Abstract: A current sensor for detecting a magnitude of a current flowing through a measuring object has a magnetic core having a first magnetic core and a second magnetic core that is arranged magnetically in parallel to the first magnetic core, wherein the first magnetic core has a magnetic permeability that is higher than that of the second magnetic core in a first frequency band, and the first magnetic core has a magnetic permeability that is lower than that of the second magnetic core in a second frequency band, the second frequency band being higher than the first frequency band, and the current sensor detects the magnitude of the current in a frequency band that is constituted by combining the first frequency band and the second frequency band.

Abstract: A current sensing method measures a fractional current through a coil having a plurality of coil windings by using a current sensing resistor to measure a current through a subset of the plurality of coil windings and using a voltage sensor to measure a voltage drop across the current sensing resistor. The measured current and voltage values are provided to a processor to determine the fractional current and phase of the coil. For example, the fractional current and phase of the coil may be determined by calculating a total current of the coil as I=n(V/Rx), where n is the number of coil windings of the coil, V is the measured voltage, and Rx is the impedance of the current sensing resistor. The coil may be a secondary winding used in a wireless power transfer system.

Abstract: A sensor circuit may comprise or otherwise be connected to a transformer. The transformer may comprise a primary winding and a secondary winding. The primary winding may be configurable and/or connectable to sense a current flow in the primary winding. A configurable circuit with an output may be connected to the input of a comparator circuit. The output of the comparator circuit and one or both of the input of the configurable circuit or the output of the configurable circuit may connect across the secondary winding.

Abstract: A temperature-sensing apparatus for sensing the temperature of an electrical conductor (31), comprising a sensor frame (210) including a frame body (2101) and a channel (2102) adapted to accommodate the electrical conductor (31). At least a portion of a temperature sensor is received in a chamber (2103) of the sensor frame (210). At least a portion of a thermal contact member is disposed between the electrical conductor (31) and the temperature sensor and configured to enhance thermal-contact therebetween. At least a portion of the thermal contact member is radially pressable against the electrical conductor (31).

Abstract: An apparatus for measuring an electric current through a bus bar comprises a compensation coil and a magnetic field sensor. The bus bar has a through-hole dividing the electric current flowing through the bus bar into at least two partial currents flowing around the through-hole. The compensation coil is disposed in the through-hole and generates a compensation field. The compensation field compensates a plurality of magnetic fields generated by the partial currents and/or an external magnetic field such that a magnetic flux density of a resulting magnetic field at a predetermined position of the through-hole does not exceed a predetermined threshold. The magnetic field sensor is disposed in the through-hole and detects the magnetic flux density of the resulting magnetic field at the predetermined position. The magnetic field sensor emits an output signal corresponding to the detected magnetic field.

Abstract: A circuit for receiving the output from one of either a current transformer or a di/dt sensor includes: an input pair having a first input and a second input; a first output; a second output; a current transformer input circuit connected between the first input and the second input; and a di/dt sensor input circuit connected between the first input and the second input. The current transformer input circuit is configured to receive output from a current transformer connected to the input pair and to output a signal representative of the current sensed thereby via the first output. The di/dt sensor input circuit is configured to receive output from a di/dt sensor connected to the input pair and to output a signal representative of the current or time rate of change of the current sensed thereby via the second output.

Abstract: A method for determining a lone temperature of an overhead power line of a power transmission setup. The method includes capturing an image of a section of the power transmission setup. The image of the section represents the overhead power line carrying current and a non-current carrying element of the power transmission setup. The method also includes analyzing the captured image to determine temperatures of the overhead power line and the non-current carrying element. The temperature of the overhead power line is based on a heat generated by the carried current and an environmental factor around the section of the power transmission setup, and the temperature of the non-current carrying element is based on the environmental factor. The method further includes using the determined temperatures of the overhead power line and the non-current carrying element for determining the lone temperature of the overhead power line.

Abstract: The present invention discloses a method for lightning stroke identification and location on optical fiber composite overhead ground wire. In the method, according to the property that the lightning stroke will cause a sudden temperature rise at the lightning stroke position on the optical fiber composite overhead ground wire, optical fiber resources in the optical fiber composite overhead ground wire and the high-sensitivity detection and high-precision event locating capability of a distributed optical fiber temperature sensor can be fully utilized.

Abstract: Accurate measurements of electrical power at various points of a power grid is becoming more important and, at the same time, is getting more difficult as the old power distribution model of a few, large power generating stations and a multitude of relatively linear loads is replaced by a newer model containing a multitude of smaller, and to some degree unpredictable power sources, as well as a multitude of not always linear and often smart (essentially also unpredictable) loads. Embodiments of the invention provide for management of AC current measurements in the presence of a DC current. Such current measurement management including at least alarms, feedback, and forward correction techniques exploiting magnetic field measurements from within the magnetic core or upon the surface of magnetic elements and/or shields within the current transducer.

Abstract: A system for measuring current includes a conductive trace comprising N substantially parallel straight sections having a substantially constant cross-section, N?4. Adjacent substantially straight sections are spaced apart by a given distance and each pair of adjacent straight sections is connected by a respective loop of the current trace such that current in odd-numbered straight sections flows in a first direction and current in even-numbered straight sections flows in an opposite direction. The N magnetic field based current sensors are each positioned on a respective straight section of the conductive trace.

Abstract: The disclosed invention mitigates unnecessary electric utility and first responder intervention in the event of a downed electrical cable that may not present a voltage hazard. The disclosed downed power line status indicator invention serves to protect the public while increasing the ability to repair lines damaged due to an unplanned natural calamity or other incident. In the preferred embodiment, the invention can capture the status of a downed line and if it is energized, provide a local visual arid audible alarm of hazardous conditions to anyone in the vicinity of the downed line. In addition, the invention can generate a message or notification sent to the utility's operations center.

Abstract: A sensor and method for identifying a downed power transmission conductor or structure is disclosed. The method includes the steps of securing a sensor to a power transmission conductor or structure, using the sensor to measure inclination of the power transmission conductor or structure, comparing the measured inclination to a set threshold, and alerting a utility if the measured inclination exceeds the set threshold.

Abstract: A sensor includes a core, first and second windings, an integrating amplifier circuit and a DC balancing circuit. The first and second windings are wrapped around the core. The integrating amplifier circuit has a first input coupled to the first winding, and an output operably coupled to the second winding. The DC balancing circuit is operably coupled between the output of the integrating amplifier circuit and the first input of the integrating amplifier circuit.

Abstract: A demagnetizing device includes, in one embodiment, a demagnetizer. The demagnetizer is operable to generate a corrective magnetic field. The corrective magnetic field is operable to act upon a ferrite-based core to maintain suitable performance of a network-connected device which includes such core.

Abstract: A power controller controls power to a load and includes a primary current sensor, a controller and a current source. The primary current sensor includes a primary conductor and an auxiliary conductor. The primary conductor carries a primary current to the load and the auxiliary conductor carries an auxiliary current in the opposite direction of the primary current to provide partial flux cancellation. The primary current sensor provides an output voltage based upon a magnetic field generated by the primary current and auxiliary current. The controller determines the primary current based upon the output voltage and the auxiliary current. The current source provides the auxiliary current. The controller controls the current source to provide the auxiliary current to the auxiliary conductor if the primary current is greater than a threshold value.

Abstract: Disclosed is a method for the improvement of the line quality in a system, in which a common feeding (1), via at least one distribution transformer (3), feeds at least two non-linear loads (11) drawing non-sinusoidal currents from the common feeding (1), wherein between the common feeding (1) and the distribution transformer (3) there is at least one primary side transformer line (2) and between the at least one distribution transformer (3) and the loads (11) there is at least one lower voltage secondary side transformer line (22), wherein at least one active filter (24) attached to at least one lower voltage secondary side transformer line (22) is used for the attenuation or elimination of higher order harmonics experienced by the common feeding (1). Furthermore a high power distribution system for use of such a method is disclosed, in particular for the operation of an electrostatic precipitator.

Abstract: An apparatus is provided for securing to and collecting power from an electrical conductor including a wire clamp that clamps to and secures the apparatus to the electrical conductor, a current transformer (“CT”) that clamps to the electrical conductor and collects power from the electrical conductor, and a housing including a cavity that encloses circuitry associated with the apparatus. According to various aspects, the circuitry may include one or more sensors and wireless communications circuitry, and the CT may include a core and an electrical winding that receives an induced current from magnetic flux generated according to alternating current present on the electrical conductor.

Abstract: A device for sensing electrical current or voltage in an electrical distribution system using an actively compensated current ratio transformer that includes a first magnetic core having a first permeability and a second magnetic core having a second permeability higher than the first permeability. A primary winding having P turns is coupled with the first and second magnetic cores, a measurement winding having M turns is coupled with the first and second magnetic cores so that current in the primary winding induces current in the measurement winding, and a sense winding having S turns is coupled with the second magnetic core. An amplifier coupled to the sense winding receives a voltage developed across the sense winding and produces a compensation current in response to the received voltage. The amplifier has an output coupled to the sense winding to feed the compensation current through the sense winding to reduce the voltage developed across the sense winding voltage to substantially zero.

Abstract: An apparatus and technique that reduces induced cross-talk current between transformer windings. The apparatus includes a transformer having a first secondary winding that provides a first voltage relative to earth ground, a second secondary winding that provides a second voltage relative to floating ground, and a shield disposed between the first and second secondary windings. A correction circuit connected to the first secondary winding is configured to generate a correction voltage. The correction voltage drives a shield to induce a correction current into the second secondary winding to reduce cross-talk current induced between the first and second secondary windings.

Abstract: A device for sensing electrical current or voltage in an electrical distribution system using an actively compensated current ratio transformer that includes a first magnetic core having a first permeability and a second magnetic core having a second permeability higher than the first permeability. A primary winding having P turns is coupled with the first and second magnetic cores, a measurement winding having M turns is coupled with the first and second magnetic cores so that current in the primary winding induces current in the measurement winding, and a sense winding having S turns is coupled with the second magnetic core. An amplifier coupled to the sense winding receives a voltage developed across the sense winding and produces a compensation current in response to the received voltage. The amplifier has an output coupled to the sense winding to feed the compensation current through the sense winding to reduce the voltage developed across the sense winding voltage to substantially zero.

Abstract: Phase angle error and ratio error correction is provided in a current transformer by a bucking voltage opposite in phase to the voltage drop across the burden resistor and inherent winding resistance.

Abstract: Provided an error compensating method for an instrument transformer, in which an error of an instrument transformer is compensated by reflecting hysteresis characteristics of iron core. When such error compensation is performed, a hysteresis loop indicating the relationship between magnetic flux and excitation current is not used as it is, but core-loss resistances and magnetic flux-excitation current curves are used, thereby achieving more precise compensation. According to the present invention, an error of an instrument transformer can be significantly reduced. Therefore, it is possible to manufacture an instrument transformer with high accuracy and to significantly reduce the size of the instrument transformer. Further, a material with high permeability does not need to be used in order to increase the accuracy.

Abstract: This invention relates to a nulling current transformer. More particularly, this invention relates to a nulling current transformer for accurately detecting current and giving an improved response, accuracy and stability using toroidal current transformer technology along with active components. This invention finds particular application in switchgear devices such as residual current devices and metering operations. The nulling current transformer is implemented in a closed magnetic core having at least one primary winding inductively coupled thereto. A secondary winding is also inductively coupled to said magnetic core, the secondary winding being responsive to any magnetic flux generated in said magnetic core. A separate tertiary winding is also inductively coupled to said magnetic core, the tertiary winding being responsive to any magnetic flux generated in the magnetic core.

Abstract: An impedance-compensated current transformer comprising a primary winding, a power source electrically coupled through the primary winding; a secondary winding magnetically coupled to the first primary winding, the secondary winding having a secondary winding impedance and a secondary winding resistance; and an impedance-compensation circuit electrically coupled across the secondary winding; wherein the impedance-compensation circuit actively reflects to the secondary winding a virtual impedance which is equal in magnitude and opposite in polarity to the secondary winding impedance.

Abstract: An impedance-compensated current transformer comprising a primary winding, a power source electrically coupled through the primary winding; a secondary winding magnetically coupled to the first primary winding, the secondary winding having a secondary winding impedance and a secondary winding resistance; and an impedance-compensation circuit electrically coupled across the secondary winding; wherein the impedance-compensation circuit actively reflects to the secondary winding a virtual impedance which is equal in magnitude and opposite in polarity to the secondary winding impedance.

Abstract: The magnetic flux of a magnetic body is controlled with voltage pulses from an active voltage source. The voltage pulses are applied to a winding circuit which is magnetically coupled to the magnetic body. An electronic switch means is used to generate the voltage pulses from a d-c power supply. A control circuit receives information about the winding current, and utilizes known loop impedances to optimize the voltage pulses for optimal magnetic control. Utilizing voltage pulses rather than a continuously variable voltage source has the advantage of lower cost and improved energy efficiency for many applications. The invention may be utilized for measurement of a-c current and d-c current utilizing ordinary current transformers. The switched-voltage control that is disclosed also may be used to facilitate accurate measurement of a-c current in a self-powered manner, with the power supply for the electronics deriving its power from the current transformer secondary circuit.

Abstract: A capacitive voltage transformers for distribution of the power from 10 kv high potential line, includes a insulating column with a high potential terminal, a ground terminal and capacitors C1 and C2 in series connection. The column is filled with oilless dry filler. The capacitors C1 and C2 formed by a plurality of separated metallized film capacitors respectively in series or in parallel connection. At the tapping point between the capacitors there is a leading-out terminal of the secondary voltage which is connected to an induction transformer L in parallel. The transformer includes a frame with “C” shaped iron cores and windings wound around the cores. There is an over-voltage protector P connected in parallel between the tapping point and ground. A capacitive voltage divider is integrally combined with the transformer to provide a small volume, low cost device with a savings in materials.

Abstract: A system and method for AC line voltage analysis is disclosed. According to one embodiment of the present invention, a system for AC line voltage analysis on an AC line includes a transformer that steps down the AC line voltage, a rectifier that rectifies the stepped down AC line current, a filter that filters the rectified AC line current, a voltage divider that reduces the AC line voltage; and an A/D converter that converts the reduced AC line voltage to digital bits. According to another embodiment of the present invention, a method for AC line voltage analysis of an AC line includes the steps of (1) calibrating equipment for measuring AC line voltage analysis, (2) adjusting for at least one load, (3) filtering an adjusted measurement; and (4) determining an actual line voltage.

Abstract: The exciting current of a current transformer is calculated and added to the measured secondary current to produce a corrected signal. The exciting current is calculated by first calculating the current transformer induced voltage. The induced voltage is calculated from a parameter related to secondary current and known characteristics of loop impedances through which secondary current flows. The parameter related to secondary current may be the secondary current itself, or a voltage associated with secondary current flowing through an impedance. The calculated induced voltage is then applied across an inductor having similar magnetic properties as the current transformer. By scaling the applied voltage properly, the current flowing in the inductor is approximately proportional to the exciting current of the current transformer. The current in the inductor is measured, and, by applying an appropriate constant of proportionality, the exciting current of the current transformer is determined.

Abstract: A voltage source connected in the secondary circuit of a current transformer is controlled so as to provide a secondary current that is accurately and continuously proportional to a primary current that is either pulsed d-c electric current or pulsed a-c electric current. Similar to U.S. Pat. No. 6,180,697, the voltage source is controlled so as to compensate for the voltage drop caused by secondary current flowing through secondary circuit impedances, thereby reducing the effective burden of the secondary circuit. However, to prevent the accumulation of error when measuring pulsed currents that are not symmetrical, the present invention turns the burden-reducing compensation off whenever secondary current is near zero amperes, thereby providing for the decay of current error and magnetic flux, so that current error remains very small and the current transformer does not saturate.

Abstract: Current sensor according to the compensation principle, in which the magnetic field produced by a primary winding (1) through which the current to be measured flows is compensated by the compensation current in a secondary winding (6), and in which for the controlling of the compensation current at least one sensor (3) that is influenced by the magnetic field acquires deviations from the zero current and supplies this measurement value to a driver circuit (5) for the production of the compensation current, whereby at the output of the driver circuit (5) the secondary winding (6) is connected in series to a terminating resistance (7), a voltage (Ua) that is proportional to the current to be measured is present at the terminating resistance (7), two amplifiers (5a,5b) in a bridge circuit, which are controlled by the measurement value and which supply output signals in phase opposition to one another, are used as a driver circuit (5), and the series circuit of the secondary winding (6) and terminating resistance

Abstract: A current transformer for mains alternating current with dc components is formed of at least one transformer core with a primary winding and at least one secondary winding, of load resistor is connected in parallel to the secondary winding and terminates the secondary circuit in low-impedance fashion. A semiconductor component that opens during a suitable time span within every cycle and is in turn closed is provided in the secondary circuit. During this time span, the secondary circuit is in a no-load condition. As a result thereof, the build-up of the core magnetization generated by the dc components is collapsed, and thus the transformer core cannot be driven into saturation, so that an over-dimensioning of the transformer cores is unnecessary.

Abstract: A current ratio device for use in forming a hand-held openable-core clamp-on type of current transformer. The device employs electronically-aided three-stage circuitry for forming a current transformer capable of accurate low current measurements over a wide range of operation. Such a current transformer is specifically adapted for use with highly accurate active/reactive power and energy meters, and harmonic power analysers. For example a preferred form of clamp-on transformer can be used to measure currents in the range from 1 A to 200 A with ratio errors of less than 50.times.10.sup.-6 for both the in-phase and quadrature components.

Abstract: An alternating current sensor employing a mutually-inductive current sensing scheme comprises a conductive pipe and a cylindrical-shaped conductive element at least partially surrounded by the pipe. The pipe is substantially concentric to the conductive element and a conductor electrically connects a pair of corresponding ends of the pipe and conductive element to form a connected conductive path through the sensor. The conductive element may include a passage or opening shaped to form a magnetic field within the passage during current flow along the conductive path.

Abstract: The present invention relates to an arrangement in a current detection circuit. There is a primary coil for the current to be detected, a separate transformer core which is influenced by the current of the primary coil, a secondary coil conducting a transformed secondary current, as well as a tertiary coil connected to an operational amplifier including a feedback resistor and constituting a current-voltage converter circuit with an input resistance of nearly zero ohms.

Abstract: Method and apparatus for linearizing the performance of electrical transformers using negative feedback. Two circuits are disclosed which use an operational amplifier to compensate a three-winding transformer, yielding an improved low-end frequency response, reduced harmonic distortion, and substantially resistive input and output impedances.

Abstract: A current ratio device is used for forming a current transformer that can accurately scale down high currents to usable metering levels. The transformer has associated circuitry that renders it capable of functioning not only with ac and a mixture of ac and dc, but also when dc alone is present in the primary winding. The device employs a toroidal core and winding assembly that is cut along a plane containing the toroidal axis through a pair of diametrically opposite sections of the assembly that contain no windings, in order to separate the device into a pair of sub-assemblies that can be readily placed over a single turn primary, e.g. a busbar, without dismantling the same.

Abstract: A transformer having a primary winding and a secondary winding across which load is coupled is compensated. A third winding is provided on the transformer. A first output terminal of an amplifier is coupled to a first terminal of the primary winding. A first terminal of the third winding is coupled to the second terminal of the primary winding. A second terminal of the third winding is coupled to an input terminal of the amplifier.

Abstract: The disclosure is directed to a transformer circuit apparatus which receives an input signal and generates an output signal representative of the input signal. For example, the input signal may be an AC current, and the output signal to be generated may be a voltage that is proportional to the current. A transformer is provided, and has a core, a primary winding for receiving the input signal, a sense winding, and a feedback winding. A first circuit is coupled to the sense winding, and is responsive to the magnetic flux sensed by the sensed winding, for applying a signal to the feedback winding that tends to reduce the flux sensed by the sense winding. A feedback circuit is provided, and includes a low-pass filter, for feeding back a signal that depends on the output signal to the first circuit means. A circuit is provided for determining the presence of input signal offsets, and for generating offset indication signals in response thereto.

Abstract: A circuit arrangement for providing a store of energy for actuating an electrically operable device, incorporating a reservoir capacitor, comprising a transformer having low resistance windings, the primary winding of which is connectable to an alternating current high voltage supply in series with at least one resistance capacitor, and the secondary winding of which is connected to the reservoir capacitor through a rectifier, the capacitor being connectable to an electrically operable device, with the turns ratio of the transformer such as to produce a secondary current of sufficient magnitude to charge the reservoir capacitor in the time available for successive operations or successive operational sequences of the device.

Abstract: A sensor for measuring large magnitudes of A.C. current utilizes a current divider having parallel conductors and a current comparator coupled to one of the conductors so arranged as to perform first and second stages of scaling of the A.C. current to obtain an output signal from the sensor proportional to the A.C. current. The overall sensor ratio is the product of the ratios of the first and second stages, thereby permitting very large ratios to be obtained. Components of the sensor are arranged so as to cause cancellation of magnetic fields by the sensor and to make the sensor immune from incident magnetic fields.

Abstract: A transimpedance circuit for generating an output voltage replica of an alternating current input has its accuracy improved by the use of a current comparator, the ratio windings of the comparator respectively carrying a current proportional to the input current and a current proportional to the output voltage. A further winding of the comparator detects any ampere-turns imbalance in the ratio windings, and, as a result, generates a correction signal proportional to such imbalance. This correction signal is then employed to correct the output voltage.

Abstract: A current sensing apparatus includes a first transformer having a core which is cyclically driven into forward and reverse saturation, and a second transformer having a separate core. The sensing apparatus includes circuitry for separating the sensed current component from the magnetizing current in the secondary winding of the first transformer. The apparatus may also include correction circuitry to cancel the effects of ripple current on the output due to both the magnetization current and errors due to the presence of the ripple cancellation circuitry itself. The present sensing apparatus provides electrical isolation between the primary circuit and the sensing circuit, has wide bandwidth, and is sensitive to temperature, temperature gradient, mechanical forces, aging (creep) and noise.

Abstract: An active current transformer has a primary conductor in which a current is to be measured and a secondary conductor in which a measuring current is generated in use. A feedback sensor provides an induced voltage and an amplifier receives a signal induced in the feedback sensor and generates the measuring current in the secondary conductor. The primary and secondary conductors are located in first and second magnetic circuits respectively, the first and second circuits having a common path over at least a part of their respective lengths. The feedback sensor is disposed on the common path of the first and second magnetic circuits so that, in use, the magnetic flux in the second path can be made substantially equal to that in the first path by operation of the amplifier in response to the voltage in the feedback sensor.

Abstract: An apparatus for recovering an alternating variable having a direct current component in a controlled semiconductor component includes an electromagnetic transducer for measurement having a secondary winding. A sample and hold element has a trigger input, an output and another input connected to the secondary winding of the transducer. A control system for the semiconductor component is connected to the trigger input for feeding trigger pulses from the control system to the trigger input at respective control times of the semiconductor component. A comparator has a first input connected to the output of the sample and hold element for receiving an output signal proportional to the direct current component, a second input connected to the secondary winding of the transducer and an output supplying the recovered alternating variable.

Abstract: An adjustable electronic load for testing current transformers and/or voltage transformers, the load having connected, between its input current terminals, a series connection including the input of a current-to-voltage converter and the output of a controlled generator, and having connected, between its input voltage terminals, the input of a voltage-to-voltage converter. The outputs of the current-to-voltage converter and the voltage-to-voltage converter are each connected via an impedance to a control input of the controlled generator. The voltage-to-voltage converter and the current-to-voltage converter each comprise at least one amplifier with adjustable amplification. The amplifications of the two adjustable amplifiers are adjustable jointly in opposite directions.

Abstract: A remote sensing and communications system for installation on energized high voltage conductors is disclosed herein. The sensor modules are capable of measuring electrical, mechanical or environmental parameters in the vicinity of a high voltage conductor. The module digitizes and communicates the measured quantities via a communications subsystem mounted on and powered by an energized high voltage conductor without requiring a circuit interruption. Communications to a Central or Regional dispatch center at any desired distance from the sensing location is achieved using Ku-band or C-band spread spectrum satellite communications, or using the Geosynchronous Orbiting Environmental Satellites (GOES), or through fiber optic communications links.Individual subsystem modules are generally toroidal in shape and can be mounted on an energized high voltage conductor using a hot-stick or other means.

Abstract: The invention is a locally isolated regulated power supply providing a regulated dc power output from an ac current source having a large dynamic range. The power supply comprises an ac-to-dc converter for providing a rectified dc output from an ac current input. The converter includes a current transformer in combination with a rectifier. The current transformer has a saturable magnetic core for receiving primary and secondary windings. The current transfomer produces a reduced secondary output voltage that is a function of the ac system current characterized by the decreased coupling between the core and secondary winding as the core approaches saturation during substantial increases in the ac system current. One or more secondary windings and associated circuitry can be provided. In addition, an electronically controlled switch or shunt having as inputs a predetermined reference voltage and the dc output voltage of the rectifier or a signal equivalent thereto is connected across the converter.

Abstract: Two ferromagnetic cores (11, 12) are provided for a transformer, only one of the cores (11) exhibits an air gap (13) in which a Hall effect element (3) is housed. The current flowing in a conductor (10) can be direct or alternating current and induces in the core (11) a corresponding magnetic field which makes it possible to obtain a signal on the element (3). This signal is amplified by an amplifier (8). The output current from amplifier (8) is applied to a winding wound around both cores (11, 12). For direct current and low frequency current, the winding current is proportional to the current in conductor (10). When the frequency of the current flowing through conductor (10) exceeds a certain value (several kHz), the gain of the amplifier (8) diminishes. A linear relationship between the conductor current and the current in the winding is maintained, however, because the high frequency is transmitted to the winding by the core (12).

Abstract: In conventional subminiature current transformers, voltage withstandability property is not reliable and frequency characteristics are inferior. The current transformer of the invention, advantageously, is able to withstand high voltages and also has other advantageous characteristics. A primary coil and a secondary coil are wound about individual bobbins disposed on two L-shaped legs connected together to form a square "O" shaped core. Compensation for various errors is accomplished by a condenser and a resistor connected between the input and output terminals of an operational amplifier (of the integrated circuit type) which is connected to the output of the secondary coil. The primary and secondary core areas are selectively controlled as to the currents applied to enable the transformer to withstand the high voltages.