Turbine Unit Research Articles

Comparative Analysis of wear on Hard and Soft Coated Francis Runners: A Case study of Kali Gandaki ‘A’ Hydro Power Station

Abstract Surface coating on Turbine components is a regular practice in hydro power plants to tackle with wear. The Kali Gandaki ‘A’ hydro power station of Nepal having 3x48 MW Francis Turbine units made of CN 13/4 material has been regularly coating its Runners entirely using Tungsten Carbide based alloy through HP-HVOF hard coating process. In 2021 for the first time one of the Runners was partially coated around the blades using elastomeric semi-soft coating material manually via brush application, while the remaining portion of the Runner was hard coated. This study was conducted to compare the wear on the hard and soft coated runners after a similar period of operation under similar circumstances. Both the Runners were found to be heavily worn out at the upper and lower wearing rings, suction side of all blade inlets at the shroud and all blade outlets. The soft coated runner was found to have more erosion and cavitation wear than the hard coated runner. A unique canal-type cavity was found on the hub side wearing ring of the soft coated runner but no such pattern was seen on the hard coated Runner. The sections of the soft coated Runner where the coating was still intact had the parent material fully protected, but the sections with coating completely washed away were found to have deeper and wider cavities showing that the parent material had significantly washed away. The major reason behind the soft coated Runner being more worn out could be the manual application of coating material using hand brush which could have resulted in blade profile being distorted due to which the Runner efficiency might have reduced and thus higher erosion and cavitation occurred. This study could be useful to assess the applicability as well as the benefits and drawbacks of hard and soft coating on Francis Runner.

On the Potential of Biomass-Fueled Externally Fired Micro-Gas Turbines in the Energy Transition: Off-Design Performance Analysis

Abstract The potential of replacing the use of natural gas with biomass gasification syngas through an externally fired micro-gas turbine (EFMGTs) is the main scope of this study. This includes the performance assessment at various off-design and ambient conditions compared to a reference natural-gas-fired Micro-Gas Turbine. The penetration of biomass use in the decentralized combined heat and power (CHP) sector can reduce fossil fuel dependency and contribute to the achievement of the net-zero emissions target. For this purpose, an analytical externally fired thermodynamic model is incorporated and validated with an artificial neural network (ANN) based on a natural-gas-fired micro-gas turbine unit. An operating strategy is proposed to ensure the system's safe operation under any fuel input conditions. The performance between the investigated cases is compared using an exergetic analysis. The main loss contributors that determine each case's performance are the exit losses. The substantial decrease of the latter results in high externally fired part-load efficiency, maximizing 110% of design-point efficiency. System performance has a linear dependency on ambient conditions. The increased flexibility introduced by the proposed operating strategy case facilitates the transition from natural gas to biomass, especially for higher heat-to-power ratio demands. The analysis highlights that the current externally fired configuration lags behind in high electrical demands (>90 kWel). However, this deficiency is diminished in cold ambient temperatures (<0 °C), indicating that the proposed technology is very opportune for these climatic conditions.

Thermodynamic and Economic Analyses of a Novel Cooling, Heating and Power Tri-Generation System with Carbon Capture

The combined cooling, heating, and power (CCHP) system has attracted increasing attention due to its potential outstanding performance in thermodynamics, economics, and the environment. However, the conventional CCHP systems are carbon-intensive. To solve this issue, a low-carbon-emission CCHP system (LC-CCHP) is firstly proposed in this work by integrating a sorption-enhanced steam methane reforming (SE-SMR) process. In the LC-CCHP system, CO2 is continuously captured by the calcium loop so that low-carbon energy can be generated. Then, the LC-CCHP system thermodynamic model, mainly consisting of a dual fluidized bed reactor which includes the SE-SMR reactor and a CaCO3 calcination reactor, a hydrogen gas turbine, a CO2 reheater, and a lithium bromide absorption chiller, is built. To prove that the LC-CCHP model is reliable, the system major sub-unit model predictions are compared against data from the literature in terms of thermodynamics and economics. Finally, the effects of reforming temperature (Tref), the steam-to-carbon mole ratio (S/C), the calcium-to-carbon mole ratio (RCC), the equivalent ratio for gas turbine (RAE), and the hydrogen separation ratio (Sfg) on total energy efficiency (ηten), total exergy efficiency (ηtex), and carbon capture capability (Rcm) are detected. It is found that the minimum exergy efficiency of 64.5% exists at the calciner unit, while the maximum exergy efficiency of 78.7% appears at the gas turbine unit. The maximum energy efficiency and coefficient of performance of the absorption chiller are 0.52 and 1.33, respectively. When Tref=600 °C, S/C=4.0, RCC=7.62, RAE=1.20, and Sfg=0.27, the ηten, ηtex, and Rcm of the system can be ~61%, ~68%, and ~96%, and the average specific cost of the system is 0.024 USD/kWh, which is advanced compared with the parallel CCHP systems.

Vortex rope identification in Francis turbine based on cyclostationary extended dictionary learning

Francis turbine is one of the most commonly used hydraulic machinery for hydroelectric power generation, but its stability is frequently jeopardized by vortex rope. It is crucial to promptly and accurately detect vortex rope for the reliable operation of turbine unit. To address this challenge, the Cyclostationary Extended Dictionary Learning (CEDL) approach is proposed to identify vortex rope in Francis turbine. CEDL utilizes the Fisher discrimination criterion and low-rank constraints through the preprocessing and extending strategies to achieve accurate identification. Preprocessing specifically refers to the construction of filter for raw data based on cyclostationarity Then, the trained dictionary is used to extract features, and a linear classifier is developed based on these features. To evaluate the proposed method, vortex rope experiments are conducted in a Francis turbine under five conditions, and every condition includes four states: normal state, initial vortex rope, stable vortex rope and severe vortex rope. The results reveal three main findings. Firstly, the trained atoms in each sub-dictionary exhibit unique characteristics such as tonal frequency at 7 kHz and broadband frequency during 12–20 kHz, which are linked to the evolution stages of vortex rope. Secondly, the dictionary trained for a specific condition can achieve a classification accuracy of up to 90%, and even exceed 97% in some cases. Finally, the dictionary trained in a specific working condition can achieve relatively high classification accuracy in the scenarios of other working conditions.

Isothermal turbines − New challenges. Numerical and experimental investigations into isothermal expansion in turbine power plants

The efficiency of power plants with steam or gas turbines depends on the efficiencies of a thermodynamic cycle and devices implementing this cycle. In the case of high power outputs, we cannot expect a significant increase in the efficiency of individual devices. Therefore, what remains is to increase the efficiency of the implemented thermodynamic cycle − the complex Rankine cycle in the case of steam turbines or the extended Brayton cycle in gas turbine units. The efficiencies of these cycles depend on the hot reservoir temperatures, limited by the materials used. The solution seems to be the thermodynamic cycles with the highest efficiency within given temperature limits, the „generalized Carnot cycles”. About gas turbines, such a cycle is the Ericsson cycle. The most difficult element of this cycle is carrying out high-temperature expansion. So far, there is no literature data on a technical device implementing this process. In this article, we present a method for designing turbine nozzles for isothermal expansion and the results of experimental tests of the first isothermal turbine. In the case of gas microturbines with a regenerator, isothermal expansion can increase efficiency from 24% to 28% up to 36%. An increase in efficiency of several to a dozen percentage points is expected for Organic Rankine Cycle (ORC) turbines. Due to such significant increases in energy generation efficiency, an isothermal turbine may become a future solution for energy systems.

Assessment of the intensity of intermodule interaction and the choice of means of its organization in vibration monitoring systems of turbine units

Assessment of the intensity of intermodule interaction and the choice of means of its organization in vibration monitoring systems of turbine units

Optimization of governor parameters for transient process of hydropower system with two turbine units sharing a super long headrace tunnel

AbstractThe governor parameters affect the stability and regulation quality of hydropower system with two turbine units sharing a super long headrace tunnel (SLHT). To improve the transient process of hydropower system, this study investigates the optimization of governor parameters. First, the model of hydropower system with two turbine units sharing an SLHT is established. Second, the optimization scheme of governor parameters for transient process of hydropower system is designed by genetic algorithm. The mathematical formulation of genetic algorithm is illuminated. The implementation procedure of genetic algorithm is illustrated. Then, the optimization results of governor parameters by genetic algorithm are analyzed by illustrating the regulation quality of hydropower system under two operating conditions. Finally, the effect of asymmetrical factors on optimal governor parameters is revealed. The asymmetrical layout of bifurcated penstocks, asymmetrical layout of turbine units, and asymmetrical load disturbances are considered. The results indicate that the objective function of hydropower system is composed of the dynamic indexes for frequency oscillations of two turbine units and water level oscillation in surge tank. The fitness function evolves in the direction that makes the regulation quality of hydropower system become better. Under the symmetrical or asymmetrical bifurcated penstocks, turbine units, and load disturbances, the optimal parameters of governors are asymmetrical. The regulation quality of hydropower system under the governor parameters of genetic algorithm is obviously better than that under the governor parameters of Stein formula. The optimal governor parameters are directly affected by the asymmetrical factors of hydropower system. With the increase of the flow inertia of one bifurcated penstock, the optimal parameters of the other governor become greater.

Performance, economic, and statistical analysis assessment for the hybrid solar dish concentrator with turbine, generator, and reverse osmosis desalination unit

The development of a thermodynamically modeled hybrid commercial solar dish with reverse osmosis is conducted in this study with a rated concentrate thermal and a receiver temperature of 853 °C. To simulate and assess the performance characteristics of the suggested TJ-SDC/RO hybrid system in the city of Tianjin-republic of China, a theoretical model was created and built with MATLAB application. A daily and yearly performance study of the TJ-SDC/RO system under investigation is accomplished. Furthermore, energy analysis viability is achieved in order to evaluate the TJ-SDC/RO system’s life cycle. According to the findings, the suggested TJ-SDC/RO system can produce enough desalinated water to meet daily changes in solar radiation. In June of Tianjin-China’s climate, the superior efficiency of the Rankine cycle was 33.92 %, while the SDC-RO system maximum cycle efficiency peaked at 24.95 % with minimum production costs per unit of electricity of 0.0902 $/kW.h and average water production costs yearly 7.09 $/m3. A mathematical model by Minitab commercial software of the nonlinear regression technique is used with an adjusted R2 of 0.99999485, which indicates the accuracy and reliability of the prediction correlation.

INTEGRATION OF HYBRID ENERGY PLANT OPERATION

Integrated use means the use of several energy sources, all at the same time or in some combination. At the same time, it is possible to use exclusively renewable sources, which significantly limits user capabilities. More common and justified from many points of view is the use of both renewable and traditional sources, autonomous (universal boilers, diesel generators, gas turbine units, etc.) or centralized (power grid) sources. A correct assessment of such a combined energy system also requires taking into account the main component of the system - the consumer, that is, taking into account the features of the local network and nearby consumers, which will have a direct or tangible indirect effect on the operating mode of the complex of renewable sources. To ensure adequate power quality, energy storage systems can be used, and the need for them depends on the discreteness of energy flows and the requirements for power quality. In foreign terminology, combined systems are often called hybrid, reflecting the diversity of both energy sources and methods of combining them (sometimes this name extends to arbitrary complexes). However, the term “hybrid power supply” usually refers to a combination of installations using renewable and traditional energy sources. The article presents a new hybrid energy system that provides private households with electricity, hot water supply, heating and hot air in the required temperature range for comfortable living. Together with a wind power generator and an electric water heater, a heat pump, electricity and heat accumulators are used, which allows: - reducing the cost of thermal energy by reducing material consumption and equipment costs, saving organic fuel; produce electricity and send the excess to the state power grid; reduce heat load and environmental pollution. The automation system allows you to control the hybrid installation without human intervention all year round.

Transient Flow-Induced Stress Investigation on a Prototype Reversible Pump–Turbine Runner

Pump–turbine units with high heads are subjected to strong pressure pulsations from the unsteady transient flow in fluid channels, which can produce severe vibrations and high stresses on the pump–turbine structural components. Therefore, reducing transient flow-induced stresses on prototype reversible pump–turbine units is an important measure for ensuring their safe and efficient operation. A high-head prototype reversible pump–turbine with a rated head of 440 m was used to investigate the transient flow characteristics and the flow-induced-stresses in this study. First, the flow passages of the pump–turbine unit and the structure of the reversible pump–turbine runner were constructed with CAD tools. Next, CFD simulations at the full load were performed to investigate the pressure pulsation characteristics of the pump turbine in both the time domain and the frequency domain. After this, the pressure files calculated by the CFD were exported and applied to a finite element model of the pump–turbine runner to calculate the transient flow-induced dynamic stresses. The results show that the pressure pulsations in the flow passage are closely related to the rotational speed, the guide vane number, and the runner blade number of the pump–turbine unit. The maximum flow-induced stresses on the pump–turbine runner at the full load were below 2 MPa and lower than the allowable value, which reveals that the designs of the pump–turbine runner and the flow passage are acceptable. The conclusions can be used as a reference to evaluate the design of high-head pump–turbines units. The approaches used to carry out the transient flow-induced stress calculations can be applied not only to pump–turbines units but also to other types of fluid turbomachinery such as pumps, turbines, fans, compressors, turbochargers, etc.

Application of Multi-Dimensional Hill Chart in the Condition Monitoring and Cost Estimation of the Francis Turbine Unit

With a large-range-operation head, the Francis turbine unit is the most widely used type of hydraulic turbine in the world. The general range of the Francis turbine is 20–700 m. Because of this, the operating stability of the Francis turbine needs to be focused on. In this paper, a multi-dimensional hill chart is applied to a low-head Francis turbine unit to describe its vibration characteristics. Firstly, a field test was conducted on the unit in order to obtain vibration data under different operating conditions. Secondly, the condition indicators were calculated and extracted from the experimental data. Then, the condition indicators under different head values and outputs were fitted to form a multi-dimensional hill chart. In the end, the vibration characteristics of the researched low-head Francis turbine unit were analyzed based on the multi-dimensional hill chart.

Fault diagnosis of power equipment based on variational autoencoder and semi‐supervised learning

SummaryThe issue of fault diagnosis in power equipment is receiving increasing attention from scholars. Due to the important role played by bearings in power equipment, bearing faults have become the main factor causing the shutdown of wind turbines units. Therefore, this paper takes bearing equipment as an example for research. In order to solve the problem of insufficient and unbalanced fault sample data of wind turbines bearings, a fault diagnosis (FD) method based on variational autoencoder and semi‐supervised learning is proposed in this paper. Firstly, based on Label Propagation‐random forests (LP‐RFs) and a small number of labeled fault samples, a semi‐supervised learning algorithm is proposed to label the original data samples. Secondly, a small number of training samples are preprocessed by the variational autoencoder to reduce the imbalance of the fault samples. Then, the RFs‐based method is adopted to train the processed fault samples to obtain a mature FD classifier. Finally, the proposed method is applied to FD for bearings, and the results show that the proposed method can realize bearings fault diagnosis (BFD). And meanwhile, the proposed method can also be applied for fault diagnosis in power transmission and transformation systems.

Assessing the eco-environmental aspects of fossil fuels-based units substitution of Point Aconi thermal power plant by green-based energies: a case study of Canada

AbstractCanada possesses significant potential in harnessing renewable energy from its vast and diverse geography, which can generate clean electricity. This paper presents a model that replaces fossil fuels used in a proposed thermal power plant in Point Aconi, Nova Scotia, with photovoltaic and wind turbine units based on the region’s climate conditions. The research results are based on evaluating multiple thermal power plants worldwide and examining various wind turbines and PV panels from different companies to ensure accuracy. The chosen units that best suit the location’s geographical and biological conditions, transmission, and operation costs demonstrate that the power plant currently consumes approximately 47 tons of coal and petroleum coke per hour. Replacing these materials with the proposed green units makes it possible to reduce environmental pollution by eliminating almost 165 tons of CO2 and other pollutants per hour while increasing the plant’s efficiency and independence from fossil fuel price variations. The presented structure’s ROI is approximately 20 years, which is reasonable compared to the economic and environmental benefits of utilizing such a structure and converting the thermal power plant to green units.

Design of Pelton Turbine Test Stand in Plateau Environment

Abstract In recent years, with the continuous development of China’s hydropower projects, Pelton turbines are gradually being valued, and the focus of development has shifted from plain areas to plateau areas. Environmental impacts such as high altitude, water temperature, and high sediment content in the plateau area have caused serious interference to equipment that originally worked in a stable environment, for example, the failure of the cooperation between the parts of the turbine and the mutual seizure, the increased wear of the nozzle needle, the decrease of the flow rate and the water outlet speed of the nozzle, and the decrease of the air pressure in the plateau environment lead to the change of the flow state of the nozzle. In view of the above problems, this paper puts forward the design scheme of impulse turbine test-bed, using the method of changing specific speed to determine the basic parameters of impulse turbine unit, so as to eliminate the influence of plateau environment on the normal operation of turbine, obtain the efficiency condition of model experiment under low ambient pressure, and improve the operation efficiency and reliability of turbine unit.

Effect of uneven inflow on hydrodynamic performance of bulb turbine

Abstract Bulb turbine unit is characterized by its low head, large discharge, and short flow passage. The guiding wall separating the power house section from the flood discharge section may cause uneven inflow before its neighbor units when the power house section is located off the river’s mainstream. In this study, selecting a bulb turbine hydropower station in China as the subject, we establish a three-dimensional CFD model that contains the full flow passage of the turbine unit and partial upstream reservoir, to analyze the effects of uneven inflow on the hydrodynamic performance of the bulb turbine. The results show that under this power station layout, flow separation occurs on the left side of the guiding wall, resulting in a low pressure zone and causing the flow in a three-dimensional vortical pattern. The low pressure and flow energy loss lead to the reduction of the neighbor units’ head, causing the discharge decreasing, and the output cannot reach the expectations. This situation can be improved by shortening the guiding wall, indicating that the unit’s performance is strongly related to the hydraulic structure arrangement. The results can provide some references for the design and operation of the related project.

Study on the flow characteristic of pump turbine at partial load

Abstract Pump turbine adopts the same runner to realize forward pumping for pumping condition and reverse power generation for turbine condition, which is a widely used power equipment in pumped storage power station. Compared with conventional pump units or turbine units, the pump turbine has a complex internal flow, especially under part load conditions, and the vibration and noise problems of the structure are prominent. In this paper, the internal flow characteristics of the pump turbine at 60% load are studied by numerical simulation. The low-frequency pressure pulsation 3.5fn and 5.5fn that occur under this operating condition are analyzed. The results show that under partial load conditions, the opening of the guide vane decreases, the angle of attack of the water entering the runner increases, and the rotating stall phenomenon occurs in the pump turbine. The stall vortices show periodic variations on the blade inlet pressure surface and undergo the processes of vortex reduction, fusion, splitting and increase, respectively. The frequency of change is 0.5 times the runner rotation frequency (0.5fn ). The frequency of the corresponding monitoring points in the 7 blade rotor is 7 times (1fn -0.5fn ), which is 3.5fn .

Analysis of oil film flow characteristics and lubrication performance of thrust bearing of 1000MW Hydraulic Turbine Unit

Abstract Hydro-generator unit is the core component of the hydropower station, and the stability of the shaft system directly determines the safety of the hydropower station. Thrust bearing is the only component to bear axial load, and working performance directly affects the stable operation and efficiency of the unit. In this study, a full 3D model of the shaft system of a 1000 MW hydro-generator unit is established, and the oil flow of thrust bearing oil film and oil in the oil tank considering the spray system and the overall model is analysed by means of the thermo-hydrodynamic method. The results show that the load increases with increasing inclination angle. Within certain limits, the pressure and temperature of the oil film increase with increasing inclination. And there are many vortices in the tank. Although the spray system reduces the oil churn, the lubricating oil flow between pads is chaotic. The loss is mainly caused by the chaotic flow between pads. Analyzing the effects of oil film thermal effects on bearing loads, lubricant flow, and bearing surface temperatures of tilting pads provides valuable insights for bearing design and maintenance guidance.

Study on the design of short blade offset for the long and short blade runner of 1000 MW hydraulic turbine units

Abstract For such complex rotating machinery as hydraulic turbine, the hydraulic operation characteristics of the hydraulic turbine unit are significantly impacted by the short blade of the runner used as the splitter blade. To find the optimum position of the short blade, the study object is the 1000 MW hydraulic turbine, selects three circumferential offset positions of the short blade for numerical simulation calculation, obtains the runner flow pattern at different offsets, and explores the impact on the short blade offset on the vortex and pressure pulsation in the runner. The results show that the counterclockwise offset of the short blade will improve the flow pattern of the runner, reduce the scale of vortex in the runner and enhance the efficiency of the hydraulic turbine. The counterclockwise offset will increase the interference while decreasing the pressure pulsation in the vaneless region, at the runner’s inlet, and downstream of the short blade. When the offset δ=0.6, the peak-valley difference of pressure fluctuation in the vaneless zone is the smallest, accounting for only 1.38 % of the rated head. The main frequency of the vaneless zone gradually changes from 15fn to 30fn , and the main frequency of the runner inlet and the short blade downstream is 24fn . Due to the different weakening effects of short blades on the interference, low-frequency pulsation components of 4fn and 8fn appear.

Strength Evaluation of the Flow Passage Stationary Structures of a Large Francis Turbine Unit

Abstract The multifield design and multifield coupling performance of the Francis turbine unit is a topic that needs to be studied deeply. In this paper, the strength evaluation of the stationary structures of the flow passage of a large Francis turbine unit under extreme conditions has been performed based on the fluid-structure coupling theory. The calculated stationary structures include the spiral casing, bottom ring, and head cover. The pressure load applied on the structures is 1.5 times the maximum head of the unit. The results show that there is stress concentration in the spiral casing, and the weld length with equivalent stress greater than 345 MPa reaches 800 mm; the maximum stress at the rib plate of the head cover reaches 357 MPa, which is greater than the yield limit 345MPa. Based on the evaluation results, the local and overall defects of the unit design can be found. The suggested strength evaluation methodology can provide references for the optimization of the unit and a theoretical basis for the operation of the unit.

Numerical simulation of fish damage in a bulb tubular turbine with different guide vane openings

Abstract Tubular turbines have advantages in developing low-head hydropower, however, the development of hydropower shouldn’t forget to maintain a balance with ecology. In this paper, a three-dimensional model of the flow channel of a low-head power plant bulb tubular turbine unit is established using Unigraphics NX, and the hydraulic characteristics and fish damage mechanisms of the turbine under different guide vane openings of 45∼85 mm in rated operating conditions are simulated and analyzed using STAR-CCM+, and it is found that the fish mainly suffers from impact damage and pressure damage in the downstream process with the highest probabilities of 15.73% and 15.72%, respectively. Furthermore, with the increase of the opening of the guide vane, the probability of shear damage to the fish first decreases and then increases, while the probability of pressure, pressure gradient, and impact damage all gradually increase, and the probability of all four types of damage reaches the highest when the opening of the guide vane is 85 mm. Although the unit will have a large output at large opening operating conditions, from the point of view of fish protection, it is better for such turbines not to be operated with large opening of the guide vane for a long time.