Boots – shoes – and leggings
Patent
1983-07-28
1987-02-24
Krass, Errol A.
Boots, shoes, and leggings
324 54, 364550, G01R 1900, G01R 3112
Patent
active
046462481
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to measurement of insulation resistance, and other related properties, of a specimen using a method and preferably employing a novel insulation analyzer apparatus in accordance with the present invention.
BACKGROUND OF THE INVENTION
Since close to the beginning of the century, insulation measurements have been made using techniques which have been highly developed and instruments built specifically for that purpose such as the Megger.RTM. sold by James G. Biddle Company. Such instrumentation requires a high degree of knowledge and skill on the part of the operator in order to obtain readings which are reliable and, by following a painstaking procedure, can achieve a high degree of accuracy in measuring insulation resistance. Persons with the skill and patience to practice this method are becoming relatively unavailable.
In 1958, E. B. Curdts made a technical analysis of insulation testing entitled "Insulation Testing By D-C Methods" which he revised and reprinted in 1964 in Biddle Technical Publication 22T1. In that publication, Curdts showed that when d.c. voltage is applied, the current existing in the insulation of a capacitive specimen is always made up of three components, to wit: geometric capacitance current, i.sub.g ; absorption current, i.sub.a ; conduction or leakage current, i.sub.z. These currents will be explained more fully hereafter, but it will be understood that the current which was measured by all conventional insulation testers was i.sub.TOT, various elaborate techniques have been evolved to estimate the value of i.sub.c in the presence of i.sub.g and i.sub.a. Typical examples are time-resistance tests, step-voltage tests, polarization index and dielectric absorption ratio tests. These tests have been developed to a considerable degree of sophistication and achieve excellent results when applied by skilled technicians. However, they suffer from the disadvantages of taking comparatively long periods of time and requiring great care and skill in the measurements and their interpretation.
In 22T1, previously referenced E. B. Curdts has described a method of calculating i.sub.c. He shows that since the absorption current is a power function of time, constant n (with a value between 0 and 1.0) is the slope of the straight-line current-time curve plotted on a log-log basis.
The leakage current i.sub.c will represent a deviation from this curve, and may be calculated from ##EQU2## where i.sub.1, i.sub.3.16 and i.sub.10 are three values of i.sub.TOT measured at different times, based on a constant unit of time multiplied by their subscripts, i.e., 1, 3.16 and 10 minutes.
This relationship is true provided that:
a. i.sub.g has fallen to a negligible value compared to i.sub.a and i.sub.c ; which therefore also assumes that
b. i.sub.g is negligible at that voltage level when compared to i.sub.a and i.sub.c.
NATURE OF THE PRESENT INVENTION
The present invention involves apparatus for automatically accomplishing these tests. In particular, the present invention employs an insulation analyzer apparatus which employs a high voltage direct current power supply. Current sensing means is employed and specimen terminals are provided for connecting the insulation specimen across the power supply in series with the current sensing means. A voltage comparator is connected across the specimen terminals to sense effective voltage across the specimen. Timing means is provided. Computation means for recovering input from the timing means, current sensing means and voltage comparator in calculating insulation current as a function of elapsed time measurements of total current through the insulation specimen to calculate insulation current, and the insulation resistance of the specimen's insulation. Means are provided to adjust the high voltage direct current power supply. Display means are also provided permitting reading of various insulation and other properties of the specimen.
In accordance with the present invention, the following method of analyzing an insulation specimen
REFERENCES:
patent: Re30692 (1981-07-01), Ellson
patent: 4117397 (1978-09-01), Fukao et al.
patent: 4214311 (1980-07-01), Nakashima et al.
E. B. Curdts, "Insulation Testing by D-C Methods" 1958, reprinted in 1964 in Biddle Technical Publication 22T1.
James G. Biddle Company
Krass Errol A.
Teska Kevin J.
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