Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Patent
1997-04-30
1999-10-12
Wachsman, Hal Dodge
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
702 77, 702 64, 702187, 702193, 36452827, 324522, 324 7621, G06F 1714
Patent
active
059666757
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method and device for monitoring a power supply network.
BACKGROUND INFORMATION
Fault recorders are used for detecting and recording faults in electrical power supply networks; said fault recorders sample the network with a frequency that is high compared to the network frequency, so that higher-frequency faults are also detected. Network faults can be detected, for example, by comparing the network voltage sampling values in successive periods. Since, on the one hand, the full signal variation cannot be recorded, since this would require a huge number of irrelevant data to be stored and, on the other hand, mere recording of a fault is in general insufficient for analysis regarding its origin and effects, the previous history a few seconds before and the subsequent variation of current and voltage for a few seconds after their decay are recorded. The sampled values can be made available in a memory or a register for later recording, or they can also be transmitted to a central unit where they are stored and analyzed. Despite limiting the method to faults and the immediate previous and subsequent history, considerable amounts of data must be stored and/or transmitted. For example, if the fault has a duration of 0.25 seconds and the 5-second previous and subsequent history are to be recorded, a recording rate of 80 Kbyte/sec results considering a sampling rate of 5 Khz, eight channels (four for voltages and four for currents), and a digitizing resolution of 16 bits. Therefore 820 Kbytes are required for describing the assumed fault during 10.25 sec. At a transmission rate of 300 Baud, their transmission would require 6 hrs, i.e., an intolerably long time. Even at a higher transmission rate of 9600 Baud, the transmission time would not be reduced to a satisfactory level.
Therefore, European Patent Application 477,690 A1 proposes that the sampling values be subjected to data reduction prior to their storage or transmission. Different data reduction methods are known from the literature, e.g., from K. Riedel's book "Datenreduzierende Bildcodierung" [Image coding for data reduction], 1986, Franzis'-Verlag, Munich.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for monitoring power supply networks with a particularly effective data reduction. Furthermore, a device for carrying out this method is to be provided.
The present invention provides a method for monitoring a power supply network wherein a voltage or a current is cyclically sampled and the sampling values are digitized, wherein faults are detected, wherein the sampling values recorded during a fault of the voltage or the current, as well as during a time period prior and subsequent to the fault are compressed and are transmitted and/or stored and decompressed to be analyzed. In the method of the present invention, spectral values are obtained from an integer multiple of the number of sampling values spanning the network period, using a discrete Fourier transformation. The amplitudes of the spectral values are compared with a threshold value and only those spectral values that are greater than the threshold value are transmitted and/or stored. An inverse discrete Fourier transformation is performed with the transmitted spectral values and constant values that are smaller than the threshold value, preferably equal to zero, and which replace the spectral values suppressed by the comparison with the threshold value, to compress the data.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of an embodiment of a system in accordance with the present invention.
FIG. 2 shows spectral values of a data set when there is no fault present.
FIG. 3 shows the spectral values of a data set in the event of a fault.
FIG. 4 shows a method corresponding to the operation of the system of FIG. 1.
DETAILED DESCRIPTION
In FIG. 1, the voltage of an AC line SL is to be monitored for faults. In general, not only a single-phase voltage is monitored, but also
REFERENCES:
patent: 4855861 (1989-08-01), Bergman et al.
patent: 4878142 (1989-10-01), Bergman et al.
patent: 5453903 (1995-09-01), Chow
patent: 5519645 (1996-05-01), Bohley
K. Riedel, "Datenreduzierende Bildcodierung," 1986, Franzis'-Verlag, Munich, (No translation and no month).
N. Hesselmann, "Digitale Signalverarbeitung," 2. Auflage, 1987, Vogel-Verlag, Wuerzburg, pp. 113-118. (No translation and no month).
Siemens Aktiengesellschaft
Wachsman Hal Dodge
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