GB2254488A - High voltage switch - Google Patents

Description

2 2 5 4 4 -, -', HIGH VOLTAGE SWITCH ADAPTED TO ESTABLISH AND CUT OFF THE

BAR TRANSFER CURRENTS IN A LOOPED CIRCUIT The present invention relates to a switch for high-voltage current supply network, said switch being adapted to establish and to cut off the bar transfer currents in a so-called "looped" high-voltage supply circuit.

It is well known to use a so-called "looped" supply circuit for a conventional electrical highvoltage A.C. supply network. Consumers are, in that case, supplied via a first set of bars, and a.second sekt of replacement bars is further provided, which is generally identical to the first and which is connected in parallel thereon. During normal operation, the supply current does not pass through this second set of bars, a switch placed on this set of bars being in open position. However, it is provided to supply it, when replacing the first set, when it is desired to insulate the latter, for example to proceed with repair or simply maintenance works.

A so-called bar transfer operation, from the first set of bars towards the second set, must then be effected, which is conventionally carried out, without interrupting the supply of electrical energy to the consumers, in the following manner:

- The switch which is placed on the second set of bars is firstly closed. The voltage at the terminals of this switch, which, before closipg, is equal to the ohmic drop dV in the first set of bars, then passes from this value dV to zero value, whilst, virtually simultaneously, the intensity of the current in this switch passes from zero value to a value which is approximately equal to half the line current which passed through the first set of bars before closing of this switch. To give a plausible numerical example, the ohmic drop dV is about 20b volts for a line length of some hundreds of kilometres and a line current 1 - n 1 - of 1300 amps, with the result that this switch must establish a current of about 650 amps, with a voltage at its terminals of 200 volts before closing.

- The switch which is placed on the first set of bars is then opened. In the numerical example considered, the intensity of the current in this other switch then passes from the value of 650 amps to zero value, whilst the voltage at its terminals passes from zero value to the approximative value of 200 volts mentioned above.

It is obvious that, at least for sufficiently high ohmic drop values dV, which is the case for the numerical example considered, such closing of the switch of the second set of bars and such opening of the switch of the first set, do not occur without creating sparks in these switches, which can be very damaging, not only because such sparks reduce the life duration of these switches, but also, and especially, because there is a risk of serious accident which may be caused by a phenomenon of thermic runaway.

Different devices have recently been offered on the market, such devices more or less conventionally providing the installation of a "sparkarrester" on each switch used during bar transfer. In fact, this problem has not been able to be solved sufficiently simply and reliably, taking into account the stresses due to inclement weather to which the collector bars are subjected in particular, for the various solutions retained heretofore to be really satisfactory both from the technical point of view and from the standpoint of cost price and exploitation cost.

It is an object of the invention to overcome this drawback. To that end, it relates to a high-voltage switch adapted to establish and to cut off the bar transfer currents in a "looped" supply circuit, this switch generally comprising means for opening or closing a female contact on a male contact by disconnecting or connecting two terminals of the same line bar which are connected, one, to said male contact and, the other, to said female contact, other means being provided on this switch in order, upon closing, firstly to immobilize said male contact between at least two jaws and, in accordance with the general principle of a spark-arrester, to establish a preliminary electri- cal connection, by a separate conductor member, between said male contact and said other terminal, and, only then, to make the direct electrical connection proper between said female contact and said male contact, and vice versa for the operation of opening of this switch.

The invention will in any case be more readily understood, and its advantages and other characteristics will appear, on reading the following description of a non-limiting embodiment of this switch, with reference to the accompanying schematic drawings, in which:

Figures 1 to 3 illustrate the general operational principle of this switch.

Figures 4 and 5 show the two extreme positions of the semi-pantograph which, in this particular embodiment, actuates this switch.

Figure 6 shows, in perspective, this switch totally open, the semipantograph being in low position.

Figure 7 similarly shows this switch totally closed on its collector bar, the same semi-pantograph being in high position.

Figure 8 is a simplified plan view of the switch in its position according to Figure 7.

Referring firstly to Figures 1 to 3, reference 1 designates the male contact conventionally constituted by the silvered copper collector bar which is traditionally suspended elastically from the line bar via a "trapezium" (not shown here).

The female contact is likewise very conventionally constituted by two sets 2, 3 of contact blades opposite each other, also made for example of silvered copper.

These two sets of blades 2, 3 are mobile with respect to each other and they are mounted on the switch so, as shown in Figure 1, as to be spaced apart from the bar 1 before male-female electrical contact assembly has been effected and, on the contrary, as shown in Figure 3, so as to clamp this bar very tightly when this assembly, and therefore the electrical connection, is effected.

The device for manoeuvring the switch is, of course, such that, when this switch is in totally open position, the contact blades 2, 3 are respectively spaced apart from the bar 1 by the distance in accordance with regulations which guarantees sectioning -of the line, this distance being able to be several metres.

According to the invention, four fingers or jaws are in addition provided for gripping and immobilizing the collector bar 1, viz:. two insulating fingers 4, 5 which are placed, with respect to bar 1, on the same side as the series of silver contact blades 3;. two other fingers 6, 7, of which the first, 6, is also insulating, whilst the other, 7, is made of currentcarrying material such as copper, which are both placed on the same side as the set of blades 2 so as to cooperate with the first fingers 4, 5 for prior immobilization of bar 1.

The current-carrying finger 7 is placed at a duitable distance from contact 2 and, in addition to its function of gripping, it performs a function of "spark-arrester". Consequently, it is connected to the potential of the female cont act 2, 3 by a metal braiding 8 and, as will be seen hereinafter, is arranged to produce the electrical contact with the male element 1 before the latter touches the female contact 2, 3, which enables it to operate as spark-arrester.

All elements 2 to 7 are, furthermore, mounted on respective powerful pressure springs 9 to 14 which are symbolically represented here by arrows.

Preliminary spark-arrester contact between the currentcarrying finger 7 and the bar 1 is here effected on a removable bush 15, made of material different from the copper of which finger 7 is constituted, and preferably of stainless steel, this bush constitu- ting a consumable, easily interchangeable piece which is closely fixed around the bar 1. This difference in materials avoids the phenomena of bonding by copper on-copper welding.

These gripping and spark-arrester contact jaws 4 to 6 and 7 are borne by the particular system for actuating the switch, for example by the two arms of the pantograph if such is the case, so as to operate, for example during an opening manoeuvre, in the follo- wing manner illustrated by successive Figures 1 to 3:

According to Figure 1, the two arms (not shown) of the pantograph have almost arrived at the end of stroke, but fingers 4 to 7, as well as female contacts 2, 3, are still all slightly distant from the male bar 1.

The two arms of the pantograph continuing their movement of closure, the device is arranged so that, whilst the blades 2, 3 remain spaced apart from bar 1, the four fingers are strongly applied under the -6 pressure of their respective springs 11 to 14, against bar 1, totally immobilizing the latter. Furthermore, the fact that, in this latter movement, the metal finger 7 is strongly applied against the stainless steel bush 15, produces a preliminary electrical connection between the collector bar 1, which is connected to one of the two high-voltage terminals to be connected (between which only a potential difference of the order of 200 volts prevails), and the other highvoltage terminal, which is connected to this finger 7 as well as to the principal female contact 2, 3.

The spark which is possibly produced in that case sparks between the two consumable ancillary elements 7, 15 which are easily replaceable and which are located at a suitable distance from the principal contact formed by the blades 2, 3 and that part of the bar 1 that they embrace.

In final phase of closure, i.e. at the end of stroke of the pantograph, the female contact 2, 3 is in turn strongly applied against bar 1 at the location provided to that end, far from the consumable bush 15, as shown in Figure 3. In that case, no spark is produced at that spot, since the voltage at the terminals of this principal contact is in that case virtually negligible (equal to the drop in voltage in the pre-established contact 7/15). Furthermore, all the problems relative to the sparkarrester devices of the prior art are avoided, since the bar 1 is immobilized, which was not the case beforehand.

Opening of this switch is, of course, manoeuvred by the reverse movements and with the inverse phenomena. The female contacts 2, 3 are firstly separated from the male bar 1 whilst it is still firmly maintained between fingers 4 and 7 (Figure 2). Thus is guaranteed a total immobilization of the bar 1 upon opening of the principal contact, in the same way as a virtually zero voltage at opening (no spark at the level of this principal contact). It is only then (Figure 1) that the bar is released, the spark upon opening then being produced solely between the consumable pieces 7 and 15.

It should be noted that, before changing the bush 15, it is firstly advantageously possible virtually to "renovate" it once or several times by rotating it simply on itself through an angle guaranteeing it a rotation less than 360' with respect to its first position. This may be effected each time either, without touching the flanges fixing the bar 1, by rotating the bush 15 about this bar which remains fixed, after having, of course, previously loosened screws 29 bloc- king this bush on the bar, or by rotating the whole bar 1 on itself, therefore without touching the bush 15 proper, after having, of course, loosened the flanges for fixing this bar on its supporting trapezium. 20 The metal finger 7 is changed rapidly and easily with the pantograph in totally open position. A practical embodiment, employing the general means which has just been described with reference to Figures 1 to 3, will now be described with reference to Figures 4 to 8.

Figures 4 and 6 show this switch in its totally open position, with its semi-pantograph 16 for actuation in extreme low position, i.e. totally folded.

Said collector bar 1 (constituting a high-voltage terminal) is conventionally elastically suspended from the line bar 17 by means of the trapezium 18. The upper arm 19 of the conventional semi- pantograph 16 bears the high-voltage contactor 20 according to the invention, this contactor comprising, like the one according to Figures 1 to ?, the female contact blades 2 and 3, the two insulating jaws or fingers 4 and 5, as well as the other two jaws or fingers which cooperate with the latter, viz. on the one hand, the insulating finger 6 and, on the other hand, the current-carrying finger 7, which is connected to the potential (constituting the other high-voltage terminal) of the head 20 of the pantograph by the metal braiding 8 mentioned above.

Head 20 conventionally comprises a fork joint 22, fast with the free end of the arm 19 and in which may pivot a piece 23 comprising two side elements 24, 25 on either side of the contact blades 2, themselves fast with the metal chassis 21 of the head 20. This metal chassis bears two insulating end flange elements 27, 28 on which rests the bar 1 during and after the operation of closing the switch.

Piece 23 bears the insulating fingers 4 and 5, as well as, conventionally, the secon.d set of contact blades 3, and it pivots progressively through almost 1800 in anti-clockwise direction during the lifting movement of the semi- pantograph, under the traction which is conventionally exerted thereon by a tie-rod 26.

During this lifting movement, the contactor 20 of the invention progressively "closes" to come to the position of total closure which is shown in Figures 5, 7 and 8, and which corresponds, moreover, to that of Figure 3, after, just before, having passed through the successive positions, according to the invention, of immobilization of the bar 1, with spark-arrester effect, which correspond to those described previously with reference to Figures 1 and 2. It should be noted that the four fingers 4 to 7 are mounted as shown on their respective springs 35 11 to 14. Springs 9 and 10 of Figure 3 are here naturally included in the elasticity of the contact blades 2 and 3.

It goes without saying that the invention is in no way limited to the embodiment which has just been described. The number of holding fingers may be different. It is preferred to provide only one current-carrying finger in order to limit the points of wear by sparks, but, in fact, the insulating character of the other fingers is not really compulsory. On the contary, all the immobilizing jaws may be provi- ded to be insulating, and the preliminary spark-arrester contact may, in this case as in general, be provided on a current-carrying terminal which itself does not participate in the immobilization of the bar, or other male contact. The general means of the invention is easily adaptable to all types of switches: semi pantographs, pantographs, "twin-columns", etc. ..

Claims (11)

1. A high-voltage switch adapted to establish and to cut off the bar transfer currents in a "looped" supply circuit, this switch generally comprising means (16) for opening or closing a female contact (2, 3) on a male contact (1) by disconnecting or connecting two terminals of the same line bar (17) which are connected, one, to said male contact (1) and, the other, to said female contact (2, 3), wherein other means (4 to 8, 11 to 14) are provided on this switch in order, upon closing, firstly to immobilize said male contact (1) between at least two jaws (4 to 7) and, in accordance with the general principle of a spark-arrester, to establish a preliminary electrical connection, by a separate current- carrying member (7), between said male contact (1) and said other terminal, and, only then, to make the direct electrical connection proper between said female contact (2, 3) and said male contact (1), and vice versa for the operation of opening of this switch.

2. High-voltage switch according to Claim 1, characterized in that one of the immobilizing jaws is constituted by said separate current-carrying member (7).

3. High-voltage switch according to Claim 2, characterized in that the other jaws(s) (4, 5, 6) are electrical- ly insulating.

4. High-voltage switch according to Claim 1, characterized in that said immobilizing jaws are electrically insulating.

5. High-voltage switch according to one of Claims 1; 1 to 4, characterized in that said male contact compri ses a current- carrying wear piece (15) on which said preliminary electrical connection is established.

6. Switch according to Claim 4, characterized in that this wear piece (15) is made of a metal different from that of said male contact (1).

7. Switch according to Claim 5 or Claim 6, characterized in that this wear piece (15) is interchangeable.

8. Switch according to one of Claims 5 to 7, characte- rized in that this wear piece is constituted by a metal bush (15).

9. Switch according to one of Claims 5 to 8, characterized in that means are provided to "renovate" this wear piece (15) once or more times by rotating it on itself each time through an angle defining a rotation less than 360' with respect to its first position.

10. Switch accordincj to one of Claims 1 to 9, characterized in that said separate current-carrying member. (7) is constituted by an interchangeable piece.

11. A high voltage switch adapted to establish and cut off the bar transfer currents in a looped supply circuit substantially as hereinbefore described with reference to the accompanying drawings.