Communications: electrical – Systems – Selsyn type
Patent
1998-11-13
2000-03-07
Pope, Daryl
Communications: electrical
Systems
Selsyn type
34031001, 340538, 324509, 324521, H04M 1104
Patent
active
060345926
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for producing signals indicating faulty loops in a polyphase electrical power supply network using impedance excitation.
BACKGROUND INFORMATION
A known method of indicating faulty loops is described in the Siemens instruction manual "Digitaler Abzweigschutz" (Digital Feeder Protection) 7SA511 V3.0, Order No. C53000-G1100-C98-1, 1995 on page 36. In this conventional method, an impedance excitation is carried out in the form of a loop-related excitation process. It this context, after carrying out a first method step for detecting ground faults, the phase-to-ground loops are monitored in the event of at least one detected ground fault, and the phase-to-phase loops are monitored if there are no detected ground faults. A loop is considered as excited if the corresponding ascertained impedance indicator lies within the excitation polygon effective for the respective loop. If a plurality of loops are excited simultaneously, the impedances are compared, during which only those loops are classified as excited whose impedance is not more than 1.5-fold the smallest loop impedance.
SUMMARY OF THE INVENTION
An object of the invention is to provide a method for producing signals indicating faulty loops in a polyphase electrical power supply network, in which, with great reliability, all the loops are eliminated that are actually not faulty, in spite of initial excitation, so that only the loops which are actually affected by an error are checked by, for instance, an allocated distance impedance protection. To achieve this objective, according to the present invention, comparing, according to amount and phase, virtual impedances calculated with regard to the detected phase-to-phase loops, to the impedances ascertained during the impedance excitation, the actually faulty loops are determined; and amounts of virtual impedance values formed from the impedance values of the phase-to-ground loops detected as faulty, to the smallest virtual impedance value, fault-free phase-to-ground loops are recognized and eliminated; detected as faulty and not eliminated, differently developed testing methods are used in light of the number of phase-to-ground loops detected simultaneously, in each case that testing method of said testing methods being run through which corresponds to the respective number of phase-to-ground loops determined.
An advantage of the method of the present invention is that, to eliminate apparent impedance excitations, tests are conducted in succession according to various criteria, the subsequent test in each case being dependent on the result of the respective previous test, so that, focusing on the goal, only the actually fault-free loops are eliminated in each case. Another advantage is that loops mistakenly excited, (i.e, fault-free), can be separated out relatively reliably using the method of the present invention. This can be attributed to the use of virtual impedances, for whose calculation, one falls back only upon one of the currents utilized for determining the loop impedance, it being assumed that the other current has the same amplitude and is shifted by 180.degree. in phase compared to the utilized current. The use of virtual impedances avoids the disadvantages of using positive phase-sequence system impedances according to the theory of symmetrical components, because in certain fault cases, the positive phase-sequence system impedance of a faulty loop can be greater than the positive phase-sequence system impedance of a fault-free loop. Reference is made to the book by R. Roeper, "Kurzschlu.beta.strome in Drehstromnetzen", (Short-Circuit Currents In Three-Phase Systems) 6th edition, 1984, pages 48 to 53 for the definition of positive phase-sequence system impedances.
With a view to a very reliable and goal-focused elimination of excited, but actually fault-free loops, in the method of the present invention, it has proven to be advantageous if, in the case of a single detected phase-to-ground loop, the testing method is conduc
REFERENCES:
patent: 3612989 (1971-10-01), Souillard et al.
patent: 3800215 (1974-03-01), Souillard et al.
patent: 5349644 (1994-09-01), Massey et al.
Siemens Aktiengesellschaft, "Digitaler Abzweigschutz" 7SA511 V3.0, Order No. C53000-G1100-C98-1, 1995 on p. 36.
R. Roeper, "Kurzschlussstrome in Drehstromnetzen", 6th edition, 1984, pp. 48 to 53.
AEG Akiengesellschaft, "Distanzschutzeinrichtung", PD 551, Firmendruckschrift Nr. A232.06.04052/1093, 1993.
Jurisch Andreas
Kereit Matthias
Pope Daryl
Siemens AG
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