Showing papers on "Isolation transformer published in 1978"

A Calculation Method for Impulse Voltage Distribution and Transferred Voltage in Transformer Windings

Abstract: This paper presents a calculation method for impulse voltage distribution in the complex winding arrangement encountered in large power transformers. This method takes into account the electrostatic and electromagnetic combinations of windings, and, therefore, permits a precise analysis of voltage response in the windings to which an impulse voltage is applied and of the transferred voltage in other windings to which an impulse voltage is not applied directly.

Self-referencing power converter

Abstract: A self-referencing power converter operates at a high frequency with a low loss, light weight ferrite core transformer. The transformer primary is selectively connected across a DC source of rectified AC power to provide energy storage followed by a predetermined time period of disconnect to provide energy transfer by way of transformer flyback. The energy storage cycle begins when the voltage across the primary winding of the transformer does not exceed a predetermined value and the predetermined time period of disconnect has ended. A current sensing circuit senses the current flowing through the primary winding, permitting such current to flow until a power reference is reached. A comparison circuit in the transformer secondary compares a reference voltage with an operating voltage and returns any error voltage to the primary circuit, the error voltage then being used to set the power reference.

Direct access coupler

Abstract: A direct access coupler for connecting a piece of terminal equipment, such as a modem to a telephone line pair, the coupler being of reduced size achieved in part by the use of a miniaturized isolation transformer and a constant current circuit to divert the off-hook current which would otherwise flow through the isolation transformer or a current-shunting choke and by the use of both an optical isolator off-hook circuit and an optical isolator ring detector circuit.

Isolation and multiple output extensions of a new optimum topology switching DC-to-DC converter

Abstract: The recently introduced new optimum topology dc-todc converter is extended in a simple and elegant manner to provide dc isolation and multiple outputs. In comparison with the sinle-transistor isolated forward and flyback converters operated under the same conditions, the single-transistor isolated new converter is shown to have equal or lower stress levels on the transistor, diode, and capacitor ripple current, and can utilize an isolation transformer with lower core and copper losses. Measurements of cross- and self-regulation properties of a two-output 45 W test converter are presented.

Filament heating apparatus

Abstract: A filament heating apparatus for an X-ray tube having an isolation transformer through which a control signal is digitally transmitted regulates the filament current to be constantly stable. The control signal is comprised of one of a reference signal based upon the characteristics of the X-ray tube and a component of the filament current.

Solid state transformer differential relay

Abstract: A transformer differential relay monitors the current flowing through the primary and secondary windings of a power transformer and disconnects the transformer from a power source feeding the transformer whenever the magnitudes of these currents indicate a fault condition in the transformer. First and second current transformer generate primary and secondary winding voltage signals representative of the magnitude of the current flowing through the power transformer primary and secondary windings, respectively. A solid state restraint signal generator is responsive to the primary and secondary winding voltage signals and generates a restraint signal representative of the magnitude of the larger of the primary and secondary winding currents, respectively, at each measurement instant. An operate signal generator is responsive to the primary and secondary winding voltage signals and generates an operate signal representative of the magnitude of the vector sum of the currents flowing through the power transformer primary and secondary windings. Finally, means are provided for disconnecting the power transformer from the power source when the magnitude of the operate signal operates above a predetermined percentage of the restraint signal.

Interleaved High-Voltage Transformer Windings

Abstract: Interleaved-turn high-voltage transformer windings are a useful alternative to continuous disc and layer windings for a wide range of transformer output and voltage ratings. Many configurations have been devised to meet different requirements. This paper reports the discovery that the original and most- commonly-used form of interleaved winding has an unexpectedly large internal oscillatory response to chopped-wave or front-of-wave impulse (lightning surge) voltages. It describes the subsequent development of a less-oscillatory winding which allows smaller insulation clearances for equivalent reliability.

Test fixture having switching means for facilitating transformer turns ratio testing

Abstract: This disclosure relates to a transformer terminal switching unit or fixture with specially designed output terminals and transformer attachment cables. The disclosed transformer terminal switching unit is especially useful as an accessory to the BIDDLE Transformer Turn Ratio (TTR), tester, catalogue number 55003. The design of the transformer terminal switching test fixture is especially useful to test delta-star connected, three phase utility transformers with subtractively connected winding polarity. A transformer with additive windings can also be tested with the disclosed testing fixture.

Current transformer input system for AC conversion devices

Abstract: An improved input system for isolating resolver or synchro outputs from inputs to demodulators or analog-to-digital converters uses current transformers rather than voltage transformers. The resistances of resistors connected in series with the primary windings of the isolation transformers are adjusted to standardize the input currents of the transformers.

Power supply circuit for electrical machining

Abstract: A power-supply circuit for electrical machining of all types in which a tool is juxtaposed with a workpiece, the circuit having an alternating current input connected to the mains and receiving the alternating current at the mains' frequency, a rectifier connected to the input for converting the commercial alternating current to direct current, a solid-state switching device for converting the direct current to a high-frequency signal, a transformer whose primary winding receives the high-frequency signal and which produces a high-frequency output at a desired voltage level, a rectifier connected to this transformer at its secondary, and switch means for transforming the direct-current output of the latter device into the machining signal. The system permits the transformer to be of substantially reduced size by comparison with transformers used in earlier high-power electrical machining systems.

Pulse transformer technique for optical switch

Abstract: Optical communication apparatus is disclosed whereby the voltage controlled load device typically requiring a relatively high energizing voltage is operated by means of a wide band step-up pulse transformer and a low voltage power source. The step-up transformer permits operation of the fiber optic communication system from a power source as low as 5 volts D.C. to obtain the necessary modulation potential required by the electro-optic and piezoelectric load device.

Input transformer arrangement for use in a television receiver

Abstract: An input transformer arrangement includes an unbalanced signal suppress transformer for suppressing unbalanced signal carried in a feeder line extending between a television receiver and an antenna therefor, and an impedance transformer for dropping the impedance. These two transformers are arranged on one core for unifying and simplifying the arrangement.

Control logic for an inverter ripple controlled power system

Abstract: A load management system utilizing a three phase solid state inverter for applying a ripple signal on a high voltage line with the system having means (a) for conducting backfeed current from the line through a portion of the inverter, (b) for balancing the current and phase distribution through an isolation transformer, (c) for selectively sequentially connecting and disconnecting the transmission of the ripple signal from the high voltage line, (d) for providing a wide angle of conduction to assure conduction of the solid state devices over a wide time period to avoid current imbalance and core saturation.

Push-pull inverter including starter circuit

Abstract: In a push-pull inverter (including a transformer) for changing direct current into alternating current, a circuit is disclosed for starting the inverter in which the first pulse of a rectangular pulse train applied to the transformer has a duration of one half that of the subsequent pulses. This aids in reducing the initial magnitude of the flux excursion in the transformer core.

Isolation amplifier with high linearity

Abstract: A transformer-coupled isolation amplifier which can accept signals over a wide dynamic range while maintaining very high linearity. An input signal is applied to an input winding of a transformer. The secondary winding of the isolation transformer is connected across the differential inputs of a high-gain amplifier. Negative feedback is provided around the amplifier so that the transformer secondary winding is connected across a virtual short; and the negative feedback tends to drive the voltage applied to the inputs of the amplifier to a very small value. The negative feedback from the amplifier induces a current in the transformer secondary which cancels the flux produced by current flowing in the primary, thereby reducing the effects of non-linearities in the BH curve of the transformer.

Fluxbucking line transformer with electronic equivalent line terminating impedance

Abstract: A fluxbucking line transformer is disclosed in which fluxbucking primary windings in the line transformer compensate for the DC flux generated by the passing of DC currents by the primary windings. No feed-back circuitry is required for sensing the DC components of the magnetic field in the transformer core or to sense the DC current through the transformer to provide adjustment of the fluxbucking current. The disclosed transformer circuit is a bridge configuration which cancels the DC flux independently in separate primary windings, and is advantageously employed in telephone line circuits in which large DC currents are passed through the line transformer while smaller ac signals are coupled to the secondary without distortion of the ac signals due to saturation of the transformer core.

Arrangement for reducing no-load current in an energized transformer

Abstract: A two-terminal control and power switching circuit for substantially reducing electric current flow in the primary winding of an energized power transformer when no load is connected to the transformer secondary. A triac, in series with the power transformer primary and AC source, remains off when a load remains unconnected to the secondary of the power transformer. An oscillator circuit causes a resistive path to be periodically connected across the nonconducting triac. When a load is connected across the power transformer secondary, the resulting increase in voltage developed across a portion of this resistive path is sufficient to cause voltage-amplitude-sensing circuitry to fire the triac. After the triac is turned on by this voltage-amplitude-sensing circuit, conduction of the triac is maintained by a feedback arrangement whereby a low-impedance, current-sampling transformer, having its primary winding also in series with the triac, power transformer primary winding, and AC source, delivers lagging current from its secondary winding to the input terminals of the triac, with amplitude sufficient to fire the triac after every zero-crossing of the AC source voltage as long as the load remains connected to the power transformer secondary. When the electrical load on the power transformer secondary is removed, the magnitude of the current flowing through the current-sampling transformer falls below the level required to fire the triac, and the triac ceases to conduct at the next zero-crossing.

High voltage resistant signal transmission device with isolating transformer

Abstract: The isolating transformer has two windings galvanically separated from each other and each connected to a respective point, which points are set at various high voltage potentials. At least one additional transformer is provided in series with the isolating transformer, and has two galvanically separated windings, with one winding being galvanically separated from the isolating transformer and the second winding being galvanically connected to a first winding of the isolating transformer. The second winding of the additional transformer is connected to one of the points and is split relative thereto in a manner such that a parasitic current produced between the two windings of the isolating transformer, and which is split with component currents flowing to both terminals of the first winding of the isolating transformer and therefrom to and into the split second winding of the additional transformer, produces, in the additional transformer, partial current flows which are mutually compensating to at least a great extent in their effect on the one winding of the additional transformer. Preferably two additional transformers are provided in series with the isolating transformer, each being operatively associated with a respective winding of the isolating transformer. One winding on one additional transformer is connected to the input and to ground, and one winding on the other additional transformer is connected to the output of the device. Each additional transformer may be a compensated transformer with one toroidal core, a compensated transformer with two toroidal cores, or a double compensated transformer with two toroidal cores.

Line overvoltage protection for electrical device - has symmetrical variable resistors coupled to isolating transformer secondary

Abstract: The over-voltage protection for an electrical device (34) with an input isolating transformer (40) uses symmetrical variable resistances (43, 44) in parallel with the transformer secondary winding (42) and between one of the secondary conductors and an earth contact The electrical device (34) is isolated from the local earth (50) and is coupled to the earth contact (33) via a direct line (52) The isolating transformer (40) has a primary winding (41) divided into several separate parts by open screens at the potential of the points separating the two parts

Zero sequence current source for transformer having a nonwound tertiary

Abstract: A three-phase electrical transformer utilizes a conductor independent of the transformer windings for sensing zero sequence current upon the occurrence of a ground fault. A current transformer coupled with the independent conductor provides polarization to protective relay devices. One embodiment utilizes the transformer internal tank shield in combination with the current transformer for providing zero sequence current.

Power supply unit for a plasma plant

Abstract: A power supply unit for a plasma plant, in particular for a plasma spraying plant, comprises an isolating transformer for connection to three-phase mains, a current control array and a rectifier array. The rectifier array comprises silicon wafer thyristors in a three-phase bridge configuration, which thyristors are electronically controlled through a current control loop, and an exterior voltage control loop is provided for additional electronic control of the silicon wafer thyristors. In the output from the thyristor array, a filter with a transient voltage suppressor may be provided as high-frequency protection and with di/dt limitation.

Circuit for controlling induction in current transformers

Abstract: The present invention is directed to a circuit for controlling induction in current transformers so as to maintain such induction at a level below its saturation level in presence of a primary current having an asymetric component. The control circuit comprises a detection part connected to the secondary of the current transformer for detecting an increase in the transformer induction; an auxiliary load of high resistive value at the secondary of the transformer; and a switching part governed by the detection part operative to insert the auxiliary load in series with the secondary of the transformer when the polarity of the secondary wave reaches a polarity inverse with respect to the asymetrical component of the primary current.

Printer and control circuit therefor

Abstract: A printer, comprising a printing element which, when in operating position, is placed in a magnetic field, and is connected to a secondary winding of a transformer. This transformer has two additional secondary windings and two primary windings which are connected to a circuit so arranged that after a start pulse, two current pulses of opposite directions are successively supplied to the transformer of which only the second pulse effects movement of the printing element. The two primary windings are each connected to an amplifier, each of which supplies one of the current pulses. The input of the circuit and the amplifiers are coupled in such a way that the start pulse controls one of the amplifiers which in turn, through the two additional secondary windings and a blocking circuit, controls the other amplifier to produce the second pulse. This magnetizing of the iron in the transformer first in one direction and then in the other enables a greater change of flux to be realized with a relatively weak magnetizing current.

Active transformers for off-hook sensing in telephone applications

Abstract: A novel transformer and circuit for off-hook sensing and isolation functions required in telephone applications are described. The transformer features a thin-film InSb Hall sensor integrated into the gap of a modified E -core transformer, connected in a feedback circuit. A prototype transformer with 1000 turn 800 mH 100 Ω windings was demonstrated to pass 10 mA voice signals in the presence of 50 mA dc off-hook signals nulled to less than 1 mA by feedback. The sputtering process used to deposit 1-μm thick InSb films on polished ferrite, fabrication of sensors, and the design and implementation of the transformer are also described.

Energy transfer from a low-voltage capacitor bank to a high inductance with the aid of an air pulse transformer

Abstract: The energy transfer from a capacitor bank to a high inductance was investigated. When the stored energy is greater than 30 kJ, direct coupling is impractical, and it is proposed to use a simple air pulse transformer for the purpose. The efficiency of the energy transfer depends strongly on the coupling constant k of the transformer. A reduced-scale pulse transformer with a coupling factor of k=0.95+or-0.01 was constructed; this transformer ensured a total energy transfer efficiency of more than 55%. Since the transformer is reliable and its construction is simple, it may be used with advantage in many systems.