages of large steam turbines to derive the required moving blade twist distribution to achieve near-zero incidence. The method incorporates the influence of nozzle twist and of casing flare which is shown to enter the analysis mainly through its effect on the distribution of streamline curvature. Provided flare is properly incorporated into the design, there appears to be no inherent reason why higher flare should limit performance unduly. Optimisation of moving blade twist for variations in load and back pressure is also investigated. Blade skeletons derived analytically are subjected to full throughflow calculations and refined where necessary to improve their likely performance. The results are compared with results of calculations with published commercial blade angle distributions, designed for both low- and high-flare turbines. The results of the throughflow calculations on the blades derived here, and the comparisons with apparently successful commercial blades, suggest that this method can be used as a preliminary design tool, freeing the designer from repetitive trial runs with a full throughflow calculation.

A High Integrity Software Based Turbine Governing System

Large steam turbines used for electrical power generation demand governing systems of very high integrity (safety) and availability. The latest generation of electronic governors uses microprocessors in a distributed, two level architecture to achieve the required integrity and availability and in addition provides greater configuration flexibilities and wider facilities than earlier governors. Intelligent self checking by the processors is fundamental to the structure of the governor. Software quality control is maintained by rigorous use of structured analysis and design techniques.

Heat treatment of high-temperature rotors for large steam turbines

Heat treatment of high-temperature rotors for large steam turbines

End-Winding Vibrations in Large Synchronous Generators

A variety of generator problems are associated with end-winding vibrations. Understanding these vibrations can, therefore, contribute significantly towards improving the generator's overall availability rate. The vibration measurements taken on a large 2-pole steam turbine generator operating in the field have been reported in this paper. Tests showed significant increase in vibrations at leading power factors, which is explained by considering the effect of core vibrations on the end-windings. An approximate formula has been developed to predict the rated load vibrations from the open-circuit and shortcircuit vibrations which can be measured in the factory.

最近の大容量蒸気タービンの技術動向

最近の大容量蒸気タービンの技術動向

Regression Estimates of Damages in Price-Fixing Cases

In an antitrust price-fixing case, damages are measured by the difference between the prices paid by the plaintiff purchasers and the prices they would have paid in the absence of defendants' conspiracy. Even small variations in the determination of these differences may become significant because plaintiffs are entitled by statute to receive three times their actual damages.1 Moreover, in a class action there may be thousands of purchasers whose recoveries are based on an industrywide overcharge formula. The difficulty of course lies in estimating the "but for" prices. An obvious idea is to assume that competitive prices during the conspiracy period would have been the same as they were before or after the conspiracy or in interludes of competition within the conspiracy period. Thus, the difference between the conspiratorial price and the actual price from other periods measures the damage. This estimate, however, meets the immediate objection that it is likely to be incorrect because changes in factors affecting price other than the conspiracy would have produced changes in competitive prices if there had been competition during the conspiracy period. These arguments may be illustrated by Ohzo Valley Electrc Corp. v. General Electric Co., 2 one of the well-known antitrust cases involving electrical equipment manufacturers. Plaintiffs contended that the purpose and effect of the manufacturers' conspiracy was to keep transaction prices for large steam turbines close to book prices; they proposed to measure damages by the difference between the average 11% discount during the conspiracy period and the average 25.33% discount that prevailed after the conspiracy had been terminated. Defendants replied that economic conditions for the sellers had worsened in the postconspiracy period and that these conditions accounted for the increase in the discount. They pointed to the presence for the first time of effective foreign competition, an increase in the manufacturers' capacity to produce steam turbine generators (which caused an oversupply), a lessening of growth in demand, and a drop in manufacturing costs (which permitted defendants to offer their products at a lower price). After a bench trial, District Judge Feinberg initially found that these factors did account for some of the increase in the discount in the postconspiracy period. He then confronted the question of how much. Treating the matter as one of

Variable structure servomechanism design and applications to overspeed protection control

A new class of variable structure feedback systems capable of rejecting a persistent disturbance is developed. This type of system which is called the VS servo is structurally similar to linear multivariable servomechanisms. Its behavior on the switching manifold and its internal stability and output regulation properties are examined using the theory of variable structure systems and sliding modes and existing results on high gain feedback. The concepts of the VS servo are particularly well suited for the study of ‘emergency’ control system design. The design of the VS servo is applied to the problem of overspeed protection control for large steam turbines. This study leads to an understanding of the generic difficulty associated with the application of overspeed protection control to large coal fired power plants and provides a feedback control structure with considerable promise for such applications. In addition, the paper serves as a useful illustration of the flexibility and potential applicability of variable structure designs. The effect of actuator parasitic dynamics is considered.

An Application of a Variable Structure Servomechanism Design to Turbine Overspeed Protection Control

The concepts of variable structure systems and sliding mode are particularly well suited for the study of ‘emergency’ control system design. In this paper, recent results pertaining to the design of variable structure servomechanisms are applied to the problem of overspeed protection control for large steam turbines. The study leads to an understanding of the generic difficulty associated with the application of overspeed protection control to large coal fired power plants and provides a feedback control structure with considerable promise for such applications. In addition, the paper serves as a useful illustration of the flexibility and potential applicability of variable structure designs. The effect of actuator parasitic dynamics are considered.

Damping shaft Torsional Oscillations with Application to High Speed Reclosure

A method of damping torsional oscillations in large steam turbine generators is presented. The method utilizes a small AC-DC converter connected to the high voltage side of the generator step up transformer. The DC side of the converter is connected to a large inductor which is used to store energy. By modulating the inductor energy appropriately, damping can be added to the torsional modes of a turbo-generator. It is shown that this added damping significantly reduces the shaft torques occurring as a result of unsuccessful high speed reclosure thus reducing the possibility of shaft damage

Liquid film and droplet stability consideration as applied to wet steam flow

The state of art and ongoing research concerning the flow of wet steam in large steam turbines is reviewed, particularly from the viewpoint of the behavior of the liquid film deposited upon the stationary blading. New experimental results concerning the non-steady behavior of the film and the resultant wavelet formation patterns under the action of high-velocity low-pressure steam flow are presented. These results are then correlated as a flow regime “map” showing various flow regions in terms of steam velocity (or relative steam-film velocity since film velocity is relatively very small) vs. film flow rate per unit transverse distance.

The Effect of Water Chemistry on the Reliability of Modern Large Steam Turbines

The results of a survey of 50 once-through steam generators and 60 drum boiler steam supplies for modern large steam turbines are presented in this paper. A questionnaire was circulated and the information gathered was used to assess current industry practices related to feedwater treatment, boilerwater chemistry and steam purity measurements. Further information was gained by visiting 28 of the surveyed power plants and developing more information concerning their water chemistry practices. The results of the survey and visitation information are then related to individual cases of major corrosion damage that have occurred in the turbines of the participating utilities: The once-through steam generators provide the best measure of steam purity because, in general, the steam purity is equal to the feedwater purity. Major corrosion damage, in many instances stress corrosion cracking, appears to be related to upset conditions of steam purity and water chemistry.

Torsional Fatigue of Turbine-Generator Shafts Caused by Different Electrical System Faults and Switching Operations

The torsional stresses that occur in large steam turbine- generator shafts due to both planned and unplanned system switching operations are discussed. These operations include routine line switching, reclosing line-to-ground faults by either triple-pole or single-pole breaker operation, reclosing line-to-line and three-phase faults, malsynchronization and load rejection. The calculation of cumulative fatigue of individual turbine-generator shafts from computer-plotted torsional swing traces is explained. The benefits of single-pole breaker operation and of dividing the output of large generators between different electrical systems are briefly mentioned.

Embrittling characteristics of Ni-Cr-Mo-V steels designed to exhibit low susceptibility to temper embrittlement in large steam turbine rotor applications

Test steels containing 0.25 pct C, 1.0 pct Ni, 3.0 to 4.5 pct Cr, 0.8 to 2.0 pct Mo, 0.12 pct V and two levels of such impurities as phosphorus, tin and antimony, quenched and tempered to a 825 MPa (120 ksi) minimum yield strength level, have been examined for temper-embrittlement susceptibility. The susceptibility is influenced by a combination of chromium and molybdenum contents rather than by contents of individual elements. The susceptibility in steels with 3 pct Cr-0.8 pct Mo and 4.5 pct Cr-0.8 to 1.6 pct Mo was significantly lower than that of a 3.5Ni-1.7Cr-0.5Mo-0.1V steel at the same impurity level.