GB2120477A

GB2120477A - Protecting against current loading and short-circuiting

Info

Publication number: GB2120477A
Application number: GB08312504A
Authority: GB
Inventors: Konstantin Kelaiditis
Original assignee: Hager Electro GmbH and Co KG
Current assignee: Hager Electro GmbH and Co KG
Priority date: 1982-05-15
Filing date: 1983-05-06
Publication date: 1983-11-30
Also published as: AT389405B; FR2527003A1; GB8312504D0; GB2120477B; FR2527003B1; CH660647A5; ATA168583A

Abstract

A main current path (5) can be opened (8) by means of a rapid acting mechanism (7, 8) which responds to short-circuiting; and a less rapid acting mechanism (6) responds to current overloading less than short circuit. Another slow acting mechanism 11 operates switch 12 in a subsidiary current path (9) containing an electrical resistance (10). A further current path (13) has a third switch (14) connected to the first switch (8) in such a way that it closes when the latter is opened and can be opened by a further rapid acting mechanism (15). If, after a short circuit opens 8 (and closes 14), the short circuit is removed by a down line breaker (not shown), then current through 10, 11, 12, 14, 15 opens 14 and recloses 8. If the short circuit is not removed, slow acting switch 11 eventually opens 12 to lock 8 open. A current overload less than short circuit opens switches 12 and 8. <IMAGE>

Description

SPECIFICATION A switch for protecting a conductor and/or equipment against current overloading and short-circuiting The invention relates to a switch for protecting a conductor and equipment against current overloading and short-circuiting which is selective relative to any devices for protection against current overloading and short-circuiting which may possibly be connected in front of and/or after it, and which has a main current path which can be separated by means of a more rapid movement mechanism which responds to short-circuiting and by means of a less rapid movement mechanism which responds to current overloading.

There are extremely various possibilities for the use of such protective switches. They are particularly in demand in appiications in distributor systems, whether in domestic dewllings or in industry, as unit protection switches in front of various branches which are each protected by a conductor-protecting switch.

Selectivity is necessary or at least desirable in protective switches connected successively in a distributor so that at any one time only the smallest possible part of the distributor system is switched off, wherein the short-circuit exists or the cause of the current overloading lies.

It can be established without any difficulty with fuses. With regard to overloading, selectivity again presenst no problems with protective switches.

The trips in these which respond to overloading, usually thermal trips, can quite simply be set with different delays so that the subsequently connected protective switch, in the branch whereof the cause of the overloading lies, separates the conductor, rather than the protective switch connected in front of it.

However, problems arise in the case of shortcircuiting. The magnetic trips which are normally provided in protective switches for this and which should be particularly rapid, cannot be made so that the conductor is without fail always separated first by the protective switch connected after the short circuit and then by the protective switch connected in front.

A solution which is certainly acceptable, but which is very costly, is known from DE-OS 25 25 192. However, for reasons of cost it is already only used in the high voltage range.

Simpler selective protective switches are the subject of development which has resulted in DE-PS 28 54 623, DE-OS 28 54 637 and DE-OS 30 21 867.

All these solutions are based on the principle, in the case of short-circuiting, of allowing the protective switch, after which further protective switches are connected, to be switched in again one or more times after it has been switched out, in the event that in the meantime a subsequentlyconnected protective switch, after which the short-circuit lies, has responded; only after switching in and out a certain number of times does switching out remain final.

The invention is based on the problem of providing a protective switch which is in particular selective towards subsequently-connected protective switches, and which switches out and, in cases where this is desired, switches in again only once.

To this end, the invention is based on an arrangement of the type described in the introduction and known from DE-OS 30 21 867, and provides that the separation point in the main current path, which is operated by the movement mechanism responding to short-circuiting, is bridged over by a subsidiary current path with an electrical resistance and a second separation point which can be opened by the said movement mechanism and/or a further less rapid movement mechanism, and that a device is provided for closing the first-named separation point when the short-circuiting is eliminated before the second separation point is opened.

Should there be a short-circuit after this protective switch the main current path is separated at the separation point operated by means of the more rapid movement mechanism which responds to short-circuiting. However, in the subsidiary current path which bridges this separation point a current flows on, albeit reduced by the resistance. If a subsequently-connected protective device also responds, i.e. if the shortcircuit point is separated, then the said device closes the first separation point and thus reestablishes the main current path. If the shortcircuit point lies in front of the subsequentlyconnected protective switch or if the short-circuit continues for some other reason, then the first named separation point remains open.The increased current flowing through the subsidiary current path under these circumstances now allows the first-named or the said further less rapid movement mechanism to open the second separation point and thereby to interrupt the subsidiary current path as well The said further current path then also contains no more current.

The immediate and final separation of the short-circuit point, either by the protective switch in question or by the next protective switch following thereafter, protects the conductor system, and in the case of a switch protecting equipment, the equipment as weli, to a very considerable extent compared with the known solutions, and is also advantageous in other respects.

Moreover, the new protective switch is selective to an unlimited extent, since the response time of the relevant less rapid movement mechanism can be set accordingly. On the other hand, the selectivity of the known protective switches and also of the fuses is not available beyond certain current-strength limits. The nevv protective switch can also be adjusted with infinite selectivity relative to the protective switches or fuses connected in front of it. Furthermore, the new protective switch can be built more simply and compactly.

Finally, it can also be used for direct current.

All of the above applies both for the protection of conductors and also of equipment.

However, the invention affords yet another possibility for the protection of equipment. The new protective switch can also be used in this case to quite exceptional advantage at a last point, i.e. without a protective device connected after it to which it would be selective: It simply switches off temporarily during the switching-on current surge in that it detects this as a short-circuit, and it can therefore be adapted more closely to the current strength of the equipment and therefore has a better protective effect than the known protective devices which have to be made so that they do not respond to the switching-on current surge.

There are various possibilities for constructing the device for closing the first-named separation point However, as a particularly advantageous embodiment and development of the invention it is proposed that after the second separation point a further current path should be branched off to the neutral conductor or the conductor of another phase, having a third separation point which is connected to the first-named separation point in such a way that it closes when the latter is opened by the effect of the said more rapid movement mechanism, and which can be opened by a further more rapid movement mechanism arranged in the said further current path, while the first-named separation point then clsoes.

In this instance, if the short-circuit point is separated by a subsequently-connected protective device, the current interruption which would otherwise be occasioned by the short-circuit in the said further current path, which was closed when the first-named separating point was opened, does not occur, and the current strength in the said further current path rises until the third separation point is opened again by the said further more rapid movement mechanism and the first-named separation point is closed. If the short circuit situation continues, then the said third separation point remains closed and the first named open. The conductor is then completely separated, as described.

Instead of drawing the energy for the re connection of the first-named separation point from the said further current circuit, other auxiliary current circuits could also be provided, or accumulators or batteries.

For use as the said more rapid movement mechanisms, at the present time magnetic mechanisms are available, for example, and for the said less rapid movement mechanisms there are thermal bi-metal trips which are generally operated via a switch lock. However, many other devices may also be considered for these purposes. The more rapid movement mechanisms could be magnetic mechanisms with a more rapid bi-metal trip, while the less rapid ones could be magnetic mechanisms with mechanical delay elements, or could have delay elements made of the so-called memory alloys, amongst many others. The one important factor is the different response times between the more rapid and the less rapid movement mechanisms.

If the protective switch has a further protective device connected after it (a protective switch or a fuse), to which it should be selective, the response time of the less rapid movement mechanism which opens the second separation point must also be longer than the response time of the subsequently-connected protective device in the event of a short-circuit. If the protective switch is used as an equipment-protective switch, particularly such a switch arranged directly in front of some equipment, then the response time of the less rapid movement mechanism which opens the second separation point must be longer than the duration of the switching-on current surge.

An inherently more rapid movement mechanism such as a magnetic mechanism with a delay device is particularly advantageous for the said further less rapid movement mechanism, for the following reason: It affords the most precise time adjustment and therefore the most reliable selectivity, differentiated at will. The delay device in this case will expediently be initiated by the first-named more rapid movement mechanism. It can be based on a half-wave counting device, for example, in the case of alternating current.

Basically the electrical resistance can be an ohmic resistance, an inductive resistance and/or a capacitive resistance. An inductive resistance could be used for the above-mentioned trip for the delay device, instead of the first-named more rapid movement mechanism.

Insofar as no specific arrangement is given for the said elements of the protective switch, there are many different possibilities. With respect to the said further current path, care must be taken to ensure that it is connected to the same conductor -- generally it should be the neutral conductor -- to which the consumer device is also connected, i.e. that it is connected in parallel with the consumer device.

If the first-named less rapid movement mechanism which responds to overloading is not to operate a special separation point disposed outside the subsidiary current path in the main current path, but, as is to be preferred, is to act on the first-named separation point as well, it is proposed that the first-named less rapid movement mechanism primarily operates, preferably via a switch lock, the second separation point which is closed in the normal state, and that the latter is connected to the first-named separation point in such a way that the first-named separation point opens jointly with the second separation point.

thus, in a simple way the opening and closing of the first-named separation point in the event of a short-circuit is made possible independently of the second separation point, i.e. it is possible when the second separation point is closed, while nonetheless, in the event of overloading, both the main current path and the subsidiary current path are interrupted.

However, there is also the other basic possibility of a second separation point which is open in the event of a short-circuit. The second separation point which is closed in the normal state would be a simpler and more reliable solution, however.

The first-named less rapid movement mechanism which responds to overloading expediently acts on the first-named separation point via a switch lock in which a manual switch and/or a remote control switch is integrated for switching the protective switch in and out at will.

The said further less rapid movement mechanism can act via the same switch lock.

However, it is superfluous if, under the given conditions, the first-named less rapid movement mechanism can operate the second separation point in the desired way when there is no separation by the subsequently-connected protection device.

The protective switch according to the invention is particularly suitable for remote control since it requires only a relatively small amount of operating power and remote control is therefore possible with small and inexpensive electromagnets, since with the re-connection conception according to the invention the energy required for closing the actual switch contact, i.e.

the first-named separation point, is in any case available on the spot in some form or another.

The connection of the third separation point to the first-named separation point can be carried out directly mechanically so that one always opens when the other closes, no matter which movement mechanism is involved. However, in principle only the operating processes indicated in the above definition of the invention are involved.

Further advantageous developments of the invention are described in the subsidiary Claims and in the following description of embodiment examples which are shown on the drawings.

Figure 1 shows the arrangement of a protective switch according to the invention in a current distributor system.

Figure 2 is a circuit diagram for the protective switch.

Figure 3 shows a mechanical concrete realisation of the protective switch.

Figure 4 is a circuit diagram for a further protective switch.

Figure 5 is a circuit diagram for a third protective switch.

Figure 6 shows another mechanical concrete realisation of part of the protective switch shown in Figure 2, with reference to Figure 3.

The conductor-protecting switch 1 according to the invention is arranged in a distributor system in each case between a safety device 2 which is at the same time a conductor-protecting switch, and a group of subsequently-connected conductorprotecting switches 3. Consumer devices are indicated by the numeral 4. The conductorprotecting switch 1 should be selective both to the safety device 2 and to the subsequentlyconnected conductor-protecting switches 3.

A main current path 5 in which there are a thermal trip 6 which responds to current overloading, a magnetic mechanism 7 which responds to short-circuiting, and a separation point 8 which is operated from the thermal trip 6 and by the magnetic mechanism 7, passes through the conductor-protecting switch 1.

The magnetic mechanism 7 and the separation point 8 are bridged over by a subsidiary current path 9. In this an electrical resistance 10 or, for example, 0.1 to 5 or even up to 10 ohms for nominal current strengths of 6-100 A, a further thermal trip 11 and a second separation point 12 are arranged. After the separation points 8 and 12 a further current path 13 branches off to the neutral conductor.

The thermal trip 6 acts via a switch lock 1 6 on the second separation point 12. The latter is connected mechanically and via a further switch lock 1 7 to the separation point 8 in such a way that the separation point 8 can open and close independently of the second separation point 12, but also opens when the second separation point 12 opens. The further thermal trip 11 also acts via the switch lock 1 6 on the second separation point 12.

The magnetic mechanism 7 also acts mechanically on the separation point 8, as well as via the further switch lock 17.

The further magnetic mechanism 1 5 acts on the separation point 8 mechanically.

The third separation point 14 is connected mechanically to the separation point 8 in such a way that one opens when the other closes.

The relevant lines of effect are drawn in in Figure 2.

The mechanical elements involved are shown in Figure 3.

As can be seen in Figure 3, the magnetic mechanism 7 and the further magnetic mechanism 1 5 act in different rotary directions on a two-armed lever 1 9 mounted at 18, which bears a contact piece 21 on its end, which co-acts with a fixed contact 20.

The parts 1 9 to 21 form the separation point 8.

The said third separation point 14 is formed by a contact piece 22 mounted on a leaf-spring 40 and a contact piece 24 mounted on a leaf-spring 23.

The spatial arrangement is such that in the position shown in Figure 3 wherein the contacts 20 and 21 are touching, i.e. in the closed position of the separation point 8, the contacts 22 and 24 is or are held apart from each other, i.e. the said third separation point 14 is in its open position, and when the separation point 8 is in its open position, the end of the lever 1 9 presses the contacts 22 and 24 against each other, deflecting first the leaf-spring 23 and then the leaf-spring 40 as well, thus closing the third separation point 14.

By the attraction of the magnetic mechanism 7 the lever 1 9 is rotated counter-clockwise and the separation point 8 is opened and the separation point 1 4 simultaneously closed. If then the further magnetic mechanism 1 5 attracts, it pivots the lever 19 back in the clockwise direction and closes the separation point 8, while the leaf-spring 23 opens the separation point 14.

Via its end furthest away from the contact 21 the two-armed lever 19 co-acts with a further two-armed lever 26 mounted at 25, which in turn acts via its other end in an eye or the like (not shown) on a longitudinally displaceable rod 27.

The rod 27 connects the separation point 12 with the switch lock 17, which it trips by traction.

In the same way the switch lock 1 6 is tripped by the thermal trip 6, and also by the thermal trip 11, via a longitudinally displaceable rod 29, but in this case by pushing. The opening of the separation point 12 which is brought about in this way is indicated by the line of effect 30.

The direction in which the described mechanical connections are effective or ineffective in each case can be seen on the Drawing, as can also the effect of the co-action between the two levers 19 and 26 in both directions.

Finally, the arrow 31 indicates the operation of the switch lock 1 6 by an integrated manual button.

The normal current flow passes through the main current path 5 when the separation point 8 is closed. The simultaneous current flow via the subsidiary current path 9 in which the separation point 12 is also closed in insignificant, due to the resistance 10. The further current path 13 is interrupted by the open separation point 14.

If a short-circuit should occur, the magnetic mechanism 7 attracts and moves the lever 1 9 in the direction which opens the separation point 8.

The traction thereby exerted via the lever 26 on the rod 27 trips the switch lock 1 7 simultaneously, which assists and accelerates the opening of separation point 8. The spark created by the separation of the contacts 20 and 21 is conducted into a suppression chamber 32 of conventional design and is quenched therein.

The main current path 5 is thereby immediately broken. Only a considerably reduced current continues to flow via the subsidiary current path 9.

If the short-circuit lies in the section of the conductor between the conductor-protecting switch 1 and one of the subsequently-connected condcutor-protecting switches 3, after the specific period of time for which it is made the thermal trip 11 operates the switch lock 16 via the rod 29 and thereby opens the separation point 12 as well. The interruption by the conductor-protectng switch 1 is now complete and final.

If the short-circuit lies after one of the subsequently-connected conductor-protecting switches 3 then this responds as a rule approximately simultaneously with the magnetic mechanism 7, but in any case well before the thermal trip 11, and separates the short-circuit point. The voltage at the input to the further current path 1 3 rises accordingly. In the current path 13 wherein, as described above, the separation point 14 was closed when the separation point 8 was opened, a current now flows with a current strength such that the magnetic mechanism 1 5 responds and, via the lever 19, closes the separation point 8 again and opens the separation point 14.The latter does not occur until the last phase of the movement of the end of the lever, namely, when the leaf-spring 40 has returned into its normal position and the contacts 22 and 24 move apart with the further return movement of the leaf-spring 23. The magnetic mechanism 1 5 thereby receives energy for a relatively long time, thus a relatively large amount of energy.

The normal state of the condcutor-protecting switch 1 is thereby re-established. All the subsequently-connected consumer devices 4 other than the one with the short-circuit located in its branch have voltage again.

If current overloading should occur, then, when the cause lies after one of the subsequentlyconnected conductor-protecting switches 3, this switches off from the start before the conductorprotecting switch 1. The thermal trips which respond to overloading in the conductor protecting switches 1 and 3 can simply be made sufficiently precisely with different response times so that they are mutually selective.

If the cause of the overloading lies in the conductor between the conductor-protecting switches 1 and 3, then the thermal trip 6 in the conductor-protecting switch 1 responds. It trips the switch lock 1 6 via the rod 29. The latter opens the separation point 12 which in turn, via the rod 27, firstly on the further path via the lever 26 and secondly on the further path via the switch lock 17, moves the lever 19 and opens the separation point 8. In this case again the interruption by the conductor-protecting switch 1 is complete and final.

This can also be effected by operating the manual button 31. The re-setting of the conductor-protecting switch 1 is accomplished manually so that the separation point 12 is closed via the switch lock 16, whereupon the magnetic mechanism 15 in the further current path 13 responds and, as already described above, opens the separation point 14 and closes the separation point 8 in the main current path 5.

With the protective switch shown in Figure 4, in which the same parts have the same reference symbols as in Figures 1 to 3, the said further separation point 12 is a double-contact with a center tapping point to which the said further current path 13 is connected. The electrical resistance 10 is split approximately in halves; it is mounted as partial resistances 34 or 35, one on either side of the double-contact. In this version the protective switch is independent of the current flow direction. The said further separation point lies on both sides of the branch, so that the branch therefore always lies after the separation point from the part of the conductor which is still under voltage. By dividing the resistance into partial resistances 34 and 35 there is a resistance connected in front of the further more rapid magnetic mechanism 1 5 in both current flow directions.

In Figure 5, in which again the same parts bear the same reference symbols as in Figures 1 to 4, instead of the two thermal trips 6 and 11, in the subsidiary current circuit of the protective switch there is a thermal trip 36 which fulfils the functions of both the former trips. Between this trip and the resistance 10 the subsidiary current circuit is connected to the separation point 8 which in this case is constructed as a doublecontact. With this solution the trip 36 may be a more sensitive one.

Figure 6 shows a mechanical connection whereby the third separation point 14 opens at the same time as the second separation point 12.

The arrangement of the separation point 8 and the third separation point 14 is approximately as shown in Figure 3, but these two separation points are connected here by a rod 37, and the second separation point is arranged between them and is similarly connected to the third by a rod which is designated 38. The separation point 8 and the second separation point 12 open and close, independently of each other, each reciprocally with the third separation point 14.

The arrangement has the advantage that a voltage which, in the event of a fault somewhere after the protective switch, arrives via the main current path 5 thereof does not give rise to any flow of current in the said further current path 13, and cannot therefore result in damage to the further magnetic mechanism 1 5 or even lead to reconnection of the protective switch.

The improved embodiment shown in Figure 4 also affords the same security.

However, it would also be possible in principle to allow the said further current path 1 3 with the further magnetic mechanism 1 5 or another rapid movement mechanism to be connected continuously and to dispense with the third separation point 1 4. The drop in voltage arising at the input to the further current path 13 in the event of a short-circuit would then weaken the closing force of the magnetic mechanism 1 5 and would therefore enable the first-named separation point to open.

However, a constant loss of current would have to be taken into account with this solution.

The further magnetic mechanism 1 5 can be temperature-compensated so that its response threshold does not vary with temperature variations. possibly by means of an NTC resistance series-connected with a (copper) winding.

Finally, with regard to the resistance 10, it should be observed that when fuses are to be connected after the protective switch, the resistance must have an adequately large volume to allow the fuses to blow within a certain suitable period of time, and to ensure selectivity.

The protective switch according to the invention is advantageous in all fields of application, whether domestic or industrial, for protecting conductors or equipment, with low or higher tension and/or current strengths.

Claims

1. A switch for protecting a conductor and/or equipment against current overloading and shortcircuiting which is selective relative devices for overloading and short-circuiting protection which may possibly be connected in front of and/or after it and which has a main current path which can be separated by means of a more rapid movement mechanism which responds to short-circuiting and also by means of a less rapid movement mechanism which responds to overloading, characterised in that the separation point in the main current path, which is operated by the movement mechanism which responds to shortcircuiting, is bridged by a subsidiary current path with an electrical resistance and a second separation point which can be opened by the said less rapid movement mechanism and/or a further less rapid movement mechanism, and that a device is provided for closing the first-named separation point when the short-circuit is eliminated before the second separation point is opened.

2. A protective switch according to Claim 1, characterised in that the said device consists of a current path which branches off after the second separation point to the neutral conductor or to the conductor of another phase and which has a third separation point which is connected to the firstnamed separation point in such a way that it closes when the latter is opened under the effect of the said more rapid movement mechanism, and which can be opened by a further more rapid movement mechanism arranged in the said further current path, while the first-named separation point then closes.

3. A protective switch according to Claim 1 or 2, characterised in that the first-named less rapid movement mechanism which responds to overloading also acts on the first-named separation point in that it primarily operates the second separation point, which is closed in the normal state, and the latter is connected to the first-named separation point in such a way that the first-named separation point opens jointly with the second separation point

4. A protective switch according to one of Claims 1 to 3, characterised in that the firstnamed less rapid movement mechanism which responds to overloading and/or the said further less rapid movement mechanism acts or act on the first-named separation point via a switch lock in which a manual switch and/or a remote control switch is or are integrated for switching the protective switch on and off at will.

5. A protective switch according to one of Claims 1 to 4, characterised in that the third separation point is directly connected mechanically to the first-named separation point in the said manner.

6. A protective switch according to one of Claims 2 to 5 characterised in that the third separation point is connected to the second separation point in such a way, preferably directly mechanically, that it opens jointly with the second separation point

7. A protective switch according to one of Claims 2 to 5, characterised in that the second separation point is a double-contact with a central tapping point for branching off the said further current path, and the said electrical resistance is preferably split up into two resistances arranged one on either side of the double-contact in the subsidiary current path.

8. A protective switch according to one of Claims 1 to 7, characterised in that the firstnamed separation point is a double-contact with a central tapping point which is connected to the subsidiary current path at a point which lies, in the direction of the current, after the first-named less rapid movement mechanism disposed in the siihqidiarv current path and in front of the resistance and the second separation point.

9. A protective switch according to one of Claims 1 to 8, characterised in that the said further less rapid movement mechanism for opening the second separation point has an inherently more rapid movement mechanism with a delaying device which is preferably initiated by the first-named more rapid movement mechanism.

10. A protective switch according to one of Claims 2 to 9, characterised in that the said further more rapid movement mechanism has a temperature-compensated electromagnet, preferably an electromagnet with copper wire winding, which is series-connected with an NTC resistance.

11. A protective switch constructed, arranged and adapted for use substantially as hereinbefore described with reference to Figures 1 and 2, 3,4, 5 or 6 of the accompanying drawings.