Showing papers on "Isolation transformer published in 1985"

Transformer Saturation Effects on EHV System Overvoltages

Abstract: Transformer saturation affects system over-voltages caused by transformer energization, fault application and clearing, and load rejection. Only some of these effects are desirable. The paper presents an analysis of such effects supported by results obtained on a typical long EHV transmission system by means of a power system simulator. An analysis of harmonic currents generated by a saturated transformer is also presented as a contribution to a better understanding of the phenomena considered.

Harmonic-resonant power supply

Abstract: A switching inverter power supply has a harmonic semi-resonant circuit associated with an isolation transformer for reducing electromagnetic interference. Fixed-frequency operation with pulse width modulation for regulation is accompanied by controlled current rise and fall times in the transformer primary. The semi-resonant circuit comprises an inductor in series with the transformer primary and a capacitor in parallel with the transformer secondary, transformer leakage inductance being included in the resonance. In one version, the resonant frequency can be set from about the fifth to about the twentieth harmonic of the fixed switching frequency for reducing peak switching currents.

Electromagnetic pulse isolation transformer

Abstract: An isolation transformer for connection between a source of alternating current power and electrical components, the operation of which components is affected by voltage excursions occasioned by electromagnetic pulses. The transformer includes a ferromagnetic core including first and second ends and at least two legs extending between the ends and defining therewith at least one window in the core. Also included are a primary coil surrounding a first portion of the core and extending through a window in the core, and a secondary coil, spaced from the primary, surrounding a second portion of the core and extending through a window in the core. A metallic isolation shield is positioned between the coils with the shield having core apertures for receiving components of the core so that the shield passes through each window of the core. A first metallic housing is mounted on the shield and has an opening for receiving the primary coil and the portion of the core on the primary coil side of the shield. An electrically conductive foil is wrapped about and insulated from the wires in the primary coil and electrically connected to the housing so that the housing, the shield and the foil form a Faraday cage. The primary coil has leads passing through the foil and outside the housing with the shield extending beyond the housing to form a mounting flange for the transformer.

Single-ended dc-to-dc converter with lossless switching

Abstract: The leakage inductance of the isolation transformer of a single-ended DC-to-DC converter resonates with a resonant capacitor connected in series with the transformer secondary to provide substantially zero current in the switching transistor during turn-on and turn-off The overall transistor current stress is low since it is bounded by the sum of average input current and average output current These factors allow the converter to be operated at high frequencies for improved performance

Inductive transmission of power and data

Abstract: The application relates to the inductive transmission of power and data, in which a supply voltage after rectification (1) is transmitted via an inverter (2) and a transformer (U) for supporting a battery (8) and switching signals in both directions. This transmission device is preferably intended for pipelines composed of pipe sections. For further simplification of known transmission devices each pipe head is designed as a transformer into which a coil (26) is sunk, and the pipe (21) serves as the transformer core. The transmitted alternating voltage is rectified in a power supply unit (5, 6) on the secondary side of the transformer and is converted to the battery voltage.

Power supply with power factor correction

Abstract: A power supply circuit for feeding a load (1,2), such as one or more fluorescent lamps, from an alternating current source (5) comprises a first bridge rectifier circuit (4) for connection to the a.c. source to provide a unidirectional current supply, and a half-bridge inverter (3) which passes a cylically-reversing current through a load supply circuit (17,19) from the unidirectional supply. For power factor correction, the primary winding (18) of a voltage transformer (19) is connected in the load supply circuit, and the secondary winding (92) of the transformer is coupled to a second bridge rectifier circuit (80) which is connected in series between the first bridge rectifier circuit and the unidirectional supply. Magntic amplifier means (82,83) is connected in series with the secondary winding of the voltage transformer. A current transformer (90) monitors the current flowing from the source, and the monitored current is compared with the current in the load supply circuit. An error signal is derived from the comparison to control the level of magnetisation of the magnetic amplifier means, so that the secondary winding of the voltage transformer extracts current from the a.c. supply, in dependence upon the error signal, to improve the form factor of the current taken from the source. A saturable transformer (17) feeds the lamps, and the level of magnetisation of the transformer can be varied by adjustment of a variable resistance network (71,72), so that the brightness of the lamps can be varied.

High-reliability high-efficiency electronic ballast

Abstract: An electronic ballast is adapted for operation on regular 120 volt/60 Hz power line voltage and comprises: (i) full bridge rectifier means, (ii) ripple filter means consisting of an LC circuit series-resonant at 120 Hz, (iii) self-oscillating inverter means operating into an LC output circuit parallel-resonant at about 30 kHz, and (iv) means to disable the inverter in case a 30 kHz ground-fault current flows from its output circuit. A key element in achieving high reliability as well as high durability relates to the use of the series-resonant LC circuit instead of the conventional electrolytic capacitor for DC voltage ripple filtering. A key element in achieving high efficiency relates to the use of ground-fault interruption to achieve the required safety from electric shock hazard, thereby obviating the need for the more conventionally used isolation transformer with its attendant added cost and inefficiency.

Device for feeding one or a plurality of electrodes in an electrothermal furnace

Abstract: Operation control system for an electrothermal furnace having one or more electrode and a transformer unit for each electrode for supplying heating current to its associated electrode. The or each transformer unit includes a main transformer having a primary winding for receiving current from a mains and two secondary windings, and an additional transformer connected to derive an adjustable voltage from one of the second secondary windings. The adjustable voltage and the voltage across the other secondary winding of the main transformer are combined to supply the heating current to the electrode. The control system includes a switch and a current control unit connected in the transformer unit for giving the additional voltage a selected polarity relative to the voltage across the other secondary winding of the main transformer and for controlling the magnitude of the additional voltage. The system is initially controlled by a microprocessor, to bring the electrode current into a normal operating range, and is then controlled to maintain a desired electrode voltage and the desired operating current.

Electronic ballast with ground-fault protection

Abstract: An electronic ballast is adapted for operation on regular 120 Volt/60 Hz power line voltage and comprises: (i) full bridge rectifier means, (ii) ripple filter means consisting of an LC circuit series-resonant at 120 Hz, (iii) push-pull inverter means operating into an LC output circuit parallel-resonant at about 30 kHz and operative to provide a 30 kHz voltage at an output that is substantially balanced with respect to ground, and (iv) means to disable the inverter in case a 30 kHz ground-fault current flows from this output. A key element in achieving high efficiency relates to the use of ground-fault interruption to achieve the required safety from electric shock hazard, thereby obviating the need for the more conventionally used isolation transformer with its attendant added cost and inefficiency.

Input transformer circuit

Abstract: An input transformer circuit in which transformer-isolated, balanced inputs are provided operates with low distortion and employs a transformer that has an equal number of turns in the primary and secondary windings and which is operated in the current mode to drive the two inputs of an operational amplifier. One input of the operational amplifier is connected to ground and the circuit operates to drive the other input to virtual ground, so that by transformer action the signal voltage across the ends of the primary winding is essentially zero. Because the signal voltages across the primary and secondary windings of the transformer are both substantially zero, there is relatively no induced electromotive force and no signal distortion occurs in the transformer.

Snubber arrangements with energy recovery for power converters using self-extinguishing devices

Abstract: Energy trapped in the snubbers connected to a dc-ac power converter is more efficiently restored to the dc source by means of an energy recovery transformer with a reset circuit branch for improving the reset of the transformer following a period of energy recovery. The reset circuit branch damps out oscillations between the recovery transformer and the overcharged shunt capacitive snubber and may also be used to dissipate the magnetizing current of the energy recovery transformer.

Electrical transformer having a solid core surrounding winding in a loop configuration

Abstract: An electrical transformer having a rectangular core of solid magnetic material, forming a circular or rectangular-section shell in which primary and secondary windings are located. The corners of the core may be open to lighten the transformer and increase heat dissipation. A capacitor may be connected across the secondary winding to increase the efficiency of the transformer.

Transformer differential relay with speed-up apparatus

Abstract: A transformer differential relay which includes apparatus for speeding up the detection of a power transformer internal fault condition to initiate breaker action which interrupts current through the transformer is disclosed. Presently, conventional transformer differential relays include a unit for each phase of the power transformer for detecting a potential internal fault in a respective transformer phase winding and for generating a signal to operate a set of breakers. This breaker operation is inhibited for current inrush conditions of the transformer. However, a processing time is associated with the detection of such a current inrush condition. Accordingly, the breaker operating signal must be delayed for at least this processing time in order for the inhibition to be effectuated. For the case in which there is no current inrush condition, the breakers remain delayed in operation from the inception of a true internal fault. The aforementioned speed-up apparatus circumvents this time delay in breaker operation and renders breaker initiation for detected internal faults with response times on the order of 3-5 milliseconds. In addition, the speed-up apparatus is inhibited from responding to potential internal fault conditions which may arise from initial inrush or recovery inrush current conditions or an external fault condition with severe current transformer saturation.

AC power supply

Abstract: The invention is directed to an AC power supply for portable welding machines or the like which employ a transformer of either single or multi-phase power wound around a cylindrical core. The core is constructed from a continuous length of steel alloy ribbon. The individual windings of both the primary and secondary are spaced apart. In operation the transformer is submerged in a heat transfer medium to provide cooling thereof by heat transfer therefrom. The transformer may have either a tapped primary or secondary or both to provide secondary amperage for the intended use of the transformer. An external cooling radiator may be employed to provide additional cooling to the heat transfer medium.

Switched power supply of the forward converter type

Abstract: A transformer isolated switched power supply of the forward converter type in which a small bias winding is provided on the transformer so that both sides of the operating area of the B/H curve of the transformer core may be used for increased efficiency.

Liquid cooled static excitation system for a dynamoelectric machine

Abstract: An excitation system of a large dynamoelectric machine includes an excitation transformer having a liquid coolant system. The coolant system of the transformer is supplied with a liquid coolant, preferably from an existing source of de-ionized water, thereby permitting a smaller transformer to be used and/or the output rating of the transformer (and ultimately the output rating of the machine) to be increased, while using the same size transformer. The transformer may be disposed separate from, yet closely proximate, the machine.

Regulating power supply for video display apparatus

Abstract: A regulating power supply for a video display apparatus includes a switching transistor that periodically energizes a transformer winding. Input switching pulses for the transistor are varied in width and frequency to optimize power transfer via the transformer. The charge and discharge rates of a capacitor determine the pulse width and frequency. The capacitor charging current is selectively switched to be connected to the capacitor while the capacitor discharge current is controlled in response to a feedback signal derived from the regulated voltage level.

Monitoring device for low-voltage indicator lamps

Abstract: A monitoring device for an indicator lamp which is connected to a secondary winding of a transformer contains a fuse, which is connected in the primary circuit of the transformer, and a current measuring circuit which monitors the primary current of the transformer. Since, in consequence, only those defects can be monitored which result in a reduction in the current on the primary side, and short-circuits on the secondary side of the transformer cannot be detected, or can be detected only inadequately, a voltage monitoring circuit which detects the voltage on the indicator lamp is additionally provided, whose input is connected in parallel with the indicator lamp and whose output controls an electronic switch by means of which the primary current for the transformer can be positively interrupted when the voltage on the lamp is less than a minimum value.

Current-sensing arrangement utilizing two current-sensing signals

Abstract: An improved current-sensing arrangement and method are provided for supplying a signal that suitably represents line current over a wide current range. The current-sensing arrangement utilizes the signals from an iron core transformer and an air core transformer along with transition and scaling arrangements to provide the sensed current signal. The range of operation includes currents for which the iron core transformer exhibits saturation effects and currents for which the air core transformer does not contribute to the combined output signal. Additionally, the range of operation includes currents for which both the transformers contribute to the combined output signal. The output of the iron core transformer dominates the combined output signal for low currents, the output of the air core transformer dominates at high currents, and the transition from the domination of the iron core transformer to the air core transformer is gradual and occurs over a mid-range of current with contribution from both transformers. Accordingly, the combined output signal suitably represents the sensed current over a wide current range due to the contribution of the iron core transformer at low currents where no saturation effects are present and the contribution of the air core transformer at high currents with no saturation characteristic; a smooth transition being provided over a wide current range where both transformers contribute to the output and dominant contribution being provided by the transformer that is most accurate for the particular current.

Low voltage transformer coupled ink jet driver

Abstract: The invention consists of a transformer coupled low voltage power amplifiers which provides the moderate voltage (200-500 Vp-p) excitation potentials required by PZT ink jet or similar device elements. Transformer coupling is viable in that ink jet drive requirements are «return to zero» (no net DC component). Product safety aspects are enhanced since high voltage power supplies are not required, furthermore singificant reductions in cost of implementation are realized due to the absence of high voltage power supplies and by allowing the use of monolithic power amplifiers. Savings in power may also be realized by matching the transformer to the ink jet PZT element as components of a resonant network.

Circuit for driving the base of a transistor

Abstract: Disclosed is an isolation circuit for a power transistor that enables a control circuit to turn the power transistor on and off, while insulating the control circuit from DC currents that may flow to or from the power transistor The isolation circuit includes a first pulse transformer for receiving a pulse string signal corresponding to an ON command signal from the control circuit to alternatingly energize and de-energize the first pulse transformer In addition, the isolation circuit includes a fast circuit path comprising a pair of serially connected diodes coupled between the secondary winding of the first pulse transformer and the base resistor of the power transistor for rapidly supplying base current drive to the transistor as soon as the first pulse transformer is energized Also included in the isolation circuit is a base drive maintaining circuit coupled to the fast circuit path and to the base resistor of the power transistor The maintaining circuit includes a capacitor that charges while the first pulse transformer is energized and discharges to supply base current drive to the power transistor when the first pulse transformer is de-energized Furthermore, the isolation circuit includes a second pulse transformer for receiving a pulse signal corresponding to an OFF signal from the control circuit The secondary winding of the second transformer being coupled to the base drive maintaining circuit for discharging the capacitor and terminating the base current drive to power transistor when the pulse signal corresponding to the OFF signal is received

Inverter type switching power supply with transformer and short circuit arrangement therefor

Abstract: An inverter-type switching power supply circuit which comprises an inverter for converting the DC output of a DC power source to an AC output, a transformer for receiving the AC output of the inverter, a rectifier for rectifying the output of the transformer, a smoothing capacitor for smoothing the output of the rectifier and supplying it to a load, and a transformer short-circuiting circuit for short-circuiting either the primary side or the secondary side of the transformer. The transformer is frequency controlled such that the product of the applied voltage and time of the transformer becomes constant. Thus, the transformer can be designed to have a small size and a light weight.

Current drive operation in a tokamak

Abstract: Three modes of current drive operation in a tokamak — continuous, cyclic, and rfinitiated-are studied for air core and iron core transformer. It is found that the air core transformer is in general more flexible than the iron core transformer for current drive operation. For continuous operation, the shutoff time of the Ohmic heating circuit of the air core transformer can be reduced to zero by using a bias current. On the other hand, the shutoff time of the iron core transformer remains finite even if the bias current is used, because of hysteresis. For cyclic operation, methods of shortening the recharging time are investigated for both types of transformer. The effects of the transformer on rf-initiated operation are investigated. A model design of a saturable iron core tokamak for current drive experiments is also presented.

High current coaxial pulse transformer for railgun applications.

Abstract: : A high-current air-core pulse transformer has been designed and fabricated Its purpose is to reduce the output impedance {nominally 100 mn) of a 50-kJ, 1,000-muF capacitor bank for application to loads with impedances of about 25 m(omega) The system will be used for high current component testing, specifically experimental evaluation of the pressure limits of high-strength wrapped hypervelocity railgun sections The transformer will be part of a test stand consisting of five capacitor bank/transformer sets capable of delivering up to 15 million A to a load The geometry of the transformer is coaxial The secondary coil consists of circular aluminum tubes connected in parallel The primary winding is contained within the tubes and is connected in series The coaxial geometry was chosen for its high coupling coefficient and its mechanical simplicity Design improvements and future refinements are also discussed

Transformer winding arrangement for a television apparatus

Abstract: A high voltage transformer incorporates a bobbin on which the primary winding is wound. The transformer auxiliary coils are wound directly over the primary winding with no intermediate layers of insulation. The wire turns of the auxiliary coils are evenly distributed over the full traverse of the primary winding to improve magnetic coupling and simplify tuning of the transformer.

Self-contained ground fault test feature in circuit breaker

Abstract: A self-contained test feature for ground fault protection systems in circuit breakers. The ground fault protection system includes a sensing transformer having a primary winding that sums the currents through the phase current transformers. Upon the occurrence of an actual ground fault, the sensing transformer will transmit a signal to cause the breaker to trip. The test feature includes a test transformer having its secondary winding electrically connected in parallel with the primary winding of the sensing transformer. The current path between the test transformer secondary winding and sensing transformer primary winding is completed only upon the activation of a test switch. The primary winding of the test transformer is hooked to an external current source to provide the necessary current to simulate the ground fault.

Interswitch line circuit

Abstract: Interface circuits between PABX's or central office line circuits and telephone sets The prior-art use of separate detectors for ringing signal detection, forward loop current detection, and reverse loop current detection, results in high costs when per line expense is multiplied by the number of lines used by a customer The invention has one detector for detecting forward and reverse loop current, and the presence of a ringing signal A sense circuit (22) is connected to a central office or PABX through an isolation transformer's winding (16) for detection of ringing or loop current direction in response to a control signal (VC) supplied from pulse recognition hardware (26) In one embodiment (Fig 4), forward or reverse battery states may be detected when off-hook

Transformer device for electric welding

Abstract: An electric welding device comprising a three-phase transformer, a rectifier circuit and a regulator circuit which cuts-down the sinusoidal wave by thyristor control. The primary and secondary windings (19, 24) of each phase are disposed on the relative column (13) of the transformer magnetic circuit substantially concentrically, and are spaced radially from each other and from the column (13) so as to form passages for circulation of the cooling air produced by a fan.

Transformer with balanced transmission lines

Abstract: A transformer has a number of single turn primary windings 5 formed by printed circuit tracks on a flexible bendable sheet 3 which is wrapped around a core of the transformer. The primary windings are connected to output terminals 12 of an enclosure 1 of the transformer by another printed circuit board 8 having further conductive tracks on opposite sides thereof to form balanced transmission lines whose impedance is matched to the impedance of the primary windings.

A synthetic method for modelling transformer windings in the study of system switching transients

Abstract: Switching operations cause high frequency oscillations in power supply networks. During thes oscillations, transformer windings are subject to voltage stresses. For the analysis of such transient phenomena, lumped networks consisting of R, L, C parameters calculated from the geometric dimensions of transformer windings have been used. In this paper, a new method is described for modelling of transformer windings by their terminal impedance characteristics. It is shown that, by the use of the given models the transient oscillations occuring on the transformer windings can be examined through the state equations. Examples are given for a reduced scale model transformer and an industrial supply system.