Showing papers on "Three-phase published in 1985"

Energy saving system for larger three phase induction motors

Abstract: An energy-saving system for feeding an electric induction motor serving as a load, and which is operated from a 3-phase voltage power line, and in conjunction with feeding conductors for the motor includes a power-delivery sub-system operating in a magnetically linear region and coupled to the 3-phase voltage power line for providing variable feeding voltages to the induction motor, a sensing device coupled to the induction motor for generating a signal indicative of the derivatives of active power consumed by the induction motor with respect to the voltage of at least one phase provided to the induction motor, and a control apparatus coupled to the sensing device and to the power-delivery sub-system for regulating at least one of the feeding voltages, so that the derivative of the active power with respect to the voltage of that at least one phase is always substantially zero; thus for a given mechanical power output the power consumption of the induction motor is optimized, while concurrently losses in the feeding conductors are being minimized.

Brushless three-phase D.C. motor

Abstract: Collectorless (brushless) three-phase DC motor having a permanent-magnet arrangement and a three-phase winding, these being movable relative to each other, and having three position sensors which are stationary relative to the winding and controlled by the permanent-magnet arrangement to supply sensor output signals. The winding's coils are energized by current in a cyclical sequence in dependence upon the sensor output signals, the latter being offset by 120°-el. one from the next. Induced coil voltages are offset by 120°-el.; the coil voltages, in crossing zero, are alternately positive for at most 180°-el. and negative for at most 180°-el. and their sum is equal to zero for all relative positions as between the magnet arrangement and the winding. The position sensors are so arranged relative to the winding's coils that the sensors' changes-of-state substantially coincide with the zero-crossovers of the associated induced coil voltages. The winding's coils are energized via winding driver stages by means of driver voltages which either directly correspond to the sensor output signals or else are derived therefrom.

A Sinusoidal Pulsewidth Modulated Three-Phase AC to DC Converter-Fed DC Motor Drive

Abstract: The external performances such as power factor, displacement factor, harmonic factor, and ripple factor of a three-phase ac to dc converter-fed separately excited dc motor drive employing sinusoidal pulsewidth modulation (SPWM) control technique are obtained for different speeds and modulation indexes. Since separately excited dc motors with armature voltage control provide constant torque operation, the external performance is also determined for the drive motor operating at different values of constant load torque. Motoring and regenerating operations of the dc drive machine are considered. The three-phase PWM converter-motor drive system is analyzed, taking commutation effects into account in motoring and regenerating operations. The analysis has revealed 27 common modes in one repetitive period of the output voltage. The sequence of modes for all pulses in one period of the output voltage is established. Experimental oscillograms of typical waveforms from a laboratory-sized dc motor are illustrated to verify the basic principles of operation. Although the converter circuit requires some additional components in comparison with the commonly used phase-controlled converter, the improved performance characteristics make it attractive for industrial applications involving large power ratings.

Analysis and Performance of Three-Phase Phase-Controlled Thyristor AC Voltage Controllers

Abstract: A simple generalized approach, based on numerical evaluation of the Fourier coefficients, is presented to evaluate the comprehensive performance of three-phase phase-controlled thyristor ac voltage controllers. Three-phase balanced resistive and inductive loads of different power factors are considered. The method of solution adopted is simple, accurate, fast, and does not require the derivation of Fourier coefficient equations. Various electrical properties are compared graphically for the different circuit configurations. The branch-controlled deltaconnected load is considered to have the best performance, giving the highest power factor per unit of power delivered.

Prediction of Power System Harmonics Due to Gaseous Discharge Lighting

Abstract: A harmonic power flow algorithm which predicts the levels of low audio range frequency harmonics in a power system produced by several types of nonlinear loads has been recently developed [1-5]. Specifically, the new method solves for the truncated Fourier series of bus voltages and line currents in a balanced three phase network with line commutated converters and nonlinear resistive loads. Most harmonic signal analysis techniques previously developed assume sinusoidal network voltages or known current injection levels. In many cases, especially in resonant or other conditions of relatively high harmonic voltages, considerable inaccuracy results. The new algorithm uses a Newton-Raphson solution technique and does not require these assumptions. Modeling emphasis is restricted to harmonic orders in the low audio range (fundamental to the 25-50th multiple). Interaction between voltage and current harmonics of different order in a nonlinear device is permitted. The power system is considered to be balanced i.e. the nonlinearities are assumed to be equally distributed among the three phases. Gaseous discharge lighting (such as fluorescent, mercury arc, high pressure sodium) is a significant source of power system harmonics, particularly in metropolitan areas. The electrical characteristics of this type of lamp are quite nonlinear. Lamp ignition occurs during each half cycle when the applied ac voltage reaches some required firing potential. During conduction, the lamp exhibits a negative resistive characteristic, and a nonlinear ballast circuit is placed in series with the lamp to limit the current.

Power supply system

Abstract: A power supply system is disclosed in which each of the phases of a three phase AC source are rectified and inverted During inversion high frequency signals are obtained corresponding to the phases of the AC source which are synchronized so that their zero cross points occur at the same time The high frequency signals are superposed in series to produce an output signal for a load which has a constant power and diminished current distortion

Static phase conversion circuits for three-phase motors

Abstract: A three-phase AC motor having three stator windings with stator winding power input terminals T1, T2 and T3, is energized from a single-phase AC line through a static phase conversion circuit that connects terminals T1 and T2 directly to the single phase line and that includes a main dephasing capacitor connected between terminals T1 and T2; a phase correction capacitor is connected in parallel with a stator winding that is not connected to terminal T3 for materially improved full load performance

Apparatus for converting single-phase power to three-phase outputs

Abstract: An inverter apparatus for converting a single-phase A.C. power source to three-phase A.C. outputs is described wherein the single-phase power source is directly connected to a first phase load and is connected through a one-phase converter to a second phase load, and the single-phase power source and the one-phase converted single-phase power source are connected to a third phase load and a fourth phase load, the third and fourth phase loads being formed by dividing a single load, so that three-phase power outputs are provided for the first phase load, the second phase load, and the third plus fourth loads.

Single phase to three phase signal converter

Abstract: An apparatus for converting a single phase electrical signal into a three phase electrical signal is disclosed. A converter includes a rectifier connectable to a single phase electrical power source. One output of the rectifier is connected through a smoothing ciruit to four switching transistors. The other output of the rectifier is connected to center taps of a first and a second load coil. The first phase load coil is connected across a first pair of the switching transistors and the second phase load coil is connected across a second pair of the switching transistors. Third and fourth phase load coils are connected to opposite sides of the first and second phase load coils. The first, second, and third phase load coils are delta connected and the first, second, and fourth phase load coils are delta connected. The first and second pairs of switching transistors are controlled by first and second pairs of phase shifting signals. Each of the first and second pairs of phase shifting signals includes positive and negative pulses which provide three phase conversion across the first, second, and third plus fourth phase load coils.

Method and apparatus for the protection of a thyristor power conversion system

Abstract: Each of the three phase power source voltages coupled to a three phase (3.0.) thyristor power converter are respectively half-wave rectified to provide both positive and negative voltages. Signals representing the largest positive rectified voltage and the smallest positive rectified voltage are developed as are signals representing the largest negative rectified voltage and the smallest negative rectified voltage. Using signals from both the positive and negative rectified voltages, at least one comparison is made to determine a difference which, when in excess of a predetermined limit, effects a logic signal to provide an indication that an asymmetrical fault exists either phase to neutral or phase to phase across the power converter and the power lines connecting the converter to a polyphase alternating current (AC) source. Following a suitable delay, protective action is initiated, which action comprises either phasing back of gating to the converter thyristors and/or tripping of a circuit breaker or contactor which operates to interrupt the supply of AC power to the converter.

Noise filter for three-phase four-wire system

Abstract: A noise filter for an electric wire of star-connected three-phase four-wire system, in which a neutral conductor has a sectional area which is larger than a sectional area of each of voltage conductors. Three voltage conductors are wound on a magnetic core that constitutes a closed magnetic path. The neutral conductor is coupled to the three voltage conductors via three respective capacitors.

Root mean square measuring device for negative sequence current

Abstract: To protect electrical three-phase machines from damage on the appearance of an unbalanced load between the phases, so-called negative sequence current protection is used. Conventional measurement of the negative sequence current takes place in filters which contain frequency dependent LC components. Frequency variations in a three-phase supply, because of an unbalanced frequency response for harmonics in the three phase filters, may lead to an erroneous indication of negative sequence current. The invention provides a novel method for determining both the positive sequence and the negative sequence currents to a three-phase load. For grounded systems the zero-sequence current is eliminated. Measuring each phase current (I R , I S , I T ) and the phase sequence, the positive sequence and/or negative sequence current are/is determined as the solution of an equation derived in advance from the electrical relationships between the phase currents. The invention also relates to a device for carrying out the method.

Electrical short-cicruit monitoring arrangement for variable-speed, three-phase motors, including their feed lines

Abstract: An electrical short-circuit monitoring arrangement for a three-phase motor, including its supply lines, whose speed is controlled by a constant-current d.c.-link converter. The harmonic ripple voltage superimposed on the motor voltage generated as a consequence of the commutation by the constant-current d.c.-link converter at the output of the converter is determined, filtered, and supplied to a phase-monitoring unit, which when dropping below a selected amplitude variable of the harmonic voltage of at least one phase, triggers the switching module whose switching mechanism activates a disconnect switch to interrupt the motor circuit upon occurrence of a switchoff signal.

Method and circuit arrangement for reducing the torque ripple of a converter motor in the low speed range

Abstract: In the case of reducing the torque ripple of a converter motor (3) having two DC-isolated three-phase stator winding systems (U1, V1, W1; U2, V2, W2) which are offset by 30 DEG with respect to one another and are supplied from two converters, which each consist of a mains converter (NSR 1, NSR 2), and intermediate-circuit inductor (Ld1, Ld2) and a machine converter (MSR 1, MSR 2), with intermediate-circuit currents (Id1, Id2) whose amplitude can be influenced separately by driving the valves of the mains converter (NSR 1, NSR 2), it is intended, in the low speed range, both to suppress oscillating forks and to overcome discontinuities during the further switching of the electric loading (ratio of the total current per slot divided by the tooth pitch) of the converter motor (3). For this purpose, the valves (11... 16; 21... 26) of the mains converters (NSR 1, NSR 2) are driven in such a manner that two intermediate-circuit currents (Id1, Id2) flow, offset through 90 DEG with respect to one another, as sinusoidal half cycles which continuously follow one another in time. The valves (1A, 1F, 1C, 1D; 2A, 2B, 2D, 2E) of the machine converters (MSR 1, MSR 2) are driven in such a manner that each of the two intermediate-circuit currents (Id1, Id2) are switched on alternately in the positive and negative direction per sinusoidal half cycle via exclusively two (u1, v1 and u2, w2 respectively) of the three phase connections through windings of the two stator winding systems (U1, V1, W1; U2, V2, W2) whose electrical effect is mutually orthogonal.

Analysis of a Three-Phase Delta-Connected Inductive Load Controlled by an SCR-Diode Switch

Abstract: A detailed analysis is presented of a system consisting of a three-phase delta-connected inductive static load controlled by a thyrode (SCR and diode) controller. The current equations are developed for a three-phase delta-connected inductive circuit representing the steady-state model of an induction motor. The simulated and actual current and voltage waveforms of an induction motor controlled by such an SCR-Diode controller are illustrated. The frequency/power spectra of the phase and line current are also presented.

Method and apparatus for generating a control power delivered to a load by a polyphase power line

Abstract: A microprocessor determines the zero cross-over times and direction of the phase voltages of the AC power line; a multiplexer has three parallel inputs which are respectively connected to the three phase conductors of the line and an output delivering a voltage formed by successive portions of the phase voltages; a flip-flop sensitive to the change of sign is connected to the output of the multiplexer; and EXCLUSIVE OR gate has an input connected to the output of the flip-flop and an other input to an output of the processor; and a NAND gate has an input connected to the output of the EXCLUSIVE OR gate and another input which receives a signal formed of a succession of square waves forming enabling windows.

Three-phase leakage protection by electronic control

Abstract: A system is provided for early detection of leakage currents through ground connections of loads such as three-phase motors connected to isolated secondary windings of supply transformers An alarm device is energizable when leakage current is a small fraction of a predetermined value which might present a potential hazard, the point of energization being adjustable by an operator until the predetermined value is reached Thereafter, it is adjustable only by a supervisor, after operation of a key switch Circuitry is provided to obtain sensitive, stable and reliable operation

DC current sensors of instantaneous response using amorphous cores

Abstract: A new current sensor made of three transistor core multivibrators of high frequency is presented. Three multivibrators are synchronized with external pulses so that rectangular three phase voltages may be obtained. The core flux in each multivibrator changes along the minor hysteresis loop. We have no ripple dc output voltage from the outputs of the three multivibrators in the same way as that of a mixing amplifier. The amorphous cores with excellent rectangularity are effectively used for this purpose.

Subharmonic oscillations in three-phase circuits

Abstract: This paper analyzes the subharmonic oscillations generated in three-phase circuits by the asymptotic method. As the result of the analysis, we find that there are three kinds of the 1 3 -harmonic oscillations, 1 3 -harmonic oscillation with beats, 1 3 -harmonic oscillation without beats and 1 3 -harmonic oscillation occurring in a single phase of the three-phase circuit. By means of an experimental circuit we confirm these oscillations.

Phase decision apparatus

Abstract: PURPOSE:To enable accurate decision on the phase whether it is single or three phase by judging the phase based on a line voltage signal and a phase current signal. CONSTITUTION:Line voltages P12 and P32 are converted into line voltage signals V12 and V32 of a square waveform with comparators 1 and 2 and fed to single/three phase discriminator section 10, which sends a discrimination signal G of H level to a switching section 20b when judging it as single phase while that of L level, as three phase. When single phase is found, the switching section 20b sends a signal V12 to an input terminal D of an FF30 while when three phase is found, it sends a line voltage signal Vs delayed in the phase by 90 deg. with a delay section 20a to a terminal D of the FF30. Depending on the lag or advance of the phase between the voltages V12 and Vs and the phase current signal I obtained by the conversion of a phase current I1, an H-level signal is outputted from an input terminal Q of the FF30 when the phase is in lag while an L-level signal is outputted when it is in advance. Thus, whether the power source is single or three phase, it can be automatically judged by lag or advance in the phase. As the phase current I1 is amplified to a specified level with an amplifying section 40, the magnitude of the phase current I1 will not affect the decision on the phase however it may be limited.

Power System Measurements Using Microprocessors

Abstract: Developments in power system measurements starting from the conventional analogue, through digital to microprocessor based measurements are reviewed. Then is presented a microprocessor- based power system monitor (μPSM) that scans the three phase voltages and currents and computes therefrom RMS voltages and currents, average active, reactive and complex power, as well as power factor and maximum demand. Our μPSM is thus meant to replace the conventional analogue meters and recorders on control panels used in generating, receiving and sub stations, load despatch centres, control rooms of bulk power consumers, etc. μPSM can also find application in power system data loggers, alarms and annunciators, power system relaying, load frequency control, etc, as the basic data acquisition unit.

Electrical electrode three-phase heating system having stepped regulation of the power

Abstract: The invention relates to an electrode three-phase heating system having stepped regulation of the power, which system ensures balanced loading of the electrical three-phase supply system for every power step. The system consists of seven electrodes (1, 2, 3, 6, 7) which are arranged in the form of a hexagon having a central electrode (7) on the axis of the cylindrical vessel (8), which vessel (8) is filled with the electrically conductive fluid (17) which is to be heated. There are various versions of the circuit for varying the power of the power [sic] according to the invention. There are likewise various versions of the design of the vessel (8) and of the support for the entire system. The system according to the invention is particularly suitable for the direct electrical heating of the hot water for hot-water storage heating, and the preparation of the hot water used for chemical purposes etc.

Three-phase A-C speed control for variable torque motor

Abstract: A three-phase A-C speed controller for small integral and fractional horsepower motors includes a phase locked loop comprised principally of a phase comparator and voltage controlled oscillator to generate phase delayed trigger signals for energizing the windings of a three-phase A-C motor. A pair of shift registers are cascaded with a flip-flop to generate the 60° phase delay between phases as is necessary in a three-phase system.

Voltage detecting device for three-phase alternating current

Abstract: PURPOSE:To detect the effective value of a three-phase alternating current without any lag by reading instantaneous values of voltages of respective phases at the same time, summing up the square of the resulted values, and calculating the square root of the sum. CONSTITUTION:Instantaneous voltage read-in circuits 9, 10, and 11 read the instantaneous values of voltages of the 1st phase (a), the 2nd phase (b), and the 3rd phase (c) of a three-phase AC system L3phi to be detected. A timing control circuit 12 controls the circuits so that the values are read in simultaneously or almost simultaneously at specific intervals. Squaring circuits 13, 14, and 15 square the values of said read-in circuits 9, 10, and 11 individually. The sum of the square outputs is calculated by an adding circuit 16. A square-root circuit 17 calculates the square root of the output of the adding circuit 16. Consequently, the output of the square root circuit 17 has neither pulsation nor time lag.

Optimization of induction motor efficiency. Volume 1. Three-phase induction motors

Abstract: This report describes an optimization technique where variables, variable constants and constants are used, instead of variables and constants as is done in an ordinary optimization problem. This novel classification of the parameters leads to a better accuracy of the optimal results as compared with a classification in variables and constants only. At the outset of the study, the motor performance equations describing the power factor, the locked-rotor current ratio, the starting to rated torque ratio, the maximum to rated torque ratio, the efficiency, the slip and the temperature rise are derived from geometric quantities and the properties of the active materials. Subsequently the motor cost equations (e.g. production cost, capitalized cost and annual cost) are discussed. The sequential decomposition of the optimization method is based on closed-form equations of the above-mentioned motor performance and cost equations, which may represent the constraints as well as the objective function. The incorporation of the design program, updating the variable constants in the optimization procedure, is described next. As an example, a 100 hp induction motor is used to study the effect of different electrical steels, power factor, locked-rotor current and the production cost on the maximum efficiency, which serves as the objectivemore » function. The report also compares the increased efficiencies of motors obtained by the addition of materials with those of the optimally designed motors.« less

Calculation of currents for internal short-circuits in a stator of a three-phase slip-ring induction machine

Abstract: A new method of calculation of steady currents of a three-phase slip-ring induction machine with internal short-circuits in a stator is presented in the paper. The given method takes interaction of space harmonics both in the stator and in the rotor into consideration. Problems of interaction of the zero-sequence system and the substitutional two-phase system are also discussed. Examples of currents calculations for internal short-circuits in the stator are given.

Method and apparatus for switching three-phase loads with an ohmic-inductive character, in particular asynchronous machines and transformers to the mains.

Abstract: The invention relates to the control of the switching process of three phase loads with ohmic-inductiv caracter, particularly asynchronous machines wherein the phase of the mains voltages is observed and for switching the phases controllable switching elements are used. According to the invented method one phase voltage is selected, and following a switch-on order in a vicinity of a zero-crossing of it a line voltage represented by the difference of the other two phase voltages is connected, and observing the connected line voltage in the vicinity of a very-next zero-crossing of it the selected and remaining phase voltage is switched on. An apparatus for realizing the process comprises controllable switching elements (2) inserted in at least two phase-lines (A,B) and provided with a triggering unit (3), a comparator unit (5) and a mains voltage converter (4) for detection of zero-crossings. The comparator unit (5) is connected to the three-phase mains via the mains voltage converter (4) and a logic unit (6) for controlling the proper time sequence of the switching process is provided. The logic unit (6) is connected to inputs (5a, 5b) of the comparator unit (5), and its outputs (6a, 6b) are connected to the triggering units (3) controlling the switching elements (2). The logic unit (6) has further inputs for switching in and out the load.

Correction of Phase Voltage Measurements Referenced to an Ungrounded Neutral

Abstract: Recording voltmeters are often used to provide a permanent record of three phase bus voltages. If the meters are improperly installed, using an ungrounded neutral, the recorded phase to neutral voltages can indicate severely unbalanced conditions, even for a balanced system. The purpose of this paper is to present a Newton-Raphson based iterative solution technique which can be used to reconstruct balanced three phase voltage phasors from unbalanced recorded values which were mistakenly referenced to an ungrounded neutral.