Electricity: electrical systems and devices – Safety and protection of systems and devices – Voltage regulator protective circuits
Patent
1983-10-13
1985-07-09
Salce, Patrick R.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Voltage regulator protective circuits
361 58, 361 94, 361 98, 361101, 323278, H02H 3087
Patent
active
045286086
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an electronic current interrupter included in a DC distribution system, particularly for telephone stations, and intended to replace fusible fuses and automatic fuses in such systems. More specifically, there is intended an electronic current interrupter which limits the short-circuiting current in the system.
BACKGROUND ART
When short-circuiting occurs in power distribution systems using conventional fuses very large short-circuit currents occur, these are serious transient over- and undervoltages as a result. In telephone stations, for example, undervoltages cause the cessation in the functioning in the electronics cease with the risk of long operational interruptions. Overvoltages carry the risk of destroying electronic circuits. It is already known, e.g. from Ericsson Review No. 4, 1974 page 120, to solve the problems occurring in short-circuiting by making the power system "high-ohmic". The appended FIG. 1 illustrates an example of such a high-ohmic system. The rectifier RL supplies a load L via a filter F, a fuse S1 and a cable K. A battery B with a voltage E emk and internal resistance R.sub.i is connected as a standby to the system. The fuses S2-S6 are connected to further, unillustrated loads. The high-ohmic situation in the system means that the resistances in the various circuits are distributed between battery and cable in the ratio of 1:10, for example. This means that the internal impedance R.sub.i of the battery and the line impedance of the cable K do not fall below certain values. For a 48 V system, for example, R.sub.i =4.5 m .OMEGA. and the cable resistance R.sub.K =45 m .OMEGA. in spite of this not being desirable from the point of view of losses. Due to the high-ohmic situation, the short-circuiting current occurring is therefore limited in this example to a maximum of 1000 A. This solution gives a voltage drop of max 4.5 V. in the distribution, even for a short circuit. Loads connected to fuses, i.e. to S2-S6, other than the short-circuiting load L can therefore be kept at an acceptable voltage level.
For a short circuit in the load L there is obtained a transient sequence at the point A (FIG. 1) illustrated in the accompanying FIG. 2. FIG. 2 shows in a diagram that the voltage falls rapidly at the short-circuiting instant, and is thereafter constant, to rise rapidly at the instant when the fuse S1 has melted. With a high-ohmic system according to the above (graph b) there is obtained a maximum voltage drop and a maximum voltage rise of about 4.5 V, respectively, at the short circuiting instant and when the fuse has melted. The curve plotted with a full line illustrates the sequence for a conventional relay system which is not high-ohmic, and the chain-dotted curve c the sequence when using an electronic current interrupter in accordance with the invention. The high-ohmic solution to the transient problem described above requires large batteries, however, and is therefore only possible in practice for large power distribution systems. In small systems with batteries of less than about 2000 Ah, very large capacitors are required to keep the transients between acceptable levels.
DISCLOSURE OF INVENTION
An object of the present invention is to provide an electronic current interrupter which limits the short-circuiting current, whereby voltage drops and transients during short-circuiting and fuse-blowing can be reduced to very low values.
The invention is thereby characterized as disclosed in the following claim 1.
With the proposed electronic interrupter, wholly or partially replacing the fuses S1-S6 in the accompanying FIG. 1, there is thus obtained an improved current limitation which is achieved in the known system with the aid of the high-ohmic dimensioning of battery and cable. The advantage of the current interrupter in accordance with the invention is that such dimensioning is no longer necessary, signifying a simplification of the system, and lower losses in it. By using the proposed current interrupter, current limitation f
REFERENCES:
patent: 3113260 (1963-12-01), Wiley
patent: 3209205 (1965-09-01), Olson
patent: 3558982 (1971-01-01), Greenwood
patent: 3624490 (1971-11-01), Fisher
patent: 3703679 (1972-11-01), Heidt
patent: 3899718 (1975-08-01), Schafe
patent: 3903475 (1975-09-01), Mokrani et al.
Andersson Hans O. V.
Rundkvist Kjell D.
Samsioe Per E.
Salce Patrick R.
Telefonaktiebolaget LM Ericsson
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