Generator Shaft Research Articles

A decision making tool concerning retrofit of shaft generator frequency converter

This paper considers the area of fuel saving through retrofitting shaft generator frequency converter during a vessel operational phase. This retrofit enables the vessel to slow steam with the shaft generator engaged to the main switch board and still maintaining the proper voltage and frequency. An exploratory case study approach is adopted, to achieve an empirically anchored theoretical insight. By considering the trade-off between a cost-benefit analysis and risk area identification a theoretical framework for decision making of the retrofit is proposed. Data is collected from ship-owners and machinery system suppliers. This study shows: (1) In the case of the multipurpose dry bulk ship, the fuel price is demonstrated to have the strongest impact on profitability, (2) the importance of the cost of retrofitting the system appears to be more significant in the short-term, compared to the long-term perspective, (3) eight risk areas that have an impact on the retrofit profitability are identified and mapped in a risk matrix from acceptable to intolerable, and (4) it is revealed that liner operators - in opposite to ship owners – are the most common customers of the shaft generator conversion.

Elimination of System-Induced Torque Pulsations in Doubly-Fed Induction Generators Via Field Reconstruction Method

Effects of system unbalance and system harmonics on the operation of doubly-fed induction generator (DFIG) used in wind energy harvesting are of great concern. This is primarily due to the fact that system unbalance and harmonics can generate unwanted torque undulations that can potentially undermine the mechanical integrity of the tower, and reduce the lifetime of the moving components that are attached to the generator shaft. This paper focuses on the development of a solution for the above problem by judicious selection of the rotor currents to actively eliminate/mitigate these undesirable vibrations. The enabling technology for optimal calculation of the rotor currents is based on the field reconstruction method (FRM). FRM is an analytical tool for the approximation of the magnetic field distribution in the middle of the air gap. Once the FRM formulation is setup, it is capable to predict the tangential/normal components of the magnetic forces. In this paper, the FRM is applied to compute the rotor phase currents in lieu of the availability of the real-time stator currents such that the resultant field will generate a smooth torque.

Permanent-magnet synchronous generator voltage stabilization by rotation frequency variation in self-contained power supply systems

Under consideration is feasibility of voltage stabilization in permanent-magnet synchronous generator with variable frequency in self-contained systems of power supply. The method of stabilization is based on varying speed of rotation of generator shaft. The authors have derived analytical expression for regulating characteristics and determined required ranges for rotational frequency variation at preset parameters of generator and loading. The symmetry conditions are found for a regulating characteristic relative to rotational speed change.

Analysis of Turbine Generator Shaft Torsional Vibration Caused by Self‐Commutated Converters

SUMMARYThis paper presents a simple analysis tool for torsional vibration of the rotor shaft of a turbine generator which is interconnected with a power system with self‐commutated converters. The evaluation is based on analysis of measurement data in the field and instantaneous value‐based power system simulation. A number of power converters with large capacity are installed in industrial power systems. Especially, interharmonics originating from self‐commutated converters cause torsional vibration at the rotor shaft of rotating machines. The interaction between rotating machines and converters is known as sub‐synchronous torsional interaction. The resonance between interharmonics from converters and the natural frequency of the rotor shaft causes large torsional vibrations, leading to shaft damage. In this paper, the influence of interharmonics on turbine generators is investigated. If there were air gap torque fluctuations with a frequency near the natural frequency caused by interharmonics, which have frequencies below 100 Hz of the sideband wave caused by asynchronous pulse width modulation, the rotor shaft may be damaged by the torsional vibration. In this paper, the emerging condition of the torsional vibration and the impact on the generator are investigated.

Convergence non-destructive evaluation system for the parts and materials

Ultrasound infrared thermography non-destructive analysis system for main shaft of offshore wind power generator is established. As preliminary study, optimal design of ultrasound excitation equipment and infrared thermography analysis for optimal design and external energy control is investigated. For the improved defect detection capability through higher energy penetration, optimal design for ultrasound transducer and excitation time (defect detection time) is determined. Impact of ultrasound incident angle and contact point of ultrasound horn is analysed. In addition, amplitude is controlled through controller for ultrasound excitation, and elastic wave from ultrasonic energy will be injected to test unit in a short amount of time using lock-in wave mode. Periodic injection causes heat generation in defect area, and time for preventing significant temperature increase and cooling time is also controllable. Using the specially designed and fabricated jig for ultrasound infrared thermography, optimal design for ultrasound equipment can be achieved.

A novel hybrid transmission for variable speed wind turbines

We herein advance a novel, power summation hybrid transmission, which has the ability to convert the variable speed of a wind turbine rotor shaft into the constant speed required at a generator shaft for a whole range of wind speeds, thereby eliminating the need for a frequency converter. The transmission consists of a single one-stage planetary gear train (PGT) with three rotating shafts and a simple control system consisting of a few sensors and a control motor controlled by a microprocessor. One of the PGT shafts is the input, another is the output, and the third is coupled to the control motor as second input. The optimal tip-speed ratio is kept constant at low wind speeds by controlling the speed of the control motor, maximising the capture of energy from the wind. The wind-rotor speed continues to vary above the rated wind speed zone, but the rotor shaft power is kept constant by using the same control system. In this way, a constant electrical power output is achieved without altering the blade pitch, i.e., with the rotor in a fixed geometry. A frame design procedure for the transmission is proposed, efficiency expressions are derived, an example transmission operation is presented and efficiency comparisons to a mainstream variable speed wind turbine are carried out.

Study of HVDC System and Subsynchronous Oscillation

With the application and development of Power Electronics, HVDC is applied more widely China. However, HVDC system has the possibilities to cause subsynchronous torsional vibration interaction with turbine generator shaft mechanical system. This paper simply introduces the mechanism, analytical methods and suppression measures of subsynchronous oscillation. Then it establishes a power plant model in islanding model using PSCAD, and analyzes the effects of the number and output of generators to SSO, and verifies the effect of SEDC and SSDC using time-domain simulation method. Simulation results show that the more number and output of generators is detrimental to the stable convergence of subsynchronous oscillation, and SEDC、SSDC can restrain unstable SSO, avoid divergence of SSO, ensure the generators and system operate safely and stably

Dynamic and Steady-State 3-D Thermal Design and Investigation of the Rotating Power Electronic IGBT Converter

This paper deals with a 3-D development of a thermal model of a power electronic converter mounted on the generator shaft and rotating with it. The dimensions of the heat sink are determined, and the temperature gradients of the converter, its heat sink, and shaft during natural and forced convection are analyzed for variable rotor speeds. It is shown that the chosen sizes of the insulated gate bipolar transistor (IGBT) and the heat sink offer a compact design of the rotating converter, which is sufficient for its mounting in limited space offered by the generator shaft. Furthermore, a transient temperature profile is also presented. In addition, a transient thermal profile of the converter and dimensions of the cooling fan are also calculated. Besides, the analysis of the cooling requirements of the converter during over-currents due to grid faults is also investigated.

Multi Area Load Frequency Control Using Particle Swarm Optimization and Fuzzy Rules

Abstract This paper present heuristics based study of multi area power network. Heuristic procedures involving Particle Swarm Intelligence and Fuzzy based inferences have been employed to effectively obtain the optimized gains of PID controller. Any change in the load demand causes generator's shaft speed lower than the pre-set value and the system frequency deviates from the standard value results in malfunctioning of frequency relays. A five area load frequency model is constructed in Matlab/simulink by implementing the PID (Proportional, Integral and Differential) controllers to control the frequency deviations. The effect of interconnection of multi area power system as ring connection has been discussed. Simulations performed show the effectiveness of the current approach over simple fuzzy inferences in terms of performance as well as execution efficiency.

Mitigation of SSR Oscillations in Series Compensated Line using LCAP Subsynchronous Damping Controller

Subsynchronous Resonance (SSR) is a growing problem in power systems having series compensated transmission lines. Subsynchronous resonance with low frequency that surpasses aggregate fatigue threshold of the generator shaft frequently could significantly reduce the shaft service life, which is a new problem that emerges in recent years. Flexible AC transmission systems (FACTS) controllers are widely applied to alleviate subsynchronous resonance. A line current and active power (LCAP) supplementary subsynchronous damping controller (SSDC) is proposed to damp subsynchronous resonance caused by series capacitors. Both eigenvalue investigation and time-domain simulation results verify that the proposed control strategy can effectively damping power system oscillations of the power system with SVS and SSDC. Time domain simulations using the nonlinear system model are also carried out to demonstrate the effectiveness of the proposed damping controller. The recommended control approach has been accumulated with the IEEE first benchmark model for SSR study. The analysis indicates that SVS using the proposed control strategy has better alleviation effect and output characteristics. All the simulations are validated by using MATLAB/Simulink environment.

Vibration Characteristics and Damage of Turbine Generator Shaft Rubbing

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

Torsional Dynamic Response of a Shaft With Longitudinal and Circumferential Cracks

Turbo generator shafts are often subjected to cyclic torsion resulting in formation of large longitudinal cracks as well as circumferential cracks. The presence of these cracks could greatly impact the shaft resonance frequencies. In this paper, dynamic response of a shaft with longitudinal and circumferential cracks is investigated through a comprehensive analytical study. The longitudinally cracked section of the shaft was modeled as an uncracked shaft with reduced torsional rigidity. Torsional rigidity correction factor (i.e., the ratio of torsional rigidity of the cracked shaft to that of the uncracked shaft) was obtained from finite element analysis and was shown to be only a function of crack depth to the shaft radius. The resonance frequency and frictional energy loss of a shaft with a longitudinal crack were found little affected by the presence of the crack as long as the crack depth was less than 20% of the shaft radius even if the entire shaft is cracked longitudinally. Moreover, we showed that the longitudinal crack location could be more conveniently identified by monitoring the slope of the torsional response along the shaft. The circumferential crack was modeled as a torsional spring with a torsional damping. The torsion spring and damping constants were obtained using fracture mechanics. For a shaft with both a longitudinal crack and a circumferential crack, the resonance frequency was governed by the longitudinal crack when the circumferential crack depth was less than 30% of the shaft radius.

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.

Improved Step Response of Power System Stabilizer using Fuzzy Logic Controller

As every power system is constantly being subjected to disturbances, we should see that these disturbances do not make the system unstable. Therefor additional signals derived from speed deviation, excitation deviation and accelerating power are injected into voltage regulators. The device to provide these signals is referred as power system stabilizer. The use of power system stabilizers has become very common in operation of large electric power systems. The conventional PSS which uses lead-lag compensation, where gain settings designed for specific operating conditions, is giving poor performance under different loading conditions. Therefore, it is very difficult to design a stabilizer that could present good performance in all operating points of electric power systems. In an attempt to cover a wide range of operating conditions, Fuzzy logic control has been suggested as a possible solution to overcome this problem. In this paper, a systematic approach to fuzzy logic control design is proposed. The study of fuzzy logic power system stabilizer for stability enhancement of a single machine infinite bus system is presented. In order to accomplish the stability enhancement, speed deviation and acceleration of the rotor synchronous generator are taken as the inputs to the fuzzy logic controller. These variables take significant effects on damping the generator shaft mechanical oscillations. The stabilizing signals were computed using the fuzzy membership function depending on these variables. The performance of the system with fuzzy logic based power system stabilizer is compared with the system having conventional power system stabilizer and system without power system stabilizer

Geometry Optimization of Synchronous Machines Used on Ship Shaft Generator Systems

In this paper, the geometry optimization and analysis of two synchronous machines for ship shaft generator applications was carried out. The use of shaft generators in marine applications is a convenient and effective way to supply electric energy to the ship, operating in conjunction with conventional diesel generators. On a first step, state of the art topologies of shaft generator systems are identified and evaluated. In addition, potential improvements in shaft generator systems are proposed. On a second step, a low-speed, direct-driven Permanent Magnet Synchronous Generator (PMSG) for shaft generator applications is designed and optimized in terms of torque production as well as efficiency. The PMSG is compared with an equal power Salient-Pole generator driven by a step-up gear, which is a set-up commonly used in shaft generator systems. The machines are evaluated and optimized in terms of torque production, efficiency and electromotive forces (EMF) harmonic content in nominal operating conditions.

Development of a Reclosing Scheme for Reduction of Turbine Generator Shaft Torsional Torques: A Decision Method to Achieve Optimal Reactor Capacity

It is well known that line switching operations like reclosing are able to cause transient power oscillations which can stress or damage turbine generators. This paper presents a reclosing scheme to reduce the shaft torsional torques of turbine generators by inserting an additional reactor. A novel method to determine optimal reactor capacity to minimize the torsional torque generated in a turbine generator is also proposed. In this paper, the turbine generator shaft is represented by a multi- mass model to measure torsional torques generated in the shaft between the turbine and the generator. Transmission systems based on actual data from Korea are modeled to verify the proposed scheme using ElectroMagnetic Transient Program (EMTP) software. The simulation results clearly show the effectiveness of the proposed scheme and torsional torque can be minimized by applying the proposed scheme.

Perspectiva práctica del humanismo: teatro social experimentado por estudiantes universitarios del Centro de Estudios Generales

The purpose of this article focuses on the assessment of the academic year Theatre of the Oppressed: A Practical Perspective of Humanism as an art critic and space given to the student population Geenerales Studies Center. The proposal is accompanied by the theoretical position of Augusto Boal and specific elements of Carlos Taibo and Mattelart experimentation and practice their own course and scope, the academic process is analyzed, its importance and necessity in overcoming literalism and passivity university professional future, with a view of the inherent social commitment to training. The experience of the participant group transforms the conventional conception of theater, this being a generator shaft that promotes social mobilization capacity of individual and collective critical consciousness in the university community, as an expressive instrumentreflective, organizational and recreation, which encourages citizen participation.

Mitigation of Multimodal Subsynchronous Resonance Via Controlled Injection of Supersynchronous and Subsynchronous Currents

This paper presents a novel approach to analyze the mechanism of torsional interaction (TI) and its solution for series-capacitor-compensated power systems. The relationship between the oscillation of the generator shaft and the consequent electromagnetic torque is deduced by a time-domain analysis. It is revealed that the subsynchronous currents caused by torsional oscillations provide negative damping electromagnetic torque and are the cause of TI. A family of subsynchronous dampers (SSDs) is proposed, which is based on the controlled injection of supersynchronous and subsynchronous damping currents into the generator stator. The design procedure of subsynchronous damping controller (SSDC) of series SSD is elaborated. Eigenvalue analysis and simulations for the IEEE first benchmark model (FBM) have verified the effectiveness of the proposed SSDs in solving the multimodal subsynchronous resonance problem.

Electromechanics complex of the wind power generating fluidizer the use in underground making of iron-ore mines

Today, the problem of high-quality power supply to consumers occupies one of the most prominent places in power engineering and electrical engineering. Considering the wind electromechanical complex operation, it is necessary to pay attention to the fact that the wind wheel operation is variable in nature, caused by the stochastic feature of the air flow. Operation of generator, which is a part of the wind electromechanical complex, depends directly on the wind wheel operation nature, therefore, the generator output parameters such as voltage and frequency will vary depending on the air flow speed and, consequently, generator shaft rotation speed. In view of the above features, the issue of output parameters control of wind electromechanical complex is relevant and so there is a need to solve this problem. It is proposed to solve the problem of variable output generator parameters by creating a control system based on microcontroller. Control is proposed to carry out using fuzzy sets, which will allow to take into account changes in the system, caused by the stochastic nature of air flows. Using this control system for wind electromechanical complexes will provide stable and high-quality power supply to consumers.

Subsynchronous Resonance-Series Compensated HV Lines and Converter Cascades

When electrical network exchanges energy with a turbine generator at one or more natural frequencies, below the synchronous frequency of the system, the phenomena is called subsynchronous resonance. The interaction can bring the mechanical frequency of the shaft of the generator coinciding with a disturbing frequency, resulting is shaft damage and disturbing stresses. Much advancement in technology has taken place to mitigate SSR due to series compensation of HV transmission lines. The ASD and HVDC systems converter cascades can also give rise to SSR, as described in this paper, with appropriate EMTP simulations