Showing papers on "Induction motor published in 1973"

Transient Load Model of an Induction Motor

Abstract: The power invariant, nonlinear differential equations, that describe the behavior of a two-phase equivalent of a balanced three-phase induction motor, are linearized about an arbitrary nominal point. Under the assumption that terminal voltage and system frequency can be approximated by a straight line segment over any interval of time, solutions of these small perturbation equations are used to give expressions for active and reactive power delivered tb the motor during transient conditions. These newly developed expressions for power, which turn out to be implicit functions of voltage and frequency, and explicit functions of time and the rates of change of voltage and frequency, are proposed as a load model represeptation of an induction motor for use in transient stability studies. An intuitively appealing, corrective technique, which reduces the error introduced by the use of a linearized model, is presented. Eigenvalues of the linearized system of equations for a group of typical induction motors are given. For a small low voltage motor, a sensitivity study of the dominant eigenvalue to changes in nominal point quantities and parameters is made. Values of active and reactive power calculated by a numericzal solution of the motor nonlinear differential equations are compared with those values of power predicted by the model for certain specific rates of change of voltage and frequency.

Quasi-sine-wave fully regenerative invertor

Abstract: The paper shows that, if a cage induction motor is fed with a quasi-square-wave current, the motor terminal voltage is approximately sinusoidal under normal operating conditions. A simple analytical approach, based on the assumption that the motor resistances and inductances do not change with frequency, is shown to describe adequately the motor-terminal voltage. The quasi-square-wave-current supply is derived by modification of a known variable d.c.-link-voltage invertor. These modifications result in numerous advantages. The modified invertor is capable of regeneration back into the mains supply, has only 12 noninvertor-grade thyristors, and is undamaged by short-circuiting of the output terminals or by misfire of the output thyristors. Overall, the invertor lends itself to a simpler electrical and mechanical arrangement.

Power supply for refrigeration units

Abstract: An electronic power supply which derives power from a DC battery to operate the AC induction motor of a refrigeration compressor unit. The amplitude and frequency of the AC voltage developed by the power supply from the DC battery are functions of the battery voltage. When the battery voltage increases, the amplitude and frequency of the AC voltage for driving the motor increase and vice versa to thereby efficiently operate the motor in spite of fluctuation in the level of battery voltage.

Identification of principal factors causing unbalanced magnetic pull in cage induction motors

Abstract: The precise effect of the static eccentricity of the rotor of an induction machine on the magnetic field in the airgap is demonstrated and explained. The relation between the unbalanced pull and the eccentricity of a cage rotor is determined through measurements of the electromagnetic field at the rotor surface, and the significance of the tangential-flux component in the machine airgap is assessed.

Method and apparatus for testing electric motors

Abstract: An electric motor being tested is rigidly mounted in a stationary platform, and is fixedly coupled through a torque and speed transducer to a load electric motor. Initially, the load motor is energized to drive the unergized test motor up to a running speed. Electric power is then switched from the load motor to the test motor. The field winding of the load motor, which now acts as a generator, is coupled to a linear circuit which passes controlled direct current to variably load the electric motor in order to produce linear deceleration followed by linear acceleration over a short testing interval. Transducers generate analog signals which are converted to digital form and are stored in a memory. Subsequently, the stored signals are read over a time period substantially longer than the testing interval.

Analysis of Induction Motor Drives with a Nonsinusoidal Supply Voltage Using Fourier Analysis

Abstract: A method of analysis of induction motor performance with nonsinusoidal supply is presented. It is based on the Fourier analysis of the impressed voltage waveform. Equivalent circuits for the various harmonics are derived, and the resultant harmonic currents are calculated. Experimental verification of the method is obtained by calculating the current waveform from the Fourier components and comparing it with oscillograms. Experimental data obtained from a cycloconverter and different types of inverters are used and show good agreement with calculated results. Evaluation of different schemes of power control and effects of a rapid variation of slip frequency are examined.

A generalized machine theory of the linear induction motor

Abstract: A formulation of the linear induction motor based on the generalized machine theory is derived from the e.m. field theory formulation. The study includes short-stator end effect and a physical interpretation for the performance degradation due to end-effects. Results from the formulation are correlated with published data.

Propulsion and levitation forces in a single-sided linear induction motor for high-speed ground transportation

Abstract: A realistic mathematical model of the single-sided linear induction motor (SLIM) is presented. Using this model, propulsion and levitation forces are computed for a SLIM with back iron. The validity of the analysis is verified by tests on a laboratory model. Some associated problems are outlined, and the feasibility of SLIM's for high-speed ground transportation (HSGT) is discussed. With regard to HSGT, SLIM is compared with the double-sided linear induction motor.

Electrically driven industrial vehicles

Abstract: An electrically driven vehicle employs an induction motor as a drive train motor with a gear matching transmission connecting it with the drive train of the vehicle so the transmission matches its rotational speed to be compatible with the drive train arrangements of a conventionally-driven diesel engine drive train at several different frequencies of its alternating power source, which is supplied through a cable connecting the vehicle to a suitable power source In addition, the induction drive motor may be configured for four- or six-pole operation, whereby switching therebetween will provide a dual operating speed range for the motor at any single frequency of the power source, giving the machine additional flexibility

Generalised theory of induction motors with asymmetrical airgaps and primary windings

Abstract: The paper develops an analysis of induction machines with any number and configuration of stator windings, and a general nonconstant airgap. The analysis involves resolution into harmonic series, together with matrix inversions. It is ideally suited to solution by digital computer. The work is supported by experimental evidence from a variable-gap shaded-pole motor.

Induction motor system with constant horsepower

Abstract: An electric induction motor/control system that provides the desirable high starting torque and wide speed characteristics of direct current motors. The stator of the induction motor has two specially interrelated winding sets per phase. The motor windings are supplied with unidirectional current pulses from silicon controlled rectifiers that are programmed to provide advantageous modes of operation for the motor. The unique relation and interaction between the motor windings hereof and the associated electronic circuitry results in high power factor, good efficiency, and self-clearing SCR commutation action. The preferred motors use a squirrel cage rotor with no commutator, brushes, or slip rings. The complementary stator winding arrangements are not voltage limited, and thereby permit the construction of large power motor systems. Practical motor ratings are from fractional to over 500 horsepower, at speeds ranging from 600 to 40,000 rpm, and higher. The electronic control sections for even the high horsepower motors are operated at low voltage and with few watts. Control circuitry is provided that can operate the motor systems: (a) at constant output torque over a wide speed range; (b) at constant horsepower over a selected speed range; (c) with traction output characteristics similar to that of series motors; (d) at constant speed; (e) and with direct speed reversal in any of these modes. These motor systems require little maintenance, and may be hermetically sealed.

Brushless stator-controlled synchronous-induction machine

Abstract: It is well known that an induction motor will tend to run at half its normal speed when rotor asymmetry exists in two axes electrically at right angles. Several disadvantages are associated with this mode of operation as compared with a conventional machine wound with twice the number of poles. A means is described, however, by which two such machine elements may be mechanically and electrically coupled so as to eliminate the disadvantages of one machine acting alone. The coupled machine elements may be combined in a single frame in which there may, in some circumstances, be one rotor common to separate stators.This new arrangement can be operated asynchronously, with slip-energy control; or may be run synchronously, with power-factor control. No connections to the rotor are needed in either mode of operation. Experimental work and a theoretical treatment are included.

Induction motor system with constant torque

Abstract: An electric induction motor/control system that provides the desirable high starting torque and wide speed characteristics of direct current motors. The stator of the induction motor has two specially interrelated winding sets per phase. The motor windings are supplied with unidirectional current pulses from silicon controlled rectifiers that are programmed to provide advantageous modes of operation for the motor. The unique relation and interaction between the motor windings hereof and the associated electronic circuitry results in high power factor, good efficiency, and self-clearing SCR commutation action. The preferred motors use a squirrel cage rotor with no commutator, brushes, or slip rings. The complementary stator winding arrangements are not voltage limited, and thereby permit the construction of large power motor systems. Practical motor ratings are from fractional to over 500 horsepower, at speeds ranging from 600 to 40,000 rpm, and higher. The electronic control sections for even the high horsepower motors are operated at low voltage and with few watts. Control circuitry is provided that can operate the motor systems: (a) at constant output torque over a wide speed range; (b) at constant horsepower over a selected speed range; (c) with traction output characteristics similar to that of series motors; (d) at constant speed; (e) and with direct speed reversal in any of these modes. These motor systems require little maintenance, and may be hermetically sealed.

End-Effect of High-Speed Linear Induction Motor

Abstract: This paper presents a new theory of the end-effect of a high-speed linear induction motor, an experimental proof of the theory, and several countermeasures to eliminate the end-effect. The theory is developed on the basis of a two-dimensional solution of electrodynamic equations and compared with the experimental results. The experiment has been made by use of a rotary type test facility; the maximum test velocity is 450 km/h. It is found that the theory agrees well with the experiment and that the end-effect exercises a very adverse influence on motor performance. The end-effect is investigated as functions of design parameters by making use of the theory. Some measures to counter the end-effect are proposed and discussed. A parallel-connected linear induction motor is also proposed as a measure to compensate the end-effect, and its performance is studied.

Current collection means for electric motors

Abstract: An electric motor in which the communicating means is controllable and operable individually of the armature of the motor to effect a speed control for the motor. An electric motor the communicating means of which has fixed electric contacts which are an integral multiple of the coils of the motor stator whereby the rate of operation of the commutating means with respect to the rate of operation of the motor is reduced. An electric motor the commutating means of which utilizes a liquid metal to effect an electrical connection between fixed and moving contacts.

Permanent magnet rotor for alternating current generators and motors

Abstract: A rotor for an electrical alternator or motor is described. The rotor has a number of disc shaped, axially magnetized, permanent magnets separated by steel discs, and elongated pole shoes parallel to the rotor axis making up the rotor periphery. The pole shoes are fixed to appropriate steel discs to give pole-shoe polarities which alternate around the rotor periphery. In order to allow starting as a motor, alternate pole shoes are divided near one end and fixed to the same steel discs as transversely adjacent pole shoes to give a solid metal rotor section which gives starting by induction motor action, and forms a toothed wheel which runs at synchronous speed by reluctance motor action.

Variable frequency inverter for ac induction motors with torque, speed and braking control

Abstract: A variable frequency inverter for driving an AC induction motor which varies the frequency and voltage to the motor windings in response to varying torque requirements for the motor so that the applied voltage amplitude and frequency are of optimal value for any motor load and speed requirement. The slip frequency of the motor is caused to vary proportionally to the torque and feedback is provided so that the most efficient operating voltage is applied to the motor. Winding current surge is limited and a controlled negative slip causes motor braking and return of load energy to a DC power source.

Electrical transportation system

Abstract: In a transportation system, a vehicle driven by an induction motor, is guided along a given path. Adjacent to the path is at least a section of electrical conductor which is electrically connected to the induction motor by means of pickup or collector shoes on the vehicle. The speed of the vehicle is controlled by varying the frequency of the electrical power fed to the electrical conductor. This can be accomplished by using a power source whose frequency varies with time or by using several power sources, each having a different frequency; each of such power sources being connected to a different segment of the section; such segments being insulated from each other.

Control apparatus for induction motor

Abstract: A three-phase induction motor has wye-connected primary windings connected to a three-phase electric source through respective thyristors connected in parallel opposition across semiconductor diodes. A transformer includes a primary winding connected across two phases of the source and a secondary winding having both ends connected together to one of the motor windings through thyristors, and a center tap connected to another motor winding. If a voltage representing the actual motor speed is higher than a reference voltage, those thyristors connected to the source are conducting to control AC voltages applied to the motor windings along with the associated diodes. The voltage for the motor speed less than the reference voltage causes the thyristors connected to the secondary transformer winding to be conducted to DC brake the motor. The combination of thyristor and diode may be replaced by a reverse conducting thyristor.

Stabilizing system for an inverter-driven induction motor

Abstract: In a motor control system in which an induction motor is driven by an inverter and the motor tends to resonate, the resonant frequency of the motor and the extent of its damping are adjusted to desirable amounts by a local feedback circuit. An output signal of the local feedback circuit is algebraically added to a speed command voltage for the motor control system. A sum signal thus produced is connected to the input of the inverter to control the motor speed. The sum signal is also employed as one of two input signals to the local feedback circuit, the second input signal being proportional to the speed of the rotor of the motor and obtained from a sensor connected with the rotor shaft. The two input signals to the local feedback circuit are subtracted and their difference signal is processed through a lag circuit and a filter network to produce the output signal of the local feedback circuit. When the inverter and motor are thus stabilized by the local feedback circuit just described, it is much easier to stabilize a larger speed-control feedback loop in which the inverter and motor may be employed.

Analysis of a Cycloconverter-Induction Motor Drive System Allowing for Stator Current Discontinuities

Abstract: A variable speed drive, which includes a prime mover driven alternator, a 36-SCR cycloconverter, and an induction motor, is simulated on a digital computer. The induction motor model is developed to permit a general solution when any number of the stator currents is zero. Using conduction criteria for individual SCRs, a new cycloconverter model is derived which results in an input/output transfer function.

Constant tension line-tensioning mechanism

Abstract: Constant line tension can be maintained in a ship''s mooring or towing line extending from a winch by supplying to a polyphase phase-wound induction motor driving the winch alternating current from an alternating-current source the frequency of which is variable in response to the load on the winch. Such variablefrequency source may be an alternator driven by a phase-wound induction machine powered to operate as a motor. The variablefrequency AC source is connected to the winch motor to drive the winch only in the reeling-in direction, but the tension on the line can retard the motor speed or stall the motor or rotate the winch and motor in the opposite, paying-out direction against the reeling-in driving torque of the motor. The winch motor torque can be adjusted by varying the value of resistance shunted across the rotor winding of the winch motor. The line can be retrieved very quickly by having a squirrel-cage alternating-current motor connected mechanically to the phase-wound induction machine. During constant-line-tension operation, such motor is simply idly rotated with such machine, but for rapid line retrieval the motor can be powered by the same AC supply as powers the phase-wound induction machine and such motor will then drive the phase-wound induction machine positively. The winch-motor torque can be adjusted by varying the value of resistance shunted across the rotor winding of the winch motor. Also, for towing applications the voltage of the variable-frequency source can be altered in response to variations in the length of line paid out or reeled in to control the winch motor in turn in response to sensing the extent of rotation of the winch drum in paying out or reeling in the towing line and correspondingly varying the field excitation of the alternating-current generator supplying current to the winch motor to operate the winch motor for restoring the line to its original length.

Resistance device for use in energizing the starting winding of a split phase induction motor

Abstract: A resistance device for a split phase induction motor having a main field winding and a starting field winding, said device having a high temperature coefficient resistor adapted to be connected in series with the starting field winding. The device is in the form of a unitary structure and is provided with a set of terminals whereby it may be removably connected to an electrical connector provided on the motor.

Method and apparatus for automatic IR compensation

Abstract: In induction motors operating at low speeds and at low counter volt levels the terminal voltage component securing the desired machine flux is obscured by the IR drop component. Control of the current and flux density can be objectively accomplished by impressing the correct terminal voltage on the motor. This is accomplished by comparing the desired motor current with the desired motor slip frequency and varying the motor voltage in response to the ratio thereof. The flux signal generated by the summation of the desired values is multiplied by the stator frequency to obtain motor voltage and thereby maintain constant loop gain. An integrator may be used to maintain a zero steady state error.

A comparative analysis of two commutation circuits for adjustable current input inverters feeding induction motors

Abstract: A hybrid mathematical/graphical technique for quick determination of instantaneous voltages on components in two types of adjustable current input (ACI) inverters feeding a standard induction motor is presented with practical examples. A comparison between the synthesized voltage waveforms of the two inverter types, auxiliary thyristor and autocommutated, reveals better overall performance for the auto-commutated inverter.

Electric drive transmission systems

Abstract: A battery driven car is provided with a transmission system which includes an induction motor fed by way of an inverter from the battery and which drives the wheels through a gear box and a clutch. The gear box enables the induction motor to maintain a sufficient speed to cool itself even when the car is driving at slow speed up a steep hill. The gear box and clutch may be conventional manually operated mechanisms and there is provision for the inverter to be used to charge the battery.

Electric motor controlling system

Abstract: An electric motor controlling system comprising an induction motor system consisting of at least one induction motor having motoring torque generating means and braking torque generating means, antiparallel connection of thyristors connected between an Ac source and the motoring torque generating means, means for controlling the thyristors such that the motoring torque generating means generates, when the speed deviation is positive, a motoring torque corresponding to the value of the speed deviation, a controllable rectifying circuit connected between the AC source and the braking torque generating means, means for controlling the controllable rectifying circuit such that the breaking torque generating means generates, when the speed deviation is negative, a braking torque corresponding to the value of the speed deviation, and means for giving the torques of the motor system a push-pull characteristic depending upon the speed deviation by biassing the two control means.

Accelerator for car transmission system

Abstract: A battery driven car provided with an inverter supplying an induction motor which drives the wheels, has the speed of the motor and its torque controlled by the frequency and power output of the inverter. This is controlled by an analogue voltage obtained from an accelerator pedal assembly and by a second analogue voltage obtained from a tachometer driven by the motor. The accelerator pedal has a rest position corresponding to idling of the induction motor and two ranges of movement. Movement of the accelerator pedal through the first range of movement causes a slip speed signal from the accelerator pedal assembly to diminish progressively in a range corresponding to the generation of a negative torque by the induction motor, and during the second range the slip speed signal increases progressively corresponding to a positive torque being produced by the induction motor.

Principles of operation of linear induction devices

Abstract: An approach to the analysis of linear motors, based on the Fitzgerald superpotential is outlined. The usefulness of the approach is demonstrated in calculations of the fields, the streamline pattern, and the performance characteristics of some versions of the linear motor. Analysis of the streamline pattern brings out, in turn, the influence of the end effects.

Circuit for a rotary anode x-ray tube

Abstract: A circuit is used for actuating the driving motor of a rotary anode of an X-ray tube. The driving motor is an a.c. asynchronous motor fed from a converter. The converter is provided with actuating means which increase the frequency of the feeding voltage during the starting of the rotary anode from an initial value to an end value so as to provide the shortest possible starting time. The device of the present invention is a component part of an X-ray apparatus feeding an X-ray tube.