Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Patent
1997-08-11
1998-09-15
Gaffin, Jeffrey A.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
361 36, 361 44, 361 94, 361 97, H02H 316
Patent
active
058088440
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a current differential protection arrangement for an electric power supply unit with a measured value pre-processing device where differential current values are formed continuously from currents detected at the ends of the power supply unit when a fault has occurred, and with an analysis device that checks on the basis of a known dependence of the differential current on the stabilizing current (response characteristic curve) to determine whether the differential and stabilizing current values thus formed describe a point on one side of the response characteristic curve (blocking range) or a point on the other side of the response line (triggering range). The analysis device is designed with regard to the formation of the blocking range so that an additional stabilization range that is provided in the blocking range to achieve an additional stabilization is defined by a section of the blocking range that is below a limit characteristic curve, which begins at a predetermined stabilizing current value and increases linearly with the stabilizing current in a predefined manner.
BACKGROUND INFORMATION
A conventional current differential protection arrangement is Siemens digital differential protection device 7UT51 V2.1, whose design is described in the respective equipment handbook, order no. C 73000-G 1100-C77-7. With this known current differential protection arrangement, as is customary with current differential protection arrangements in general, the currents I.sub.1 and I.sub.2 (see also FIG. 1) are detected at ends 1 and 2 of an electric power supply unit 3, which may be, for example, a motor, a transformer, or a line section of an electric power supply network. As FIG. 1 also shows, a positive direction of currents I.sub.1 and I.sub.2 is selected so that the currents flowing into electric power supply unit 3 to be monitored have a positive direction. As is also conventional, in the event of a fault in electric power supply unit 3, differential current values that can be described by the following equation (1) are also formed from the detected currents I.sub.1 and I.sub.2 with current differential protection arrangement 4:
Furthermore, stabilizing current values I.sub.STAB that correlate with the differential current values are generated according to the following equation (2): formed in a measured value pre-processing device (not shown in detail in FIG. 1). Furthermore, as stated on page 27 of the above-mentioned handbook, the respective vector group is also taken into account in the measured value preprocessing device when the electric power supply unit is a transformer, and the zero currents are also eliminated.
With the conventional current differential protection arrangement, the differential and stabilizing current values are analyzed in an analyzing device downstream from the measured value preprocessing device to the extent that a check is performed on the basis of a given dependence of the differential current on the stabilizing current (response characteristic curve) to determine whether the current values thus formed describe a point on one side of the response characteristic curve, i.e. in the blocking range, or a point on the other side of the response characteristic curve, i.e., in the triggering range. If the current values are in the triggering range, a triggering command is issued by the current differential protection arrangement. When a point described by the differential current value and the respective stabilizing current value is in the blocking range, no triggering command is issued, because this indicates a fault outside the electric power supply device to be monitored.
It is also described on page 19 of the aforementioned equipment handbook that additional stabilization is used with the conventional device which stabilization is to be achieved in the event of saturation of the transformers required for detection of the current, e.g., transformers 5 and 6 shown in FIG. 1, i.e., an internal fault can be simulated by transf
REFERENCES:
patent: 3754163 (1973-08-01), Sykes
patent: 4204237 (1980-05-01), Zocholl
patent: 4772978 (1988-09-01), Oura et al.
patent: 4951170 (1990-08-01), Fromm
Siemens, "Digitaler Differentialschutz fur Transformatoren Generatoren und Motoren",7UT51, V.2.1,Betsell-Nr. C73000-G1100-C77-7,pp. 19 and 27.
H. J. Hermann; U. Forster, "Einsaltz von Mikrorechnern fur den digitalen Transformatordifferentialschutz" MSR, Berlin 28 (1985), H.4,pp. 157-160.
Noack Steffen
Schiel Ludwig
Schuster Norbert
Gaffin Jeffrey A.
Sherry Michael J.
Siemens Aktiengesellschaft
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