US1960068A - Excess voltage protective system for electric feeders - Google Patents

Description

S. RUPPEL May 22, 1934.

EXCESS VOLTAGE PROTECTIVE SYSTEM FOR ELECTRIC FEEDERS Filed March 6, 1951 2 Sheets-Sheet 1 May 22, 1934. RUPPEL 1,960,068

EXCESS VOLTAGE PROTECTIVE SYSTEM FOR ELECTRIC FEEDERS Filed March 6, 1931 2 Sheets-Sheet 2 Fig. 6.

Fig.7

' v INVE/VTQR 5 WM fi/WWM/W Patented May 22, 1934 I UNITED STATES EXCESS VOLTAGE PROTECTIVE SYSTEM FOR ELECTRIC FEEDERS Sigwart Ruppel, Frankfort-on-the-Main,

' Germany Application March 6, 1931, Serial No. 520,517 In Germany May 16, 1925 22 Claims.

My invention relates to apparatus for the protection of electric conductors against excess voltage. For this purpose, spark gaps or evacuated containers have already been employed connected between the conductor and earth, and intended to lead away to earth the excess voltage surges which occur. With such a device, the difliculty exists of ensuring that the device will again attain its insulating action after disappearance of the excess voltage surge. Moreover, the oscillating sparking across the gap gives rise again to excess voltages so that the devices themselves endanger the distributing network.

In light current installations, gas-filled vacuum tubes have already been employed for protection against excess voltage the electron current flowing being employed for actuating relay coils when -a definite value of voltage is exceeded. Since,

however, this electron current has only a very small value, the relay coils must be furnished with a large number of turns, that is to say, they must have a high inductance. Consequently, such a device is not able to lead away the current rapidly upon the occurrence of excess voltages. Surges with steep fronts which may lead to sparking over at another point in the mains are, therefore, more easily handled by a high ohmic resistance than by such high inductances. For electrical networks for heavy currents, therefore, such excess voltage devices are in general not employed. However,

in smaller installations where the chief consuming devices are electric incandescent lamps, excess voltages are very undesirable since they seriously affect the length of life of the incandescent lamps.

An effective protection from excess voltages for electric feeders is obtained, according to the present invention, in a device for the protecting of elecfrical conductors against excess voltage,

is consisting of a gas-filled discharge tube with cold electrodes and an ohmic resistance in series arranged between points of different potential, e. g. outer conductor and earth, wherein the resistance is so chosen that upon the occurrence of an excess voltage, an arc discharge occurs in the discharge tube but the switching-out of the main feeder is effected as a result of the action of the discharge current on an overload device only on the attainment of a particularly large value or extremely lengthy durationof the discharge current. As the result of the connecting in series with the tube of a suitably dimensioned current-limiting ohmic resistance, the tube itself cannot to lead away smaller excess voltages up 05 to a certain duration of time, and also larger excess voltages of very short duration so that only in the rarest cases of extremely high or extremely lengthy excess voltages does there occur the troublesome switching-oft of the mains from the branch conductor concerned. If, as the result of an excess voltage, the tube is caused to respond, a. current flows through the tube under the action of the alternating voltage of the mains even if the excess voltage disappears again immediately. As a result of the peculiar kind of the arc discharge, this current would rise to an unlimited extent and thus the release of the overload switch would be brought about on every response of the tube, even with momentary excess voltages, if a current limiting resistance were not provided in series with the tube according to the invention. This resistance ensures that, under the influence of the mains voltage after the response to the tube, when the excess voltage in the meantime has again disappeared, only a current of a certain ma nitude may flow, namely a current the value of which is dependent upon the mains voltage and the magnitude of the ohmic resistance. Tube and resistance are therefore so chosen, according to the invention that this current does not cause the overload switch of the conductor to respond, but excess voltages up to a certain magnitude and duration can be led away by the current flowing through the tube. By the use of a. resistance connected in series with the tube it is also ensured that the tube is protected from damage by overloading, and thus destruction of the tube or the changing of its characteristics in an undesired manner in consequence of it being too greatly stressed are avoided. The effect of the latter would be that the tube would respond even at relatively small voltages, and therefore even under the influence of the mains voltage undesired leading-away currents would be brought into being without excess vollages arising. Thus, the provision of an ohmic resistance of suitable magnitudein series enables certain excess voltages to be led away in the manner described, without leading to a switching off of the mains voltage on every occasion. It is essential, that in the arrangement according to the invention, in the branch conductor which serves for the leading-roff of the excess voltages, the tube is only connected in series with a purely ohmic resistance and not with inductive resistance as is necessarily the case with the known arrangement. Inductive resistance in the leadingofl' branch conductor is, as is well known, disadvantageous as regards the leading ofl' of excess voltage. The switching-off of the mains voltage in the case of the arrangement according to the invention, is eflected by the discharge current which passes through the excess current protective switch in the main conductor and, at any rate initially, through the tube also. In certain of the arrangements according to the invention hereinafter described this discharge current, although passing initially through the tube, passes by way of a conductor short-circuiting the latter if the excess voltage 'is of lengthy duration.

In one particularly advantageous form of construction according to the invention there is connected in series with the tube, besides the ohmic resistance referred to, a'thermal switch device and this thermal switch device is such that, on the occurrence of excess voltages of extremely lengthy duration or extreme magnitude the tube is shortcircuited by means of the thermal switch device and as a result of the large current flowing away over the thermal switch device and the ohmic resistance, the excess current protective device or fuse also provided in the mains branch is actuated. The series circuit of discharge tube and ohmic resistance according to the invention is able to lead away relatively lengthy excess voltages and also relatively high excess voltages. In

many cases it is however desired to ensure that the branch conductor concerned is not loaded for too long a time with the leading away current flowing over the tube, especially if the excess voltages exceed a certain relatively high value. In order .to attain this, a thermal switch is, according to the invention, connected in series with the discharge tube, besides the ohmic resistance, in the manner described. As a result of the use of the thermal switch, the advantage is obtained that, even with these forms of construction according to the invention, the leading-away branch for the excess voltage has only ohmic resistance. It is particularly advantageous to I arrange for the thermal switch, in the'case mentioned, to short-circuit the discharge tube, the release of the excess current protective device or fuse also provided in the mains being effected as a result of the large leading-away current which then flows. It is in this way possible to bring about the switching-oil of the mains by the excess voltage protective device and by means of the overload device or fuse also provided in the network, without there being necessary a mechanical engagement or a constructional moditication of the overload device of the mains which is already provided.

It is expedient in many cases to arrange matters so that if necessary not only the discharge tube but also at least a part of the ohmic resistance connected in series with the discharge tube is short-circuited by means of the thermal switch device. Inother cases it has been found to be advantageous to provide a second ohmic resistance in series with the discharge tube, the ohmic resistance and the thermal switch device in such a manner that in the position of rest of the thermal switching device this second resistance is short-circuited, this short-circuit being broken on the response of the thermal switch device and the second mentioned resistance then heating the thermal switch device.

In particular cases it is advantageous to make use of a magnetic switch device for short-circuiting the tube, or the series circuit of tube and resistance. in such a manner that the excitation coil of the switch device which is likewise connected in series with the tube is first shortclrcuited by the thermal switch device, and this short-circuit is broken on response of the thermal switch device and the magnetic switch device then effects the short-circuit of the tube or the series circuit of tube and resistance.

Further features of the invention will appear from the following description of examples of arrangements according to the invention, reference being had to the accompanying drawings, in which:--

Figures 1 to 6 are circuit diagrams of different protective arrangements; and

Figure 7 shows a vacuum tube with a built-in thermostat.

Figure 1 shows an arrangement according to the invention in which the excess voltage protective device consists of the discharge tube 8 and the ohmic resistance member 7. The series circuit consisting of the discharge tube 8 and the earthed conductor 3. An overload or excess current switch 1 is provided in the external conductor 2. Excess voltages up to a certain magnitude and time of duration are led away by the tube 8 and the ohmic resistance 7, without the switch 1 responding. If excess voltages of extremely long duration or extreme magnitude occur, then the release of the excess current switch 1 is brought about as a result of the large current flowing away through the tube 8 and the ohmic resistance 7.

In the example illustrated in Figure 2, there is arranged between the external conductor 2 and an earthed conductor 3, the discharge tube 8 in series with the ohmic resistance 7 and a thermal switch device 10. If the discharge tube 8 responds as a result of the occurrence of an excess voltage, and ,if the arc current in the tube exceeds a certain size or duration of time, then the thermal switch device 10 sags, resting against the contact 9 and thereby short-circuits the discharge tube 8. As a result of the large current which further hows, the release of the excess current switch situated in the external conductor, and thereby the switching off of the mains, is. now effected. The contact distance between the members 9 and 10 at the same time represents a coarse spark gap wh ch is connected in parallel with the discharge tube 8.

The ohmic resistance 7 can also be divided into two parts as shown in Figure 3, of which the part b always remains in circu'-.t with the discharge tube and is short-circuited with it by means-of the thermal switch device 10, while the part a of the resistance of full magnitude remains in the connecting conductor between 2 and 3 and thereby prevents the flowing of a current beyond a definite value.

The arrangement of Figure 4 is similar to that of Figure 2 or Figure 3 except that here a separate ohmic resistance 7 is dispensed with and the thermal switch device 10 itself constitutes the ohmic resistance. It is mounted on a supporting.

member 11 of insulating material and is connected in series with the discharge tube 8 as before. In this case also the thermal device cooperates with a contact 9 so that when the device sags and makes contact with the contact 9 the tube and the resistance constituted by the lower part a of the thermal device is short circuited, while the resistance constituted by the part b of the thermal device remains in crcuit between 2 and 3.

In Figure 5 there is shown a thermal switch device 10, which is arranged in parallel with the series with the discharge tube 8.

place forathe -short.circuiting -.,of the resistance 6. This is so arranged that 'itserves indirectly forthe heating of the thermal switch device 10- After, the thermal switch device 10 has separated from the contact'5 as ,theresultof the cur-.

rent; flowing through it, itis iurtherheatedzby the heat from the resistance '6 until :it comes into contact, on the further fiowingof' current. with the contact :9. The interruption of the short-circuit orthezresistance 6 takes place very quickly on the other-hand, the short-circuiting of the tube;8 is delayed.; -l

In the constructional example of :thezinvention as illustrated in Figure 6, use is; made of a magnetic switch device for the short-circuiting oi! the discharge tube -8.: The magnet coil 16 situated' in the leading-oil conductor is normally .short-circuitedp The contacts 40 and41 serve for this purpose, these being connected with one. anotherv by means. ofa contact bridge 4.

A thermal device 10 (also connectedin the leading-off conductor) and also the winding 16 act upon the contact arm 4, and, in fact, in such a way that the movement of I the contact arm 4 is initiated by the thermal device 10 and consequently, theshort-circuit of'the coil 16 is opened. The contact arm 4 then moves further under the influence of thecurrent flowing through the coil 16 until it comes into contact with the contact 9 and thus bridges the tube 8, the resistance 7, and the thermal device 10. ;If the excess voltage lasts a short time, it is dispersed by arcing of the disa charge tube 8 without the contacts 4, 47 opening.

If the excess voltage lasts longer, then after the opening of the contacts 4, 47, the current flowing through the discharge tube 8 is reduced for now the coil 16 is in series with the discharge tube. The discharge tube is thereby protected from damage. It is quite possible that the excess voltage is dispersed after the contacts 4, 47 are opened and before the contact 4, 9 is closed. If the excess voltage, however, lasts longer, then the contact 4, 9 is closed within a short time after the opening of the contact 4, 47. The current passing through these contacts is thensufiiciently strong to cause the device 1 to be actuated. The coil 16 can be so arranged that it also temporarily exerts a blow-out action on the spark arising between the contact 41 and the contact arm 4.

The thermal device which serves for short-circuiting the tube may at the same time be built into the tube. An example of this is shown in Figure 7.. The discharge tube 8 is provided with two leading-in wires 17 and 18 which are connected with the bi-metal strips 22 and 23 forming movable supports, on which the electrodes 19 and 20 are mounted. The electrode 20 is, moreover', externally connected with a contact piece 21 adjacent the electrode 19, and the electrode 19 with a contact piece 24 adjacent the electrode 20. In order to accentuate the movement of the contact supports, the electrodes 19 and 20 may be provided with pieces of iron upon which a magnet winding 26 acts through aniron yoke 25. The winding 26 is then connected in series or parallel with the discharge tube, or with a resistance in the discharge circuit so that it is excited when current flows. It thus serves not only I for accentuating the movement of the contacts,

but moreover, gives rise to a blow-out action which serves to extinguish the arc. Onthe occurrence of an excess voltage a discharge takes place between the two electrodes 19 and 20. The current flows through the bi-metal strips/or thermo- elements 22 and 23, the coil 26 and the resistance '7. The bi-metal strips bend and thus bring the electrode 19 into contact with the contact piece 21, and the electrode 20 into contact with the contact piece 24. As soon as one or other of these contacts is made, the discharge tube 8 is short-circuited as'is to be seen by following the connections shown. It the excess voltage has not in the meantime disappeared there now flows through the coil 27 and the resistance 7 a current which is suificiently large to cause the excess current cut-out device 1 to be released.

For protecting the discharge tube, high ohmic resistances or condensers may be permanently connected in parallel as shown at 50 and 51 in Figures 1 and 2 respectively so as to lead away the smaller excess voltages and so that the discharge tube is put into operation only upon the occurrence of high excess voltages which exceed the ignition point. A number of discharge tubes with their corresponding parallel circuits connected in series may be provided depending upon the voltage.

Since furthermore, ,it has only been possible hitherto to produce discharge tubes for a certain value of voltage, in many cases a transformer is connected to the terminals of the discharge tube in the excess voltage circuit in order that a sufficiently high voltage may be impressed on the discharge tube. The iron of the transformer may, in this case, serve at the same time as the core of the coil which operates the overload device.

There may be employed in the above arrangements a discharge tube which is such that even at normal voltage a weak current flows, the presence of this current giving rise to a glow.

Although the excess voltage protective device shown in the drawings is in each case illustrated as being provided with a delay action device, such a delay action device is not in all cases necessary for the reason that a discharge tube responds substantially instantaneously, whereas anexcess current protective device has, by virtue of its nature, a time lag.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

1. An excess voltage protective system for an electric conductor, including a gas-filled discharge tube with cold electrodes and an ohmic resistance connected in series with said tube, the series circuit of tube and resistance being connected between points of different potential, and an excess current protective device in said conductor, said ohmic resistance being of such a magnitude that an arc discharge is brought about in said tube on the occurrence of an excess voltage and only on the occurrence of an excess voltage of extremely lengthy duration or extreme magnitude is there brought about the actuation of said protective device as a result of the curit to interrupt said conin said tube on the occurrence of an excess voltage, and means for short-circuiting said tube on the occurrence of an excessvoltage of extremely WW duration or extreme magnitude, the large current which then flows through said protective device causing its actuation to interrupt said conductor.

8. An excess voltage protective system for an electric conductor, including a gas-filled discharge tube with cold electrodes and an ohmic resistance connected in series with said tube, the series circuit of tube and resistance being connected between points of different potential, and an excess current protective device in said conductor, said ohmic resistance being of such a magnitude that an arc discharge is brought about in said tube on the occurrence of an excess voltage, and means for short-circuiting said tube and part of said resistance on the occurrence oi. an excess voltage of extremely lengthy duration or extreme magnitude, the large current which then flows through said protective device causing its actuation to interrupt said conductor.

4. An excess voltage protective system for an electric conductor, including a gas-filled discharge tube with cold electrodes and a non-inductive switch device and an ohmic resistance connected in series with said tube, the series circuit of switch device, ohmic resistance and tube being connected between points of different potential, and an excess current protective device in said conductor, said ohmic resistance being of such magnitude that an arc discharge is brought about in said tube on the occurrence of an excess voltage, and said switch device responding on the occurrence of an excess voltage of extremely lengthy duration or extreme magnitude to short-circuit said tube, the large current which then flows through said protective device causing its release to interrupt said conductor.

5. An excess voltage protective system for an electric conductor, including a gas-filled discharge tube with cold electrodes and a thermal switch device and an ohmic resistance connected in series with said tube, the series circuit of switch device, ohmic resistance and tube being connected between points of diflerent potential, and an excess current protective device in said conductor, said ohmic resistance being of such a magnitude that an arc discharge is brought about in said tube on the occurrence of an excess voltage, and said switch device responding on the occurrence oi an excess voltage of extremely lengthy duration or extreme magnitude to short-circuit said tube, the large current which then flows through said protective device causing its actuation to v interrupt said conductor.

8. An excess voltage protective system for an electric conductor, including a gas-filled discharge tube with cold electrodes and a thermal strip device and an ohmic resistance connected in series with said tube, and a short-circuiting connection for said tube co-operating with said strip device, the series circuit of switch device, ohmic resistance and tube being connected between points of different potential, and an excess current protective device in said conductor, said ohmic resistance being oi. such a magnitude that an arc discharge is brought about in said tube on the occurence oi an excess voltage, and said thermal strip device bending on the occurrence of an excess voltage of extremely lengthy duration or extreme magnitude to iorm with said connection a short-circuit for said tube, the large current which then flows through said protective device causing its actuation to interrupt said conductor.

9. An excess voltage protective system for an electric conductor, including a gas-filled discharge tube with cold electrodes and a thermal switch device and anohmic resistance connected in series with said tube, the series circuit of switch device, ohmic resistance and tube being connected, between points of diii'erent potential, and an excess current protective device in said conductor, said ohmic resistance being or such a magnitude that an arc discharge is brought about in said tube on the occurrence of an excess voltage, and said switch device responding on the occurrence of an excess voltage of extremely lengthy duration or extreme magnitude to short-circuit said tube and part of said resistance, the large current which then flows through said protective device causing its actuation to interrupt said conductor.

10. An excess voltage protective system for an electric conductor, including a gas-filled discharge tube with cold eiectrodes and a thermal strip device and an ohmic resistance connected in series with said tube, and a short-circuiting connection for said tube and part of said resistance co-operating with said strip device, the series circuit of switch device, ohmic resistance and tube being connected between points of difierent potential, and an excess current protective device in said conductor, said ohmic resistance being of such a magnitude that an are discharge is brought about in said tube on the occurrence of an excess voltage, and said thermal strip device bending on the occurrence of an excess voltage of extremely lengthy duration or extreme magnitude to form with said connection a short-circuit for said tube and said part of the resistance, the large current which then flows through said protective device causing its actuation to interrupt said conductor.

11. An excess voltage protective system for an electric conductor, including a non-inductive switch device and a gas-filled discharge tube connected in series therewith, the series circuit of switch device and tube being connected between points oi. diiferent potential, and an excess current protective device in said conductor, the ohmic resistance of said device being oi? such a magnitude that an arc discharge is brought about in said tube on the occurrence of an excess voltage, and said switch device responding on the occurrence of an excess voltage of extremely lengthy duration or extreme magnitude to shortcircuit said tube and part of said resistance, the large current which then flows through said protective device causing its actuation to interrupt said conductor.

12. An excess voltage protective system for an electric conductor, including a gas-filled discharge tube with cold eiectrodes and a thermal switch device connected in series therewith, the

series circuit of switch device and tube being connected between points of different potential, and an excess voltage protective device in said conductor, the ohmic resistance of said device being of such a magnitude that an arc discharge is brought about in said tube on the occurrence of an excess voltage, and said thermal switch device operating on the occurrence of an excess voltage of extremely lengthy duration or extreme magnitude to form with said connection a short-circuit for said tube and part of said resistance, the large current which then flows through said protective device causing its actuation to interrupt said conductor.

13. An excess voltage protective system for an electric conductor, including a gas-filled discharge tube with cold electrodes and a thermal strip device connected in series therewith, and a short-circuiting connection for said tube and part of said resistance cooperating with said strip device, the series circuit of strip device and tube being connected between points of difierent potential, and an excess current protective device in said conductor, the ohmic resistance of said strip device being of such a magnitude that an arc discharge is brought about in said tube on the occurrence of an excess voltage, and said strip device bending on the occurrence of an excess voltage of extremely lengthy duration or extreme magnitude to form with said connection a shortcircuit for said tube and said part of the resistance, the large current which then flows through said protective device causing its actuation to interrupt said conductor.

14. An excess voltage protective system for an electric conductor, including a gas-filled discharge tube with cold electrodes, and an ohmicresistance connected in series with said tube, the series circuit of tube and resistance being connected between points of diiferent potential, and said ohmic resistance being of such a magnitude that an arc discharge is brought about in saidtube on the occurrence of an excess voltage, an excess current protective device in said conductor, a switch opened by the action of the current'flowing in said series circuit on the occurrence of an excess voltage of extremely lengthy duration or extreme magnitude, and a short-circuiting connection for said tube co-operating with said switch, and means normally short-circuited by said switch but acted upon by said current and operating on said switch when said switch is open to cause it to short-circuit said tube if the excess voltage persists, the large current which then flows through said protective device causing its actuation to interrupt said conductor.

15. An excess voltage protective system for an electric conductor as in claim 14in which said switch is a thermal switch.

16. An excess voltage protective system for an electric conductor as in claim 14 in which said means is a coil which operates on said switch electric conductor, including a gas-filled discharge tube with cold electrodes, a switch and connections for short-circuiting said tube, a non-inductive device for opening said switch, means for operating on said switch, said means being normally short-circuited by said switch, and an ohmic resistance, said tube, device, resistance and means being connected in series and this series circuit being connected between points of different potential, and an excess current protective device in said conductor, said ohmic resistance being of such a magnitude that an arc discharge is brought about in said tube on the occurrence of an excess voltage, and said device on the occurrence of an excess voltage of extremely lengthy duration or extreme magnitude opening said switch tobreak the short-circuit of said means and cause it to operate on said switch so that if the excess voltage persists said switch short-circuits said tube, the large current which then flows through said protective device causing its actuation to interrupt said conductor.

18. An excess voltage protective system for an electric conductor as in claim 1'7 in which said switch short-circuits said ohmic resistance as well as said tube.

19. An excess voltage protective system for an electric conductor as in claim 17 in which said switch short-circuits said ohmic resistance and said device as well as said tube.

20. An excess voltage protective system for an electric conductor, including a gas-filled discharge tube with cold electrodes, a switch and connections for short-circuiting said tube, a thermal device for opening said switch, a coil for operating on said switch, said coil being normally short-circuited by said switch, and an ohmic resistance, said tube, device, resistance and coil being connected in series and this series circuit being connected between points of different potential, and an excess current protective device in said conductor, said ohmic resistance being of such a magnitude that an arc discharge is brought about in said tube on the occurrence of an excess voltage and said device on the occurrence oi. an excess voltage of extremely lengthy duration or extreme magnitude opening said switch to break the short-circuit of said coil and cause it to operate on said switch so that if the excess voltage persists said switch short-circuits said tube, the large current which then flows through said protective device causing its actuation to interrupt said conductor.

21. An excess voltage protective system for an electric conductor as in claim 1 and including a high ohmic resistance connected in parallel with said discharge tube.

22. An excess voltage protective system for an electric conductor as in claim 1 and including a condenser connected in parallel with said discharge tube.

SIGWART RUPPEL.

Images