Electricity: electrical systems and devices – Safety and protection of systems and devices – Feeder protection in distribution networks
Reexamination Certificate
2001-11-28
2002-12-03
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Feeder protection in distribution networks
C361S063000, C361S093900, C361S078000, C361S018000
Reexamination Certificate
active
06490141
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a power distribution system in the low-voltage range, in particular, in the 24V DC range, having a number of circuits each having an electronic circuit breaker as a short-circuit and/or overload protection.
Such a power distribution system is disclosed, for example, by German Published, Non-Prosecuted Patent Application DE 197 03 236 A1, corresponding to U.S. Pat. No. 6,157,089 to Xu.
In a power distribution or power supply system having a plurality of circuits fed jointly by a low-voltage power supply unit, high requirements are placed on operational reliability. In the main application of plant construction, there are loads, for example, in the form of actuators or sensors, in the circuits or current paths that are connected in parallel with one another and fed jointly by the power supply unit. In such a case, a mechanical circuit breaker, possibly a switching element (relay) and the actual load or the actuator or the sensor is usually disposed one behind another in each circuit or stream. The mechanical circuit breaker can operate in accordance with a thermal or in accordance with a thermal and a magnetic disconnection characteristic.
In a linearly controlled power supply unit or transformer power supply unit, usually employed in practice to supply power (having a rated current of, for example, 30 A and a short-circuit current of about 300 A) in the event of a short circuit, it is ensured, within an individual circuit, for example, that the fuse in the circuit also triggers. The reason for such is that the short-circuit current is always sufficiently high (for example, 100 A) to trigger the circuit breaker quickly enough. In addition, for the conventional case, in which twenty or more circuits are supplied simultaneously by such a single power supply unit, it is additionally ensured that, in the aforementioned short-circuit case, the output voltage supplied by the linear or linearly controlled power supply unit does not break down or breaks down only to an insignificant extent. As is also the case in the on-board controller for a motor vehicle disclosed by Xu, the aforementioned means that the circuits that are not affected continue to be supplied with the necessary power without disruption and, in particular, in a functionally reliable manner.
The behavior is different in the case of clocked power supply units that, on account of their comparatively small dimensions, are to be employed increasingly for the aforementioned application in plant construction. These clocked power supply units likewise supply the desired output voltage of, for example, 24 VDC, but only a short-circuit current of, for example, 33 A. The latter is, therefore, frequently only 10% higher than the rated current of the clocked power supply unit of, for example, 30 A. As opposed to the linearly controlled power supply unit, in the case of a clocked power supply unit it is not ensured that, in the event of a short circuit, that is to say, in the event of a short circuit within an individual circuit downstream of the circuit breaker, the latter also triggers reliably. The reason is because the clocked power supply unit, which protects itself by limiting its output, controls the voltage down appropriately or, in the case of long load lines, the short-circuit current necessary for triggering cannot flow because of the purely resistive line component.
In the extreme case, that is to say, also in the case of a short circuit in only one circuit, it is, therefore, possible for the output voltage from the clocked power supply unit, and, therefore, the supply voltage for the parallel circuits, to be controlled down at least approximately to zero volts (0 V). As such, virtually no (short-circuit) current flows through the actual circuit breaker in the relevant circuit. At the least, however, the latter is often too small to trigger the mechanical circuit breaker. A conventional circuit breaker as fuse in the relevant circuit may, therefore, trigger only thermally. However, this means that the triggering of such a circuit breaker, on account of the conventional thermal characteristic, only takes place after 20 sec, for example. During such time, the supply voltage is too low for the other circuits or current paths to ensure their reliable operation (power reset). Therefore, the entire part of the plant that is supplied by the clocked power supply unit is disrupted and, accordingly, no longer serviceable. In other words, in the event of a short circuit, even in only one individual circuit or current path, there is a reaction on the other, intact circuits, as a result of which the intact circuits are likewise disrupted. Operational reliability is, therefore, not reliably ensured. This is because there is no assurance that, in the event of a short circuit or else circuits an overload, the other in parallel with the affected circuit and likewise supplied by the clocked power supply unit will receive the necessary power, if the clocked power supply unit controls down its output and, therefore, the supply voltage.
Because, in addition, the mechanical circuit breaker in the affected circuit does not trigger, or triggers only with an extreme delay, it is virtually impossible to determine which circuit is affected, particularly because the other circuits are also disrupted due to the reaction. If “power-fail resets” are incorporated in the individual circuits or current paths, then all the circuits shut down in such a “worst case.” If no such reset is incorporated, then the power in the further, intrinsically intact streams is in any case so low that the loads, in particular, the actuators or sensors, can no longer operate without faults.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a power distribution system that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that has a plurality of circuits supplied jointly by a clocked power supply unit in which the aforementioned disadvantages are avoided and ensures a high operational reliability of the overall system. In particular, a suitable protective device is supplied for such a power distribution system.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a power distribution system includes circuits each having an electronic circuit breaker as a protection for at least one of short-circuits and overloads, and a clocked power supply unit connected to the circuits and feeding power to the circuits. In particular, the power distribution system is in the 24V DC range. The electronic circuit breaker has a power stage and an adjustable current limiting device connected to the power stage. The adjustable current limiting device, in the event of an overload and when a first adjustable current threshold is exceeded, turns off the power stage after a first adjustable disconnection time has expired, and in the event of a short circuit and after a second adjustable current threshold has been exceeded, turns off the power stage after a second disconnection time has expired.
According to the invention, an electronic circuit breaker is inserted into each of the circuits supplied by the clocked power supply unit in the power distribution system. The circuit breaker is used substantially to limit the current within the circuit affected by short circuit and/or overload. In such a case, the current limiting device is advantageously adjustable, that is to say, can be regulated or controlled actively.
For such a purpose, the electronic circuit breaker expediently includes a power stage, preferably, in the form of a semiconductor, for example, a power MOS transistor, which is turned on completely in the normal state, that is to say, with an intended load current in the respective circuit.
In accordance with another feature of the invention, the adjustable current limiting device is programmed to turn off the power stage after a first adjustable disconnection time has expired in the
Fischer Erich
Naumann Michael
Ellenberger & Poensgen GmbH
Greenberg Laurence A.
Jackson Stephen W.
Mayback Gregory L.
Smith Michael
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