Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Frequency of cyclic current or voltage
Patent
1983-08-04
1987-01-20
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Frequency of cyclic current or voltage
324 57R, G01R 2700
Patent
active
046382429
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and device for measuring insulation deterioration of electric line with load, and in particular to an improved method and device for measuring and/or monitoring insulation resistance of electric line in an operating state.
2. Description of the Prior Art
Generally, a high voltage insulation resistance measuring instrument (hereinafter called megger) has been used for measuring insulation resistance of electric line in which a dc voltage is applied to the electric line, and insulation resistance is measured from a current returned to a grounding conductor. However, the insulation resistance measuring method employing the megger has the following drawbacks:
(1) Since high dc voltage is applied, a device or an element of low dielectric strength typically made of a semiconductor provided in the line as a load or the like, would be destroyed. Accordingly, the measurement should be made while disconnecting such load each time of measurement.
(2) Recently, it has become known that there is an insulation deterioration of electrical line with load, which is equivalently represented by the series coupling of resistance and capacitance in addition to one that is equivalently represented by the parallel coupling of resistance and capacitance which has been known before. However, since the megger employs a dc voltage, such resistance as represented by series coupling cannot be measured.
The various methods and devices for measuring and/or monitoring insulation resistance of electric line in operating states have been proposed but the above problem (2) has not been solved. Typical of those methods include a first method wherein a low frequency voltage is applied to electric line through electromagnetic induction via a class two grounding conductor for the transformer by such means as passing the grounding conductor through the core of the oscillation transformer of an oscillator oscillating a low frequency voltage which is a measuring signal or a transformer to which a low frequency voltage is applied, leakage current having returned to the grounding conductor is detected by a zero-phase inverter or the like, and insulation resistance is measured by detecting the effective component of the low frequency component in the leakage current; and a second method wherein the class two grounding conductor for the transformer is disconnected, an oscillator for applying a low frequency voltage being coupled in series in the disconnected part and a resistor for detecting a current having returned to the grounding conductor are connected in series, and insulation resistance is measured by detecting the effective component due to the insulation resistance of the low frequency component in the leakage current obtained across the resistor.
FIG. 1(a) and FIG. 2 show a prior art method disclosed in Japanese patent publication No. 68290/1978 (filed on Nov. 30, 1976), and FIG. 3 shows another prior art method disclosed in Japanese patent publication No. 7378/1978 (filed on July 9, 1976).
These drawings show the models in which a resistance R and a capacitance C exist in parallel between the line and the earth.
In actual situations, however, series connected R.sub.1 and C.sub.1 often exist between the line and the earth in addition to the parallel connected R and C as shown in FIG. 1(b). Hence, in conventional measuring systems based on the circuit models in which such additional elements are neglected, it is impossible to detect separately the effect of R.sub.1 and C.sub.1, thus involving great potential dangers, especially when R.sub.1 becomes small and C.sub.1 grows large, for example, when a large quantity of salt adheres to insulators.
FIG. 1(a) illustrates the above-mentioned first method. A load Z is connected across a transformer T via lines 1 and 2. Though explanation is made here about the case of the single phase two wire circuits of lines 1 and 2 to facilitate the understanding, explanation may be made similarly about the cases of s
REFERENCES:
patent: 2971152 (1961-02-01), Ranky
patent: 3155900 (1964-11-01), Hankgn
patent: 3320946 (1967-05-01), Dethloff
patent: 3419799 (1968-12-01), Papadeas
patent: 3543148 (1970-11-01), Martin
patent: 3968427 (1976-07-01), Sharrit
patent: 4142143 (1979-02-01), Daniel
patent: 4370611 (1983-01-01), Gregory
Eisenzopf Reinhard J.
Solis Jose M.
Toyo Communication Equipment Co., Ltd.
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