Transient Torque Research Articles

Macroscopic friction and dielectric relaxation

Dielectric relaxation is known to depend on whether the process is controlled by field strength or by charge density. The aim of this study is to give mechanical meaning to the constant field (or transversal) relaxation time tau and the constant charge (i.e. constant displacement or longitudinal) relaxation time theta . First, it is demonstrated that the formal difference between field and charge control disappears if the perturbation is periodic. Then tau is shown to be the relaxation time of the transient torque applied to the system by the change of the direction of the field. Similarly, theta is the relaxation time of the deformation force in the dielectric substance brought about by a sudden change of the external field. By this token, both relaxation times are recognized as quantities proportional to the reciprocal internal friction coefficients of the substance, tau being connected with rotation and theta with translation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A torque-controllable electromagnetic multiple-disc brake

This paper describes a new type of electromagnetic multiple-disc brake for controlling braking torque. The brake consists of a rare-earth permanent magnet, an electromagnet and multiple friction discs. The friction torque is controlled by the electric current in a coil of the electromagnet. In the analysis the design formulae for the brake are first derived from electromagnetic theory and tribological considerations, then the transient braking torque under the electric current control is derived and vibrations of the disc considered. To verify the present system and the analysis, experimental tests were made on the brake.

Analysis and application of three-phase induction motor voltage controller with improved transient performance

An improved transient performance of three-phase inductance machines with controlled thyristor triggering is presented. A recently developed dynamic function for the thyristor triggering angle is utilized. The triggering angle function influences the phase modulation of the machine-supplied voltage such that the normal transient problems are avoided. Simulation of transients, based on the analytical solution of the machine differential equations, for all modes of operation is provided. The simulation model results show that a smooth switching process for an induction machine, running at any speed, for both motor and generator operation, is achievable. The beneficial effect of the suggested function is smoothing the transient flux, currents and torque is illustrated. Application of the function to different switching conditions is performed with actual laboratory tests. >

High-performance direct torque control of an induction motor

A novel direct torque control method for an induction motor is presented which is quite different from field-oriented control. Improving the torque response of a large-capacity induction motor using two sets of three-phase inverters and an open-data induction motor is of special concern. Instantaneous voltage vectors applied by an inverter have redundancy characteristics which provide some flexibility for selecting the inverter switching modes. By using this switching freedom, control is achieved according to the following priorities: (1) high-speed torque control; (2) regulation of the primary flux; (3) decreasing the zero phase sequence current; and (4) minimization of the inverter switching frequency. Simulations and experiments have been carried out to verify the feasibility of this priority control, accompanied by comparisons with another control scheme. Torque frequency-response corner frequencies above 2000 Hz have been experimentally measured, and time constants of 4 ms have been achieved for rotor-speed step responses from -500 to 500 r/min. The peak transient torque during the step change is about 20 times the rate torque. >

A Nonlinear Controller Design Method for Fuel-Injected Automotive Engines

A nonlinear, “sliding mode” fuel-injection controller is designed based on a physically motivated, mathematical engine model. The designed controller can achieve a commanded air-to-fuel ratio with excellent transient properties, which offers the potential for improving fuel economy, torque transients, and emission levels. The controller is robust to model errors as well as to rapidly changing maneuvers of throttle and spark advance. The sliding mode control method offers a great potential for future engine control problems, since: it results in a relatively simple control structure that requires little on-line computing and no table lookups; it is robust to model errors and disturbances; and it can be easily adapted to a family of engines.

Performance of a newly developed torque-sensor motor

A new type of induction motor with a built-in torque sensor (called a ‘torque-sensor motor’) has been developed in order to monitor grinding torque. Its rotor shaft consists of a hollow shaft and torsion bar, each of which has a disc with equiangularly located magnets. The torque output is calculated by microcomputer from the time delay of pulses generated in detecting coils. This toque sensor has good linearity. Torque ripple and zero-point drift caused by rotational speed change are estimated to be less than 1 Nm. It is so sensitive that it can detect torque ripple from rotational error of the driving belts on the grinding machine. Further, it can accurately monitoring grinding torque by using a low pass filter to remove such torque ripple. It can also be used to estimated the time constant of the grinding wheel and workpiece system in the transient torque situation of a grinding cycle. The performance of the grinding wheel motor is as good as that of a conventional motor.

Effect of energy and voltage ratings of ZnO protective systems of series capacitors on transient stability and transient torques

The effect of voltage and energy ratings of ZnO protective systems of series capacitors on the transient stability and the transient torque phenomenon of a power system is investigated. Bonneville Power Administration's Electromagnetic Transients Program (EMTP) is used for the studies. The stability studies are also carried out by a stability program and the results are compared with the EMTP results. The investigations show that the system switching strategy, the frequency of the inertial mode, and the systems susceptibility to SSR (subsynchronous resonance), are also important factors in proper determination of voltage and energy ratings of ZnO protective systems. As compared with the EMTP results, the stability program results are erroneous if the effect of ZnO protective systems of series capacitors is not considered in the analysis. Incision of capacitor-varistor linear models in a stability program results in optimistic stability margins. However, the results can be accepted with a fair degree of confidence. >

On a new type torque-controllable electromagnetic disk brake.

This study proposes a new type of electromagnetic multiple disk brake for controlling the friction torque of the brake by using a rare earth magnet which generates very strong magnetic fields. This brake consists of a rare earth permanent magnet, an electric magnet and multiple friction disks. In this system, a control device such as a microcomputer generates an electric current in a coil of the electric magnet, and controls the friction torque of the brake. In the analysis the design formulae for the brake is first derived, based on the theory of electro-magnetic fields and the theory of tribology, then the transient friction torque is derived using the theories of Dynamics of Machinery and Automatic Control. To verify the present system and the analytical method, experimental tests have been performed for a model of the above-mentioned brake.

Transient torque and short circuit capabilities of variable speed permanent magnet motors

A high performance motor drive must produce peak torque which is much larger than its continuously rated value. This paper analyzes the capability of two types of permanent magnet motors using N d F e B magnets and shows that an essentially linear relationship between torque and stator current can be achieved up to the order of 6 times rated current without magnet demagnetization. Also, the motors can be designed to withstand terminal short circuits without magnet damage. These properties have been experimentally verified on two laboratory motors.

Computation of Saturated Permanent-Magnet AC Motor Performance by Means of Magnetic Circuits

A digital computer evaluation of transient states in a permanent-magnet (PM) machine by means of the flux tubes method is described. The influence of initial rotor phaseshift on transient torque peaks, as well as the influence of saturation on current waveforms, is shown. Several computer runs are carried out to illustrate the applicability of the flux tubes method for computation of PM machine performance.

Non-Simultaneous Reclosing Air-Gap Transient Torque of Induction Motor: Part II, Sample Studies and Discussion on Reclosing of ANSI C50.41

Using the analytical method derived in Part I, this paper shows the variations of air-gap reclosing transient torques caused by (1), the initial angle of system phase voltage waveform at switching off, (2), the dead time (i.e. time interval between switching off and reclosing), (3), the delay of the reclosing of the third switch pole, (4), the value of the slip and (5), the parameters of the motor and capacitors. Examination of the resultant p.u. voltages per hertz calculated at the instants either before the reclosing of the two switch poles or of the third switch pole does not indicate that the limit of 1.33 recommended by ANSI C50.41 has real meaning in limiting the magnitude of the peak value of the reclosing transient torque. It is recommended that one calculate the reclosing torque using the method given in Part I instead of judging the reliability by rule of thumb. Good agreement was obtained between calculated and test results.

Nonsimultaneous Reclosing Airgap Transient Torque of Induction Motor: Part I, Analysis and Computation Logic

Nonsimultaneous Reclosing Airgap Transient Torque of Induction Motor: Part I, Analysis and Computation Logic

Nonsimultaneous Reclosing Airgap Transient Torque of Induction Motor: Part II, Sample Studies and Discussion on Reclosing of ANSI C50.41

Nonsimultaneous Reclosing Airgap Transient Torque of Induction Motor: Part II, Sample Studies and Discussion on Reclosing of ANSI C50.41

Two Countermeasures for Damping Torsional Interaction and Transient Torques of Turbine-Generators

Two Countermeasures for Damping Torsional Interaction and Transient Torques of Turbine-Generators

An experimental investigation of transient torques

A technique is described for measuring and recording the torque generated by a prime mover over the full range of its speed. The prime mover chosen for the investigation is an induction motor in order to demonstrate that the technique can be used even on a motor whose torque over a wide range of speed cannot be readily measured by conventional steady-state methods. A method of measuring the transient motor torque, based on the principle of the reaction torque of a motor, is described. The transducer used in the torque measurement is a strain gauge. A description is given on the bridge and voltage amplifiers. The calibration of the torque output readings is explained. Torque-speed characteristics of the induction motor are obtained, and the accuracy of the measuring system for the starting torque and transient torque is discussed. One by-product of the investigation is the experimental verification of the presence of the switching-transient torque in an induction motor.

Effects of the transient Mode II on the steady state crack growth in Mode I

Turbo-generator shafts in power plant systems are often subjected to transient torques due to electric faults and high-speed reclosures. These transient torques cause the initiation and growth of cracks in Modes II and III. However, these cracks are further subjected to cyclic bending (Mode I crack growth) due to the turbine shaft weight or possible misalignments. Such load histories are also very common in railroad tracks. An existing crack may be subjected to a sudden Mode II, followed by a steady state Mode I. In order to predict the fatigue life, the effect of the transient Mode II on a subsequent Mode I crack growth must be understood. In this paper the effects of the Modes I and II overloads on a subsequent Mode I crack growth are studied on the AISI 4340 and spherodized AISI 1090 steels using three- and four-point bending specimens. The results show that in contrast to Mode I overloads, where the crack is either arrested or retarded for a distance of the order of magnitude of the transient plastic zone size, Mode II overloads give rise to the crack growth acceleration (for a very short distance, much smaller than the Mode II transient plastic zone size with no retardation afterwards). The three known mechanisms of the crack closure in Mode I (plasticity-, roughness- and oxide-induced crack closures) were examined for the Mode II overloads and were found not to be applicable for that Mode. Fractography analysis of 1090 steel at the point of Mode II overload showed a significant amount of shear cracks and cavities. Such cavities could contribute to the crack growth acceleration in the subsequent Mode I crack growth.

Two Countermeasures for Damping Torsional Interactions and Transient Torques of Turbine-Generators

Two different schemes of thyristor-controlled static phase-shifters for damping torsional interaction and transient torques of turbine-generators, are investigated and compared. Generator speed deviation from the synchronous speed, is used as the control signal. The two schemes are the discrete step controlled phase-shifters and the point-on-wave controlled phase-shifters. The studies are carried out on the first IEEE benchmark for SSR studies, using the BPA's Electromagnetic Transients Program (EMTP). The investigation results show that the two schemes of static phase-shifters can be used to provide effective damping for torsional interaction and transient torques of large turbine-generators. The results also indicate that as compared with the point-on-wave controlled phase-shifters, the discrete step controlled phase-shifters are more effective for damping torsional oscillations.

Test Equipment for Induction Motors

The paper describes test equipment for measuring the torque of an induction motor over the full range of its speed and for plotting the motor's important torque-speed characteristic on an oscilloscope. The torque sensor is a strain gauge and the test includes the measurement of the switching transient torque.

A model for coulomb torque hysteresis in ball bearings

The frictional torque resisting rotation of an angular contact ball bearingg builds up from rest to its steady value through a small but finite angle of rotation. A similar transient torque is observed when the direction of rotation is reversed so that, in a bearing which undergoes oscillating rotations of small amplitude, the resistance torque traces out a hysteresis loop with angle of rotation. Following Dahl [AFO 4695-67-C-D158, Aerospace Corp. (1968)], the shape of the loop is expressed in terms of two parameters: (i) the initial and reversal gradient s and (ii) the steady-state torque T s. Theoretical expressions are derived for both s and T s. s depends upon the elasticity of the bearing materials but not upon the frictional conditions at the contact interface whereas the opposite applies to T s. Both depend upon the geometry of the bearing, particularly the conformity between the ball and race. Good correlation has been found between theoretical predictions and experiments carried out on three bearings of significantly different geometry.

A model for Coulomb torque hysteresis in ball bearings

The frictional torque resisting rotation of an angular contact ball bearingg builds up from rest to its steady value through a small but finite angle of rotation. A similar transient torque is observed when the direction of rotation is reversed so that, in a bearing which undergoes oscillating rotations of small amplitude, the resistance torque traces out a hysteresis loop with angle of rotation. Following Dahl [AFO 4695-67-C-D158, Aerospace Corp. (1968)], the shape of the loop is expressed in terms of two parameters: (i) the initial and reversal gradient s and (ii) the steady-state torque Ts. Theoretical expressions are derived for both s and Ts. s depends upon the elasticity of the bearing materials but not upon the frictional conditions at the contact interface whereas the opposite applies to Ts. Both depend upon the geometry of the bearing, particularly the conformity between the ball and race. Good correlation has been found between theoretical predictions and experiments carried out on three bearings of significantly different geometry.