Showing papers on "Three-phase published in 1984"

Sinusoidal line current rectification with a 100kHZ B-SIT step-up converter

Abstract: A step-up converter circuit for the sinusoidal line current rectification at a unity power factor is described. A Bipolar-Static-Induction-Transitor (B-SIT) with extremely fast switching times is utilized. The gate drive and the snubber circuits are presented. A new way to achieve current hysteresis control without noise problems for switching frequencies up to 100 kHz is developed. Measured overall efficiency and the transistor losses are presented. At 1 kw dc output, the total transistor switching and conduction losses are 9 watts at about 100 kHz switching frequency. The overall rectification efficiency is in a 97–98.5% range. Justification for the use of step-up converters is given. Component selection and the stability in the feedback loop is analyzed. The converter is especially advantageous for single phase in — three phase out, variable frequency ac motor drives in lower horsepower applications.

Measurements and Computations of Fault Current Distribution on Overhead Transmission Lines

Abstract: Improved analytical methods for assessing the effects of a ground fault on a transmission line are discussed. Both simplified and more complex calculation techniques are shown and compared with staged fault tests. The simplified approach provides approximate results for the calculation of the fault current in the structure as a fraction of the total single phase to ground fault current. The complex calculation provides results for single, double, and three phase to ground faults at any structure with variable structure resistance along the transmission line. The simple formula lends to calculator use whereas the complex calculation is geared for a computer.

Three Phase Transmisssion System Modelling for Harmonic Penetration Studies

Abstract: Three phase modelling of an a.c. transmission system is presented for harmonic penetration studies. Circuit coupling and impedance unbalance are incorporated in a simulation programme which models an 86 bus equivalent of the New Zealand South Island system. A comparison of measured and simulated results at the current injection busbar is used to select system component models; then results of impedances and sequence voltages are presented for selected busbars when the system is subjected to current unbalance and circuit configuration changes.

A Novel Method of Multistage Dynamic Braking of Three-Phase Induction Motors

Abstract: An effective braking system suitable for three-phase induction motor drives is discussed. Braking is achieved in four stages using an electronic switching circuit. Initially, a single capacitor is connected across two of the motor terminals allowing single-phase self-excitation. Following a certain speed drop, a second capacitor is added across the same terminals to sustain self-excitation and reduce the speed further. In the third stage magnetic braking is achieved by short circuiting the third terminal. Finally, the motor is brought to a standstill by dc injection. A method of determining minimum capacitor requirements is presented for both single-phase and symmetrical application. Experimental results are included, demonstrating the validity of theoretical results regarding capacitor requirements, and indicating the effectiveness of the proposed braking scheme.

Three-phase ac to dc power converter with power factor correction

Abstract: A system for converting three-phase AC to DC voltage employs three separate converter circuits having their outputs connected in parallel to reduce current harmonics. Each converter circuit includes a full wave rectifier feeding a pulse width current modulator which modulates the DC current flow to the load in a manner to maintain the magnitude of the DC current proportional to the instantaneous magnitude of the DC voltage. The current modulators act as substantially resistive loads to reduce source current harmonics and correct the power factor. The modulators include a pair of transistors connected in a push-pull circuit which are controlled by an oscillator circuit to modulate the DC current at a frequency which is many orders of magnitude greater than the line frequency of the AC source. The DC current outputs of the modulators are coupled through DC/DC isolation transformers to the load.

Semi-conductor motor control system

Abstract: A semi-conductor system for controlling three phase motors by voltage and/or frequency variations. An input circuit provides dc power, such as a three phase full wave input bridge with silicon control rectifiers to provide a voltage controlled dc power output. An output inverter bridge having six silicon rectifiers receives dc power and converts it to three phase ac power for operating an induction motor. A diverter network is connected between the dc power input circuit and the output inverter and is activated periodically for temporarily diverting the dc power from the inverter in order that the inverter rectifiers may be turned off. The diverter may include a tank circuit having a capacitor and an inductor connected across the dc power output through a diode and a silicon control rectifier is connected to the tank circuit for shunting the dc power from the inverter and applying a reverse voltage to the inverter. A harmonic suppression circuit is connected across the output of the converter and may include a capacitor connected between each of the three phase output lines of the inverter.

Reduced ripple drive circuit for a brushless motor

Abstract: A drive circuit for a three-phase brushless motor in which two Hall detectors are spaced 120° apart in electrical angle near the rotors to detect magnetic flux signals for two phases. Their outputs are summed and inverted to form the third phase signal. The three phase signals drive the respective coils on the stator. The three phase signals are also separately squared and then added to adjust, in a feedback fashion, the current through the Hall detectors, whereby torque ripple is reduced.

Method and system for interconnecting two synchronous or asynchronous electrical alternating three-phase networks by means of variable reactive impedances

Abstract: A method and a system for interconnecting two electrical, alternating three phase networks operating asynchronously or synchronously at voltages of equal or adjacent frequencies, and in which, for corresponding phases, the voltages of the first and second networks are out of phase by a constant or varying angle. A plurality of three phase variable reactive impedances interconnect the two networks for carrying out a desired transfer of active power from one of the two networks to the other. The variable impedances are operated to establish between each phase of the first network and the three phases of the second network, three interconnections each having a different susceptance, which susceptances vary with the three phase variable reactive impedances. A regulator measures electrical parameters associated with at least one corresponding phase of the first and second networks, and operates the three phase variable reactive impedances to vary the susceptances of the interconnections in relation with the measured parameters so as to establish the desired transfer of active power from one of the first and second networks to the other network, while maintaining at a desired level a reactive power engaged in the transfer of active power.

Apparatus for detecting arcing faults on low-voltage spot networks

Abstract: A protective relay for detecting power arcing faults on a three-phase electrical power spot network. A phase-to-phase power arc on a spot network produces harmonics on the phase-to-phase voltages, and the phase currents; a phase-to-ground arc produces harmonics on the phase-to-neutral voltages. The protective relay of the present invention monitors one or more of the three phase-to-phase voltages, the three phase-to-neutral voltages, or the three phase currents and indicates a fault based on the harmonic content of those signals.

Magnetizing Current, Iron Losses And Forces Of Three-Phase Induction Machines At Sinusoidal And Nonsinusoidal Terminal Voltages. Part I: Analysis

Abstract: Currents, losses, winding and iron core forces at no-load of saturated three-phase induction machines are determined based on a nonlinear magnetic field analysis. Instantaneous magnetizing currents are calculated for given balanced sinusoidal and nonsinusoidald- terminal voltages. Subsequently, the harmonic components of the magnetizing current and the induced voltage are obtained from a Fourier analysis. The coreloss- current component is derived from the sum of local core losses and the no-load current is then iteratively obtained from the sum of the magnetizing and the coreloss- current components. Finally, the calculation of winding and iron-core forces is derived from surface integrals. Part II deals with the results that are based on this analysis.

An Improved Three-Phase Multistepped-Voltage Inverter Combined with a Single-Phase Inverter Through Switching Devices

Abstract: A new multistepped-voltage waveform inverter with a total harmonic distortion (THD) of 6.25 percent is described. The proposed system consists of a three-phase inverter whose conduction intervgl is smaller than 180 °, a triple-frequency single-phase inverter, and power semiconductor switches that link the two inverters. The advantages of the proposed system over conventional stepped-voltage inverters are that it requires only a small number of switching devices, no three-phase output transformers, and an output filter of reduced size. The relation between THD and the number of steps of an output voltage waveform is discussed. Comparison with other stepped voltage inverters and experimental results using power transistors are also presented.

Electric power source device for dc arc welding

Abstract: PURPOSE:To prevent breakdown of switching elements on the primary side of an output transformer in a power source device for an inverter type DC arc welding device by detecting the DC component of the primary current of the transformer and decreasing the DC component. CONSTITUTION:A primary current signal V1 is inputted to a magnetic deviation detector 12 by a current detector 111 provided in the primary circuit of an output transformer 6 in a power source device for DC arc welding consisting of a three phase AC terminal 1, the 1st rectifier circuit 2, a smoothing capacitor 3, switching elements 4a-4d, the transformer 6, a secondary rectifier circuit 7 and a reactor 8. The AC component is cut and a DC component V3 is taken from the detector 12 and is inputted together with the output V4 of a basic voltage generating circuit 13 to a correcting circuit 14, which outputs V5, V6. The values of V5, V6 change according to whether the output V3 from the circuit 12 is positive or negative and these values are modulated to V7, V8 by pulse width modulators 15a, 15b. Said values are inputted to a base circuit 10, by the outputs from which the elements 4a-4d are controlled and the failure thereof is prevented.

Core form transformer for selective cancellation of subsynchronous resonance

Abstract: 51,191 ABSTRACT OF THE DISCLOSURE A three phase core form transformer for use in a three phase dual dynamic stabilizer system that provides reactive power compensation. The transformer has a three legged magnetic core, a plurality of primary windings corresponding to the phases, two auxiliary secondary windings per phase that are wound to provide first and second common bifilar portions, and a plurality of prin-cipal secondary windings corresponding to the number of primary windings. The first common bifilar portion, the principal secondary winding, the second common bifilar portion and the primary winding are placed coaxially and radially adjacent, in the recited order, starting from each leg of the magnetic core. The primary windings are connected in delta.The principal secondary windings and auxiliary secondary windings are connected in a forked wye wherein one auxili-ary secondary winding of each of the other two phases is electrically connected to the free end of each of the wye connected principal secondary windings. This results in all three phases being present in each combination of principal secondary windings and auxiliary secondary windings. With this arrangement of windings the leakage reactance of the principal secondary winding and the common leakage reactance of the auxiliary secondary wind-ings attached thereto for each phase are positive in value with the leakage reactance of the principal secondary winding being made to be about twice that of the common leakage reactance of the auxiliary windings. 51,191 The primary windings can be continuous wound windings with the principal secondary windings and the auxiliary secondary windings being helitran wound windings.

Method and apparatus for the conversion of a polyphase voltage system

Abstract: A three phase voltage system, balanced and sinusoidal, is converted into another one, having the same properties, but with amplitude, frequency and phase changed, by means of sequential sampling of all input phases The desired output system is synthetized through a matrix of electronic switches, which are operated sequentially by control pulses having a duration proportional to the instant value of a linear combination of sinusoidal waveforms and with a duty cycle modulated accordingly to the required output parameters

Method for the phase-gating control of the voltage half-cycles of a three-phase AC power controller having two current paths, which can be controlled in reverse-parallel, per phase, for a squirrel-cage motor

Abstract: In order to operate squirrel-cage motors with a closed stator circuit with graduated operating speeds, z > 1 triggerings are carried out successively for half-cycles of the one polarity and half-cycles of the other polarity in the individual phases with phase shifts which are as close as possible to 120 DEG electrical so that f = fN/(2z-1) is produced as the operating frequency, where fN = mains frequency.

Space-phasors for dynamic minimum-time computing and digital real-time three-phase display

Abstract: Dynamic-state calculations of power systems are generally performed with original RST-components The number of the nodes and branches can be reduced in the case of cyclic symmetry of the equipment by application of modal components Most adventageous are Space-Phasor components, because they need the least number of nodes and branches and are time-independent constant in stationary-state Differential equations can be described shortly by operators For integration a special method with factorized Eigenvalues is developed, which is necessary for the back-transformation As a result of the exact synchronization reached hereby, all admittances become real; only the source-currents in the nodes are complex outside of the homopolar components In places, where unsymmetrical faults occur or equipment with nonlinear characteristic is installed, the Space-Phasor components are coupled A digital real-time interface for transformation of original RST-quantities to Space-Phasor components was developed, which enables to measure the momentary frequency of the rotating field as well An attached calculator performes the high sensitive measurement of the desired symmetrical and harmonic component, eg the negative-sequence voltage component on fundamental frequency or any desired harmonic as term of the positiv-, negativ- und zero-sequence component

Energy efficient multi-phase dual voltage electric motor

Abstract: A circuit which enables a three phase, Y connected motor to be operated on either one phase or three phase power at either 230 or 460 AC line voltage. A modified circuit includes power factor correction capacitor banks for increasing the power factor and efficiency of the motor whether connected for one phase or three phase operation at either line voltage.

State Equation Modeling of Untransposed Three-Phase Lines

Abstract: Powerful simulation programs are available for large electric and electronic circuits with lumped parameter elements. State equation models are used for each component. This paper presents the methodology for obtaining a finite order state equation model for transmission lines, despite the distributed nature of their parameters. The lines considered are three-phase, untransposed, with full representation of frequency dependence. There is no requirement for constant (real) transformation matrices. All calculations are initially performed in the s-domain. The results are in the form of standard state equations with phase voltages at both line ends as inputs and corresponding currents as outputs. These equations can then be interfaced with those of linear or nonlinear connected components and integrated numerically using advanced numerical integration methods.

State Equation Modelling Of Untranposed Three Phase Lines

Abstract: Powerful simulation programs are available for large electric and electronic circuits with lumped parameter elements. State equation models are used for each component. This paper presents the methodology for obtaining a finite order state equation model for transmission lines, despite the distributed nature of their parameters. The lines considered- are three-phase, untransposed, with full representation of frequency- dependence. There is no requirement for constant (real) transformation atrices. All calculations are initially performed in the s-domain. The results are in the form of standard state equations with phase voltages at both line ends as inputs and corresponding currents as outputs. These equations can then be interfaced with those of linear or non-linear connected components and integrated numerically using advanced numerical integration methods.

Generator voltage regulator

Abstract: A voltage regulator circuit for a three phase AC generator includes an integrator circuit which integrates the voltage across each negative half cycle of generator output and compares it to a reference voltage to adjust the phase angle of an SCR circuit which provides the power to the exciter field of the generator. A bypass circuit is provided for bypassing the regulating circuit at low generator speeds, the bypass circuit including a FET which directly connects the anode and gate of the SCR in the exciter field power supply to directly apply the generator output voltage to the exciter field at low generator speeds and output voltage. A pair of transistors are latched as the output voltage reaches a preselected minimum value to de-energize the FET and enable the regulator circuit to take over control.

Microprocessor control for two magnetically coupled three-phase PWM inverters

Abstract: For two PWM inverters for traction purposes phase shifted by 30 degrees and coupled by a three-phase harmonic cancelling reactor the requirements on the control set and its method of operation based on a microprocessor Intel 8086 are described. Starting from a reference space vector (rsv) which represents the needed motor voltages it is shown, how the 6 respective inverter-output-potentials can be calculated in a very short time. Realized are one free running mode for low frequencies and special pulse sequences, which are synchronized with the stator frequency.

A Speed and Power Factor Controller for Small Three-Phase Induction Motors

Abstract: A form of controller/compensator is suggested for the speed control of small induction motors. This controller uses pairs of thyristors in each supply line, incorporated into a resistance/capacitance network. Smooth speed control may be realized over a wide speed range, and the motor current remains substantially sinusoidal. For a small laboratory type motor, the current was reduced by up to 30 percent, and high power factor was maintained over the whole speed range. The overall efficiency of the compensated system increased by about three percent over that of the uncompensated motor.

Three Phase, Steady-State Static Var generator Filter Design for Power Systems

Abstract: In power systems, the harmonics originating from thyristor switching are usually eliminated by filtering. Exact solutions of voltages and currents for Static VAR Generators (SVG) used in power systems are found using a state variable formulation with time-domain convolution. Each conduction period of delta-connected thyristor- controlled-reactors is a linear circuit. The initial conditions for each piece-wise linear circuit depend on the prior firing sequence of the thyristors. An additional condition is zero initial current through the thyristor when turning on. There are six possible thyristor conduction sequences for every half cycle of the periodic system voltage. An iterative method is used to determine the initial conditions for the first of the six conduction sequences in order to force the system response into periodic operation at the line frequency. State variable transition matrices and initial conditions are then used to calculate circuit, voltages and currents at any instant of time. It is thus possible to obtain peaks or determine harmonic distributions. Unbalanced three phase voltages and component unbalances may be introduced in the circuit using this analysis. Filters, which are capacitive compensation at the line frequency, are then sized to limit harmonic content in the voltage supply.

Spotting method of short-circuited point of three-phase high-voltage distribution line

Abstract: PURPOSE:To spot a short-circuit with high precision even in case of the short-circuiting of the whole line regardless whether in a balanced or an unbalanced state by deciding on a positive-phase voltage and a positive-phase current from three line voltages and line currents based upon measured values and arithmetic values, and further calculating a specific virtual phase voltage and calculating reactance from the result. CONSTITUTION:Two line voltages and line currents of three-phase high-voltage distribution lines R, S, and T are measured through transformers CT1-CT4 and current transformers PT1-PT4 and applied to a CPU through an A/D converter ADC to determine three line voltages and line currents. Then, the positive-phase voltage and positive-phase current are calculated by a symmetric coordinate method from those voltages and currents, and the reactance is calculated from the positive-phase current and the virtual phase voltage obtained by dividing the positive-phase voltage by three and delaying the phase by pi/6 (Rad). This reactance is divided by the reactance of the line per unit length to perform spotting from a power transmission side to the short-circuited point P with high precision even in case of the short-circuiting of the whole line regardless of whether in the balanced and unbalanced states.

Rotary angle displacement detecting device

Abstract: PURPOSE:To make it possible to miniaturize the entire device and to reduce manufacturing costs, by computing the phase of an AC voltage and the phase of an induced voltage by an exclusive OR circuit, closing switching circuits based on the computed signal, and outputting the detected signal. CONSTITUTION:A first three phase winding is wound around a stator and has phases U1, V1, and W1, and a second three phase winding has phases U2, V2, and W2; and an AC voltage is supplied. An induced voltage corresponding to the rotary displacement is outputted across U1 and V2, and received by first and second switching circuits. The phase of the AC voltage and the phase of the induced voltage are computed by an exclusive OR circuit. When the phases of the AC voltage and the induced voltage are the same, the first switching circuit 10A is closed; and when the phases are different, the second switching circuit 10B is closed. The output of each switching circuit is received by an impedance element and the detected signal is outputted. Therefore the entire device can be miniaturized, and the manufacturing costs can be reduced.

An analysis of delta PWM inverter

Abstract: At present, various modulation techniques are in use for PWM inverters in AC motor drives. This thesis is devoted to the analysis and implementation of a newly proposed modulation technique for inverter operation. The technique known as delta modulation has been used previously in voice transmission. In inverter applications, analog implementation of DM has several distinct advantages over other modulation techniques. These are easy implementation, inherent V/f ratio control, low order harmonic attenuation and easy harmonic and commutation controls. -- In this thesis, the delta modulation technique as the applied for inverter switching waveforms generation is analyzed. A Fourier analysis of the delta modulated inverter output has been carried out in order to study the harmonic behaviour of the inverter output. The analytical results confirms the advantageous features of the delta modulation technique. Practical implementation of the modulation process for inverter operations was realized and the results obtained in analytical studies were verified for a single phase bridge inverter. -- Loading characteristics of a single phase delta modulated inverter were studied under different types of passive and dynamic loads. The passive loads were resistive and R-L loads. The dynamic loads were single phase induction motors. Theoretical results are verified experimentally for loading characteristics. -- A modulation and a logic circuit were designed and implemented for a three phase inverter switching. The implementation involved the design and construction of a three phase sine reference wave generator, a three phase modulation circuit and the logic circuits for generation of proper switching waveforms of the three phase inverter switches. -- A comparison has been made in the study between the proposed delta modulation technique and conventionally used sine PWM technique. Several suggestions have been put forward for the further study.

100 Amp Switched Mode Charging Rectifier for Three-Phase Mains

Abstract: Uninterruptible power supply increases the availability of telecommunication systems decisively. Consisting of a large battery plant for 48 V or 60 V dc with a suitable charging rectifier, this fundamental power source maintains the secure operation of central offices or PBXes, independent of mains supply fluctuations. Considerable volume and cost are the well known disadvantages of such power systems. While the battery producers have been developing the new generation of sealed cells, designers of rectifiers have been investing remarkable efforts in reducing the size of large current range units. It is only the success on both fields that enables a reasonable integration of complete uninterruptible power supply within the communication system. The best way of avoiding the very large magnetic components used in SCR of ferro resonant controlled rectifiers, is to apply the switched mode technology. This paper is to present our latest achievements on the field of SM charging rectifiers for three-phase off-line operations. Power range up to over 8 kW and high efficiency of about 95 % will be discussed as the main features of the new power conversion system.

Eddy-current losses in three-phase power cable and pipe-sheathing systems

Abstract: In the paper the method of calculation of eddy-current losses in conductors and pipes is presented. The current distribution within the conductors is derived from integral equation formulation. The presented method permits computation of the eddy-current losses in the pipe without integrating the Poynting vector.