EP2599100A1

EP2599100A1 - Protection system for electric transformer

Info

Publication number: EP2599100A1
Application number: EP11757370.9A
Authority: EP
Inventors: Jean-Francis Faltermeier
Original assignee: Societe Nouvelle Transfix Toulon SA
Current assignee: Transfix SAS
Priority date: 2010-07-28
Filing date: 2011-07-28
Publication date: 2013-06-05
Also published as: FR2963498A1; WO2012022901A1; FR2963498B1

Abstract

Protection system for an electric transformer (1) connected to a network of a first voltage (11) and to a network of a second voltage (12), comprising a protection means (6) and a cutoff member (7) capable of disconnecting phases of the transformer (1) of the network of first voltage (11), characterized in that said protection means (6) is linked to said cutoff member (7) and to another cutoff member (13) able to disconnect phases of the transformer (1) from the network of second voltage (12).

Description

Ί

PROTECTION SYSTEM FOR ELECTRIC TRANSFORMER

TECHNICAL FIELD OF THE INVENTION

[001] The invention relates to a protection system for an electrical transformer and to a transformer operating with such a system.

[002] The invention is in the field of protection systems against the effects of internal defects of an electrical transformer. STATE OF THE PRIOR ART

[003] More particularly the invention relates to a protection system for transformers intended for example for use on three-phase networks, as described in patent EP 0817346. [004] Such a protection system comprises a device safety device comprising fuses connected in series respectively to a phase of the transformer, said fuses being able to consecutively cut off the current of the electrical current of the phases and to activate a cut-off device for disconnecting said phases of the electrical network to which they are connected.

[005] In particular, protection systems such as those described in patent EP 0817346 are generally used in medium-voltage / low-voltage distribution transformers immersed in a liquid dielectric.

Indeed, these systems generally comprise a disconnection device comprising a protection means capable of eliminating a fault current if there is a failure of the transformer, said protection means being associated with a switching device which intervenes consecutively to isolate the transformer of the network which feeds it by establishing a sectioning of all the phases. [007] Such a transformer 1 is illustrated in FIG. 1, and comprises a hermetic tank 2 on which medium-voltage 3 and low-voltage connection vias 4 are located. In addition to the various electrical functions, this tank 2 is completely filled with a liquid dielectric 5 which may be, for example, mineral oil.

The protection means 6, the cut-off device 7 of this protection system and the medium-voltage electrical windings 8 of the transformer are successively connected downstream of the medium-voltage bushings 3 and in the tank 2. The protection means 6 being consisting of three medium voltage current limiting fuses. The low-voltage windings 9 are, in turn, directly connected to the low-voltage bushings 4.

The cut-off device 7, corresponding to a polyphase breaking means 7, is controlled by the protection means 6 by means of a command 10. This command 10 is a mechanical link between the fuse pins of the protection function. 6 and the trigger mechanism of the sectioning means 7 which then performs a cutoff function.

These medium voltage / low voltage transformers are commonly used for the distribution of electrical energy. The direction of flow of electrical energy from the medium-voltage network to the low-voltage network.

These transformers are therefore powered by a source medium-voltage, whose short-circuit power justifies the presence of this medium-voltage protection system. This system eliminates the risk of explosion and fire in case of internal transformer fault. The cut-off device 7 introduces an additional sectioning between the transformer and the medium-voltage network so as to eliminate any risk of disturbance thereof by the presence of the transformer in default.

[007] However, such a protection system is not suitable for transformers used in the context of applications such as the decentralized generation of electrical energy.

Such applications typically correspond to a wind farm or photovoltaic farm in which the transformer is used as a step-up transformer for injecting the energy produced at low voltage into the medium-voltage network of the distributor.

However, in this case, this transformer is likely to be fed by the low-voltage network as the medium-voltage network.

A failure of the transformer would cause the appearance of a fault current coming in whole or in part from the medium-voltage network, which failure would be eliminated by the protection system known from the state of the art mentioned previously which aims to isolate the transformer of the medium-voltage network.

However, one of the major drawbacks of this protection system is related to the fact that the transformer remains connected to the low-voltage network, which has the effect of maintaining the defect in the device, with the consequent risk of destruction, or even of external manifestations of transformer, as well as a risk of damage to the low - voltage installation.

SUMMARY OF THE INVENTION

[008] The invention aims to solve the problem related to the technical difficulties encountered to improve the security level of a transformer so as to ensure the interoperability and portability of such a transformer in many different application frameworks.

[009] To this end, the present invention comprises a set of protection means and cuts to ensure in case of internal fault insulation of the transformer vis-à-vis the two voltage networks to which it is connected.

In this regard, one aspect of the invention relates to a protection system for an electrical transformer connected to a network of a first voltage and to a network of a second voltage, comprising a protection means and a switching device capable of disconnecting transformer phases of the first voltage network, characterized in that said protection means is connected to said breaking device and to another cut-off device able to disconnect phases of the transformer from the second voltage network.

According to particular embodiments: - the cut-off members are connected to said protection means;

the protection means comprises at least one detection means; the protection means is chosen from one of the following elements:

• element for detecting a fault current, and

• element for detecting variations in physical quantities

the cut-off member is located inside the transformer;

the breaking device is located outside the transformer, and

the first voltage network and said second voltage network relate respectively to a medium-voltage network and a low-voltage network.

The invention also relates to an electrical transformer comprising input transformer power phases and distribution phases output of said transformer and an active portion capable of performing the transformation of electrical energy, said transformer being provided with a protection system in which a cut-off member is between said supply phases and the active part, and another cut-off member is located between said distribution phases and said active part.

According to particular embodiments:

a protection means connected to the two cut-off members is between the supply phases and the active part, and the transformer is immersed in a dielectric liquid contained in a tank connected to the earth and to a mass of the active part.

BRIEF DESCRIPTION OF THE FIGURES

Other features and advantages of the invention will emerge on reading the description which follows, with reference to the appended figures, which illustrate:

- Figure 1, a schematic view of a protection system for a transformer in the prior art;

- Figure 2, a representation of the protection system for a transformer according to one embodiment of the invention;

- Figure 3, a representation of the protection system for a transformer according to another embodiment of the invention wherein one of the two cut-off members is located outside the transformer;

FIG. 4, an illustration of the contactor of the protection system represented in FIG. 3; FIG. 5, a representation of the protection system according to the present invention in an embodiment in which several detection means are implemented,

FIG. 6, a representation of the protection system according to the present invention in an embodiment in which several detection means are implemented, two of which are connected to the mass of the active part, FIG. 7, a representation of the protection system according to the present invention in an embodiment in which several detection means located inside the tank are implemented; FIG. 8, a representation of the protection system; according to the present invention in an embodiment in which several detection means are implemented, one being located outside the tank, and

FIG. 9, a representation of the protection system according to the present invention in an alternative embodiment to that illustrated in FIG. 8.

For the sake of clarity, identical or similar elements are marked with identical reference signs throughout the figures. DETAILED DESCRIPTION OF AN EMBODIMENT

In an exemplary embodiment of the present invention, the transformer 1 described relates for example to a polyphase or single-phase electrical transformer 1.

This transformer 1 is connected to a network 11 of a first voltage - in a nonlimiting way: medium voltage - and to a network of a second voltage 12 - in a non-limiting way: low-voltage

In the present embodiment, the transformer is a three-phase electrical transformer transforming for example a low voltage medium-voltage, and is immersed in a liquid dielectric 5 contained in a vessel 2 connected to the ground and to a ground of the active part 38 adapted to perform the transformation of electrical energy. This transformer 1 relates non-exhaustively and indifferently to a step-up transformer, or a step-down transformer.

This transformer 1 comprises input supply phases of the transformer 1 passing through the bushings 3 and distribution phases at the output of said transformer 1 passing through the bushings 4.

FIG. 2 is a diagrammatic representation of a polyphase electrical transformer 1 comprising: a hermetic tank 2 containing a dielectric 5

Liquid;

- Medium-voltage connection vias 3, here three bushings for the three power phases;

low-voltage connection bushings 4, here three bushings for the three distribution phases;

a cut-off member 7 of the medium-voltage supply network 11 with the active part 38 of the transformer 1

a cut-off member 13 of the low voltage supply network 12 with the active part 38 of the transformer 1;

a protection means 6;

- medium-voltage electrical windings 8;

low-voltage electrical windings 9;

a link 10 between the protection means 6 and the breaking device 7 capable of transmitting a control function to said breaking device 7, and a link 14 between the protection means 6 and the breaking device 13 able to transmit a control function to said cut-off member 13.

In this embodiment, the transformer 1 comprises a protection means 6 connected to the cut-off devices 7 and 13 respectively by electrical and mechanical or electromechanical connections 10 and 14 so as to activate these cut-off devices 7, 13 for the disconnection of the transformer 1 from the medium-voltage networks 11 and low-voltage networks 12.

This protection means 6 comprises at least one (the) detection means (s) 20,31,40,34.

Alternatively, the means (s) protection (s) 6 may be located outside the transformer, or conversely inside the transformer 1. A modification of the links 10 and 14 allows to vary these configurations.

The detection means 20,31,40,34 is provided to detect a failure of the transformer 1. This detection means relates non-exhaustively for example to:

- An element 20 for the detection of a fault current, for example a fuse 20 having a striker 19 as described in patent EP0817346. This fuse 20 is connected in series with the phase;

fuse-type detecting means 40 of a current of earth flowing between the earth 44 and the mass of the active part 39 as described in the patent EP0817346, or an element 31, 34, for example a relay, sensitive to one or more physical quantities such as an operating temperature, an internal pressure of the tank 2 of the transformer 1 or a level of liquid dielectric 5, this element being suitable for detect such a magnitude when a predefined and adjustable threshold of the physical quantity associated with it has been exceeded.

Several of these detection means 20,31,34,40 can be included simultaneously in the protection means 6. In this case, these detection means 20,31,34,40 can operate individually to detect an internal transformer fault, or in collaboration. The connection 10 between the protection means 6 and the cut-off member 7 comprises the electrical circuit portions and contactors 42 connecting the protection means 6 to the control means 19, 41, 33 as well as these control means, which are adapted to cooperate with the means (s) of detection (s) and the cutoff member 7. These control means 19,41,33 correspond for example non-exhaustive to:

a firing pin 19, included in a fuse 20 as described in patent document EP081734, adapted to cooperate with a rotating shaft 16 included in the cut-off member 7, or

- a fusible striker 41,33.

The connection 14 between the protection means 6 and the cut-off member 13 comprises the electrical circuit portions and contactors 15,24 connecting the protection means 6 to the control means 21 as well as this means of control, which is adapted to cooperate with the (the) means (s) detection (s) and the cutoff member 13. This control means 21 corresponds for example non-exhaustively to a solenoid provided to cooperate also with a rotating shaft 16 included in the breaking member 13.

The cutters 7 and 13 comprise a rotating shaft 16 on the surface of which are arranged disconnection means 18 adapted to be coupled to the connection means 17, and locking the disconnection means 18 in the connected position.

In one embodiment, the cut-off devices 7 and 13 may be located outside the transformer.

Alternatively, the cut-off members 7 and 13 may be located inside the transformer 1, or else distributed both inside and outside the transformer 1. A modification of the links 10 and 14 makes it possible to vary these configurations.

The disconnecting means 18 are connected in series respectively with the phases feeding this

transformer 1.

In FIG. 3, the transformer 1 comprises a protection means 6 and cut-off devices 7 and 13.

The detection means of this protection means 6 are fuses 20, equipped with striker 19, connected to each supply phase and arranged in the tank 2.

When one of these fuses 20 detects a fault current, the striker associated with it is triggered and then causes the rotation of the rotating shaft 16 and the activation of the contactor 15. The rotation of the rotating shaft 16 triggers the disconnection of the disconnection means coupled together by being included on this shaft 16, with the respective connecting means 17. This results in a simultaneous disconnection of all the phases at the medium-voltage supply of the transformer 1, when these disconnection means pass from the closed position to the open position.

Galvanic isolation between the active part 38 of the transformer 1 and the medium-voltage supply network 11 is then obtained.

The connection 10 between the detection means 20 and the cut-off member 7 is mechanical and comprises the firing pin 19.

The triggering of the striker 19 of one of the fuses 20 also causes the activation of the contactor 15 because the contactor 15 is mechanically connected to the striker 19.

The switch 15 moves from an open position to a closed position so that the contact between the contactors 15 and 24 is established. The auxiliary electric circuit 23 is then capable of supplying a trigger solenoid 21 controlling the opening of the breaking member 13.

Indeed, the solenoid 21 when electrically powered causes the rotation of a rotating shaft 16 so that the disconnecting means 18 are disconnected simultaneously from the connection means 17. This auxiliary electrical circuit 23 constitutes with the control means 21 the connection 14 between the protection means 6 and the low-voltage cut-off member 13 located here outside the transformer 1.

This auxiliary electric circuit 23 being partially located inside the tank 2, two electrical vias 22 are necessary to seal the tank 2. But this cutoff member 13 can also be located in the tank 2 Transformer 1.

This simultaneous disconnection results from the fact that the disconnection means 18 are coupled together by being arranged on the rotating shaft 16 mechanically connected to the solenoid 21.

Thus, a galvanic isolation is obtained between the active part 38 of the transformer 1 and the low-voltage supply network 12.

In Figure 4 is illustrated an example of a device that allows for a mechanical connection between the striker 19 and the switch 15, and thus to move the switch 15 from an open position to a closed position.

This device comprises a flexible movable contact 25 which is mechanically connected to the rotating shaft 16 of the cut-off member 7 by a fastening element 26.

In normal situation, the contactor 15 is separated from the fixed contact 24, integral with an insulating support 28. In the event of detection of an internal fault of the transformer 1 by the protection means 6, a control means 19 triggers the rotation of the rotating shaft 16 at an angle sufficient to establish contact between the contactors 15 and 24. The electrical connection 27 of the movable contact 25 is made with a flexible conductor so as not to hinder movements. It will be noted that the control means 19,21 of the protection means 6 control the activation of the transformer insulation of the medium-voltage and low-voltage network when the detection means 20 of the protection means 6 detect an internal fault so that the cutters 7 and 13 are placed in the disconnected or open position.

As we have seen previously the protection means 6 comprises at least one detection means 31,34 relating to one or more relays sensitive to one or more physical variables such as an operating temperature, a pressure internal of the tank 2 of the transformer 1 or a liquid dielectric level, each of these relays, in case of exceeding a predefined threshold and adjustable by the physical quantity associated with it, causing for example the closing of an electrical circuit 30,32,23 so as to ensure the durability and safety of the installation, as well as the transformer 1 itself.

Such a system comprising detection means 31,34 sensitive to one or more physical quantities is illustrated in Figures 5 to 7.

In addition to the transformer 1 shown in FIG. 3, the transformer illustrated in FIG. 5 comprises several relays, one of which is sensitive to the temperature of the liquid dielectric 5 capable of triggering the opening of the cut-off devices 7 and 13.

If a predetermined threshold of this temperature, corresponding to an overload situation of the transformer 1, is exceeded, this relay causes the closing of a second auxiliary electric circuit 32 which supplies the triggering solenoid 21 controlling, if necessary, the opening of the low voltage switchgear 13. The use of an organ resettable low-voltage cut, that is to say that can be closed manually after opening, allows a return to service after return to normal operating conditions of the transformer.

To do this, a set of relays 31, called protection block, is installed outside the tank 2, and connected to the liquid dielectric 5 by means of a pipe 29.

Among the various relays contained in this protection block, a first relay closes a second auxiliary electric circuit 32 which controls the trigger solenoid 21 and the opening of the low-voltage cut-off member 13. One or more other relays close a third auxiliary electrical circuit 30 capable of causing the operation of the fusible striker 33 which causes the rotation of a rotating shaft 16 and the simultaneous disconnection of the disconnection means 18 with the connection means 17, thus separating the Transformer 1 of the medium-voltage network 11. The rotation of the rotating shaft 16 also causes the closing of the contactor 15, which controls the solenoid 21 trigger and the opening of the cut-off member 13 low-voltage. The transformer 1 is then galvanically isolated from medium-voltage networks 11 and low-voltagel2.

The protection means 6 of the transformer 1 of Figure 5 comprises several detection means that are the fuses 20 provided with striker 19 and all the relays 31 and 34.

It is easy to understand that all types of detection means 31,34 such as relays, adapted to detect all the physical quantities likely to reveal a Transformer internal faults can be used in the present invention.

Such internal defects are, for example, non-exhaustively revealed by a drop in the level of liquid dielectric, under the effect of the appearance of decomposition gas, or an abnormal internal pressure, or a dielectric temperature. liquid much higher than a charging operating temperature.

Several detection means as illustrated for the transformer of Figure 5 can be used simultaneously, in such a case part of these detection means, relay assembly 31,34, can be located outside the transformer and the other part, fuses 20, inside this transformer 1.

The transformer 1 shown in Figure 6 is substantially similar to that shown in Figure 3, and differs in particular in that two detection means 31 and 40 have been added in the vessel 2.

In addition, the active part of the transformer is connected to the mass 44 of the tank 2.

The element 40 is a means 40 for detecting a fault current flowing between the mass 39 of the active part 38 and the earth 44.

This detection means 40 is a fuse comprising a striker 19 which, when triggered, then causes rotation of the rotating shaft 16 and activation of the contactor 15.

The rotation of the rotating shaft 16 triggers the disconnection of the disconnection means coupled together by being included on this shaft 16, with the respective connecting means 17. This results in a simultaneous disconnection of all the phases at the medium-voltage supply of the transformer 1, when these disconnection means pass from the closed position to the open position. This means 40 makes it possible in particular to trigger the breaking device 7, from the detection means 31 for varying physical quantities, by activating the closing of a contact so as to create a fault situation by means of FIG. establishing a current flowing between a low voltage phase passing through a passage 4 of the transformer 1 and the ground 39 of the active portion 38 of the transformer 1, to which this means 40 is connected.

Note that this striker 19 is part of the connection 10 between the detection means 40 and the cutoff member 7, which connection is mechanical.

The triggering of the striker 19 of one of the fuses 20 also causes the activation of the contactor 15 because this contactor 15 is mechanically connected to the striker 19.

The switch 15 moves from an open position to a closed position so that the contact between the contactors 15 and 24 is established. The auxiliary electric circuit 23 is then capable of supplying a tripping solenoid 21 controlling the opening of the cut-off member 13. In effect, the solenoid 21 when electrically powered causes the rotation of a rotating shaft 16 so as to the disconnecting means 18 are disconnected simultaneously from the connection means 17. This auxiliary electric circuit 23 constitutes, with the control means 21, the connection 14 between the protection means 6 and the low-voltage cut-off device 13 located here outside the transformer 1. This auxiliary electric circuit 23 being partially located at inside the tank 2, two electrical vias 22 are necessary to seal the tank 2. But this cut-off member 13 can also be located in the tank 2 of the transformer 1. This simultaneous disconnection results from the fact that the disconnecting means 18 are coupled together by being arranged on the rotating shaft 16 mechanically connected to the solenoid 21.

The transformer 1 shown in Figure 7 is substantially similar to that illustrated in Figures 3 and 6.

This transformer 1 comprises two detection means 31 and 40 included in a nonlimiting manner in the tank 2. The detection means 31 of a physical quantity variation is connected in series with a fusible striker 41 and is connected to two low distribution phases voltage on three passing through the bushings 4 of the transformer 1.

This sensing element 31 of a physical magnitude variation is capable of causing the closing of a contact generating the fuse striker 41 triggering, which closes the multipolar contactor 42 thus creating a short-circuit situation between the three phases medium voltage supply, through the bushings 3, of the active part 38.

This short circuit instantly generates the fusion of the fuses 20 belonging respectively to the medium voltage phases 3. Thus, the striker associated with each fuse 20 is triggered and then causes the rotation of the rotating shaft 16 and the activation of the contactor 15.

The rotation of the rotating shaft 16 triggers the disconnection of the disconnection means coupled together by being included on this shaft 16, with the respective connecting means 17.

This results in a simultaneous disconnection of all the phases at the medium-voltage supply of the transformer 1, when these disconnection means pass from the closed position to the open position.

The connection 10 between the detection means 20 and the cut-off member 7 is mechanical and comprises the striker 19.

The switch 15 moves from an open position to a closed position so that the contact between the contactors 15 and 24 is established. The auxiliary electric circuit 23 is then capable of supplying a trigger solenoid 21 controlling the opening of the breaking member 13. Indeed, the solenoid 21 when electrically powered causes the rotation of a rotating shaft 16 so that the disconnecting means 18 are disconnected simultaneously from the connection means 17. This auxiliary electrical circuit 23 constitutes with the control means 21 the connection 14 between the protection means 6 and the low-voltage cut-off member 13. This connection is both mechanical and electromechanical.

This auxiliary electric circuit 23 being partially located inside the tank 2, two electrical vias 22 are necessary to seal the tank 2. But this cut-off member 13 can also be located in the tank 2 of the transformer 1 .

Thus, a galvanic isolation is obtained between the active part 38 of the transformer 1 and the low-voltage supply network 12. Moreover, this transformer comprises another detection means 40 whose characteristics and mode of operation for a galvanic isolation between the active part 38 of the transformer 1 and the low-voltage power supply 12 and high voltage networks 11 are the same as those described for the transformer 1 of FIG. 6.

This element 40 is a means 40 for detecting a current of earth flowing between the mass 39 of the active part 38 and the earth 44, just like that of the transformer 1 shown in FIG. Furthermore, it will be noted in particular that the multipole contactor 42 may be made to be electrically connected to two phases so as to create a short-circuit situation between the two medium voltage supply phases passing through the bushings. 3 of the active part 38, when the triggering of the fuse striker 41 closes this multipole contactor 42.

In Figure 8, the transformer 1 which is shown is an alternative to the transformer 1 illustrated in Figure 3. Indeed, this transformer 1 comprises a detection means 31 located in a non-limiting manner outside the tank 2 .

This detection means 31 is connected in series with a fuse striker 41 located inside the tank 2. The electric circuit 47 comprising this detection means 31 and the fuse striker 41, is partially located inside of the tank 2, and two electrical bushings 46 are necessary to seal the tank 2.

The detection means 31 is connected to an external power supply device capable, and without limitation, of generating a current of at least 2 A.

Indeed, this detection means 31 is able to detect an event other than that resulting from the appearance of a fault current flowing in the transformer 1.

This event may be the exceeding of a threshold of a physical quantity specific to another device located in the installation. For example, the transformer can be de-energized following the emission of a signal by a safety device corresponding to the circuit 47, in exceptional circumstances related for example to a fire imposing the certain interruption of the electrical distribution.

It is thus clear that this detection means is capable of detecting any physical quantity relative to the immediate environment in which the transformer 1 is installed. This detection means 31 may for example belong to any monitoring or security device 47 external to the device. transformer or integrated with it. This transformer 1 also comprises, like that shown in FIG. 7, a multipole contactor 42 open in a normal situation, and closed under the effect of the tripping of the fusible striker 41, caused by the appearance of an electric current following closing the detection means 31.

The multipole contactor 42 is electrically connected to the different medium voltage supply phases passing through the vias 3 of the active part of the transformer, so that if the multipole contactor 42 is closed under the action of the fusible striker 41, a short circuit is caused between the phases. This short circuit will instantly result in the fusion of the fuses 20 respectively belonging to the medium voltage phases concerned.

In FIG. 8, these are the fuses 20 relating to the three phases since they are all connected to the multipolar contactor 42.

Thus, the striker associated with each fuse 20, is triggered and then causes the rotation of the rotating shaft 16 and the activation of the contactor 15. And according to the same operating mode as the transformer 1 described in Figure 7 a galvanic isolation is obtained between the active part 38 of the transformer 1 and the medium-voltage supply network 11 and low voltage 12.

Furthermore, it will be noted that alternatively the multipole contactor 42 may be made to be electrically connected to two phases of the active part 38 so as to create a short-circuit situation between the two power phases. medium voltage passing through the bushings 3 of the active part 38, when the triggering of the fuse striker 41 closes the multipole contactor 42.

The transformer 1 illustrated in Figure 9 is substantially similar to that shown in Figure 8 except that the multipole contactor 42 is also connected to the ground 44 of the transformer 1, itself connected to the earth 44.

Thus, when the multipole contactor 42 is closed under the action of the fusible striker 31, a short circuit is also caused between the phases of the active part 38 to which this multipole contactor 42 is connected and the earth 44 to which the mass is connected. 44 of the transformer 1.

This additional short-circuit completes the effect of the short-circuit between the phases and makes the operation of the protection system reliable.

As regards the detection means 31 shown in Figures 8 and 9, it belongs to a protection means 6 forming an integral part of the transformer 1, such as a protection relay described by the standard EN 50216-3 , the power supply of the series circuit comprising the means of detection 31 and the fusible striker 41 can be provided by a voltage taken between the neutral point and a phase of the low-voltage winding 9 of the transformer 1, or between two low-voltage distribution phases passing through the bushings 4. If the detection means 31 belongs to the protection means 6 independent of the transformer, the supply of the series circuit can be provided by any other source capable of generating a current of at least 2 A.

In another embodiment, all the detection means may be located inside the transformer 1, or conversely outside this transformer 1.

Such a protection system as defined in the present invention can easily be integrated in the vessel comprising the transformer, without the need to change the dimensions.

Thus, it is understood that the invention is not limited to the embodiments described and illustrated. It is furthermore not limited to these exemplary embodiments and the variants described. Indeed, the transformer 1 described in the present invention may be polyphase or single phase, and therefore comprise one or a plurality of fuses 20, and fuses 33,41,40 fuses. The protection means 6 may be located outside or inside the tank 2. The detection means, when there are several in a tank 2 may operate alone or in combination with each other.

Claims

1. Protection system for an electrical transformer (1) connected to a network of a first voltage (11) and to a network of a second voltage (12), comprising a protection means (6) and a breaking device (7) capable of disconnecting phases of the transformer (1) from the first voltage network (11), characterized in that said protection means (6) is connected to said cut-off member (7) and to another cut-off member ( 13) adapted to disconnect phases of the transformer (1) of the second voltage network (12).

. System according to the preceding claim, wherein said protection means (6) comprises at least one detection means (20,31,34,40).

3. System according to one of the preceding claims, wherein said detection means (20,31,34,40) is chosen from one of the following elements:

a detection element (20, 40) of a fault current, and

detection element (31, 34) of variations of physical quantities.

4. System according to one of the preceding claims, wherein said cutoff member (7) is located inside the transformer (1).

. System according to one of claims 1 to 4, wherein said cutoff member (13) is located outside the transformer (1). System according to one of the preceding claims wherein said first voltage network (11) and said second voltage network (12) relate respectively to a medium voltage network (11) and a low voltage network (12).

Polyphase electrical transformer comprising transformer input power supply phases (1) and output distribution phases of said transformer (1) as well as an active part capable of performing the transformation of electrical energy, said transformer being provided with a protection system according to one of claims 1 to 6.

Transformer according to the preceding claim wherein a protection means connected to the two cut-off members (7, 13) is between the supply phase and the active part.

Transformer according to one of Claims 7 or 8, being immersed in a dielectric liquid (5) contained in a tank (2) connected to earth and to a mass of the active part.