Showing papers in "IEEE Transactions on Industry Applications in 1975"
TL;DR: In this article, the authors focus on the problem of unbalanced voltage at the point of utilization of a three-phase induction motors and the effect of such voltage imbalance on the operation of the motors.
Abstract: Three-phase electric power systems generally provide voltage supply at the generating station that is well balanced in both magnitude and displacement. For varying reasons, however, some degree of voltage unbalance occurs at the point of utilization, and, depending upon the amount of unbalance, this can have an adverse effect upon the operation of polyphase induction motors. A major cause of unbalanced voltage at the point of utilization is that single-phase loads on a system are not uniformly applied to all three phases. This is particularly true for some rural electric power systems, and it can also occur in large urban power systems where heavy single-phase demands are imposed by facilities such as extensive shopping plazas. A large manufacturing plant may have well balanced incoming supply voltage, but unbalance can develop within the plant from its own single-phase power requirements if these are not uniformly spread among the three phases. Regardless of the cause, unbalanced voltage is harmful to three-phase induction motors. The paper to follow concentrates upon that aspect of unbalanced voltage.
98 citations
TL;DR: In this article, an improved method of obtaining the slip information without the use of rotary transducers of any kind was discussed, by sensing the electrical quantities applied to the motor and performing simple signal processing operations on the sensed quantities, an analog signal proportional to the slip level was derived and used in motor control functions.
Abstract: In certain types of adjustable frequency induction motor drives, optimal control of the motor can be best implemented by using information on the motor slip frequency. Unfortunately, this generally requires the use of an electromechanical speed transducer coupled to the shaft. The presence of this transducer spoils the general characteristics of ruggedness and mechanical simplicity typical of an ac drive. This paper discusses an improved method of obtaining the slip information without the use of rotary transducers of any kind. By sensing the electrical quantities applied to the motor (voltages, currents, and phases) and by performing simple signal processing operations on the sensed quantities, an analog signal proportional to the slip level is derived and used in motor control functions.
94 citations
TL;DR: In this article, the exact equations defining steady-state operation of a controlled current induction motor drive system are derived by solving the system state equations in the stationary reference frame, which assume ideal current filtering, eliminate the difficulties involved in taking derivatives of discontinuous currents by defining a pair of pseudocurrent variables.
Abstract: The exact equations defining steady-state operation of a controlled current induction motor drive system are derived by solving the system state equations in the stationary reference frame. These equations, which assume ideal current filtering, eliminate the difficulties involved in taking derivatives of discontinuous currents by defining a pair of pseudocurrent variables. Effects of saturation are included by using the slope ratio method. Electromagnetic torque and current pulsations are computed for various load conditions, and experimental confirmation of the calculated results is made. Similarities and differences to voltage controlled characteristics are presented. It is shown that normal open-loop operation occurs on the unstable side of the torque-slip characteristic necessitating the use of feedback control for stable operation.
94 citations
TL;DR: An improved modulation scheme is presented, which allows us to extend the practical speed range of PWM ac drives, and the advantages and limitations of popular modulation methods are discussed.
Abstract: The performance of inverter drives, which use the pulsewidth modulated (PWM) technique to control motor applied voltage and frequency, are critically influenced by the choice of the modulation policy used in the control circuits. This paper deals with practical inverter drives for squirrel cage induction motors and presents some basic considerations on modulation requirements. The advantages and limitations of popular modulation methods are discussed, and an improved modulation scheme, which allows us to extend the practical speed range of PWM ac drives, is presented.
77 citations
TL;DR: In this article, a Zener diode is used to simulate the corona drop and the buffer dielectric plays a major role in controlling the voltage and the air gap.
Abstract: Electrical characterization is based on a display of voltage and charge which appears as a simple parallelogram. The area is a measure of energy input per cycle and is independent of voltage waveform but very dependent on the maximum voltage. A useful model for such corona discharges employs a Zener diode to simulate the corona drop. The buffer dielectric plays a major roll in controlling the corona power, and the air gap importance depends on the electrode system employed. Proper interpretation of the voltage-charge traces provides insight as to the corona performance and serves as a diagnostic procedure for obtaining optimum performance.
68 citations
TL;DR: In this paper, the state-variable formulation is applied to the analysis of two widely used drive systems incorporating square-wave inverters with 180° and 120° firing logic, and the results are compared to an analytical solution.
Abstract: The application of adjustable frequency static inverters to induction motor speed control has resulted in a diversity of inverter designs. In this paper, the state-variable formulation is applied to the analysis of two widely used drive systems incorporating square-wave inverters with 180° and 120° firing logic. Measured characteristics of an actual drive system are included, and the results are compared to an analytical solution. Steady-state speed-torque curves for each inverter supplying three markedly different types in induction motors are given. Performance of the two inverter drives are compared by a thorough investigation of typical operating points.
66 citations
TL;DR: In this paper, a solid-state induction motor speed regulating scheme using a rotor chopper-controlled external resistor is investigated, which provides continuous and contactless variation of rotor resistance and thereby eliminates the undesirable features of the conventional rotor resistance control method.
Abstract: A solid-state induction motor speed regulating scheme using a rotor chopper-controlled external resistor is investigated. This control scheme provides continuous and contactless variation of rotor resistance and thereby eliminates the undesirable features of the conventional rotor resistance control method. A thorough analysis of the steady-state performance of the system is presented. Both dc and ac circuit models are derived to describe the performance characteristics when the chopper operates under the time-ratio control (TRC) strategy. Effects of machine parameters on performance characteristics are studied. Theoretical results from the model are verified by comparison with experimental results. The torque?speed characteristic of this speed control system is essentially linear for a particular time ratio.
48 citations
TL;DR: In this article, an optimization method for selecting the modulation technique and carrier frequency for a PWM inverter system is presented, concerning the tradeoff between efficiency and unfiltered harmonic content, which can be made with the help of this method.
Abstract: An optimization method, which will be of use in selecting the modulation technique and Carrier frequency for a PWM inverter system, is presented. The difficult decision, concerning the tradeoff between efficiency and unfiltered harmonic content, can be made with the help of this method. A relation between second-order filter rating and unfiltered harmonic attentuation, for optimum component values, is also obtained. The optimization method is used for illustration to select the optimum modulation technique and its carrier frequency for the modified McMurray inverter [1] to be used in a rapid transit auxiliary power converter. The design aim is to obtain a constant sine wave output with a specific input supply voltage variation. The inverter efficiency is predicted for various carrier frequencies using two modulation schemes. The Schonung and Stemmler [2] modulation approach, with a carrier frequency of 900 Hz, is found to be optimum as it results in low filter rating and an efficient inverter.
33 citations
TL;DR: In this paper, the effects of electric motor vibration from the viewpoint of its causes and cures are discussed, as well as the important considerations in establishing purchase specifications consistent with final installation requirements.
Abstract: The trend of industry toward higher speed machines and longer periods between downtimes has fostered closer surveillance of those parameters that can interrupt satisfactory service. Vibration of electric motors and systems containing motors are areas identified for consideration. Electric motor vibration is discussed from the viewpoint of its causes and cures. Also covered are the important considerations in establishing purchase specifications consistent with final installation requirements.
23 citations
TL;DR: The case study demonstrates the advantages of the computer-aided design, before the physical construction of the experimental system, of a typical printer with a step motor designed with this approach.
Abstract: Basic information on modeling and digital computer simulation of variable-reluctance (VR) step motors is provided. The nonlinear equations of the system are derived, and a method for implementing them on a digital computer is presented. As an example, a typical printer with a step motor is designed with this approach. The problem is defined by giving the desired system performance criteria and the step motor parameters and characteristics. The specification of the control schemes determined the design. Computer simulation runs are made to determine the optimal control parameters of the system. The case study demonstrates the advantages of the computer-aided design, before the physical construction of the experimental system.
15 citations
TL;DR: In this article, the spectral remote sensing method is used to reconstruct the temperature distribution in glass from remotely sensed spectral emission data, and the validity and accuracy of the method are established by comparing temperature profiles in glass samples under a variety of different physical conditions with independent measurements.
Abstract: The measurement of glass temperature is essential to the understanding and control of efficient glass processing operations. The physical principles of temperature measurement using infrared techniques are described. Emphasis is primarily placed on infrared radiation thermometry (pyrometry) for measuring glass surface temperature and the spectral remote sensing method for recovering temperature distribution in glass. The radiation thermometry for measuring glass surface temperature is reviewed, and difficulties caused by the presence of spectrally selective attenuation of radiation by atmospheric constituents or combustion products such as H 2 0, C0 2 , and others are discussed. Criteria for selecting spectral bandwidths appropriate under the circumstances of glass manufacturing are given, with special emphasis on the effects of environmental spectral absorption. A technique for reconstructing the temperature distribution in glass from remotely sensed spectral emission data is presented. The validity and accuracy of the spectral remote sensing method is established by comparing temperature profiles in glass samples under a variety of different physical conditions with independent measurements.
TL;DR: In this paper, the pump and system head/flow characteristics are reviewed, with suggestions for estimating the pump characteristic and efficiency at reduced speed, and generalized pump and savings curves are developed to permit quick checking of the economics of adjustable speed flow control for various system characteristics.
Abstract: Flow control of pumps with adjustable speed ac drives can be very economical. Pump and system head/flow characteristics are reviewed, with suggestions for estimating the pump characteristic and efficiency at reduced speed. Generalized pump and savings curves are then developed to permit quick checking of the economics of adjustable speed flow control for various system characteristics.
TL;DR: In this article, the multitude of places where electrostatic phenomena occur in xerography are delineated and the relevant gas discharge phenomena are reviewed, and the underlying microscopic mechanisms are probed.
Abstract: The multitude of places where electrostatic phenomena occur in xerography are delineated. In at least one form or another, electrostatic phenomena occur in each and every step of the xerographic process. In some of these steps, many electrostatic phenomena occur simultaneously, and the situation is complicated by the fact that many of these phenomena are sensitive to ambient conditions. The relevant gas discharge phenomena are reviewed, and the underlying microscopic mechanisms are probed.
TL;DR: In this paper, concrete-encased grounding electrodes are used in low-voltage water mains systems, and the potential equalization aspect is discussed in terms of the influence of the concrete casing, the electrode dimensions and the depth of placement on the resistance-to-earth.
Abstract: Following the widespread introduction of nonmetallic water mains to the technology of water supply systems, concrete-encased grounding electrodes are now in use in low-voltage installations. The American and German approaches are discussed in terms of the influence of the concrete casing, the electrode dimensions, and the depth of placement on the resistance-to-earth. Conclusions are drawn as to how an effective equivalent to that of the metallic water mains system is obtainable. The potential-equalization aspect is also discussed.
TL;DR: If asymmetrical triggering technique is judiciously applied to a converter-controlled dc drive, it improves not only the power factor but also the overall performance of the drive.
Abstract: The static Ward-Leonard drive suffers from two major disadvantages: 1) poor power factor when the phase-controlled converter supplying the motor is operated at a delayed triggering angle, and 2) the problems associated with discontinuous armature current when the machine is lightly loaded. If asymmetrical triggering technique is judiciously applied to a converter-controlled dc drive, it improves not only the power factor but also the overall performance of the drive. It reduces the ripple content of the armature current and the value of the extra inductance necessary to achieve current continuity for low-current operation.
TL;DR: The first large gearless ball-mill in North America has been successfully installed at the Mississauga, Ontario, plant of the St. Lawrence Cement Company as discussed by the authors, where the motor rating is 8750hp (6500 kW) at 14.5 r/min (4.84 Hz).
Abstract: The first large gearless ball-mill in North America has been successfully installed at the Mississauga, Ontario, plant of the St. Lawrence Cement Company. The motor rating is 8750 hp (6500 kW) at 14.5 r/min (4.84 Hz). The electrical aspects considered of interest are discussed in the paper.
TL;DR: In this article, the design, construction, and operation of experimental models of a dc-type hybrid step motor are discussed This form of hybrid motor consists of a variable-reluctance step motor, the rotor of which is appropriately wound as a multipole dc motor A computer-aided design procedure is used to obtain the optimum parameters of the dc portion of the hybrid motor.
Abstract: The design, construction, and operation of experimental models of a dc-type hybrid step motor are discussed This form of hybrid motor consists of a variable-reluctance step motor, the rotor of which is appropriately wound as a multipole dc motor A computer-aided design procedure is discussed that is used to obtain the optimum parameters of the dc portion of the hybrid motor The results obtained with two experimental models of this type of hybrid motor are presented Both prototypes show a marked improvement in the running torque characteristics due to the dc windings Torque-speed curves indicate load torques of 400 oz-in available at speeds up to several thousand revolutions per minute with one of the proto-types This type of hybrid motor may be controlled in one of three different ways: a pure step motor, a pure dc motor, or a dc-aided step motor The relative advantages, disadvantages, and application of each control mode are discussed Several control strategies-open and closed loop-are presented for speed control as well as point-to-point type control of position The practical feedback feasibility of this concept for high-power applications in the integral horsepower range is discussed
TL;DR: In this paper, a numerical method is developed for recovering the temperature distribution in glass from spectral radiation emission data, which is obtained using an optimization scheme that determines the best temperature profile from the data in a form of discrete points or Legendre polynomials.
Abstract: A numerical method is developed for recovering the temperature distribution in glass from spectral radiation emission data. The desired temperature distribution is obtained using an optimization scheme that determines the best temperature profile from the data in a form of discrete points or Legendre polynomials. In order to evaluate the accuracy and validity of the spectral remote sensing method, the recovered temperatures are compared with independent measurements in two different experiments, one of which uses a Mach-Zehnder interferometer. Experimental results are reported for Corning Code 7940 fused silica using a Perkin-Eimer spectrometer to measure the spectral radiant energy emerging from the glass. The recovered and interferometrically measured temperatures are found to be in good agreement, i.e., within about 1 ? percent at temperatures up to about 800 K.
TL;DR: In this article, a transverse electric field is used for the deflection of air ions in an airstream by a transversal electric field and the resulting ionization is produced by alpha radiation from a source mounted on one of the electrodes.
Abstract: A novel type of flowmeter is described that is based upon the deflection of air ions in an airstream by a transverse electric field. The ionization is produced by alpha radiation from a source mounted on one of the electrodes. The resulting ions follow a path determined by the air velocity, combined with a superimposed electric field having two components: a control or deflection field and a collection field. Variation of the shape and magnitude of the control field produces an ion current that varies as a function of the air flow. The use of the control field allows the device to be used over a broad range of flows with very little loss of sensitivity. Depending upon the design it can function as an anemometer, volume flowmeter, or a mass flowmeter. The device produces no obstruction to the flow and is ideally suited to in-line monitoring applications that require very low pressure losses.
TL;DR: In this paper, the authors proposed a revision to IEEE Red Book Chapter III that includes a description of typical intertie relaying practices for industrial plants both with and without in-plant generation.
Abstract: One of the most important considerations in the development of the overall protection scheme in an industrial plant is the special relaying requirements of the industrial plant-utility power system intertie. The proposed revision to IEEE Red Book Chapter III includes a description of typical intertie relaying practices for industrial plants both with and without in-plant generation. The application of this relaying will be reviewed and several problem areas that must be recognized and dealt with for satisfactory system performance will be discussed.
TL;DR: In this article, the authors evaluate the conventional losses in rectifier transformers, as performed according to various national standards, and particularly as performed under International Electrotechnical Commission (IEC) recommendations.
Abstract: Evaluation of conventional losses in rectifier transformers, as performed according to the various national standards, and particularly as performed according to International Electrotechnical Commission (IEC) recommendations, is scarcely satisfactory because it does not take into proper consideration the pulsating nature of the current and neglects some elements that give a fair contribution to total losses. Some test elaboration methods are proposed, as well as a test circuit to evaluate in a more accurate way the losses in transformers, interphase transformers, and saturable reactors. Some examples are given, and the available experimental result is in a good agreement with the calculations.
TL;DR: The Megaverter ® (Megawatt Power Converter) as discussed by the authors utilizes the thyristor for control and rectification to supply 52.5 MW of dc power for electrochemical use.
Abstract: In recent years, the use of thyristors for regulation of bulk power has grown appreciably. The Megaverter ® (Megawatt Power Converter) utilizes the thyristor for control and rectification to supply 52.5 MW of dc power for electrochemical use. The system consists of three Megaverters, each rated at 17.5 MW, connected in parallel. The thyristor assemblies are sized for worst-case short circuit surge, thereby providing maximum protection for critical components and eliminating costly downtime through nuisance tripping. Aluminum extrusion is used for the thyristor cabinet, allowing modular construction, reduction in size, and maximum design flexibility. Aluminum is also used for busbar and the thyristor water-cooled heatsink assemblies. The overall design approach results in simplified maintenance, reduced downtime, and simplicity of control for large thyristor controlled power converters.
TL;DR: In this paper, a guide to the generated line currents from six-pulse converters is presented, including the effects of commutating reactance, phase angle retard, partially inductive loads, and general comments on plant distribution layout, especially electrochemical plants.
Abstract: A guide to the generated line currents from six-pulse converters is presented. Included are the effects of commutating reactance, phase angle retard, partially inductive loads, and general comments on plant distribution layout, especially electrochemical plants. It is intended as a concise general guide to predicting the level of harmonics to be expected in a specific case, and as a guide in minimizing the occurrence of the more complex circuit effects of a total system. Harmonic currents in large thyristor converters, Megaverters ®, are found to be not significantly greater than in diode converters; however, more care must be given to plant layout of multiphase systems in order to benefit from the attempt at harmonic reduction.
TL;DR: A system of vehicular movement warning devices is described in this paper that mighty improve to some extent the safety of grade crossing operations.
Abstract: Railroad operations have for many years been plagued with poor safety performance at grade crossings. Many lives are lost each year in accidents at crossings, to say nothing of costly injuries and property damage sustained. The situation has gotten worse with the advent of soundproofed cars, being driven at high speed in conditions of poor visibility. Clearly then, some improved method of warning motorists as they approach a grade crossing is needed. Analysis of a critical encounter between a road vehicle and a locomotive reveal that the presently used equipment is inadequate to meet the needs of present day high-speed vehicles. A system of vehicular movement warning devices is described in this paper that mighty improve to some extent the safety of grade crossing operations. Two methods are detailed. One involves static directional sonic devices positioned at the crossing; warning activation is made on a real-time closing velocity determination. The other system employs a special variety of cattle guard in the roadway, to issue a tactile warning. Both systems are designed to give adequate warning to a motorist in a critical encounter situation as he approaches the crossing with a convergent locomotive on the track(s). A bonus feature in the use of selectively activated static directional sound warning sources would be the curtailment of urban noise levels, where trains presently use the mobile audible source to issue warnings.
TL;DR: The design and performance characteristics of homopolar and derived tachogenerators are discussed, making them particularly suitable for velocity-control systems using high-performance dc motors as the power actuators.
Abstract: Analog dc tachogenerators are widely used as velocity transducers in industrial control systems. Despite the widespread use of miniature dc generators for this purpose, there are practical alternatives that should be considered for the analog measurement of velocity. The design and performance characteristics of homopolar and derived tachogenerators are discussed. These transducers are unique in their low inertia and noise generation, making them particularly suitable for velocity-control systems using high-performance dc motors as the power actuators.
TL;DR: In this article, a single-phase bridge inverter system is analyzed using a modified Lyapunov theorem on bounded-input bounded-output (BIBO) stability in the stability analysis of the discrete state equations for the system.
Abstract: A single-phase bridge inverter system is analyzed. It is assumed that the inverter output voltage waveform is pulse-width modulated to control the system voltage. The system involves a closed-loop control containing a pulse modulator supplying a general filter. A feedback signal which is a function of the filter output is compared with a reference constant to deliver the error signal which determines the pulsewidth. A modified Lyapunov theorem on bounded-input bounded-output (BIBO) stability is used in the stability analysis of the discrete state equations for the system. Sufficient conditions for BIBO stability are derived. The results are verified by a digital computer simulation of the system. Systems with linear parts that have distinct or repeated eignvalues that are either real or complex may be analyzed using this method.
TL;DR: In this article, an improved current rating system for high-current high-frequency thyristors is described, which incorporates a combination of simultaneously measured highfrequency parameter data with a computer program based on thyristor models.
Abstract: The composition and use of an improved current rating system for high-current high-frequency thyristors is described. Commonly accepted methods for rating thyristors at low-frequency wide-pulsewidth conditions were not adequate for this task. To fill this void, a new system was developed that incorporates a combination of simultaneously measured high-frequency parameter data with a computer program based on thyristor models using device parameters measured at low frequency. A complete description of the high-frequency simultaneous parameter data is given, including the direct measurement of peak junction temperature, turnoff time, which is used as an indirect check on the junction temperature measurement, and dissipated power. A description of the computer models, including those for instantaneous active area, charge modulation, and thermal impedance as a function of area, is also given. These models generally require the input of empirical parameters, the value of which can be measured at low repetition rate. These include the steady state and dynamic forward drop for the charge modulation model, the plasma spreading velocity for the instantaneous active area model, and the steady state dc thermal resistance for the thermal impedance model. A direct comparison between computer predictions and actual performance for a particular device is presented as a check on rating system performance. When the computer correctly predicts device performance for specific cases, it can be used to derive ratings for any arbitrary current waveform.
TL;DR: In this paper, general mathematical relations for the power factor and harmonic contents of the currents and metering voltages of the thyristor controlled inductive loads fed from a source having significant impedance were developed.
Abstract: General mathematical relations are developed for the power factor and harmonic contents of the currents and metering voltages of thyristor controlled inductive loads fed from a source having significant impedance. This impedance has previously been neglected; it could be that of the supply feeder or transformer. The general relations developed cover the special cases described in the literature. Numerical solutions and the results obtained by an analogue computer study agree with those of actual tests. The voltage regulation caused when feeding a thyristor controlled load is slightly less than when feeding an uncontrolled load of the same power and equal power factor. The voltage regulation decreases with decrease of power factor for the same thyristor controlled load.
TL;DR: The importance of selecting the proper transformer winding connections because of its influence on power system operation and relaying is emphasized in this article, where the delta-wye connection is recommended.
Abstract: The importance of selecting the proper transformer winding connections because of its influence on power system operation and relaying is emphasized. The delta-wye connection is recommended.
Journal Article•
TL;DR: In this paper, the advantages and limitations of popular modulation methods are discussed, and an improved modulation scheme is presented to extend the practical speed range of PWM ac drives, which can be used to improve the performance of inverter drives for squirrel cage induction motors.
Abstract: The performance of inverter drives, which use the voltage and frequency, are critically influenced by the choice of the inodulation policy used in the control circuits. This paper deals with practical inverter drives for squirrel cage induction motors and presents some basic considerations on modulation requirements. The advantages and limitations of popular modulation methods are distussed, and an improved modulation scheme, which allows us to extend the practical speed range of PWM ac drives, is presented.