DEVICE AND METHOD FOR ASSESSING THE DEGRADATION OF THE INSULATION OF AN OIL-INSULATED TRANSFORMER

• US 20140347071A1
• Filed: 11/14/2012
• Published: 11/27/2014
• Est. Priority Date: 11/23/2011
• Status: Abandoned Application

• Current Assignee: Techimp HQ S.r.L.
• Original Assignee: Techimp Technologies S.r.l.
• Inventors: Montanari, Gian Carlo, Serra, Stefano, Fattori, Matteo
• Application Number:
  US14/355,992
• Publication Number:
  US 20140347071A1
• Time in Patent Office: Days
• US Class Current: 324/553
• CPC Class Codes: G01N 17/00 Investigating resistance of materials to the weather, to corrosion, or to light
• CPC Class Codes: G01N 17/02 Electrochemical measuring systems for weathering, corrosion or corrosion-protection measurement
• CPC Class Codes: G01N 33/28 Oils , i.e. hydrocarbon liquids edible oils or edible fats G01N33/03
• CPC Class Codes: G01R 31/1281 of liquids or gases
• CPC Class Codes: H01F 2027/404 Protective devices specially adapted for fluid filled transformers
• CPC Class Codes: H01F 27/402 Association of measuring or protective means

Abstract

A device (1) for assessing the corrosion of the transformer windings in an oil-insulated transformer comprising a copper conductor (2) immersed in the oil. The change of the resistance of the copper conductor (2) over time is measured, e.g. using a Wheatstone bridge (2, 12a, 12b, 12c), and used to assess the degradation of the copper exposed to the insulation oil. The temperature of the copper conductor can be controlled by an heating element and a temperature sensor.

Claims

1. A method for assessing the degradation of the insulation of an oil-insulated transformer due to the corrosion of the transformer windings, characterized in that it comprises the following steps:

preparing a structure (18) comprising a copper active element (2) defining a conductive path (3);

coupling the structure (18) to the transformer in such a way that the active element (2) is in contact with the oil;

keeping the active element (2) immersed in the oil at least for a predetermined interval of time between a starting instant and a final instant;

measuring a value representing the resistance of the active element (2) at the final instant;

comparing the value measured at the final instant with a value representing the resistance of the active element (2) at the initial instant in order to obtain an indication of the degradation.

2. The method according to claim 1, comprising a step of heating the active element (2) in order to take it to a predetermined temperature.

3. The method according to claim 2, wherein the step of heating the active element (2) comprises keeping the active element (2) at a constant temperature in the predetermined interval of time.

4. The method according to claim 2, wherein the active element (2) is heated to a variable temperature according to a profile corresponding to a load profile of the transformer in the predetermined time interval.

5. A device (1) for assessing the degradation of the insulation of an oil-insulated transformer due to the corrosion of the transformer windings, characterized in that it comprises:

a structure (18) having a first portion (5) and a second portion (4), the structure (18) being configured to be attachable to the transformer in such a way that the first portion (5) is outside the transformer and the second portion (4) is inside the transformer and in contact with the oil;

an active element (2) made of copper, defining a conductive path (3) and connected to the second portion (4) to be operatively in contact with the oil;

electrical contacts (17) electrically connected to the element (2) at the terminals of the conductive path (3) to allow reading of a value representing the resistance of the element (2) when the structure (18) is attached to the transformer.

6. The device according to claim 5, wherein the electrical contacts (17) are located in the first portion (5) to allow reading of the value representing the resistance of the active element (2) from outside the transformer without removing the device.

7. The device according to claim 5 or 6, wherein the active element (2) is made in such a way as to define a conductive path with elongate shape and reduced cross section.

8. The device according to any of the claims from 5 to 7, wherein the active element (2) is located on an outside surface of the second portion (4), the outside surface being defined by an electrical insulating element.

9. The device according to any of the claims from 5 to 8, comprising heating means (8) operatively connected to the second portion (4) of the structure (18) in order to heat the active element (2) coupled thereto.

10. The device according to claim 9, wherein the heating means (8) comprise a heating element inside the second portion (4) of the structure (18) and a thermally conductive support (6) interposed between the heating element and the active element (2).

11. The device according to claim 10, comprising a layer (7) of insulating material interposed between the active element (2) and the support (6).

12. The device according to any of the claims from 9 to 11, comprising a temperature sensor configured to measure the temperature of the active element (2) and control means for driving the heating means (8), connected to the temperature sensor to receive a signal relating to the temperature of the active element (2) and programmed to take the active element (2) to a predetermined temperature.

13. The device according to any of the claims from 5 to 12, comprising three further copper elements (12a, 12b, 12c), connected to the electrical contacts (17) in such a way that the active element (2) defines one of the legs of a Wheatstone bridge connected to the electrical contacts (17).

14. The device according to any of the claims from 5 to 13, comprising means (9) for measuring the resistance of the active element (2), connected to the electrical contacts (17) to measure a signal representing the resistance of the conductive path (3), the measuring means (9) being positioned in a housing defined by the first portion (5) of the structure (18).

15. The device according to claim 14, comprising a processor programmed to process at least one resistance value measured for the active element (2) at least at the final instant of a predetermined interval of time during which the device has been kept coupled to the transformer, by comparing the value measured at the final instant with a value representing the resistance of the active element (2) at the starting instant in order to derive an indication of the degradation.

16. Use of a device according to any of the claims from 5 to 14 for assessing the degradation of the insulation of an oil-insulated transformer due to the corrosion of the transformer windings, comprising the following actions:

coupling the device (1) to the transformer in such a way that the active element (2) is in contact with the oil;

keeping the device (1) coupled to the transformer for a predetermined interval of time, between a starting instant and a final instant in such a way that the active element (2) remains immersed in the oil during the predetermined interval of time;

measuring a value representing the resistance of the active element (2) at the final instant;

comparing the value measured at the final instant with a value representing the resistance of the active element (2) at the initial instant in order to obtain an indication of the degradation.