Method for evaluating deterioration of insulating paper

Details Method for evaluating deterioration of insulating paper Method for evaluating deterioration of insulating paper

1999-01-26

2001-08-21

Warden, Jill (Department: 1743)

Measuring and testing

Testing of material

C073S865900, C436S002000

Reexamination Certificate

active

06276222

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a method of evaluating the deterioration of insulating paper. In particular, it relates to a method of evaluating deterioration of insulating paper at an operating temperature of an oil-filled electric apparatus such as an oil-filled transformer, an oil-filled reactor or the like, in order to diagnose the life thereof.
BACKGROUND ART
When insulating paper in an insulating oil deteriorates, the decrease in the mechanical strength thereof is quite large, while the decrease in the dielectric breakdown voltage is small. When external short-circuiting occurs in an oil-filled electric apparatus such as an oil-filled transformer, oil-filled reactor or the like, a large electromagnetic mechanical force is generated inside the electric apparatus. Accordingly, from the stand point of the lowered mechanical strength, the life of the electric apparatus has been estimated from the degree of deterioration of the insulating paper used to insulate conductive material.
The degree of deterioration of the insulating paper is evaluated by measuring its tensile strength the degree of polymerization and the like, or by observing the deterioration speed. Evaluating the degree of deterioration of the insulating paper by determining the amount of a component such as furfural, acetoaldehyde, acetone, carbon dioxide, carbon monoxide and the like which is generated by deterioration of the insulating paper is another method currently being studied.
These methods of evaluating the deterioration of insulating paper are carried out by an accelerated deterioration test at an elevated temperature of over a hundred ten degrees centigrade to two hundred degrees centigrade. Generally, an oil-filled electric apparatus is operated at a temperature of not more than 110° C., and the degree of deterioration of the insulating paper is predicted by extrapolating the accelerated deterioration test data obtained at the elevated temperature at the operating temperature of the oil-filled electric apparatus (typically up to 110° C.).
The above-mentioned method in which the high temperature accelerated deterioration test data is extrapolated to 110° C. or less to estimate the degree of the deterioration of the insulating paper presents the following problem.
Water (H
2
O) and methane (CH
4
) have the same molecular weight, 18, but the boiling points thereof are very different; that of water is 100° C. and that of methane is −164° C. The difference in the boiling points is felt to result from the hydrogen bond formed in the water molecule. The material of the insulating paper is typically cellulose, which has many hydroxyl groups (—OH) and also since oxygen is an atom having a large electronegativity, that is the capacity for attracting electrons of neighbouring atoms to which the oxygen is bonded, the electron of the hydrogen atom is attracted, the oxygen itself is negatively polarized and the hydrogen is positively polarized. Hydrogen and oxygen also approach each other and hydroxyl groups attract each other to form a physical hydrogen bond. As is shown by the difference in the boiling point of water and methane, the hydrogen bond has a large effect on thermal characteristics. One can expect that a similar phenomenon also occurs in the insulating paper the raw material thereof being cellulose having many hydroxyl groups. That is, one can expect that the mechanism of deterioration of the insulating paper also changes at around 100° C. due to the intervening hydrogen bond.
Accordingly, it became clear that the above-mentioned conventional evaluation method, in which the accelerated deterioration test data obtained at an elevated temperature is extrapolated to the operating temperature of the electric apparatus which is not more than 110° C., has a problem in precision.
Even with the high temperature-accelerated deterioration test which has been conventionally carried out at a temperature of from over a hundred ten degrees centigrade to around two hundred degrees centigrade, several months are required to obtain data; if a deterioration test is carried out at a temperature as low as 60° C., at about which the oil-filled electric apparatus is operated, a period of 10 years or more is required. A test requiring such a long period of time is not always preferable from a practical stand point. However, if the data of the low temperature deterioration phenomenon is different than the data extrapolated from the high temperature deterioration test data, the diagnosis of the life of the oil-filled electric apparatus cannot be accurately carried out based on the results thereof. Accordingly, in order to improve the precision of diagnosing the life of the electric apparatus, a long-term low temperature deterioration test still needs to be carried out.
SUMMARY OF INVENTION
An object of the present invention is to develop a method of evaluating deterioration of insulating paper with high accuracy. The present inventors have found that the specific nature of the insulating paper is such that the insulating paper is less susceptible to deterioration at a low temperature of not more than about 110° C., while it deteriorates more quickly at a temperature higher than this, and achieved the present invention.
That is, the present invention relates to a method of evaluating the degree of deterioration of kraft pulp insulating paper which deteriorates in an insulating oil at a temperature of not more than 110° C., based on the physical and/or chemical properties of said insulating paper.
In a preferred embodiment of the present invention, said physical and/or chemical properties are the polymerization degree or the decomposition rate of the insulating paper.
In another preferred embodiment of the present invention, said polymerization degree is expressed by the following evaluation equation wherein 1925≦A≦1930, 3.6≦B≦3.7;
D=D
0
×10
−N×10
{−A/(273+t)+B}
wherein, D is the polymerization degree of the insulating paper, D
0
is the initial polymerization degree of the insulating paper, N is the number of years of heating and t is the heating temperature (° C.).
In still another preferred embodiment of the present invention, said decomposition rate is expressed by the following evaluation equation wherein 15.8≦&agr;≦14.6, 10500≦&bgr;≦10700;
 
X
=&agr;exp(−&bgr;/
RT
)
wherein K is the generation rate (ml/gh) of (CO
2
+CO), R is 1.987 cal/mol·deg, and T is the absolute temperature (K).
In still another preferred embodiment of the present invention, the time required for said polymerization degree to reach 450 is expressed by the following equation wherein 0.7≦X≦1.7, 8200≦Y≦8800;
&thgr;=
X
exp(−
Y/RT
)
wherein &thgr; is the time (h) required for the polymerization degree to reach 450, R is 1.987 cal/mol deg and T is the absolute temperature (K).


REFERENCES:
patent: 5309766 (1994-05-01), Nanba et al.
patent: 5309776 (1994-05-01), Nanba et al.
patent: 61-150305 (1986-07-01), None
patent: 3-211806 (1991-09-01), None
patent: 4-241407 (1992-08-01), None
patent: 5-055050 (1993-03-01), None
patent: 7-043414 (1995-02-01), None
patent: 8-124751 (1996-05-01), None
“Physicochemical Characterization of the Thermal Aging of Insulating Paper in Power Transformers” by Lessard et al., 1996 IEEE Intl. Symposium on Electrical Insulation, Jun. 1996 pp. 533-537 vol. 2.
“Crystallinity of Electrical Insulating Paper” by Tsuchie et al, Transactions of IEEJ, 101(40, p. 250, 1981 with English summary.

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