Hydraulic Generator Research Articles

Devising a calculation method for modern structures of current-conducting elements in large electric machines in a three-dimensional statement

The jumpers of rotor pole-to-pole connections are highly stressed elements in a hydraulic generator structure. These assemblies often fail due to deformation that exceeds the size of an air gap. Existing methods do not take into account the thermal component and attempts to improve the design are not based on mathematical models that make it possible to perform calculations with an accuracy of more than 50 %. The method devised in this work makes it possible to obtain boundary conditions of the third kind on the basis of three-dimensional mathematical modeling of the ventilation system of the hydraulic unit without simplifications. The method accuracy is explained by taking into account the spatial thermal component. The heat transfer coefficient determined by this method in the pole-to-pole connections area was ~250 W/(m2·K). Using FEM, mathematical modeling of the thermal stress state of pole-to-pole connections was carried out, taking into account mechanical and thermal factors. This made it possible to design the improved connection structure with additional fastening elements, which make it possible to reduce the displacement to 0.03 mm, and the stress to 53 MPa at the rotor rotation frequency of 880 rpm. This design makes it possible to enable reliable operation of the hydraulic unit under the condition of increasing the rotor rotation frequency to overspeed with disconnected combinatorial dependence, provided that the actual stresses are 0.95 % of the material yield strength. The convergence of the values obtained by the proposed method and by the HSS method exceeded 99 %. The practical result is the proposals for the hydraulic generator design modernization

Measuring uncertainty of hydraulic generator efficiency by calorimetric method

Abstract Calorimetric method is generally performed on determination of hydraulic generator efficiency. Generator losses could be evaluated by measuring the heat taken by cooling medium or dissipated from a reference surface. To satisfy the requirements of measuring uncertainty in IEC 60034, special attention must be paid. An estimation method is proposed and performed on a hydraulic generator for calorimetric test. Estimation result shows that discharge of cooling water must be reduced to a rather low value to ensure the measuring uncertainty of calorimetry within 3%. Also, a lower cooling discharge can bring higher temperature rise then reduce the measuring uncertainty caused by temperature measurement. Furthermore, to reduce the measuring uncertainty of cooling discharge, flowmeters must be installed correctly.

Power Flow Analysis of Distribution Systems with Large-Scale Wind and Conventional Energy Generation

This paper is devoted to the development of a methodology suitable to be used to determine the impact of the grid integration of wind farms in distribution networks that are also supplied with other classical generation facilities based on thermal and hydraulic energy. The methodology is based on an automated analysis system that varies the level of the electric generation for both the hydraulic and thermal generators by using PSS, Phyton and Matlab. The user can define multiple scenarios considering wind, thermal and hydraulic generators so the line capacity can be computed and compared in order to know where the systembottleneck is located and which situations occur. All the results computed can be analysed in a single or compared way by using tables and plots and considering the static rate of the distribution lines. The developed system can also be applied to the computation of the sensitivity of the power flow to the variation of the parameters that define the power system.

Failure mode analysis and severity measurement method for hydropower equipment

To meet the practical needs of effective failure management and safe operation of hydropower systems, the classification and description standardization of the failure modes are studied based on the statistical analysis of historical maintenance data of in-service hydropower equipment. The method of building the failure mode library is then offered, followed by the specification of failure mode codes. Given the characteristics of the hydropower equipment, a severity rating method and the severity measurement model of failure modes for hydropower equipment are proposed, with definition criteria built using fuzzy semantic techniques. Finally, a thrust bearing system of the hydraulic generator sets is used as an example to validate the method of failure mode analysis and severity measurement, and practical suggestions for implementation of severity measurement are given in this paper.

Технологія відновлення форми ротора гідрогенератора

The object of research in this article is the change in the rotor shape during the operation of hydraulic units. The subject of study in this article is the design and geometric state of the shape of a rotor with irregular geometry of hydraulic generators-engines. This study produced a three-dimensional mechanical calculation of the rotor segment for further use during strain gauge tests. Tasks: investigate the peculiarities of the rotor shape restoration technology; to describe the basic assumptions for the three-dimensional mechanical calculation of rotor deformations at the overspeed; and perform a three-dimensional calculation of rotor movements considering the main forces falling on the pole connection, which are obtained using classical methods. The methods used are: finite element method of mathematical modeling of the thermal stress state of nodes. The following results were obtained: a detailed description of the technological process of restoring the shape of the rotor using the hot wedging method is given. Three-dimensional models of the rotor segment were developed, and a three-dimensional mechanical calculation of this model was performed, as a result of which satisfactory values of the displacement of the rotor of the hydraulic generator at the overspeed were obtained, considering the recovery technology. To reconstruct the rotor rim, it is necessary to heat the rotor rim to a temperature difference between the rim and the frame of at least 60 °C. Next, the hot wedging of the rotor rim is performed with the driving of each of the driving wedges by the same amount, which ensures the creation of the necessary diametrical tension between the rim and the frame of the rotor and avoids the displacement of the rotor rim relative to the frame. The control of this process is performed using strain gauges. If necessary, it is necessary to cool the rotor rim until the temperatures of the rim and the frame of the rotor are equal. Conclusions. The scientific novelty consists of a combined approach to the evaluation of the deformation of the rotor rim after restoring its shape, which includes elements of analytical mechanical calculation and calculation in a three-dimensional setting. The presented technology for the rotor restoration process meets European requirements.

Cause Analysis and Treatment of Abnormal Vibration of Hydraulic Generator Unit Caused by Coupling Defect

When a hydropower station 25MW hydropower unit is operated with load after overhaul, the upper bracket vibration will exceed the standard. To find out the cause of the problem and eliminate the fault, the mechanical, electromagnetic, and hydraulic aspects are mainly analyzed and checked. The results show that the excessive vibration of the upper bracket of the unit is caused by the incomplete pre-tightening force between the coupling bolts of the turbine and generator of the unit, as well as the improper location and thickness of the padding. It is characterized by a vibration component whose frequency is between the rotational frequency and twice the rotational frequency. By fully pre-tightening the coupling bolts and restoring the original padding position and thickness, the vibration of the upper bracket, upper guide swing, and other data are significantly improved, and the desired purpose is achieved. The cause analysis and fault treatment of the abnormal vibration of the hydro-generator unit can provide some reference for diagnosing other similar faults.

Ultra-low frequency oscillation analysis considering thermal-hydro power proportion

The Ultra-low Frequency Oscillation (ULFO) has attracted much attention due to its field test capture in China, and it is believed that the ULFO is related to the hydraulic generator. To clarify the cause and innate essence of ULFO, the develop of the ULFO under different thermal-hydro power proportions is investigated. A small-signal model of two-machine system considering different thermal-hydro power proportions is established. Based on the small-signal model, the influence of hydropower proportion on the oscillation characteristics is analyzed in different conditions, and it is found that a higher proportion of hydro power results in a lower oscillation frequency, though the hydropower proportion is not the crucial cause in ULFO. Then Based on the eigenvalue analysis, it is observed that the essential cause of ULFO is the weak grid condition rather than the high hydropower proportion. The system connection strength determines whether the system is prone to ULFO. In addition, the participating factors of the generators’ significant state variables are obtained, which indicates that the governor plays a more vital role in ULFO in the case of weak grid connection. To verify the theoretical analysis, the simulations of the two-machine system and six-machine nine-node system are implemented, respectively. The results reveal that system with all thermal power is still prone to ULFO when the connection is weak. Conversely, when the connection is strong, the ULFO does not occur even if all the generators are hydraulic. Furthermore, in a weak grid condition, the oscillation frequency and damping ratio decrease with increasing hydropower proportion, which indicates that a high hydropower proportion deteriorates the ULFO problem.

Control of a Hydraulic Generator Regulating System Using Chebyshev-Neural-Network-Based Non-Singular Fast Terminal Sliding Mode Method

A hydraulic generator regulating system with electrical, mechanical, and hydraulic constitution is a complex nonlinear system, which is analyzed in this research. In the present study, the dynamical behavior of this system is investigated. Afterward, the input/output feedback linearization theory is exerted to derive the controllable model of the system. Then, the chaotic behavior of the system is controlled using a robust controller that uses a Chebyshev neural network as a disturbance observer in combination with a non-singular robust terminal sliding mode control method. Moreover, the convergence of the system response to the desired output in the presence of uncertainty and unexpected disturbances is demonstrated through the Lyapunov stability theorem. Finally, the effectiveness and appropriate performance of the proposed control scheme in terms of robustness against uncertainty and unexpected disturbances are demonstrated through numerical simulations.

Key technologies and development tendency of airborne distributed electro-hydraulic generation system

The airborne distributed electro-hydraulic generation system (ADEHGS) enables power transfer and management in the form of electric energy, which can supply hydraulic power for the power consumers far away from the airborne central hydraulic generation system, e.g. braking and nose wheel steering systems. It can meet the actuation requirements of more electric aircraft, and provides power backup for more electric aircraft in the currently unproven electric actuation situation. This paper summarizes the existing conditions of the application of airborne distributed hydraulic generation system and the key technologies in distributed hydraulic generation system sealing and high-efficiency compound control of high-power motor, high-pressure high-speed variable displacement pump and variable-speed variable-displacement pump, looks forward to the future development trend of ADEHGS, and explores new development direction of airborne hydraulic system.

Investigation of Flow Characteristics of Flow Passage Components in Francis Turbine under No-load and 50% Load operating conditions

Due to the varying demand of power grid for the electric supply of hydraulic power stations, the units are often under low-load operating condition and no-load standby state, causing a significant flow instability in hydraulic generator units. To further investigate the inside flow characteristics of hydraulic turbines under such operating conditions. In this study, a CFD (computational fluid dynamics) numerical simulation with applying RNG (Renorm alization Group) k-ε turbulence model is performed to study the inside flow characteristics of each flow passage components of a Francis turbine under no-load and 50% load conditions. The results indicate that under the two operating conditions, the flow distribution inside and outside the draft tube pier is significantly nonuniform. Simultaneously, the large-scale vortex in the runner area caused by the high-speed flow in the vane-free area with small opening and the nonuniform flow velocity distribution in the straight cone section of the draft tube are the main reasons for the increase of hydraulic loss and the decrease of efficiency.

Optimization Model for the Integration of the Electric System and Gas Network: Peruvian Case

This paper presents a method for multi-period optimization of natural gas and electric power systems incorporating gas-fired power plants to analyze the impact of the interdependence between those commodities, in terms of cost and energy supply. The proposed method considers electricity network constraints, such as voltage profile, electrical losses, and limits of the transmission lines, as well as the technical restrictions on the gas network, such as the diameter, length, pressure, and limits for those variables. The proposed method was applied to a 12-bus electric network and a 7-node gas network, and several interdependencies between the electricity and the natural gas system network can be observed. The results show how the restrictions cause the behavior of the gas-fired power plants—in a low demand stage, it is restricted even when the gas-fired power generation prices are below the hydraulic generation prices, while in scenarios of higher demand, saturated cargo flows are observed, causing bus bar prices to be affected with higher operating costs. In this sense, the results of the variation in bus bar prices show little price stability in some bus bars in different stages, due to the behavior of the generation supply that is forced to operate by system restrictions.

Evaluation of Energy Potential from Coffee Pulp in a Hydrothermal Power Market through System Dynamics: The Case of Colombia

Colombia has abundant solar, wind, and biomass resources for energy production with non-conventional renewable energy (NCREs) sources. However, the current participation of NCREs is negligible in the electricity mix of the country, which has historically depended on hydroelectric plants. Meteorological phenomena, such as the El Niño–Southern Oscillation (ENSO), threaten the energy supply during periods of drought, and the generation of energy using fossil fuels is necessary to offset the hydric deficit. Since Colombia is one of the largest coffee producers in the world, this study used system dynamics to evaluate the energy potential from cherry coffee pulp and analyze trends in the energy supply for different energy sources in scenarios of climatic vulnerability. First, the causal relationship of the system was identified, and the key variables of the model were projected. Then, the behavior of the system was evaluated by simulating a 120-month period. The results showed a generation potential from coffee pulp of 177 GWh per year and a power generation of 11,250 GWh and 7537 GWh with solar and wind resources, respectively, by 2030. Finally, it was confirmed that including new renewable resources is a key factor in supporting hydraulic generation in the warm phase of ENSO while reducing thermal generation dependence.

Modelling and Analysis of Frequency-Responsive Wind Turbine Involved in Power System Ultra-Low Frequency Oscillation

This paper presents a dynamic analysis for ultra-low frequency oscillations (ultra-LFOs) observed in the wind-hydropower hybrid systems. In such systems, DFIG wind turbines (WTs) are required to be frequency-responsive with providing the inertia and frequency support. First, this paper establishes an analytical model to capture the dynamics of frequency-responsive DFIG WTs at the electromechanical timescale. A systematic analysis is then conducted on a 2-machine system (include a hydraulic generator (HG) and an aggregated DFIG WT) to reveal WTs’ dynamic behaviors and their interference mechanism with the HG, accounting for the system ultra-LFO mode. The result shows that WTs’ frequency control, speed control, MPPT control and pitch control would be involved in the system ultra-LFOs, but they have different effects under different operating modes. Cases studies are carried out on the 2-machine system and a modified 10 machine 39-bus New-England power system. Based on the modelling effort and simulation studies, some recommendations are made for using DFIG WTs to help damp the ultra-LFO in wind-hydropower hybrid systems.

A Constant-Pressure Hydraulic PTO System for a Wave Energy Converter Based on a Hydraulic Transformer and Multi-Chamber Cylinder

This paper presents a constant-pressure hydraulic PTO system that can convert stored pressure energy into electrical energy at a stable speed through hydraulic motors and generators. A multi-chamber cylinder can be connected to the main power generation circuit by check valves, and the motor displacement can be controlled by a fuzzy controller to maintain the main power generation circuit under stable pressure. The hydraulic transformer can control the forces applied to the floater. The hydrodynamic parameters of the floater are calculated by AQWA, and the optimal PTO damping of the hydraulic system is analyzed as the target of transformer control. MATLAB/Simulink and AMESim are used to carry out the co-simulation. Three kinds of wave elevation time-series for the specific state are designed for the simulation. In the co-simulation, three approaches are carried out for the simulation including no control strategy, fuzzy control with a fixed transformer ratio, and fuzzy control with a variable transformer ratio. Under the fuzzy control with a fixed transformer ratio, the floater displacement and captured energy do not increase significantly, but the oil pressure fluctuation is very stable, which indicates that the fuzzy controller maintains the stability of the main power circuit. While under fuzzy control with a variable transformer ratio, the power generation is not larger than those under no control strategy or fuzzy control with a fixed transformer ratio, which proves that this hydraulic transformer concept is less efficient.

Firm location, regional weather conditions and bid pricing strategies in the Colombian wholesale electricity market

ABSTRACT Weather conditions in Colombia vary greatly throughout the territory. This fact, in the context of Colombian wholesale electricity, plays a key role in the bid pricing strategies and intensity of the strategic behaviour among plants. We estimate a dynamic spatial Durbin model to factor in the effects weather conditions have on bid pricing. The results show how energy inputs become critical for setting bid prices, a fact that is reinforced by the predominance of hydraulic generation technologies. One potential policy recommendation is the need to implement balancing markets to signal efficiently the pricing strategies in these markets.

Fault Diagnosis of Hydraulic Generator Bearing by VMD-Based Feature Extraction and Classification

Fault Diagnosis of Hydraulic Generator Bearing by VMD-Based Feature Extraction and Classification

New Hydraulic High-Pressure Impulse Generator for Long-Duration Impulse Tests

Water hammer wave is widely applied to test hydraulic components in various areas. A new hydraulic high-pressure impulse generator is presented in this paper in order to provide the standard water hammer wave for long-term usage. A combination of a sleeve and a rotary spool was used to build the impulse generator, and a booster piston was applied to amplify the output pressure. Mathematical models were established using commercial software, and a prototype and a test rig were built based on the simulation results. The experimental results for both single wave and repeated periods show the feasibility of the new design and indicate that the new hydraulic high-pressure impulse generator can be used for long-time impulse tests.

The occurrence mechanism and damping method of ultra‐low‐frequency oscillations

The ultra-low-frequency oscillation (ULFO) problem has reappeared in China recently. Although the hydraulic generator is supposed to have a strong connection to this problem, the conditions for ULFO appearance and detailed reasons are not clear yet. In order to clarify the occurrence mechanism of ULFO, this paper studies each important part of hydraulic generator system, including the governor, exciter and power system stabiliser (PSS). The weak connection is confirmed to have an important impact on the occurrence of the ULFO. Nevertheless, by studying each device's contribution to ULFO through the complex torque coefficient method, it is shown that the negative damping effect of the hydraulic governor will cause the instability in the ultra-low-frequency band, while the exciter and the PSS have little influence on ULFO. Additionally, the proportional–integral parameters of the hydraulic governor system are also studied to clarify their influence on ULFO based on the complex torque coefficient method. Based on the above analysis, two damping methods for ULFO suppression are finally proposed. To verify theory and damping methods, the simulations are implemented in PSCAD and PSASP software.

Influence of rainfall on wind power generation in Northeast Brazil

Wind power has been emerging as one of the main renewable energy sources in Northeast Brazil, which concentrates 87% of the country’s installed wind capacity, especially in recent years, due to water scarcity and its seasonal energy complementarity to hydraulic generation. The objective of this article is to present a method to evaluate the influence of rainfall on the behavior of wind power generation, considering rainfall anomaly index and extreme climatic indices of precipitation. We utilized daily rainfall data from cities located near wind farms CE1 and CE2 in the state of Ceará — Aracati, in the 1974-2016 period, and Trairi, in the 1976-2016 period —, as well as daily wind power generation data for the same period, provided by the Electric System National Operator (ONS). The RClimdex software was used to calculate 11 indices of climatic extremes dependent on rainfall. The capacity factor for wind power generation was calculated for the period from 2011 to 2016 for the CE1 and CE2 wind farms. The application of this method found an inversely proportional relation between rainfall anomaly index (RAI) and the wind power capacity factor, with a decrease in total rainfall and a greater number of consecutive dry days and concentrated rain in the short term. From 2012 to 2016, the rainfall anomaly index was negative. However, wind power factors were higher than in 2011. The developed methodology can be applied to other wind farms, contributing to the medium and long term energy planning of the National Interconnected System.

UHVDC Islanded Operation System Ultralow-Frequency Oscillation and Its Countermeasures

There exists serious frequency instability in the UHVDC islanded operation system consisting of a large capacity UHVDC and its corresponding power source with hydraulic power generators. Ultralowfrequency oscillation (ULFO) is one of the frequency instable problems, which will happen because of the inconsistent frequency control features between UHVDC and hydraulic power generators. Through the frequency-domain analysis, there exists a frequency band with negative damping in the hydraulic turbine control system, and UHVDC is negative damping for frequency deviation with constant power control mode. There are four negative damping contributing factors as hydrowater starting time constant, hydrogenerator governor forward gain, islanded system total inertia, and UHVDC power. These four factors are analyzed in this article in the frequency domain. Based on the detailed ULFO damping analysis, effective frequency control strategies for UHVDC islanded system are proposed in this article by withdrawing a part of primary frequency control functions of generators or coordinating the frequency controls between hydraulic generator governors and UHVDC frequency limitation controller (FLC). Through the proposed frequency strategies, islanded system frequency is mainly controlled by UHVDC FLC, which can successfully suppress the ULFO. Validation simulations are performed on the RTDS platform, and the simulation results prove the proposed strategies.