Turbogenerator Unit Research Articles

Innovative rotary friction welding of heat exchanger tube nozzles on high pressure headers

This paper describes an innovative application, driven by an industrial requirement for an alternative welding process to submerged arc welding of header heat exchanger tube nozzles, of an automated friction hydro-pillar processing (FHPP) welding platform (WeldCore©). This was the first successful application of rotary friction welding of heat exchanger tube nozzles to high pressure-headers used in the high-pressure heaters of a boiler on a 609 MW steam turbo-generator unit. The FHPP WeldCore platform allows highly time- and cost-effective welding and repair of high temperature, high pressure power plant using a procedure that was approved in the 2015 ASME Boiler and Pressure Vessel Code, Supplement 3 as Code Case 2832 (WPS qualification for Friction Taper Hydro-Pillar (FTHP) welding). This certification opened the way to using FHPP welding for repair and refurbishment of power generation and high temperature process plant. After completing the welding of 448 nozzles onto each of two HP headers, all welds were found to be defect-free using ultrasonic testing, and test nozzle welds passed the weld qualification procedure required by industry.

Stochastic modeling and parameter estimation of turbogenerator unit of a thermal power plant under classical and Bayesian inferential framework.

The work reported in present study deals with the development of a novel stochastic model and estimation of parameters to assess reliability characteristics for a turbogenerator unit of thermal power plant under classical and Bayesian frameworks. Turbogenerator unit consists of five components namely turbine lubrication, turbine governing, generator oil system, generator gas system and generator excitation system. The concepts of cold standby redundancy and Weibull distributed random variables are used in development of stochastic model. The shape parameter for all the random variables is same while scale parameter is different. Regenerative point technique and semi-Markov approach are used for evaluation of reliability characteristics. Sufficient repair facility always remains available in plant as well as repair done by the repairman is considered perfect. As the life testing experiments are time consuming, so to highlight the importance of proposed model Monte Carlo simulation study is carried out. A comparative analysis is done between true, classical and Bayesian results of MTSF, availability and profit function.

A Case Study on Condition Assessment of Fire-Damaged RC Members of Turbo-Generator

Many researchers across the globe have carried out fire safety risk analysis to gather evidence and pertinent data for different Reinforced Cement Concrete (RCC) members exposed to fire. Assessment of fire-damaged structures furnishes the minute details of the effect of fire on the properties of concrete.The study indicates the condition assessment of the turbo-generator (TG) unit, comprises of concrete bearing pedestals, deck and supporting columns. The research was conducted using Non-Destructive Testing (NDT) techniques using Rebound hammer test, Ultrasonic Pulse Velocity (UPV) test, Concrete Cover measurement, Carbonation and Crack depth measurements followed by microstructural studies using an X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Optical Microscope (OM), and Mercury Intrusion Porosimetry (MIP). The samples were taken from a fire-damaged concrete bearing pedestal B2 and a non-fire-damaged concrete bearing pedestal B4 of the TG unit. The approach enabled us to find the extent of damage to the RCC members exposed to fire. The above mentioned test witnessed that the concrete bearing pedestal B2 was the moderately distressed member, expressed doubtful quality of concrete, higher porosity, reduced residual compressive strength and reduction in yield strength of steel. However minor distress in form of crushing at the top grout portion was observed in concrete bearing pedestal B4, and no apparent distress was observed in supporting columns of TG unit. Based on the distress identified, repair and remedial measures were proposed to concrete bearing pedestals in order to improve the performance of the TG unit.

Strategy and Technique of High Efficiency Balancing in Field for Turbo-Generator Units with Large Capacity

.This paper aims at the high efficiency of field balancing for turbo-generator with large capacity currently, and introduces the strategies and key techniques of the rotor system balancing with practical cases of power plant in field. The acquisition, analysis and former processing of the original vibration data for balance calculation are included. Furthermore, they involve complete measuring points and conditions, accurate judgment for the types of unbalance exciting force and selection of stable vibration data, all these could reduce the blindness of balancing effectively. The strategies and techniques also contain the determination for axial plane of unbalance by the modal method, then the optimal steps and the plane of adding weight are chosen during the implementation of balancing. Besides, this paper also introduces the analysis and selection of influence coefficients and the phase of trial weight, these can help determine the final correction weight accurately in order to guarantee the balancing process prompt and efficient. Meanwhile, the restriction of practical location for adding weight and construction period of maintenance and production for the units should be considered during the high efficiency balancing in field. These strategies and techniques of high efficiency balancing have practical application value in promoting the technology of field balancing for turbo- generator units with large capacity.

The Analysis of a Generator Shaft Crack Cause by Torsional Vibration due to SSR

.This paper introduces the serious crack accident of the rotor of a 600 MW turbo-generator unit in Vietnam, which leads to the rotor scrapped. After excluding the material and design reasons, it is considered that the electrical torque is the possibility. Through the operation parameters and theoretical calculation of the unit, the fault reason is positioned as Sub-synchronous resonance. The most important criterion is that the vibration of Unit 1 increases simultaneously with that of Unit 2, which is physically isolated from Unit 1. Further theoretical calculation shows that the natural frequencies of torsional vibration are 13.74 Hz, 26.23 Hz and 30.30 Hz, which are complementary to the grid frequency at that time cause of the change of grid structure.

Seismic Test and Simulation of Spring Vibration Isolated Foundation for Turbo-Generator

The 1 : 8 model of turbo-generator vibration isolated foundation of common islands in nuclear plants was established for vibration characteristic tests and pseudodynamic experiments. The finite element model was established by SeismoStruct for time-history analysis. Frequencies, modal shapes and seismic responses, deformation curves, and spring deformations were compared and analyzed. Results from tests and experiments show that the natural frequencies of spring vibration isolation foundation are lower than those of common frame foundations and the vertical frequencies are far from the working disturbance frequency of the turbo-generator units. The spring vibration isolation device can reduce the acceleration response of the TG (turbo-generator) deck and redistribute the horizontal earthquake action of the foundation according to the stiffness to give full play to the seismic capacity of the columns. The errors of natural vibration frequencies and maximum seismic response are approximately 15% and 10%, respectively, and the simulation results are in good agreement with the test and experiment data. The proportion and distribution of spring deformation are close, and the test study shows the convenient and precise realization of the simulation. Results of seismic experiments and numerical simulations show that the foundation design meets the standard of the “Code for Seismic Design of Buildings” in China, which realizes the goal of spring vibration isolation and seismic resistance. The foundation design is also reasonable, safe, and reliable.

Troubleshooting of a 330MW turbo generator unit during commissioning

During the commissioning stage of a 330MW turbo generator unit, several serious defects occurred, such as low vacuum of condenser, abnormal vibration of shafting and bearing damage. Through fault analysis and vibration test, the hidden danger in design, manufacture and installation were found out and solved, the unit successfully completed 168 hours full load test run and put into operation.

Experimental investigation of insulation resistance for turbo generator digital protection

Insulation of all electrical machinery is practically in the form of organic compounds that contain water as part of their make-up. Excessive temperature tends to dehydrate and oxidize the insulation and make it become brittle and disintegrate under vibration and shock. The insulation lifespan of turbo generators deteriorates slowly at low temperatures and more rapidly at high temperature. Economic factors, such as initial cost, replacement cost, obsolescence, and maintenance, are of prime importance when determining the years of useful service desired for the electrical insulation. Generator digital protection- fault diagnosis test was carried out to find out the cause of insulation breakdown on the turbo generator unit 411G3. The experimental procedure consists of an insulation resistance test, meggering (time-resistance absorption test), and pendulum over-speed test. A thorough investigation was conducted to identify all the stator bars that constituted the Red phase and other connections. Voltage drops on these stator bars were measured and values were used to detect ground faults which were rectified via an intelligent protection scheme.

Design and Implementation of Subsynchronous Damping Controller for HVDC

The interaction between High Voltage Direct Current (HVDC) transmission lines and turbogenerator units will cause the damage of the generator shafting and the electrical system by exchanging energy at one or more lower synchronous frequencies, resulting in the damage or even breakage of the generator shafting, seriously affecting the safe operation of the power system. To solve this problem, the Supplementary Subsynchronous Damping Controller (SSDC) is an effective method to suppress the secondary synchronous oscillation of turbogenerator units connected to rectifier side caused by HVDC. This paper combines the first standard model parameters of IEEE subsynchronous oscillation with CIGRE HVDC transmission system, and builds a HVDC transmission test system for Subsynchronous Oscillations(SSO) research in PSCAD. Based on signal test method, a narrow band SSDC is designed, and the damping in each synchronization frequency band is greatly increased. When the proportional coefficient is appropriate, the electrical damping is positive. The effectiveness of the designed SSDC is also verified by time domain simulation.

Reconstruction of the Hydraulic Turbines of the Maina Hydropower Plant on the Basis of Propeller Runners with a Variable Rotational Speed

The use of turbogenerator units with a variable rotational speed is the leading world tendency to which due attention is not being devoted in our country. The expediency of replacing the operating adjustable-blade turbines that have exhausted their standard service life by propeller turbines of the same type with a variable rotational speed is shown for the example of the Maina HPP. Substantiation of the angle of setting the blades of the propeller runner and an evaluation of the energy effects obtained are given.

Modal Analysis of Quill Shaft in Turbo-generator Unit Based on SolidWorks

The main goal of this work is to carry out a numerical modal analysis of a Quill shaft of turbo-generator unitaffiliate to Mosul gas turbine station, using a trail version of popular finite element analysis software SolidWorks. The main function of Quill shaft is to protect the turbo-generator unit against overloads due to electrical network faults. The high flexibility of this shaft makes it capable of absorbing high displacements of resonance phenomena. This analysis is essentially needed to study the effect of transient loads applied to Quill shaft of turbo-generator unit under severe loading conditions such as electric network disturbances. The first five values of critical frequencies and mode shapes of axial, bending, and torsional vibrations were studied and analyzed. Each mode has been isolated separately by applying a special type of boundary conditions (restraints) available in program. The three types of natural frequencies have been found and reported. It was observed that the fundamental values of each three types of natural frequencies are relatively high and out of the range of Quill shaft operating speed. Finally, it has been concluded from all analyses that Quill shaft under consideration is safe from the stand point of modal analysis. The results show that the Quill shaft is not running at any of each three types critical speeds. Therefore, the resonance phenomenon for all three types of vibrations can not be happened no matter how high the amount of transient load applied.

Analysis on corrugated pipe break in the expansion joint of a turbo-generator set

In a power plant, the bellows of the lower part of the expansion joint for pumping and heating of the NO.8 turbo-generator unit breaked, and the internal guide plate was teared along the welding seam. Through observation of macroscopic morphology, hardness analysis, metallographic examination, energy spectrum analysis and other means, the corrugated pipe material itself unqualified performance, stress corrosion cracking, corrosion and other reasons were eliminated. According to the micro-characteristics of fatigue fracture and the service environment of the bellows, it is concluded that the main reason of break is the fatigue cracking of the bellows under the impact of the air flow and vibration.

Fault diagnosis based on a novel weighted support vector data description with fuzzy adaptive threshold decision

The fault diagnosis of generator units is critical to guarantee the high efficiency of the electric system. However, detailed fault samples are difficult to obtain, and the distribution of fault samples usually shows the characteristics of unevenness and unbalance, which may lead to low fault diagnosis precision. Nevertheless, it has been seldom considered in the traditional classifier of fault diagnosis for generator units until now. In this paper, a novel fault classifier of weighted support vector data description (SVDD) with fuzzy adaptive threshold decision is proposed and applied in the fault diagnosis of generator units. To tackle the drawback that SVDD is sensitive to the distribution of samples, a novel SVDD model based on a complex weight is proposed. The complex weight is assigned with local density and size-based weight, while local density of each data point is obtained with the k-nearest neighbour approach and the size-based weight of each data point is computed according to the proportion of classes. Then the conventional SVDD is reformulated with the complex weights. Furthermore, new decision rules based on the relative distance and fuzzy adaptive threshold decision are applied to identify the class of testing samples. Finally, the proposed method is applied in the identification of several standard datasets, as well as the fault diagnosis for a turbo-generator unit. Experimental results and the engineering application reveal that the proposed method shows good performance in accuracy and universality, and is suitable for the fault diagnosis of generator units.

Subsynchronous Resonance in Independent Energo with Distributed Semiconductoring Load

A subsynchronous eleсtromechanical resonance in autonomous power systems is caused by the coincidence of the natural frequency of power network and one of the natural frequencies of turbogenerator unit in the electrical power plant. The occurrence and development of subsynchronous resonance causes subsynchronous oscillations of generators rotors, which are dangerous for shaft elements of turbogenerator units. Besides that, load angle oscillations having small amplitude under frequencies of 10-15 Hz create radial vibrations in bearing supports of turbogenerator units. The vibrations cause the emergency disconnection by vibration protection. In this paper the feature of subsynchronous resonance development in autonomous power system is present in the load power uncontrolled asynchronous motors and a large amount of similar frequency-controlled asynchronous various power drives through numerical simulations are discussed.

Useful life estimation and condition inspection of a 28,800 kW gas turbine components

In the present work, the current condition and non–destructive testing results of a gas turbine rotor are presented. Moving blades and nozzles of a turbo generator unit were inspected. Important longitudinal cracks were found in convex and concave sides of most nozzles blocks after more than 20 years of operation. Estimation of life prediction by means of a simplified method programmed in Matlab was elaborated in order to calculate fatigue and creep damage in the rotor due to steady and transient operation during normal start–ups and shut–downs of the turbine. Fatigue models were implemented in the programme taking into account low cycle fatigue phenomenon and high temperature effects on thermal and mechanical properties of rotor material. A simplified creep analysis calculation was accomplished by using a programme for mathematical calculations. Some conclusions on fatigue life and creep predictions were obtained and some recommendations for reliable operation are issued in order to improve mechanical behaviour and extend useful life of the main hot gas path components.

Vibration Characteristics and Damage of Turbine Generator Shaft Rubbing

An abnormal journal vibration occurred when a 660MW turbo generator unit was in daily operation. It was identified that rubbing vibration had taken place based on the behavior of the journal vibration and the temperature change of lubricating oil. The rubbing was located inside the bearing box between the HIP rotor and the LP rotor. However, no elimination measures had been taken in time because the damage caused by rubbing was underestimated. Few months later a full inspection revealed that the LP rotor shaft had been worn out with a 70mm wide and 28mm deep groove, which greatly weakened the strength of the LP rotor. The analysis presented here may help in diagnosing and understanding rubbing-vibration-related problems in similar situations.

Analysis on Torsional Vibration Characteristics of Turbo-Generator Units Based on Finite Element Method

The torsional vibration problems of turbo-generator shafts are increasing widespread and sever under the coupled action between the turbo-generator unit and the power grid because of the complicated power grid structure. Thus, the accurate solution of torsional vibration inherent characteristics of the shafts is of great significance to do the safety evaluation. The finite element method (FEM) with higher accuracy is adopted to calculate the torsional vibration inherent characteristics in this paper. A 1000 MW turbo-generator shaft is taken as a studying object and its torsional vibration finite element (FE) model and solving process are introduced, using ANSYS software as implementation platform of the FEM. The simulation results show that the torsional vibration characteristics calculated by FEM are accurate and reliable.

Study of Intelligent Fault Diagnosis Method for Turbo-Generator Unit Based on Support Vector Machine and Knowledge

For the low efficiency and poor accuracy of turbo-generator Unit s fault diagnosis, this paper divided the common 18 kinds of vibration fault into four categories, and took advantage of support vector machine to distinguish the fault cluster for early fault diagnosis according to the characteristics of vibration signal spectrum. For different fault cluster, different fault pattern recognition model was established. With the use of certain symptom group and weighted fuzzy logic, this article engaged in knowledge reasoning to obtain the specific fault recognition mode. Besides, the searching methods of fault cause, fault influence and troubleshooting measures in the knowledge base were proposed, which made the diagnosis process more meticulous and comprehensive. Case analysis shows that it is feasible to use this method to develop a system for intelligent fault diagnosis of turbo-generator unit, which is valuable for further study in more depth.

Application of Harmonic Wavelet Analysis to Rubbing Vibration Signals for Rotating Machinery Fault Diagnosis

Harmonic wavelet transform (HWT)and harmonic wavelet time-frequency profile plot (TFPP) is introduced firstly in practice to identify weak singularity in a signal with noise clearly. With TFPP method, emulational signal and vibration data of the rubbing of the large practical turbo-generator units are analyzed successfully, which prove that the method is effectively extract the rubbing signal feature which is can not gained by the other signal analysis methods, and the rubbing of the turbo-generator units is identified effectively.

Influence of rotating speed on the coupled bending and torsional vibrations of turbo-generator unit with rub-impact

Rub-impact fault causes complicated vibration to the rotor system and is one of the main reasons for the system instability. The increment transfer matrix method is used to analyze the dynamic response of the coupled bending and torsional vibrations of turbo-generator shafts with rub-impact in this work. Aimed at a turbo-generator unit with different rotating speed, the vibration character of rub-impact fault is analyzed. The research results show that the influence of rotating speed on vibration amplitude is obvious. When the speed is lower than the first order inherent frequency, rubbing will cause bending and torsional vibration amplitudes of each shaft segment increase largely. When the speed is higher than the first order inherent frequency, vibration amplitudes slightly change by rubbing. The sensitive to rubbing position is different for increased vibration amplitude of each shaft segment. The shaft segment is more near to the rubbing position, the increased vibration amplitude is more obvious.