Showing papers on "Three-phase published in 1970"

Digital Simulation of Three-Phase Induction Motors

Abstract: The problem of solving the general three-phase induction motor performance equations is discussed and methods of digital solution for both the three-phase motor and the two-axis model are described.

Phase failure detection system

Abstract: A system for detecting single phase operation or total loss of power in a three phase electrical network. In this system, sensing circuits monitor the line-to-line voltages available from a three phase source of electric power. These sensing circuits cooperate with an indicating means to provide an indication upon the occurrence of either a phase failure or a total loss of power. The sensing circuit include monostable multivibrators which are connected across pairs of supply conductors connected with the output of the three phase source. These multivibrators provide output pulses of a predetermined time duration in response to input voltages exceeding a predetermined magnitude and, accordingly, the multivibrators are sequentially and periodically switched in accordance with the voltages provided by the three phase source. Thus, the three multivibrators connecting the various pairs of supply conductors produce time displaced pulses except during those periods when the three phase source ceases its three phase operation. By monitoring the output pulses from the three multivibrators, an indication is derived when the three phase source ceases its three phase operation.

Pole-changing, three-phase alternating current induction motor, with single-layer stator winding

Abstract: A three-phase, two-speed pole-changing induction motor, using the pole-changing method of pole-amplitude modulation, which has a single-layer stator winding, diamond or concentric coils being used as preferred. The stator coil layout is derived from the stator coil layout of a corresponding double-layer winding for the same alternative pole-numbers. The present invention provides a two-speed, three-phase alternating current electric motor having a single layer stator winding with alternative connections providing alternative polenumbers by a modified method of pole-amplitude modulation.

Analysis and Performance of a Three-Phase Ring Inverter

Abstract: An analysis of a three-phase ring inverter for purely resistive loads is presented. The initial voltages on all of the six condensers have been taken into account. The instantaneous output voltages and the harmonic content of the output have been obtained. The analysis can be easily extended to circuits with more than six stages, to circuits using a ballast inductance in series with the dc source, and for inductive loads. Experimental results are presented for comparison with the predicted results. In addition, a modified form of circuit, which was found quite adequate for operation on the highly inductive load presented by an induction motor on no load, is presented.

Output Voltage in Three-Phase Pulsewidth-Modulated Inverters

Abstract: A theoretical analysis of pulsewidth control in three-phase pulsewidth-modulated inverters, is presented. Two general classifications of commutation schemes are discussed with respect to controllability of output voltage and commutation requirements. It is shown that for one scheme the output waveform is always defined regardless of load conditions but for the other scheme the output waveform is dependent on the load. A method of analysis is described whereby the output voltage, in the latter case, can be determined for sinusoidal load currents. Another method is then introduced whereby these results can be extended to applications with nonsinusoidal load currents.

Traffic control system

Abstract: The traffic system includes a vehicle and pedestrian section and may be used for complex traffic flow conditions. A three phase traffic controller is disclosed defining phases A, B, and C. Each section of the system is provided with an indicator panel, a binary counter for indicating phase and interval timing, timing circuitry, and relay drive circuitry for actuating traffic signals. Separate gate and memory circuits are also used for each phase. The operation of the system is such that if the system is in any phase such as phase C and there are no calls from the other phases it remains in phase C. If there is a call from another phase and there are no vehicles being detected or prior pedestrian signals being displayed in phase C it moves to that other phase. If phase C is still detecting vehicles or displaying prior pedestrian signals a predetermined time period elapses before the system selects the phase that has called. The system also has the capability of skipping phases that have not called by going from C directly to B skipping A if A has not called.

Servo compensation including a non-linear synchro transmitter

Abstract: A conventional synchro device; including a rotor, a stator, a three-phase winding and a single phase winding, is modified by the addition of a trim winding which is inductively coupled to the three phase winding and provides non-linear operation of the synchro. The trim winding is electrically coupled to the single phase winding to provide a null indication when the respective output voltages from these windings are substantially equal. In order to obtain the null indication, output angle data from the synchro must vary in a non-linear manner with respect to applied input angle data. An additional shorted damping winding, may be inductively coupled to the single phase winding and the trim winding to produce a flux which counteracts flux induced in the single phase and trim windings thereby reducing the voltages in the trim winding and the single phase winding. The voltage in the single phase winding is reduced to a greater extent than the voltage in the trim winding and the non-linearity between the input angle data and the output angle data over limited ranges of input angle is further increased.

Three-phase delta-connected voltage-regulating system and method therefor

Abstract: A system and method for regulating the voltage from a threephase delta-connected source to a three-phase delta-connected load circuit that includes a voltage regulator for each phase with the input to each regulator being made to be conductively independent of the other phases, while the outputs of the regulators are interconnected into a three-phase delta connection with each regulator thereby being essentially unaffected by the power controlled in the other phases.

Three-phase static dc welding machine

Abstract: Three-phase static dc welding machine.. G7-. For arc-, hand- and automatic welding comprises a three-phase transformer, a rectifier with diodes and thyristors, a pulse generator, a control circuit with a feed circuit, a shunt, a choke and an operating circuit, and contains electrodes. The rectifier is connected as a three-phase, half-bridge circuit, with an auxiliary load resistor for the diode and has an auxiliary load resistor for the half bridge, an auxiliary diode rectifier and a charging choke circuit. The synchronising circuit of the pulse generator is connected to the secondary winding of the transformer and the outputs of the pulse generator are connected to the control electrodes of the thyristor group. The generator is supplied from a replenishing circuit which has a diode group and a choke. The control circuit contains a current characteristics, a nominal value display and stabilization circuit. The current regulator is connected to the shunt and the current for the working circuit of the electrodes is passed through a choke.

Frequency-Controlled A.C. Drive

Abstract: 1,197,984. Control of A.C. motors. GOSUDARSTVENNY PROEKTNY INSTITUT "TYAZHPROMELEKTROPOEKT." 10 Aug., 1967, No. 36686/67. Heading H2J. [Also in Division H3] An induction motor is energized via magnetic amplifiers, one for each phase, supplied from A.C. mains but whose outputs are modulated by an auxiliary, variable-frequency source, each amplifier having two such outputs which are undirectional but are connected to respective halves of the phase windings in bridge formation across the diagonals of which are connected non- contact switches energized in succession so as to provide alternating current in the phase windings. Fig. 1 shows the arrangement for one motor phase; the amplifier has two-phase mains energized input windings 6, 6 and 7, 8, and control windings 25 . . . 28 energized from the auxiliary source 29. Two second-harmonic outputs are each comprised of four secondary windings 9 . . . 12 and 17. . . 20 connected through diodes 13, 14 and 21, 22 to output terminals 15, 16 and 23, 24, and these form a bridge network with motor half windings 30, 31 with thyristor switches 32, 33 across the diagonals. These are triggered in succession at current zero, e.g. by Schmitt triggers 38, 39 whose inputs are connected to resistors 36, 37 or transformers. The output waveform (Fig. 2B, not shown) has a component which is the second harmonic of mains frequency but this is smoothed out by capacitors 34, 35. The diodes 13, 14 and 21, 22 also provide internal feedback, the effect of which can be varied by a D.C. bias winding (not shown); this produces a current zero band of variable width between each half-cycle. In the arrangement shown the output frequency is always less than that of the main, but in an alternative (Fig. 3, not shown) an output at 60 c.p.s. is obtained with 50 c.p.s. mains; in this each amplifier has six phases arranged on twelve cores and energized from three phase mains using a Scott connection arrangement of the input windings.

Comparison Of Physical Modelling And CADRepresentation Of Compensated RailwaySystems

Abstract: A 25kV, 75km single phase traction feeder with two SVCs has been modelled both on a physical simulator and on a CAD package (SABER). The controls of the SVCs, which use a phase locked loop technique, have been included in both simulation models. Some of the simulated results are given; comparisons made with the results obtained from each model show very good agreement INTRODUCTION Many main line railway electrification systems use 25kV ac to transmit electrical power to the locomotives. At this voltage level the railway system is usually divided into electrical sections of about 25km length. Longer sections result in excessive voltage drop (more than 25%) with severe loss of performance to the most distant locomotives. In many countries, particularly those of Northern Europe and the USA, it is relatively easy to feed track lengths of 25km from existing electrical supply networks. In more sparsely populated regions there is not a sufficiently large number of potential feed points and, in order to achieve a 25km feeder length, additional three phase power lines must be installed. This is an expensive process which can affect the economic viability of electrification. There is therefore a need to investigate methods that could be used to extend the feeder length beyond 25km. The large voltage drops which occur in 25kV power supplies are mainly due to the flow of reactive currents generated by the locomotives. These voltage drops can be minimised by providing local reactive power support in the form of Static Var Compensators (SVCs). Earlier theoretical studies (Morrison et al.[l]) have shown that, with 2 SVCs on a feeder, a length of up to 75km can be achieved, which is a significant improvement over the uncompensated length. However, Transactions on Engineering Sciences vol 3, © 1993 WIT Press, www.witpress.com, ISSN 1743-3533 290 Software Applications in Electrical Engineering this requires the SVCs to operate and maintain stability in very difficult conditions. To study the performance of a feeder with 2 SVCs requires a reliable model of a complete feeder with the SVCs and several locomotives. A complex time domain model can be constructed but it is desirable to have independent validation of the results in some other form. This paper describes the use of comprehensive time domain analysis, to model a system with 4 locomotives and 2 SVCs all operating interactively, and its comparison with a physical model of the same system. SYSTEM DESCRIPTION AND PARAMETERS USED The system studied and the parameters used in the study are given in Figure 1. A 75km single track section is shown with X/R ratio of about 3. In order to enable easy comparison with the physical model, the feeder is divided into 4 equal lengths with a busbar at each break point where trains may be connected. The train loads are conventional electrical locomotives as shown in Figure 3. For these studies, one SVC was located at the middle and the other at the end of the feeder. Each of the SVCs is composed of a Thyristor Controlled Reactor (TCR) and a fixed shunt capacitor. The shunt capacitor is arranged as a single arm filter, tuned at about the 3rd harmonic. This is an economic arrangement which, for a single SVC, has been shown to be adequate to meet the requirements for harmonic attenuation in railway applications (Hu et al. [2]). The ratio of the rated reactive power of each of the SVCs (12.4MVAr) to the short circuit level at the end of the track section is 0.7, which is very high compared with normal industrial application of SVCs. Under these conditions it is important to model the controls of the SVCs, which are of the phase locked loop type (Ainsworth [3]). THE CAD MODEL OF THE SYSTEM The CAD simulation model of the system is shown in figure 2 and the values of the components calculated from the system parameters are given in table 1. In the model the feeder is represented by four -equivalent circuits and the locomotive loads are modelled as controlled single-phase converters. The main power circuit of the locomotive is given in figure 3(a) which is a half-controlled bridge connected in cascade with a diode bridge. Two kinds of locomotive models were created and used in this study. The first model, shown in Figure 3(b), is a simplified model which contains only a diode bridge and a current source at the dc side. This simplified model can be used to simulate the working conditions of the locomotives at full conduction. The second model is a full representation of Transactions on Engineering Sciences vol 3, © 1993 WIT Press, www.witpress.com, ISSN 1743-3533 Software Applications in Electrical Engineering 291 the locomotive circuit, which is useful when a locomotive operates under partial conduction. When several locomotives are running together as a consist, they are modelled as one equivalent locomotive with appropriately modified load current and transformer inductance. The SVCs in the system are modelled in full, including the controls of the TCR. The CAD package used in the study is called SABER, which is a comprehensive, flexible, time domain analysis system. One of the big advantages of this package is that it leaves much freedom to the user to create his own components and sub-circuits used in the system simulation, by using a special language, MAST. In the CAD model of the compensated railway system, the basic components such as the resistors, inductors, capacitors and the single phase ac source are provided by a library. However, some of the special parts, particularly the thyristors, the power transformers and the controls for the SVCs, are created using the various features of the package.

Electrical supply systems

Abstract: 1,253,520. Automatic voltage control. JOSEPH LUCAS (INDUSTRIES) Ltd. March 21, 1969 [April 1, 1968], No. 15506/68. Heading G3R. In a battery charging system for a vehicle of the type wherein the rectified output 4, 5 of a permanent magnet three phase alternator is regulated to maintain a predetermined voltage, one set of rectifier diodes 10, 11, 12 is provided with thyristors 13, 14, 15 each in anti-parallel connection with a respective diode and controlled by a conventional regulator comprising members 21----28, the arrangement being such that the thyristors are turned on or off when the voltage is above or below the predetermined value to respectively by-pass the alternator output or cause it to be applied to the battery 6. All the thyristors receive gate current from the regulator and thus the alternator output is always by-passed by one of the thyristors and diodes, only these members being provided with heat sinks. A transistorcontrolled warning lamp circuit indicates when the generator is not producing current, Fig. 2 (not shown). Application of the invention to a single phase permanent magnet alternator is described, Fig.3 (not shown).

Method of simulating the zero voltage increased by means of measured electrical quantities

Abstract: Method of simulating the zero voltage increase at loads in three phase synchronous generators caused by load unsymmetry. The method utilizes terminal voltages measured at the synchronous generator and a zero current measured at the generator neutral and provides that an equivalent quantity Uo'' is similated by means of an open delta connection which accomplishes a vectorial addition of the three terminal voltages and Uo'' is converted into Uo by means of a transformer.

Attachment for magnetic starters to protect three-phase electric motors

Abstract: This invention provides a small, simple and extremely inexpensive electric motor protector that can be quickly attached and become a part of the circuitry of a conventional magnetic starter, and can thus exert an on/off control over the magnetic starter and the 3-phase electric motor to which said magnetic starter is connected under certain conditions. By the arrangement and connection of two or more magnetic relays which are the components of this electric motor protector, it allows the electric motor to run as long as all three power phases are actively available to the magnetic starter. In the event that any one of the three power phases is lost, due to a blown fuse or other problem, all three phases are shut off, as is the electric motor. As a result, this motor protector positively eliminates dangerous and destructive single-phasing of the motor (operation on the two remaining phases).

Resistance heating of wire during drawing - or the like

Abstract: A heating current circuit is formed in the wire, as it passes through its processing, by applying two or more contacts to the wire with a space between them. Two separate heated paths are formed by the use of three contacts each outer pair being connected to the secondary windings of each of two transformers whose primaries are Scott connected to a three phase supply. The second heated length downstream is regulated in temperature e.g. by using a pair of antiparallel connected thyristors or the like in the primary lead from one phase to the appropriate transformer, the current control by their means being continuous and without steps.