Large Turbine Generators Research Articles

Fabrication of a Scaled MgB2 Racetrack Demonstrator Pole for a 10-MW Direct-Drive Wind Turbine Generator

Field windings made of MgB2 wires or tapes are considered for their potential to reduce volume, weight, and cost of large offshore wind turbine generators. To gain experience of how to use this relatively new material in full-scale generators, tests of different winding methodologies and techniques are needed. In this paper, we describe in detail the steps used to wind a racetrack coil with a length of 1 m and a width of 0.5 m out of 4.5 km of MgB2 superconducting tape. The width corresponds to a full-scale pole of a 10-MW generator, whereas the length of the straight section is shorter than the corresponding full-scale pole. The coil was built up of ten double pancake coils. Each double pancake coil was wet wound using a semiautomatic winding process, where Stycast 2850 was applied directly to the MgB2 tape without any other dedicated electrical insulation. The strengths and weaknesses of the winding process are discussed and compared to the dry-winding method.

Influence of Stator Parameter Variation and Phase-Shift Under Synchronizing Out of Phase on Turbine Generator Electromagnetic Field

Synchronizing out of phase may sometimes occur to a turbine generator due to the misoperation or failure of a synchronizing controller. There could be a large impulse current in stator windings during out of phase synchronizing. The impulse current could seriously damage the windings insulation, and the magnetic flux density might be easily supersaturated at the rotor pole surface, leading to stronger stress on the rotor tooth and damage the turbine generator. Aiming at studying the electromagnetic field when synchronizing out of phase occurs, a mathematical model of the transient electromagnetic field with field-circuit-grid coupled is established by taking a 150 MW air-cooled turbine generator for consideration. Impulse current in stator winding and supersaturation at the rotor pole surface are calculated respectively in different angles between the vector of the turbine generator electromotive force and voltage vector of power grid. According to the largest impulse current in stator windings at the 180° out-of-phase synchronization, the influence on the magnetic field distribution and saturation at the rotor pole surface of turbine generator stator resistance and the end region leakage inductances that vary in a certain range is studied. The results could provide theoretical basis for researching of electromagnetic field at out-of-phase synchronization of large turbine generator in the end zone.

Performance of natural draft hybrid cooling system of large scale steam turbine generator unit

To overcome the shortage of dry cooling technology for large scale steam turbine generator unit in summer, the potential feasibility of hybrid cooling was investigated numerically. The physical model was established for the thermo-flow performances of a hybrid cooling system, which combined the air-cooled heat exchangers and water spray facility in a natural draft cooling tower. The mathematical model included the heat and mass transfer between circulating water and cooling air, as well as the condensation of exhaust steam from turbine. The impacts of cooling modes, operating parameters and ambient conditions of the natural draft hybrid cooling system were investigated accordingly. The results showed that both dry and wet cooling sections determined the thermo-flow performances of hybrid cooling system. Due to the blocking effects of upstream air-flows with medium wind speeds, the hybrid cooling mode may have poorer performance than that of dry cooling system. The large droplet diameter and low spray water flow ratio could deteriorate the thermo-flow performances of hybrid cooling mode, which were even worse than that of dry cooling mode and dry cooling system. The operating parameters obtained and the conditions of cooling mode selection may benefit the future application of the hybrid cooling technology.

Shafting Alignment Computing Method of New Multibearing Rotor System under Specific Installation Requirement

The shafting of large steam turbine generator set is composed of several rotors which are connected by couplings. The computing method of shafting with different structure under specific installation requirement is studied in this paper. Based on three-moment equation, shafting alignment mathematical model is established. The computing method of bearing elevations and loads under corresponding installation requirements, where bending moment of each coupling is zero and there exist preset sag and gap in some couplings, is proposed, respectively. Bearing elevations and loads of shafting with different structure under specific installation requirement are calculated; calculation results are compared with installation data measured on site which verifies the validity and accuracy of the proposed shafting alignment computing method. The above work provides a reliable approach to analyze shafting alignment and could guide installation on site.

Relative ability of UHF antenna and VHF capacitor methods to detect partial discharge in turbine generator stator windings

On-line partial discharge (PD) monitoring is widely used to detect stator winding insulation deterioration. The most common type of on-line PD sensor for turbine generators is the 80 pF capacitive coupler installed at the machine terminals which detects the PD in the very high frequency (VHF) range. More recently, ultra high frequency (UHF) antennae have also been used to detect stator winding PD in large turbine generators. Both types of sensors have been installed in 16 turbine generators. This paper discusses the results from near simultaneous measurements from both types of sensors on the same machines. It was expected that the UHF sensors would have stronger discrimination of the electrical disturbances internal to the machine compared to the VHF sensors, but the VHF sensors would be more sensitive to PD. As expected, the VHF sensors were generally more corrupted by electrical disturbances. However, in about half of the machines investigated here, the UHF sensors were significantly more sensitive than the VHF sensors. Many examples of phase-resolved PD patterns that illustrate these findings are presented.

Electromagnetomechanical Coupled Vibration Analysis of a Direct-Drive Off-Shore Wind Turbine Generator

In large direct-drive off-shore wind turbine generators one challenge is to engineer the system to function securely with an air gap length of about a thousandth of the outer rotor diameter. Compared to the large diameter of the generator rotor, the rolling element bearings can only be constructed with a relatively limited size. This makes it challenging to design appropriate constructions able to transmit the large applied magnetic forces encountered in the air gap of direct drive wind turbine generators. Currently, this challenge is met by designing stiff heavy rotors that are able to withstand the forces in the air gap. Incorporating flexibility into the design of the rotor structure can lead to a lighter less expensive rotor. In order to be able to do this the magnetomechanical coupling in the air gap and its effect on the structural dynamics need to be taken into account when predicting the intended flexibility. This paper introduces an approach for a multiphysical modal analysis that makes it possible to predict the dynamics of the strongly coupled magnetomechanical system. The new method is validated using measurements of a simple lab setup. It is then applied to a single-bearing design direct-drive wind turbine generator rotor to calculate the changes of the structural dynamics caused by the electromagnetomechanical coupling.

Study of Three-Dimensional Temperature Field with Changed Structures of Air-Cooled Turbo Generator Stator

Aimed to ventilation system of large air-cooled turbine generator, using the principle of CFD and following characteristics of the stator cooling system, mathematical and physical models of three-dimensional flow and heat ventilation systems built, and two schemes proposed. One was only changing the thickness of the iron core lamination with stableness total effective length of the core, total ventilating ducts, and every duct constant axial length, the other was changing the number of ducts with stableness total effective length of the core. Corresponding basic assumptions and boundary conditions selected, fluid field and temperature field coupled solutions solved, flow field and temperature field of the original and variation structure and the spatial distribution characteristics of each part of the motor analyzed, as well the performance of the stator under different structure was compared. More effectively Structure selected.

Hydrodynamic Design of Thrust Ring Pump for Large Hydro Turbine Generator Units

Abstract Thrust-ring-pump is a kind of extreme-low specific speed centrifugal pump with special structure as numerous restrictions from thrust bearing and operation conditions of hydro-generator units. Because the oil circulatory and cooling system with thrust-ring-pump has a lot of advantages in maintenance and compactness in structure, it has widely been used in large and medium-sized hydro-generator units. Since the diameter and the speed of the thrust ring is limited by the generator set, the matching relationship between the flow passage inside the thrust ring (equivalent to impeller) and oil bath (equivalent to volute) has great influence on hydrodynamic performance of thrust-ring-pump. On another hand, the head and flow rate are varying with the operation conditions of hydro-generator units and the oil circulatory and cooling system. As so far, the empirical calculation method is employed during the actual engineering design, in order to guarantee the operating performance of the oil circulatory and cooling system with thrust-ring-pump at different conditions, a collaborative hydrodynamic design and optimization is purposed in this paper. Firstly, the head and flow rate at different conditions are decided by 1D flow numerical simulation of the oil circulatory and cooling system. Secondly, the flow passages of thrust-ring-pump are empirically designed under the restrictions of diameter and the speed of the thrust ring according to the head and flow rate from the simulation. Thirdly, the flow passage geometry matching optimization between thrust ring and oil bath is implemented by means of 3D flow simulation and performance prediction. Then, the pumps and the oil circulatory and cooling system are collaborative hydrodynamic optimized with predicted head-flow rate curve and the efficiency-flow rate curve of thrust-ring-pump. The presented methodology has been adopted by DFEM in design process of thrust-ring-pump and it shown can effectively improve the performance of whole system.

A two-level SSR protection system and its application at the Shangdu Power Plant

Abstract For large turbine generators connected to transmission lines compensated by series capacitors, potential subsynchronous resonance (SSR) poses a big threat to the safe and stable operation of both the generator and the system. To protect them against the harm of SSR, a novel two-level protection scheme is proposed in this paper. It consists of unit-level torsional stress relays (TSRs) and a plant-level coordinator called TMaster. TSR is equipped for each generator to determine the stability of its torsional modes and to estimate the fatigue loss-of-life caused by system disturbances. TMaster summarizes the judgments of modal stability from TSRs and decides if and which generator should be tripped to suppress SSR. The whole protection scheme provides three types of tripping functions, namely, modal instability trip logic, fatigue over-limit trip logic and instant trip logic. They can protect the generator shaft from damage caused by unstable SSR, accumulated fatigue, and intolerable transient torque, respectively. The SSR protection system was applied in a practical series-compensated system and its effectiveness in a real SSR event was demonstrated with field data recorded during the event.

Experimental Study of Flow Field of Large Air-Cooled Turbine Generator for Multi-Ventilation Ducts of Stator

To study rotational air flow field of rotor and complicated flow distinction owing to multi-ventilation ducts of stator in a large air-cooled turbine generator, considering axial symmetry of air supply, an experiment setup of ventilation system of semi-machine configuration was built in this paper. At condition of rotating, ventilation is measured by hot-wire anemometer. Firstly, ventilation in 16 different semi-circle radius is got. Measurement shows that ventilation in different radius varies much. Then ventilation of outlet of stator ducts is measured. The result shows that ventilation which is affected by flow back and jet less is higher. The conclusion will provide theoretical references for ventilation cooling of rotor ducts in large air-cooled turbine generators.

Hydro energy generation and instrumentation & measurement: hydropower plant efficiency testing

ydroelectric power generation was one of the first forms of large-scale electrical energy generation. In recent years, the hydro power industry has reached a new summit with China's Three Gorges Dam providing an amazing generation capacity of 22 500 MW of renewable energy. In 2012, around 16 % of the world?s consumed electricity was generated from hydropower [1]. Hydropower has a number of advantages compared to other types of electrical energy generation. One of them is using a renewable source of energy: water. By using water reservoirs as the source of energy, hydroelectric power plants can easily and quickly vary their power output. Water in hydropower plants? large reservoirs is used as a valuable energy storage resource (in the form of potential energy) in low-demand periods and transformed into electricity when desired. For large turbine-generator units, the mechanical-to-electrical energy conversion process can have a combined efficiency of over 90%.

3D loss and heat analysis at the end region of 4-poles 1150 MW nuclear power turbine generator

Abstract To study the principle of loss and heat at the end region of large 4-poles nuclear power turbine generator, 3D transient electromagnetic field and 3D steady temperature field finite element (FE) models of the end region are established respectively. Considering the factors such as rotor motion, core non-linearity and time-varying of electromagnetic field, the anisotropic heat conductivity and different heat dissipation conditions of stator end region, a 50 Hz, 1150 MW, 4-poles nuclear power turbine generator is investigated. The loss and heat at the generator end region are calculated respectively at no-load and rated-load, and the calculation results are compared with the test data. The result shows that the calculation model is accurate and the generator design is suitable. The method is valuable for the research of loss and heat at the end region of large 4-poles nuclear power turbine generator and the improvement of the generator’s operation stability. The method has been applied successfully for the design of the larger nuclear power turbine generators

Effect of unbalanced magnetic pull and hydraulic seal force on the vibration of large rotor-bearing systems

The influence of unbalanced magnetic pull (UMP) and hydraulic seal force on the vibration of large rotor-bearing systems is studied. The UMP caused by rotor eccentricity imposes important effects on rotating machinery, especially for large generators such as water turbine generator sets, because these machines operate above their first critical speed in some instances and are supported by oil film bearings. A magnetic stiffness matrix for studying the effects of the UMP is proposed. The magnetic stiffness matrix can be generated by decomposing the expression of air gap magnetic field energy. Two vibration models are constructed using the Lagrange equation. The difference between the two models lies in the boundary support condition: one has rigid support and the other has elastic bearing support. The influence of the magnetic stiffness and elastic support on the critical speed of the rotor is studied using Lyapunov nonlinear vibration stability theory. The vibration amplitude of the rotor is calculated, taking the magnetic stiffness and horizontal centrifugal force into account. The unbalanced hydraulic seal force is produced because of the asymmetry of seal clearance. This imbalance is one of the factors that causes self-excited vibration in rotating machinery, and is as important as the UMP for large water turbine generator sets. The rotor-bearing system is supported by an oil film journal bearing, whose characteristic also impose considerable influence on vibration. On the basis of the above-mentioned conditions, a three-dimensional finite element model of the rotating system that includes the oil film journal bearing is constructed. The effect of the UMP and unbalanced hydraulic seal force is considered in the construction, and studied in relation to the magnetic parameters, seal parameters, journal bearing stiffness, and outer diameter of the rotating machine critical speed. Conclusions may benefit the dynamic design and optimized operation of large rotating machinery.

Identifying torsional modal parameters of large turbine generators based on the supplementary-excitation-signal-injection test

Torsional parameters, especially modal frequencies and mechanical damping, of large turbine generators play critical roles in evaluating and solving the subsynchronous resonance or oscillation (SSR/SSO) problem. To accurately identify these torsional parameters, this paper proposes a systematic approach based on the supplementary-excitation-signal-injection test. The identification process is fulfilled via three steps, i.e., (i) accurate detection of modal frequencies by stimulating controllable torsional vibration with the injection of supplementary modal signals into the excitation system; (ii) online identification of total modal damping using modal filtration, improved discrete Fourier transform (DFT) and least-square fitting technique; (iii) separating electrical damping from the identified modal damping to get the pure mechanical modal damping. The proposed approach was verified through digital simulation and then was applied to the torsional-parameter identification of four practical turbine-generators in Shangdu Power Plant. The results demonstrated that, with the proposed approach, the modal frequencies and mechanical damping can be obtained accurately, intactly and without interfering with the normal operation of on-grid generators.

3D Magnetic Field and Loss Analysis at the No Load Condition in the End Region of 4-Poles Large Turbine Generator

To study the principle of magnetic field and loss at the end region of large 4-poles large turbine generator, 3D transient electromagnetic field finite element (FE) models of the end region are established respectively. Considering the factors such as rotor motion, core non-linearity and time-varying of electromagnetic field, the anisotropic heat conductivity and different heat dissipation conditions of stator end region, a 50Hz, 1150MW, 4-poles large turbine generator is investigated. The magnetic field and loss at no-load condition of the generator end region are calculated and the calculation results are compared with the test data. The result shows that the calculation model is accurate.

Periodic steady-state solution of a synchronous generator based on a voltage-behind-reactance formulation and the Poincaré map method

A powerful blend based on a voltage-behind-reactance (VBR) model and the Poincaré map method, suitable to carry-out harmonic oriented analyses, is presented in this paper to compute the periodic steady-state solution of a synchronous generator. The VBR model, as originally conceived, is modified and instead a per-unit version, tailored to the acceleration procedure, is used. The acceleration of the convergence to the periodic steady-state is accomplished with a Newton method and the Poincaré map. A Numerical Differentiation approach allows the computation of the transition matrix involved in the acceleration procedure using a sequential perturbation of the state variables. The periodic steady-state solution of synchronous generators is reported for a set of operating conditions such as change of load, a three-phase fault and a single-phase fault. Furthermore, the harmonic analysis of a system comprising a RLC circuit with a varying degree of unbalance, fed from a synchronous generator is carried-out with the acceleration procedure. Important speedup factors up to 145 are reported for large turbine generators. The application of a Newton based acceleration procedure to a VBR synchronous machine model yields important benefits for the efficient computation of periodic steady-state solutions and it is particularly useful for test cases involving large rotary machines with an inherently large inertia.

Permanent Magnet Generator with Ventilation Flues between Poles in the Clover Leaf Structure Rotor for a Large Wind Turbine Generator System

Permanent Magnet Generator with Ventilation Flues between Poles in the Clover Leaf Structure Rotor for a Large Wind Turbine Generator System

Coupled Three Dimensional Numerical Calculation of Forces and Stresses on the End Windings of Large Turbo Generators via Integral Formulation

A novel numerical approach to calculate the time evolution of the three dimensional distribution of the magnetic field and forces in the end winding regions of large turbine generators is presented. The proposed approach is based on an integral formulation for nonlinear magnetostatic problems. Its main advantage is the reduction of the discretization to only the conductors and magnetic materials. In this paper the solution of a coupled magnetostructural problem consisting in the calculation of the mechanical stresses and deformations caused by the electrodynamic forces is presented. The analysis is based on a time stepping simulation where the currents are derived from the integration of a lumped parameter model.

Temperature Calculation on Phase Lead Connecting Structures of 1100MW Generator Stator Parallel Rings

The temperature rise of generator components has a great impact on operation performance for large turbine generator. In this paper, applying the general FE calculation software-ANSYS, with a sequential electromagnetic-thermal field coupling calculation method, temperature calculation on phase lead connecting structures of 1100MW nuclear power turbine generator parallel rings is presented. The calculation results could offer a basic analysis to optimize the design of the generator.

大型風力用発電機の技術動向と高温超伝導技術の適用可能性

Development and introduction of wind power generation have recently advanced in the R & D of renewable energies. Scaling-up of wind turbines is one of recent R & D trends because of the scale merits. In the wind farms in Europe, a significant number of 5 MW turbines are being installing. Further increase in the turbine size is expected. There are high expectations for a break-thought technology that will enable to develop light weight and compact wind turbine generators with large capacity of more than 10 MW. Applying high temperature superconducting (HTS) technology to the wind turbine generators can provide the light weight and compact design, since the magnetic field can be higher than that of conventional generators and the iron core can be considerably reduced. Therefore, it is considered that the application of the HTS technology to the wind turbine generator is one of the key issues to overcome the technical power limit of conventional wind turbine generators. This article reviews the recent technical trends of large capacity wind turbine generators and related R & D problems. In the article, the recent studies on the electromagnetic design of the HTS wind turbine generators are reviewed. The features of the design of HTS wind turbine generators are summarized.