Chemistry: analytical and immunological testing – Lubricant – grease – mineral oil – hydrocarbon oil product – or...
Reexamination Certificate
1999-07-22
2001-05-22
Alexander, Lyle A. (Department: 1743)
Chemistry: analytical and immunological testing
Lubricant, grease, mineral oil, hydrocarbon oil product, or...
C436S128000, C436S164000, C436S166000, C422S067000, C422S082050
Reexamination Certificate
active
06235532
ABSTRACT:
The present invention relates to detection of furfuraldehyde (FFA) in transformer oil.
The lifetime of a transformer is often limited by the ageing or degradation (polymerisation) of the paper insulation which is used on the transformer windings. Indirect methods of examining the paper insulation inside a transformer have to be used because it is impractical to examine the paper insulation inside a transformer directly.
A known method of determining the quality of the paper insulation relies on the fact that the thermal ageing process of the paper is accompanied by the evolution of several paper by-products into the transformer oil in which the transformer core is immersed. These by-products include gases such as CO and CO
2
and a chemical compound called furfuraldehyde.
The gases CO and CO
2
can be produced by the thermal degradation of the oil itself. Furfuraldehyde, however, is only produced by degradation of the paper, so its detection can provide an early indication of the overheating of the paper insulation.
The current practice involves periodically collecting samples of oil from the transformer or transformers to be tested, transporting the samples to a laboratory, usually remote from the transformers, and analysing the samples using a colourimetric process.
The colourimetric process relies on the specific reaction between FFA and the compound aniline acetate which yields a complex with a bright pink colour the intensity of which is a characteristic which can be measured photo-optically and which correlates with the concentration of FFA in the transformer oil. The liquid reagents used during the chemical analysis (and the fumes produced) are toxic if ingested and therefore great care must be taken during the laboratory chemical analysis.
Present practices therefore do not enable an on-the-spot assessment (or estimate) of the state of the paper insulation via FFA measurements to be made. The analyses are conducted in a chemical laboratory, sometimes days after the oil samples were actually extracted from the transformers. Thus the analysis is slow and expensive. This procedure also introduces a long time delay (for example one week) between taking a sample of oil from a transformer containing faulty paper insulation and determining that the paper insulation is faulty. The effect of this delay is that the transformer is in use for the delay period (one week) even though the paper insulation is faulty and in need of replacement.
It is an object of the present invention to mitigate or obviate one or more of the above disadvantages.
This is achieved by entrapping aniline acetate which is indicative of the state of the paper in an inert matrix to produce a porous solid sensor which facilitates on-site detection of paper degradation without exposing the user to toxic chemicals.
According to a first aspect of the present invention there is provided a solid sensor for detecting furfuraldehyde in oil, where the sensor comprises a solidified matrix in which aniline acetate is entrapped, and where the matrix is made of an inert material which allows ingress of furfuraldehyde from the oil to react with the aniline acetate to yield an entrapped complex having a characteristic which is photo-optically measurable and which correlates with the concentration of furfuraldehyde in the oil.
Preferably, the matrix material is a sol-gel.
The sold sensor may have sufficient thickness to be self-supporting or it may take the form of a thin film or coating carried by a substrate which may be transparent (e.g. glass), or optically reflective to permit photo-optic measurement by an interrogating beam. The solid sensor and its substrate may alternatively form a waveguide structure for an interrogation beam.
According to a second aspect of the present invention there is provided a method of manufacturing a solid sensor for detecting furfuraldehyde in oil, the method comprising the steps: of forming a colloidal suspension (sol) of methyltrimethoxysilane (MTMS) in a catalyst at an elevated temperature, reducing the temperature of the sol to ambient, preparing liquid aniline acetate, where the reaction temperature is maintained below ambient (20° C.) during the preparation of the liquid aniline acetate, and thereafter stirring into the sol at ambient temperature a quantity of the prepared aniline acetate in liquid form so as to form a sol and aniline acetate mixture, and thereafter gelating and drying the mixture in air substantially at ambient temperature.
By virtue of the low temperatures used in preparing the solid sensor, and particularly the low reaction temperature during preparation of the liquid aniline acetate, the chemical functionality of the liquid aniline acetate is retained despite being encapsulated in the solid sensor.
According to a third aspect of the present invention there is provided a method of determining the status of paper insulation in an oil-filled transformer, comprising the steps of: providing a solid sensor formed of a porous solidified inert matrix in which aniline acetate is entrapped, inserting the sensor into the oil for a time sufficient to allow furfuraldehyde to react with aniline acetate encapsulated in the sensor so as to form a complex having a characteristic which is photo-optically measurable and which correlates with the concentration of furfuraldehyde in the oil, thereafter irradiating the sensor with an optical input signal of a fixed wavelength, detecting and measuring an optical output signal received from the sensor, comparing the output signal with a reference to determine the amount of furfuraldehyde that was detected, and providing a qualitative indication of the state of the paper insulation based on the amount of furfuraldehyde that was detected.
Preferably, an additional step of removing the sensor from the oil is performed prior to irradiating the sensor with the optical input signal of a fixed wavelength.
It will be understood that the method also includes the step of selecting the fixed wavelength from the range of 500 nm to 600 nm.
The characteristic which correlates with the concentration of furfuraldehyde in the oil may be the pink colour intensity of the complex, which is measurable by absorbance of the optical input signal so that the output signal is of the same wavelength as the input signal. Alternatively, the characteristic may be the fluorescence of the complex when irradiated by the optical input signal so that the output signal is of a different wavelength from the input signal.
These and other aspects of the invention will become apparent from the following description when taken in combination with the accompanying drawings in which:
REFERENCES:
patent: 4514503 (1985-04-01), Orelup
patent: 5646047 (1997-07-01), Bird et al.
patent: 27 32 288 A1 (1979-02-01), None
patent: 93 21513 (1993-10-01), None
Ingersoll Christine M, Bright Frank V; “Using sol-gel-based platforms for chemical sensors”; vol. 27, No. 1, Washington, DC, USA, p. 26-31 XPOO2060846.
Pahlavanpour B et al; “Development of a rapid spectrophotometry method for analysis of furfuraldehyde in transformer oil as an indication of paperageing”; IEEE 1993 Annual Report; pp. 493-498, XPOO2060847.
Blue Robert George
Uttamchandani Deepak Gulabrai
Alexander Lyle A.
Alston & Bird LLP
University of Strathclyde
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