GROUND FAULT CIRCUIT BREAKER

Abstract: A device for interrupting and protecting a load supply circuit against ground faults, comprising: an interruption unit which has input terminals for connection to a load supply circuit, and at least one fixed contact and one moving contact which are operatively connected to actuation means for opening/closing the power supply circuit; a residual-current protection unit, operatively associated with the interruption unit and comprising a current sensor which is suitable to detect the presence of a residual current, and a control unit which is operatively associated with the sensor and with the actuation means and is suitable to check whether the detected residual current is higher than a preset limit and to cause, in this case, the intervention of the actuation means; the particularity of which resides in the fact that load supply conductors are directly connected to output terminals of the interruption unit and that the current sensor is arranged directly on the conductors.

Description: GROUND FAULT CIRCUIT BREAKER DESCRIPTION The present invention relates to a device for interrupting and protecting a load supply circuit against ground faults, particularly suitable for use in electric power supply lines for low- voltage industrial systems, and to an electrical panel which uses said device. More particularly, the present invention relates to a device for interrupting and protecting against a ground fault current which differs from known types of device in the particular arrangement and configuration of its components, according to a solution which allows to improve the operation of said device, increase its safety and optimize its installation. It is known that the use of an adequate protection against ground faults is crucially important in electric power distribution systems. This kind of protection is in fact meant to safeguard people against direct contacts, i.e., accidental contacts with a phase conductor which is normally live, and against indirect contacts, i.e., for example, with a metallic mass which is normally isolated but is in contact with a phase due to a fault; furthermore, it allows to keep under control the state of the ground insulations of the system in which it is used. In general, residual-current devices are used in order to provide this type of protection; said devices are capable of directly or indirectly interrupting the flow of current in the electric circuit in which they are included when a ground fault current higher than a preset limit occurs. In particular, specific relays, known in the art as residual-current relays, associated with interruption devices, generally automatic circuit breakers, are used in low-voltage industrial systems for this purpose. Figure 1 illustrates a typical configuration of a coupling between an automatic circuit breaker 1 and a residual-current relay 2, according to an embodiment which is well-known in the art. In particular, the automatic circuit breaker 1 comprises a block 10 in which there are terminals 3 for connection with conductors 4 of a power supply circuit; fixed contacts and moving contacts are arranged inside the block 10 and can be mutually coupled/uncoupled. In output from the block 10 there are additional terminals 5 to which conductors 6 for electrical connection to the relay 2 are connected; said conductors 6 can be constituted, for example, by copper bars or cables. In turn, the relay 2 comprises a current sensor and a residual-current protection unit, not shown in the figure; in output from the relay 2 there is another series of terminals 7 for the connection of conductors 8 for supplying a load, schematically designated by the reference numeral 9 in Figure 1. In practice, the current sensor comprises, according to embodiments which are well-known in the art, a magnetic core inside which the conductors 6 pass and a secondary winding across which a voltage is generated when a ground fault current is present. This voltage is supplied to the protection unit, which measures its value and compares it with a threshold value; if the measured value exceeds the threshold, the protection unit determines, directly or indirectly, the opening of the circuit breaker. Although this solution adequately meets the intended protection requirements, it is not entirely satisfactory as regards its structure and constructive configuration. The need to use multiple series of conductors in order to carry the current from the circuit breaker to the relay and from there to the load in fact forces a redundant use of terminals, with a consequent disadvantage from the point of view of production. This solution is furthermore particularly disadvantageous during the assembly of the devices owing to its space requirements and to the connections to be provided. It should also not be ignored that the presence of a plurality of conductors and series of terminals on the one hand entails an increase in the electrical resistance of the power supply circuit, with a consequent increase in dissipated power, and on the other hand entails a reduction in the safety and reliability of said circuit as a whole. The aim of the present invention is to provide a device for interrupting and protecting a load supply circuit against ground faults, in which the connection among the various elements occurs in a simplified manner with respect to the prior art, accordingly facilitating assembly and installation. Within the scope of this aim, an object of the present invention is to provide a device for interrupting and protecting a load supply circuit against ground faults which reduces the number of connections to be performed, consequently reducing the number of terminals required and providing an advantage from the point of view of production. Another object of the present invention is to provide a device for interrupting and protecting a load supply circuit against ground faults which allows to reduce the electrical resistance of the circuit in which it is inserted and the corresponding dissipated power. Another object of the present invention is to provide a device for interrupting and protecting a load supply circuit against ground faults which provides higher safety and reliability than the prior art. Another object of the present invention is to provide a device for interrupting and protecting a load supply circuit against ground faults which is more compact than known devices. Another object of the present invention is to provide a device for interrupting and protecting a load supply circuit against ground faults which is highly reliable, relatively easy to manufacture and at competitive costs. This aim, these objects and others which will become apparent hereinafter are achieved by a device for interrupting and protecting a load supply circuit against ground faults, comprising: ~ an interruption unit which has input terminals for connection to a load supply circuit, and at least one fixed contact and one moving contact which are operatively connected to actuation means for opening/closing said power supply circuit; ~ a residual-current protection unit, operatively associated with the interruption unit and comprising a current sensor which is suitable to detect the presence of a residual current, and a control unit which is operatively associated with the sensor and with the actuation means and is suitable to check whether the detected residual current is higher than a preset limit and to cause, in this case, the intervention of said actuation means; characterized in that load supply conductors are directly connected to output terminals of the interruption unit and in that the current sensor is arranged directly on said conductors. In this manner one has the advantage of being able to eliminate at least one junction point, and therefore the corresponding terminals, in the chain for transmission of electric power to the load. Further characteristics and advantages of the device according to the invention will become apparent from the description of preferred but not exclusive embodiments, illustrated only by way of non-limitative example in the accompanying drawings, wherein: Figure 1 is a schematic view of an automatic circuit breaker coupled to a residual-current relay according to a configuration which is known in the art; Figure 2 is a general view of an electric diagram of the interruption and protection device according to the invention; Figure 3 is a front view of the interruption and protection device according to the invention. The expression "device for interruption and protection against a ground fault current" is used to designate any device suitable to interrupt the flow of current in a load power supply circuit when a ground fault current higher than a preset limit occurs. Said device c?n be constituted, for example, by an automatic circuit breaker with which a residual-current relay is associated, and this is the embodiment to which reference is made hereinafter without intending to limit in any way the scope of application of the invention. As an alternative, the interruption and protection device might comprise a circuit breaker associated with a residual-current block or an interruption unit which directly integrates in its structure components suitable to provide protection against residual currents. With reference to Figures 2 and 3, the interruption and protection device according to the invention, generally designated by the reference numeral 100, comprises an interruption unit 11 which has connection terminals 12 in input to the conductors 13 of a circuit for supplying power to a load 14 which is arranged downstream; as shown schematically in Figure 2, the interruption unit 11 internally uses, for each phase of the power supply circuit, a fixed contact 15 and a moving contact 16 which are operatively connected to actuation means 17 for opening/closing the power supply circuit. The device 100 furthermore comprises a residual-current protection unit 20 which is operatively associated with the interruption unit 11; said unit 20 comprises a current sensor 21 which is suitable to detect the presence of a residual current, and a control unit 22 which is operatively associated with the sensor 21 and with the actuation means 17 and is suitable to check whether the residual current detected by the sensor 21 is higher than a preset limit and to determine, in this case, the intervention of the actuation means 17. Advantageously, in the embodiment of the device according to the invention, the power supply conductors for the load 14, designated by the reference numeral 19 in Figures 2 and 3, are directly connected to terminals 18 in output from the interruption unit 11, with the current sensor 21 arranged directly on said conductors 19 which constitute the primary windings. As shown in Figure 3, in a preferred embodiment the current sensor 21 has a substantially elliptical annular body on which the secondary windings 23 are arranged; said annular body is arranged transversely to a longitudinal axis which is orientated along the line that connects the input terminals 12 and the output terminals 18 of the interruption unit 11, with reference to a front view of said interruption unit 11. In this manner, with respect to said front view, the current sensor 21 is arranged downward with respect to the interruption unit 11, with the control unit 22 arranged laterally adjacent to said interruption unit. Said control unit 22, depending on the various applications and/or specific requirements, can comprise a digital electronic unit or an analog electronic unit, with advantages as regards flexibility of application. In practice, in normal operating conditions the vector sum of the currents that circulate in the conductors 19 is zero; when a ground current occurs, said vector sum is no longer zero and a voltage is induced on the secondary windings 23. The value of the voltage is made available to the control unit 22, which measures it and compares it with a preset threshold value. If the measured value is higher than the threshold, the unit 22 sends a signal to the actuation means 17 so as to open the contacts. Advantageously, with this constructive solution it is possible to eliminate at least one junction point in the chain of transmission of the power supply energy to the load 14, consequently eliminating one series of terminals and providing an advantage both from the point of view of production and from the point of view of assembly; furthermore, the elimination of a junction point allows to reduce the electrical resistance of the power supply circuit and proportionally reduce the dissipated electric power. Another advantage of the device according to the invention is that the elimination of a series of connecting terminals provides an overall increase in the reliability and safety of the power supply circuit as a whole. Another advantage of the device according to the invention is the fact that by virtue of the arrangement of the sensor 21 and of the protection unit 22, the space requirements of the device during installation are reduced. In particular, with this constructive configuration the device 100 can be installed equally in secondary electrical distribution panels, with mounting on supporting guides of the DIN type, and in general distribution panels, with fitting on the door rear. Accordingly, the present invention also relates to an electric power distribution panel which comprises a plurality of electrical devices, for example circuit breakers, which are connected to a power supply circuit, characterized in that it comprises at least one interruption and protection device according to the invention. In practice it has been found that the device according to the invention fully achieves the intended aim and objects, since it allows to have a connection among the various components which is at once simple and effective, according to a solution which furthermore allows to reduce dissipated power, increase safety and reliability, and reduce the necessary space occupation. Attention is also drawn to the fact that all the innovative functions and the inventive aspects of the device can be achieved by using commonly commercially available elements and materials with extremely low costs. The device thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept; all the details may furthermore be replaced with other technically equivalent elements. In practice, the materials used, so long as they are compatible with the specific use, as well as the dimensions, may be any according to the requirements and the state of the art.

Claims: CLAIMS 1. A device for interrupting and protecting a load supply circuit against ground faults, comprising: ~ an interruption unit which has input terminals for connection to a load supply circuit, and at least one fixed contact and one moving contact which are operatively connected to actuation means for opening/closing said power supply circuit; — a residual-current protection unit, operatively associated with the interruption unit and comprising a current sensor which is suitable to detect the presence of a residual current, and a control unit which is operatively associated with the sensor and with the actuation means and is suitable to check whether the detected residual current is higher than a preset limit and to cause, in this case, the intervention of said actuation means; characterized in that load supply conductors are directly connected to output terminals of the interruption unit and in that the current sensor is arranged directly on said conductors. 2. The interruption and protection device according to claim 1, characterized in that with respect to a front view of the interruption unit the current sensor is installed transversely to a longitudinal axis which is directed along the line that connects the input and output connection terminals of said interruption unit. 3. The interruption and protection device according to claim 1, characterized in that said current sensor comprises a substantially elliptical annular body. 4. The interruption and protection device according to claim 1, characterized in that with respect to a front view of the interruption unit, the current sensor is arranged below said interruption unit. 5. The interruption and protection device according to claim 1, characterized in that with respect to a front view of the interruption unit the control unit is laterally adjacent to said interruption unit. 6. The interruption and protection device according to one or more of the preceding claims, characterized in that said control unit comprises a digital electronic unit. 7. The interruption and protection device according to one or more of claims 1 to 5, characterized in that said control unit comprises an analog electronic unit. 8. An electrical power distribution panel, comprising a plurality of electrical devices connected to a power supply circuit, characterized in that it comprises at least one interruption and protection device according to one or more of claims 1 to 7.

Inventors: DOSMO RENATO, DOSMO, RENATO
Applicants: ABB RICERCA SPA, DOSMO RENATO, ABB RICERCA S.P.A., DOSMO, RENATO
Application year: 2000
Main classification: H01H83
IPC codes: H01H71, H01H83