Turbine-generator Units Research Articles

A Comparison of the Mechanical Vibration Evaluation Standards of Steam Turbine Generator Foundation

In the paper, the basic design standards (GB50040-96 and ISO10816-2) of various mainstream steam turbine generators at home and abroad were reviewed and their similarities and differences were analyzed in detail. Moreover, the paper also provides the vibration test data on the disturbing points of the foundation and corresponding bearing bracket of three typical 600MW turbine generator units during normal operation so as to search for the relationship between vibration of bearing brackets and vibration of the foundation. The safety coefficient of the chosen foundations using GB50040-96 and ISO10816-2 were also given to compare the severity of each standard. It is hoped to provide designers with accurate grasp of various standards.

Dynamic Optimal Power Flow Incorporating Gas Turbine Generator Unit with Compressed Natural Gas Systems

In developing countries, gas infrastructures are not well established yet. Consequently, insufficient gas supply for gas turbine generator unit may occur during peak load hours. Dual firing unit can overcome such limitation by switching the fuel to High Speed Diesel Oil. However, it will significantly increase the operation cost since High Speed Diesel fuel is much more expensive than natural gas. Recently, a compressed natural gas system has been widely used to solve inadequacy of gas supply during peak load hours. This system compresses the remaining natural gas supply from gas provider during off-peak load hours and stores it into gas tubes. The compressed gas is then released to top up gas supply to gas turbine during peak load hours. Thus, the unit can fully operate on gas at both peak and off-peak load hours. As a result, the operation cost will be lower. This paper proposes an approach in optimizing system operation cost of large system, which has gas turbine generator unit with compressed natural gas system. Furthermore, load curtailment and implementation of take or pay energy contract is also included. The problem is formulated as dynamic optimal power flow and solved using quadratic programming. The proposed approach is tested using IEEE 30 bus and Jawa Bali 500 kV. The results show the effectiveness of the approach in optimizing daily gas usage as well as satisfying take or pay energy contract.

Experience in the Development and Implementation of Modernized Designs of Sliding Bearings of Turbine Generator Units

Bearing assemblies in many respects determine the operating reliability of turbine generator units. Experience in operating a number of hydropower plants indicates that these assemblies remain a problem and require redesigning. This article describes the authors’ technical developments in modernizing bearings and experience in their implementation, showing the reliability and effectiveness of the proposed solutions.

Damping of low-frequency oscillation in power systems using hybrid renewable energy power plants

Global warming, increase in environmental pollution, and high cost of electrical power generation using fossil fuels are considered the most important reasons for the application of renewable energy power plants (REPPs) around the world. In recent years, a new generation of REPPs called hybrid renewable energy power plants (HREPPs) has been implemented in order to have higher efficiency and reliability than conventional REPPs such as wind power plants and photovoltaic power plants. The HREPPs include two or more renewable energy generation units such as wind turbine generation units, and PV generation units. In case of high penetration of these types of power plants, the most common tasks of synchronous generators should be supported by them. One of these tasks is the ability to reduce the low-frequency oscillation (LFO) risk through power oscillation damper such as the power system stabilizers of synchronous generators. In this paper, a novel method is proposed for LFO damping by HREPPs, which is based on the design of an optimal power oscillation damper (OPOD) implemented in the generic HREPP controller model. The structure of the proposed OPOD is a 2nd-order single-input lead-lag controller, and its performance is investigated in a modified two-area test system. The simulation results show the proper performance of the HREPP for LFO damping using the proposed OPOD in the various loading levels and different short circuit ratio values.

Reduction of Fluctuation of Wind Turbines’ Output Power by Modeling and Control

This paper presents the development of a simplified model for wind turbine-generator unit by empirical and physical principles and enhancing its output power and frequency fluctuations. The model has been implemented by MATLAB® / SIMULINK and has reflected the main variation trends of the real wind turbine which is located in Al-Fujeij, southern Jordan. The simulation results for different sets of data have shown the validity of the proposed model and its suitability for power system studies. Furthermore, the study suggests two algorithms of the smoothing of the output power using a control system for the wind turbine generator with Energy Storage System (ESS). The idea is based on developing a computerized programmed manager for the battery, in the regulatory level, in order to perform a repeated charge / discharge process to in order discharge or inject the power to aid the real power output when it is below the external reference power and continue in the charging phase when there is much available wind energy that may exceed the reference load command sent by the energy control center. Encouraging results that may lead to feasible implementation in practice and increasing the penetration of wind energy without negatively affecting the power system frequency have been obtained.

The experimental study on influence of turbine wheel position and mass on rotor critical speed

The rotor critical speed of turbine generator unit when the amplitude of the rotor increases sharply, bring to unit certain harm, rotor critical speed calculation method often results with the actual error is bigger. Through Bode diagram method and frequency spectrum analysis method, the rotor critical speed measurement was carried out. Through the experimental results it was concluded that two methods the test results are basically identical, and bode diagram was determined the selection method of measuring rotor critical speed more accurate. By changing the rotor on the quality of the wheel and position change, the use of Bode diagram method for rotor critical speed measurement. It was concluded that with the increase of the quality of the rotor critical speed decreased, the impact is not big in the center of the deviation from the rotor position far; The same quality case, the farther wheel deviating from the center of rotor, the rotor critical speed increases faster. The test results can guide the engineering practice, for the calculation of the rotor critical speed, the simulation and experiment have certain reference function.

Design method of nonlinear adaptive controller for the main steam valve of turbogenerator set considering state constrain

Aiming at the main steam-valve control of turbine generator unit with amplitude constraint and parameter uncertainty, adaptive backstepping is implemented on the main steam valve controller. The controller not only has an adaptive ability to uncertain parameters of the system and a good transient response performance, but also does not linearize the system. Meanwhile, the problem of state limit in the main steam-valve control of turbogenerator is effectively solved by using the Lyapunov function with constraints. Simulation results are presented to show the performance of the adaptive backstepping control.

Health condition assessment of wind turbine generators based on supervisory control and data acquisition data

As the running time of a wind turbine generator unit (WTGU) increases, the ageing and wear of its components will be aggravated gradually, which leads to deterioration of its operation condition. In order to ensure the safe and stable operation of WTGU and prolong its service life, it is of great significance to know the health condition of the WTGU and reasonably arrange maintenance. Based on the structure of the WTGU and the operation principle of the wind turbine generator (WTG), the condition assessment indexes of WTG were built, and the factors influencing the assessment index were determined. The relationship function between the assessment indexes and their influencing factors was established by using the least square support vector machine, which was used to determine the dynamic limitation of condition assessment index of WTG. The dynamic weight of each assessment index was used to characterise the influence of deterioration degree of different components on WTG conditions. Then the health conditions of WTG were evaluated using a similar cloud and fuzzy comprehensive assessment method separately. Finally, the proposed methods were verified by two examples including a direct-drive permanent magnet wind generator and a doubly-fed wind generator.

Experimental analysis of the operation of a small Francis turbine equipped with an innovative aeration device

Development of hydropower as renewable energy source is an actual trend within the worldwide energy strategy. Thus, the manufacturers and operators of hydraulic turbines are currently engaged in their ecological use. Some of the solutions tested for the development of environmentally-friendly turbines are the aeration devices. Their aim is to increase the dissolved oxygen level in the flow discharged from the turbines in order to improve the quality of the aquatic life downstream hydropower plants. The present paper presents the experimental analysis of an innovative air injection device influence over the main operation parameters of a small Francis hydraulic turbine. The aeration device is mounted downstream turbine runner, at the entrance of the turbine draft tube. The tests are focused on determining the operating parameters evolution of the turbine - generator assembly and the vibrations in the shaft bearings and in the casing of the unit during normal regime and with different injected air flow rates. The pressure in the elbow of the draft tube is recorded, in order to determine the influence of the air injection over the flow at the runner outlet. Six operating regimes of the turbine are analysed, between a minimum power output value and a maximum value. For each operating point various air flow rates are injected in hydraulic system, between 1% and 8% water flowrate. The results will present the influence of the air injection over the dynamic behaviour of the turbine-generator unit.

The Experience in Operation and an Efficiency Analysis for the Use of a Backpressure Steam Turbine Generator Unit in a Boiler House

Turbine generators can be used for utilization of the potential of steam lost in pressure-reducing and cooling units of operating boiler houses. This approach brings about an independent source of power the price of which can be much lower than the established tariff. The features in reconstruction of a boiler house in the city of Bratsk, Irkutsk oblast, carried out in 2012 are examined. Steam generated in a KE-50-14-225 boiler is routed to a 0.3–0.5 MPa common header for use in deaerators and steam-water heaters. Considering an increase in the electricity tariffs, a decision was made to install a 500-kW backpressure turbine generator in the boiler house in parallel with the pressure-reducing unit to generate auxiliary power. The criteria for selecting the number and power of turbine generator units depending on the required steam generation, operating conditions of the consumer, the level of electric loads of the boiler house, and the existing heat supply system are shown. The specifics in operation of the turbine generator unit are examined. To ensure safe and reliable operation of the unit, it is advisable to increase the number of monitored parameters through extension of the normal instrumentation system. The discounted payback period for the reconstruction cost and additional costs for installation of a second turbine generator unit are estimated. The boiler house regimes, a change in the prices for fuel and electricity, and the operator’s labor cost are considered. After installation of the turbine generator, the specific fuel consumption for electricity generation amounts to 180 g.c.e /(kW h). In 2017, the electricity generation cost was 1.23 rubles/(kW h) with the average tariff of 2.13 rubles/(kW h). The discounted payback period for the performed reconstruction does not exceed 6 years, and that for further reconstruction is 8 years.

Priority analysis for risk factors of equipment in a hydraulic turbine generator unit

Ensuring the safe operation of hydropower stations is one of the key challenges for electric generation. Clearly the safe operation of such systems can only be archived with proper and effective maintenance scheduling. The objective of this study is to analyze, rank and prioritize the risk factors responsible for equipment failures of a hydraulic turbine generator unit (HTGU) based on operating data and expert elicitation. Here a simple qualitative risk evaluation model is proposed able to consider seven typical failures in HTGU. The proposed tool is applied for the risk prioritization of equipment failures, e.g. shaft torsion, misalignment, rotating fault, axis bend, runner fault, water guide, and wicket gate of a hydropower station in China. The obtained results have been compared against the actual statistics of equipment failures of a hydropower station in China, considered showing good agreement. All of these results provide theoretical guidance for digitalization realization of equipment failures.

Специальные турбогенераторные установки

Special-purpose turbine—generator units (TGUs) with a capacity of up to 10 000 kWfor converting the mechanical energy of steam into electricity with improved vibroacoustic characteristics are studied. The TGU includes a steam turbine, a synchronous generator excited from permanent magnets, and a frequency converter regulating the parameters of the electric power output. The turbine and generator rotation frequency is such that the TGU output frequency varies from 50 to 300 Hz depending on the TGU power. Different basic circuits of self-contained units equipped with generators excited from permanent magnets are considered. The design of a turbine—generator unit equipped with parallel-connected frequency converter is proposed, the use of which makes it possible to achieve essentially better mass and dimension characteristics of the converter and enhance the TGU reliability as a whole.

Investigation of subsynchronous control interaction in DFIG-based wind farms connected to a series compensated transmission line

The aim of this paper is to investigate the risk for subsynchronous control interaction (SSCI) in doubly-fed induction generator (DFIG) based wind farms connected to series-compensated transmission lines. For this purpose, a detailed analytical model of the frequency-dependent input admittance of the DFIG is derived. The developed admittance model is then used to get insights on the frequency characteristic of the DFIG wind turbine generator unit. In particular, the power-dissipation properties of the DFIG are used to identify those control parameters and operating condition that mainly impact the behaviour of the wind turbine in the subsynchronous frequency range. The admittance model of the wind farm together with the impedance model of the series-compensated transmission line are used to identify the risk for SSCI. Through the use of the Generalized Nyquist Criterion, it is shown that the closed-loop bandwidth of the current controller that regulates the rotor current has a major detrimental impact on the stability of the system. Furthermore, results show that the active power set-point and the level of series compensation also play an important role on the overall system’s stability. Time-domain simulations are conducted to validate the theoretical findings.

Improving Hilbert–Huang transform for energy-correlation fluctuation in hydraulic engineering

Intense vibrations in hydraulic turbine generator unit draft tubes lead to a run-out of the unit shafting and threaten its safe and stable operation. Correct maintenance is therefore important for the safe operation of such units. This study involves assessing the condition of the turbine generator unit by extracting the feature information of its vibration signals. Based on previous research, we present an enhanced Hilbert–Huang transform (HHT) method with an energy-correlation fluctuation criterion to extract feature information and effectively verify the method with simulated signals. An inspection application based on the signal from a vortex strip in the draft tube of a prototype turbine under suboptimal operating conditions indicates that this method is more effective than the traditional one, with a better component identification capability and better suited to the analysis of the complex and dynamic feature information of hydro turbines.

Performance of Wind Energy Conversion System with Parallel Wind Turbines Topology

Worldwide, a significant growth has been noticed in wind turbine installed capacity which encourages the exploration of new Wind Turbine topologies and developed it. In this paper, a parallel connected Wind Turbine generation units based on variable speed directly coupled Permanent Magnet Sync

Supplementary frequency regulation in non-synchronous AC system connected via MTDC

In smart grid power system operation, frequency regulation is one of the most critical tasks towards power balance in the grid. This paper presents the schemes for improvement in operation of secondary loop of turbine-generator unit for frequency regulation in non-synchronous AC areas connected via multi-terminal direct current (MTDC) network. Two schemes have been discussed; (i) voltage droop based lead/lag compensator and (ii) DC power modulation at converter terminal depending upon frequency deviation from each AC area. In the first scheme, droop design based on lead/lag compensator using DC voltage deviation is introduced as supplementary signal at turbine-generator unit in each AC area, to balance the active power, following the load disturbance on AC side and DC power flow conditions. On other hand, in second scheme, frequency regulation is addressed, adopting DC power modulation at MTDC converter, defined in terms of cumulative frequency deviation of AC areas connected to droop controlled terminals. Both the schemes, utilizing converter signals, thus being fast in action compensates the inherently slow response of secondary loop control of turbine-generator unit.Further, effectiveness of derivative based virtual inertia (VI) is also demonstrated to fully compensate the initial frequency response. It is shown that variation of turbine power, i.e. its contribution towards power balance remains minimum with inclusion of voltage droop based lead/lag compensator or/and DC power modulation technique(s). Finally, the comparison between the above control schemes is also discussed. It is indicated that the frequency deviation remains minimum using combined control scheme.

Generator Out-of-Step Prediction Based on Faster-Than-Real-Time Analysis: Concepts and Applications

This paper introduces a new approach, based on faster-than-real-time (FTRT) analysis, to predict out-of-step (OOS) condition of a turbine-generator (T-G) unit subsequent to a fault scenario. The proposed FTRT analysis is based on 1) solving a state-space model of the T-G electromechanical system and corresponding controllers without the need for online measurements, and 2) an estimated Thevenin equivalent of the rest of the power system. The measurement-free FTRT analysis is carried out after the Thevenin parameters are estimated subsequent to the fault clearance instant. Equal area criterion is applied on the predicated variables to detect OOS condition. A reliable decision can be made based on this approach, since it does not involve simplifying assumptions contrary to the existing approaches. The FTRT approach accurately considers the impacts of the detailed model of the generator, automatic voltage regulator, prime mover, governor system, and the host power system. This paper provides detailed mathematical formulation for the proposed OOS detection method and verifies its feasibility and accuracy based on single machine and large test systems. The proposed approach is also implemented on an industrial platform and evaluated. The results confirm that the proposed approach can accurately identify OOS conditions, earlier than the rotor angle noticeably increases.

Three-dimensional CFD simulation of the load rejection transient process considering regulating system

Both the flow patterns in hydraulic turbine and the governor regulating system of turbine-generator unit have great influence on the operation stability of units, but they were treated separately in previous studies. In this paper, the equation for regulating system is cooperated into the three-dimensional (3D) computational fluid dynamics (CFD) model of a hydraulic turbine, for attempting the simulation of the small disturbance transient processes in hydropower plants. The 15% load rejection transient process for a model pumped-storage system with a low specific-speed pump turbine is successfully simulated; reasonable torque, speed and other macro parameters are provided; the flow patterns inside the runner are analysed. The results show that the regulation characteristics of the small fluctuation are acceptable and accordant with practical experience, with the stability guaranteed and the attenuation of fluctuating parameters obvious. These verify the feasibility of using 3D CFD to simulate the load rejection transient process, and lay a foundation for further studying the starting stability of units.

Dynamic hydraulic characteristics of a prototype ball valve during closing process analysed by 3D CFD method

During the runaway process of high-head turbine-generator units due to wicket gate failure, the ball valve should be closed promptly to prevent accidents, and the dynamic hydraulic characteristics during the closing process should be studied. In this paper, the flows through a prototype ball valve are simulated by the latest 3D CFD method. First, the steady flows in different openings are calculated, and we find that the headloss coefficients agree well with experimental results. Then, the water hammer led by linear closing of the ball valve is simulated by both 3D CFD and 1D Method of Characteristic (MOC), and the reasonable agreements further validate feasibility of the 3D CFD method. After that, we investigate the evolution laws of flow patterns, pressure and forces around the valve, and find that the pressure variations before, within and behind the valve differ greatly. Besides, the unstable flow fields within the valve are essential causes of pressure and force fluctuations, bringing potential danger to the safety of ball valve operation. This research provides basic information for studying ball valve vibration and its impact on the turbine and hydraulic system.

Coordinated Optimization of Multi Control System for Steam Turbine Generator Unit

A method of the coordinated optimization of multi control system for steam turbine generator unit was proposed in this paper. The primary frequency modulation performance and dynamic stability of the power system were taken into account in the method. The multi-control system to be optimized includes the excitation regulation system, the power system stabilizer (PSS), the speed control system and the boiler-turbine coordinated control system (CCS). And the taboo search (TS) algorithm was introduced as a means to obtain the optimal values of the system control parameters. The simulation result shows that the method can coordinate the primary frequency modulation performance and the dynamic stability of the system, and can effectively prevent the low frequency oscillation caused by the improper multi control system parameters setting.