Showing papers on "Isolation transformer published in 1972"

Electric shock hazard

Abstract: A long-standing expert on electric-shock hazards summarizes the studies that determined the effective body impedance under varying conditions. He describes perception currents, reaction currents, let-go currents, and fibrillating currents. Turning to means for reducing low-voltage (120-240-volt) hazards, double insulation, shock limitation, isolation transformers, and the use of either high frequency or direct current are discussed for various environments. Macroshock is always a hazard in the home, in industry, and in the hospital. But the extreme vulnerability to microshock of patients with cardiac catheters, for example, requires special precautions in intensive-care and coronary-care units. Equipment such as the ground-fault interrupter (GFI) and a special isolation transformer are cited.

Ferroresonance in a Transformer Switched with an EHV Line

Abstract: One transformer of a 1000-MVA 525/241.5-kV 60-Hz Y-connected bank of autotransformers, left connected to a 19-mi (30.5-km) 525-kV line but otherwise disconnected from the power system, was overheated after operating for nine minutes in ferroresonance sustained by capacitive coupling to a parallel, energized, 525-kV line. It was later untanked, tested and inspected, and no damage was found. However, to prevent recurrence of ferroresonance, the bank was modified to permit a set of existing 34.5-kV windings to be connected in delta. In similar situations where a Y-connected bank without tertiary windings is switched together with a 525-kV line paralleled by another 525-kV line, it was decided to disconnect the transformer from the line promptly after each de-energization of the transformer.

Failsafe multiple transformer circuit configuration

Abstract: A failsafe multiple transformer circuit configuration, useful in providing power to electrical loads is disclosed A circuit configuration for applying power to direct current loads includes a plurality of transformer circuits connected in parallel Each transformer circuit includes a diode bridge rectifier circuit having the input terminals thereof connected across a secondary coil and the output terminals thereof mutually coupled in parallel with the output terminals of all other transformer circuits Equalizing reactors are connected in series with the secondary coils to compensate for voltage imbalances that may be developed in the respective transformer circuits A direct current load may be connected across the mutually coupled output terminals of the respective transformer circuits Alternating current loads are accommodated by a plurality of parallel coupled transformer circuits each including a transformer having a pair of secondary coils The respective secondary coils are parallel connected in two sets, one set for each half cycle A diode rectifier is connected in series with each secondary coil and a silicon-controlled rectifier (SCR), associated with each set of secondary coils, is serially connected with an alternating current load Equalizing reactors are employed in both sets of secondary coil circuits in the same manner as they were employed in the direct current configuration

Transformer apparatus and monitoring system

Abstract: A remote control system for transformers which monitors the critical parameters of transformer operation. Current transformers are coupled to currents flowing in primary and secondary windings of the transformer. A switch is connected in the circuit of the primary winding and a temperature sensing means is positioned within the structure of the core and coil assembly of the transformer. Signals from the current transformers and the temperature sensing means are transmitted to a remote monitor. The monitor compares the transformer secondary current and the temperature with reference values and compares the primary and secondary current and turns ratios for equivalence. When the comparisons are not acceptable according to a predetermined program, a disconnect signal is originated by the monitor to open the switch and deenergize the transformer.

Protection of transformers

Abstract: A system for the protection of electrical power transformers in the event of a fault occurring in which measurements of both the differential current and the voltage at the terminals of one of the windings of the transformer are utilised to provide a tripping signal to disconnect the transformer in the event of a fault occurring. The system distinguishes between a fault and a magnetising inrush situation by detecting saturation of the transformer core and operates faster than protective devices utilising a measurement of differential current only.

Motor operated bed having low leakage current

Abstract: A motor operated adjustable hospital bed having a mattress supporting frame pivotally mounted on a lower supporting frame. The mattress supporting frame is pivoted with respect to the lower supporting frame by an actuating means which is driven by an electric motor mounted on the lower supporting frame. An on/off electrical control controls the electrical power supplied to the motor. A power supply means supplies power to the electrical control which power supply means includes a transformer having isolated primary and secondary insulated windings, the electrostatic coupling between the primary and secondary windings being less than 241 picofarads. Supplementary electrical insulation is disposed on the transformer and the electrically insulated transformer is mounted on the lower supporting frame. The primary winding of the transformer is connected to a source of alternating current power and the secondary winding is connected to the electrical control.

Electrical power inverter with sinusoidal output

Abstract: An improved inverter circuit developing sinusoidal output signals in response to dc input signals without the use of filters external to the inverter circuit. The inverter includes a commutator transformer and resonant circuit in the primary side of a load transformer. Periodic inverting of the dc signal is accomplished using switching transistors and a feedback transformer coupled to the commutator transformer and resonant circuit through the primary of the load transformer.

High voltage generating device having an operational monitoring device

Abstract: A high voltage generating device consisting of a ceramic transformer and a drive power source, said ceramic transformer being composed of a drive portion and electrical generating portion integral therewith and said drive power source being adapted to supply a drive voltage to said drive portion. This high voltage generating device is provided with a novel operational monitoring device which is adapted to operate for identifying the normal operation of said ceramic transformer by using the voltage induced to an electrical receiving unit located in the close vicinity of said electrical generating portion of said transformer.

Current transformer connection control

Abstract: An apparatus for detecting specific conditions in a current transformer during the establishment of a short circuit current and anticipating saturation to prevent the connection of the transformer output to a utilization device. The apparatus include a voltage divider connected to the secondary winding and an integrater connected to integrate a portion of the voltage developed across the divider. The result of the integration is monitored as to direction and magnitude and an output signal is generated which is indicative of both direction and whether or not the magnitude has exceeded a predetermined threshold. This value is used as being representative of the generation of flux in the magnetic circuit. Simultaneously, the sign of the derivative of the current is determined. The signals thus generated are coupled to a circuit which performs the logical decision S A.B + A.C. A signal resulting from this decision inhibits connection of the transformer to the utilization device.

Method of winding a transformer

Abstract: A method of winding a transformer is disclosed, such a transformer being particularly useful as an isolating transformer for use between a television receiver and an image recording apparatus. The primary and secondary coils are wound one over the other with insulating intermediate layers, at least one primary layer and at least one secondary layer being alternately wound on to a winding mandril. An intermediate layer of insulating material is then applied as a cover and an auxiliary winding is wound adjacent to transformer being wound with the wire of a previous layer of turns during the winding of the next layer onto said previous layer. The wire of the auxiliary winding is used for winding a subsequent layer of turns onto the transformer.

Inverting bridge circuit

Abstract: A power inverting bridge circuit for a highly regulated direct current power supply to provide high efficiency and increased current handling capacity. The inverting bridge circuit includes at least one pair of series-connected gate elements, preferably power transistors, connected across the leads of a DC power source and having a series-connection point between the gate elements defining one bridge output point. An alternating current path is provided between each power source lead and a second bridge output point. The primary coil of a transformer is connected across the two bridge output points. The gate elements are controlled by a high frequency square-wave generator to produce an alternating current in the primary coil of the transformer. A high frequency alternating current signal is produced in the transformer secondary coil which is easily rectified and filtered to produce the highly regulated output. An anti-crossconduction transformer ensures that each gate element ceases conducting before the other gate element is permitted to conduct. The anti-crossconductiontransformer includes feedback from the transformer to the gate elements anti-crossconduction transformer ensure the gates are not overdriven by the squarewave generator. In addition, anti-crossconduction transformers are included to prevent the switching gate elements from conducting at the same time. For regulating the power supply output, a DC source boosting circuit is provided to raise the DC voltage to the inverting bridge circuit as the output voltage varies due to load or AC power source fluctuations.

Partial Discharges Triggered by Switching Surge in Power Transformers

Abstract: Discharge phenomena resulting from switching impulses superimposed on ac voltages have been studied on typical transformer insulation configurations and on full-scale winding A modified test procedure for power transformers is proposed on the basis of experimental ental results

Direct current power supply for electrical appliances

Abstract: An arrangement in which a center-tapped transformer supplies power for operating a DC motor, as well as charging a battery. Alternating current from the secondary winding of the transformer is rectified through one diode mounted within the transformer unit, and a second diode mounted within the unit carrying the motor. The transformer unit is connected with a three wire plug to the load means, for example, a motor or appliance unit. When the transformer unit is not connected to the applicance unit, the battery operates the motor.

Automatic degaussing in a television receiver with constant voltage transformer

Abstract: A solid state color television receiver incorporates a voltage regulating transformer having a filament winding supplying substantially constant operating voltage to the picture tube filament for prolonging picture tube life. Instant play operation is achieved by providing a filament transformer having a high impedance primary winding, connectable in series with the input of the regulating transformer and a secondary winding connected in series with the regulating transformer filament winding. Automatic degaussing of the picture tube is accomplished with a thermal element each time the receiver is switched on from a ''''cold start'''' with a degaussing circuit coupled across the transformer input. The receiver single pole, single throw on-off switch is connected across the primary winding of the filament transformer. When the switch is open, the regulating transformer input and the primary of the filament transformer are in series which substantially reduces the voltage across the regulating transformer input and drops its secondary voltages below operating levels for the television receiver. The filament transformer secondary winding supplies the tube filament with reduced power during standby operation and is ''''poled'''' on the transformer core to generate flux opposing that normally resulting from primary energization, reducing residual current in the degaussing coil and allowing the thermal element to cool.

Transformer coupled power switch demodulator

Abstract: A power switch demodulator comprising a pair of power transistors having their collector electrodes connected together and to a source of DC voltage and their emitter electrodes connected together and to a load. A transformer comprising a primary winding and two secondary windings controls the conduction of the two power transistors to demodulate a pulse width modulated drive signal applied to the primary of the transformer.

Isolated two wire signal transmitter

Abstract: There is disclosed a process variable signal transmitter system which features a two-wire transmission line yet provides conductive isolation between the transmitter, the power source and the utilization device. The transmitter is powered from a power supply link which is transformer coupled to the power source. The power supply link includes a current transformer to couple a modulated data signal to an output circuit.

Pulse transformer for driving thyristors

Abstract: In a pulse transformer used to drive thyristors two metal shields are provided to reduce undesirable displacement currents and other interference currents. The two overlapping metal shields, which are separated from each other, are arranged between the primary and secondary windings of the pulse transformer. One shield is connected with the cathode of the driven thyristor and the other is connected with chassis ground or the primary potential of the pulse transformer.

Transformer-coupled power converter sampling system

Abstract: A transformer coupled DC-DC converter wherein the regulation of the output voltage is achieved by sampling the voltage across the transformer primary winding during a particular interval of the cycle. This sampling is achieved by the use of a field effect transistor that is gated on at a time just prior to the time the transformer field collapses. This sample voltage is held by a charged capacitor and used to control a blocking oscillator.

Today's Transformer Insulation Systems

Abstract: Insulation system integrity is probably the most important factor in satisfactory transformer performance; changes and improvements in transformer insulation systems take place continuously. Insulation systems are described, as they are currently constituted in oil immersed, askarel insulated, dry type, gas insulated, and encapsulated power transformers. Since transformer life is directly related to the insulation system and its time-temperature characteristics, the performance of the complete system, rather than that of individual components, is stressed.

Potential-current transformer device

Abstract: The line potential and current measuring device consists of a standard or toroidal bushing current transformer, a desired number of cascaded current transformers connected in parallel with a series of precision or non-precision type grading impedance devices such as resistors, capacitors or the like alone or in conjunction with a low-loss potential transformer. This supplies electrical outputs which make the device suitable for accurately checking line potential and current on an indicating or recording instrument.

Power supply for electronic circuits at high-voltage potential

Abstract: A power supply apparatus supplies power from a low-voltage potential to an electronic circuit at a high-voltage potential such as an electronic circuit for detecting the current in high-voltage conductors and the like. The electronic circuit is connected to an associated transformer for receiving electric energy. The apparatus includes a power oscillator connected to the low-voltage potential which in turn has an output transformer. A current path is provided for conducting electric power from the output transformer of the oscillator at low-voltage potential to the associated transformer connected to the electronic circuit at high-voltage potential. A power source means supplies electric power to the power oscillator independently of the value of the electrical energy at the high-voltage potential.

Flexible snake-like string of components encased in tubular sheath immersed in oil

Abstract: A high voltage accelerator power supply for providing a substantial current flow at a high D.C. voltage level including a step-up transformer mounted on an upright insulating frame at an intermediate level approximately midway between bottom and top of the power supply with the transformer being horizontally positioned and corona rings encircling the upper and lower edges of its core. One capacitor is below the level of the transformer core and another is above that level in a voltage-doubling arrangement while the core is electrically connected to a junction intermediate the two capacitors to be at an intermediate voltage level. A modular, flexible snake-like electrical device containing a plurality of series-connected rectifier cartridges positioned end-to-end, or similar components, enclosed within a plastic sheath enables connection with substantially uniform voltage stress distribution between a low voltage and a high voltage terminal by conveniently arranging the device in a helical or snake-like path. An isolation transformer system includes first and second widely separated cores one at ground potential and the other at the high D.C. output voltage of the supply, with an endless loop coupling winding at intermediate D.C. level and encased in a heavy insulation covering wound a few turns on each core.

Advantages of symmetrical isolation transformers in the reduction of patient hazards

Abstract: A brief outline is given of the various advantages and disadvantages of using isolation transformers in conjunction with equipment connection to patients. Particular attention will be paid to the use of symmetrical isolation transformers.

Transformer coupled signal power feedback circuit

Abstract: An alternating signal is transformer coupled to an input circuit with rectification to provide an isolated source of potential without the use of a power supply.

Inverter power supply employing series connected multi-transistor switches

Abstract: The disclosure describes an inverter circuit which may be used as a power supply. The circuit includes an even number plurality of transistors connected in series with a source of potential connected to the mid-point of the series arrangement. Each of the transistors has a secondary transformer winding connected across its base and emitter which is coupled to a primary transformer driven by an input signal source. The secondary transformer windings are connected through capacitors to a common point, for example, one end of a DC power supply. A resistor is connected across the emitter and collector of each transistor for uniform static voltage distribution and the transistors are connected in series by separate ones of a set primary output transformer windings connected between each transistor. A ''''poled RC'''' circuit including a diode, a capacitor and a resistor is connected across each transistor for dynamic voltage distribution. A secondary output transformer winding is also included across which an output voltage is produced which in the preferred embodiment may be a square wave voltage.

The multi terminal active transformer

Abstract: A method is presented for realizing an active multiterminal transformer which can then be used to produce a multiport transformer. This technique overcomes previously encountered restrictions and permits replacement of the floating transformer used in conventional network synthesis

Number glow tubes having transformer energizing circuits

Abstract: Apparatus is provided for generating electrode voltage for a number tube utilizing a center-tapped transformer to transmit pulses to a number tube anode. The transformer primary is center-tapped and supplied with opposing pulse potentials at the outer ends through non-linear resistors at a time corresponding to the appearance of voltage on a selected cathode electrode. A d.c. bias potential is connected to the tube anode to complement the pulse voltage of the transformer. The pulses are derived from a ring counter.