Showing papers on "Three-phase published in 1986"

Fault detector for a three-phase alternating current supply

Abstract: A microcomputer based fault detector for identifying a phase reversal, a phase loss, and a power loss in three-phase circuits. A microcomputer samples a pattern of timing signals generated in response to three current transformers associated with each of the three phases. The changing pattern of timing signals represent the phase relationship of each of the three phases. The sampling rate of the microcomputer is synchronized to the alternating current in each of the three phases by an interrupt signal indirectly generated by one of the phases. In the absence of current in this interrupt generating phase, a backup interrupt, internal to the microcomputer, is enabled which directs the microcomputer to determine if the absence of the first interrupt is due to a phase loss or a power loss. Either interrupt prompts the microcomputer to sample the pattern of signals and compare it to a predetermined pattern. By counting any deviant patterns and classifying them as characteristic of either a phase reversal, phase loss, or power loss, the microcomputer identifies the specific fault as the occurrence of a predetermined number of deviant patterns within a classification.

Internal armature current monitoring in large three-phase generator

Abstract: A three-phase generator includes an internal neutral junction to which one end of each of the windings of the generator is connected thereby forming a wye-connected generator. An air-core current transformer is disposed over each of the three conductors leading to the internal neutral junction for monitoring neutral current therein. A corresponding air-core current transformer is disposed over high-voltage terminals connected to the other ends of the generator windings. A shielded differential amplifier on the output of each air-core current transformer produces a signal corresponding to the difference between two bifilar half windings in its associated air-core current transformer. The difference currents from the neutral and high-voltage ends of each generator winding are compared, and, if their difference exceeds a predetermined threshold, a threshold circuit produces a trigger signal which is latched by a latching relay to produce a trip signal for use by the generator control system. Connectors are provided for isolating two of the three generator windings from the internal neutral junction to enable isolated testing of the three windings.

Winding arrangement of a stator and/or rotor of a three-phase generator or electromotor with improved performances

Abstract: Winding arrangement of a stator and/or rotor of a three-phase generator or electromotor makes possible an improvement of all performances of these electric machines. The improvement is obtained in that to star-connected windings (1, 2, 3) there are connected additional delta-connected windings (4, 5, 6), which in relation to the star-connected windings (1, 2, 3) are spatially shifted for an angle of , p being the number of pole pairs. Such a winding arrangement is symbolically expressed by: Y + j Δ =

Analysis of the Effect of Source Voltage Fluctuations on the Power Factor in Three-Phase Controlled Rectifiers

Abstract: The effect of source voltage fluctuations on the harmonics and the power factor is analyzed for a six-pulse line-commutated converter. Exact expressions are derived for currents in the filter network and the ac supply lines as a function of the size of a series inductor in the LC type low-pass filter connected to a resistive load. The harmonics are calculated according to a method which is unorthodox in power engineering and which is based on the convolution theorem. Switching functions required for the discontinuous conduction mode are derived from time-domain analysis. The method is applicable to a wide class of switching networks.

Dual current transformer current sensing method and sensor

Abstract: A current sensor for use in a three phase ac system for producing a signal indicative of the average value of the sum of the squares of the ac current and of the phase imbalance between the three phases using two current transducers and an associated method.

Method and apparatus for electrically balancing three-phase arc discharge furnaces

Abstract: A method and apparatus for electrically balancing the phases of a three phase arc furnace, the furnace having a vessel containing a molten bath, three electrodes above the bath, and a transformer arrangement composed of three phases, each phase including a winding, the transformer arrangement being connected to the electrode so that each electrode conducts an arc current proportional to the voltage across the winding of a respective phase, by the steps of: matching the voltages between the electrodes and the bath to one another by adjusting the spacing between at least one electrode and the bath; and establishing symmetry among the arc currents by: varying the voltage across at least one phase winding by a selected increment; measuring the arc current amplitude in the electrode associated with the at least one phase winding after each variation step; and repeating the steps of varying and measuring until the differences between the arc current amplitudes of the three electrodes are less than a given value.

Pulse width modulation system for AC motor drive inverters

Abstract: A pulse width modulation system for AC motor drive inverters consists of a ROM for storing data of values of cos θ and cos(θ-π/3) with respect to a phase θ in the range of electrical angle of 60°, a programmable counter for counting the phase θ, an operational circuit for performing logical operations to evaluate each period of time for which a three phase AC motor is energized in accordance with each switching pattern, and a programmable timer for counting each period of time for which the motor is energized in accordance with each switching pattern. The motor is energized in accordance with each switching pattern for the period of time the data of which is gained at the operational circuit so that three phase output voltage resultant vectors form a circular locus.

Three-phase exciter for synchronous machines

Abstract: A synchronous machine with alternating-current exciter, wherein the stator of the exciter machine, the rotor of which runs in the opposite direction of rotation to that of the stator field, is fed from a three-phase power controller. The voltages induced in the rotor of the alternating-current machine are rectified by diodes in a three-phase star circuit. In order to minimize the effect of the voltage peaks originating from the hole-storage effect during the commutation of the diodes, which peaks are abnormally high as a result of the mutual interaction of the harmonics, there is produced a parallel path for high-frequency currents in the form of a protection circuit having low-pass characteristic so that the mutual interaction between stator and rotor harmonics if greatly reduced. Because of the risk of self-excitation, the elements of the protection circuit are matched to the machine and cause as few additional losses as possible. To reduce the voltage peaks at the diodes sufficiently and, at the same time, also keep the losses within acceptable limits, a reactor is connected in series after the three-phase power controller.

Microprocessor Control for Two Magnetically Coupled Three-Phase PWM Inverters

Abstract: The requirements on the control set for two PWM inverters coupled by a three-phase harmonic canceling reactor are described, and its method of operation, based on a microprocessor Intel 8086 is explained. The input information is a reference space vector (rsv), which represents the required motor voltages. It is shown how the six respective inverter-output potentials can be calculated in a very short time based on this reference vector. One free running mode for low frequencies and special pulse sequences which are synchronized with the stator frequency are realized.

DC to three phase switched mode converters

Abstract: A dc to three phase ac switched mode converter is described wherein a six switch bridge is provided to interconnect the dc source to a three-phase load. A plurality of dc sources are described, each of which employs an inductor/capacitor combination for energy storage, which stored energy is subsequently applied to the output load. The stored energy is delivered by connecting the capacitor across two legs of the three-phase load, while assuring that the third leg is invariably short-circuited back upon itself. As a result, three of the six switches in the bridge are closed at any instant to prevent any current interruption in the load.

Stability aspect of a six phase transmission system

Abstract: Recently, there is a growing interest on the concept of six phase transmission as an alternative to the voltage upgradation of a line, to increase the power transfer capability, within the existing right of way. Allegheny Power System has been investigating the conversion of some of their 138 kV three phase double circuit lines to 138 kV six phase lines as an alternative to 230 kV three phase double circuit lines. So far, the stability aspect of a six phase system has been only estimated approximately from the possible power transfer capability under fault. This paper deals with the stability aspect of a six phase system in greater detail, defining a new transformation and calculation of critical clearing angles under fault and comes to the conclusion that the six phase system is more stable compared to the original and upgraded three phase double circuit lines.

Apparatus for generating a symmetrical three-phase voltage system with a neutral wire capable of carrying current

Abstract: A device which generates a symmetrical output voltage system at the output of a transformer with a neutral point which can carry current on the secondary side or a Y-point former, even if the load is asymmetrical, each primary terminal being fed from a pair of bridge arms of a pulsed inverter. The device further comprises a decoupling network in which the conductor voltages measured on the secondary side are converted into substitute actual values according to the structure of the transformer circuit, which actual values represent symmetrical output voltages or a likewise symmetrical system with a free Y-point. These substitute actual values are controlled to form a system of symmetrical reference values.

Heating by three-phase electrically driven compressor

Abstract: PURPOSE:To permit the efficient heating without driving a compressor by permitting the electric conduction only in two phases of a three-phase electric motor. CONSTITUTION:A control circuit 6 transmits an instruction into a frequency converter 5 when a compressor 1b is in stop. The frequency converter 5 operates to permit the electric conduction only in two-phase so that a three-phase electric motor 1a does not start. In said electric conduction, heating time is shortened by supplying the normal electric power. The heating is adjusted by varying the chopping frequency during the conduction time.

Highpass filter of a filter arrangement for a three- phase network connected to converters

Abstract: For reducing the amount of circuitry and losses in double highpasses for filter arrangements in networks with a high voltage level, the two resonance frequencies and Q-factors of the double highpass are tuned so that in a critical harmonic range, at most a harmless slight resonance peak can occur, for which purpose a series capacitor together with a series choke are connected in series with a shunt circuit grounded, in the case of high voltage and ungrounded in the case of medium voltage, of ohmic, inductive and capacitive circuit elements connected to the network.

Apparatus for forming the actual value of a torque in a three-phase synchronous machine with current-block feeding

Abstract: In two of the three phases of a synchronous machine, the feeding or driving current is measured. During 240° of an operating cycle of the synchronous machine, a reference signal is generated which is proportional to the measured current of one or the other of the feeding signals, whereas during the remaining 120° the magnitude of the sum of the feeding currents of the two phases constitute the reference signal.

Internal common neutral bus in large three-phase generator

Abstract: A common neutral bus is formed in a lower frame extension of a large three-phase generator by disposing three sets of neutral current transformers within the lower frame extension and interconnecting the three phases downstream of the neutral current transformers to form an internal neutral bus. The neutral bus is connected to an external neutral transformer through a neutral terminal of small size and low cost. Clamshell clamps are provided in the internal neutral bus for isolating the neutral ends of the generator winding for test purposes. Rigid support of the current transformers and a hollow copper tube passing therethrough permits use of light and low-cost hollow copper tubing in place of the relatively substantial and expensive neutral terminals conventionally required.

Single phase to three phase dynamoelectric converter

Abstract: Single phase to three phase dynamoelectric converter for generating three-phase current from a single-phase input comprising a three-phase electric motor generator having first, second and third Y-wound stator windings, a bank of run capacitors connected between the first powered stator winding and the third unpowered stator winding, a normally closed potential-type relay with its winding connected between the second and third stator windings, a normally open slave relay with its winding connected between the first stator winding and the potential relay winding through the set of normally closed potential relay contacts, and a bank of starter capacitors connected between the third stator winding and one of the slave relay open contacts adapted to provide phase shifted starting power to the third stator winding when the single phase energy is applied and disconnect from the third stator winding to allow the converter to run and produce balanced three-phase power that can be drawn from all three stator windings for use to start and drive externally located three-phase motors.

Switched-mode power supply for three-phase networks

Abstract: In order to achieve a power factor of cos phi APPROX 1 with a small structural volume and a low power to weight ratio per network phase, a three-phase switched-mode power supply has a full-way rectifier and a connected transformer with a primary winding and a secondary winding, to whose primary winding the unsmoothed rectifier voltage is connected by means of at least one electronic switch which is connected in the primary circuit. The secondary windings of the three transformers are connected to the power supply output in parallel with one another. The control inputs of the at least three electronic switches have a switching pulse sequence jointly applied to them, which sequence is at a constant pulse repetition frequency (pulse repetition rate) which is very much higher than the network frequency, said switching pulse sequence also being at a duty cycle which is dependent on the DC voltage at the power supply output.

Method and device for transmitting three-phase electric currents through a contactless removable connection system

Abstract: The invention relates to a method and device for transmitting three-phase electric currents through a contactless removable connection system. A three-phase electric current is applied to the primary of a supply transformer 12 transforming three-phase electric currents into two-phase electric currents, the secondary of this transformer consisting of two turns 18a and 18b, and a three-phase electric current is gathered corresponding to the secondary of at least one distribution transformer 14 transforming two-phase electric currents into three-phase electric currents, the primary of this transformer 14 consisting of the two turns 18a and 18b and the secondary of this transformer 14 being arranged in a removable member. Application to the transmission and distribution of an electric current through a wall.

Arrangement for monitoring the load state and the speed of alternating voltage or three-phase motors, especially hysteresis motors

Abstract: of EP00950411. Arrangements for monitoring the load condition and the speed of a.c. motors of three-phase motors (2, 3, 4), in particular hysteresis motors, which respectively drive a low-friction centrifuge (6, 7, 8) comprising the following components : a) devices (16, 17, 18) for converting the currents flowing in the motor supply lines into corresponding a.c. measuring signals ; b) a discriminator (23) to which the a.c. measuring signals are consecutively fed by means of a multiplexer (19) and which determines the zero transits of the measuring signals ; c) a phase comparison circuit (24) connected following the discrimator (23) and supplied with a signal corresponding to the supply voltage of the motors (2, 3, 4) to emit pulses whose durations correspond to the phase differences between the supply currents and the supply voltage ; d) an evaluation circuit (27, 28, 29, 30) supplied with the pulses corresponding to the phase differences, which measures the duration of said pulses and transmits an alarm signal if a predetermined limit value is exceeded ; e) a changeover device (20, 21, 24, 25) by means of which the measurement of the phase difference between supply current and supply voltage of the motors (2, 3, 4) and the measurement of the speed of the motors (2, 3, 4) can be alternatively switched on, where in the case of speed measurement the supply voltage of the motors is switched off and the duration of a period or a plurality of periods of the signals emitted by the discriminator (23) is measured, characterized in that by means of the changeover device (20, 21, 24, 25) the upper limit frequency of the signal path from the multiplexer (19) to the discriminator (23) can be changed over in such a manner that in the case of phase difference measurement the upper limit frequency is high compared to the frequency of the supply voltage and in the case of speed measurement the upper limit frequency is only slightly above the frequency of the supply voltage.

X-ray high voltage generating device

Abstract: PURPOSE:To obtain a minituarized, lightweight device, by connecting the primary coils of a three-phase transformer to each other by Y-connection, by connecting the secondary coils of the three-phase transformer to each other by either Y-connection of DELTA-connection, and by rectifying the current by three phase- twelve phase rectification method. CONSTITUTION:The A.C. voltage supplied from a power source 1 is rectified by a rectifying means 2, smoothed by a smoothing capacitor 3 to become a D.C. voltage, and applied between the terminal of a switching means 4, composed of a three-phase bridge inverter. Each witching element A-F of the switching means 4 passes the current by the electric angle 120 deg. and its ignition is executed in cycle in the order of A F C B E D with a delay of 60 deg.. A primary current flows in primary coils 6a, 6b, 6c of a three phase transformer T, and a high voltage is induced in secondary coils 6d-6i of the three phase transformer T which are connected to each other. The induced voltage is rectified and smoothed by a high voltage rectifying means 7 and smoothing capacitator 8 respectively, and is applied between an anode 9a of an X-ray tube 9 and filament 9b. Thus, when X-ray is emitted in the X-ray tube 9, a large amount of current of several hundred Amp flows on the primary side.

Fuel cell for generating electrical energy in the form of direct current, alternating current or three-phase current

Abstract: A novel fuel cell and the associated technology are described. This cell permits the direct generation of direct current, alternating current or three-phase current via the combustion of conventional, gasifiable fuels. This is achieved by the irreversible oxidation processes taking place wholly or partly upstream of the catalyst electrodes, it being possible to expose these to a pulsating gas stream having an oxidant concentration which fluctuates in a contrary sense. Owing to reduced internal resistances, the cell is endowed with an improved efficiency and better power capacity. It is intended to be used both in large-scale industrial fields and for mobile applications.

Method and device to control the supply of loads starting from a three-phase network

Abstract: 1. Process for controlling the supply of loads from a three-phase supply source, according to which at each trip of the supply of the loads the flow of current in each load is only permitted during a time corresponding to a certain number of periods of the alternating supply current defining a wave train, and on each trip of the supply of the loads current is first of all permitted to flow, during the passage to zero of the voltage between two phases, in two lines for supplying loads corresponding to two different phases of the three-phase supply current and then, with a predetermined delay, current is permitted to flow in the third supply line of the loads corresponding to the third phase, characterised in that for each trip of the supply of the loads (R1 , R2 , R3 ) a specific voltage between two phases (U12 or U23 or U31 ) and a specific direction of development, increasing or decreasing, of this voltage are selected in order first of all to permit current to flow in two specific lines (Y1 and Y2 or Y2 and Y3 or Y3 and Y1 ) for supplying the loads during the passage through zero of the said determined voltage (U12 or U23 or U31 ) in the said determined direction of development, and that for a series of six successive trips of the supply of the loads permutations among the phases and directions of development under consideration are made in order to define the said determined voltage (U12 or U23 or U31 ) and the direction of development taken into account for this voltage in order to cause each trip during a passage to zero corresponding to a different combination of a voltage determined between phases and a direction of development of this voltage (U12 increasing, U31 decreasing, U23 increasing, U12 decreasing, U31 increasing, U23 decreasing), in such a way that for the currents (I1 , I2 , I3 ) flowing through each line (Y1 , Y2 , Y3 ) for supplying the loads (R1 , R2 , R3 ) on a cycle of six trips loading to the formation of six wave trains, the continuous component is cancelled.

Circuit arrangement for inductive three-phase loads, especially for three-phase drives

Abstract: The invention relates to a circuit arrangement for inductive three-phase loads, especially three-phase drives, which is operated via an invertor in a three-phase bridge circuit and via an upstream DC intermediate circuit, the supply being effected via a DC controller from a DC network with a network capacitor. In order to improve the recovery and in order to reduce the voltage load on the components such as valves, capacitors and motor it is proposed to connect a rectifier bridge (15) to the three-phase connections of the invertor (WR), which bridge feeds back to the network capacitor (CN) via a parallel-connected buffer store (CKap), it being possible to set the mean voltage value on the buffer store (CKap) via short-circuiting DC controllers. Further advantages are a considerable reduction in the weight and the volume of the capacitors required and a reduced adjustable voltage load on the elements, with an extended frequency adjustment range of the valves.

Current collection apparatus for electric vehicles and their supply systems

Abstract: Current collection apparatus 10 for a vehicle with a pantograph, e.g. a trolley bus, is energised by a supply system having overhead current conductors (21-22 or 21-23) carrying current of different energising characteristics (P1, P2 or 0, 02, 03) plus an auxiliary conductor (23 or 24) routed along a vehicle route and is provided with a current collection bar (30) having a number of current collection segments (31 to 33 or 34) electrically insulated from each other and engageable with the overhead conductors without any one segment bridging or short circuiting the overhead conductors. The number of segments is at least equal to the number of overhead conductors including the auxiliary conductor. Bus bars (41, 42) carried on the vehicle are connected to the segments through unidirectional current conducting devices (D1, D2) so as always to receive current of a given polarity (P1, P2) regardless of the energising characteristics of the current (e.g. direct current P1, P2, single phase alternating current 0, 02 or three phase, delta alternating current 0, 02, 03) supplied to the overhead conductors. The arrangement affords at all times a current path between each bus bar and a current conductor so that the vehicle can change paths without lateral displacement of the current collection bar relative to the vehicle.

Circuit for a single-phase apparatus power supply from a three-phase mains

Abstract: Electrical energy and power measurement apparatuses are currently being discussed which require a dedicated single-phase power supply for their evaluation electronics. In order to increase the operating reliability, it is alternately intended to make it possible for the power supply to be derived from the phases of the three external mains conductors L1, L2 and L3. The proposed solution is based on an "OR circuit", which represents assessment logic, the external conductor L1 in each case having priority over the external conductors L2 and/or L3. The same also applies to the external conductor L2, which has priority over the external conductor L3 in the absence of the external conductor L1. A relay A, which produces the priority by means of its contacts a1 and a2, is used for this purpose. The priority for the external conductor L2 over the external conductor L3 is ensured by a relay B.

Conduction Limits of a Three-Phase Controlled Converter in Inversion

Abstract: The basic six-SCR converter circuit generally used in dc motor drives can provide regenerative braking when operated in the inversion mode. When the motor is operated near rated voltage, however, troublesome commutation failures will occur unless the SCR firing delay angles are severely limited or limited as a function of motor current magnitude. The required delay angles for both light and rated motor currents are discussed, from which it is apparent that a limit on the delay angle should be dependent on the magnitude of the motor current. Since there is a range of values that the delay angle may have, many ways exist in which the delay-angle limit might be implemented. One delay-angle-limit concept is presented to demonstrate the principle.

Three-phase current motor

Abstract: of EP0226087The invention relates to a three-phase motor with a plug that can be plugged in in various positions, by means of which different speeds can be set. A second plug is provided which can be fixed in place of the first plug and which has a circuit which permits operation at a second mains supply voltage differing from that of the first mains supply voltage.

Single phase output electric and magnet current system of transformer while equilibrium of three-phase input

Abstract: The device is a new kind of electric and magnet current system of transformer The key point is the throw-in of the primary coil of a transformer and the secondary coil of another transformer The coils are set on the magnet current with two loops The primary and secondary coils of transformers are devided into relevent two parts to form a loop of its own The invention solves the inequilibrium of three-phase electric current net caused by large volume single phase load, and the transform of single phase to three-phase which single phase system to drive the three-phase motors