# US 2014/0191774 A1 · Apparatus and a method for testing winding resistances of transformers > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0191774 A1 - Document ID: US20140191774A1 - Status: Published application - Kind: A1 - Application number: 14/116,476 - Filed: 2012-05-07 - Published: 2014-07-10 - Earliest claimed: 2011-05-17 - Assignees: Haefely Test AG - Inventors: Marc Muller - Web page: https://patentgrep.com/patent/US20140191774A1 ## CPC - G01R 27/14: Measuring resistance by measuring current or voltage obtained from a reference source (G01R27/16, G01R27/20, G01R27/22 take precedence) - G01R 31/62: Testing of transformers - G01R 31/72: Testing of electric windings (testing of transformers G01R31/62) - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) ## Abstract The present invention relates to an apparatus for measuring winding resistances of windings in a delta-connected transformer, comprising at least a first and a second DC current source (S1, S2) connected each between the phase ends of a first (A) and a second leg (C; B) respectively of the primary side (P) of the transformer and at least a third DC current source (S3) connected between two nodes (a, b) of the secondary side (S) of the transformer. Furthermore the invention relates to a method for measuring a winding resistance of windings in delta-connected transformers, comprising the steps of applying a first and a second measuring current to each one of two corresponding legs (C, B), applying a third measuring current (I2) between two nodes (b, a) of a pair of windings on the secondary side (S) and measuring at least a winding resistance of the winding between said nodes (b, a) on the secondary side (S) of the transformer and/or the winding resistance of a leg (A) of the primary side (P) as soon as an inductive voltage drop in the windings substantially equals zero. ## Claims ### Claim 1 Apparatus for measuring at least a winding resistance of windings in a delta-connected transformer, comprising at least a first and a second DC current source connected each between phase ends of a first and a second leg respectively of a primary side of the transformer and at least a third DC current source connected between two nodes of a secondary side of the transformer and a first and/or a second voltage measurement device, wherein a first DC voltage drop on a third leg of the primary side is measurable by the first voltage measurement device and/or a second DC voltage drop on a leg of the secondary side of the transformer is measurable by the second voltage measurement device. ### Claim 2 (depends on 1) Apparatus according to claim 1, wherein the first and the second current source deliver equal measuring DC currents. ### Claim 3 (depends on 1) Apparatus according to claim 1, wherein a total current delivered by both the first and the second current sources, the total current being a sum of a first measuring current and a second measuring current, is substantially equal to a third measuring current, corrected by the turns ratio and a vector group of the transformer, delivered by the third current source and the total of the first and second measuring currents flows in an opposite direction to the third measuring current in such a way that no magnetic flux is generated in the transformer's core. ### Claim 4 (depends on 1) Apparatus according to claim 1, further comprising at least a temperature sensor by means of which the temperature of a winding is measurable. ### Claim 5 (depends on 1) Apparatus according to claim 1, comprising a multiplexer connecting the first, second and third DC current sources to selectable phases of the transformer and/or the first and/or the second voltage measurement device. ### Claim 6 (depends on 5) Apparatus according to claim 5, further comprising a control system connected to the multiplexer and/or the first and/or the second and/or the third DC current source and to the first and/or the second voltage measurement device. ### Claim 7 (depends on 6) Apparatus according to claim 6, wherein the control system comprises a graphical user interface by means of which at least a measurement configuration parameter is selectable by an operator. ### Claim 8 (depends on 6) Apparatus according to claim 6, wherein a first and/or a second measuring current delivered by the first and the second current source respectively is adjustable by the control system. ### Claim 9 (depends on 5) Apparatus according to claim 5, wherein a wiring configuration of the multiplexer is configurable by the control system. ### Claim 10 (depends on 1) Apparatus according to claim 1, further comprising a demagnetization circuit by means of which the magnetization of the transformer's core is substantially eliminated. ### Claim 11 Method for measuring a winding resistance of windings in Delta-connected transformers, comprising the steps of: applying a first and a second measuring current to each one of two corresponding legs of a primary side of the transformer by means of a first and a second DC current source, respectively, applying a third measuring current between two nodes of a pair of windings on a secondary side of the transformer by means of a third current source, and measuring at least a winding resistance of the winding between said nodes on the secondary side of the transformer and/or the winding resistance of a leg of the primary side as soon as an inductive voltage drop in the windings substantially equals zero. ### Claim 12 (depends on 11) Method according to claim 11, wherein a total current delivered by both the first and the second current sources and the third measuring current delivered by the third current source are adjusted in such a way that the total of the first and second measuring currents is substantially equal to the third measuring current corrected by the turns ratio and a vector group of the transformer and that the total of the first and second measuring currents flows in an opposite direction to the third measuring current in such a way that no magnetic flux is generated in the transformer's core. ### Claim 13 (depends on 11) Method according to claim 11, wherein the first, the second and the third measuring DC currents are applied via a multiplexer connecting the DC current sources to the transformer. ### Claim 14 (depends on 13) Method according to claim 13, wherein the multiplexer has been configured, previously to applying the first, second and third measuring currents, by switching such a connection of the first, second and third DC current sources to the transformer that a phase shift configuration of the transformer is taken into account. ### Claim 15 (depends on 13) Method according to claim 13, wherein the multiplexer is configured programmatically by specifying at least a connection type and a phase shift of the transformer and subsequently triggering the according switching connections between inputs and outputs of the multiplexer. ### Claim 16 (depends on 11) Method according to claim 11, wherein the measure for the winding resistance is corrected by taking into account a respective winding temperature measured by means of at least a temperature sensor. ### Claim 17 (depends on 11) The method of claim 11, wherein the transformer is in a generator or motor.