Transient Torque Research Articles

Reduced order models for induction motors with two rotor circuits

Induction motor behavior is commonly simulated by a fifth order differential equation model which includes two stator state variables, two rotor state variables, and shaft speed. Normally two more variables must be added to account for the effects of a second rotor circuit representing deep bars, a starting cage, or rotor distributed parameters. This paper presents a technique for including the effects of a second rotor circuit without adding more state variables to the fifth order model. Transient, as well as steady state effects are included. The model may be useful in cases where switching introduces transient torques and losses that are invisible to the fifth order model, and it is not desirable to expand the model to include two more state variables. A laboratory test is included. >

A method for analysis of back‐swing phenomena of synchronous machine in multimachine power systems

AbstractThis paper describes a new approach to the analysis of the back‐swing phenomena in multimachine power systems. When a short‐circuit fault occurs in a power system, some generators decelerate in a short period immediately after the fault in some cases. The phenomenon called back swing is caused by the transient responses in armature winding of synchronous machines and in transmission lines. To represent the back swing in detail by a mathematical model, these transient behaviors have to be described by sets of differential equations. Then not only does the order of differential equations increase, but the convenient expression of the transmission system by a set of node equations becomes useless.In this paper an equivalent power system model for the simple representation of the back swing has been proposed. First, an impedance for each machine that represents the transient of transmission system has been introduced. It is assembled into the differential equations associated with armature winding response. Then the transmission system is represented by a constant impedance matrix. This model makes it possible to calculate the transient behavior of armature flux in multimachine power systems. The transient torque brought to the rotor shaft by the flux is calculated directly and it represents the back‐swing phenomena effectively.

Analysis and an Improvement of Transient Characteristics of Pole-Changing Induction Motor with Single Primary Winding.

Pole-changing is a simple method for changing the speed of a cage induction motor. However, excessive currents and torques appear during deceleration of the motor by pole-changing. These characteristics are unfavorable for shafts and couplings of the motor system. And further, these cause the sudden voltage drop of the supply. From user's viewpoint, it is desirable to control these currents and torques as low as possible.In order to decelerate the speed by pole-changing, first, the supply is removed from the delta connected high speed terminals. Next, the supply is connected to low speed terminals, and finally, the winding is changed to the parallel _??_ connection. From the simulation results, the authors discuss the effects of the supply removal period, impressed voltage phase and the period between the supply impression and the changing to the parallel _??_ on the motor. This discussion gives the conclusion that the transient current and torque can not sufficiently controlled even when the above conditions are appropriately selected.In order to reduce these transient current and torque sufficiently, this paper proposes a method in which external resistors are inserted in series with the three-phase primary winding. From the simulation results, it is found that the inserted resistance of 1.55 times the locked rotor impedance of the induction motor, can sufficiently reduce the excessive transients.

Control of a dynamic brake to reduce turbine-generator shaft transient torques

A resistive, thyristor-controlled brake is used to damp transient torques in large thermoelectric generators supplying series-compensated transmission lines. Emphasis is placed on developing a suitable control algorithm and testing the algorithm through a wide variety of different operating configurations. Discrete-level generalized predictive control (GPC) is examined as one possible approach to optimal control of the brake. Some problems with implementation of GPC on the system are discussed. Prony analysis is used to identify system transfer functions, which are then related to control design considerations and robustness properties. >

Noncontact torque sensor using the difference of maximum induction of amorphous cores

A novel noncontact torque sensor which uses the difference of the maximum magnetic induction of two cores was constructed. The torque sensor utilizes the change in the maximum magnetic induction by AC magnetization due to the stress-induced magnetic anisotropy of negative magnetostrictive amorphous ribbons which are attached on a rotatable shaft in a chevron pattern. This sensor shows that the linearity was better than 1%, and the transient torque can be measured at the sampling rate of 10 kHz, which is the same as the magnetizing frequency of the core. >

A method for reducing transient torsional stresses of turbine-generator shaft segments

The author presents a method for reducing transient torsional stresses of steam turbine-generators in series-capacitor-compensated power systems, which are equipped with ZnO varistor schemes. The fundamental concept is to reduce the coupling between the electrical network and the shaft system with respect to the troublesome torsional frequency. The electrical network and the rotating shaft system are coupled through the generator air-gap torque. This coupling can be attenuated by unbalancing the network with respect to the phenomenon of torsional oscillations. This is achieved by setting the protective voltage levels of the three phases of a three-phase series capacitor at unequal values. The technical feasibility of the proposed method is demonstrated on a test system, using the BPA Electromagnetic Transients Program (EMTP) as the study tool. The impact of the proposed countermeasure on the transient torques of the system, as a result of different disturbances, is demonstrated. The limitations of the proposed method are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Prototype Steering Weave Stabilizer for Automobiles

A prototype high-speed steering stabilizer for automobiles applies transient steering torques so that the sum of natural steering restoring torque and the control torque is more nearly in phase with steer angle than the natural restoring torque alone. The resulting reduction in the phase lag from steer angle to restoring torque mitigates the steering weave mode. Since steering restoring torque is nearly proportional to vehicle lateral acceleration, weave controller circuitry could subtract instantaneous lateral acceleration from expected steady-state lateral acceleration calculated from steer angle and vehicle speed, and thence command a steering torque actuator depending on the difference signal. The prototype performs the same function using a concentrated mass on the lower steering wheel rim which is passively sensitive to both steer angle and lateral acceleration, thereby applying only transient steering torques in the desired manner at a vehicle speed of 30 m/s. The additional steering system inertia alone affects the weave mode, so a non-stabilizing configuration with the same mass distributed around the steering wheel rim is tested for direct comparison. The experimental data show a dramatic stabilization of weave for the configuration which applies control torque.

Measurement of torque in steam turbine-generator shafts following severe disturbances on the electrical supply system-analysis and implementation

Phenomena that affects the performance of transducers that measure torque at positions along a turbine-generator shaft are reviewed, and the design of a transducer for precise measurement of torque at positions on a steam turbine-generator shaft that results from severe disturbances of the electrical supply system is discussed. Torque at shaft couplings following severe supply system events predicted using continuum models of turbine-generator shafts are analyzed and compared with that obtained over a section of the shaft by shaft twist and overall stiffness of the section. Algorithms for processing torque deduced from twist over a section to estimate true torque at specific shaft locations are discussed. Studies are performed for severe L-L-L short circuits with clearance. The design of a transient shaft torque transducer which uses disks with slits which are secured to the rotating shaft is described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modeling and simulation of point-on-line switching of VSI-fed induction motor

A method of mathematical solution to simulate point-on-line switching of an induction motor after a brief moment of disconnection is presented. A comparative simulation study of an induction motor transient air-gap torque with delayed reclosing on to a sinusoidal and voltage source inverter (VSI), six-step, and pulse-width modulated (PWM) supplies for various delayed reclosing times is outlined. The three phases supplying the motor are simultaneously disconnected and are reconnected back to the motor simultaneously or in some sequence. The effect of such an operation on the transient air-gap torque is analyzed. The authors investigate simultaneous and sequential reclosing mechanisms of a motor to sinusoidal or VSI supplies to ameliorate switching transients.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

ANALYTICAL SOLUTION OF THE TRANSIENTS IN INDUCTION MOTORS DUE TO ASYMMETRICAL TERMINAL FAULT

ABSTRACT When supply to the induction motor is short circuited the energy stored in machine, causes the machine to behave as a generator. This can result in very large transient negative torque and large transient current, especially in case of asymmetrical fault. This article provides an analytical solution of the transient current and the torque for the asymmetrical fault condition, and from these, practical equations are developed to determine the peak transient torque and the transient current. The analytical solution assumed constant shaft speed. The results obtained compared with the experimental results and with the machine exact deferential equation. It has shown that the results obtained agree well with both the theoretical results obtained from the numerical exact variable speed solution and the experimental results.

An Approximate Analysis of Transient Phenomena of Synchronous Machines for Armature Voltage Disturbances.

This paper presents approximate equations of transient currents and torque of synchronous machines during sudden three-phase short circuit phenomena and synchronizing phenomena. Although there are a lot of reports analyzing these problems, most of them study a relatively simple synchronous machine operated under special conditions which is easy to analyze; i.e., for example, three-phase short circuit for unloaded synchronous machines modeled to have one damper circuit both in d and q axis. However, recently more complicated models of synchronous machines with two or three damper circuits both in d and q axis are studied and used to analyze transient phenomena of synchronous machines.The analytical technique presented in this paper is developed on the basis of a new approximate method. The method studies an armature transient neglected model at first and derives the solution taking no effects of armature transient into consideration. Next, the components arising from the effects of armature transient is solved. The complete solution is obtained by adding these two solutions. In addition, the derived solution has a general form for damper structure. Thus, it is easy to obtain a particular solution for the synchronous machines with any number of damper circuits. To confirm the accuracy of the derived solution, numerical simulations of above two problems are carried out for the synchronous machine with three rotor circuits both in d and q axis. As a result, good agreements are obtained between the approximate solution and the exact solution obtained by simulating the basic differential equations

MODULATION OF THE STRETCH REFLEX DURING VOLITIONAL SINUSOIDAL TRACKING IN PARKINSON'S DISEASE

Sinusoidal visually-guided wrist tracking, in normal and parkinsonian subjects, was perturbed by torque transients every 90 degrees throughout the movement. Long-latency stretch reflex and volitional EMG amplitude modulations were assessed as functions of the tracking phase. Reflex modulation during tracking, both in wrist flexor and extensor muscles, was found to differ significantly between parkinsonian and normal subjects. In the parkinsonian group, the abnormality consisted of an increased reflex activity during tracking phases in which the muscle was lengthening. At these phases the reflex generated torque is opposite in direction to the volitionally generated torque and the tracking movement. No differences in the unperturbed volitional EMG modulation were observed between groups for this error constrained tracking paradigm. Significant correlations were found between ratings of bradykinesia and the amount of abnormal reflex modulation in the wrist flexor. These data suggest that a component of bradykinesia results from a defective coordination of supraspinal reflex and volitional control systems.

Transient Torque Produced in Arm Shaft of an Industrial Sewing Machine

This study considered the effects of needle penetrating force, needle thread tightening tension, and pressing force of the presser foot on torque produced in the arm shaft of an industrial sewing machine. The results obtained are as follows. (1) Penetrating force, especially the initial triangular wave fluctuation, induces noticeable transient vibration in torque. (2) The penetrating force is considerably more transient than the pressing force. The time ratio of the duration of the penetrating force to the natural period of the motion system is close to 1. (3) Consequently, when estimating torque, it is necessary that the arm shaft of the thread take-up lever and needle bar mechanism motion system be considered as elastic. On the other hand, the arm shaft of the feed mechanism motion system can be treated as a rigid body.

Nonlinear algorithms for automotive engine control

Nonlinear automotive engine control methods that would enhance shift quality are discussed. In the course of a typical automotive transmission upshift, there is an extreme decrease in the transmission's output torque during the torque-phase of the shift. This is due to the torque being transferred from a high to a low gear ratio. In the speed phase, due to inertial effects and the negative slope of the friction coefficient, the output torque rises and peaks when the shift ends, changing engine speed. Modulating engine torque can smooth these output torque transients. The sliding-mode control method is used, and a solution to the multivariable control problem (i.e. coordinated throttle and spark control) is presented. A speed-control approach is used, and relationships between speeds and desired torque (or acceleration) trajectories are discussed. >

Computation of transient electromagnetic torque in a turbogenerator under the cases of different sudden short circuits

A method for the computation of the transient electromagnetic torque in turbogenerators is given in which the iron saturation and the relative motion of the rotor and stator are taken into account. This method is based on the finite-element computation using a dynamic model coupled with the equations of external electric circuits. To avoid the airgap mesh distortion caused by the movement of the rotor, moving boundaries are introduced in the airgap. An example is given that involves the computation of the distribution of transient magnetic field and the electromagnetic torque of a 200-MW turbo-generator following different types of sudden short-circuits. The computed results agree with the measurements very well.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A PHENOMENA THAT CAUSES MOST SEVERE TRANSIENTS IN THREE-PHASE INDUCTION MOTORS

ABSTRACT The dynamical behaviour of a 3-phase induction motor supplied through a distribution transformer and during starting period, subjected to a very short time supply disturbance from the primary side of the transformer, while the secondary side is still connected to the machine, has been studied. The analysis has been made by simulating the machine in time domain by using traditional d-q model, including the effect of transformer secondary vinding impedance during the disturbance period. To verify the accuracy of the digital model, the normal starting transient torque-time pattern under free acceleration is computed and compared with the previously measured results. The transient torque-time, speed-time and current-time patterns of two different machines are computed for the phenomenon under investigation and are compared with their counterparts resulting from starting under free acceleration. Also the effect of the supply disturbance time duration on the transient torque peak has been studied. It w...

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.

The study of characteristics of redial inward-turbines for exhaust gas turbocharges under non-steady flow conditions. The prediction of turbine performances by quasi-steady analysis for sinusoidal wave forms.

This paper describes performances of a radial turbine for turbocharger under pulsating flows. The tests were carried out at sevral pulse frequencies with sinusoidal velocity wave forms produced by a rotary type pulse generator rig. Power measurement using digital torque detector based on phase difference method has successed to get the transient and mean torques. Turbine power was absorbed by two manners: one is done by a radial compressor under unsteady turbine flow and the other by a D.C motor generator under steady turbine flow conditions respectively. The quasi steady analysis was carried out using the steady turbine performance curves to predict the unsteady turbine performances. The test results show that the evaluated mass flow rate agrees well with measured experimental values all range of the velocity amplitude ratio. And the power output prediction becomes a little underestimations as increasing the ratio of velocity amplitude. The influence of pulse frequency is not remarkable.

Transient currents and torques in wound-rotor induction motors using the finite-element method

The paper describes a time-stepping finite-element technique for modelling transient torques and currents in a slip-ring induction motor. The method is based on a coupled fields and circuit equation approach that allows the winding inductances to be modified to account for certain three-dimensional effects. The numerical solution incorporates a moving rotor so that slotting and saturation effects can be modelled accurately. The method is verified by direct comparison with experimental results obtained from a motor subjected to a supply reconnection at speed. It is shown that the general method can be extended in a straightforward manner to accommodate cage induction motors.

Pyroelectric transient torque. Theoretical and experimental study

Pyroelectric transient torque. Theoretical and experimental study