SE1351510A1 - Device for the protection of an electrical appliance supplied by a multi-phase network - Google Patents

Description

According to a first example, which is generally a three-phase network, the original protection device consists of a set of three medium-voltage fuses installed on a fuse holder insulated in air, without any physical protection against accidental contact when the station housing is open. However, such an arrangement that has been accepted in the past no longer meets the current safety requirements described, among other things, in standard CEI 62272-202, which relates to prefabricated stations.

According to a second example, in addition to three fuses, the protection device comprises a medium-high voltage switch, all of which are located in a specific space and are insulated in air. However, experience shows that as certain types of medium-voltage circuit breakers age, they become sensitive to climate variations and more specifically to condensation phenomena, which lead to leakage currents to ground causing unforeseen power outages for the entire medium-voltage network, resulting in deprived electricity customers.

According to a third example, the protection device comprises a set of three fuses and a medium-voltage switch of the associated type. In the event that an isolation fault occurs in the electrical transformer, only the fuse or fuses which are supplied by a fault current intervene without causing the three-phase switch to open. Usually one or two fuses remain conductive. This has at least two disadvantages. In a first case, a leakage current may continue to circulate between one or two phases and earth, causing a voltage drop for the medium-voltage network, with the consequences previously mentioned. In another case, where leakage currents to earth do not occur, the damaged transformer remains partially supplied and then generates deviating voltages on the low voltage side with a risk of major damage to the receivers of the customers connected to the transformer station.

According to a fourth example, the protection device comprises a set of three fuses and a medium-voltage circuit breaker of the combined type, all of which are insulated in air. Experience shows that in many installations the opening mechanism of the switch no longer reacts after a fuse fusion, in the absence of efficient maintenance. This dysfunction can often be attributed to corrosion phenomena of moving parts or even to rubber phenomena at the height of the bearing of the mechanism. The disadvantages of such a situation are identical to those for the preceding cases relating to the protection device with medium-high voltage circuit breakers of the associated type.

In all these situations, the operator is anxious to replace the original protective device with a safer and more reliable device.

Such safer and more reliable protection devices are available on the market, but they are generally integrated in medium-voltage equipment under metal housings such as those described by the international standard CE1 62271-200, which also include operating functions provided by the circuit breakers in the network. Such equipment is expensive and bulky. For the most compact among them, the bottom surface is larger than 1 m2 and the height is greater than 1.3 m. They are therefore difficult to integrate in a station casing that is not originally intended to receive such equipment.

Another solution is to replace the transformer with a transformer that has integrated interrupt protection functionality as defined by standard CE1 60076-13. For example, the patent EP 97401477 describes such a transformer whose use solves all the previously mentioned problems. Nevertheless, this presupposes that the supplier replaces its old transformer with a new transformer with interrupt protection functionality, which entails a significant cost, and is even less acceptable when it comes to upgrading a used transformer station. In this context, the present invention provides a device for protection and insulation that is economical and compact enough to be easily integrated into an existing installation such as a medium voltage / low voltage transformer station whose housing has limited dimensions, without requiring the transformer replaced, and whose functionalities allow for the improvement of the safety of the operator, the public and property, as well as of the quality of service by avoiding unexpected general interruptions of the medium-voltage network, or even the transmission of deviating voltages to customers connected to the station. Description of the invention For this purpose, the device according to the invention, which otherwise corresponds to the general definition given in the introduction above, is essentially such that it comprises: - protection means against short circuits, which means consist of fuses whose breaking capacity is at least equal to the short-circuit current of the mains supplying the electrical appliance, the number of which is at least equal to the number of phases supplying the electrical appliance minus one, - isolating means consisting of a breaking and disconnecting device comprising as many phases as the phases supplying it electrical apparatus, and which engages after fusion of one or more fuses by means of striking pins provided with the fuses, and - a hermetic container of conductive material connected to ground potential in which the protection and insulating means are integrated, said container being filled with a dielectric liquid or gas and includes electric penetrations whose number is at least twice as large as the number of phases which supply the electrical appliance, so that the fuses are not accessible and the breaking and disconnecting device cannot be reset without the opening of the hermetic container being required.

The object of the present invention is an economical and sufficiently compact protection device which can be easily integrated into an existing installation, such as a medium voltage / low voltage transformer station, without the need to replace the transformer, and whose functionalities allow improvement of the safety of the operator, the public and property, as well as by the quality of service by avoiding unexpected outages that are widespread throughout the medium voltage network, or even by deviating supply of voltage to the customers connected to the station.

The protective device thus advantageously means that operating personnel are not exposed to a risk of electrical voltage shocks when touched. In addition, since the protection device thus only comprises a function for protection and insulation which is neither manoeuvrable nor resettable at the operating site, it is simple to manufacture, not bulky and economical.

According to one embodiment, the protection device further comprises, for each phase in the network, at least two electrical bushings which are connected to a set of wires, the latter itself being connected to the protection means.

The protection device according to this embodiment can advantageously be connected as a passage to the network.

According to another embodiment, the protection device further comprises an operating means which is suitable for causing opening of the breaking and disconnecting device, when the operating means is supplied by an electric current originating from an auxiliary electrical circuit.

According to a variant of the preceding embodiment, the protection device further comprises a current transformer in which a primary winding is connected between the body of the electrical apparatus to be protected and its earth connection and a secondary winding is connected to the electrical auxiliary circuit, so that the current transformer supplies the electrical auxiliary circuit. a ground insulation fault in the electrical appliance.

According to another embodiment, the protection device further comprises a contactor suitable for establishing according to the choice of continuity or discontinuity of a second electrical auxiliary circuit, when the breaking and disconnecting device goes from a closed state to an open state.

According to another embodiment, the protection device further comprises partitions of conductive material, which are electrically connected to the body of the container and arranged so as to electrically insulate the phases of the protection means and the insulating means between them.

The protective device is thus advantageously designed so that it suppresses the risks of internal electric arcs which can lead to dangerous external events.

According to another embodiment, the protection device further comprises an orifice formed in an upper wall of the container through which a defined volume of dielectric liquid is removed and replaced by a gas bed, and wherein the protection device, for each phase of the device, further comprises a conductor 10 which connects the fuse to the mains via the electrical bushing and an electrically insulated tube in which the part of the electrical bushing located on the inside of the container is located, as well as the fuse and the part of the conductor located on the inside of the container, the e | The electrically insulated tube comprises an end with which a seal of an upper wall of the container is ensured.

The device thus advantageously allows, in particular if the container is dimensionally stable and if the dielectric used is an incompressible liquid, compensation for the expansion of the dielectric liquid according to its temperature, the dielectric liquid being fully maintained in the entire volume of the tube in this way. that the suppression of the risks of internal arcs is maintained.

According to another embodiment, the electrical apparatus is a transformer for electrical distribution of medium voltage / low voltage.

Other advantages may also be apparent to those skilled in the art upon reading the illustrative examples provided below, which are illustrated by the accompanying drawings.

Brief Description of the Drawings Figure 1 schematically shows the electrical circuit of a multi-phase electrical distribution network comprising the inventive device for protecting an electronic device.

Figures 2a and 2b are a sectional view from the front and from the side, respectively, of the electronic circuit of the device for protecting an electronic device according to the invention.

Figure 3 is a perspective view of the device for protecting an electronic device according to the invention, the housing being partly shown as transparent.

Figure 4 schematically shows the electrical circuit of a first variant of the protection device shown in Figure 1.

Figure 5 schematically shows the electrical circuit of a second variant of the protection device shown in Figure 1. Figure 6 schematically shows the electrical circuit of a multi-phase electrical distribution network comprising the protection device according to a third variant of the protection device shown in Figure 1.

Figure 7 schematically shows the electrical circuit of a fourth variant of the protection device shown in Figure 1.

Figure 8 is a front sectional view of a fifth variant of the protection device shown in Figure 1.

Figure 9 is a side sectional view of a sixth variant of the protection device shown in Figure 1.

Referring to Figure 1, an economical protection device 3 is compact enough to be easily integrated into an existing installation such as a medium I low voltage transformer station, without the need to replace the transformer. It is completely contained in a hermetic container 4 of conductive material and which is connected to earth potential, and therefore this device does not expose the operating personnel to the risk of voltage shocks when touched. In addition, since the device only comprises a function for protection and insulation which can neither be operated nor reset at the operating site, the protection device 3 is simple to manufacture, not bulky and economical.

The electrical apparatus 2, like the electrical network 1 which supplies it, is generally multiphase and more specifically three-phase. It should be noted that to the extent that the abnormally high supply current is an error between the phases, it is sufficient to interrupt a number of phases equal to the number of phases in the network 1 minus one to ensure its interruption. On the other hand, the complete insulation of the electrical device 2 to be protected means disconnection of all the phases.

The principle of the protection device 3 is described in Figure 1 which schematically shows its electrical circuit and in Figures 2a and 2b, which represent a sectional view from the front and from the side of the device 3, respectively, in a version which is raised relative to that shown in Figure 1.

The device 3 is intended to be inserted between a multi-phase electrical network 1, and more specifically with three phases as shown in Figure 1, and the electrical device 2 to be protected. The hermetic container 4 is filled with a dielectric liquid or gas 5 and is provided with electrical bushings 11 whose anta! is equal to twice the number of phases that supply the electrical appliance 2.

In the case of a medium voltage installation supplied by an electrical network 1 consisting of insulated cables, the electrical bushings 11 are preferably of a plug-in type with a directional field.

In the container 4 there are integrated: ~ protection means 6 which ensure a protection function, which means 6 consist of fuses 7 whose breaking capacity is at least equal to the current of the short circuit in the electrical network 1, whose insulation capacity is at least equal to the maximum voltage in the same electrical network 1, and the number of which is not lower than the number of phases which supply the electrical device 2 minus one, and - insulating means 9 which ensure an insulating function, which means consist of a breaking and disconnecting device 10 comprising as many phases as the phases supplying the electrical device 2, whose breaking capacity is at least equal to the minimum current I3 according to the definition given by the standard CEI 60282 which the fuses 7 are capable of breaking, and whose disconnecting capacity is at least equal to the maximum overvoltages that may occur on the electrical network. In the case of a three-phase device, the number of fuses 7 can thus be two or three. If it is equal to two, the unaffected phase is provided with a single conductor which replaces the missing fuse. The fuses 7 are provided with percussion pins which are pushed out of the body of the fuse 7 in the event of fusion, due to an abnormal overcurrent strength.

The breaking and disconnecting device 10 is normally in a closed position. It is only in the event of the fusion of one or more fuses 7 that it transitions to an open position under the influence of one or more percussion pins belonging to one or more fuses 7 which have suddenly merged as a result of being traversed by an abnormal current. .

Different solutions can be considered for the performance of the protection and insulation functions. In particular, one can go back to the patents EP 97401477 and EP 00403420 which describe a particularly preferred embodiment.

Unlike devices that are usually integrated in protective equipment intended for installation for medium or low voltage, the fuses 7 here are inaccessible to the operator and cannot be replaced on site.

Similarly, the insulating functionality of the insulating means 9 is not reset in place, as no means for maneuvering from the outside of the container 4 is provided for this purpose. Since the function of the device 3 is systematic as a result of a breakdown of the electrical device 2 which it protects, the functionality of the electrical device 2 and the protection device 3 needs to be reconfigured at a repair shop. This results in a simple and economical construction of the protection device 3. Furthermore, the need for a reconfiguration in a workshop does not constitute a significant inconvenience, given the low probability of the occurrence of a fault in the electrical device 2, especially in the case of a electric transformer for general distribution. In fact, the average error rate noted in Europe for this type of device is in the order of 1.10 ”errors per operating hour.

The device 3, as previously defined and adapted for a medium-voltage three-phase network, is compact and easy to integrate into an existing installation such as a transformer station. For illustrative purposes, Figure 3 shows a device 3 intended to protect a transformer with a power of 1000kVA connected to a mains with a voltage of 22000V, and whose size is limited by: - a width of 600mm, - a depth of 360mm, and a height except for the connection of connections of 800mm.

This device is thus easily installed in the immediate vicinity of the transformer that it is to protect. In Figure 3, the container 4 is shown partly as transparent, which makes it possible to see the location of the fuses 7 and the breaking and disconnecting device 10. Figure 4 shows a variant of the device 3 as shown in Figure 1.

The electrical bushings 11 are connected on the inside of the container 4 to a set of conductors 12, which themselves are connected to electrical bushings 13 whose type may or may not be identical to that of the electrical bushings 11. This arrangement allows coupling of the protection device 3 as a passage to the network 1, while the principle of the device 3 shown in Figure 1 only allows single feeding. In another variant which is not shown, the number of additional bushings can be increased in such a way that a star point is formed in the electrical network 1. Thus, for a three-phase network, in addition to the bushings 11 whose number is equal to three, bushings 13 of numbers equal to 3 can be provided. , 6, or 9, according to the diagram for the desired network 1. The device 3 thus combines the function of protecting by means of protective means 6 and the function of insulating an electrical device 2 by means of insulating means with a function for interconnecting different conductors belonging to the same network 1.

Figure 5 shows a variant in which the breaking and disconnecting device 10 is provided with an operating means 14, which is shown in Figure 3, among other things, and which can cause the opening of the breaking and disconnecting device when an electric current flows through an auxiliary circuit 15.

The actuator 14 may, for example, consist of a safety device which, under the influence of an electric current, releases a finger driven by a compression spring, which finger will cause the opening of the breaking and disconnecting device 10. The auxiliary circuit 15 may be connected to a monitoring device such as for example, a thermal probe mounted on the electrical apparatus 2 to be protected and which causes it to shut down in the event of an abnormal temperature increase, and this before the temperature increase leads to a fault in the electrical apparatus 2.

Figure 6 shows another use of this actuator 14, which is then intended to realize a protection against a possible earth insulation fault of the electrical apparatus 2. In this case the auxiliary circuit 15 is fed by a secondary winding of a current transformer 16 whose primary winding is connected between the body of the the electrical apparatus 2 to be protected and its ground connection 17. Thus, the current resulting from the insulation fault and flowing towards ground causes the generation of a current circulating in the auxiliary circuit 15, which causes the actuator 14 to turn on, which may be a fusible percussion pin and, as a consequence, opening of the breaking and disconnecting device 10 and isolating the electrical apparatus 2.

The device 3 can thus be used for protection of all kinds of electrical devices 2 which are supplied by a network 1 with low or medium voltage, by interrupting the supply of the electrical device 2 as soon as the latter exhibits a fault of such a nature that an abnormally high supply current generated. In Figure 7, the foregoing device 3 is supplemented with an electrical contactor 18 which, according to the alternative selected, has the possibility of closing or opening a second auxiliary circuit 19 when the breaking and disconnecting means 10 go from a closed state to an open state. The second auxiliary circuit 19 may be useful for controlling a protection means such as, for example, a low voltage switch located downstream of the transformer corresponding to the protected electrical apparatus 2, in such a way that the latter is isolated from the secondary network to which it is normally connected.

In accordance with the requirements of the applicable standards, and more precisely the standard CEI 62271-200 which refers to high voltage equipment in metal casing for voltages included between 1 and 52 kV, one needs to take into account the event of an insulation fault in the device 3 and the consequences that may result therefrom.

If this insulation fault affects the portion of the electrical circuit 7 downstream of the fuses 7, this fault will be harmless as it is immediately eliminated as a result of the intervention of these same fuses 7.

On the other hand, if this insulation fault relates to a portion of the electrical circuit located upstream of the fuses 7, it will be supplied by the mains 1 as long as the latter remains energized; or the network 1 can have a very significant multiphase short-circuit effect, depending on its nature.

In the case of a medium voltage network, such as a network for the general distribution of a voltage of 22 kV, this power is of the order of 100 MVA. The constructive arrangements need to be adapted to avoid the significant thermal and mechanical consequences that result from this insulation failure, such as electric arcs, an explosion or a fire, and which may prove dangerous to the environment of the installation or to the operating personnel.

The peculiarity of the majority of public distribution networks, and this especially in countries located in Europe such as France, Germany and Sweden, is that these networks operate under a regime called compensated neutral. The interest in such a neutral regime lies in the fact that an insulation fault that establishes itself between a phase and earth only generates a current that is limited to a few amperes and thus a monophase short-circuit effect which itself is very limited and in the order of tens of kVA. In a variant whose principle is shown in Figure 8, the device 3 has partitions 20 made of a conductive material, for example the same material as that used for the design of the container 4, which are connected to the potential of this same container 4 with suitable electrical connections 21. The partitions 20 divide the volume of the container 4 into compartments by separating the different phases of the means for protection 6 and insulation 9, without still having to ensure a liquid or gas tightness between the volumes.

The role of the partitions 20 is to ensure that if an insulation fault 24 occurs on a conductor 25 fed by the network 1 and located in the container, this fault can only be converted as an electric arc extending between the conductor 25 and a wall 26 of the container or a partition wall 20 which is connected to the body of the container 4. In this way and according to the above-mentioned peculiarity of the majority of general distribution networks, this electric arc has an energy which is low enough not to pose a risk to the environment of the protection device 3 or to the personnel operating the installation.

As long as each partition is well connected to the body of the container, holes are allowed in the partitions or distances between the edges of the partitions 20 and the inner walls of the container whose dimensions are between 5 and 10 mm, without impairing the insulating function of the partitions 20. Figure 9 shows an arrangement which is complementary to that described in connection with the previous figure. This arrangement is also necessary if the container 4 is dimensionally stable and if the dielectric 5 used is an incompressible liquid. In this case, a gas bed 27 should be provided to compensate for the expansion of the dielectric liquid according to its temperature. This gas bed 27 can be obtained, for example, with a volume of nitrogen gas. Since its dielectric strength is much lower than that of the dielectric liquid 5, the purpose of the arrangement shown in Figure 9 is to restore a sufficient level of insulation around the conductor 25 located upstream of the fuses 7. For this purpose, a tube 28 of insulating material concentrically placed around the group formed by the conductor 25 and the fuse 7 for each phase of the protection device 3. This tube 28 has at its upper end 29 a gas seal opposite the upper wall 30 of the container 4.

The filling of the container 4 with the dielectric liquid 5 takes place in its entirety after performing vacuum replacement of the device 3, whereupon a defined volume of dielectric liquid 5 is removed from the orifice 31 and replaced by an identical volume of nitrogen gas constituting the gas bed 27. The dielectric 5 is retained. fully in the entire 28 volume of the tube.

It should be apparent to those skilled in the art that the present invention allows embodiments according to many other specific forms without departing from the scope of the invention as claimed. The present embodiments should thus be considered as an illustration, but may be modified within the scope defined by the scope of the appended claims.

Claims (8)

10 15 20 25 30 14 PATENT REQUIREMENTS Device for protection (3) of an electrical device (2) supplied by a multiphase network (1), characterized in that it comprises: - protection means (6) against short circuits, which means consist of fuses (7) whose breaking capacity is at least equal to the short-circuit current of the mains (1) supplying the electrical appliance (2), and whose number is at least equal to the number of phases supplying the electrical appliance (2) minus an isolating means (9) consisting of a breaking and disconnecting device (10) comprising as many phases as the phases which supply the electrical device (2), and which engage after fusion of one or more fuses (7) by means of striking pins with which the fuses (7) are provided, and - a hermetic container (4) of conductive material connected to earth potential in which the protection (6) and insulating means (9) are integrated, said container (4) being filled with a dielectric liquid or gas (5) and comprising electrical bushings (11) vars ant al is at least twice as large as the number of phases feeding the electrical appliance (2), so that the fuses (7) are not accessible and the breaking and disconnecting device (10) cannot be reset without opening the hermetic container (4) required. Device for protection (3) according to claim 1, characterized in that it further comprises, for each phase in the network (1), at least two electrical bushings (11, 13) which are connected to a set of wires (12), wherein the the latter itself is connected to the protective means (6). Device for protection (3) according to any one of claims 1 or 2, characterized in that it further comprises an operating means (14) which is suitable for causing opening of the breaking and disconnecting device (10), when the operating means (14) is fed by a electric current originating from an electric auxiliary circuit (15). 10 15 20 25 30 15 Device for protection (3) according to claim 3, characterized in that it further comprises a current transformer (16) in which a primary winding is connected between the body of the electrical device (2) to be protected and its earth connection (17) and a secondary winding. is connected to the auxiliary circuit (15), so that the current transformer (16) supplies the auxiliary circuit (15) in the event of a ground fault in the electrical appliance (2). Device for protection (3) according to one of Claims 1 to 4, characterized in that it further comprises a contactor (18) suitable for establishing according to the choice of continuity or discontinuity of a second auxiliary electrical circuit (19), when the breaking and disconnecting device (10) goes from a closed state to an open state. Device for protection (3) according to any one of claims 1 to 5, characterized in that it further comprises partitions (20) of conductive material, which are electrically connected to the body of the container (4) and arranged so as to electrically insulate the phases of the protection means (6) and the insulating means (9) between them. Device for protection (3) according to any one of claims 1 to 6, characterized in that it further comprises an orifice (31) formed in an upper wall of the container through which a defined volume of dielectric liquid (5) is removed and replaced by a gas bed. (27) and, in that, for each phase of the device (3), it further comprises a conductor (25) which connects the fuse (7) to the mains (1) via the electrical bushing (11, 13) and an electrically insulated tube. (28) in which the part of the electrical bushing (11) located on the inside of the container (4) is located, as well as the fuse (7) and the part of the conductor (25) located on the inside of the container (4) , the electrically insulated tube (28) comprising an end (29) with which a seal of an upper wall (30) of the container (4) is ensured. 16 Device for protection (3) according to one of Claims 1 to 7, characterized in that the electrical apparatus (2) is a transformer for electrical distribution of medium voltage / low voltage.