Showing papers on "Isolation transformer published in 1979"

DC-to-DC switching converter with zero input and output current ripple and integrated magnetics circuits

Abstract: An improved dc-to-dc converter is provided comprised of two inductances, an input inductance in series with the input source and an output inductance in series with the load, and between the two inductances, two storage capacitances in series with the two inductances. Switching means alternately connect the junction between the input inductance and the first series capacitance, and the junction between the second capacitance and output inductance, to a junction common to the source and load. A third inductance is connected between the junction of the two capacitances and the return current paths for the source and load. In one of the embodiments of the invention, all three inductances are combined on the same core thus comprising a single magnetic circuit with three windings. In another embodiment of the invention an isolation transformer is first used to replace the third inductance. Again, both input and output inductor and isolation transformer are merged into a single magnetic circuit with four windings. In any of the embodiments of the invention, a zero current ripple can be obtained at both the input and the output simultaneously by a proper design of the magnetic circuit. A new method of integrated magnetics design is then disclosed to improve performance of other converter structures by properly merging their magnetics components.

Electrostatics in Power Transformers

Abstract: In this paper, the streaming electrification in core type forced oil cooled power transformers is investigated, using a full-scale model transformer and various experimental models. It has been clarified that streaming electrification in transformers is influenced mainly by flow rate, oil temperature, surface conditions of insulating materials and characteristics of insulating oil. Electrostatic discharge occurs eventually when the amount of local charge exceeds a certain limit.

Driving system for an ultrasonic piezoelectric transducer

Abstract: A driving circuit for ultrasonic tools which uses a piezoelectric transducer to convert ultrasonic electric signals into ultrasonic mechanical vibrations including a voltage-controlled oscillator which produces an output signal at a frequency that is proportional to an input voltage, a power amplifier stage having its input coupled to the output of the voltage-controlled oscillator, the power amplifier stage including an output transformer which couples the output of the power amplifier stage to the piezoelectric transducer, the power output transformer further acting as both an insulating transformer and a boosting transformer for the driving circuit and a feedback transformer coupled in series with the secondary side of the output transformer and the piezoelectric transducer, the feedback transformer having a secondary side through which a current flows which is proportional to the current flowing through the piezoelectric transducer, a phase comparitor which detects the phase difference between two signals applied to two inputs of the phase comparitor, the two inputs being respectively coupled to the output signal of the voltage controlling oscillator and the secondary side of the feedback transformer and a low pass filter which blocks high frequency components to pass therethrough connected between an output of the phase comparitor and the input of the voltage controlled oscillator.

Bubble Formation in Power Transformer Windings at Overload Temperatures

Abstract: The radio influence voltage (RIV), discharge, and visual detection of gas bubbles from models simulating present standard loading practice appear to be the first tangible basis for reducing the maximum allowable hot-spot temperature in power transformer loading guides.

Powerline carrier control installation

Abstract: A powerline carrier control installation includes a control transmitter with an audio frequency output voltage, an isolation transformer, a coupling capacitor for parallel coupling to an a-c voltage network, and a device for suppressing a line frequency backward voltage. For coupling the audio frequency output voltage to the a-c voltage network, a resonant circuit tuned to the audio frequency is provided, the resonant circuit capacitance being supplied by the coupling capacitor and the resonant circuit inductance formed essentially by the main field inductance of the isolation transformer, eliminating the need for a separate coupling choke. A device, specifically the powerline carrier control transmitter itself, is equipped to deliver, in addition to the audio frequency output voltage, a line frequency compensating a-c voltage which has a low amplitude in comparison to the line a-c voltage in order to suppress the line frequency feedback transmitted from the network.

Start-up circuit for switch mode power supply

Abstract: A switch mode power supply for electronic circuits includes a rectifier for providing direct current from an alternating current line, a transformer connected to the rectifier, and an oscillating switching circuit connected in series with the transformer and the direct current source, operative to chop the direct current source to power the transformer. Power for starting up the oscillator, which requires a substantially lower voltage than that of the rectified source, is derived from a capacitor charged by the direct current source. A comparator senses the voltage on the capacitor and a reference voltage, and controls a transistor switch to discharge the capacitor into the switching circuit, when the proper voltage is attained, initiating the oscillator. A running switch mode power supply connected to a secondary of the transformer then provides power to the oscillator and turns off the transistor switch.

Variable reluctance electric motor systems

Abstract: A variable reluctance electric motor system including a variable reluctance motor having main windings (A, B, C, D) and auxiliary windings closely coupled to the main windings, a main storage battery for driving the motor terminals (10, 11) (that will be referred to as DV supply terminals), and a power converter circuit (Figure 2) for charging the battery from the D.V. supply, in which the motor is included in the power converter circuit to function as an isolating transformer to isolate the battery from the supply when on charge.

Means for automatically compensating DC magnetization in a transformer

Abstract: Apparatus for providing automatic compensation of direct current magnetization of a current transformer in an alternating current watthour meter utilizing a magnetic field sensor and electronic circuitry to keep the transformer operating in its linear region when a DC component is superimposed on an AC current being provided to the transformer.

A Three Megavolt Transformer for PFL Pulse Charging

Abstract: High voltage pulse transformer powered by low voltage capacitor banks have proven to be simple reliable systems for charging pulse forming transmission lines (PFL) up to the one megavolt range. A new transformer has been developed which will operate up to three megavolts in a PFL charging application. This transformer establishes the feasibility of multimegavolt operation and retains the features of compactness and high energy transfer efficiency that has been characteristic of lower voltage systems. This report includes a description of the physical features of the transformer, its electrical characteristics and a discussion of the operational results.

The Dynamic Response of Low Voltage, High Current, Disk type Transformer Windings to through Fault Loads

Abstract: In 1973, Louisiana Power & Light Company and New Orleans Public Service Inc. joined to sponsor research aimed at improving the core-form, power transformer design methods published in the literature. The specific improvement sought was in the mechanical design of continuous low voltage secondary windings of stepdown transformers to withstand the high, transitory currents caused by secondary short circuits.

Power supply for magnetron and the like loads

Abstract: A flyback-type high-frequency, high-voltage power supply for energizing a self-rectifying load, such as a magnetron microwave power generator for a microwave oven and the like. A switching device is connected in series with a primary winding of a transformer to provide pulses of energy to a self-resonant circuit at the transformer secondary winding. The self-resonant circuit includes the electrical capacitance of the load connected across the transformer secondary winding. The load conducts only for unipolarity excitation exceeding a minimum magnitude. A clamping diode is positioned in parallel with the switching device, at the transformer primary winding, to protect the switching device from reverse-voltage effects. A high-voltage rectifier is not required in this relatively light-weight power supply.

Control system for an electro-magnetic brake

Abstract: A control system for providing controllable direct current power for energizing an electromagnetic brake having an alternating current power supply and a power rectifier for converting and supplying direct current power to the brake. A power switch controls the amount of direct current power supplied to the brake. A control circuit controls the actuation of the power switch and includes a brake control actuating a variable output transformer. The output from the transformer is converted to a variable pulse width signal for actuating the power switch. Preferably, the transformer is a variable ratio transformer having a movable core connected to the operator's control. A battery charger and batteries may be connected to the ouput of the power rectifier for maintaining brake power in the event of alternating current line failure. Multiple transistor power switches connected to separate brake coils maintain a portion of brake power in the event of partial equipment failure. An oscillator provides a sine wave voltage to the transformer primary and the actuation of the operator's control provides a substantially linear output from the transformer secondary. Protective circuits such as an RC filter may be connected across the power rectifier to limit overshoot upon actuation and a rectifier is connected across the brake for current flow during the time the power switch is off.

Off-resonance transformer charging for 250-kV water blumlein

Abstract: An off-resonance transformer for charging a 250-kV Blumlein system provides a viable alternative to other charging schemes by permitting the use of conventional thyratrons. Such a transformer must have reliability, a reasonable voltage stepup, and a nonreversing primary current. This paper presents the analysis, design, and performance data for such a transformer. The strong interrelationship between transformer design and Blumlein requirements necessitates that Blumlein description and design criterion be briefly presented prior to transformer design such that transformer load requirements be defined.

Current Transformer Application for Power Switching Transistor Drive

Abstract: Current transformers present inherent advantages for driving power switching transistors over alternative driving methods. This paper presents advantages and design problems of current transformer drives in two applications: a) free running push-pull inverter b) switched mode regulator Each application is discussed with respect to: Driver circuit application Design problem analysis of 20 kHz current transformer Performance analysis Northern Telecom uses inverters and P.W.M. converters with current transformer drives designed by the author. They show excellent reliability, performance, and efficiency exceeding 90%.

Iron coreless instrument transformer system with air gap transformer - through whose primary flows current to be measured and which is decoupled from compensation transformer

Abstract: The air gap transformer (Tr1) is toroidal with a primary (W1) through which flows the current to be measured (Le). A compensation transformer Tr2) of identical design is magnetically decoupled from the current transformer whose secondary (W2) is in series with the compensation transformer secondary and a resistor (r1) thus forming a compensation circuit. The voltage drop at this resistor is supplied to a negative feedback amplifier (A1), at whose output (11) can be tapped a current (I3), proportional to the current to be measured. This current can be supplied as feedback magnitude to a control circuit including the compensation transformer primary (W3). This control current generates in the compensation transformer secondary (W4) a voltage (U4), opposing the current (I2) through the current transformer secondary.

Switching power supply having energy storage inductor in primary circuit of output transformer

Abstract: A switching power supply including a rectifier for rectifying input AC line power to provide a source of DC voltage, an output transformer having a primary winding for receiving power from the DC source and a plurality of secondary output windings for providing a plurality of regulated output voltages, an inductor coupled to the primary winding of the output transformer for returning stored energy to the source during switching dead times, a control circuit for monitoring the magnitude of the source voltage and for generating first and second switching control signals, the duty cycle of which is directly related to the magnitude of the source voltage, switching transistors for alternately completing oppositely directed current paths from the source through the transformer primary and inductor to ground, and diodes for creating a uni-directional current path to the source for energy stored in the inductor.

100:1 Step-Up Amplifier-Aided Two-Stage Current Transformer with Small Ratio Errors at 60 Hz

Abstract: An electronically aided 100:1 step-up two-stage toroidal current transformer is described which has very small ratio error. Two-stages of amplifier aiding are used. One stage reduces significantly the burden seen by the transformer while the other enables almost exact ampere-turn balance to be achieved between primary and secondary currents within the inner core of a two-stage arrangement. Practical operation of the circuit is described, together with analysis of circuit stability considerations at low and high frequencies. Measurement techniques are included and the effect of practical circuit performance upon the current ratio error is discussed.

Method of driving piezoelectric transformer

Abstract: PURPOSE: To stabilize the output of a piezoelectric transformer in a high voltage power supply using the transformer by the negative feedback of pulse width control type. CONSTITUTION: An oscillating transformer 7 is driven in push-pull state by a drive circuit 8 and transistors 9, 10 to thus drive a piezoelectric transformer 6. The drive current of the transformer 6 is detected by inserting a series resistor 16. The drive voltage is displaced at its phase at 90° with a capacitor 17 and a resistor 18 inserted across both ends of the transformer 7 to set the voltage in phase with the current. Thus, the current is converted to a voltage by a phase detector 15. Then, the frequency is counted at a voltage controlled oscillator 14. The sectified output voltage V 0 of the transformer 6 is compared by a comparator 11 with standard voltage E, and also compared with the voltage of the oscillator by a comparator 13. Thus, the pulse output corresponding to the error level is applied to the drive circuit 8. When the output voltage V 0 is lowered, the drive pulse width of the transformer 7 is increased to thereby raise the voltage of the fundamental component of the oscillated frequency at the secondary side of the transformer 7. Thus, the drive current of the transformer 6 is increased to thereby increase the output. Accordingly, the output of the transformer is stabilized with respect to the load variation. COPYRIGHT: (C)1980,JPO&Japio

Control of power semiconductors through center-tapped transformer with self-demagnetizing circuitry

Abstract: In order to control a power semiconductor which can be triggered into conduction by pulses of one polarity and quenched again by pulses of the opposite polarity, by transmitting such pulses via a transformer to the power semiconductor connected at the secondary side of the transformer, such a pulse is formed by turning on a first transistor connected between one pole of a voltage source and a tap which divides the primary winding of the transformer into two partial windings, and by selectively turning on either one of second and third transistors each connected to the ends of a respective partial winding, and such a pulse is terminated by switching off the first transistor, while maintaining on the selected second or third transistor in order to cause the demagnetization current of the transformer to flow through the selected transistor and through a Zener diode connected between the tap of the primary winding and the other pole of the voltage source, the anode side of the first Zener diode being connected to the tap of the primary winding.

An Electronic Ratio Error Set for Current Transformer Calibrations

Abstract: A direct-reading electronic ratio error set for current transformer calibrations is described. It is capable of generating direct and quadrature error currents from 1 ppm to 5 percent of transformer secondary currents up to 10 A. The uncertainty is less than one percent of the generated current. The set features electronic display of the direct and quadrature components with three digits each and is direct reading at 50, 60, and 400 Hz.

Vital voltage regulator and phase shift circuit arrangement

Abstract: The primary winding of a saturable transformer is coupled to an alternating current source by a series tuned filter network. The transformer secondary winding is coupled to a load network by a second series filter tuned to the source frequency to block harmonics generated by the saturation limiting action of the transformer, which occurs below the normal voltage level of the source and regulates the output voltage supplied to the load within predetermined limits over the source operating voltage range. The first filter is tuned at a predetermined level above the source frequency to cooperate with the equivalent inductance of the unsaturated transformer and output network to hold the secondary output in phase with the input signal at a low levels of the source voltage. The first filter further cooperates with the reduced equivalent inductance of the saturated transformer and output network to change the effective frequency tuning to shift the phase of the secondary output with respect to the input signal at normal source voltage levels.

Transformer differential safety systems

Abstract: A transformer differential safety system includes a plurality of active power measuring converter circuits (4), one for each phase winding of the transformer. An array of adding circuits (5) combine the outputs of these circuits with the output of a copper and iron loss calculating circuit (11) in such a manner as to generate an output signal related to the difference between the transformer input and output power. A comparison circuit (6) provides a tripping output when this output signal exceeds a set level.

Feeding bridge with d.c.-compensation for both directions of the feed current

Abstract: A bridge circuit comprising an isolation transformer having six primary windings which are connected so that the voice currents do and the supply currents do not generate, for either direction of current flow, a resulting flux in the core of the transformer. The bridge comprises two transistor circuits which prevent the voice currents from flowing through a supply source connected to the bridge and also balance the bridge circuit so that the influence of longitudinal noise signals which are produced in a transmission line connected to the bridge circuit are suppressed. The direction of the feed current in the transmission line can be reversed by means of the transistor circuits.

Regulated DC power supply circuits

Abstract: A regulated DC power supply circuit comprises first and second transformers (T1 and T2), a transistor (Q) and trigger means to periodically cause the transistor to conduct to supply DC current to the transformers. On application of such current, flux builds up in the core of the second transformer (T2) and a winding (P2) of the second transformer (T2) maintains conduction of the transistor (Q) until the core saturates, whereupon the flux reverses and drops in value, the transistor is switched off and collapse of the field in the first transformer dumps electrical energy into a rectifier circuit (58, 60) connected to the first transformer (T1) to produce a DC output voltage. A Zener diode (66) or the like connects the DC output voltage to a winding (P3) of the second transformer (T2) to control the value to which the flux in the core of the transformer drops to after saturation, thereby to control the time taken for saturation when the transistor (0) next conducts, and therefore the amount of energy dumped into the rectifier circuit (58,60), in a sense to stabilize the DC output voltage at a desired value.

Transformer Noise Abatement Using Tuned Sound Enclosure Panels

Abstract: This report covers work performed by the Allis-Chalmers Corporation (A-C) on transformer noise shells under contract to the Electric Power Research Institute (EPRI). The program is directed at reducing noise emitted from power transformers using a close-fitting, integrally-mounted noise shell technique. The noise shell consists of a series of panels attached to the tank by means of isolators. Sound absorptive materials are not required and reductions in excess of 20 dBA can be achieved by proper design of the panels. The program is divided into two phases 1) Phase 1 for development, and 2) Phase 2 for commercial production design and demonstration. The approach requires no state-of-the-art breakthroughs. However, the concept is considered new and as a result the primary objectives of Phase 1 of the program are to establish if it is practical and economical. The follow-on Phase 2 would take the concepts into full product design. This document reports the work performed under two related contracts, covering a period from October 1, 1975 through September 30, 1978.

Device for transforming an alternating current to a direct current, and application thereof to the charging of storage batteries

Abstract: A device for transforming an alternating current to a direct current particularly adapted for charging of storage batteries, the device comprising a transformer, a rectifier element in series with the secondary of the transformer, a semiconductor rectifier bridge having an alternating current diagonal in series with the primary of the transformer and a direct current diagonal connected to the output of the rectifier element for diverting and rectifying part of the alternating current and delivering it in the same direction as the secondary current.

Self-controlled push=pull inverter - has transmission device with two transformers,each with two windings and transistor control in main winding

Abstract: The inverter is esp. for an a.c. voltage transformer, and has two push-pull transistors. A transmission device is supplied by the transistors, and possibly a starting curcuit. The transmission device consists of a main and a control winding, both in two parts, and a load winding. The transmission device (7) is divided into a main (12) and a control (13) transformer. The main transformer (12) has the main (9) and the load (11) winding, and the control transformer (13) the control (10) and a feed-back (14) winding, the latter in series with the main transformer (12) load winding (11). The control transformer becomes saturated before the main transformer.

Hot spot detector helps predict transformer life

Abstract: A compact device has been developed that can be safely imbedded in transformer winding to give direct and accurate readings of the transformer's hottest spot. This device, which has been model tested, will have economical and safety benefits and will provide information on loading and thermal stress that could lead to design improvements. The Westinghouse-designed device is a temperature-sensitive mechanical resonator which is excited through fiber waveguides and then translates the acoustic signal to a temperature reading. It combines accuracy, resolution, reliability, and safety. Comparison tests are summarized, but full-sized transformer use with varying load currents is still needed.

Blood circulation stimulation appts. - has electrically heated foot-bath combined with electrical pulses at low voltage supplied by mains transformer

Abstract: In order to alleviate circulatory disorders, this simple and safe apparatus has been designed to provide a footbath with regulated water temperature and which also provides electrical stimulation. A heating element (2) covered by a plate (3) is placed loosely in a footbath (1). A low voltage supply is provided by an isolating transformer (5) and current regulator (8). In the transformer housing is included an electrical pulse generator (9) with one lead connected to the footplate (3) and another terminating in an electrode (10).