Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific quantity comparison means
Patent
1989-06-14
1990-08-21
DeBoer, Todd E.
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific quantity comparison means
361 93, 361 97, 364483, H02H 308
Patent
active
049511700
ABSTRACT:
So that internal faults (7) on high-voltage lines (4), generators (5), transformers (6) and other objects to be protected are more reliably detected even with saturated current transformers (3,8) and a tripping of protective measures such as, for example, an opening of switches (2,9) is reliably prevented in the case of external faults and short circuits (10), alternating current measurement signals (I.sub.1 ',I.sub.2 '), which are proportional to the alternating currents (I.sub.1, I.sub.2) flowing into the object to be protected, are detected by means of the current transformers (3,8). The alternating current measurement signals are then supplied via a low-pass filter (12), a transformer (13), a channel selection device (14), an analog/digital converter (15) to a microcomputer (16) for analysis. In the case of a fault, the microcomputer (16) provides a protective tripping signal (F=1) to switches (2,9) which open and thus isolate the object to be protected (4-6) from high-voltage lines (1,11). The protective tripping occurs in dependence on a difference current I=.vertline.I.sub.1 '+I.sub.2 '.vertline. and a holding current ##EQU1## for cos(I.sub.1 ',-I.sub.2 ')>0; I.sub.H is otherwise said to be equal to 0. The protective tripping occurs in accordance with a bent .DELTA.I/I.sub.H characteristic, a conditional tripping range being additionally provided for large .DELTA.I and I.sub.H values. An unwanted protective tripping, which, for example, can originate from a switch-on current surge during the switch-on of a parallel transformer, can be prevented in dependence on an external tripping inhibit signal (V), among other things.
REFERENCES:
patent: 4672501 (1987-06-01), Bilac et al.
patent: 4722059 (1988-01-01), Engel et al.
"Digital Differential Protection of a Generating Unit", Hope et al., IEEE Transactions, vol. PAS-96, No. 2, Mar./Apr. 1977.
"A Current Differential Relay for Use with Digital Communication Systems: Its Design and Field Experience", Stranne et al., GEC Measurements, 13th Annual Western Protective Relay Conference, WSU, Spokane, Washington, Oct. 21-23, 1986.
"Crosscorrelation Technique for Differential Protection Schemes with a Digital Computer", Proc. IEE, vol. 123, No. 2, Feb. 1976.
Asea Brown Boveri Ltd.
Deboer Todd E.
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