Electricity: electrical systems and devices – Safety and protection of systems and devices – Impedance insertion
Patent
1996-07-08
1999-12-07
Leja, Ronald W.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Impedance insertion
361 93, H02H 900
Patent
active
059993871
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a current limiter for limiting overload currents by means of a semiconductor element with at least one controllable semiconductor which has characteristic curves typical of a field-effect transistor (FET).
BACKGROUND INFORMATION
In the case of protective switchgear, such as power switches, motor protection switches or automatic cut-outs, and in the case of automatic circuit-breakers in general, it is desirable to sense overload currents, in particular short-circuit currents, quickly and to limit the overload currents to minimum possible values and finally to disconnect the overload currents. In the case of substantially mechanical automatic circuit-breakers, for example automatic cut-outs, use is made of so-called instantaneous trips, in which both the magnetic circuit is optimally designed and a magnet armature, often a plunger armature, quickly and forcibly makes impact with the contact system. Nevertheless, it has not been possible in practice to achieve contact opening times any shorter than about one millisecond. In this case, the short-circuit current continues to increase unhindered until contact opening. Only after contact opening is an arc produced, quickly conducted into an arc chamber and cooled at quenching plates, splitting the arc. The high arc voltages which this generates have the effect of limiting the short-circuit current and finally disconnecting it.
In the case of known automatic circuit-breakers, with a prospective short-circuit current of 6 kA, cos phi=0.6 and psi=60.degree., it is scarcely possible to obtain current time values any less than 4 ms for the rise time to the peak value, with a switching current of 4000 A, and an integral of the square of the current over time of 30,000 A.sup.2 s.
It has been suggested to use semiconductors for the current limitation in protective switchgear. This approach, however, is hampered or prevented in practice by various circumstances: 1) semiconductor elements generally have an inadequate current-limiting effect and an insufficient permissible energy absorption; 2) semiconductor elements generally have, in normal operation, a forward resistance of above 10 milliohms at 16 A; and 3) semiconductor elements also generally have an insufficient dielectric strength.
PCT International Application WO 93/11608 describes a power switch which acts as a current limiter for limiting overload currents by means of a semiconductor element with at least one controllable semiconductor with an electron source (source), an electron acceptor (drain) and a control electrode (gate) controlling the electron flow, which current limiter has characteristic curves of a field-effect transistor (FET), the load current flowing through the semiconductor element and, in the case of alternating voltage, two FETs being antiserially connected. In this case, an external control voltage is provided.
SUMMARY OF THE INVENTION
The present invention is based on the object of developing a current limiter comprising a semiconductor element with at least one controllable semiconductor, which reduces the previously customary disadvantages of semiconductor circuits to a technically usable extent.
The described object is achieved according to the present invention by a current limiter for limiting overload currents by means of a semiconductor element with at least one controllable semiconductor with an electron source (source), an electron acceptor (drain) and a control electrode (gate) controlling the electron flow of the load current flowing through the semiconductor element. The current limiter of the present invention has characteristic curves typical of a field-effect transistor and includes, if appropriate, as in the case of alternating voltage, two FETs connected antiserially, and means for internally obtaining the control voltage required for driving the semiconductor element from at least part of the voltage drop over the semiconductor element and/or at least part of the load current flowing through the semiconductor ele
REFERENCES:
R. Crawford Mosfet in Circuit Design, McGraw-Hill, 1967, pp. 46, 124-132.
CXMEHbIE IIPMEHEH MOII-TPAH3CTOPOB*, 1970pp. 172-175.
Roesch Helmut
Zierhut Hermann
Leja Ronald W.
Siemens Aktiengesellschaft
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