FR2699016A1 - Auxiliary power supply for ground-mounted secondary substation - has ring-type CTs on HV feeder cable connected to rectifier/pre-regulator unit providing substation auxiliary supply. - Google Patents

Abstract

The kiosk-type substation(2), on a buried base(1), contains a remotely controlled 3-phase HV circuit breaker(3), control cabinet(4) and HV underground cable terminations(5,6,7). The cable cores of one HV circuit (e.g. 5) pass through three ring-type CTs encased together(11), forming with the rectifier/pre-regulator box(19) the auxiliary supply unit(10). The star-connected CT secondaries terminate on studs, which are butt-connected to corresponding contacts in the rectifier box, and automatically short-circuited when the box is detached. Before rectification, CT circuits enter a pre-regulator. Pairs of thyristors, reverse-parallel connected between each secondary pair, shunt the CTs during those parts of each cycle when current exceeds that required by the auxiliary load, giving consistent supply from low(20A) to nominal full-load(400A) primary current. ADVANTAGE - Less costly than present methods.

Description

"Auxiliary power supply for electrical substation"
The present invention relates to an auxiliary power supply assembly for an electrical substation. This invention relates generally to the technical field of "high voltage" underground electrical distribution networks, and it is more particularly interested in equipping simple electrical posts, bypass or star, encountered on such networks, and comprising, as the case may be, one, two or three remote-controlled switches.

 Such a substation usually contains at least one three-phase remote-controlled switch, and a control-command box, which combines the functions necessary for the remote control of the switch. An auxiliary power supply is necessary for these functions linked to the remote control, in particular for the electrical control proper, and for the electronics associated with the remote communication system and with various measurement systems for operating assistance.

To constitute such an auxiliary power supply, three technical solutions are currently known.
A first existing solution consists in using a low voltage current source, belonging to a neighboring network. This solution has the advantage of providing a simplified energy conversion.

Its disadvantages are its costly implementation, due to the need to draw an additional power line from the neighboring network, and its low reliability.

 Another known solution consists in the use of a high voltage / low voltage transformer. The advantages of this solution are the simplicity of the energy conversion, and its high availability. However, the use of a voltage transformer leads to a very bulky auxiliary power supply, posing connection difficulties due to the use of insulated cables, and very expensive.

A final solution currently applied is the use of solar panels. The advantage of this solution is its independence from the "high voltage" network. However, its availability is low in regions with poor sunshine, for example in
France. The use of solar panels also involves complex energy conversion. In addition, it is subject to vandalism due to the location of the solar panels necessarily outside. Finally it is a very expensive solution.

 The present invention aims to remedy the drawbacks of the current solutions mentioned above, by providing another purely electrotechnical and internal solution to the station concerned, but not using a voltage transformer, the solution proposed here for the auxiliary supply being simple, space-saving, quick to install, and inexpensive.

 To this end, the subject of the invention is an auxiliary power supply assembly for an electrical substation of the aforementioned type, this assembly essentially comprising, in combination, three current transformers disposed respectively around three line conductors terminating at the substation, and a rectifier and pre-regulator subassembly whose input terminals are connected to the secondary windings of the three current transformers, and whose output provides a DC supply voltage for the equipment to be supplied.

 Thus, by recommending the use of current transformers, the invention proposes a simple and economical solution for constituting an auxiliary power supply in a substation not comprising a "low voltage" source, this solution taking advantage of the electric current circulating in the "high voltage" conductors, insofar as this current is not zero and of sufficient intensity. The implementation according to the invention of current transformers, in particular of toroidal transformers, makes it possible to set up these transformers around "high voltage" cables (with a transformer for each phase) without particular precautions, since these cables are already isolated The three current transformers are advantageously grouped together in a compact form in the same block of transformers, provided with three passages of parallel axes intended to be crossed, respectively, by the three line conductors. The power supply assembly can thus be easily installed, in particular at the bottom of the electrical station where there is usually sufficient free space, the transformer block being able to be provided with a handle which further facilitates its handling.

The design of the rectifier and pre-regulator sub-assembly must be adapted to make it possible to exploit the line current between its extreme values, for example by satisfying the constraints below
- For a line current of 20 amps, which is the minimum load envisaged, the rectifier and pre-regulator sub-assembly must already supply its nominal power.

 - For a current of 400 amps, corresponding to the maximum load, the rectifier and pre-regulator sub-assembly must retain its output characteristics, by limiting the supply of energy by the current transformers.

 - For a shock intensity of 10 kiloamperes, of duration limited to one second and corresponding to a polyphase short circuit, the rectifier and pre-regulator sub-assembly must always retain its output characteristics.

 In order to satisfy these requirements, the invention provides that, in a preferred embodiment of the invention, said rectifier and pre-regulator sub-assembly comprises, in addition to an output rectifier bridge of the Graetz bridge type, a pre-regulator comprising six thyristors arranged two by two head to tail, respectively between the terminals corresponding to the ends of the branches of circuits comprising the secondary windings, coupled in star, of current transformers, with each thyristor being associated a circuit for controlling its trigger, such as at low current of line current in the conductors passing through the current transformers, the pre-regulator transmits the sine waves in full to the output rectifier, while at a high current of the line current, the pre-regulator supplies the output rectifier with chopped sine waves. particular, these chopped sine waves have an amplitude which does not exceed a certain predetermined threshold value. The rectifier and pre-regulator sub-assembly may also include means for smoothing and stabilizing the DC supply voltage, supplied at its output.

 Advantageously, the power supply assembly according to the invention further comprises, interposed between the three current transformers and the rectifier and pre-regulator sub-assembly, a short-circuit making it possible to temporarily short-circuit the respective secondary windings of the current transformers . The short-circuiter, thus placed at the interface between the transformer block and the rectifier and pre-regulator sub-assembly, makes it possible in particular to safely separate this rectifier and pre-regulator sub-assembly designed as a separable block, for reasons of maintainability.

 In the latter case, the short-circuiter is advantageously made as a mechanical short-circuiter, establishing the electrical connections between the transformer block and the rectifier and pre-regulator block only when the latter is fixed to the transformer block, and short-circuiting automatically the secondary windings of said transformers when the rectifier and pre-regulator block is separated from the transformer block. More particularly, the short-circuiting can be carried out using at least one screw for fixing the rectifier and pre-regulator block, a screw whose loosening causes the displacement of a movable conductive member ensuring the desired short-circuiting.

 Thus, the separation of the rectifier and pre-regulator block is done by automatically avoiding leaving the secondaries of the current transformers in open circuit, which could generate dangerous electric voltages.

In any case, the invention will be better understood with the aid of the description which follows, with reference to the appended schematic drawing representing, by way of nonlimiting example, an embodiment of this auxiliary power supply assembly for substation. electric
Figure 1 is an overall perspective view of an electrical substation equipped with an auxiliary power supply assembly according to the present invention
Figure 2 is a general electrical diagram of the station in Figure 1, with its auxiliary power supply
Figures 3 and 4 are more detailed electrical diagrams of parts of this power supply
Figure 5 is a diagram illustrating the operation of this power assembly
Figure 6 is a perspective view showing a particular practical embodiment of this power supply
Figure 7 is a partial sectional view of the device of Figure 6.

 FIG. 1 shows a semi-buried post for an electrical distribution network, the post comprising a buried base 1 and an external part 2 provided with at least one access door. This station mainly contains a three-phase remote-controlled switch 3, and it also houses a control-command box 4, which combines the functions necessary for the remote control of the switch 3. Cable arrivals and departures 5,6,7 are connected at the switch 3, the base 1 having side openings 8.9 for the passage of the cables.

 The power supply assembly according to the invention, generally designated by the reference 10, constitutes an auxiliary power supply necessary for the operation of the remote control of the switch 3. This power supply assembly 10 is housed at the bottom of the station, at the inside the base 1 and, more particularly, on the incoming cables 5. The general electrical diagram of the supply assembly 10 is given in FIG. 2.

 This power supply assembly 10 comprises a transformer block 11, with three toroidal current transformers 12,13,14 respectively disposed around the three cables 5, corresponding to the three phases, the cables 5 constituting the primaries of the toroidal transformers 12,13, 14.

 The respective secondary windings 15, 16, 17 of the three toroidal transformers 12, 13, 14 are coupled in a star, and the ends of the branches of the star assembly are connected, with the interposition of a mechanical short-circuiter 18, to a rectifier and pre-regulator block. 19, whose rectifier and pre-regulator functions are symbolized respectively at 20 and 21.

Conductors 22 connect the output of block 19 to the control-command box 4 to be supplied, the latter acting in particular on the motorization 23 of the remote-controlled switch 3 via an electrical connection 24.

 FIG. 3 shows, in more detail, the internal electrical circuit of the rectifier and pre-regulator block 19, which has three input points A, B, C corresponding respectively to the ends of the branches comprising the secondary 15,16,17 of the three transformers toric 12,13,14.

 Block 19 consists of an output rectifier of the Graetz bridge type, symbolized at 20, and a preregulator 21 comprising six thyristors 25,26,27,28,29,30, arranged two by two head to tail, respectively between the pairs of terminals AB, BC and AC linked to the secondary 15,16,17 of the toroidal transformers 12,13,14. The trigger of each of the six thyristors 25 to 30 is connected to a control circuit 31, the details of which are shown in FIG. 4. The control circuit 31 comprises a transistor 32, three resistors 33,34,35, three diodes 36 , 37.38 and a Zener diode 39, with the connections indicated in Figure 4.

 The output of the rectifier and pre-regulator block 19 supplies, between the conductors 22, a continuous and stabilized supply voltage, according to a particular mode illustrated by the diagram in FIG. 5.

 As shown in the upper part of FIG. 5, if the intensity of the line current in the cables 5 is low, the toroidal transformers 12, 13, 14 supply the rectifier and pre-regulator block 19 with a current in the ratio of their number of turns. The voltage available at the Us output then depends on the load of the use. At nominal load, this voltage Us is less than a preset threshold S; under these conditions, the preregulator 21 does not intervene, and the sine wave of its input voltage Ue is supplied in full to the rectifier 20.

 On the other hand, at high intensity of the line current, the energy supplied by the toroidal transformers 12,13,14 is limited by the active shunts, constituted by the thyristors 25 to 30 which short-circuit the secondary 15,16,17 of these transformers as soon as the output voltage Us exceeds the set threshold value S.

Thus the output rectifier receives a chopped sine wave Ue, the amplitude of which never exceeds the threshold value S, as illustrated in the lower part of FIG. 5.

 FIGS. 6 and 7 show a particular mechanical configuration of the supply assembly 10, and they also indicate the structure of the mechanical short-circuiter 18.

 The transformer block 11 has here the external shape of a prism with a substantially triangular base, and the rectifier and regulator block 19 is fixed against a lateral face of the transformer block 11. The latter has three passages of parallel axes 40,41 , 42 intended respectively to be crossed by the three incoming cables 5, insulated. The three toroidal transformers 12,13,14 are located, respectively, around the three passages 40,41,42. These toroidal transformers can be of the closed or opening type, depending on the needs of the use (installation in a station being assembled, or in a station already assembled). The transformer block 11 can rest directly on the ground or the bottom of the substation, by one of its lateral faces other than that supporting the rectifier and regulator block 19.

This transformer block 11 can be provided with a handle 43 facilitating its handling.

 The mechanical short-circuiter 18 is provided to short-circuit the secondary 15,16,17 of the toroidal transformers 12,13,14, by the points A, B, C previously defined, when the rectifier and pre-regulator block 19 is disconnected of the transformer block 11. This short-circuiter 18 comprises a cylindrical insulating housing 44, inserted in the transformer block 11, and traversed by three conductive threaded rods 45 in an axial direction, materializing the points A, B, C, these three rods 45 threaded being arranged at 120O relative to each other (Figure 7 showing only one).

 Each threaded rod 45 constitutes, by its inner end, a connection pad with a conductor 46 coming from one of the secondary windings 15, 16, 17 of the toroidal transformers 12, 13, 14. The outer end of each threaded rod 45, forming an output contact, is designed to cooperate with an input contact 47 of the rectifier and pre-regulator block 19. A fixed metal washer 48, constituting a short-circuiting contact, is mounted around of each threaded rod 45, in conductive connection therewith and against the internal wall of the housing 44.

 Along the central axis of this housing 44 is also mounted a movable metal short-circuiting washer 49, provided with a support axis 50 sliding axially in a guide well 51 produced in one piece with the bottom of the housing 44 A helical return spring 52 is compressed between the washer 49 and the bottom of the housing 44.

 The rectifier and regulator block 19 is removably fixed to the transformer block 11 by at least one captive screw 53, with interposition of seals 54 and 55. The fixing screw 53 is designed to be screwed into a thread 56 formed in the cover of the housing 44, along its central axis.

 When the rectifier and pre-regulator block 19 is mounted and fixed on the transformer block 11, the end of the fixing screw 53 is applied to the mobile short-circuiting washer 49 and pushes this washer 49 towards the bottom of the housing 44 , by compressing the return spring 52. The washer 49 is then kept separate from the fixed washers 48, thus neutralizing the short-circuiting and allowing the normal intervention of the supply assembly 10 (this operating position being that illustrated by Figure 7).

 By cons, when the fixing screw 53 is loosened to separate the rectifier and pre-regulator block 19 from the transformer block 11, the movable washer 49 is released by the screw 53 and pushed by the return spring 52, so that it is applied against the three fixed washers 48. These three fixed washers 48 are thus put in electrical connection with each other by means of the movable washer 49, and the short-circuiting is carried out simultaneously for the three secondary windings 15,16,17 (the schematic representation of the short-circuiter 18 with two contacts, in Figure 2, is purely functional and does not prejudge any concrete achievement).

It goes without saying that the invention is not limited to the sole embodiment of this auxiliary power supply assembly for an electrical station which has been described above, by way of example; on the contrary, it embraces all of the variant embodiments and applications respecting the same principle. Thus, in particular, that one would not depart from the scope of the invention
- by the use of all equivalents, in particular by replacing the toroidal current transformers by current transformers of different shape, for example of square shape;
- by modifying the detail of the electrical circuit of the rectifier and pre-regulator block;
- by making the transformer block with a different external shape
- By a provision of this auxiliary power supply at another location inside the station.

Claims (12)

 1. Auxiliary power supply assembly for an electrical substation of a "high voltage" electrical distribution network, more particularly for a substation (1,2) containing at least one three-phase remote-controlled switch (3), and a control-command box (4) which combines the functions necessary for the remote control of the switch (3), characterized in that it comprises, in combination, three current transformers (12,13,14) arranged respectively around three line conductors ( 5) leading to the station (1,2), and a rectifier and pre-regulator sub-assembly (19) whose input terminals (A, B, C) are connected to the secondary windings (15,16,17) of the three transformers current (12,13,14), and whose output (22) provides a continuous supply voltage (Us) for the equipment to be supplied.  2. Auxiliary power supply assembly for electrical station according to claim 1, characterized in that the three current transformers are toroidal transformers (12,13,14).  3. Auxiliary power supply assembly for electrical station according to claim 1 or 2, characterized in that the three current transformers (12,13,14) are grouped in the same transformer block (11) provided with three passages (40 , 41,42) of parallel axes intended to be crossed, respectively, by the three line conductors (5).  4. Auxiliary power supply assembly for electrical station according to claim 3, characterized in that the transformer block (11) is provided with a handle (43) for its manipulation.  5. Auxiliary power supply assembly for electrical station according to claim 3 or 4, characterized in that the rectifier and pre-regulator sub-assembly (19) is designed as a separable block, fixed against the transformer block (11).  6. An auxiliary power supply assembly for an electrical substation according to any one of claims 1 to 5, characterized in that the rectifier and pre-regulator sub-assembly (19) comprises, in addition to an output rectifier bridge (20) of the bridge type. Graetz, a preregulator (21) comprising six thyristors (25 to 30) arranged two to two head to tail, respectively between the terminals (A, B, C) corresponding to the ends of the circuit branches comprising the secondary windings (15,16,17 ), coupled in star, current transformers (12,13,14), with each thyristor (25 to 30) being associated a control circuit (31) of its trigger, such as with a low intensity of the line current in the conductors (5) passing through the current transformers (12,13,14), the pre-regulator (21) fully transmits the sine waves to the output rectifier (20), while at a high current intensity of the line, the pre-regulator (21) supplies the rectifier with Nettle (20) of chopped sine waves, these chopped sine waves preferably have an amplitude which does not exceed a certain predetermined threshold value (S).  7. Auxiliary power supply assembly for a substation according to claim 6, characterized in that the rectifier and pre-regulator sub-assembly (19) further comprises means for smoothing and / or stabilizing the DC supply voltage (Us), supplied at its output.  8. Auxiliary power supply assembly for electrical station according to any one of claims 1 to 7, characterized in that it comprises, interposed between the three current transformers (12,13,14) and the rectifier and pre-regulator sub-assembly ( 19), a short circuit (18) for temporarily short-circuiting the respective secondary windings (15,16,17) of the current transformers (12,13,14).  9. Auxiliary power supply assembly for electrical substation according to all of claims 5 and 8, characterized in that the short-circuiter is produced as a mechanical short-circuiter (18), establishing the electrical connections between the transformer block ( 11) and the rectifier and pre-regulator block (19) only when the latter is fixed to the transformer block (11), and automatically short-circuiting the secondary windings (15,16,17) of said transformers (12,13,14) when the rectifier and pre-regulator block (19) is separated from the transformer block (11).  10. Auxiliary power supply assembly for electrical station according to claim 9, characterized in that, in the mechanical short-circuiter (18), the short-circuiting is carried out using at least one fixing screw (53 ) of the rectifier and pre-regulator block (19), a screw whose loosening causes the displacement of a movable conductive member (49) ensuring the short-circuiting.  11. Auxiliary power supply assembly for electrical station according to claim 10, characterized in that the aforesaid conductive movable member is a movable metal washer (49), cooperating with the end of the fixing screw (53) of the rectifier block and pre-regulator (19), and subjected to the thrust of a return spring (52), the movable metal washer (49) being designed to cooperate, when the screw (53) is loosened, with three fixed metal washers (48) respectively in conductive connection with the secondary windings (15,16,17) of the three current transformers (12,13,14).  12. Auxiliary power supply assembly for electrical substation according to any one of claims 1 to 11, characterized in that this auxiliary power supply assembly (10) is placed at the bottom of a semi-buried electrical substation (1,2 ), on cable inlets (5) connecting to the switch (3) contained in the station.