Showing papers on "Isolation transformer published in 1987"

Shielded electrical wire construction, and transformer utilizing the same for reduction of capacitive coupling

Abstract: A current carrying wire is provided with a tubular shield construction which essentially covers the wire with conductive material, and preferably emulates a classical Faraday shield. The shield is formed of a multiplicity of insulated shield wires for minimized eddy current loss. When such a shielded wire construction is formed into a primary winding of a power transformer for a switching power supply, the secondary circuit is protected from electric shock hazards while enabling use of a gap free toroidal core for close coupling between primary and secondary windings. In another embodiment, such shields are used on both the primary and secondary windings of a matching transformer and are arranged for common mode rejection of noise associated with low power data signals.

MOSFET fullbridge switching regulator having transformer coupled MOSFET drive circuit

Abstract: An FET full bridge regulator has a driving transformer for the gates of the power FETs of the regulator, and a driving circuit for the primary of the driving transformer, the driving circuit including a full bridge formed by first and second sets of driving FETs, each set formed by a complementary pair of FETs and being connected across the transformer, primary, one FET of each set being driven ON to together form a series of conducting paths across the primary of the transformer in the absense of driving signals. The voltage supply for the driving FETS in the driving circuits of the primary of the driving transformer includes a resistance across which there is developed a voltage proportional to the current drawn by the driving transformer primary in each half cycle of its operation for reducing imbalance between the half cycles.

Phase controlled DC-AC converter with high frequency switching

Abstract: A novel type of the sinusoidal DC-AC converter is presented, where a pair of switches is placed in each side of the primary and the secondary of the isolation transformer. This converter is controlled by the phase difference between the two pairs of switches. As a result, the transformer is miniaturized by making the switching frequency high. This converter is especially suitable for small UPS systems.

Transformer coupled power switching circuit

Abstract: A power switching circuit for switching power repetitively to a load at a relatively low frequency employs a power switching device which is driven across an isolating transformer interface. The drive signals are high frequency pulse signals which are modulated with the low frequency switching information, the modulations being detected in the secondary circuit of the transformer. Such an arrangement affords isolated driving with fast switching edges and requires only a small transformer. Power for the detection circuit is derived by rectification of the high frequency signals induced in the transformer secondary.

D.C. voltage converter with overload protection

Abstract: In a d.c. voltage converter 1 including a series arrangement of a transformer 3 and a pulse-switched current source 7 the power converted by means of the transformer 3 is kept constant with the aid of a control circuit 13. In the event of a short-circuit in one of the secondary windings 5-1, 5-2 a voltage drop across an auxiliary winding 6 of the transformer 3 is used to limit the converted power during the short-circuit.

Switching regulator having parallel diode isolated primary windings and plural secondary windings

Abstract: A switching regulator comprising a first diode inserted in series with and in a forward direction to a primary winding of the main power transformer, at least one subsidiary power transformer having a primary winding connected in parallel with the primary winding of the main power transformer, and a second diode inserted in series with and in a forward direction to a primary winding of the at least one subsidiary power transformer, which uses one switching control circuit and one switching means and applies chopped voltages to many transformers simultaneously, and generates many mutually insulated DC power sources, which can be small in size and have simple printed circuits.

Transformer coupling for transmitting direct current through a barrier

Abstract: The transmission system for transmitting direct current from an energy source on one side of an electrical and mechanical barrier to a load on the other side of the barrier utilizes a transformer comprising a primary core on one side of the transformer and a secondary core on the other side of the transformer. The cores are magnetically coupled selectively by moving a magnetic ferrite coupler in and out of alignment with the poles of the cores. The direct current from the energy source is converted to a time varying current by an oscillating circuit, which oscillating circuit is optically coupled to a secondary winding on the secondary core to interrupt oscillations upon the voltage in the secondary winding exceeding a preselected level.

Comparison of the square-wave and quasi-resonant topologies

Abstract: The waveforms of a square-wave and a quasi-resonant dc-dc converter are examined in detail so that a comparison between the switching and conduction losses for each topology can be made. Using data from commercially available semiconductor devices, conservative estimates are then given for the switching frequency at which the resonant approach becomes advantageous. The effect of an isolation transformer on this comparison is also addressed.

Method for changing the transformation ratio of a transformer on the primary side, and a device for carrying out the method

Abstract: In the case of the method for changing the transformation ratio of a transformer (1) on the primary side, the transformer (1) together with the load (2) connected on the secondary side is automatically isolated from the power supply before operation of the stepping switch (4) for selective connection of sections of the primary winding (3) via a load switch (9) on the primary side, the changeover is carried out, and the power is connected again. Used in the case of transformers having a large voltage and current range, especially for supplying X-ray tubes.

Method and circuit arrangement for the insulation testing of test pieces with large intrinsic capacitance and for the localisation of faults in power cables

Abstract: A description is given of a method and circuit arrangement for the insulation testing of test pieces with large intrinsic capacitance and for the localisation of faults in power cables The method is characterised in that the high-voltage transformer is electronically driven on its primary side via a charging capacitor with a very low frequency voltage, which is overlaid with a higher frequency, and that on the secondary side of the high-voltage transformer, the component with the higher frequency is synchronously filtered out (demodulated), and that the high secondary voltage with low frequency is fed to the test piece, and that the measuring device is connected with the test piece via a switching device in the pulse-free period to the high-voltage transformer. The circuit arrangements for carrying out the method provide essentially for the primary-side driving of the high-voltage transformer in the form of pulse packets or in the form of a slowly changing voltage with superimposed square-wave pulses. Provided for demodulation on the secondary side of the high-voltage transformer is either a voltage-dependent resistor or spark gaps or a motor-driven, rotating synchronous switch.

Discharge lamp circuits

Abstract: A.C. mains, coupled through a simple filter F to a full wave rectifier bridge B supplies power to an inverter circuit having d.c. input terminals 12, 13, coupled by a bypass capacitor C0. A primary high frequency circuit includes series resonant capacitor C and inductor L components, the capacitor C being in parallel with a primary inductor L1 which, through the resonant inductor L, is in series with a diode D1 that blocks the flow of direct current from the positive rectifier output terminal 12 to the negative terminal 13. To establish the resonant frequency current in the primary circuit, a switch S1 is connected anti-parallel to the diode D1. A drive circuit 14 drives the switch S1 to execute switching cycles at a rate equal to the series resonant frequency of L and C. The high frequency current is propagated in a secondary circuit including a discharge lamp 11 in series with a current limiting capacitor C1, an inductor L1' which is part of an autotransformer formed by L1 and L1', and a further inductor L3 which is inductively coupled to the primary inductor L1 or inductor L so as to cancel harmonics of the resonant frequency of L and C1 the inductor L3 being of a size which with the capacitor C1 is series resonant at an unwanted harmonic of the said resonant frequency. The switch S1 may be a gate turn off thyristor, a gate turn off thyristor in series with a transistor (30), (Figure 10), or an FET (Figure 8). The autotransformer may provide voltage step-up or current step-up (Figure 5) for use with low and high pressure lumps respectively. Alternatively, an isolating transformer may be used (Figure 6), in which case the primary circuit resonance inductor may be provided by leakage reactance of the transformer and the associated resonance capacitor by the capacitive reactance, reflected into the primary circuit via the transformer, of a capacitor & connected in parallel with the secondary L1' (Figure 7).

Protective grounding and referencing arrangement for high voltage bulk supply

Abstract: A protective grounding and referencing arrangement for a high-voltage, high-energy bulk supply is provided in the present invention. Isolation from ground is provided through the use of an isolation transformer connected between the a-c utility supply and the rectifiers which are provided for conversion to d-c. The d-c bus and its energy storage capacitors are then referenced to ground by a high resistance divider network. In such an arrangement the likelihood of an insulation breakdown to ground is significantly reduced. More importantly, in the event that such a breakdown should occur from one or the other terminal of the d-c bus the fault currents that result are limited by the referencing arrangement to a safe level. The energy hazard is thus very significantly reduced for the equipment.

Electronic hybrid circuit

Abstract: An analog electronic hybrid circuit having a complex internal impedance includes a coupling transformer. The loss resistances of the transformer are used together with a measuring resistor to establish a predetermined complex internal impedance, thereby providing a balancing network. In one embodiment, nonideal characteristics of the transformer (nonlinearities, parasitics) have only very little effect because the transformer is contained in a feedback loop.

Magnetron with temperature probe isolation

Abstract: An arrangement provides for the electrical grounding of a temperature probe and allows its use in conjunction with a cooking appliance control circuit having a floating signal ground. An isolation transformer connects the temperature probe to the control circuit. A temperature sensing circuit includes two parallel voltage-dividing legs. One of the legs includes a primary winding of the isolation transformer, whereas the other of the legs includes a variable resistor allowing a consumer to set the predetermined temperature at which the control circuit will stop heating. Preferably the control circuit is used to control a full wave full bridge inverter connected to an AC input line by way of a bridge rectifier. The inverter is connected to a magnetron by way of a power transformer. The voltage-dividing legs are connected to receive gate pulses from the control circuit, which gate pulses also are used for controlling switches within the inverter.

Unrestricted frequency changer with current source output

Abstract: Three terminal, six and twelve pulse unrestricted frequency changing circuits are provided by inserting controllable bidirectional switching circuits between open star configured coils in multiple phase windings of isolation transformers. Where the switched winding are secondaries of the isolation transformer, interphase transformers are provided between each pair of three pulse circuit groups and additional interphase transformers are required between six pulse circuit groups to provide a three terminal output. Where the switched windings are primary windings of the isolation transformer, the secondary windings are electrically connected in series with each other to provide the three terminal output.

Power feeding apparatus

Abstract: A power feeding apparatus which is used in a high-frequency heater or the like, is further power-convert­ed by a transformer after the power provided by the power supply such as commercial power supply or the like has been converted into the high-frequency power by a transducer including a semiconductor, feeds the converted power into the load having the unidirectional electrical current characteristics of magnetron or the like. The generating voltage is dropped so that the stable power may be fed without the corona discharge and the arc discharge to be caused, the insulating withstand voltage between the wind­ings of the transformer, the pulling of the wirings, and the insulating withstand voltage may be reduced.

Dc power supply circuit for fluorescent lamps

Abstract: The DC power supply circuit has an isolating transformer (13'), whose inductance (16) is alternately charged via an electronic switch (T2) and discharged via a diode (17) onto a capacitor (18). The initial voltage (UA) of the isolating transformer is continuously monitored. If a threshold value is exceeded, the switch (T2) located in an input line (11) of the isolating transformer is switched to the off state. The off state is terminated as soon as the initial voltage drops below the threshold value again. The DC power supply circuit allows loads which require a specific DC voltage to be connected to different supply voltages without any changeover switching being required. The circuit provides good safety against overvoltage originating from the mains. It is self-monitoring and protects the connected load. … …

Combined high-voltage current and voltage transformer

Abstract: A combined high voltage current and voltage transformer of head-type construction with a column of insulating material carrying the top housing whereby the active parts of the current transformer and above the same the active parts of the voltage transformer are arranged within the top housing. A simple manufacture of the top housing and a good seal with as few as possible lead-outs to be sealed off inside of the top housing is made possible by the construction of this invention. At the same time, the primary conductor of the current transformer as also the secondary system of the current transformer and the active parts of the voltage transformer are to be assemblable in a simple manner. This is achieved in that the primary conductor of the current transformer is constructed U-shaped whose base extends at least approximately concentrically through the ring of the secondary system of the current transformer. The two legs of the primary conductor protrude downwardly and are secured exclusively on the closure plate of the top housing from the inside thereof. At least one leg is electrically insulated from the metallic closure plate and is adapted to be contacted through the same from the outside and from below. The ring of the secondary system of the current transformer is also secured exclusively on the closure plate by way of supports.

Small UPS using Phase Control

Abstract: A small UPS using phase control has been developed. The isolation transformer used in the phase-controlled inverter is extremely minimized by the high frequency switching. This inverter is of simple construction and allows bidirectional power flow. The basic operation of the phase-controlled inverter and its applications to UPS are presented with some experimental results.

Bus network and measurement or control units linked to the bus

Abstract: The network includes a two-line bus, possibly a shielded twisted pair 10, and several units or stations 12 connected up to the bus. The bus is equipped with a general supply transformer 22 and each unit of the electrical supply system is coupled to the bus by a transformer 26. Each unit 12 is coupled to the bus by an isolating transformer intended for transferring digital signals between bus and unit, with ferrite core.

Transmission line pulsed transformer

Abstract: A pulsed transformer capable of providing up to 500 kilovolt or higher, 10 nanosecond rise time, and 1000 joule or higher pulses comprising non-conducting or insulated transformer cores each separated by conductive grading rings wherein n coaxial cables in combination with the grading rings are connected in parallel at one end and in series at their other ends. The transformer may function as either an inverting or non-inverting transformer. In a transformer with n cables, if a pulse voltage of V is applied to the input, an output voltage of nV will appear at the output. The cores function to isolate the coxial cables and permit them to be connected in series at their one end. Weight may be minimized by operating the transformer in gaseous Freon rather than transformer oil.

A common bus multimode sensor system

Abstract: A multinode noise immune sensor system that transmits AC power and returning sensor signals from remote units through a coaxial cable. An isolation transformer and an integrated circuit type pin programmable bus inter­face are also used. A carrier is provided by a ripple counter producing a frequency divided signal compared to a fixed reference frequency, where the result of the compari­son controls a voltage-controlled oscillator, which produc­es a signal which is applied to the coaxial cable. Receivers at the end of the coaxial cable are each tunable to a designated carrier frequency and each decode the respective encoded signal.

Device for power supply of gas-cleaning electrical precipitators

Abstract: A device for power supply of gas-cleaning electrical precipitators comprises two constant voltage sources (1,2), the unlike poles (5,6) of each of the sources being grounded. Two high-voltage commutators made as triode-type thermionic rectifiers (7,8) with a hollow anode (11) are connected between the other unlike poles of each of the constant voltage sources (1,2) and a corona displaying electrode (16) of an electrical precipitator (17). Connected to a cathode (9) and a control electrode (10) of each of the triode-type thermionic rectifiers (7,8) are modulators (18, 19) of alternating polarity voltage which are connected through isolation transformers (38,39) to a control unit (40), the latter being connected to pickups (49,50,51,52) of electrical and physical parameters. Each electric circuit is provided with series-connected inductive storage elements (13,15), the electric circuit comprising series-connected the constant voltage source (1,2), the triode-type thermionic rectifier (7,8) and the corona-displaying electrode (16) of the electrical precipitator (17).

Device for demagnetising the transformer of a flow transducer and a method for its operation

Abstract: In the case of a flow transducer, the otherwise obligatory demagnetizing winding is dispensed with since, according to the invention, the primary winding (L1) of a transducer transformer (5) together with a capacitor (8) forms a series tuned circuit, as a result of which the demagnetization energy of the transformer (5) is buffer-stored in the capacitor (8) and is used for negative premagnetization of the transformer core. A switching element (12) in the secondary circuit of the transducer transformer (5) is closed at the correct point in time so that the negative premagnetization is maintained until a new flow cycle starts.

Circuit arrangement for detecting and measuring the output current of an isolating transformer (flyback converter)

Abstract: A circuit arrangement for detecting and measuring the output current of an isolating transformer, said circuit arrangement comprising a current transformer which is arranged in the output circuit of the isolating transformer.

Electromagnetic induction furnace for the thermic treatment of wires

Abstract: The wire is moved axially at a suitable speed by external means, such as for example the means for collecting the annealed wire, is passed around preferably idle pulleys so as to form in contact therewith closed loops or turns one flight of which is passed through a window in the toric core of a transformer which generates a magnetic flux by means of a feeding primary circuit. Said wire loops constitute, substantially, the secondary circuit of said transformer and are heated due to the Joule effect by the current induced by the electro-magnetic flux generated by said transformer. Since the secondary of said transformer is shortcircuited, said transformer needs very low electric voltages at the secondary in order to produce the power required for the treatment. A plurality of loops or turns of wire may be arranged in parallel to each other to reduce the electric voltage required for the thermal treatment of said wire, so as to achieve high working speeds without exceeding the voltage limits established by the present safety regulations. A suitable winding method permits to concentrate the heating electric power in the flight of wire extending between two successive pulleys and passing through the window in the core of the induction transformer. Means are described for maintaining the temperature in the pulleys substantially uniform, and other means are described for ensuring a suitable tractive force on the wire. The adjustment of the electric voltage in the primary circuit of the induction transformer permits the furnace to operate in combination with variable-speed wiredrawing machines, while a grounded stainless steel screen interposed between the primary and the secondary of said transformer, with no formation of turns, grants the safety to the operator. This solution may be used either with single-wire and multiple-wire systems, while the variation in the number of the turns of wire in series or in parallel permits the use of the same electric voltage for different wires moved at the same speed, thus reducing the electric power requirements.

Pulse conditioning circuit for controlling electrically controllable valves in a hydraulic control apparatus

Abstract: Pulse conditioning device for electrically controlling valves in hydraulic control apparatus whereby a regulating signal is transmitted to the actuator of the respective electrically controllable valve. A filter is connected to the input side of an isolating transformer and a unidirectional rectifier is serially connected to an input side of the isolating transformer through the filter. An oscillator generates a sinusoidal output signal and a summing amplifier receives both the regulating signal and the sinusoidal signal to provide an output signal which is input to the unidirectional rectifier. To complete a modular pair of identical circuits for the control circuit, a second unidirectional rectifier is serially connected to a second filter and also connected to the output side of the isolating transformer. The second filter provides a zero offset compensation, and an output buffer amplifier is connected to the output of the second filter for producing an output signal which is the regulating signal for the actuator of the electrically controllable valve.

Frequency Spectra for Admittances and Voltage Transfers Measured on a Three-Phase Power Transformer

Abstract: A large number of frequency spectra for admittance and voltage transfer has been measured. The measurements have been carried out on a 25 MVA 150/11 kV transformer. Recorded input and output pulses have been processed with the aid of an FFT algorithm to give admittances and voltage transfers. The results are reliable between 1 kHz and some hundreds of kHz. Below 1 kHz additional measurements have been carried out with a sweep generator and with stationary frequencies. The spectra show large scale phenomena with superimposed maxima and minima probably caused by part-winding resonances. A simple model, consisting of lumped capacitances and inductances is given to reproduce the large scale behaviour. Bollen, M.H.J. and P.T.M. Vaessen FREQUENCY SPECTRA FOR ADMITTANCE AND VOLTAGE TRANSFERS MEASURED ON A THREE-PHASE POWER TRANSFORMER. Faculty of Electrical Engineering, Eindhoven University of Technology, 1987. EUT Report 87-E-181 Addresses of the authors: ir. M.H.J. Bollen, Division of Electrical Energy Systems, Faculty of Electrical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 ME EINDHOVEN, The Netherlands ir. P.T.M. Vaessen, Research and Development Division, N.V. KEMA, Utrechtseweg 310, 6812 AR ARNHEM, The Netherlands

Dielectric strength tester

Abstract: A dielectric strength tester is disclosed for use with high-voltage, high-volt amperage electrical equipment. The step-up transformer has a high-voltage secondary winding which is connected through first and second primary windings of a sensing transformer to first and second test terminals. If an operator should contact the second test terminal, which is at high voltage, this would cause a fault-to-ground current, which is an imbalance on the two primary windings, and hence supply an output on the secondary winding of the sensing transformer. This voltage is rectified and passed through a set point resistor means to trigger a thyristor into conduction. This thyristor is connected to de-energize a triac in series with the primary of the step-up transformer. The sensing is rapid because it is carried out in the high voltage secondary, yet the control is in the lower voltage primary of the step-up transformer. The response is very rapid, taking place in less than one-half a millisecond, so that should an operator receive a shock, it would not be a fatal shock and he would be able to let go of the electrical contact. The fore-going abstract is merely a resume of one general application, is not a complete discussion of all principles of operation or applications, and is not to be construed as a limitation on the scope of the claimed subject matter.