FR2936909A1 - PROTECTION SYSTEM FOR ELECTRIC POLYPHASE TRANSFORMER AND ELECTIC TRANSFORMER COMPRISING SUCH A PROTECTION SYSTEM - Google Patents

Abstract

The system has a disconnection device (5) with disconnection units (6) for three power supply phases (3). Fuses (8, 9) of a safety device (7) cut electric current from two of the phases and control a blocking device (13) of the disconnection device to pass the units from a connected state to a disconnected state. The third phase is not provided with the fuses, and the disconnection device is provided such that the unit of the third phase not provided with the fuses is displaced from the connected state to the disconnected state after the two phases. An independent claim is also included for a polyphase electric transformer comprising a tank.

Description

Protection system for polyphase electrical transformer and electrical transformer including such a protection system.

The present invention relates to protection systems for a polyphase electrical transformer and to an electrical transformer comprising such a protection system. More particularly, the invention relates to a polyphase electrical transformer protection system, comprising: - a plurality of phases, - a disconnecting device comprising disconnecting members for each phase each having a connected state in which an electric current can passing into the corresponding phase and a disconnected state in which said electric current can not pass into said corresponding phase, said disconnecting members being normally all in connected state, said disconnecting device further comprising a blocking device adapted to pass said disconnecting members of the connected state in the disconnected state, - a safety device comprising fuses, each fuse being connected in series on a phase and adapted to cut off the electrical current of said phase and to control the blocking device of the disconnection device, so as to make switch the disconnecting devices from the connected state to the disconnected state. EP 0 817 346 describes an example of such a protection system, comprising a disconnecting device and a safety device comprising three fuses. The disconnecting device is intended to isolate the electrical transformer of a power supply network when a fault is detected and to avoid propagating said fault in the network. The safety device is intended to interrupt the current in the transformer in the event of a fault and limit the energy dissipated therein. It avoids the risk of deterioration of the transformer. The safety device of this transformer comprises three fuses, that is to say one on each electrical phase of the primary of the transformer. The present invention aims to provide a protection system for a polyphase electrical transformer with fewer components, so less expensive, while ensuring a high level of security.

For this purpose, a protection system of the aforementioned type is characterized in that at least one of said phases is devoid of a fuse and the disconnection device is adapted so that the disconnecting member of the phase without fuse toggles the state. connected to the disconnected state after the other phases. Thanks to these provisions, the protection system of the polyphase electrical transformer is less expensive, reliable and offers all the security for the electrical network to which the electrical transformer is connected.

In various embodiments of the protection system according to the invention, one or more of the following provisions may also be used: each fuse comprises a striker adapted to control the locking device when said fuse is activated when an electric current of the phase of said fuse is greater than a predetermined electric current; the protection system further comprises a fault detection system, and a short-circuit device having: an open state normally in which the other phases are not short-circuited when no fault is detected by said fault detection system, and - a closed state in which said other phases are short-circuited when at least one fault is detected by said fault detection system; the fault detection system comprises a level detector adapted to control the short-circuit device to the closed state when a level is below a predetermined level, said level detector being intended to detect a level defect; dielectric liquid in the electrical transformer; the fault detection system comprises a pressure detector adapted to control the short-circuit device to the closed state when a pressure is greater than a predetermined pressure, said pressure detector being intended to detect an overpressure in the transformer electric; the fault detection system comprises an earth fault detector adapted to control the short-circuit device when a ground current is greater than a predetermined earth current, said earth fault detector being for detecting a leak of electric current to the earth of the electrical transformer; - The disconnecting device comprises: - a support adapted to support at least two fuses in a longitudinal direction X, each fuse having in this longitudinal direction X a firing pin, - a locking device articulated in rotation relative to said support around a first transverse axis Y1 substantially perpendicular to the longitudinal direction X between a locking position and a release position, the locking device having a rear face in a direction opposite to the longitudinal direction X facing the firing pin and a front face in the longitudinal direction X having a bridge between two portions of said front face, the rear face being adapted to be pushed in the longitudinal direction X by at least one of the striker fingers for tilting said locking device around the first axis Y1 between said locking position and said release position, an articulated trigger e in rotation relative to said support about a second transverse axis Y2 substantially perpendicular to the longitudinal direction X between an armed position and a pulled position, said trigger comprising a hook engaging with the bridge of the locking device when the device blocking is in the locked position and being released when the locking device is in the release position, - an elastic element adapted to abut the hook against the trigger guard when the trigger is in the armed position and toggle the trigger towards its pulled position when the locking device is in the release position, so that said trigger switches the disconnecting members from the connected state to the disconnected state; the protection system is such that: the support comprises at least three first elements of the disconnecting members, each first element being electrically connected to an input phase, the trigger comprises at least three levers arms, each lever arm accommodating a cable corresponding to an electrical phase and a first end of which is equipped with a second element of the disconnecting members adapted to be removably connected to one of the first elements when the trigger is in the armed position, and adapted for being disconnected to one of the first elements when the trigger is in the pulled position; the protection system is such that: the blocking device switches in a first direction of rotation R1 when the latter moves from the blocking position to the release position, and the trigger switches in a second direction from R2 rotation opposite said first direction of rotation R1 when it passes from the armed position to the fired position; the elastic element is a torsion spring having a branch resting against the support, another arm resting against the trigger, and at least one winding around the second transverse axis Y2; at least the cable of the phase without a fuse has a strand between the lever arm and the second element of a longer length than the other strands of the other phases, so as to delay the disconnection of said phase without a fuse; - The trigger guard is equipped with a roller to limit friction with the hook when the locking device passes from the locking position to the release position. The invention also relates to an electrical transformer comprising a plurality of input supply phases of said transformer, an active part for transforming electrical energy supplied to the transformer, such as a voltage change, and a protection system such as defined above, connected in series between the power supply phases of the transformer and said active part. According to one variant, the electrical transformer comprises a protection system having a disconnection device between the input power supply phases of the transformer and the safety device. According to another variant, the electrical transformer comprises a tank and a ground cable connected to ground, and the ground fault detector is electrically connected to said tank and to said grounding cable.

Other features and advantages of the invention will become apparent from the following description of one of its embodiments, given by way of non-limiting example, with reference to the accompanying drawings. In the drawings: FIG. 1 is a diagram showing an electrical transformer comprising a protection system of the type of the invention; FIG. 2 is a perspective view of the protection system of FIG. 1; FIG. is a partial perspective view 10 of the protection system of FIG. 1, without the fuses, - FIG. 4 is another close-up partial view of the protection system of FIG. 1. In the various figures, the same references designate elements identical or similar. FIG. 1 schematically represents a polyphase electrical transformer 1 comprising: a tank 2 containing a liquid dielectric, supply phases 3 input to said transformer 1, powered by a power supply network 20 (not shown), and distribution phases 4 at the output of the transformer 1, supplying an electrical distribution network (not shown). In the remainder of this description, the term "upstream" refers to an element located on the phases in the direction of the input of the transformer, and by the term downstream, an element located on the phases in the direction of the output of the transformer. transformer. In the remainder of the normal description, a condition of an element as it is during the installation of the transformer will also be referred to in normal operation. Transformer 1 represents a three-phase transformer transforming, for example, a medium voltage into low voltage. The feed phases 3 comprise a first, a second and a third feed phase. The electrical transformer 1 comprises in series successively from the supply phases 3 to the distribution phases 4, that is to say from the upstream to the downstream: - a disconnection device 5 comprising disconnecting members 6, represented in FIG. 1 by a first switch 6-1 on the first phase, a second switch 6-2 on the second phase and a third switch 6-3 on the third phase, - a safety device 7 comprising a first fuse. 8 on the first phase and a second fuse 9 on the second phase, - a short-circuit device 10, controlled by a fault detection system, - three primary windings 11, for example connected in a triangle, and schematically represented in FIG. 1, - three secondary windings 12, for example star-connected, and schematically represented in FIG. 1. The disconnection device 5 and the safety device 7 constitute a system e protection for 25 electrical transformer. A magnetic circuit (not shown) magnetically couples the primary and secondary windings 12 to achieve the voltage transformation. The first switch 6-1 comprises an upstream terminal 6-la and a downstream terminal 6-lb. The second switch 6-2 comprises an upstream terminal 6-2a and a downstream terminal 6-2b. The third switch 6-3 comprises an upstream terminal 6-3a and a downstream terminal 6-3b. The disconnecting members 6 each have: a connected state in which the upstream terminal 6-1a, 6-2a, 6-3a is connected to the downstream terminal 6-lb, 6-2b, 6-3b of the phase corresponding, and an electric current can pass into said disconnector 6, and - a disconnected state in which the electric current can not pass.

The disconnecting members 6 are all initially normally in the connected state. The disconnecting device 5 further comprises a mechanical locking device 13, adapted to move the disconnecting members 6 from their connected state to their disconnected state. In addition, the disconnecting members 6 are designed to change state at different time instants under a single control of the locking device 13, so that the locking device 13 can be operated with a low mechanical effort and very quickly . In particular, the third switch 6-3 changes state after the first and second switches 6-1, 6-2. In this way, the third switch 6-3 disposed on the phase having no fuse goes from the connected state to the disconnected state, while the other phases are already completely disconnected and the current in this third phase is already weak. Indeed, after the disconnection of the first and second phases equipped with fuses, the transformer is then only under single-phase voltage by the third phase. If there is still a current in this third phase, it corresponds to a ground fault with a low current. Unlike the prior art, the input phases of the disconnection device 5 corresponding to the upstream terminals 6-1a, 6-2a, 6-3a are connected directly to the supply phases 3. The safety device 7 is thus located downstream of said disconnecting device 5. In this way, when all the disconnecting members 6 are in the disconnected state, only the upstream terminals 6-1a, 6-2a, 6-3a and the electrical connections to the supply phases 3 are under the voltage of the power supply network. These elements are easily isolated electrically. No other element of the electrical transformer 1 is energized. With this arrangement, it is possible to limit the risks of internal defect and it is easier to achieve effective electrical insulation of the internal elements of the electrical transformer 1. The first fuse 8 comprises upstream a first upstream terminal 8a and downstream a first downstream terminal 8b. The second fuse 9 comprises upstream a second upstream terminal 9a and downstream a second downstream terminal 9b. The upstream terminal 8a is connected to the downstream terminal of the switch 6-1 of the first phase. The upstream terminal 9a is connected to the downstream terminal of the switch 6-2. Each fuse, 8, 9 is adapted to cut the electric current in its phase and also comprises a striker adapted to control the locking device 13, so as to move the disconnecting members 6 from the connected state to the disconnected state . In addition, the downstream terminals 8b, 9b are connected to the short-circuit device 10. As can be seen in FIG. 2, each fuse 8, 9 comprises two conductive ends, the upstream terminals 8a, 9a and the downstream terminals 8b, 9b. , an insulating outer envelope 8c, 9c in the form of a tube. The fuses are equipped with strikers, so that a finger 8d, 9d substantially coaxial with the tube extends outside the upstream end. Each fuse encloses a rigid element conducting the electric current between the two conductive ends and put in mechanical tension by an internal spring (not visible). The conductive element is activated, i.e. broken, when the electric current flowing through the fuse is greater than a predetermined current. When the conductive element is activated, the internal spring moves the finger 8d, 9d which moves axially towards the outside of the fuse. The finger can easily be used to control mechanical devices inside the tank 2 of the electrical transformer 1, and in particular to mechanically control the disconnection device 5 of the protection system.

The short circuit device 10 is initially normally open, that is to say it does not connect the terminals 8b and 9b downstream of the fuses 8 and 9. When at least one fault is detected in the transformer by the fault detection system, the short circuit device 10 is closed, so as to short circuit the first and second phases equipped with fuses. Since the protection system according to the invention comprises only two fuses, the short-circuit device 10 bypasses only two terminals, terminals 8b, 9b. The fault detection system comprises at least one of the following detectors: a level detector 15 adapted to measure a level of the dielectric liquid contained in the tank 2, a pressure detector 16 adapted to measure a pressure internal to the tank 2 a ground fault detector 17 adapted to measure a current flowing through an earth cable 17a connected between the tank 2 and the earth 1a, the tank 2 being isolated from said earth 1a by insulation means 1b, for example placed between said tank 2 and rolling elements 1c for supporting said tank 2 on earth la. As can be seen in FIG. 1, the defect detection system advantageously comprises the three detectors mentioned above. The level detector 15 makes it possible to measure the level of the liquid dielectric. If the level is below a predetermined level, the level detector 35 controls the short circuit device 10 to a closed state, in which the terminals 8b and 9b are electrically connected. This level detector is placed in the upper part of the tank 2 of the transformer to ensure that all internal elements of the transformer are properly isolated by the liquid dielectric.

The pressure detector 16 makes it possible to measure the pressure of the liquid dielectric contained in the electrical transformer. If the pressure exceeds a predetermined pressure, the pressure detector 16 controls the short-circuit device 10 to a closed state, in which the terminals 8b and 9b are electrically connected. Ground fault detector 17 detects current leakage to earth by measuring a ground current. If said ground current is greater than a predetermined ground current, the ground fault detector 17 controls the short circuit device 10 to a closed state, in which the terminals 8b and 9b are electrically connected. When the short circuit device 10 switches from the open state to the closed state, this causes a high current draw in the first and second phases and causes the activation of the fuses 8, 9, then the control of the device. disconnection 5. Figures 2 to 4 show more precisely the protection system according to the invention. The protection system comprises a support 20 having the shape of a beam in a longitudinal direction X and having open rings 20a arranged laterally at two longitudinal position of this beam, in which are nested the fuses 8, 9. The two fuses 8 , 9 are nested in said open rings 20a of the support 20, so that said fuses are arranged with their fingers 8d, 9d strikers in the longitudinal direction X.

The locking device 13 is articulated in rotation relative to the support 20 around a first transverse axis Y1 substantially perpendicular to the longitudinal direction X, between a normal locking position (shown in the figures) and a release position (not shown in the figures). The locking device 13 moves from the locking position to the release position by pivoting about its first axis Y1 in a first direction of rotation R1. The locking device 13 comprises: - a rear face 13a a direction opposite to the longitudinal direction X which faces the striker fingers 8d, 9d, and - a front face 13b in the longitudinal direction X having a bridge 13c extending between two portions 13d advanced said front face.

The front face 13b, the two forward portions 13d and the bridge 13c thus form an opening 14 of the locking device 13. The rear face 13a is adapted to be pushed in the longitudinal direction X by one of the fingers 8d, 9d of strikers , so that the blocking device 13 switches around the first axis Y1 between the locking position and the release position, when one of said fingers moves in the longitudinal direction X. A trigger 18 is articulated in rotation relative to the support 20 about a second transverse axis Y2 also substantially perpendicular to the longitudinal direction X, between a normal armed position (shown in the figures) and a pulled position (not shown in the figures). The trigger 18 moves from the armed position to the pulled position by pivoting about its second axis Y2 in a second direction of rotation R2 opposite said first direction of rotation R1. This trigger 18 comprises three lever arms 18-1, 18-2, 18-3 extending substantially in longitudinal direction X and a hook 19 extending in the opposite direction to the longitudinal direction X, towards the device of FIG. blocking 13. Said hook 19 engages with the bridge 13c partially surrounding and through the opening 14, when the locking device 13 is in the locking position. The hook 19 is released from the bridge 13c when the locking device is in the release position. A torsion spring 21 comprises at least one branch 21a bearing against the support 20, a winding 21b surrounding the second axis Y2, and a branch 21c resting against the hook 19 of the trigger 18. The torsion spring 21 stops the hook 19 against the bridge 13c when the trigger 18 is in the armed position, and toggles the trigger 18 to its pulled position when the locking device 13 is in the release position, to pass the disconnecting members 6 of the state connected to the disconnected state. The bridge 13c optionally supports a roller 13e so that a friction force between the hook 19 and the locking device 13 is low. In this way, the disconnecting members 6 can change state quickly with little effort. The support comprises three tubes 20-1, 20-2, 20-3 on which are mounted the upstream terminals 6-1a, 6-2a, 6-3a of the disconnecting device 6, each tube being arranged opposite one of the three lever arms 18-1, 18-2, 18-3 of the trigger. As can be seen in FIG. 4, each lever arm accommodates a cable corresponding to one phase. Each cable comprises two ends and an intermediate portion between said ends, said intermediate portion being attached to a lever arm. A first cable 22-1 fixed to the first lever arm 18-1 comprises a first end corresponding to the downstream terminal 6-lb of the disconnection device 5 and a second end connected to the terminal 8a of the first fuse 8. This downstream terminal 6-lb is a male plug. The upstream terminal 6-la of the tube 20-1 is a female plug. Similarly, a second cable 22-2 fixed on the second lever arm 18-2 comprises a first end corresponding to the downstream terminal 6-2b of the disconnecting device 5 and a second end connected to the terminal 9a of the second fuse 9. This downstream terminal 6-2b is a plug. The upstream terminal 6-2a of the tube 20-2 is a female plug. A third cable 22-3 fixed on the third lever arm 18-3 comprises a first end corresponding to the downstream terminal 6-3b of the disconnecting device 5 and a second end connected to the primary winding 11. This downstream terminal 6- 3b is a male plug. The upstream terminal 6-3a of the tube 20-1 is a female plug. The plugs are engaged in the sockets when the connection member 6 is in the connected state, and the plugs are separated from the sockets when the connection member 6 is in the disconnected state. Possibly the plugs and sockets are reversed, or other removable connection members are used. The third cable 22-3 has a strand between the third lever arm 18-3 and the end corresponding to the terminal 6-3b of a longer length than the similar strands of the other cables. In this way, the disconnection of the third phase is delayed with respect to the other phases, and said third phase is disconnected after the total disconnection of the other phases. On the other hand, it will be noted that when the hook 19 is released by the bridge 13c, only the torsion spring acts thanks to the energy stored in the torsion spring 21 when the trigger 18 is in the armed position to rotate the trigger 18 to its withdrawn position and to disconnect the plugs of the disconnect devices 6. It is found that the protection system described above, includes only two fuses, a hook, a spring and a single support to support all these components and fixing said protection system in the tank 2 of the electrical transformer 1. It appears that such a design is economical and pezmet to provide a reliable protection system for disconnecting and isolating an electrical transformer of the power supply network.

Claims (16)

REVENDICATIONS1. Protection system for a polyphase electric transformer, comprising: - a plurality of phases, - a disconnecting device (5) comprising disconnecting members (6) for each phase each having a connected state in which an electric current can pass through the corresponding phase and a disconnected state in which said electric current can not pass into said corresponding phase, said disconnecting members (6) being normally all in connected state, said disconnecting device (5) further comprising a blocking device (13). ) adapted to move said disconnecting members (6) from the connected state to the disconnected state, - a safety device (7) comprising fuses (8, 9), each fuse being connected in series to a phase and adapted to cut the electric current of said phase and control the locking device (13) of the disconnecting device (5), so as to pass the gold disconnection ganes (6) from the connected state to the disconnected state, characterized in that at least one of said phases is devoid of fuse and the disconnecting device (5) is adapted for the disconnecting member (6) phase of the fuse-free phase switches from the connected state to the disconnected state after the other phases. 2. Protection system according to claim 1, wherein the disconnecting device (5) is upstream of the safety device (7). 3. The protection system according to claim 1 or claim 2, wherein each fuse (8, 9) comprises a striker adapted to control the blocking device (13) when said fuse is activated when an electric current of the phase of said fuse is greater than a predetermined electric current. The protection system according to one of the preceding claims, further comprising a fault detection system, and a short-circuit device (10) having: - an open state normally in which the other phases are not short-circuited circulated when no fault is detected by said fault detection system, and - a closed state in which said other phases are short-circuited when at least one fault is detected by said fault detection system. The protection system of claim 4, wherein the fault detection system comprises a level detector (15) adapted to control the short circuit device (10) to the closed state when a level is less than a predetermined level, said level detector (15) being for detecting a dielectric liquid level fault in the electrical transformer. The protection system of claim 4, wherein the fault detection system comprises a pressure detector (16) adapted to control the short-circuit device (10) to the closed state when a pressure is greater than a predetermined pressure, said pressure detector (16) being intended to detect an overpressure in the electrical transformer. The protection system of claim 4, wherein the fault detection system comprises a ground fault detector (17) adapted to control the closed state of the short circuit device (10) when a current of earth is greater than a predetermined ground current, said ground fault detector (17) being for detecting an electrical current leak to the earth of the electrical transformer. 8. Protection system according to one of the preceding claims, wherein the disconnecting device (5) comprises: - a support (20) adapted to support at least two fuses (8, 9) in a longitudinal direction X, each fuse having in this longitudinal direction X a firing pin (8d, 9d), - a locking device (13) articulated in rotation relative to said support (20) about a first axis transverse Y1 substantially perpendicular to the longitudinal direction X between a locking position and a release position, the locking device (13) having a rear face (13a) in a direction opposite to the longitudinal direction X facing the firing pin ( 8d, 9d) and a front face (13b) in the longitudinal direction X comprising a bridge (13c) between two portions (13d) of said front face (13b), the rear face (13a) being adapted to be pushed in the longitudinal direction X by at least one of the striker fingers (8d, 9d) for tilting said locking device (13) about the first axis Y1 between said locking position and said release position, - a trigger (18) hinged rotati relative to said support (20) about a second transverse axis Y2 substantially perpendicular to the longitudinal direction X between an armed position and a pulled position, said trigger (18) comprising a hook (19) engaging with the trigger guard ( 13c) of the locking device (13) when the locking device (13) is in the locking position and being released when the locking device (13) is in the release position, - an elastic element (21) adapted to abut the hook (19) against the trigger guard (13c) when the trigger (18) is in the armed position and toggle the trigger (18) to its pulled position when the locking device (13) is in the release position, so that said trigger (18) switches the disconnecting members (6) from the connected state to the disconnected state. 9. Protection system according to the preceding claim, wherein: - the support (20) comprises at least three first elements of the disconnecting members (6), each first element being electrically connected to an input phase, - the trigger ( 18) comprises at least three lever arms (18-1, 18-2, 18-3), each lever arm accommodating a cable (22-1, 22-2, 22-3) corresponding to an electrical phase and whose a first end is provided with a second element of the disconnecting members (6) adapted to be removably connected to one of the first elements when the trigger (18) is in the armed position, and adapted to be disconnected to one of the first elements when the trigger (18) is in the pulled position. 10. Protection system according to claim 8 or claim 9, wherein: - the locking device (13) switches in a first direction of rotation (Rl) when it moves from the locking position to the release position and the trigger (18) switches in a second direction of rotation (R2) opposite to said first direction of rotation (R1) when the latter moves from the armed position to the fired position. 11. Protection system according to one of claims 8 to 10, wherein the elastic member (21) is a torsion spring having a branch (21a) bearing against the support, another branch (21c) bearing against the trigger, and at least one winding (21b) around the second transverse axis (Y2). The protection system according to claim 9, wherein at least the non-fusible phase cable has a strand between the lever arm and the second element of a length longer than other strands of the other phases, so that delaying the disconnection of said phase without fuse. 13. Protection system according to one of claims 8 to 12, wherein the bridge (13c) is equipped with a roller (13e) to limit friction with the hook (19) when the locking device (13) passes from the lock position to the release position. 14. An electric transformer comprising: - a plurality of supply phases (3) at the input of said transformer, - an active part for transforming electrical energy supplied to the transformer (1), such as a voltage change, - a system protection device according to one of the preceding claims connected in series between the power supply phases (3) of the transformer and said active part. 30 15. Electrical transformer according to the preceding claim comprising a protection system having a disconnecting device between the supply phase (3) at the input of the transformer and the safety device (7). 35 25 16. An electrical transformer according to claim 14 or claim 15, including a protection system according to claim 7, wherein the electrical transformer (1) comprises a tank (2) and a ground cable (17a) connected to the ground (the ), and the ground fault detector (17) is electrically connected to said tank (2) and to said ground wire (17a).