Boots – shoes – and leggings
Patent
1995-03-06
1998-05-26
Trammell, James P.
Boots, shoes, and leggings
361 87, 364492, H02H 726
Patent
active
057576513
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/DE93/00791 filed Aug. 25, 1993.
BACKGROUND OF THE INVENTION
The invention relates to a process for obtaining triggering signals by the comparison of currents at the ends of a section to be monitored of an electric power transmission path. More particularly, the present invention relates to a process for obtaining triggering signals where at both ends of the section to be monitored the measurement quantities obtained from the currents are phase-selectively digitized, digital current measurement values are obtained, and from which subsequently filtered current measurement values are obtained by sine filtering. A stored reference current measurement value is subtracted from the present filtered current measurement value, forming an auxiliary measurement quantity. A sign signal denoting the sign of the current auxiliary measured quantity is retained for evaluation at one end and is also transmitted through a data transmission path for evaluation to the other end of the section to be monitored. An exciting quantity providing the current evaluation is obtained if the auxiliary measured quantity is greater than a previously determined threshold value.
A known process of this type is described in the Siemens Differential Current Protection System 7 SD 51 and its basic process steps are described in the journal "Elektrie," 45(1991)7, pp. 272-276. This current differential protection system is a fast-acting selective short-circuit protection system for cables or aerial lines which form power transmission paths. In this current differential protection system, the direct components contained in the monitored current are suppressed and the harmonics dampened. Also, in this differential protection system, a filtered current measurement value, detected two periods of the current earlier on the transmission path, or a predefined current threshold value is used to build the auxiliary measured quantity. The sign signals, formed at both ends of the section to be monitored of the electric power transmission path from the auxiliary measured quantities, are compared at either end as long as the auxiliary measured quantity is greater than a predefined threshold value. Depending on the sign of the sign signals that are compared to each other, a triggering counter is activated during evaluation; this activation occurs by addition or subtraction of constants having different values depending on whether the comparison results in the need for quick triggering or for a high degree of stabilization.
An object of the present invention is to configure the process described above so that it operates with a high degree of reliability even when the current frequency on the section to be monitored of an electric power transmission path changes relatively quickly.
SUMMARY OF THE INVENTION
This and other objects are achieved by the method of the present invention. The present invention provides for subjecting the digital current values to digital cosine filtering at both ends of the section to be monitored, thus additional filtered current values are obtained. An absolute value measurement quantity is generated from the first and additional filtered current values through absolute value generation and low-pass filtering. A stored absolute value reference measurement quantity is subtracted from the actual value of the absolute value measurement quantity, thus an absolute value comparison quantity is generated. The absolute value comparison quantity is compared to a predefined threshold value and another exciting quantity is produced if the absolute value of the absolute value comparison quantity is greater than the threshold value. Also, the sign signal with the corresponding sign signal from the other end of the section to be monitored are evaluated if both exciting quantities are present.
An important advantage of the process of the invention is its considerable independence with respect to frequency. This means that even in the case of relatively rapid frequency changes in the current on the section to
REFERENCES:
Elektrie, vol. 45, No. 7, 1991, Berlin, DD, pp. 272-276; G. Koch et al.: Ein numerischer Stromvergleichsschutz mit digitaler Messwertubertragung uber Lichtwellenleiter.
Cole Tony M.
Siemens Aktiengesellschaft
Trammell James P.
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