Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – For fault location
Patent
1998-04-21
2000-10-10
Metjahic, Safet
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
For fault location
324552, 324520, 324521, G01R 3106
Patent
active
061305405
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a measurement system for electric disturbances in an encapsulated high-voltage.
BACKGROUND INFORMATION
A brochure entitled "Diagnostic Monitoring Systems," University of Strathclyde, Scottish Power, and European Patent Application No. 488,719 describe a conventional measurement system which taps and analyzes interference signals using measurement probes.
To determine the relative phase angle of interference signals with respect to the useful voltage, the useful voltage is tapped in the phase in which an interference signal has occurred, and a signal proportional to the useful voltage is sent to the measurement system.
In investigating disturbances in the various phases, the appropriate phase must be selected for determination of the useful voltage signal to ascertain the phase angle of the interference signal.
Errors can easily occur in the correlation of phases with the interference signals, so that the wrong phase angle is assigned to an interference signal.
According to German Patent application No. 43 10 619, an interference signal in the high-frequency range is picked up using resonant circuits and conventional partial discharge measurement units, but this is not related to a useful signal (e.g., 50 Hz power supply voltage). Only high-frequency signals in different frequency ranges are detected.
U.S. Pat. No. 5,223,795 describes a method where a loss of high-frequency signal components relative to a fundamental frequency is detected. To monitor the high-frequency signal components of the voltage, the phase conductor is connected electrically or by way of a current transformer to a high-frequency analyzing unit as well as a device for analyzing the fundamental frequency.
German Patent No. 69,100,721 describes an arrangement for detecting conducted interference signals in conjunction with electric machines. Detection takes place exclusively through capacitive coupling of the measurement device to the system.
U.S. Pat. No. 5,396,180 describes a detection system for signals in a high-voltage switchgear where signals in the UHF range are obtained by operating a measurement electrode as an antenna, but information about the variation over time of the line frequency (see U.S. Pat. No. 5,396,180, FIG. 5, upper right) is evidently obtained from a separate device.
SUMMARY OF THE INVENTION
The present invention relates to a measurement system for measuring electric disturbances in an encapsulated high-voltage switchgear which carries a useful voltage in the form of a low-frequency a.c. voltage. The measurement system includes at least one measurement probe for each phase for tapping electromagnetic interference signals from the switchgear. The system further includes an analyzing unit to determine the time of the occurrence of interference signals with respect to the period of the useful low-frequency voltage of the respective phase at which the interference signals occur. Both the interference voltage and the useful voltage are picked off in at least one phase by the same measurement probe. The measurement probe is designed as a measurement electrode without an electrical connection. An object of the present invention is to make available in the simplest possible way a signal that corresponds to the useful voltage and which can be correlated with an interference signal in a certain phase.
This object is achieved according to the present invention because the interference signals and the useful voltage are accessible separately from one another at a filter arrangement which simultaneously triggers both antenna mode in the high-frequency range between approximately 300 MHZ and 3 GHz through a first protective circuit, and at the same time capacitive voltage divider mode in the low-frequency range through a second protective circuit.
The design according to the present invention ensures that the correct phase with the proper useful voltage signal will be reliably assigned to an interference signal that occurs, and therefore the relative phase angle can
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patent: 5223795 (1993-06-01), Blades
patent: 5396180 (1995-03-01), Hampton et al.
"Techniques and Instrumentation for Measurement of Transients in Gas-Insulated Switchgear," Boggs et al., IEEE Transactions on Electrical Insulation, vol., EI-19, No. 2, Apr., 1984, pp. 87-92.
"Operation and Diagnosis Assisting System for Solutions," Fujikawa et al., Hitachi Review, vol. 40, No. 5, 1991, pp. 359-366.
"Sensors for Measuring Rapid, Transient, Electromagnetic Fields in External Space of Gas-Insulated Switching Stations," Andreas Welsch, etz Archiv [Archive], vol. 10, No. 12, 1988, pp. 389-396.
"Capative Sensors for Measuring Transient Electrical Fields and Voltages," A. Kuchler et al., Archiv fur Elektrotechnik [Archive for Electrical Engineering], vol. 68, 1985, pp. 335-344.
Metjahic Safet
Siemens AG
Solis Jose M.
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