EP0280616B1 - Electric power supply device for a cable, and its use - Google Patents

Abstract

Device for supplying an electrically conducting cable, or equivalent, with electrical power. The device comprises, in addition to a transformer (2) provided with a primary (12) and a secondary (22) to which is connected the joining end of the cable (10), a diode (14) mounted in series with the abovementioned secondary (22), as well as preferably, a discharger (24) mounted in parallel across the terminals of the diode. Other components of this diode/discharger type can be mounted in the circuit of the device so as to regulate and protect its operation. The invention applies in particular to the electrical powering of a fence. <IMAGE>

Description

The invention relates to an apparatus for supplying electrical energy to a cable or equivalent, an electrical conductor, in particular intended for electrifying fences.

From document FR-A-1 582 799, it is known to use such an apparatus comprising a transformer provided with a primary winding connected to a current generator and a secondary winding to which is connected one end of said cable; a switch ; and a first current rectifier, such as a diode disposed passing in the direct direction considered of the current flowing from the secondary of the transformer to the cable, this first rectifier being mounted in series between the secondary of the transformer and said end of the cable.

As for the document FR-A-1 280 381, it teaches the use of a spark gap mounted in parallel at the terminals of a current rectifier (diode) in order to obtain a priori increased protection of this rectifier against jolts of overvoltage.

However, the fact remains that on such devices, if a prolonged short circuit occurs (caused for example by falling branches on the conductive cable), the operation of this device deteriorates, the drop in impedance causing a relatively rapid discharge of the generator. Soon the cable is no longer electrified. In addition, taking into account the practical conditions of use, it turns out that the components "suffer" from the sometimes large and abrupt supply variations. Their reliability can therefore sometimes be improved.

The invention aims in particular to remedy these defects.

• un premier éclateur monté aux bornes de l'interrupteur, qui est un interrupteur statique connecté d'un côté à une borne du bobinage primaire et de l'autre à une borne du générateur de courant,
• un second éclateur monté en parallèle aux bornes dudit premier redresseur pour le protéger contre les surtensions en limitant la décharge du générateur en cas de court-circuit,
• et un second redresseur de courant, tel qu'une diode disposée passante dans le sens inverse considéré du courant, ce second redresseur étant monté en parallèle aux bornes dudit premier éclateur.

For this, it therefore proposes to perfect the apparatus of the publication FR-A-1 582 799 by adding to it:

• a first spark gap mounted at the terminals of the switch, which is a static switch connected on one side to a terminal of the primary winding and on the other to a terminal of the current generator,
• a second spark gap mounted in parallel at the terminals said first rectifier to protect it against overvoltages by limiting the discharge of the generator in the event of a short circuit,
• and a second current rectifier, such as a diode arranged to pass in the considered opposite direction of the current, this second rectifier being mounted in parallel at the terminals of said first spark gap.

Preferably, the conductive cable belonging to an electric fence, the static switch will be controlled by a timer subjected to the voltage of the current generator and the voltage across the primary winding of the transformer will be substantially equal to the difference of the voltages prevailing at the terminals of the current generator and of said switch.

In this way, we will obtain a device whose current generator will not accidentally discharge and whose operation will be particularly reliable, for a cost price quite competitive.

• la figure 1 illustre l'appareil de l'invention au moyen d'un schéma synoptique,
• - la figure 2 présente un schéma synoptique partiel explicatif du fonctionnement de l'appareil, en considérant tout d'abord que le secondaire du transformateur n'est pas chargé,
• - les figures 3a, 3b et 3c représentent trois diagrammes explicatifs du fonctionnement de l'appareil en relation avec la figure 2. Plus précisément, la figure 3a représente l'état de l'interrupteur statique en fonction du temps (T), la figure 3b représente l'intensité (I) au seul primaire du transformateur en fonction du temps (T) , la figure 3c représente la tension (V) aux bornes de l'interrupteur en fonction du temps (T), et
• - la figure 4 est une schéma synoptique partiel dans lequel on prend en compte le secondaire du transformateur et l'impédance en ligne du câble de la clôture.

We will now give a more detailed description of the invention, with reference to the accompanying drawings in which:

• FIG. 1 illustrates the apparatus of the invention by means of a block diagram,
• FIG. 2 presents a partial block diagram explaining the operation of the apparatus, considering first of all that the transformer secondary is not charged,
• - Figures 3a, 3b and 3c show three explanatory diagrams of the operation of the apparatus in relation to FIG. 2. More precisely, FIG. 3a represents the state of the static switch as a function of time (T), FIG. 3b represents the intensity (I) only primary of the transformer as a function of time (T), FIG. 3c represents the voltage (V) across the terminals of the switch as a function of time (T), and
• - Figure 4 is a partial block diagram in which the secondary of the transformer and the line impedance of the fence cable are taken into account.

Most of the devices which are used to deliver electrical energy in a cable 10, such as a fence, include in particular a current generator, such as for example a battery 3, and a voltage transformer 2 provided with a primary 12 and a secondary 22. This is the case of the apparatus of the invention illustrated in FIG. 1.

However, usually in known devices, the cable 10 to be electrified is directly connected at one of its ends to the output terminal of the secondary 22. In this case, no protection is provided to avoid rapid discharge of the battery 3, in the event of a short circuit leading to a prolonged drop in line impedance along the cable. As has been said, such short circuits are frequently encountered. They can for example be caused by the fall of a branch on the cable, which then connects the cable to earth.

By planning to mount an electronic component of the current rectifier type, such as a diode 14, in series with the secondary 22 of the transformer, this problem is solved.

As illustrated in FIG. 1, this diode 14 can be mounted between the output 22a of the secondary and the connection end 10a of the electrified cable. The diode will be mounted pass-through in the agreed direct direction of current, flowing here from the transformer secondary to the cable. Arrows 13a and 13b indicate the direct direction agreed to the current.

(U : tension aux bornes du générateur 3, $\frac{\text{N2}}{\text{N1}}$

: rapport secondaire/primaire du transformateur 2).In such an application to fence electrification, the direct voltages delivered to the cable are generally very high. Theoretically, the reverse voltage to which diode 14 can be subjected is limited to the value U x $\frac{\text{N2}}{\text{N1}}$

(U: voltage across generator 3, $\frac{\text{N2}}{\text{N1}}$

: transformer secondary / primary ratio 2).

However, this limit value is very often lower than the instantaneous reverse voltages developed. This is why, the invention provides for mounting a spark gap 24 in parallel across the terminals of the diode 14, so as to protect it and to avoid any deterioration, whatever the value of the line reverse voltages.

It will be noted that the diode 14 and the spark gap 24 can completely be integrated into a single industrially usable electronic component, which has been identified as a whole 4.

We clearly understand the practical interest of such a component. Indeed, by simply mounting on an existing electrification device, the component 4 which will behave essentially as a diode in the agreed direct direction of the current and as a spark gap in the opposite direction, we will be able to avoid for a relatively reduced cost and in complete safety, any untimely discharge of the generator 3 whatever the electrical disturbances that may occur.

This improvement made to known devices is appreciable.

However, these existing devices are sometimes unreliable, especially when used for extended periods in difficult terrain and weather conditions.

This is why the invention also proposes, as illustrated in FIG. 1, a new supply device. in electrical energy intended in particular for the electrification of fences. Of course, this device incorporates the component 4 that has just been presented. It also includes, in addition to the transformer 2 with the air gap 32, the self-inductance 12 and the wound secondary 22 connected at 11 to earth, an electronic unit 5 subjected to the voltage of the generator 3, and a static switch 6. Tel as illustrated, the primary 12 of the transformer is subjected to the difference of the voltages prevailing at the terminals of the generator 3 and of the switch 6.

The electronic unit 5 consists of a timer which controls the switch 6. The duration of the control pulses can for example be of the order of a few tens of milliseconds, the interval between two pulses possibly being of the order of 1 to 1.5 seconds.

The switch 6 comprises, as illustrated, two transistors, one of the "NPN" type 16, the other of the "MOS" type 26.

At the terminals of the switch 6 is mounted in parallel a component 7 similar to the aforementioned component 4. Indeed, the component 7 comprises a spark gap 27, with parallel to its terminals, and preferably, a diode 17. The diode 17 is mounted passing in the considered opposite direction of the current. This component 7 protects the static switch 6 from any overvoltage, as will be seen in more detail below.

Still in order to avoid any untimely deterioration of the components and to ensure the reliability of the device, the protection against possible overvoltages of the transistor 26 is ensured by a component 8, of the same type as that 7 which we have just presented. The component 8 mounted across the transistor 26 therefore includes a spark gap 18 with a diode 28 in parallel at its terminals.

However, it should be noted that, in components 7 and 8, the spark-gap element is essential and essential, the diode only intervening for safety reasons and to improve the reliability of the component.

In 9, a good functioning indicator is shown which can be mounted at the terminals of the switch 6, so that the operator can check the power on or off state of the device 1.

The indicator 9 comprises in series two resistors 19, 29 and a display device 39, such as a "neon" bulb.

Depending on the intended use of the device, if the voltages supplied are high, the resistors 19 and 29 will preferably be resistors of the high voltage type.

The list of the main components that the apparatus of the invention comprises having been drawn up, we will now present its operation with reference to FIGS. 2 to 4.

Consider firstly with reference to Figures 2, 3a, 3b and 3c that the secondary 22 of the transformer is not charged, that is to say that it is somehow disconnected. The circuit then closes by the primary 12.

   Le courant I croît jusqu'à la valeur I_m (figure 3b).In this case, when, under the control of the timer 5, the switch 6 closes at time T = 0 (FIG. 3a), the supply voltage U at the terminals of the generator 3 is applied to the terminals of the self-inductance " L "marked 12, and a current I, flowing in the direction of arrow 13b, appears in this self, according to the expression,

$$\text{I =}\frac{\text{1}}{\text{L}}\text{x U xt}$$

The current I increases to the value I _m (FIG. 3b).

When the static switch 6 opens at time t1, still under the control of the timer 5, (FIG. 3a) the current I is closed by the spark gap 27 and brings the voltage across its terminals to the value V _t (FIG. 3c ). The voltage at the terminals of switch 6 is therefore thereby limited to this value which is such that it can bear it without deterioration.

En pratique, on règle l'intensité de ce courant en adaptant la durée du maintien en position fermée de l'interrupteur 6.The voltage across the inductor 12 then reverses and becomes V _t - U. The current I decreases according to the expression,

$${\text{I = I}}_{\text{m}}\text{-}\frac{\text{1}}{\text{L}}{\text{(V}}_{\text{t}}\text{- U) x (t - t1)}$$

In practice, the intensity of this current is adjusted by adapting the duration of the holding in the closed position of the switch 6.

Let us now consider the load of the secondary 22 of the transformer 2, by closing the circuit on an impedance "Z", marked 10b in FIG. 4, this impedance representing the line impedance of the cable 10 to be electrified.

The currents I₁ and I₂ flowing in the absence of component 4 respectively in the primary and the secondary of the transformer, are related in intensity and direction. The direction of the current I₁ (represented by the arrow 13b) is considered to be direct, while the direction of the current I₂ is opposite (arrow 13d).

. (I : courant dans la self inductance 12 seule ; N₁ et N₂ : respectivement primaire et secondaire du transformateur).The relationship between them is $\text{N₂I₂ = -N₁I₁ + N₁I}$

. (I: current in the inductor 12 alone; N₁ and N₂: respectively primary and secondary of the transformer).

   Si cette impédance est "infinie", c'est-à-dire si elle est très élevée, on est placé dans le cas de la figure 2 explicité précédemment.The voltage V _z across the impedance 10b is then equal

If this impedance is "infinite", that is to say if it is very high, we are placed in the case of FIG. 2 explained above.

However, in the absence of the component 4, and in particular of the diode 14, if the line impedance 10b decreases and takes a finite value, following a short circuit caused for example by the fall of a branch on the cable, the current in the self-inductor 12 will, when the switch 6 closes, increase significantly.

The short circuit in secondary is reduced to primary.

. En d'autres termes, en l'absence de la diode 14, et en cas de court-circuit, l'énergie électrique puisée dans le générateur 3 est dissipée et non pas stockée dans la self-inductance 12. Cette énergie ne sera donc pas restituée au générateur 3.As for the electrical energy stored by the self-inductance 12 and coming from the generator 3, it is always equal to $$\frac{\text{1}}{\text{2}}\text{xLxI²}$$

. In other words, in the absence of the diode 14, and in the event of a short circuit, the electrical energy drawn from the generator 3 is dissipated and not stored in the self-inductance 12. This energy will therefore not be not returned to generator 3.

It is therefore understood that in the event of a prolonged short circuit the battery 3 will more or less quickly discharge.

Of course, this malfunction is avoided if care has been taken to set up the diode 14. In fact, during the time interval when the static switch 6 is closed, the current I₂ (arrow 13d) is blocked by the diode 14. On the other hand, when the switch 6 opens, this same diode becomes conducting and the current can circulate normally in the fence to be electrified.

In the application considered for the electrification of fences, note the recommended use of a high voltage diode.

In such an application, we can now develop up to around 10 kV in secondary school. In practice, such "direct" voltages can generate instantaneous reverse voltages of the same order of magnitude. However, high voltage diodes are expensive and fragile.

This is why we recommended the use of a spark gap, in parallel with the terminals of the diode. In the selected application example, the spark gap may be able to block approximately 400 to 500 V with an instantaneous power of approximately 15 to 20 kW, thereby rendering the component as a whole almost indestructible by overvoltage.

Currently, the reaction time of known spark gaps is around 10⁻¹² second.

Claims (6)

1. Apparatus for the electrical supply of at least one cable (10) or equivalent electrical conductor, comprising a transformer (2) provided with a primary winding (12) connected to a current generator (3) and with a secondary winding (22) to which one end (10a) of the said cable is connected; a switch (6); and a first current rectifier (14), such as a diode disposed such that it conducts in the usual direction of the current circulating from the secondary winding of the transformer to the cable, this first rectifier (14) being connected in series between the secondary winding (22) of the transformer and the said end (10a) of the cable, characterised in that it further comprises:

   - a first discharger (27) connected at the terminals of the switch (6) which is a static switch connected on one side to a terminal of the primary winding (12) and on the other side to a terminal of the current generator (3);

   - a second discharger (24) connected in parallel at the terminals of the said first rectifier (14) to protect the latter against excess voltage by restricting the discharge from the generator (3) in the event of a short circuit; and

   - a second current rectifier (17), such as a diode disposed such that it conducts in the opposite to usual direction of the current, this second rectifier being connected in parallel at the terminals of the said first discharger (27).
2. Apparatus according to Claim 1, characterised in that the said cable (10) or equivalent electrical conductor is part of an electric enclosure, and the said switch (6) is controlled by a clock unit (5) subjected to the voltage of the current generator (3), the voltage at the terminals of the primary winding (12) of the transformer (2) being substantially equal to the difference in the voltages prevailing at the terminals of the said current generator (3) and the static switch (6).
3. Apparatus according to Claim 2, characterised in that the said static switch (6) comprises:

   - an NPN type transistor (16); and

   - an MOS type transistor (26).
4. Apparatus according to Claim 3, characterised in that it comprises a third discharger (18) connected in parallel at the terminals of the MOS type transistor (26).
5. Apparatus according to Claim 4, characterised in that it comprises a diode (28) connected in parallel at the terminals of the said third discharger (18), the said diode (28) being disposed such that it conducts in the opposite to usual direction of the current.
6. Apparatus according to any one of Claims 2 to 5, characterised in that it comprises, connected in parallel at the terminals of the said static switch (6), a device (9) for indicating that operation is correct and comprising, in series:

   - at least one resistor (19, 29); and

   - at least one display means (39), such as a light bulb.

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