US3072766A - Electrical resistance for heavy duty swith - Google Patents

Description

Jan. 8, 1963 H. ROTH 3,072,766

ELECTRICAL RESISTANCEFOR HEAVY DUTY SWITCH Filed June 25, 1960 2 Sheets-Sheet 2 23 LIGHT, SouRcE 24- PHOTO SENSH'IVE RESVSTANCE UNVT I I PE.CELL 21 FIGURE 3 RESISTANCE M TRANSPARENT RESIN PHoTo-SE RESISTANCE 29 \N/Noow FIGLHQL 5 INVENTOR.

Heinz Roth Ofilice 3,072,766 Patented Jan. 8, 1963 3,072,766 ELECTRICAL RESISTANCE FOR HEAVY DUTY SWlTCH Heinz Roth, Neuenhof, Switzerland, assignor to Aktiengesellschaft Brown, Boveri &' Cie, Baden, Switzerland,

a joint stock company Filed June 23, 1960, Ser. No. 38,212 Claims priority, application Switzerland June 30, 1959 12 Claims. (Cl. 200-446) This invention is related to the construction of electrical resistances and more particularly to resistances which are to be connected in parallel with one set or a plurality of series connected sets, of contacts provided on large power, i.e. heavy duty, high voltage, high current switches. The contacts of each contact set may be actuated to open and closed positions by known means such as for example compressed air.

These parallel connected resistances are used for various purposes. Such a resistance having a relatively low ohmic value is used to facilitate extinction of the are drawn between the contacts as they separate, particularly by attenuating the recovery voltage. the switch includes a plurality of series connected power switching points, each such point being represented by a set of contacts, the parallel connected, low ohmic resistance'performs the function of distributing the potential of the recovery voltage in a uniform manner over all of the switching points.

A resistance having a high ohmic value and connected in parallel with a set of contacts is useful in reducing the current flow to such a smallamount that it can be easily cut off by means of a simple construction of a so-called disconnecting switching point which may be comprised simply of a blade type of switch operating in the open air.

Thus such a parallel connected resistance having a low ohmic value is required to facilitate arc extinction by attenuating the recovery voltage while a similarly connected resistance having a high ohmic value is more advantageous for disconnecting the residual current.

It is known to design power switches having both types of resistance, the switch having, for example, two sets of power interrupting contacts connected in series, and there being a low ohmic resistance connected in parallel with one set of contacts which is the first to open, and a high ohmic resistance connected in parallel with another set of contacts which opens later. 'When the first mentioned set of contacts opens, the current is forced to take a path through the low ohmic resistance and facilitates are extinction. When the second mentioned set of contacts opens, the residual current is forced to take a path through the high ohmic resistance thus reducing this residual current to a value where it can be easily interrupted by a set of conventionally designed disconnect contacts which is connected in series with the two sets of power interrupting contacts. I

The purpose of this invention is to provide an improved arrangement for these resistances, namely a practical construction for a single resistance unit which exhibits both high and low ohmic resistance characteristics in a sequential manner thus eliminating the necessity for using separate high and low ohmic resistances. The improved resistance unit, in accordance with the invention initially exhibits a low ohmic characteristic when radiated by the switching arc in order to facilitate arc extinztion, and then rapidly assumes a high ohmic resistance characteristic as the radiation diminishes in order to rapidly reduce the current.

The presently known resistances whose ohmic values change with voltage and current are not suitable for use on power switches since their range of resistance varia- Moreover, when tion is much too low to be practical. The attenuation of the recovery voltage requires minimum values of under one ohm up to a maximum of thirty ohms, while the reduction of the current passing through it requires several thousand ohms. These resistances would, therefore, have to be variable by at least three orders of magnitude.

Photoelectric resistances have been used occasionally in electronic controls. These are sensitive to light or other electromagnetic radiation and their resistance values can be made to vary by several orders of magnitude depending upon the amount of radiation present. However, sin:e their variation in resistance requires periods of up to several milliseconds, the delay is too great for most electronic control applications and they are thus only seldom used since other and more practical means are available, for such purpose.

However, the inherent delay in response of a photosensitive type of resistance has been found to be highly desirable for use in application to power switches since the disconnection of the current flowing through the resistance is to be efiected so much later in time as is required for attenuating the oscillation of the recovery voltage. The present invention therefore is directed to use of a photosensitive type of resistance for sequential voltage attenuating and residual current reducing functions in a power switch of the construction which has been described, and wherein the required change in resistanze from low to high ohmic values by several orders of magnitude is made dependent upon the radiation produced during the separation of the switch contacts, this radiation being used to act directly or indirectly upon the resistance material to change its resistance.

The resistance unit having this sequential low and then high ohmic value is connected in the same manner as the previously used resistances, i.e. in parallel to one or more of the power switching points, and this parallel circuit is connected in series with a voltage disconnecting point. The latter is used to disconnect the current flowing through the resistance when the power switching point or points have opened. When the power switching points first open, there is a large arc and hence a large amount of radiation,'which makes the resistance assume a low ohmic value since the resistance value is inversely proportional to the amount of radiation it receives. It can therefore greatly attenuate the recovery voltage formed during the disconnection at the time of the arc extinction. Besides, at very low ohmic values, the resistance can take over a part of the current flowing in the are between the separated contacts. When the arc breaks, the current flows solely through the parallel connected resistance. The latter is then electrically in series with the impedance of the mains. The voltage caused by the mains impedance alone would normally be built up again over oscillations. The resistance eliminates these oscillations and makes the mains circuit aperiodic. After the voltage returns, the

residual current is determined only by the resistance itself, and this residual current can be disconnected by simple switch structure as soon as the resistance attains a high ohmic characteristic. This'resistance variation is possible in a photoelectric resistance unit according to the invention. In the unexposed state, the resistance has a high ohmic value: when it is subjected to radiation from the are at the breaking switch contacts, this radiation, and particularly the light effect, causes the resistance value to reduce to a low ohmic value which is several orders lower than its initially high ohmic value. After the arc is extinguished, the resistance assumes again its original, high ohmic value.- It is important that the time in which this variation in the ohmic value takes place is about one millisecond, so that the low resistance value still exists for some time after the arc has disappeared and the recovery voltage can be built up apcriodically. At the time the disconnecting switch is actuated, the resistance value must have reassumed practically its initially high ohmic value. Thus this delay, or inertia effect, in the response time of the change in resistance, which is undesirable in control engineering techniques, is advantageous when applied to power switching apparatus for the purpose intended.

As a photo sensitive resistance unit one may use a monoor poly-crystalline, semi-conductive material. An example of a mono-crystalline material is silicon.

The fault content, caused by additives to the semi-com ductive material, must be so low that the ohmic value of the resistance remains sufficiently high in the normal state, i.e. the state wherein the resistance material receives no radiation. The radiation of .the resistance material by the are generated upon separation of the switch contacts produces charge carriers which reduce the ohmic value of the resistance corresponding to their life. By admixing suitable additives to the semi-conductive material, it is possible to increase the life of the charge carriers to such an extent that the ohmic value of the resistance varies with the desired delay, i.e. inertia, corresponding to the requirements of the switching apparatus.

In one practical embodiment of the invention, the resistance units are composed of monoor poly-crystalline plates, several plates being connected electrically in series, and several of these series plate arrangements being electrically connected in parallel. In order to protect the resistance units against undesired extraneous influences, they can be encased Within a radiation transmitting tube. For this purpose can be used glass, transparent ceramic material, quartz and casting resin. Important is a good seal against atmospheric air. The resistance plates can also .be embedded in a ceramic material which has transparent windows. The radiation influence of the are on the resistance material can be direct, or it can be indirect.

The foregoing objects and advantages of the invention will become more apparent from the following detailed description and accompanying drawings.

FIG. 1 of the drawings illustrates one embodiment of the invention, the resistance unit and related switch contact structure being shown in longitudinal, central vertical section, and wherein radiation from the are produced upon separation acts directly on the photo-sensitive resistance material.

FIG. 2 is also a view in longitudinal, central vertical section of a different embodiment of the invention wherein the action of the radiation from the arc upon the photo- 7 sensitive resistance material is indirect.

FIG. 3 is an electrical schematic view of the embodiment according to FIG. 2.

FIG. 4 is an enlarged fragmentary sectional view illustrating a different structural arrangement for the .series and parallel connected photo-sensitive resistances utilized in the embodiment of FIG. 1; and

FIG. 5 is a view similar to FIG. 4 illustrating still another structural arrangement for the series and parallel connected photosensitive resistances.

With reference now to FIG. 1 it will be seen that only the switch structure in the vicinity of one set of power interrupting contacts together with a disconnecting switch has been illustrated. These contacts comprise a stationary .pin contact 1 which is supported in the horizontal position indicated by means of a spider 2 that is attached to the inner periphery of an annular plate 3 of electrically conductive material which is provided with an input terminal 4. The annular plate 3 is fitted to an end flange 5a of a tubular member 5 through which compressed air is led to the contacts to effect their separation. The end of the pin contact 1 abuts against and closes off the end opening of a movable nozzle contact member 6 which is arranged coaxially with pin contact member 1. The movable contact member 6 is provided at its opposite end with a flanged head or piston 7 which is adapted to slide within a cylinder portion 8 of an 4 exhaust outlet structure 9 provided with an exhaust aperture 10, and a helical loading spring 11 placed within the cylinder 8 bears at one end against the head 7 so as to load the nozzle contact member 6 into engagement with the end of pin contact member 1. Extending between the annular plate 3 and the cylindrical exhaust outlet structure 9 is a sleeve 12 of insulating material which thus encloses the contact members 1 and 6 and establishes an arc extinction chamber 13. The contact member 6 is disengaged from contact member 1 when compressed air is admitted into the arc extinction chamber 13 and is applied against the face of the flanged head 7 thus moving the contact member 6 to the right as viewed in the drawing against the counter action of spring 11. Separation of the contact members 1, 6 thus establishes an arc, and the radiation from the same is used to vary the ohmic value of the resistance in accordance with the principles of the invention.

A disconnecting switch unit is included to interrupt the final, residual current, and this is comprised of a stationary contact member 14 structurally united with the electrically conductive exhaust outlet structure 9 and a pivotally mounted, contact blade 15 associated therewith. The pivot mounting for the blade 15 is shown at 16 and the output terminal 17 of the switch assembly is connected to the mounting 16.

The resistance unit in accordance with the embodiment of FIG. 1 is comprised of an annular arrangement of series and parallel connected plates 18 of a semiconductive material such as silicon which are loc ted at the inner wall surface of the tubular member 12, the plates being attached to the inner Wall of the tube. At the inner periphery of the annular arrangement of resistance plates 18 is disposed a tubular member 19 of transparent material, through which the radiation from the arc, established upon separation of contact members 1, 6 located within the tubular member 19 reaches the resistance plates 18. By arranging the resistance plates 18 rotationally symmetrically about the contact members 1, 6, one is assured that the resistance plates will receive the radiation from the arc in a uniform manner.

The resistance unit consisting of the plates 18 thus arranged essentially as a hollow cylinder is electrically connected at its left end by virtue of actual engagement with one face of the annular member 3 to the contact member 1 through conductive spider 2. The right 'end of the resistance unit is electrically connected by means of contact springs 20 to the periphery of the nozzle contact member 6. Thus the resistance unit 18 is connected in parallel with contact members 1, 6.

As a modification of the structure illustrated in- FIG. 1, the resistance plates of semi-conductive material such as silicon connected electrically together in series and in parallel as desired may be held together by a refractory, transparent tubesuch as quartz into which the individual plates are cemented, this tube then surrounding, the contact members 1, 6.

It is thus seen that in the embodiment illustrated in FIG. 1, radiation from the are established by separation of contact members 1, 6 reaches the resistance unit 18 in a direct manner so as to alter the ohmic value thereof in the desired manner.

In FIGS. 2 and 3, there is illustrated a second embodiment of the invention wherein radiation from the arc is used in an indirect manner to alter the ohmic value of the resistance unit. In this embodiment, elements corresponding in structure and function to those shown in FIG. 1 have been assigned the same number in the interest of simplicity but With primes added for purpose of distinction. This embodiment of the invention differs from that of FIG. 1 principally in that theresista'nce unit of silicon or like material is notlocated in the arc chamber 13' so as to receive its radiation directly from the arcing contact members 1', 6 but rather is located. in a separate housing adjacent the arcing chamber. Disspams posed within the arcing chamber 13 are one or more photoelectric cells 21 of conventional manufacture and these may be attached to the inside of the tubular insul'ator 12'1. The photoelectricresponse of the cells 21 which isproportional to the intensity ofthe radiation they receive from thearcing contacts 1, 6 is amplified in an electronic amplifier unit 22 which can be supported by the exhaust outlet structure 9, and the output from amplifier unit 22 is used to correspondingly control the intensity of illumination of an elongated light source 23 which is mounted in parallel spaced relation to the elongated photo-sensitive resistance unit 24, the latter and the light source 23 being mounted within a housing 25 of insulating material that is supported in parallel spaced relation with the tubular insulator 12' by means of upstanding electrically conductive brackets 26, 26 secured respectively to the electrically conductive member and exhaust outlet structure 9. Opposite ends of the resistance unit 24 are electrically connected to these brackets 26, 26' and thus are effectively connected in parallel with the contact members 1, 6'.

A special advantage of the improved construction for the resistance unit is that the variation in its ohmic value is initiated automatically when the arc begins to burn and then stops after the arc has burnt out. Variations in the burning period of the are are thus automatically taken into account. When switching smaller currents,

the radiation is less intense, so that the ohmic value of the resistance unit is less varied. But in this case, the function of the resistance unit is also less required so that this phenomenon has a favorable effect. One thus obtains the further technical advantage that an additional possibility of adaptation to the switching processes has been achieved. The principal advantage of the entire arrangement, however, is that a great attenuation of-the.

recovery voltage and, at the same time, a good potential control. are achieved by a single element. Besides, the structure of the voltage disconnecting point can be as simple as possible, which means an even greater savings in cost. The duration of the variation in ohmic value of the resistance unit can be adapted from the beginning to the necessary operating conditions by suitable selection of the fault content.

Operation of the FIG. 1 and FIG. 2 embodiments are similar. In FIG. 1, as soon as the contacts 1, 6 separate, current begins to flow through the resistance unit 18 which initially has a high ohmic value. The radiation from the are established upon separation of the contacts serves to reduce this resistance to a very low ohmic value. After the arc has terminated, the resistance is restored to its high ohmic value thus reducing the residual current to a very low value safe enough to then permit the disconnect contacts 14, to be separated.

In FIG. 2, operation is similar, except that the arc radiation is directed into the photocell 21 which works through amplifier 22 to control the intensity of light source 23 which in turn efiects the desired change in resistance characteristic of the photo-sensitive resistance unit 24.

A modified arrangement for the series and parallel connected photo-sensitive resistance plates in the FIG. 1 construction would be to cast such plates as a whole into a hollow tube of transparent material.

FIG. 4 illustrates one such arrangement wherein the plates 18 are embedded in a transparent and heat-resistant casting resin 27. The'series and parallel connections between the plates are indicated by conductors 28 extending between the plates. 7

FIG. 5 illustrates a second such arrangement wherein the plates 18" are embedded in a ceramic material 29 provided with radiation-transmitting windows 30 at the inner periphery of the tube to receive light directly from r the are created upon separation of contacts 1 and 6 under load. The series and parallel connections between the 6 plates 18" areindicated by conductors 31 extending between the plates.

In conclusion, it will be understood that while two embodiments of the invention have been described and illustrated, various modifications in the construction and arrangement of component parts may be made without, however, departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. Electrical switching apparatus comprising a set of power switching contacts connected in series with a set of voltage disconnect contacts, and a resistance unit connected in parallel with said set of power switching contacts, said resistance unit being comprised of a photo sensitive resistance material having an ohmic value variable inversely by several orders of magnitude as the amount of radiation which it receives, and said resistance unit being subject to radiation proportional to that produced by the are established upon separation of said set of power switching contacts.

2. Electrical switching apparatus as defined in claim 1 wherein said resistance unit is subjected directly to the radiation emanating from said arc.

3. Electrical switching apparatus comprising a set of power switching contacts connected in series with a set of voltage disconnecting contacts, a resistance unit connected in parallel with said set of power switching contacts, said resistance unit being comprised of a photosensitive resistance material having an ohmic value variable inversely by several orders of magnitude as the amount of radiation it receives, a main housing defining an arcing chamber in which said set of power switching contacts are located, a photoelectric cell located in said main housing and exposed to the radiation produced by the are established upon separation of said set of power switching contacts, an auxiliary housing containing a light source and said resistance unit, and an amplifier, the input to said amplifier being furnished by the output from said photoelectric cell and the output from said amplifier which varies with said input being connected to said light source which has a variable radiation output dependent upon the variation in output from said amplifier, said resistance unit being exposed to the variable radiation produced by said light source.

4. Electrical switching apparatus as defined in claim 1 wherein said set of power switching contacts are disposed within a housing defining an arcing chamber, and said resistance unit is disposed also within said housing and is exposed directly to radiation from the are established upon separation of said power switching contacts.

5. Electrical switching apparatus as defined in claim 4 wherein said resistance unit is applied to the internal wall of said housing.

6. Electrical switching apparatus as defined in claim 4 wherein said resistance unit is applied to the internal wall of said housing and includes a transparent wall between it and said set of power switching contacts.

7. Electrical switching apparatus as defined in claim 1 wherein said resistance material comprises a semi-conductive material and wherein the size and rate of change of the ohmic value thereof are determined by additives.

8. Electrical switching apparatus as defined in claim 1 wherein said resistance unit is arranged symmetrically about the axis of said set of power switching contacts to assure direct and uniform radiation from the arc.

9. Electrical switching apparatus as defined in claim 1 wherein said resistance material is constituted in plate form, the plates being electrically connected in series and in parallel and being held together by a refractory, transparent tube into which the individual plates are cemented.

10. Electrical switching apparatus as defined in claim 1 wherein said resistance material is constituted in plate form, the plates being electrically connected together in series and in parallel, and said plates being cast as a whole with'transparent material to form a final product 1111111311,

lar form.

11. Electrical switchingi apparatus as idefined in claim 10 whereinsaid transparent casting material is comprised of a heat-resistant resin.

12. Electrical switching apparatus as defined in claim 10 wherein said casting material is comprised of a ceramic material having radiation-transmitting windows.

8. References Cited in thefile of this patent UNITED STATES PATENTS- 470,161 \Nurts Mar. 1, 1892 651,013 Kitsee June 5, 1900 1,134,983 Engler Apr. 6, 1915 2,043,099 Hanna June 2, 1936 2,291,263 'Ihommen July 28, 1942

Claims (1)

1. ELECTRICAL SWITCHING APPARATUS COMPRISING A SET OF POWER SWITCHING CONTACTS CONNECTED IN SERIES WITH A SET OF VOLTAGE DISCONNECT CONTACTS, AND A RESISTANCE UNIT CONNECTED IN PARALLEL WITH SAID SET OF POWER SWITCHING CONTACTS, SAID RESISTANCE UNIT BEING COMPRISED OF A PHOTOSENSITIVE RESISTANCE MATERIAL HAVING AN OHMIC VALUE VARIABLE INVERSELY BY SEVERAL ORDERS OF MAGNITUDE AS THE AMOUNT OF RADIATION WHICH IT RECEIVES, AND SAID RESISTANCE UNIT BEING SUBJECT TO RADIATION PROPORTIONAL TO THAT PRODUCED BY THE ARC ESTABLISHED UPON SEPARATION OF SAID SET OF POWER SWITCHING CONTACTS.

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