Showing papers on "Isolation transformer published in 1970"

Electrically isolated signal path means for a physiological monitor

Abstract: A circuit for providing electrical isolation between a patient and physiological monitoring apparatus comprising an amplifier, having applied to the input thereof a physiological signal from the patient, and a first circuit branch including an isolation transformer connected between a modulator and a demodulator for connecting a d.c. voltage source of relatively low magnitude to the amplifier. Connected to the amplifier output is a second circuit branch comprising an isolation transformer connected between a modulator and a demodulator, and the output of the demodulator is coupled to the input of physiological monitoring apparatus. Each of the isolation transformers includes an extremely low capacitance between the primary and secondary windings thereof to present an extremely high reactance to low frequency, including line frequency, alternating current and each is capable of withstanding relatively high voltages without breakdown.

Pulse width modulated voltage regulator

Abstract: A regulated power supply of the driven power inverter type. The widths of the driver pulses are controlled by a modulation waveform which varies in accordance with variations in the regulated output from the reference potential. The driver transistors are simultaneously turned on during the dwell periods of the modulation waveform to dissipate current in the windings of the interstage transformer and switch off the power transistors. The transformer is a current transformer which includes positive feedback windings on the secondary side. The turns ratio of the positive feedback winding and the secondary current winding associated with each power transistor is set equal to the inverse current gain of the transistor to ensure a fixed gain when the transistor is in saturation. A regulated low current voltage is applied to the midpoint of the primary side of the transformer to provide low power switching of the power transistors. A transistor switch connected from the regulator output to the primary side of the transformer removes the driver pulses from the inverter in the event of a component failure.

Rotary transformer design

Abstract: A high power rotary transformer (1 k W ) was considered as a replacement for slip-rings in a future satellite. A study was done to determine the best electrical design taking into account mechanical limitations while maximizing efficiency. Ferrite was used in a configuration which can be ground by any good machine shop. A design procedure is described which provides the engineer with a rough estimate of size and weight of a near optimum transformer given the power level, frequency of operation, and material to be used. The electrical circuit used should be considered during the transformer design. In the widely used voltage controlled push-pull square wave converter there is the problem of transistor storage and fall time. Usually one transistor is turned on before the other is off. The latter transistor then traverses through a high power dissipation region, the peak power being twice the input voltage times input current. Transistors picked for low saturation voltage are usually slower devices aggravating the turn-off dissipation problem. An operating procedure which minimizes these turn-off losses and prevents excursion through high instantaneous dissipation regions has been devised. It allowed the construction of a 1000 watt converter (dc-dc rotary transformer) which runs at a 92% efficiency (including rectifier losses) with just a total of 10 watts of transistor dissipation. Operating levels are 24 volts, 50 amps in and out.

Related power supply

Abstract: A solid-state high-voltage regulation circuit for devices such as television receivers which incorporate a flyback transformer. Voltage changes across the transformer secondary winding are compared to a stable reference, and any difference is amplified and applied to control the flow of current to the transformer primary coil. The output voltage is thus maintained essentially constant.

Low noise alternating current amplifier and compensator to reduce stimulus artefact

Abstract: Action potentials of sensory nerve evoked by stimuli of 70 mA may be as small as 0·05 μV. They are buried in noise and require electronic averaging. The signal-to-noise ratio can be improved by the use of an input transformer and by limiting the frequency range (Buchthal andRosenfalck, 1966). When recording near the point of stimulation the amplitude of the artefact exceeds that of the sensory potential by a factor of 104 and prevents its recording because of the pulse distortion caused by the limited frequency range. This was diminished by decreasing the lower limiting frequency of the input transformer by means of positive feedback. To diminish the pulse distortion in the high-pass and low-pass filter of the output stage, the filter elements were placed in the feed-back loop of an amplifier with high closed loop gain. The small tail of the stimulus artefact arising mainly from the transmission through the isolating transformer in the output of the stimulator was reduced by compensation with a pulse of the same shape and amplitude but of opposite sign.

Voltage regulator with zero current static switching between taps for a regulator transformer

Abstract: An autotransformer is connected to an unregulated voltage source, and serves as a supply transformer for a load. Interposed between this supply transformer and the load is the secondary winding of a regulating transformer, whose primary winding may be selectively coupled between various taps on the supply autotransformer winding. The primary winding of the regulating transformer is coupled to the desired points on the autotransformer winding by means of semiconductor switches, actuated when the system current waveform approaches zero.

Switching voltage and current regulator controller

Abstract: A switching voltage and current regulator controller having an isolation transformer coupling a supply voltage to a load with an isolation amplifier in a feedback loop to deliver error information from the secondary back to the primary while maintaining the required primary-secondary isolation, the error information being proportional to the pulse width in the pulse train transferred through the coupling transformer.

Electrical protective circuit

Abstract: A protective circuit for an isolated load circuit utilizing an isolation transformer having a primary winding connected to an associated source of power and a secondary winding connected to a load by a pair of load conductors which includes fault condition responsive means, a normally inoperative control circuit having a normally open electrical valve and a relay connected to the source of electrical power by an auxiliary transformer with an auxiliary circuit connected to the control circuit and to the load conductors for closing the valve at a predetermined voltage to operatively condition the control circuit upon the presence of a ground fault on one of the load conductors to energize the relay and actuate the fault condition responsive means.

Terminal device for piezoelectric ceramic transformer

Abstract: A terminal device for a piezoelectric ceramic transformer of the plate-type consists of a rectangular ring made of rubber-elastic high-molecular material has two metallic members. The metallic members are mounted at opposite portions of the ring so as to contact respective input electrodes of the transformer when the terminal device is attached to the input section of the transformer. Input leads for the transformer will be connected to the respective metallic members serving as interconnection between the input electrodes and input leads. A terminal device for the output of the ceramic transformer is attached around the output section of the transformer so that the output can be taken out from any point of the output section.

High-voltage piezoelectric transformer housed with diodes

Abstract: A support structure for a piezoelectric transformer of the kind operable in accordance with the lambda -mode, which supports the piezoelectric transformer at the node of minimum displacement of the drive section of the transformer and is an electrical conductor so that it serves also as a lead wire. An assembly including the piezoelectric transformer, the support structure and a rectifier element is housed in a casing or enclosed in an envelope made vacuous or filled with an insulating gas so that it is usable as a high-voltage generator for television receivers.

Transformer termination for metal-enclosed, compressed-gas-insulated electrical conductors

Abstract: The grounded enclosure tube of the compressed-gas-insulated electrical conductor is attached to the metal wall of a power transformer tank and the energized conductor tube extends into the interior of the transformer tank wherein it is supported and insulated from the tank wall to provide a simple and inexpensive connection between metal enclosed switchgear, for example, and power transformers in a high-voltage electrical substation.

Feasibility of a power transformer with superconducting windings

Abstract: Although only 0.2% of the total power of a large generator transformer is accounted for by I2R losses, the capitalised value of this power dissipation is about half the price of an 800 MVA transformer. Superconducting windings with no power losses are therefore a potentially attractive substitute for existing copper windings. However, existing superconductors have a.c. losses which both reduce the additional capital sum that may be spent and increase the size and cost of the refrigerator. There is virtually no net saving when the cost additional materials is added to that of the refrigerator. Variations in the size and shap of the superconducting transformer, including an air-cored toroid, probably do not give any worthwhile advantage over a conventional transformer, although, with existing superconductors, the economically most competitive design is significantly larger than its conventional counterpart. It is probable that a straightforward niobium-on-copper winding would not be able to take a short-circuit fault and the immediately ready for normal use. Either a protective system using a switched-in separate copper winding or one using a type 2 superconductor might allow fault conditions to be withstood. No deep study has been made of either the electrical insulation or mechanical loads, both of which will present difficulties. The prospects for a viable superconducting transformer would be much brighter if a low-loss superconductor were developed having running a.c. losses not much greater than 0.1 W m −2 at Js = 110A mm−1 and, under fault conditions, less than 500 Wm−2 at 800 A mm−1.

Pulse transformer for firing thyristors

Abstract: An improved structure of a pulse transformer for simultaneously firing all the gates of a multiplicity of series-connected or series- and parallel-connected thyristors as is the case with a converter in dc transmission equipment, having a greater insulation strength and a good resistivity to external shocks. Specifically, since the converter used at high tension renders the line voltage of each thyristor higher, a molded insulating cylinder is disposed between a primary conductor and secondary conductor units of the transformer, whereby potential distributions between the secondary transformer units and the insulating cylinder and between the secondary transformer units adjacent to one another can be improved by providing conductive layers embedded in the insulating cylinder, and the pulse transformer can be made of a dry tape and small in size.

Underground electrical conductor housing for accommodating a transformer

Abstract: A flush-mounted receptacle is provided for electrical connections for use in the ground and for accommodation of a transformer with a protective mounting for the transformer for preventing access of internal condensation and for dissipation of heat released by the transformer

Starting controller for electric motor

Abstract: A starting controller is provided for electric motors of the split-phase type. This controller incorporates an electrical switching circuit utilizing a bi-directional, solid-state switching device as the element which effects the switch function. The circuit elements and components are incorporated in a mechanical structure having an electrical current transformer provided with a core that also forms a heat sink for the solidstate switching device. The core thus mechanically supports both the switching device and the transformer windings, performing a heat dissipation function as well as forming a part of the magnetic circuit for the transformer controlling operation of the solid-state switching device. All components including the transformer core, are embedded in a dielectric potting compound within an outer iron core shell forming the remainder of the magnetic circuit for the transformer.

Piezoelectric transformer circuits

Abstract: In a piezoelectric transformer circuit wherein a high voltage is produced at the output electrode of the piezoelectric transformer by applying a driving voltage of a frequency equal or close to the resonance frequency of the piezoelectric transformer across the driving electrodes thereof, a DC voltage is impressed upon the driving electrode to vary the resonance frequency to regulate the output voltage characteristics.

Polyphase transformer device whose taps are changeable when loaded

Abstract: A polyphase regulating transformer device has a main transformer, a tertiary winding in the main transformer and a series transformer with its secondary winding connected in series with the output of the main transformer. The tertiary winding is connected to excite the primary of the series transformer, and is itself composed of a fixed winding section and a tapped winding section both being connected in series at a neutral point through a tap changer; the primary phase windings of the series transformer are not provided with any interphase connections and are insulated from one another. A condenser bank is connected for power factor improvement across terminals of the fixed winding section of the tertiary.

Differential ground fault protection system

Abstract: A ground fault protection system using a differential current transformer. So that an inadvertent low impedance ground of the grounded neutral conductor on the load side of a differential transformer will cause a tripping potential to be developed across the secondary winding of the differential transformer, a resistor is connected across the load conductors at the transformer.

Electrical transformer apparatus

Abstract: Electrical transformer apparatus particularly well suited for use in resistance welding equipment and employing two movable welding electrodes which together with the work piece form a single loop secondary winding in a magnetic transformer. The electrodes are translated longitudinally with respect to the transformer and with respect to each other by means of a fluid operated ram.

Transformer-coupling circuit

Abstract: An electrical circuit for coupling flashing light equipment to the series lighting circuit of an airport runway so as to obtain power for the operation of the flashing light. The circuit utilizes a series lighting ferro-resonant autotransformer of suitable power rating and having three windings to provide the desired power transfer.

Surge current limiting circuitry for direct current to direct current chopper inverters

Abstract: Surge current limiting circuitry for direct current to direct current inverters and the like of the type in which switching of transistors to reverse flux in a center-tapped output transformer is achieved by the use of a saturable core transformer. Surge currents in the saturable core transformer, as it saturates, are limited by means of switching transistors which switch the transformer drive currents to high impedance paths when the transformer saturates.

Alternate Low-Frequency Dielectric Tests of Delta Transformer Windings

Abstract: Current test procedures unduly overstress the midpoint of delta transformer windings during low- frequency dielectric testing. A revision to the USAS Transformer Standards (1) has been proposed to allow alternate test procedures to correct this problem and to allow possible economies in the design and testing of such delta winding transformers. This paper has been requested by the IEEE Working Group to explain the proposed revisions.

Resonance suppressing method and apparatus

Abstract: Resonance effects otherwise possibly occuring upon a change in energization of an unloaded power transformer having leads connected in a main alternating current electrical circuit are suppressed through the temporary connection of a resonance suppressing impedance between a lead of the transformer and an electrical ground, with such electrical connection being maintained only through a change in the state of energization of the unloaded transformer.