Generator Shaft Research Articles

Damping subsynchronous resonance using a SIMO shunt reactor controller

Stabilizing torsional oscillations using a single-input multiple-output (SIMO) shunt reactor controller is investigated in this paper. An eigenstructure assignment technique is applied to design this controller. The designed controller can be easily implemented by a multiple-proportional-integral (MPI) controller using the medium pressure turbine speed, the two low pressure turbine speeds, and the generator shaft speed as feedback signals. Eigenvalue analyses under different operating conditions and a wide range of series compensation degrees, time domain simulations under a pulsed torque disturbance, and fast-Fourier-transform (FFT) analyses for system behavior are all performed in order to demonstrate the effectiveness of the proposed controller.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Stressing of turbine-generator-exciter shafts by variable-frequency currents superimposed on DC currents in asynchronous HVDC links and following disturbances at converter stations

Ripple currents on the DC side of both HVDC synchronous and asynchronous links together with cleared HVDC and AC system disturbances can excite in some circumstances onerous torsional vibrations in large steam generator shafts. The problem has assumed importance in recent months on account of the HVDC link between Scotland and Northern Ireland going ahead, on account of the proposed Eire/Wales link, and because AC/DC/AC couplers are to be installed extensively to interconnect the East and West European grid systems. This paper discusses and analyses excitation of shaft torsional vibrations in steam turbine-generator-exciter shafts in close proximity to HVDC power converter substations by: (i) variable-frequency ripple currents superimposed on the DC currents in asynchronous links; and (ii) disturbances at bi-polar converter stations. Detailed simulation of the HVDC converter and generator is necessary for precise assessments of shaft torsional response following HVDC converter station faults. 500 MW, 660 MW, 1000 MW and 1300 MW machines are considered in the analyses that are made. >

Application of simultaneous active and reactive power modulation of superconducting magnetic energy storage unit to damp turbine-generator subsynchronous oscillations

An active and reactive power (P-Q) simultaneous control scheme, which is based on a superconducting magnetic energy storage (SMES) unit, is designed to damp out the subsynchronous resonant (SSR) oscillations of a turbine-generator unit. In order to suppress unstable torsional mode oscillations, a proportional-integral-derivative (PID) controller is used to modulate the active and reactive power input/output of the SMES unit according to speed deviation of the generator shaft. The gains of the proposed PID controller are determined by pole assignment approach based on modal control theory. Eigenvalue analysis of the studied system shows that the PID controller is quite effective over a wide range of operating conditions. Dynamic simulations using the nonlinear system model are also performed to demonstrate the damping effect of the proposed control scheme under disturbance conditions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Suppression of common torsional mode interactions using shunt reactor controllers

The paper presents the results of a study on the utilization of shunt reactors for the damping of common torsional mode interactions of a power system containing series-capacitor compensation. The IEEE Second Benchmark Model, system-2, which has two sets of nonidentical turbine-generators connected to an infinite bus via a common series-capacitor compensated transmission line, is employed to investigate the possible unstable subsynchronous resonance (SSR) modal interactions which can be suppressed by using reactive power compensation. A set of shunt reactors are proposed and connected to the studied system and a unified approach based on modal control theory is employed to design shunt reactor controllers in order that all SSR modes in the system can be stabilized. For clearly demonstrating the effectiveness of the proposed scheme, SSR mode eigenvalues under different loading conditions and sensitivity analysis of shunt reactor controllers' parameters are performed. Dynamic responses of the nonlinear system simulation under a torque disturbance on a generator shaft and a severe three-phase short-circuit fault at an infinite bus are also carried out. >

Damping torsional oscillations using a SIMO static VAR controller

Stabilising torsional oscillations using a single input multiple output (SIMO) static VAR controller is investigated. An eigenstructure assignment technique is applied to design it. The designed controller can be easily implemented by a multiple proportion integral (MPI) controller using medium pressure turbine speed, two low pressure turbine speeds, and generator shaft speed as the feedback signals. Eigenvalue analyses under a wide range of series capacitor compensations and loading conditions, time domain simulations under a pulsed torque disturbance, and fast Fourier transform (FFT) analyses for system behaviour are all performed to demonstrate the effectiveness of the proposed controller.

Damping of power system oscillations by an active and reactive power modulation superconducting magnetic energy storage unit

A method for repressing the low frequency oscillation of a synchronous generator is considered in this paper using a simultaneous active and reactive power ( P− Q) control scheme of a superconducting magnetic energy storage (SMES) unit. In order to increase the damping of the generator, a proportional-integral (PI) controller is used to modulate the active and reactive power input/output of the SMES unit according to the speed deviation of the generator shaft. The SMES unit with the PI controller can provide sufficient damping torque for the electromechanical mode. The gains of the PI controller are determined by the least square error technique, where the weighted quadratic sum of the system states is minimized. Eigenvalue analysis and digital simulation are performed to demonstrate the damping effect of the SMES unit over a wide range of loading conditions.

Damping of torsional oscillations using excitation control of synchronous generator: the IEEE Second Benchmark Model investigation

A simple lead-lag excitation controller using generator shaft speed deviation ( Delta omega ) as a feedback signal to damp all of the IEEE Second Benchmark Model, system-1 torsional oscillations is presented. In order to stabilize all the torsional modes, modal control theory is used to determine the parameters of the dynamic output feedback controller. Various degrees of series compensation, different loading conditions, and torsional mode shapes for a torsional oscillations study are also investigated. In addition, time-domain simulation using a nonlinear system model are examined to demonstrate the effectiveness of the proposed countermeasure under torque disturbance conditions. >

機関・可変ピッチプロペラ統合制御のシミュレーション

Recently, the controllable pitch propeller (CPP) has become popular because of such merits as (i) the maximum power of the main engine can be available at any speed condition of the voyage, (ii) a shaft generator can be used because of capability of keeping the engine speed constant at any navigation speed, and (iii) dead slow cruising is possible.Introduction of the CPP, however, brings not only these merits but also complexity of how to control a regulator handle position of the engine (R) and the propeller pitch angle (θ) simltaneously. It means that these two parameters, R and θ interfere the outputs such as the propulsion force or engine speed.Reported here is the simulation studies of the engine-CPP consolidated control to use a shaft generator normally at any navigation speed. For this, at first, a simulation model for the object system was made, and a decoupling control theory was applied to keep the engine speed constant. As a result, the expected performance was obtained.

Turbogenerator torsional mechanical modal parameter identification from on-line measurements

A method for measuring the torsional mode parameters of a turbogenerator is investigated. The advantages of this measurement technique are that it allows the direct measurement of the mode inertia. In addition, it makes possible the determination of the mechanical damping (excluding the electrical effects) while the turbogenerator is synchronized. The process involves the measurement of the generator's electrical torque and shaft speed. Results from digital computer simulations are presented as evidence that the method is successful. The method was used to identify specific torsional mode parameters of a laboratory multi-inertia microalternator.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

機関・可変ピッチプロペラ統合制御のシミュレーション

At 1st report. consolidated control of the engine controllable pitch propeller (CPP) was studied with the object of an ordinary use of a shaft generator at any navifation speed by adapting a decoupling control theory.Content of this paper, 2nd report is the simulation studies to control the propeller efficiency optimally at any speed condition of the voyage. For this, an increased freedom by introducing the CPP which was used as an ordinary use of a shaft generator, namely was used to keep the engine speed constant at 1st report, was put to practical for this optimization control. It means that an engine speed is commanded at each cruising conditions by the propeller efficiency optimized table which has been made beforehand. As a result, the considerable improvemunt of the efficiency was obtained.

Series compensation schemes reducing the potential of subsynchronous resonance

New series compensation schemes that reduce the potential of synchronous resonance problems in series compensated electrical power systems are presented. The schemes are phase-wise compensation schemes with three different combinations of inductive and capacitive elements. The combinations chosen have frequency characteristics that give equal reactances at the power frequency and unequal reactances at the other frequencies. This implies that the subsynchronous oscillations drive unsymmetrical three-phase currents. The developed electric torque, therefore, will be lower than what it would be if the three-phase currents were symmetrical. This results in a lower coupling strength between the mechanical and electrical systems at asynchronous oscillations. Therefore, the energy exchange between the electrical and mechanical systems at subsynchronous oscillations will be suppressed, avoiding the build-up of torsional stresses on the generator shaft systems under subsynchronous resonance conditions. The validity and effectiveness of the schemes have been demonstrated on the Second IEEE Benchmark Model, by means of time simulation analysis using the EMTP program. >

Steam turbine generator shaft torque transients: a comparison of simulated and test results

If the electrical system of a turbine generator is subjected to a fault or disturbance condition, large mechanical torques may be induced in the turbine shafts. The computer prediction of such torsional behaviour has become an important feature of system design and appraisal. Simulation results are presented in the paper for two different operating conditions: malsynchronisation and load rejection. Comparisons of these computer predictions and actual measured test results are made for the torque transients on two shafts of the turbine generator. Good correlation is obtained if electrical and mechanical damping data is chosen carefully. The computer model is shown to behave satisfactorily with respect to the predicted torsional frequencies, peak to peak torque amplitudes and rate of decay of the transients. The variations of the rate of damping for the different disturbances are also discussed.

深江丸軸発電電動機システム

Shaft generators driven by main engines have been increaseingly employed by ships to save evergy and labor. For shaft generator system, systems eguipped with thyristor inverters or differential planet gears are often used, however, they are required to be improved in reliability, effeciency and economic performance.A newly our developed shaft generator/motor system meets these requirements. This generator system is unique and first in the world as described below.The rotor (field), connected to the main engine shaft, can change its rotating speed. The armature, which is rotatery, can also be controlled to change speed independently of the rotor (field) .Recently this system is applied to the Fukaemaru of Kobe Univ. of Mercantile Marine's.

Some investigations on statistical scatter in the initiation and growth lives of surface fatigue cracks in NiCrMoV steel.

Rotating bending fatigue tests were carried out for smooth and small notched specimens of NiCrMoV steel, using the large-size turbine rotor shaft of the nuclear generator, in order to statistically investigate distributions of surface crack initiation and growth lives. Most of surface cracks of the smooth specimens initiated at inclusions on the surface. The distributions of the initiation life Ni, the growth life Np and the failure life Nf determined in this study were expressed as a two-or three-parameter Weibull distributions for the smooth and the small notched specimens. The statistical scatter of the Ni, Np and Nf distributions increased with decreases in stress amplitude σa for the smooth specimens, and the scatter of each life of the notched specimens was smaller than that of the smooth ones. The correlation coefficient of order between Ni, Np and Nf increased with increases in cycles, but decreased with increases in σa for the smooth specimens, and that of the notched specimens was smaller than that of the smooth ones during the early stage of crack growth to less than 1 mm in length.

The importance of grounding brushes to the safe operation of large turbine generators

Four sources of voltage on the shafts of large turbine generators are identified. Techniques for measuring these voltages are outlined. The consequences of not providing effective shaft-grounding brushes to reduce shaft potential, the magnitude of shaft potentials, and specific components which are at risk are discussed. Recommendations for basic installation and maintenance procedures for shaft-grounding brushes are made. Two unusual experiences attributed to grounding brushes are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

STUDY OF THE HVDC-TORSIONAL INTERACTIONS THROUGH DIGITAL DYNAMIC SIMULATION

Abstract This paper presents the detailed dynamic digital simulation for the study of phenomenon of torsional interaction between HVDC-Turbine generator shaft, dynamics using the novel converter model presented in [ 1 ] The system model includes detailed representation of the synchronous generator and the shaft dynamics, the ac and dc network transients. The results of a case study indicate the various factors that influence the torsional interaction.

Effect of Fault Clearing and Damper Modelling on Excitation and Decay of Vibrations in Generator Shafts Following Severe Disturbances on the System Supply

The paper examines the effect damper circuit modelling and the current interruption process has on amplitude and decay of torsional vibrations in turbine-generator shafts following severe supply network disturbances. A phase-variable model of a synchronous-generator with up to 2 direct-axis and 3 quadrature-axis dampers where fault current is cleared at fault current zeros is employed to calculate generator airgap torque which results from a severe disturbance on the electrical supply. Using airgap torque, effective amplitude of torque excitation acting on the generator rotor for each eigenfrequency is determined by Fourier analysis. Amplitude of torsional vibration at each shaft section for each modal frequency is then calculated. Shaft torque at each shaft location for each modal frequency is thereby deduced. These components, together with the steady-state component (and that due to rotor swing), are summed as absolute values for all modal frequencies to yield approximate peak torque at critical locations along the shaft following each disturbance. Approximate peak shaft torque estimated by frequency domain analysis is compared in some instances with peak torque predicted by solution of exact differential equations. Presented results illustrate amplitude of torque excitation and shaft torques as a function of fault clearing time for L-L-L and L-L high-voltage system short-circuits, and effect reactive power and system resistance has on damping predominant torsional vibrations in the shaft.

Effect of Fault Clearing and Damper Modeling on Excitation and Decay of Vibrations in Generator Shafts Following Severe Disturbances on the System Supply

Effect of Fault Clearing and Damper Modeling on Excitation and Decay of Vibrations in Generator Shafts Following Severe Disturbances on the System Supply

Analysis of Continuum and Reduced Shaft Models in Evaluating Turbine-Generator Shaft Torsional Response following Severe Disturbances on the System Supply

ABSTRACT The paper examines use of continuum and reduced models of turbine-generator shafts in evaluating torque response following incidence and clearance of severe disturbances on the system supply. Using airgap torque which results from incidence and clearance of system disturbances at fault current zeros, torque excitation which acts along the active length of the generator rotor for each torsional vibration is determined by Fourier analysis. Amplitude of torsional vibration at each shaft cell for each modal vibration is determined from the torque prime mover and generator shaft sections of interest for each modal vibration is then calculated. These components, together with the steady-state component (and that due to rotor swing), are summed as absolute values to give approximate peak torque at critical shaft sections. Presented results illustrate torque excitation and shaft torque estimated from continuum, simple and stiffness-adjusted shaft models as a function of fault clearing time following L-L-L and L-L high voltage disturbances with clearance. Effect of employing continuum and reduced shaft models in estimating time constants for decay of predominant shaft torsional vibrations and on peak energy of the vibrations is illustrated. The effect saturation of the stator leakage reactance has on torque response following sustained stator-terminal L-L-L and L-L short-circuits at full-load and no-load and following worst-case synchronisation is also illustrated. 66O MW and 1000 MW two-pole machines are analysed.

サイリスタインバータ方式軸発電機システムの調相機特性の選択について

Because of the importance of the synchronous-condenser (S.C) in the Thyristor-inverter Type Shaft Generator System, the characteristics of this system are examined from the view point of its effects. An expression of S.C is derived from experiments and its accuracy is verified. The results of experiments on the model of the system are1. With no Automatic-Frequency-Control equipment, it has two conditions, stable and astable, depending on the state of S.C.2. Both capacity and power factor characteristics of S.C have to be considered when the system is analyzed and designed.