FR2705840A1 - Electric load shedding system. - Google Patents

Abstract

This selective load-shedding system applies to a set of electrical devices (1, 2, 3), supplied with alternating current by the same line comprising at least one phase conductor (4) and one neutral conductor (5), coupled via an isolation transformer (8) to an "upstream" circuit comprising a main switch (7), the neutral conductor (5) thus being able to be dynamically polarized with respect to the earth (6). The set of electrical devices includes devices (1) mounted directly between the conductors (4, 5) and powered by the closing of the main switch (7), and other devices (2, 3) which are associated relays (10, 12). A control device (13) comprises load-shedding switches (15, 17), selectively inducing on the neutral conductor (5) control signals which activate the relays (10, 12). Particular application: public lighting installations.

Description

"ELECTRIC SHEDDING SYSTEM"
The present invention relates to an electrical load shedding system, applying to a set of electrical devices, such as lighting or heating devices, supplied with alternating current by the same line, the implementation of this load shedding system not requiring modification of pre-existing wiring.

 In general, the advantage of an electrical load shedding system is to allow, under certain circumstances, the selective interruption of the supply of certain electrical devices belonging to a set. More particularly, the electrical load shedding system object of the present invention proves to be interesting in the case of medium length cables, of the order of a few hundred meters, like those of urban public lighting, these cables being generally underground. and installed in trenches, which represents a fairly significant investment. In this field of application, the load shedding system proposed by the invention makes it possible to control, for example, at a predetermined time, such as midnight, the switching off of a third of the lighting apparatuses, then at another predetermined time. , such as three o'clock in the morning, switching off another third of the lighting fixtures, and finally at daybreak completely shutting down the lighting.

However, this field of application is not limiting, and the invention will also find a certain interest in all cases where one wants to extend or refine the controls of a set of electrical devices, while avoiding "rewiring "an existing industrial or domestic electrical installation. The implementation of a programmed partial load shedding with centralized control, on an electric heating installation, is a typical example of this other field of application.

To achieve the goals set out above, the invention essentially relates to an electrical load shedding system, of the kind indicated in the introduction, characterized in that
the assembly formed by the phase conductor (s) and the neutral conductor is coupled via an isolation transformer to an "upstream" circuit comprising a general switch, the neutral conductor thus being made capable of being dynamically polarized with respect to the earth,
the set of electrical devices comprises a first group of devices, each of which is mounted directly between a phase conductor and the neutral conductor, and is powered by the closing of the general switch,
the set of electrical devices comprises at least one other group of devices, each of which is mounted in series with a contact of a relay, each device with its contact also being connected between a phase conductor and the neutral conductor, while each relay, located on the site of the corresponding device, is in relation to this neutral conductor, and
- a control device, comprising at least one load shedding switch, is provided for selectively inducing on the neutral conductor control signals, of low voltage compared to the supply voltage of the devices, which activate the relays or a group of relays associated with the other group or with one of the other groups of devices.

 Thus, a line equipped with the load shedding system according to the invention comprises a general switch, and one or two load shedding switches which control relays located remotely. The receiving electrical devices, supplied by the line concerned, therefore benefit from the combined commands of the various switches, this load shedding system being based on the principle of replacing the usual neutral (neutral "impedant" or neutral "to earth"), by a neutral "piloted", dynamically polarized with respect to earth, this by means of an isolation transformer leaving the original neutral materially unchanged but allowing it to convey control signals, under low voltage.

The originality of the proposed load shedding system thus lies in the remote control obtained without adding an additional conductor, and in the control of two states for each device with passive electrical components.

 In a preferred embodiment of the invention, the control device comprises a step-down transformer, mounted downstream of the isolation transformer and having its secondary connected to the neutral conductor by at least one circuit branch comprising a load-shedding switch , the closure of which authorizes the sending of control signals to said neutral conductor. The step-down transformer can in particular supply, to its secondary, therefore on the neutral conductor, a voltage of the order of twentieth of the supply voltage supplied by the isolation transformer.

Thus this step-down transformer allows very low voltage control signals, composed of alternating current, to be injected into the neutral conductor and which can selectively include positive and / or negative alternations, making it possible to selectively reach two groups of devices. affected by load shedding.

To implement this latter possibility, it is more particularly provided, according to the invention, that
- the control device comprises two branches of circuit in parallel, one of which comprises a first load-shedding switch in series with a diode, and the other comprises a second load-shedding switch in series with a diode, the two diodes being mounted in opposite directions,
- a group of devices is associated with relays, the coils of which are connected in series with respective diodes arranged in such a way that these relays are activated only by control signals in the form of current alternations of predetermined sign, emitted on the neutral conductor when the first load-shedding switch is closed, and
- another group of devices is associated with relays, the coils of which are connected in series with respective diodes arranged in such a way that these relays are activated only by control signals in the form of current alternations of predetermined sign, reverse from the previous one, issued on the neutral conductor when the second load-shedding switch is closed.

 If the neutral conductor receives positive half-waves from the step-down transformer, all the relays associated with a group of devices are activated. Conversely, if the neutral conductor receives negative half-waves, all the relays associated with the other group of devices are activated. The two previous hypotheses can be combined, in which case all these devices are powered simultaneously.

 For the practical implementation of the invention, it suffices to have, at the start of the line, the isolation transformer and a control box which contains the step-down transformer and the load-shedding switches, as well as a device and alarm monitoring the voltage excursion of the neutral conductor. On each site comprising devices subject to load shedding, there is a load shedding box which contains two relays, the load shedding boxes more or less numerous being arranged from time to time along the line. More particularly, each load shedding box contains a first relay whose coil is connected in series with a diode, between the neutral conductor and the earth, and a second relay whose coil is connected in series with a diode, between the neutral conductor and earth, the two diodes being mounted in opposite directions. Each load shedding box still advantageously contains a protection device.

The configuration and the advantages of the electrical load shedding system defined above make it particularly applicable to a lighting installation, more particularly public lighting, comprising two or three groups of lighting devices to be supplied simultaneously or selectively
Anyway, 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, a particular embodiment of this electrical load shedding system
Figure 1 is an overall view, in the form of an electrical diagram, of a load shedding system according to the present invention, applied to a public lighting installation
Figure 2 is a more detailed electrical diagram of the control unit belonging to the system of Figure 1;
Figure 3 is a more detailed electrical diagram of one of the load shedding boxes belonging to the same system.

 Figure 1 shows a public lighting installation, which includes lighting lamps 1,2,3 etc ...

all connected in parallel between a phase conductor 4 and a "neutral" conductor 5 of the same line, which also includes a "ground" conductor 6 with respect to which the neutral conductor 5 can be dynamically polarized. The line also includes a general switch 7 and an isolation transformer 8, located between the "upstream" part comprising the general switch 7 and the "downstream" part formed by the conductors 4 and 5.

 The lamp 1 is mounted and supplied directly between the two conductors 4 and 5. The lamp 2 is mounted in series with a contact 9 of a relay 10, this lamp 2 and the associated contact 9 being connected between the two conductors 4 and 5 Similarly, the lamp 3 is connected in series with a contact 11 of another relay 12, this lamp 3 and the associated contact 11 being connected between the conductors 4 and 5. Further on the line considered, the same diagram is repeat, with other lamps such as lamp 1, directly supplied, and other lamps such as lamps 2 and 3, with which additional relays are associated.

 On the "upstream" side, there is a control box designated as a whole by the reference numeral 13, and shown more particularly in FIG. 2, which has respective connection terminals for the phase conductor 4, for the neutral conductor 5 , for the earth conductor 6 and for two load-shedding switches described below, ie a total of five terminals.

In the control unit 13, a step-down transformer 14 has its primary connected between the two conductors 4 and 5 of the line, while its secondary is mounted between the conductors 5 and 6. More particularly, the secondary of the step-down transformer 14 is connected to the neutral conductor 5 by a circuit subdivided into two parallel branches, one of which includes a switch 15 in series with a first diode 16, and the other of which also includes a switch 17 in series with a second diode 18, the two diodes 16 and 18 being mounted in opposite directions. With regard to the voltage, for a standard network of 220 volts over medium lengths, the step-down transformer 14 can supply its secondary with a voltage of 12 volts. More generally, a secondary voltage of the order of one twentieth of the supply voltage gives the best compromise; thus, for a supply voltage of 5000 volts, the step-down transformer 14 would provide a voltage of approximately 250 volts.

 The control box 13 is arranged in the electrical starting box which also contains the isolation transformer 8, or close to this electric box.

 In practice, the control box 13 also includes internal components constituting a monitoring and alarm device 19, which is used to monitor the voltage excursion of the neutral conductor 5, and to signal any fault which is due to a short -circuit or leak in one of the uses. In the event of a serious fault detected by the device 19, the supply of the step-down transformer 14 can be automatically interrupted.

 At each pair of lamps such as 2 and 3, subject to load shedding, there is provided a load shedding housing designated as a whole by the numerical reference 20, and shown more particularly in FIG. 3, this housing comprising connection terminals respective for the neutral conductor 5, for the earth conductor 6, and for the two lamps 2 and 3, ie a total of four terminals. The load-shedding box 20 contains the two relays 10 and 12, associated respectively with the two lamps 1 and 2.

 The coil of the first relay 10 is connected in series with a diode 21, between the neutral conductor 5 and the earth conductor 6. Likewise, the coil of the second relay 12 is connected in series with another diode 22, between the neutral conductor 5 and the earth conductor 6. The two diodes 21 and 22 are mounted in opposite directions.

 Relays 10 and 12 are continuous relays each comprising, in parallel with the coil, an electrochemical capacitor (not shown) intended to smooth the control voltage which can oscillate at a frequency of 100 Hertz.

 Load shedding boxes 20, such as that described above, are placed from time to time along the line, in correspondence with the lamps concerned by the load shedding. Each load-shedding box 20 also advantageously includes a protection device 23, which protects this box 20 in the event of a fault on the line.

 In general, the control unit 13 makes it possible to selectively transmit, on the neutral conductor 5, very low voltage control signals composed by positive and / or negative alternations, originating from the secondary of the step-down transformer 14. In at each point of use, the load shedding unit 20 selectively responds to these control signals, thanks to its two relays 10 and 12 and to its diodes 21 and 22, to authorize or not the supply of the lamps 2 and / or 3.

In more detail, the operation of the load shedding system is established as follows
In a first hypothesis, the general switch 7 is closed, and the two switches 15 and 17 of the control box 13 are open. No control signal is then induced on the neutral conductor 5, and the relays 10 and 12 are not energized, so that their respective contacts 9 and 11 keep their open rest position. Lamp 1 is then supplied, but the other lamps 2 and 3 remain off.

 In a second hypothesis, the general switch 7 is closed, as is the switch 15 of the control box 13, but the other switch 17 of this box 13 remains open. As before, the lamp 1 is then supplied. The closing of the switch 15 associated with the diode 16 causes, on the neutral conductor 5, the emission of a control signal in the form of alternations of determined sign, for example positive, with respect to the earth. Given the mounting of the diodes 21 and 22, the control signal excites the first relay 10 associated with the lamp 2, but cannot pass through the second relay 12 associated with the lamp 3. The contact 9 of the first relay 10 then closes, and the lamp 2 is supplied.

The other lamp 3 remains off, the corresponding contact 11 remaining open.

 In a third hypothesis, the general switch 7 is closed, the switch 15 is open, and the switch 17 is closed. The closing of this last switch 17, associated with the diode 18, causes on the neutral conductor 5 the emission of a control signal in the form of alternations of sign opposite to the preceding hypothesis, for example of negative sign. At the load shedding unit 20, the operation is then the reverse of that previously described: the contact 9 of the first relay 10 remains open, while the contact 11 of the second relay 12 closes. Thus, the lamp 2 remains off, while the lamp 3 is supplied, the lamp 1 being supplied anyway.

 In a fourth hypothesis, the three switches 7, 15 and 17 are closed. The alternations of the two signs are then transmitted on the neutral conductor 5, and they respectively activate the two relays 10 and 12, the respective contacts 9 and 11 of which close.

All the lamps 1,2 and 3 are thus supplied simultaneously.

 Of course, in a final hypothesis, if the general switch 7 is open, and whatever the state of the two load shedding switches 15 and 17, all the lamps 1, 2 and 3 remain off.

 Thus, according to the hypotheses, the neutral conductor 5 is sometimes free of voltage, but charged to the earth by the parallel impedances of the load-shedding boxes 20, sometimes traversed by alternations of current all of the same sign, positive or negative as the case may be, sometimes finally traversed by an alternating current composed of the superposition of positive and negative alternations. Of course, the operations detailed above for the three lamps 1, 2 and 3 are repeated for all the other lamps connected and controlled identically. Thus, depending on the states of the two load shedding switches 15 or 17, it is possible to supply either a single group of lamps which is "priority" (comprising all the lamps directly supplied, such as lamp 1), or two groups of lamps (such as all lamps 1 and 2, or all lamps 1 and 3), i.e. all lamps 1,2 and 3.

 It goes without saying that the invention is not limited to the sole embodiment of this electrical load shedding system 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, one would not depart from the scope of the invention by modifications of detail, adaptations or supplements made to the electrical circuits, and in particular by the addition of additional components having a safety function for the installation. and its users.

 The single-phase embodiment, described here as a simple example of implementation of the invention, is obviously transposable to a three-phase installation, with the necessary adaptations (in particular: use of a three-phase isolation transformer).

 The previously described embodiment, of essentially electrical type with sending positive or negative signals to relays, can also advantageously evolve towards an electronic embodiment of this load shedding system, in which an electronic control device transmits coded signals, in particular in the form of binary information, which can selectively control numerous relays distributed over the line concerned, at distribution points, these coded signals always being carried by the neutral conductor 5. In this case, it suffices to have between the neutral conductor 5 and the conductor earth 6 a power interface which is the output stage of a modem. The coded control signals transmitted in series can thus be in the form of bytes, which represent the address of a selected device, as well as its desired state (on or off).

 The load shedding system, applied in the example described to public lighting lamps divided into three groups, can easily be adapted to a lighting installation whose lamps would be divided into only two groups.

 The various switches of the system can be controlled manually, or automatically by means of a clock or the like, depending on the applications envisaged.

 Naturally, these applications are not limited to public lighting, and include any set of receiving electrical appliances, for example heating appliances, in collective or domestic uses. The same load shedding system can control devices that are all identical or of a different nature, for example street lamps on the one hand and light panels on the other; thus, it becomes possible to supply street lighting throughout the night on the same line, and to order luminous road signs, placed in front of schools, only at school entry and exit times, two orders that can be simultaneous, especially in winter.

Claims (9)

 1. Electric load shedding system, applying to a set of electrical devices (1,2,3), such as lighting or heating devices, supplied with alternating current by the same line comprising at least one conductor of phase (4) and a neutral conductor (5), characterized in that  - the assembly formed by the phase conductor (s) (4) and the neutral conductor (5) is coupled via an isolation transformer (8) to an "upstream" circuit comprising a general switch (7 ), the neutral conductor (5) thus being able to be dynamically polarized with respect to the earth (6),  - the set of electrical devices comprises a first group of devices (1), each of which is mounted directly between a phase conductor (4) and the neutral conductor (5), and is supplied by closing the switch general (7),  - the set of electrical devices comprises at least one other group of devices (2,3), each of which is mounted in series with a contact (9,11) of a relay (10,12), each device ( 2,3) with its contact (9,11) being also connected between a phase conductor (4) and the neutral conductor (5), while each relay (10,12), located on the site of the device ( 2,3) corresponding, is in relation with this neutral conductor (5), and  - a control device (13), comprising at least one load shedding switch (15,17), is provided for selectively inducing on the neutral conductor (5) control signals, of low voltage compared to the supply voltage of the devices (1,2,3), which activate the relays or a group of relays (10,12) associated with the other group or with one of the other groups of devices (2,3).  2. electrical load shedding system according to claim 1, characterized in that the control device (13) comprises a step-down transformer (14), mounted downstream of the isolation transformer (8) and having its secondary connected to the conductor neutral (5) by at least one circuit branch comprising a load-shedding switch (15,17), the closure of which authorizes the sending of control signals to said neutral conductor (5).  3. Electric load shedding system according to claim 2, characterized in that  - the control device (13) comprises two branches of circuit in parallel, one of which comprises a first load-shedding switch (15) in series with a diode (16), and the other comprises a second load-shedding switch (17 ) in series with a diode (18), the two diodes (16,18) being mounted in opposite directions,  - a group of devices (2) is associated with relays (10) whose coils are connected in series with respective diodes (21) arranged so that these relays (10) are activated only by control signals under form of alternating current of predetermined sign, emitted on the neutral conductor (5) in the event of the closing of the first load-shedding switch (15), and  - another group of devices (3) is associated with relays (12) whose coils are connected in series with respective diodes (22) arranged so that these relays (12) are activated only by control signals in the form of alternations of current of predetermined sign, reverse of the previous one, emitted on the neutral conductor (5) in the event of the closure of the second load-shedding switch (17).  4. Electric load shedding system according to claim 2 or 3, characterized in that the step-down transformer (14) is provided to supply its secondary therefore on the neutral conductor (5), a voltage of the order of the twentieth of the supply voltage supplied by the isolation transformer (8).  5. Electric load shedding system according to any one of claims 2 to 4, characterized in that the control device is produced in the form of a control box (13) containing, in addition to the step-down transformer (14) and the load-shedding switches (15, 17), a monitoring and alarm device (19) monitoring the voltage excursion of the neutral conductor (5).  6. Electric load shedding system according to claim 3, characterized in that the relays (10,12) are associated two by two, in load shedding boxes (20) located on the site of the corresponding devices (2,3) and containing , each, a first relay (10) whose coil is mounted in series with a diode (21), between the neutral conductor (5) and the earth (6), and a second relay (12) whose coil is mounted in series with a diode (22), between the neutral conductor (5) and the earth (6), the two diodes (21,22) being mounted in opposite directions.  7. Electric load shedding system according to claim 6, characterized in that each load shedding box (20) also contains a protection device (23).  8. Electric load shedding system according to claim 1 or 2, characterized in that the control device (13) is provided for inducing on the neutral conductor (5) coded control signals, in particular in the form of binary information, which can selectively control the relays, these coded control signals representing the address of a selected device and its desired state.  9. electrical load shedding system according to any one of claims 1 to 8, characterized by its application to a lighting installation, in particular public lighting, comprising two or three groups of lighting devices (1,2, 3) to be supplied simultaneously or selectively.