Showing papers on "Isolation transformer published in 1980"

Solid State Transformer Concept Development.

Abstract: : This report describes an effort made to determine the feasibility of developing a circuit using power semiconductor devices to duplicate the function of the power transformer A circuit concept has been developed which duplicates the primary function of voltage stepup/stepdown but does not demonstrate the DC isolation characteristic of normal transformers Several characteristics of the circuit appear very attractive, such as increased voltage regulation and relatively high efficiency (Author)

Method of, and apparatus for, inserting carrier frequency signal information onto distribution transformer primary winding

Abstract: Power line carrier frequency signals are provided at a distribution transformer primary winding by controlled current injection onto the neutral and phase conductors of the distribution transformer secondary winding circuit, with the direction of current flow in each half of the secondary winding being controlled in in-phase additive fashion. Apparatus for causing in-phase distribution secondary winding current flow includes a pair of electronic current control means supplying in-phase currents to a pair of secondary windings of an auxiliary transformer having its primary winding coupled to half of the distribution transformer secondary winding and having the auxiliary transformer secondary winding center tap coupled to local neutral through a band-stop filter and to the remaining distribution transformer secondary winding through a band-pass filter for augmentation of signal current flow into the distribution transformer.

Power supply for electrostatic apparatus

Abstract: A power supply for electrostatic apparatus provides a high voltage output. The high voltage output is provided by the half wave rectification and filtering of a pulse signal from a secondary winding of a high voltage pulse transformer. The primary winding side of the high voltage pulse transformer is connected in a series loop circuit with a capacitor and a switching device. The capacitor is charged through an input choke connected to a DC supply source. The switching device is triggered after the capacitor is charged such that the capacitor is discharged through the primary winding of the high voltage transformer. The inductive collapse of the high voltage output transformer provides for the turnoff of the switching device and also serves to partially recharge the capacitor. The half wave rectified high voltage output of the power supply is obtained from the recovery pulse of the high voltage pulse transformer. The efficiency of the power supply is improved since ringing in the transformer is dampened due to the extraction of energy from the recovery pulse. The recovery pulse is much higher in amplitude than the firing pulse during which the switching device discharges the capacitor through the primary winding of the pulse transformer. During each repetitive period, the capacitor is charged, the switching device discharges the capacitor, and a short durational recovery pulse is generated. Several independent outputs of the power supply are obtained by providing respective, independent series combinations of transformers and capacitors with the series combinations being connected in parallel across the switching device.

Static Electrification by Forced Oil Flow in Large Power Transformer

Abstract: Static electrification phenomena in forced oil cooled large power transformer are studied on two full scale models of EHV transformer and some other supplemental models. The dc field due to the static charge separation by the flow of oil can possibly exceed the dielectric strength of oil to produce a discharge in oil. The important factors in the streaming electrification and the precautions for the static charge problem are discussed in this paper.

Axial Vibration Analysis of Transformer Windings Under Short Circuit Conditions

Abstract: This paper describes two methods of calculating the axial vibration of transformer windings under short circuit conditions.

Data acquisition system and analog to digital converter therefor

Abstract: From a plurality of parallel channels of communication, each including a voltage-to-frequency (V/F) converter, a central clock synchronously timed for each channel, the derivation of a train of pulses having a number of pulses representative of the magnitude of an analog signal inputted to the V/F converter. The central clock also times the multiplexing at the measuring point of either the analog input signal or a bias voltage for calibration or a voltage reference for scaling. The central processor receives the counts from each train of pulses, combines them and threats them to provide a corrected count in each channel separately. Clocking and pulsing are effected through an isolation transformer associated with each channel, to and from the central processor.

Controlled current base drive circuit

Abstract: A base drive circuit particularly well adapted for use with bipolar transistors in high frequency power conversion schemes. The base drive circuit allows achieving desired values for both forward and reverse base drive currents simultaneously regardless of the characteristics of the bipolar transistor driven. When utilized in a transformer isolated inverter system, the base drive circuit additionally presents a polarity insensitive input impedance which eliminates the effects of cross-conduction between base drive circuits connected to the secondary side of the isolation transformer.

Lamp circuit with disconnected lamp detecting device

Abstract: A lamp circuit is provided having a constant current type AC power source and a plurality of isolation transformers connected in series with the AC power source. The secondary circuit of each isolation transformer is connected to an electric lamp. The voltage-time area, which is measured from the rise of the voltage output signal of the power source to the rise of the current output signal of the power source is detected and is compared with a reference predetermined value. Thereby when the detected value exceeds the reference value an alarm signal is generated and the number of the disconnected lamps can be determined and displayed.

Transformer coupled isolation amplifier

Abstract: A transformer-coupled isolation amplifier which has a minimally sized transformer, high common mode rejection, and a highly linear response over a wide dynamic range. A first chopper periodically alternates by 180° the connection of the input through a high resistance to the primary of a small square loop pulse transformer. The secondary, with the end of the winding closest to the primary grounded, has the inputs of an operational amplifier placed across it. Negative feedback is provided around the amplifier to provide an apparent very low impedance across the secondary of the transformer. The negative feedback induces a current in the transformer secondary which cancels the flux produced by current flowing in the primary, thereby allowing usage of the transformer normally suitable only for high speed pulses. The output of the amplifier connects to a second chopper synchronous with the first to generate the amplified analog signal. A unique isolated power supply supplies power and switching signals for the first chopper.

Ultrasonic fluid-atomizing cooled power transformer

Abstract: A vapor-cooled power transformer characterized by a transformer within a sealed housing, and means for applying ultrasonic vibrations to a dielectric liquid within the housing in order to vaporize the fluid and to apply it to the exposed surfaces of the transformer.

Voltage regulator using saturable transformer

Abstract: A voltage regulator using a saturable transformer comprises a transformer having a primary and secondary windings, an AC power source for supplying the primary winding a fluctuating alternating current, and a rectifier connected to the secondary winding for rectifying an AC voltage derived therefrom to produce a DC output voltage. The transformer includes a core having four legs and two common portions magnetically joining the four legs, and a control winding supplied with DC control bias from a control circuit. The primary and secondary windings are wound on the first and second legs and the control winding is wound on the first and third legs.

Half-wave signal isolator with means for controlling flux in the coupling transformer

Abstract: A signal isolator including a coupling transformer with modulate/demodulate switches in series with the primary and secondary windings. The switches are driven in synchronism by an oscillator. Resonating capacitors are connected in parallel with the transformer windings to form an LC tank circuit tuned approximately to the operating frequency of the switch-drive oscillator. When the switches are closed, the current in the transformer windings ramps in a linear fashion in response to application of the input voltage, and when the switches are opened, the current varies in a cosine curve to provide smooth transitions at both ends to the ramp current, thus controlling the flux in the transformer core so as to minimize instability effects.

Ignition apparatus for a burner

Abstract: A compact ignition apparatus for a burner, which rectifies the commercial power source and energizes a high-voltage transformer via a transistor blocking oscillator circuit, and in which the high-voltage transformer is provided with a control circuit for controlling the output of the transformer to a constant value against any fluctuation of the input to the transformer, whereby a secure ignition is provided.

Variable ratio transformer and static balance compensator

Abstract: Variable ratio transformer constructed around a control transformer comprising: two closed magnetic circuits each constructed around a ferromagnetic core. An alternating current magnetic field circulates in the first core and a direct current magnetic field circulates in the second core. The two circuits are located so as to define at least two common magnetic spaces in which the fields are superposed orthogonally. Around the first core is wound a primary winding, a secondary winding and, for a specific application in a three-phase circuit, a tertiary winding. A conventional transformer can be associated with the control transformer to reduce the load supported by the control transformer. The variable ratio transformer according to the invention can be used as a static balance compensator.

Method and apparatus for measuring leakage to ground

Abstract: Leakage current to ground from accessible locations on single phase electrical equipment is measured by powering the equipment through an isolation transformer and measuring the current flowing between the two power input terminals of the equipment under test via accessible locations on the equipment.

Optimum topology high voltage DC to DC converter

Abstract: A DC to DC converter is shown having an inductor with primary and secondary windings whose primary winding is serially connected to the center tap of the primary winding of a push-pull transformer. The primary of the transformer is then connected through its ends by a pair of transistor switches to ground while the ends of the secondary of the transformer connect through diodes to an output terminal. The ends of the secondary of the transformer also connect through diodes to the inductor secondary and then to the output terminal. The presence of the inductor prevents the voltage across the switches from becoming twice the input voltage as in conventional circuits. By equalizing the secondary to primary turns ratio between the inductor and transformer, it is possible to equalize the voltage output during the time intervals when the switches are on and off.

DC-DC converter with current and voltage regulation

Abstract: A DC-DC-Converter of the switching type is disclosed with energy storage on the primary side (6) of the isolation transformer (5). Four transistors (1,2,3,4) or other switching devices are switched sequentially to convert the unregulated input direct current to alternating current. If no rectifiers are used, the output is a substantially squarewave alternating current and hence the device can be used as a DC-AC converter. Multiple outputs (30,40,60) can be used; when the load through them is varied, the output voltage on the other outputs does not appreciably change. The device has a high efficiency (over 85 percent), is current limited, and has no minimum or maximum output voltage limitations. An inductor (21) is employed on the primary side (6) of the transformer (5) for temporary storage during the switching of the transistors (1,2,3,4). The output voltage is regulated by means of pulse width modulation.

Combined fault current and applied voltage tripping for solid state trip circuit and particular current transformer construction

Abstract: A solid state trip circuit is disclosed which uses a shunt path saturable transformer comprised of a current transformer having a relatively high resistance shunt which serves to apply input voltage to the transformer primary winding. The larger the input current the higher the voltage drop across the shunt and the more quickly the transformer iron will become saturated. The saturation time during each half cycle then produces a measure of the current flow in the primary line. The output of the secondary winding of the transformer as well as a direct but resistive connection from the input circuit lines are applied to a solid state trip circuit which operates a circuit breaker trip latch. Energy for tripping at lower overload current is derived directly from the applied voltage from the line. At high overload conditions however, direct tripping occurs through energy derived from the transformer rather than directly from the line voltage.

TV receiver switched mode power supply circuit - includes HF conversion of mains by regulated transistorised prim. circuit

Abstract: A transistorised switched mode power supply circuit for a TV receiver prevents the mains being connected directly to the chassis or any part of the receiver and so making safety and aerial isolation easier and more effective. The circuit uses a mains rectifier (1) to feed d.c. through a resistor (2) to a switching transistor (3) completing the circuit through the primary (4) of the isolating transformer (5). The switching operation of the transistor (3) controlling current flow through the primary (4) induces current in the secondary (6) which is rectified (7) and smoothed (8) to power the receiver's circuits. The switching transistor is operated by its base circuitry (iB) connected to the incoming mains via resistor (16) diode (15) and capacitor (17) and with a control loop through a primary winding (9) with diode (10) and resistive (11) loop so that the switching is free wheeling but with timing control for stabilisation of the output (U1) through a further primary winding (12) and transistor/zener combination (13).

Active isolation transformer for medical equipment - uses passive isolator with screens on prim. and sec. and neutralising amplifier

Abstract: An active isolation transformer for use in medical equipment reduces leakage currents to a min. since it automatically balances for them. The transformer consists of a passive isolation transformer with two screens (3, 5), one on the primary side and one on the secondary side. They are linked via a voltage amplifier (4) with an amplification factor of unity. The screen (5) on the secondary side is connected to the input of the amplifier and the screen (3) on the secondary side is connected to the output of the amplifier. There is another earthed screen between the prim. winding and the screen connected to the output of the amplifier.

Voltage stabilizing transformer

Abstract: An improved magnetic core transformer for use as a voltage stabilizer in gas discharge lamps and tube circuits. The transformer has a magnetic stack length greater than either side of the magnetic cross-section and a floating shunt assembly constructed from stacks of magnetic strips. The stack length is optimized technically and as a function of the cost of iron and copper utilized in the transformer and when conformed with an optimum shunt a greater leakage inductance variation is achieved.

Isolation type digital signal input circuit

Abstract: PURPOSE:To prevent the malfunction with a simple constitution and the damage in semiconductor and to enable high integrated mounting, by using the potential at the connecting point between the secondary winding of an isolation transformer and the drive transistor as the output corresponding to ON and OFF of the switching circuit. CONSTITUTION:The isolation transformer 33 has the primary and secondary windings, the diode 32 is connected in parallel with the primary winding, and the transistor Tr switching circuit 31 is connected in the opposite connection as the diode 32 so that the primary winding can be shortened. Further, the drive Tr 34 is connected in series with the secondary winding and also the parallel capacitor 38, and it is connected to the power supply Vcc via the resistor 37. Thus, the potential at the connecting point between the secondary winding and the drive Tr is used as the output corresponding to ON and OFF of the circuit 31. Then, with a simple constitution, malfunction is avoided in the control unit and the damages in semiconductors are prevented to enable high integration mounting.

Power supply unit for a plasma plant

Abstract: A power supply unit for a plasma plant, in particular for a plasma spraying plant, comprises an isolating transformer for connection to three-phase mains, a current control array and a rectifier array. The rectifier array comprises silicon wafer thyristors in a three-phase bridge configuration, which thyristors are electronically controlled through a current control loop, and an exterior voltage control loop is provided for additional electronic control of the silicon wafer thyristors. In the output from the thyristor array, a filter with a transient voltage suppressor may be provided as high-frequency protection and with di/dt limitation.

Half-wave signal isolator with compensator means to reduce temperature-dependent effects

Abstract: A signal isolator including a coupling transformer with modulate/demodulate switches in series with the primary and secondary windings. The switches are driven in synchronism by an oscillator. Resonating capacitors are connected in parallel with the transformer windings and tuned to the switch operating frequency to control the flux in the transformer core. A transformer turns-ratio of less than unity introduces a corresponding attenuation, and a following amplifier counteracts that attenuation to produce an output signal at the original level. A return current resistor is connected between the output signal and the transformer secondary to produce a back-flow of current towards the transformer. This current provides for supplying the losses of the coupling circuit in a symmetrical fashion, both from the isolator input and its output, to reduce significantly variations in performance resulting from changes in ambient temperature.

Feeder bridge circuit

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

Rapid action energising circuit for electromagnet - earths one end of electromagnet coil via thyristor and has capacitor cascade between earth and other coil end

Abstract: The circuit is partic. for a solenoid of a rapid closure valve with a coil surrounding the armature. One end of the coil is connected to earth via a thyristor. Between earth and the second end of the coil is incorporated a capacitor cascade. The latter consists of several capacitors, chargeable via an isolating transformer in parallel, and of temporarily bridged diodes. The cascade may have three stages, the first one between ends of a transformer secondary, and the other two between the ends of a second secondary. The capacitors may be of electrolytic type. A control line may be coupled to the thyristor control electrode for the supply of triggering pulses. The latter may be generated by a measuring unit with at least one pressure sensor.

Phase controlled thyristor triggering circuit - reduces bulk by eliminating isolating transformer whilst keeping galvanic isolation between control element and thyristor power circuit

Abstract: The circuit is for the phase control of a thyristor (2) or triac in series with a load (1) connected across an a.c. single phase power supply. The circuit reduces the bulk of the triggering circuit by eliminating an isolating transformer whilst maintaining galvanic isolation between the control element and the thyristor power circuit. A d.c. supply is derived from the single phase mains by means of a rectifier (7). This supply is connected across a switching transistor (9) and an auxiliary thyristor (8). An optically controlled transistor (10) provides the link with the control element setting the required trigger delay for the main thyristor (2). With no light signal, the switching transistor (9) conducts and there is no signal to the auxiliary thyristor (8) gate. A light signal brings the opto-transistor (10) into conduction turning off the switching transistor (9). A trigger voltage is then available to the auxiliary thyristor (8) and is turned on, triggering the main thyristor (2).

Electrical power line transient noise filtering device

Abstract: An electrical power line transient noise filtering device is disclosed in the specification and drawings comprising a step up transformer connected to two continuous resistors. The high voltage winding of a step down transformer is connected to the other ends of the resistors. Low frequency power passes easily through the system but noise pulses are effectively blocked because they must pass through a transmission line of high loss.

Aquarium light with fluorescent tube - is connected by cable to separate unit incorporating isolating transformer

Abstract: The aquarium light comprises a bowl placed on the aquarium and containing a fluorescent tube, together with a choke coil and starter. It has a separate unit in series with the light and connected to this by cable, accommodating an isolating transformer. The unit can also incorporate the choke coil and a condenser for power factor correction, and a number of plug sockets for the connection of accessories such as the aeration pump. Its housing can be of shockproof plastics.