Showing papers on "Isolation transformer published in 1974"

Response of Transformer Windings to System Transient Voltages

Abstract: Some recent transformer failures have been attributed to part-winding resonances excited by a form of switching surge voltage pulse which produced internal overvoltages. This paper takes a tutorial approach to relate a transformer winding to an equivalent electrical network which can exhibit resonant effects both at its terminals and internally. The relationship between the resonance phenomenon and pulse response is explained and illustrated with practical examples for the standard test waveforms. A proposed alternative switching surge waveform is examined for its effect on the internal response of transformer windings. The material presented should promote the understanding required for consideration of changes in standard test waveforms.

Transient Oscillations in Multiwinding Transformers

Abstract: A method of calculating voltage oscillations in transformer windings during impulse test is presented.

Switching regulator power supply

Abstract: A switching regulator power supply 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 for a predetermined time to provide energy storage followed by a predetermined time period of disconnect to provide energy transfer by way of transformer flyback The energy storage and energy transfer cycles are initiated by a novel, self-starting timing circuit The power parameters in at least one of a plurality of secondary windings are sensed and compared with a reference standard Any error, in the form of a pulse-width-modulated pulse is coupled back to a primary control for adjustment of the energy storage time period The coupling is done through a sealed opto-electronic coupler, this providing a DC coupling

Transformer coupled power transmitting and isolated switching circuit

Abstract: A transformer coupled power transmitting and isolated switching circuit is disclosed for use in an electrosurgical apparatus to transmit power from a power generator to a utilization instrument for enabling electrosurgery and to transmit mode information from the utilization instrument to the power generator for enabling control of the operational mode of the generator. The electrosurgical power generator is coupled to the utilization instrument through an isolating transformer. The isolating transformer is loaded in a preselected manner under the control of a logic circuit with the load on the isolating transformer then being sensed and the sensed loading information utilized to control the mode of operation of the power generator to assure that power generator operates in the desired mode for the electrosurgery function then required.

Electrical performance of a liquid helium‐cooled transformer

Abstract: The noise performance of an audio‐frequency transformer cooled in liquid helium and combined with a low‐noise amplifier is reported. It is found that the transformer, modified for operation at low temperatures, behaves nearly as a noiseless transformer for low source impedances. The minimum noise temperature of the transformer‐amplifier combination is 1.8 K for a 3 Ω source resistance. The bandwidth of the cooled transformer is similar to that obtained at room temperature.

Fast power ``crowbar'' system using a current transformer with extremely low leakage inductance

Abstract: A power crowbar system for fast θ‐pinch experiments is operated successfully. A current transformer with extremely low leakage inductance is used to reduce the effective impedance of series capacitor system. The leakage inductance of the transformer is reduced to 2 nH by employing a special arrangement of windings. It is demonstrated that a current of 40 kA, the rise time of which is 4 μsec, is maintained for 500 μsec.

A Phantom Burden for Current Transformer Calibration

Abstract: A technique is presented for applying a burden to a current transf ormer being calibrated in which the power and reactive volt-amperes are returned to the supply rather than being absorbed in a passive network. The transfer is accomplished either by the magnetic shield if a compensated current comparator is used as the ratio standard, or by an auxiliary current transformer in circuits which employ other standards. Electronic circuitry provides the necessary volt-amperes for exciting the magnetic shield of the current comparator or the auxiliary current transformer, and the current transformer being calibrated, to produce the desired power transfer. The circuit requirements are analyzed and equipment which can develop burdens with both in-phase and quadrature components up to 10 ohms, at secondary currents up to 10 amperes, and for a 0.6 percent accuracy class current transformer or better, is described. The burden setting, which is independent of current, may be made by in-phase and quadrature dials to an accuracy of about one percent of full scale.

Battery operated electroluminescent film identification device

Abstract: Apparatus containing a d.c. power source, a timing circuit, and a transformer to excite an electroluminescent material for use in a film identification device to imprint patient identification data on X-ray film. To preserve battery life the timing circuit will allow only enough electrical energy to be imparted to the transformer as is necessary to excite the lamp. Both the electrical energy coupled through the transformer and the energy stored in the transformer will be applied to the lamp to excite it.

False triggering protection for ground fault sensor

Abstract: A ground fault detector-interrupter, including a differential transformer for detecting the difference between currents in the hot and neutral conductors connecting a load to an a.c. source, is provided with a resistor shunting the differential transformer primary winding in series with the hot conductor. By shunting part of the current in the hot primary around the differential transformer, the transformer is effectively desensitized under high in-rush current conditions to protect against false triggering that would normally be caused by non-uniformity in the transformer windings and/or less than precise placement of transformer leads.

Measuring transformer arrangement for a high-voltage installation carrying several conductors

Abstract: A measuring transformer arrangement is provided for a fluid-insulated high-voltage installation with metal encapsulation carrying several conductors. The measuring transformer arrangement includes at least one conducting or semiconducting tube surrounding each conductor whereat at least one current transformer core with a system of secondary windings mounted on it is attached on the outside of the tube. The tubes are connected with each other and are attached to the metal encapsulation.

Instant play television receiver with constant voltage transformer

Abstract: A solid state 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. The single pole, single throw on-off switch of the receiver 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 with substantially reduces the voltage across the regulating transformer primary and drops the secondary voltages below operating levels for the television receiver. The filament transformer secondary winding supplies the tube filament with reduced power during standby operation.

Mounting assembly for a transformer and relay control device

Abstract: A simplified and cost reduced mounting plate and cover are provided for a transformer and relay normally used in the heating and cooling control industry. A mounting plate with an integral end bell for the transformer mounts the transformer and relay so that a second member can be placed over a portion of the transformer and the relay to form a complete housing or enclosure.

Power transformer having shields for shaping the electric field in the major insulation spaces

Abstract: A power transformer having at least one shield positioned in the insulation structure of the transformer and located between the high-voltage and the low-voltage windings. The shield includes a conducting member which shapes the electric field in the insulation structure in a manner which permits more efficient utilization of the insulating members in the insulation structure. The shield may be connected to an intermediate tap on the high-voltage winding in order to acquire a fixed potential thereon.

Stabilizing network for crt high-voltage power supply

Abstract: A high d-c voltage for the operation of a television picture tube is derived from the rectified output voltage of a transformer developed across a secondary winding thereof, this transformer having a primary winding periodically energized by the flyback stroke of an associated horizontal-sweep circuit. A part of the flyback current also passes an ancillary transformer winding in series with a resonant network normally tuned to the fifth harmonic of the fundamental frequency of the flyback pulse to level the output voltage as long as the transformer secondary is substantially open-circuited, i.e., in the absence of anode current generated by the beam; this secondary is connected to the input of a transistor generating a biasing current through a control winding electromagnetically coupled with the inductance of the resonant network so as to detune same in the presence of a substantial anode current, thereby increasing the primary current of the transformer to compensate for the added drain upon the high-voltage transformer output.

Dynamic Measurements During Short-Circuit Testing of Transformers Part I: Instrumentation and Testing

Abstract: The instrumentation methods and testing procedures utilized to obtain dynamic forces, displacements, pressures, and mechanical strains on a full-size 19.5 MVA three-phase, three-winding oil-filled power transformer is presented in this paper. Each phase of this transformer was constructed with different insulating materials and different clamping methods; one of these included an externally adjustable hydraulic clamping system. The data obtained on this transformer will add new and fundamental knowledge of the effects of winding prestress, clamping methods, insulating materials, and tap arrangements on the dynamic characteristics of large power transformers during short circuit. This first paper will form the foundation for the data presentation and analysis to be presented in later papers.

Instrument transformer with cone-shaped insulating layer

Abstract: An instrument transformer being applicable for a current transformer and/or a voltage transformer which is comprised of a coil for developing magnetic field related to a primary current, the Hall element for generating the voltage in response to the magnetic field developed by the coil, a shield pipe for supporting and enclosing the Hall element, and a cone shaped insulating layer being laid between the coil and the shield pipe, enclosing the shield pipe.

Traveling wave tube body current sensor

Abstract: The body current of a TWT (traveling wave tube) is measured by generating a voltage that is proportional to the difference between the cathode and collector currents of the TWT without materially affecting either by passing the cathode and collector currents through separate transformer windings, wound in opposition, on both a linear core transformer and a nonlinear core transformer with separate windings coupling each transformer to the other. A voltage pulse is introduced into another winding on the nonlinear transformer causing a current flow in the circuit coupling the two transformers, the voltage magnitude of which is proportional to the difference between the cathode and collector currents which is the body current.

Switching circuit utilizing a base storage characteristics of a transistor for use in a facsimile transceiver and the like

Abstract: A document/copy carrying drum of a facsimile transceiver is rotatably driven by a synchronous motor. The synchronous motor is connected as a load in series with a first transistor and a first power supply of one polarity. The synchronous motor is also connected in series with a second circuit and a second power supply of opposite polarity so as to apply DC voltages of opposite polarity during alternate conduction of the transistors. Conduction of the transistors is controlled by alternately applying a series of relatively low voltage pulses to the bases of the transistors through high frequency isolation transformers. The pulses are separated by a time interval less than the base storage time of the transistors so as to assure continuous conduction between the collector and emitter of a transistor while a series of pulses is applied to the base thereof.

Measuring transformer arrangement

Abstract: A measuring transformer arrangement for several high-voltage conductors disposed in a gas-filled tube includes current transformer units corresponding to respective ones of the highvoltage conductors. The current transformer units form a cohesive structural unit and each current transformer unit has at least one iron core of its own with a secondary winding system mounted thereon. Each iron core of the current transformer units is shielded with respect to high-voltage from the corresponding high-voltage conductor by a control electrode which is at or near ground potential.

Design of Imperfectly Coupled Power Transformers for DC to DC Conversion

Abstract: The equations required for analyzing the performance of imperfectly coupled transformers in dc-to-dc conversion applications are described. Results are shown for both the untuned and the tuned primary cases. Given the output power requirements and a reasonable set of limitations on the transformer parameters, the optimum transformer parameters can be detennined. An example is given of the optimization procedure used in designing the transcutaneous transformer for electric artificial heart applications.

Compact transformer with integral connector

Abstract: A compact transformer which may be used with a recharging circuit for portable electronic devices is illustrated having integral connector blades for mating with an AC power outlet, such as a wall socket. The transformer windings are wound on a standard coil bobbin having a central aperture. The connector blades pass through the central aperture and are clamped therein by the laminated core material of the transformer. An insulative laminate is used to divide the core into two sections in order to electrically isolate the two connector blades from each other. The resulting transformer may have rectifying components attached thereto and may be encapsulated for environmental protection.

Transformer with adjustable turns ratio

Abstract: The effective turns ratio of a transformer is modified by sampling the transformer primary current and injecting at least one vernier current proportional thereto into the secondary circuit of said transformer. The sampling is done by at least one vernier transformer which is arranged to respond to asymmetric mode excitation but to be transparent to symmetric mode currents.

Welding arc stabilization - using trigger pulse generator

Abstract: The stabilizer unit is fed by one phase, of the three phase supply to the welding transformer, using an interwinding screened isolating transformer whose secondary charges two trigger pulse capacitors via antiparallel diodes and limiting resistors. the discharge of the capacitors into the primary of a pulse transformer whose secondary is connected to the welding electrode and workpiece, in parallel with the main weld current feed is controlled by a pair of antiparallel thyristors triggered from the choke and filter circuit by that main feed.

A consideration on measurement of voltage callapse during chopping in chopped impulse test of transformer

Abstract: In the chopped impulse test of a transformer, a steep voltage collapse appears across the terminals of the transformer to be tested. This paper clarifies the wave shape of the voltage collapse during chopping and the requirements of a device for measuring the voltage collapse.