Showing papers on "Three-phase published in 1979"

Apparatus for sensing short circuit faults in alternating current supply lines

Abstract: Apparatus is provided for sensing and responding to short circuit faults, in particular in three phase alternating current supply lines for direct-on-line starting three phase squirrel cage induction motors. Line current in each line is sensed by a respective current transformer and signals representing both the amplitude and phase of each line current are produced. Line-to-line or line-to-neutral voltage for each phase is also sensed, by photo-electric isolator circuitry, and signals produced representative of the respective phases of these voltages. Logic circuitry is used to produce from the signals representative of current and voltage phases three phase difference signals in the form of currents each varying substantially directly with the difference between the respective current and voltage phases of the respective line. The relationships between these difference signals and the respective current amplitude signals are compared with the relationship which corresponds to conditions from starting to normal running of the motor, and an output signal is produced representing whether there is correspondence or not between the compared relationships. If lack of correspondence is indicated, a circuit breaker is operated to break the supply lines upstream of the sensing equipment.

A Versatile Voltage Controlled Three Phase Oscillator

Abstract: A new method for constructing three phase analog oscillators is suggested and dealt with. The new method is essentially an extension into the three phase domain of methods known previously for the generation of sinewaves in two phases. An electronic realization of the method has resulted in a successful instrument whose performance is tested in the present paper.

Alternating current generator for providing three phase and single phase power at different respective voltages

Abstract: The stator windings of a dynamo electric machine include three phase and single phase output windings for generating alternating current output power at different voltages. The machine output voltage is kept relatively constant by means of a brushless exciter having control and compounding field windings which are energized through stationary rectifier circuits. The rectifier circuit for energizing the field windings of the exciter is connected to or near the neutral leads of the stator windings to maintain a low voltage between the diodes of the rectifier and ground. The energization of the compounding field winding is controlled by means of a variable resistor in dependence upon whether the load connected to the dynamo electric machine is supplied with single phase or three phase current. Alternatively, the output current from the three phase windings can be full wave rectified and the output current from the single phase windings can be half wave rectified to adjust the energization of the compounding field winding.

Two-Frequency Heat Run - A Method of Examination for Three-Phase Induction Motors

Abstract: The system equations for a three-phase induction motor fed at two frequencies are derived. The system of equations for the steady-state quantities, characterizing the average steady- state operating point, and for the "deviations" which determine the superposed multi- frequency oscillations, are established. The scope and the mutual dependenceof the systems of equations do not permit a general analytical solution; they have to be solved by numerical iteration. Considering the results obtained by numerical calculation , the operational behaviour of the three-phase induction motor fed at two frequencies is discussed. A heat run performed with the induction motor by the two-frequency method and the results obtained are compared with the results of a conventional heat run in which the motor shaft is mechanically loaded. It is found that, provided the voltage and frequency of the back-up system are judiciously chosen, the noinal temperature rise in the induction motor can be accurately determined by the two-frequency method.

Electronic damping of stepper motor

Abstract: A damping control system for a three phase stepper motor. A reluctance velocity transducer is used for each of the three phases. The output of each of the transducers is proportional to the rotational velocity of the motor. Each of the transducers is rotationally phase shifted 3.75 with respect to one another and phased to the motor rotor rotationally such that the zero voltage crossings of the transducers correspond to the zero torque crossings of the motor. During damping or detenting of the motor the selected phase has current applied to it which is equal to a predetermined fixed value plus the feedback from its associated transducer. The windings on each side of the detent position have current applied to them which is proportional to the voltage from their respective feedback transducers. The voltage in each of the windings is amplified by a selected gain constant. The current in each of the windings is such that maximum torque is applied to drive the motor to the detent position with appropriate current reversals in the windings to damp out any kinetic energy in the rotor during detenting.

Energy economizer for polyphase induction motors

Abstract: A standard three phase induction motor starts with all three of its input connections connected to the three phase power line. Two of these connections are through triacs which remain continously conducting below said motor's particular most energy-efficient speed, which is above about 95% of synchronous speed. This assures full starting torque and undiminished overload handling capability. The triacs, in response to a control signal, may open the circuits over a sufficiently wide portion of the sine wave input voltage to substantially maintain said particular efficient speed under all rated load conditions. To assure smooth operation and maximum energy savings, the two triacs conduct differently at very light motor loads. The DC control voltage which determines the operation of the triacs is generated by a frequency discriminator circuit which receives its information from a load detecting device that is frequency modulated by load/speed related properties inherent to induction motors.

Solid state circuit breaker with three phase capability

Abstract: A solid state circuit breaker is provided with circuitry for permitting off/on/reset operations actuated by mechanical toggle switch for close simulation of magnetic circuit breaker operation in three phase or other multiphase systems. A power continuity feature is provided for load power by locating the control switch so that it opens all of the circuit except the static power switch branch. The control switch is located between two of the supply voltage phases and the power supply for the control circuitry. The correct zero crossover of one phase is utilized to produce turn-on at zero degrees of that one phase while the other two phases are respectively at minus 120° and plus 120° without any significant impairment of overall circuit breaker performance. An overcurrent protection system is included that uses optical isolators with reduced sensing voltages developed directly from terminals of the power switch elements.

A multikilowatt polyphase AC/DC converter with reversible power flow and without passive low frequency filters

Abstract: An efficient ac to dc converter with reversible power flow, which embodies an active, low frequen­cy filter, is presented. A non-dissipatively controlled, nonlinear resonant oscillator is used to extract electric energy directly from the phase pairs of the polyphase supply line and to generate a mixed amplitude and frequency modulated carrier. The demodulated carrier and the therefrom resulting 20 kHz pulse train produces, after being pro­cessed by a high frequency filter, an active, low frequency filtering effect for attenuation of the 360 Hz ripple of the apparently "rectified" three phase supply line.The system is governed by means of a pulse area control mechanism with a verified response time of one 10 kHz cycle, or 100 micro­-seconds. The customary dc link between the three phase line and the converter's 20 kHz pulse processing mechanism in the form of a common rectifier­-filter is completely eliminated. Data obtained from the test of a 3 kW feasibility model are ana­lyzed in support of presentation of the significant aspects of design and technology.

Constant current welding power supply with an upslope starting current

Abstract: A constant current welding power supply having a single transformer with a primary winding connected to a three phase input source of line voltage and two secondary windings each having a bridge rectifier for providing an open circuit starting voltage separate from the arc working voltage. Each bridge rectifier is fired by separate firing means controlled by a logic control means. One bridge rectifier is energized with an advancing firing angle proportional to a ramp output signal enabled through the control means in response to a predetermined drop in output voltage. The other bridge rectifier is energized in synchronism with the line voltage for a predetermined period of time following the predetermined drop in output voltage.

Three phase undervoltage monitor

Abstract: A three phase undervoltage monitor separately converts the voltage on each phase to a D.C. voltage, compares each of the separate D.C. voltages with a reference voltage, and operates an output signal whenever one or more of the voltages drops below the reference voltage.

Controller to adjust voltage of transformers under load - allows three=phase networks to be coupled together by use of temporary boosting

Abstract: The voltage controller, is for adjusting the voltage on 3-phase transformers whilst still under load, and has one adjustment winding (7-9) per phase connected directly to a primary winding (1-3) of the excitation transformer. The voltage fed to the excitation windings (13-15) of the separate phases in the extra transformer is obtained via staging switches (10) from the adjustment windings associated with the other phases. The connected-in parts of the adjustment windings are in series.

Three=phase supply protection circuit - has current converter connected to unit with filtering, rectifying and delay stages operating relay

Abstract: The overload protection circuit for a three phase supply has a summing current converter which may be a frame converter for holding a set of conductor rails. This is connected to an evaluating and cut-out unit with a relay followed by a device for converting the secondary current of the converter into a voltage which is amplified and from which the h.f. component is filtered out. The filtered signal is compared with a reference value after rectification. The rectified signal is used as a logic signal and passed through a delay storage with a delay period corresponding to at least half the frequency of the supply, to obtain a constant logic signal. This is used to trigger a further delay stage to operate a relay after the delay period, to cut-off the fault current. The second delay stage can have its delay continuously varied or in stages by a programming device.

Three-phase time overcurrent detector

Abstract: A polyphase time overcurrent detector provides a variably delayed control signal wherein the delay is inversely related to both the current magnitude and the number of faulted phases. Current transducers produce input signals representative of the current flowing in each phase of the polyphase system. The input signals are added together to produce a charging signal. If at the end of a predetermined time period the fault has not been cleared, the charging signal will begin to charge a capacitor. If the capacitor charges to a predetermined voltage level within a fixed time period, the control signal is initiated.

Double drum coal mining machine electric drive circuit - has switching system for supply transformer and two DC drive motors

Abstract: The rotary drum coal mining machine has a cutting drum at each end, each mounted on a swinging arm. The machine can be driven in each direction, using winches and a rack and pinion drive system, with the racks supported on a face conveyor. Each drive is powered by a d.c. motor which have their armatures (15, 16) in series, and also their field windings (18, 19) switched in series. The armatures and windings are controlled by a rectifier (21) which receives power from a transformer (26) connected to a three phase supply (22). The armatures and windings are operated by switches (30) with common connections between. The phases of the transformer also include bridging switches (28).

Third harmonic auxiliary commutated inverter having selectable commutation capacitance as a function of load current

Abstract: Three pairs of series-connected inverter main thyristors are coupled in parallel across a unidirectional current source with the junction between thyristors of each pair being adapted for coupling to a respective phase of a three phase wye-connected inductive load. A first and second pair of serially-connected auxiliary thyristors are coupled in parallel across the current source, with the junction between thyristors of the first and second auxiliary pairs coupled by a first and second commutating capacitance, respectively, to the load neutral. Control means, responsive to conduction of a main thyristor, render a respective one of the thyristors of the first and second auxiliary thyristor pairs conductive in accordance with inverter load current to commutate a conductive main thyristor by coupling a respective one of the first and second commutating capacitances in series with a respective load phase across the conductive main thyristor. Inverter commutation capacitance is thus varied in accordance with load current, thereby extending inverter operating range and reducing likelihood of inverter commutation failure.

A new three-phase to single-phase AC to AC frequency converter

Abstract: A new ac to ac frequency converter which uses two six-pulse fully controlled bridge rectifiers and converts three-phase power frequency to a single-phase higher frequency is introduced in this paper. The power elements in the bridge rectifiers may be power transistors or thyristors provided with external means of commutation. The basic operation of the system with variable frequency and variable voltage is described for a resistive load. Analytical expressions for the frequency converter with a resistive load are presented and the results are compared with the existing three-pulse frequency converter. The operation of the system with a series RLC load is described and experimental results are presented from which pertinent characteristics of the frequency converter are discussed. Compared with the existing three-pulse frequency converter, the six-pulse frequency converter provides the advantages of improved input power factor and hence reduced input filter size and a wider range of power control without an increase in the KVA per unit output power rating of the power devices.

Cross-Field Analysis of Asymmetric Three-Phase Induction Motors Extensions to Single- and Two-Phase Machines Thereof

Abstract: The cross-field theory as applied to single-phase induction motors is extended to develop a concise yet comprehensive theory for asymmetric three-phase induction motors. Each phase is represented by its equivalent circuit not only to allow for uneven direct transformer interactions due to asymmetric locactions of phase windings but also to account for the different number of turns, wire size, winding factor, etc., each phase may have. The accuracy of the theory was confirmed by actual measurements on symmetric and asymmetric three-phase induction motors. Computed and test data on some motors are included for illustration. It is also shown that the general three-phase development can be easily applied to determine the behavior of two- and single-phase induction machines-a useful feature for unified computer-aided design - by eliminating one and two phase windings respectively. Not only the procedural details for determining the performance of single-and two-phase induction motors are given but comparisons of numerical and test results on some output entities are included as well.

Industrial induction heating system - uses three=phase supply with three rectifiers supplying ultrasonic frequency driving signal generators

Abstract: The industrial induction heating system includes an induction heating coil and a converter receiving power from a three phase supply network, and providing an ultrasonic signal. Three ultrasonic signal generators are connected in star formation, or in triangular formation to the three-phase network. Each generator operates in mono-phase and includes a rectifier for rectifying the monophase current and an oscillator to transform the rectified current into an ultrasonic frequency signal. Each rectifier is a full-wave rectifier.

Heat source apparatus

Abstract: PURPOSE:To carry out the proportional control of capacity corresponding to load by using an inverter consisting of a forward converter, a chopper, a reverse converter, the speed instructing circuit of a motor, and a torque limiting circuit. CONSTITUTION:Three phase 200 volt AC from the commercial power source 11 is rectified and smoothed by a forward converter 12, and changed to DC voltage. This DC voltage is changed to a DC voltage corresponding to the input signal of a chopper regulating circuit 22 by the action of a chopper 16. Transistors 24 - 29 in a reverse convent 23 turn on and off at mutually related cycles and generate three phase AC voltage, and this voltage is supplied to motor 4. A torque limiting circuit 38 limits the running torque of a compresor 3 so as not to exceed a specified value. A speed instructing circuit 41 gives speed instructing signals to control the revolution speed of the compressor 3, based on the temperature signals from a thermistor 42 and the room temperature setting signals from a variable resistor 43.

Phase comparison relay device

Abstract: PURPOSE:To inspect a level detecting circuit and filter analog malfunctions by aligning three phase comparison relays and energizing these three relays with the same currents. CONSTITUTION:I1-I3 indicate phase currents of respective three phase AC currents flowing through a power system, and are flown from input transformers T1-T3 to the filters FIL1-FIL3 in a relay device to thereby remove high frequency and DC components thereat. The outputs from the filters are applied to level detectors LD1-LD3, respectively to thereby convert the outputs to rectangular waveforms together with level detections. The outputs from the level detectors are applied to exclusive OR gate EX-ORs (inspecting circuit), which produce their outputs (incoincident outputs) at operating time to a delay circuit TDET to thus obtain a detecting output.

HV three=phase power transformer short circuit protection appts. - uses current input circuit with input current transformers and measuring system for comparing transformer currents

Abstract: A short-circuit protection appts. is for primary-side and secondary-side main current-transformer groups whose output currents are compared in a protection relay. The current input circuit comprises input current transformers and measuring system for comparing the currents of the input current transformers. The appts. is designed to protect against short-circuits and to eliminate the need for any intermediate current-transformers. Thus, the current input circuit for the discrete rotary switching groups is arranged so that it forms predetermined relationships, for comparison in the measuring system, from the interlinked transformer currents and/or difference magnitudes from the discrete transformer-phase currents and the transformer sum-current.

An algebraic aggregation of interconnected power system loads

Abstract: The electrical power system loads, as seen from a substation level, consist of numerous load elements and network elements. A subsystem consisting of load elements which are interconnected by network elements is connected to the rest of the power system at several points called reference nodes. This paper is concerned with a description of interconnected loads for a study of their interactions with the rest of the system through the reference nodes. The voltages at the reference nodes are the electrical inputs to the interconnected loads. Only balanced phase operations of symmetrical three phase loads are considered. The voltage dependencies of individual load elements are algebraically aggregated into a voltage dependent admittance matrix which describes the interconnected loads explicitly in terms of the voltages at the reference nodes.

Apparatus for protecting ac threeephase load against phase omission

Abstract: PURPOSE:To permit reliable phase detection without using any expensive current transformer by providing rectifying elements in series with resistors and capacitors between adjacent ones of the three phase bus bars and bridging the output terminals of the rectifying elements with a DC relay. CONSTITUTION:A parallel circuit consisting of capacitors C1 to C4 and resistors R1 to R4 is connected to points R', S' and T' of the respective three phases through diodes D1 to D5. A DC relay RY is connected to the output terminals of the diodes D2, D3 and D5, and a brake contact b of the relay RY is controlled by an on-off control circuit 4 to open contacts 3 of a load circuit main switch 2. Thus, when the three phases are normal, the difference voltage impressed between the opposite terminals of the DC relay RY is low. In case of phase omission, a high difference voltage is applied due to the discharge characteristics of the capacitors and resistors to cause momentary operation of the relay RY. In this way, burning of the motor can be prevented.

Three=phase induction control with regenerative braking - has smoothing choke linked to supply by switching elements and anti-parallel diode

Abstract: The three phase traction control incorporates an inverter and thyristor control to ensure that the motor voltage is above the line voltage, which is unregulated. A smoothing choke and switching elements provide the alternate supply lines to the DC line. An anti-parallel diode and a seires resistance for braking control ensure that the circuit operates in both directions. During braking excess energy is put back into the supply line.

Investigation of a generator system for generating electrical power, to supply directly to the public network, using a windmill

Abstract: A windpowered generator system is described which uses a windmill to convert mechanical energy to electrical energy for a three phase (network) voltage of constant amplitude and frequency The generator system controls the windmill by the number of revolutions so that the power drawn from the wind for a given wind velocity is maximum A generator revolution which is proportional to wind velocity is achieved The stator of the generator is linked directly to the network and a feed converter at the rotor takes care of constant voltage and frequency at the stator

Semi conductor rectifier

Abstract: PURPOSE:To suppress a direct current voltage raise at a light load time without inviting a large cost up by series connecting thyristors and diodes at rectifiing arms and making only control of a predetermined direct current voltage width. CONSTITUTION:Rectifiing arms 2u of a rectifier 1 of a three phase full wave connection are formed by a series body of thyristors 3 and diodes 4, an output voltage is detected by a detector 5 and compared with an output of a standard voltage signal generating device 6, together with performing phase controlling of thyristors 3, a limitter device 8 to make a phase control angle to thyristors 3 not to exceed a predetermined maximum value not greater than 90 deg. is made provided. Accordingly as maximum normal choke voltage may be sinalphamax X 100% of maximum reverse choke voltage, thyristors of arms 2u can partially be replaced with diodes and a device of low cost can be made.

Threeephase voltage difference and phase difference detection circuit

Abstract: PURPOSE:To detect the voltage difference and phase difference between a three- phase power source and a load through one circuit, by determining the absolute values of the negative-phase-sequence voltage differences among all the phases and comparing the sum of the absolute values with a set level. CONSTITUTION:The three phase voltages detected by a power voltage detector PT6 and a load voltage detector PT7 are added to each other by phase addition circuits 21U, 21V, 21W, respectively. Each phase output of the power voltage detector PT6 is anti-phase to the corresponding phase output of the load voltage detector PT7. The outputs of the phase addition circuits are converted into the absolute values by absolute value circuits 22U, 22V, 22W. The absolute values are applied to a three- phase input adder 23. The output of the adder 23 is compared with the output of a set level power source 24 by a comparator 25.

Inverter control circuit for motor driveng

Abstract: PURPOSE:To prevent a generation of a hunting phenomenon of an induction motor by performing a phase control of a gate pulse by a phase difference detecting signal between an output voltage and an output current of a driving inverter. CONSTITUTION:In a driving system supplying a three phase alternating current voltage to an induction motor 10 through a frequency converting device 18 output voltage and current of an inverter 16 are input to a flip-flop 28 through pulsing circuit 24,26 respectively and a phase comparison is performed, the output is through an analogue converter 36 consisting of an integrator 32 and an analogue holding circuit 34 and through a differential processor 38 to obtain a signal representing a phase variation quantity, this is supplied to a phase angle controller 40 and a phase angle of a pulse oscillator 44 output is controlled. An output of a circuit 40 is supplied to a gate of an inverter 16 through a ring counter 46 and a pulse amplifier 48.

Control unit for induction melting furnace

Abstract: PURPOSE:To provide a control unit for induction melting furnace equipped with a circuit with best combination of three phase balance control and power factor control. CONSTITUTION:Power factor is controlled by detecting the reactive current portion of the current for an induction melting furnace F, i.e., a load, from the furnace current input given through a transformer CT1 and the furnace voltage input given through a transformer PT1 by a reactive-current-detecting circuit A, so as to make the reactive current become nearly zero, i.e., the power factor becomes nearly 1.0. The furnace current input iRS and the T phase current input iT are converted into a d.c. level and computed by means of a computing-amplifying unit 0A3 so that a prescribed equation may hold, then positive or negative d.c. level signals depending upon balancer quantities are obtained. According to the signals, a control circuit C' is operated so as to perform three-phase balancer control. Hence a transformer is used for both the three phase balancer control and the power factor control, consequently, the control unit is miniaturized.