# US 10,139,432 B2 · Methods and systems relating to improved AC signal performance of dual stage transformers > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,139,432 B2 - Document ID: US10139432B2 - Status: Granted - Kind: B2 - Application number: 15/220,058 - Filed: 2016-07-26 - Published: 2016-11-17 - Granted: 2018-11-27 - Earliest claimed: 2013-10-21 - Assignees: Guildline Instruments Limited - Applicants: Guildline Instruments Limited - Inventors: Tomasz Barczyk - Web page: https://patentgrep.com/patent/US10139432B2 ## CPC - G01R 15/183: {using transformers with a magnetic core} - G01R 15/185: {with compensation or feedback windings or interacting coils, e.g. 0-flux sensors (using galvano-magnetic field sensors G01R15/20; conversion of DC into AC using transductors G01R19/20)} - G01R 19/0092: {Measuring current only} - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) ## 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. ## Claims ### Claim 1 A method of improving the AC accuracy of a dual stage transformer comprising: providing the dual stage current transformer comprising a plurality of magnetic cores, a primary winding, a first secondary winding, and a second secondary winding; either providing a first resistor across only the first secondary winding to generate a first voltage and providing a second resistor across only the second secondary winding, the second resistor disposed in series with the first resistor in order to add a compensating voltage to the first voltage; or connecting a first end of the first secondary winding to a first end of the second secondary winding at a midpoint of a pair of load resistors disposed in series, connecting a second end of the first secondary winding to another end of a first load resistor of the pair of load resistors and to a first input of a differential amplifier via a first resistor, and coupling another end of the other load resistor of the pair of load resistors and to a second input of the differential amplifier via a second resistor, where the first ends of the first and second secondary windings are both disposed in the same direction along a magnetic core of the plurality of magnetic cores relative to their respective second ends; measuring a DC signal within a second stage of the dual stage transformer, the DC signal generated in dependence upon a DC aspect of a signal applied to a first stage of the dual stage transformer; measuring an AC signal applied to the first stage of the dual stage transformer, the AC signal measurement being made across the first and second resistors; and generating with a processing circuit a corrected AC signal measurement in dependence upon the measured DC signal and the measured AC signal. ### Claim 2 (depends on 1) The method according to claim 1, wherein measuring the DC signal comprises at least one of: disposing a magnetic field sensor within a core of the second stage of the dual stage transformer; and disposing a magnetic field sensor upon a surface of the second stage of the dual stage transformer. ### Claim 3 (depends on 1) The method according to claim 1, further comprising applying a predetermined magnetic field to the first stage of the dual stage transformer, wherein the predetermined magnetic field is determined by the processing circuit in dependence upon at least the DC signal. ### Claim 4 (depends on 3) The method according to claim 3, further comprising applying a first predetermined magnetic field to the first stage of the dual stage transformer; applying a second predetermined magnetic field to the second stage of the dual stage transformer; wherein the first and second predetermined magnetic fields are determined by the processing circuit in dependence upon at least the DC signal. ### Claim 5 (depends on 1) The method according to claim 1, wherein generating a corrected measurement of the measured AC signal comprises applying a correction derived from a predetermined mathematical function with the DC signal as a variable having coefficients established at least one of generically for all transducers and specifically the transducer. ### Claim 6 (depends on 1) The method according to claim 1, wherein the processing circuit integrates an output signal from a magnetic sensor disposed within a core of the second stage or upon a core of the second stage of the dual stage transformer thereby allowing operation of the magnetic sensor with small AC flux components and improved AC to DC signal ratio. ### Claim 7 A dual stage AC transformer comprising: first and second transformer stages, a primary winding, a first secondary winding, and a second secondary winding; a first resistor across only the first secondary winding thereby generating a first voltage in dependence of a current flowing within a first stage of the dual stage AC transformer; a second resistor across only the second secondary winding, the second resistor disposed in series with the first resistor in order to add a compensating voltage to the first voltage, the compensating voltage generated in dependence of a current flowing within a second stage of the dual stage AC transformer; a DC magnetic sensor coupled to the second stage of the dual stage AC transformer for generating a signal proportional to a DC magnetic field within the dual stage current transformer; and a processing circuit for generating a corrected AC signal measurement in dependence upon the output of the DC magnetic sensor and the voltage across the first resistor and the second resistor. ### Claim 8 (depends on 7) The dual stage AC transformer according to claim 7, wherein the DC magnetic sensor is at least one of: disposed within a core of the second stage of the dual stage transformer; and disposed upon a surface of the second stage of the dual stage transformer. ### Claim 9 (depends on 7) The dual stage AC transformer according to claim 7, wherein a predetermined magnetic field is applied to the first stage of the dual stage transformer, wherein the predetermined magnetic field is determined by the processing circuit in dependence upon at least the DC signal. ### Claim 10 (depends on 7) The dual stage AC transformer according to claim 7, wherein generating a corrected measurement of the measured AC signal comprises applying a correction derived from a predetermined mathematical function with the DC signal as a variable having coefficients established at least one of generically for all transducers and specifically the transducer. ### Claim 11 (depends on 7) The dual stage AC transformer according to claim 7, wherein; a first predetermined magnetic field is applied to the first stage of the dual stage transformer; a second predetermined magnetic field is applied to the second stage of the dual stage transformer; wherein the first and second predetermined magnetic fields are determined by the processing circuit in dependence upon at least the DC signal. ### Claim 12 (depends on 7) The dual stage AC transformer according to claim 7, wherein the processing circuit integrates an output signal from a magnetic sensor disposed at least one of within a core of the second stage and upon a core of the second stage of the dual stage transformer thereby allowing operation of the magnetic sensor with small AC flux components and improved AC to DC signal ratio. ### Claim 13 A dual stage AC transformer comprising: first and second transformer stages, a primary winding, a first secondary winding, and a second secondary winding, wherein a first end of the first secondary winding is coupled to a first end of the second secondary winding at a midpoint of a pair of load resistors disposed in series; a second end of the first secondary winding is coupled to another end of a first load resistor of the pair of load resistors and to a first input of a differential amplifier via a first resistor; and a second end of the second secondary winding is coupled to another end of the other load resistor of the pair of load resistors and to a second input of a differential amplifier via a second resistor; wherein the first ends of the first and second secondary windings are both disposed in the same direction along a magnetic core of the plurality of magnetic cores relative to their respective second ends; a DC magnetic sensor coupled to a second stage of the dual stage AC transformer for generating a signal proportional to a DC magnetic field within the dual stage current transformer; and a processing circuit for generating a corrected AC signal measurement in dependence upon the output of the DC magnetic sensor and the voltage across the first and second resistors. ### Claim 14 (depends on 13) The dual stage AC transformer according to claim 13, wherein the DC magnetic sensor is at least one of: disposed within a core of the second stage of the dual stage transformer; and disposed upon a surface of the second stage of the dual stage transformer. ### Claim 15 (depends on 13) The dual stage AC transformer according to claim 13, wherein a predetermined magnetic field is applied to the first stage of the dual stage transformer, wherein the predetermined magnetic field is determined by the processing circuit in dependence upon at least the DC signal. ### Claim 16 (depends on 13) The dual stage AC transformer according to claim 13, wherein generating a corrected measurement of the measured AC signal comprises applying a correction derived from a predetermined mathematical function with the DC signal as a variable having coefficients established at least one of generically for all transducers and specifically the transducer. ### Claim 17 (depends on 13) The dual stage AC transformer according to claim 13, wherein; a first predetermined magnetic field is applied to the first stage of the dual stage transformer; a second predetermined magnetic field is applied to the second stage of the dual stage transformer; wherein the first and second predetermined magnetic fields are determined by the processing circuit in dependence upon at least the DC signal. ### Claim 18 (depends on 13) The dual stage AC transformer according to claim 13, wherein the processing circuit integrates an output signal from a magnetic sensor disposed at least one of within a core of the second stage and upon a core of the second stage of the dual stage transformer thereby allowing operation of the magnetic sensor with small AC flux components and improved AC to DC signal ratio. ### Claim 19 A coreless AC transformer comprising: a magnetic field sensor; a primary winding for connection to an electrical circuit; a secondary winding for generating a measurement current to be employed in determining a current flowing within the electrical circuit to which the primary winding is connected; and the primary winding and secondary winding are in either; a first configuration wherein the primary winding and secondary winding are axially aligned and disposed either side of the magnetic field sensor; or in a second configuration wherein the primary winding and secondary winding are axially aligned and disposed such that the magnetic field sensor is disposed within both the primary winding and the secondary winding; wherein the primary winding, second winding, and magnetic field sensor are not coupled via a magnetic material. ### Claim 20 (depends on 19) The coreless AC transformer according to claim 19, wherein the magnetic field sensor outputs are coupled to a differential amplifier; the output of the differential amplifier is coupled to one end of the secondary winding; and the other end of the secondary winding is coupled to ground via a resistor.