NZ720910B - A transformer and method of manufacture - Google Patents

Abstract

transformer including a tube within the transformer windings that is wound with the windings to form a coil around the core. The tube is dimensioned to receive an optical fibre for measuring temperature and optionally other parameters. The temperature sensor may be one or more Bragg grating provided at intervals along the optical fibre. The optical fibre may pass through oil surrounding the transformer to allow measurement of parameters relating to the oil. The arrangement allows optical fibres to be installed or replaced after transformer manufacture. ided at intervals along the optical fibre. The optical fibre may pass through oil surrounding the transformer to allow measurement of parameters relating to the oil. The arrangement allows optical fibres to be installed or replaced after transformer manufacture.

Description

A TRANSFORMER AND METHOD OF MANUFACTURE FIELD This invention relates to a transformer, a method of manufacture and methods of monitoring a transformer. More particularly, but not exclusively, it relates to use of a fibre Bragg grating positioned within a transformer to monitor temperature and optionally other parameters.

BACKGROUND When distribution transformers are under volatile loads, it is necessary to monitor the temperature of hot spots with the greatest accuracy possible for accurate modelling. These models can be used to determine the health of the transformer and whether it is overloaded. With the power grid being increasingly exposed to volatile loads with the growing use of electric vehicle chargers and photovoltaic systems there is an increasing need to accurately monitor transformer health.

Measuring temperature using fibre optics is well established. Fibre Bragg grating (FBG) sensors are one such suitable sensor. Fibre Bragg gratings are formed by providing a refractive index modulation in the core of an optical fibre. When a broadband light pulse is propagated down the fibre, a narrow wavelength of the pulse is reflected back while the rest is transmitted.

The reflected wavelength is dependent on the spacing (grating period) and effective refractive index of the modulations, which are dependent on temperature and applied strain. Therefore a change in temperature will cause a shift in the reflected, or Bragg wavelength.

Fibre Bragg gratings can be used to measure other parameters that may be important to the transformer health analysis, such as chemical content or measurements relating to the strain dependence.

One of the major advantages of the fibre Bragg grating sensor is the multiplexing capability. Sensors with distinct Bragg wavelengths having different grating periods can be formed on a single fibre, so that when a broadband light pulse is transmitted through the fibre, there are several distinct reflected pulses.

Optical fibres are reasonably fragile and may be broken during manufacture as the windings are being wound with an optical fibre. It is time consuming and expensive to unwind a transformer and replace a faulty optical fibre. Further, if the optical fibre is not optimally positioned to measure transformer hot spots it is not possible to adjust the optical fibre position without unwinding the transformer windings. Finally, should an optical fibre fail in use it is extremely expensive and inconvenient to remove a transformer and replace an optical fibre.

It is an object of the invention to provide a transformer and methods of forming and repairing a transformer that overcome the above disadvantages or to at least provide the public with a useful choice.

SUMMARY According to one example embodiment there is provided a transformer, having a core with one or more windings wound about the core wherein a separate tube is wound with the windings, to form a coil about the core, and dimensioned to receive an optical fibre, after the windings and tube are wound on the core.

According to another example embodiment there is provided a method of manufacturing a transformer comprising the steps of: i. providing a transformer core; and ii. winding one or more windings about the core whilst winding a separate tube between the one or more windings, wherein the tube is dimensioned to receive an optical fibre after the windings and tube are wound on the core.

There is also provided a method of repairing a transformer by withdrawing an optical fibre from the tube and inserting a new optical fibre in the tube.

It is acknowledged that the terms “comprise”, “comprises” and “comprising” may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, these terms are intended to have an inclusive meaning – i.e., they will be taken to mean an inclusion of the listed components which the use directly references, and possibly also of other non-specified components or elements.

Reference to any document in this specification does not constitute an admission that it is prior art, validly combinable with other documents or that it forms part of the common general knowledge.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings which are incorporated in and constitute part of the specification, illustrate embodiments of the invention and, together with the general description of the invention given above, and the detailed description of embodiments given below, serve to explain the principles of the invention, in which: Figure 1 Is a schematic diagram illustrating a transformer having a tube provided within the transformer windings for accommodating an optical fibre; Figure 2 is a diagram of a transformer measuring system according to one embodiment, having a single fibre Bragg grating sensor; Figure 3 is a diagram of a transformer measuring system according to another embodiment, having a several fibre Bragg grating sensors on a single fibre; Figure 4 is a diagram of a transformer measuring system according to another embodiment, having a several fibre Bragg grating sensors on several fibres; and Figure 5 is a diagram of a transformer measuring system according to another embodiment, having a several fibre Bragg grating sensors on several fibres and a wavelength reference.

DETAILED DESCRIPTION Figure 1 shows a transformer 1 having a ferromagnetic core 2 about which is wound one or more conductive winding 3 (it may be a single winding with taps or multiple windings). A tube 4 has been provided within the winding space and has been wound on the core as the conductive windings 3 are wound. The tube 4 is dimensioned so as to allow an optical fibre 5 to be inserted into tube 4 after the windings 3 and tube 4 have been wound on the core 3.

The tube 4 may suitably be formed of an outer PTFE (Polytetrafluoroethylene) tube and an inner PEEK (Polyetheretherketone) tube. The PTFE tube may suitably have an internal diameter of 1.6mm and an outer diameter of 3mm. The PEEK tube may suitable have an internal diameter of 0.3 to 0.6mm and an outside diameter of 0.6 to 0.9mm. The optical fibre typically has a diameter of about 0.2 mm. The optical fibre may be provided within the PEEK tube and sealed at one end and be free at the sensor end to allow oil within the transformer to come into contact with the sensor. This arrangement isolates the optical fibre from stress and so improves the accuracy of temperature measurement. Due to the low coefficient of friction of the PTFE tube the PEEK tube and optical fibre may be easily inserted into and removed from the PTFE tube. An end stopper may be provided to secure the components in desired relative positions. Where only a single sensor is employed it is preferred to position the fibre Bragg grating about 2/3 of the distance from the core to the outside of the transformer windings.

Where multiple fibre Bragg gratings are employed these may be distributed throughout the windings.

The transformer 1 is in this case housed within a housing 6 filled with oil 7, although other suitable liquids may be substituted. In this example the optical fibre 5 passes through oil 7 at or near the surface of the oil so as to provide a "top oil" temperature measurement as will be described below.

Figure 2 schematically illustrates a transformer 101 and reader unit 102 according to an example embodiment. Initially, the measuring system will be described with the sensors measuring temperature only, however similar principles apply to other measurements.

The transformer 101 has a winding 103 and a tube 104, which may be located so that it passes any hot spots or points of interest as per Figure 1. The tube is sized so that an optical fibre 105 which may contain a fibre Bragg grating 106 may be inserted and removed. There is an optical connector 107 between the fibre 105 and the transformer wall. The fibre 105 may be connected to the reader unit 102 using another optical connector 107 in the reader unit wall.

The reader has a three port circulator 108, which directs laser light from a laser source 109 into the transformer towards the fibre Bragg grating, and receives the reflected light from the fibre Bragg grating and directs it towards a photodiode 110. The Bragg wavelength measurement is sent to processor 111 and the temperature is determined. Whilst only a reflectance based system is described in this specification it is to be appreciated that a transmittance based system may also be employed where the light received at the other end of an optical fibre is analysed.

An improved profile of the transformer can be obtained when multiple fibre Bragg grating sensors are used to measure several areas of interest, including hot spots and the top oil. Figure 3 shows an alternative embodiment including transformer 201 and reader 202 where the fibre 205 contains multiple fibre Bragg grating sensors 206, each measuring at different transformer locations. The fibre Bragg grating sensors are constructed with distinct Bragg wavelengths (grating periods), so the photodetector will detect reflections in several distinct frequency ranges.

It is also possible to have multiple fibres. This may be useful when there are several areas of concern spread around the transformer windings. Figure 4 shows an example having two fibres, though there may be more depending on the required measurements. The laser source 309 may be directed to a coupler unit 312 which directs the same laser beam to each of the three port circulators 308. These circulators 308 prevent further feedback from the fibre Bragg gratings into the laser. Each fibre 305 requires a separate three port circulator 308 and photodiode 310. The fibre 305 may have a single fibre Bragg grating 306 or several, depending on the number and location of the areas to be monitored.

Any of these previously discussed configurations may also have an additional wavelength reference channel. This may be used to calibrate out any non-linearity in the laser sweep signal. An example configuration is shown in Figure 5. The etalon 413 receives an additional beam from the coupler unit 412. The etalon 413 has a comb-like transmission function, with the comb peaks occurring at regular frequency intervals. This is detected by an additional photodiode 410. The etalon 413 may also be connected external to the reader unit 402 for this calibration.

The equation for the change in Bragg wavelength is given by Δλ = λ (β ΔT + β ε) B B T S Where λ is the Bragg wavelength, β is the temperature coefficient, ΔT is the change in temperature, β is the strain coefficient and ε is the strain. It has been found that coating the optical fibre, particularly with a organic modified ceramic material known as Ormocer® which improves the temperature coefficient of the fibre but is relatively expensive. Polyimide coatings improve high temperature performance but are moisture sensitive. Acrylate coatings are suitable for temperatures up to 80 degrees Celcius and are not sensitive to moisture.

The fibre Bragg grating sensors are not limited to sensing temperature. If it is desired to know other information about the transformer including pressure, vibration patterns, or hydrogen or water content, these parameters may also be measured using the same optical fibre. As shown above, the Bragg wavelength of the fibre Bragg grating sensors is dependent on both temperature and strain, so for accurate temperature measurements the sensors should be isolated from strain and vice versa. For the substance measurements, the sensor may be coated in an absorbent material which expands in the presence of a target substance, for example a Palladium coating may be used to measure hydrogen.

These measurements allow for the transformer to be profiled to determine both health and its aging rate. Important measurements include load factor, or the unbalanced loading between the top oil and hot spot temperatures and harmonic distortion on each phase for the top oil and hot spot temperatures. Additional measurements include the effects of moisture and oxygen on the transformer aging rate and the pressure rise with transformer temperature. For a full profile of the transformer health, a wide range of measurements are required.

The tube(s) allow the fibre(s) to be inserted and removed after the transformer has been constructed. This allows the attributes monitored to be changed in use by changing the optical fibre. If more or less precision is required in the temperature readings, the number of Bragg gratings and their positions may be adjusted to suit. Additionally, if different sensors are required, then these may also be substituted in. If there are changes in the performance or physical properties of the transformer during its life, it may be useful to change the sensors to give a more useful profile.

This system allows for the sensors to be introduced after manufacture and allows easy replacement. The system allows for an adaptive and accurate profile of the transformer health. The tube also protects the fibre. With these improved transformer profiles, the life and maintenance can be planned with more certainty.

While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of the Applicant’s general inventive concept.

Claims (23)

CLAIMS 1.:

1. A transformer, having a core with one or more windings wound about the core wherein a separate tube is wound with the windings, to form a coil around the core, and dimensioned to receive an optical fibre after the 5 windings and tube are wound on the core.

2. A transformer as claimed in claim 1 wherein the tube is positioned so as to allow effective measurement of transformer hot spots. 10

3. A transformer as claimed in claim 1 or claim 2 wherein the tube is formed of PTFE.

4. A transformer as claimed in claim 3 including an optical fibre located within the PTFE tube having one or more fibre Bragg grating provided along its 15 length.

5. A transformer as claimed in claim 4 wherein the optical fibre is contained within a further tube. 20

6. A transformer as claimed in claim 5 wherein the further tube is formed of PEEK.

7. A transformer as claimed in any one of claims 4 to 6 wherein a plurality of Bragg gratings are provided along the length of the optical fibre, each 25 having a different grating period.

8. A transformer as claimed in claim 7, wherein the transformer is housed in a liquid and the optical fibre passes through the liquid with one or more fibre Bragg grating being provided within the portion of the optical fibre within 30 the liquid.

9. A transformer as claimed in claim 8 wherein the liquid is oil.

10. A transformer as claimed in claim 9 wherein a Bragg grating is positioned at 35 or near the surface of the oil.

11. A transformer as claimed in claims 4 to 10 including a light source for supplying light along the optical fibre and a detector for monitoring light transmitted through or returning along the optical fibre.

12. A transformer as claimed in claim 11 wherein the detector measures temperature based on transmitted or returning light in a reflectance frequency band of the Bragg grating.

13. A transformer as claimed in claims 4 to 12, wherein one or more fibre Bragg gratings are used to measure hydrogen content.

14. A transformer as claimed in claim 13 wherein a Palladium coating is applied 10 to a fibre Bragg grating.

15. A transformer as claimed in claims 4 to 14, wherein one or more fibre Bragg grating is used to measure water content. 15

16. A transformer as claimed in claims 4 to 15, wherein one or more fibre Bragg grating is used to measure pressure.

17. A transformer as claimed in claims 4 to 16, wherein one or more fibre Bragg grating is used to measure vibration patterns.

18. A transformer as claimed in claims 4 to 17, wherein the fibre is coated with an organic modified ceramic material.

19. A transformer as claimed in claims 4 to 18, wherein the fibre is coated with 25 Polyimide.

20. A transformer as claimed in claims 4 to 19, wherein the fibre is coated with Acrylate. 30

21. A method of manufacturing a transformer comprising the steps of: i. providing a transformer core; and ii. winding one or more windings about the core whilst winding a separate tube between the one or more windings, wherein the tube is dimensioned to receive an optical fibre after the windings and tube 35 are wound on the core.

22. A method as claimed in claim 21 including the further step of feeding an optical fibre having one or more Bragg gratings along its length into the tube so that it is positioned to measure desired transformer hot spots.

23. A method of repairing a transformer as claimed in any one of claims 4 to 20 comprising withdrawing an optical fibre from the tube and inserting a new optical fibre in the tube.