Showing papers on "Three-phase published in 1973"

A Theoretical Study of the Three Phase Salient Pole Type Genetaror with Simultaneous AC and Bridge Rectified DC Output-Part II

Abstract: This paper presents theoretical equations, describing the relations between the performance and design details of a three phase salient pole type generator with simultaneous AC and DC output, the latter being obtained by bridge rectification. The AC voltage is regulated and the DC voltage floats; however, the inverse condition is also included. The start and duration of DC commutation, all damper and field winding currents, the DC commutation current and both average, RMS and instantaneous DC and AC voltages are determined.

Circuit breaker and static trip circuit therefor

Abstract: A circuit breaker including separable contacts, an operating means for opening and closing the contacts and a trip coil responsive to a static control circuit for tripping the circuit breaker when instantaneous power in one of the phases of a three phase alternating current circuit exceeds adjustable predetermined levels for adjustable predetermined times as well as ground faults. A separate non-saturated iron core current transformer detects the current in each of the phases independently and powers independent cascaded current transformers having outputs of the same polarity connected to form OR circuits and provide a voltage signal correlated with the instantaneous current in a single one of the protected lines with the highest signal back biasing the others. This signal is amplified and delivered to a plurality of independent solid state adjustable time delay circuits for instantaneous time delay, short time delay and long time delay actuation of the trip coil dependent upon the extent to which the current levels in the protected line providing the signal exceeds a predetermined level of line current. Ground fault protection is also provided.

Three Phase brushless DC motor

Abstract: A three phase brushless DC motor incorporates a stationary armature having three symmetrically positioned sets of windings, a two pole permagnet rotor having photoelectric self commutation means for producing three switching signals, and square wave generation circuitry which produces a three phase square wave e.m.f. in response to said switching signals to energize the windings.

Circuit for detecting phase unbalance in a three phase supply

Abstract: According to the invention an AC voltage, which is a function of line current, is obtained from each line of a three phase AC source. A half-wave rectifier converts the three AC voltages into three trains of pulses of like polarity. Two different ones of the three trains of pulses are applied to the two inputs of each one of three differential integrating circuits. Each circuit integrates the difference of its inputs and gives an output voltage which is proportional to this difference. The voltages of one polarity are selected from the outputs of the three differential integrating circuits and summed. The level of this sum represents the current imbalance of the source. A level detector may be used to detect this voltage level and initiate a control function in response to a predetermined level. A time delay will usually be provided to delay the control function.

Voltage regulator with controlled current

Abstract: A voltage regulating system for AC generators including a three phase current boost and a voltage responsive control circuit having a full converter type output stage. The three phase boost circuit and the full converter output stage are connected in series with the field winding of the exciter. At high power output levels, the inverting capability of the full converter power stage is used to oppose the voltage generated by the current boost to prevent loss of control over the generator, by diverting excessive boost currents through a load means connected to the current boost circuit.

Multilevel current sensing detector system for overcurrent protection of multispeed ac motors

Abstract: The specification discloses a system for preventing current overload in a three phase dual speed motor in both low and high speed modes. The system includes current transformers for sensing the current level in each of the three phases applied to the motor. A divider network is connected to each of the current transformers. Each of the divider networks has a first configuration for converting the sensed current in the low speed mode into a proportional voltage and further includes a second configuration for converting the sensed current in the high speed mode into a proportional voltage. Circuitry is responsive to the proportional voltages generated from the divider network in both first and second configurations in order to generate an overload signal when the voltages from the divider networks exceed a predetermined magnitude. The overload signal operates a relay in order to terminate current flow through the three phases in order to protect the motor.

Selectively switched, malfunction-responsive three phase and parallel logic box for plural static inverters

Abstract: Circuitry for operating static inverters which individually are capable of developing a regulated a.c. output at a controlled frequency rate from a d.c. input. The circuitry derives its d.c. input from one or more of the static inverters for developing synchronizing signals to operate the static inverters so as to enable them to develop three phase a.c. and enables the inverters to be connected in either wye or delta fashion. By means of a single phase/three phase switch a second mode of operation can be obtained for operating the static inverters in a single phase parallel manner. The logic box operation is controlled by a master oscillator which is continuously monitored to ascertain its operation. During normal operation of the master oscillator, the local oscillators of the static inverters connected to the logic box are disabled. In the event of a failure in the master oscillator the local oscillators of the static inverters are automatically enabled to permit continuous operation of the static inverters. The logic box, when combined with three static inverters provides means for driving three phase equipment through the use of single phase power sources (i.e., static inverters) or alternatively, provides an increase in the power capability of the static inverter equipment when operated in single phase parallel fashion.

D. C. power supply for arc welding with SCR controlling three-phase power

Abstract: A D.C. arc welding power supply is supplied with three-phase power through a three-phase transformer. The secondaries of the transformer are connected to a three-phase rectifier bridge with an SCR connected in each phase. A timing pulse generator receives phase reference from the secondaries and produces timing pulses at a controlled time in each phase. A firing signal generator responds to such timing pulses by generating firing signals and applying them to the respective gate electrodes of the SCR''s. A torch switch turns the timing pulses off and on to turn the welding arc off and on, even though full voltage is applied to the primaries. The timing circuit preferably comprises a relaxation oscillator circuit. Multiple torches may be supplied with controlled power simultaneously from the same transformer. A hot start circuit provides greater voltage for a predetermined interval at the beginning of a weld. A MIG spot circuit turns the arc off at the end of a predetermined time for spot welding.

Detector for reverse and open phase in a three phase circuit

Abstract: According to the invention a transducer coupled to a three phase AC supply for a load provides three trains overlapping voltage waveforms displaced 120 DEG in time and of phase sequence following the supply sequence. A waveform converter converts these voltage waveforms into three trains of square waveforms of the same repetition rate, substantially the same duration, and displaced 120 DEG in time but overlapping in duration. The square waveforms are then impressed on a wye circuit configuration consisting of a resistor and a gate controlled semiconductor connected in series and to the wye point in that order for each leg. Each semiconductor is gated on upon its anode going positive by another waveform which is of gating polarity and overlaps the positive going anode waveform. During normal three phase operation of the load, the positive voltages on the anodes of the semiconductor are substantially zero. During reversal or loss of phase of the load, these voltages are no longer zero and are detected by a detector circuit which signals the presence of the fault.

Well logging system using 3 phase AC power supply

Abstract: An improved system for logging tools useful in well bores traversing earth formations is disclosed in which a surface generated direct current is transmitted via a logging cable to a downhole tool and inverted to a three phase alternating current which can be used for powering a three phase synchronous motor in a downhole logging tool. In the logging tool a logic circuit converts clocking pulses to phase related signals. The phase related signals are used to operate bridge inverter circuits for developing alternating current signals which are in a three phase relationship.

Rectifier circuit for providing six-phase rectification of three-phase alternating current

Abstract: A circuit is provided to convert a three-phase alternating wave form to a six-phase rectified wave form Three groups of three controlled bilateral switches are provided each of which selectively and sequentially couples each phase of the threephase wave form in 60* segments to a respective transformer, the signal coupled to each transformer having a frequency that is three times the frequency of the three-phase alternating signal Each of the three groups of controlled switches couples a respective one of the phases of the three-phase alternating wave form to its respective transformer at any given instant of time The positive signals at the outputs of the transformers are combined to provide a positive six-phase rectified wave form and the negative signals at the outputs of the transformers are combined to provide a negative six-phase rectified wave form

A New Three-Phase Static Variable Frequency Changer

Abstract: A new three-phase ac to ac static frequency changer is described. It accepts power from a conventional three-phase constant frequency (e.g., 60 Hz) source, and control signals from an auxiliary circuit, also three phase. The converter output may be represented by positive, negative, and zero sequence voltage systems, each system characterized by a particular frequency. By appropriate control, the lowest (fundamental) output frequency becomes f c -f s Hz, where f c is continuously controlled and f s is the constant supply frequency. Fundamental output frequency is associated with positive and zero sequence voltages. The process of conversion involves both free and forced commutation. It may be accomplished by four thyristors per phase, triggered by the square-wave control signals.

Control system for induction motors

Abstract: A simple and inexpensive control system for induction motors comprising a three phase induction motor, a three phase AC source, a rectifying bridge circuit consisting of a pair of thyristers and a pair of rectifying elements, a first contactor group for connecting an antiparallel circuit consisting of the thyristors in the bridge circuit between one terminal of the AC source and one terminal of the induction motor at the time of motoring of the induction motor, a second contactor group for connecting the AC terminals of the bridge circuit to two terminals of the AC source and connecting the DC terminals of the bridge circuit to two terminals of the induction motor at the time of braking of the induction motor, a single phase shifter for ignition controlling the pair of thyristers, means for supplying the difference between two line voltages of the AC source to the phase shifter at the time of motoring of the motor, and means for supplying one line voltage of the AC source to the phase shifter at the time of braking of the motor.

Arrangement for measuring the crater voltages in a three-phase electric furnace with electrodes arranged in a delta

Abstract: A plurality of measuring conductors leading from the bottom of a multi-phase electric furnace and symmetrically disposed with respect to one another and with respect to said furnace, and each connected to an associated impedance, each of said impedances having a common junction. In this fashion, cancellation of induced voltages in the measuring conductors is effected, thereby enabling generation of a potential at the common junction of the aforementioned impedances accurately representative of the potential at the bottom of the furnace. Volt meters connected from this common junction to the electrodes in the furnace can then give an accurate reading of the crater voltages. BACKGROUND OF THE INVENTION The invention relates to apparatus for measuring the crater voltages in a three-phase electric furnace with the electrodes arranged in a delta. For optimum operation of large electric smelting furnaces, it is important to be able to measure the correct power distribution among the smelting craters beneath the electrodes. Such measurements are usually performed by measuring the electrode current and the crater voltage, i.e., the voltage between the electrode and the furnace bottom. The furnace bottom is usually equipped with a contact from which the potential of the furnace bottom is transferred to the measuring instruments in the control room by means of a conductor. It is no problem to measure the electrode current correctly. The measurements of the crater voltages have, however, so far been uncertain due to induced voltages in the loops formed by the measuring conductors between the bottom contact and the instruments in the control room. Until now, it has not been possible to estimate the extent of these induced voltages. The applicant has discovered an arrangement for three-phase smelting furnaces with electrodes arranged in delta which makes it possible to measure the induced voltages and to correct for them. These induced voltages can be of considerable importance as illustrated by the below example: In a smelting furnace with electrode current 100 kA and a voltage between the electrodes of 200 V, the induced voltage was approximately 10 V. The crater reactance and resistance were about equal. At symmetrical furnace load, the power beneath each electrode would be: 100 kA × 200 V/√ 3 × √ 2 = 8.2 MW By conventional measuring arrangement and with an induced voltage of 10 V, the power measured beneath the three electrodes would be 7.5 - 9.2 - 7.9 MW, respectively. Considerably error may thus arise when measuring the power distribution. Such errors can complicate the control of operation and the adjustment of the furnace to optimum conditions. SUMMARY OF THE INVENTION The present invention is embodied in and carried out by voltage measurement apparatus comprising three measuring conductors connected to the furnace bottom and symmetrically disposed at substantially equal angles of about 120° in relation to each other. The conductors are preferably led, with as similar geometry as possible in relation to respective electrodes and to the adjacent structural steel parts, to a point above the furnace where the magnetic fields are weak, and are here connected through three resistances to a star connection point at which the potential of the furnace bottom is accurately reproduced. Voltmeters connected between associated electrodes and the star connection point provide crater voltage readings.

Quadrature Axis Force and Generator Core Vibration

Abstract: In earlier papers1 2 the authors described investigations into the behaviour of stator end windings and stator cores. Details were given of the results of vibration measurements at the external circumference of the stator core laminations2. It was postulated that the vibration levels observed at rated current conditions were principally determined by the electromagnetic forces generated by the interaction of the currents in the stator and rotor conductors. This paper gives core vibration results from a generator running on test under no-load conditions, both at rated voltage on open circuit and at rated current on three phase sustained short circuit. The measured levels of vibration are compared with those determined by calculation. Because the magnitude of the exciting force is influenced by the length of the air gap, which in turn controls the short circuit ratio, a study is made of the way in which the choice of short circuit ratio can determine the vibration level. Also considered is operation under load conditions and, since the power factor at which the generator is operating determines the phase relationship of the two principal components of force, a study is made of the effect of power factor. Finally some anomalous behaviour observed on a large generator is discussed together with the possible effect of core vibration on the losses in, and temperature rise of, the stator core end laminations.

Molecular solid-state inverter-converter system

Abstract: A modular approach for aerospace electrical systems has been developed, using lightweight high efficiency pulse width modulation techniques. With the modular approach, a required system is obtained by paralleling modules. The modular system includes the inverters and converters, a paralleling system, and an automatic control and fault-sensing protection system with a visual annunciator. The output is 150 V dc, or a low distortion three phase sine wave at 120 V, 400 Hz. Input power is unregulated 56 V dc. Each module is rated 2.5 kW or 3.6 kVA at 0.7 power factor.

Time Domain Analysis of a Three-Phase Ring Inverter with Reactive Load

Abstract: The operation of a three-phase ring inverter with resistive and reactive loads has been analyzed here directly in time domain. The initial conditions on all the six condensers have been taken into account. The instantaneous output voltage and the harmonic content of the output have been obtained. In an earlier paper the author has presented a frequency domain analysis of such an inverter. The general method of writing circuit equations in frequency domain as well as directly in time domain presented in these two papers can in fact be applied to the study of the recurrent transients of many complex switching circuits. Experimental results reported in the earlier paper by the same authors are also presented here for comparison with the predicted results.

A Dynamic Circuit Model for Pole Amplitude Modulated Induction Motors

Abstract: A dynamic circuit model for a pole amplitude modulated three phase, induction motor is developed. The only parameter values required, in addition to the standard ones for ordinary induction motors, are an equivalent rotor slot depth to model skin effect in the bars and the distribution of rotor resistance and leakage reactance between the endrings and bars. Characteristics predicted by the model are compared with those measured on a 6/8-pole and a 6/4-pole machine. The effects of the mmf harmonics are correctly modelled, the difference between computed and measured torques being consistent with stray loss effects.