CA1129460A - Pressure-operated high-voltage circuit protecting device with high continuous current rating - Google Patents
Pressure-operated high-voltage circuit protecting device with high continuous current ratingInfo
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- CA1129460A CA1129460A CA341,244A CA341244A CA1129460A CA 1129460 A CA1129460 A CA 1129460A CA 341244 A CA341244 A CA 341244A CA 1129460 A CA1129460 A CA 1129460A
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Abstract
ABSTRACT OF THE DISCLOSURE An improved high-voltage device having a high continuous-current rating, which may include both a fuse and an improved switch. The device has a first, high-current-capacity path and a second, low-current-capacity path surrounding the first path in a compact configuration. Current is selectively commutated from the first path to the second path, which may include a fuse, regardless of the nature of the first path. The improved switch has a pair of normally electrically interconnected contacts. The con-tacts are relatively movable apart along a fixed line of direction to break the electrical interconnection. At least one of the contacts, or a part thereof, defines an enclosed chamber which is pressurized to rapidly drive the contacts apart. The chamber may be pressurized by ignition of a power cartridge therein. The switch may be included in the first path of the device, regardless of the nature of the second path. Preferably, the im-proved device comprises a current-limiting fuse which helically, coaxially surrounds the improved switch in a common housing.
Description
l~Z9~
PRESSURE-OPERATED HIGH-VOLTAGE CIRCUIT PROTECTING
DEVICE WITH HIGH CONTINUOUS CURRENT RATING
BACKGROUND OF THE INVENTION
Field of the Invention The present invention relates to an improved high-voltage device having a high continuous current rating. More specifically, the present invention relates to an improved high-voltage circuit-protection device, and to current-limiting or non-current-limiting high-voltage fuses, which constitute a portion of the improved device, both fuses more conveniently achieving a higher continuous current rating than possessed by known fuses and are reliable in operation, convenient and economical to manufacture, and partially reusable, thereby reducing replacement and maintenance costs. The present invention also relates to an improved switch which also constitutes a portion of the improved device.
Brief Discussion of the Prior Art Fault currents (used herein to mean all undesirable over-currents) impress rather stringent thermal and mechanical stresses on high-volta~e electric systems and on apparatus used in such systems. The severity of the thermal stresses is known to be generally proportional to the product of (I) the square of the fault current, and (2) time - i.e., 12t. The severity of the mechanical stresses is generally proportional to the square of the pe~k or crest value achieved by the fault current. Thermal stresses are generally manifested in the burning down of, or in other thermal damage to, lines, cables, and equipment attached to electrical systems. The mechanical stresses are manifested in the deformation of bus work and switches and in damage to items, such as transformers or reactor coils, due to the extremely high magnetic forces generated by the fault current.
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Circuit breakers and circuit switchers are well known devices for protecting high-voltage electrical systems and apparatus connected therein.
These devices have high continuous current ratings, as well as substantial fault-current interrupting capabilities. Expulsion fuses, which are also 5 used for high-voltage circuit protection, have somewhat lower continuous current ratings than breakers and circuit switchers. To the present, none of these devices, regardless of continuous current rating, possess the consistent ability to limit in all cases both fault current peaks and IZt to low values. That is, while these devices do interrupt current, they are 10 usually not able to limit current peaks or I2t until interruption occurs.
Thus, if such devices do happen to limit current peaks or I2t to low values, it is because interruption occurs by happenstance a very short time after initiation of the fault current. For these devices to be rendered consistently capable of interrupting fault currents very shortly after initi-15 ation thereof is an expensive proposition. Accordingly, although thesedevices may well protect the overall high-voltage system from severe, widespread damage, some damage may nevertheless result to either the system or to the apparatus therein due to the fact that the fault current peaks and I t may achieve substantial magnitudes.
Current-limiting fuses of the so-called silver-sand variety and other current-limiting devices are well known expedients for limiting the magnitude of fault currents . See the following commonly assigned U . S .
Patents: 4,063,208 to Bernatt; 4,057,775 to Biller; 4,035,753 to Reeder;
4~028,656 to Schmunk and Tobin; 4,011,537 to Jackson and Tobin; and 25 4,010,438 to Scherer. Unlike circuit breakers, expulsion fuses, and circuit switchers, current-limiting fuses both interrupt fault currents and peak fault current and limit I2t to tolerable levels. These tolerable levels of peak fault current and I2t are lower than the values achievable with circuit breakers, expulsion fuses, and circuit switchers. These lower 30 values of peak fault current or I2t are often termed the "let-through current" or, simply, "let through. " Current-limiting fuses, therefore, are designed to (1) interrupt fault currents, and (2) limit the peak fault current and I2t to tolerable magnitudes, thereby minimizing thermal and mechanical stresses. However, as is well known, current-limiting fuses, particularly at higher voltages, have low continuous-current ratings which impose limitations on the applicability thereof.
As electrical systems have expanded, and electric consumption has increased, continuous current in such systems has also increased.
Because of the low continuous-current rating of conventional silver-sand current-limiting fuses, such fuses have limited applicability in the systems.
The low continuous-current rating of current-limiting fuses is apparently 10 inherent; known current-limiting fuses cannot meet both requirements of low let-through and high continuous-current rating without some modifica-tion or the addition of special apparatus. Further, fault current levels have begun to exceed the capability of existing switchgear. If, in order to avoid the occurrence of increased fault currents, electrical systems are 15 arranged so that th~ey contain individual sections having low available fault currents, or if current-limiting reactors, high impedance transformers, or the like are used, certain disadvantages may nevertheless result. For example, sectionalizing and the use of current-limiting reactors are un-economical and may render voltage regulation difficult to achieve. These 20 techniques also usually produce an over-abundance of idle reserve in the electrical system. Thus, unless an economical and reliable current-limiting fuse having a high continuous-current rating becomes generally available, the only solution -- a costly one -- to solve the problem of increased fault-current levels is to replace existing switchgear with gear having 25 higher fault and overcurrent withstand capabilities and higher interrupting capabilities .
Accordingly, the fault-limiting properties of current-limiting fuses are so desirable that they have been, and remain, the subject of great interest.
Approximately twenty years ago, a device, sometimes referred to as an ~Is-Limiter, " was developed by Calor-Emag Corporation (now a llZg4fi~
division of Brown 13overi, West Germany). The Is-Limiter is constructed with a high-continuous-current-capacity main conductive path which is electrically paralleled with a more or less standard current-limiting fuse.
The current-limiting fuse may be of the well known silver-sand type having 5 a silver fusible element surrounded by a fulgurite-forming arc-quenching medium, such as silica or quartz sand. The main conductive path of the Is-Limiter includes a so-called "bursting bridge" which, upon detonation of a chemical charge contained therewithin in response to a fault current, renders the main conductive path discontinuous and rapidly transfers or 10 commutates the current flowing through the main conductive path to the current-limiting fuse.
The bursting bridge is comprised of a pair of tube sections, each open at one end and containing longitudinal slots over the majority of their length. The open ends of the tube sections are joined along a 15 brazed, weak interface to enclose the chemical charge. Detonation of the chemical charge breaks the weak interface, blowing up the bursting bridge and bending fingers defined between the slots of each tube section out and back in a "banana peel" configuration; this renders discontinuous the main conductive path. See U.S. Patent 2,892,062 to Bruckner, et al.
20 This discontinuity in the main conductive path transfers or commutates the current to the current-limiting fuse, which current is then interrupted in a conventional manner common to silver-sand current-limiting fuses. The chemical charge is detonated by means of a pulse transformer, or other electronic device, contained in one of two insulators which mounts the 25 combintation of the current-limiting fuse and the main conductive path, each housed in its own individual insulative housing.
When the bursting bridge is blown apart, an arc forms between the tube sections. The arc voltage is, sometime thereafter, sufficiently high to commutate the current to the fusible element so that interruption 30 in the current-limiting fuse may occur. If not properly fabricated, the bursting bridge may not fully open. Further, it has been found that the gap between the bent-back fingers of the tube sections may be ionized by hot ignition products, mostly gaseous, due to detonation of the chemical charge. Such ionization permits the arc to persist and lowers the arc voltage, thus slowing or preventing commutation of the current to the 5 current-limiting fuse. It has also been found, however, that the dielectric strength across the gap recovers, or at least increases rather quickly, after about 200 microseconds. Therefore, the fusible element of the cur-rent-limiting fuse portion of the Is-Limiter must be so designed and con-structed as to (a) overlap the "dead time" of the bursting bridge until the 10 200 microsecond time passes, and then (b) limit and interrupt the current.
Following the initial 200 microseconds, voltage stress across the gap has been found to be rather low, due to the lower resistance of the fusible element as compared to that of the gap. Thus, the Is-Limiter is a current-limiting device combining a fast-acting switch having a high continuous-15 current capability but poor current-interrupting capability, with an elec-trically parallel current-limiting fuse having a low continuous-current capability but high current-limiting and interrupting capability.
Several disadvantages of the Is-Limiter should be noted. First, the current-limiting fuse and the main conductive path form two scparate 20 elements in their own separate housings. This arrangement is not only somewhat clumsy and difficult to manipulate during replacement or initial placement, but increases material costs due to the duplication of certain elements, such as housings, end ferrules, conductors, and the like.
Second, commutation of the current flowing through the main current path 25 to the current-limiting fuse may be slower than it might otherwise be, because the inductance of the main conductive path and current-limiting fuse combination is relatively high. Third, there is a practical limitation to the gap that can be formed by the bursting bridge. Specifically, only so much chemical charge may be confined within a practical volume of the 30 bursting bridge to ensure that the fingers defined by the slots in the two tube sections are sufficiently blown outwardly and bent backwardly. That 112~0 is, the tube sections may be greatly elongated and filled with a chemical charge of larger size so that its detonation bends back fingers of increased length. Both the increased size of the charge and the length of the fingers, however, require a larger housing of higher burst strength, adding to the cost and inconvenience of the overall device. Fourth, as already noted, some coordination between the operation of the current-limiting fuse of the Is-Limiter and the dielectric recovery of the gap formed between the tube sections is necessary. Due to the vagaries of fault-current conditions in high-voltage circuits, this coordination may prove difficult to achieve.
A complete discussion of the Is-Limiter may be found in the follow-ing documents: "A Current-Limiting Device for Service Voltages Up to 34.5 kV" by Keders and Leibold, Paper A76 436-6, presented at the IEEE
PES Summer Meeting, Portland, Oregon, July 18-23, 1976; I'Limiting Fault Currents Between Private and Public Networks" by Blythe, The Electrical Review (Great Britain), October 5, 1973; "Fault Levels Too High?" an English language publication put out by Calor-Emag Corporation as Leaflet No. 1197/6E; "The Application of Is--Limiters in Three-Phase Systems " by Bdotger, a publication of the Calor-Emag Corporation, circa August 1967; and "The Economic Benefits of Using Is-Limiters" by Heilmann, a publication of the Calor-Emag Corporation, circa February 1963.
Other types of circuit interruptcrs utilizing the blowing apart of a conductor by an explosive charge are disclosed in the following: U.S.
Patents 466,761 to Wotton; 1,856,701 to Gerdien; 2,175,250 to Burrows et al; 2,54~,112 to Kaminky; 2,551,858 to Stoelting et al; 3,400,301 to Misare; 3,851,219 to Kozorezov et al; 3,958,206 to Klint; and French Patent 2,262,393 to Grebert.
Some general improvement of devices similar to the Is-Limiter has been effected, as described by Pflanz, Clark, and Laboni, in "A New Approach to High-Speed Current Limitation, " presented in the Symposium Proceedings, New Concepts in Fault-Current Limiters and Power Circuit Breakers, printed in a special report of the Electrical Power Research Insti-tute, Paper EPRI EL-276-SR, in April 1977.
In the Pflanz et al device, a fusible element is embedded in and surrounded by a fulgurite-forming particulate medium, such as silica sand, 5 to form a current-limiting fuse apparently of more or less standard design.
The fusible element is electrically paralleled with a large-cross-section copper conductor which constitutes a main current path. The fusible ele-ment and the conductor are contained in a common insulative housing. The large-cross-section conductor is surrounded by, and has wound around it, lO a so-called "linear charge" which, upon detonation, cuts through the large-cross-section conductor to create a plurality of gaps therein. The forma-tion of these gaps commutates the current normally flowing through the conductor to the fusible element for current-limiting interruption of a fault current. Detonation of the linear charge is initiated by a sensor/
15 initiator, which is described only as a "fuse primary charge," responsive to either current flowing through the large-cross-section conductor or to the output of a current transformer. According to Pflanz et al, the sensor and initiator may be either contained within the common housing for the device or externally thereof. As should be apparent, the Pflanz et al 20 device operates substantially the same as Is-Limiter except that plural gaps are formed in the main current conductor prior to current-limiting circuit interruption by the current-limiting fuse. The Pflanz et al device suffers at least two of the shortcomings of the Is-Limiter. Specifically, although numerous gaps are formed in the main conductive path, the length of these 25 gaps is nevertheless limited by the ability of the linear charge to render the large-cross-section conductor discontinuous. There is a practical limit to the dimensions these gaps may achieve; apparently, the gap dimensions are quite small. Thus, it would seem that the possibility exists for re-striking of arcs in the small gaps, should the arc voltage in the current-30 limiting fuse reach high levels. Second, although the Pflanz et al devicesubstantially decreases the inductance of the overall device, as compared to l~Z~61~
the Is-Limiter, by placing the fusible element and the main conductive path in the same housing, reduction of such inductance has not been optimized.
Other devices related to the Is-Limiter and the Pflanz et al device, either by their use of chemical charges or by their parallel arrangement of cur-rent paths, are also known. A summary follows.
It is known to ignite or detonate a chemical charge with heat caused by a fault current, the exothermic ignition of the charge melting or breaking a member. The member normally restrains movement of an element; melting or breaking of the member permits a stored-energy source or spring to perform work, such as moving the element to operate a cir-cuit breaker operating lever. See U.S. Patent 1,917,315 to Biermanns et al .
It is broadly known to move a contact and close a circuit by the detonation of a chemical charge. In U.S. Patent 3,184,726 to Hellgren, detonation of a pyrotechnic mixture pressurizes a housing and a bellows forming part thereof to move the end of the bellows. The bellows end ultimately engages a grounded contact to ground a circuit which includes the housing therein.
In U.S. Patent 2,721,240 to Filbert, detonation of an explosive charge everts or deforms a ductile, conductive diaphragm. Eversion or deformation of the diaphragm causes it to engage and electrically inter-connect a pair of separated contacts, thus completing a circuit there-between .
Perry and Frey, in an article entitled "Ultra-High Speed Ground Switch Application and Development" (AIEE Paper No. 62-1109, presented in Denver, Colorado, in June 1962), describe a ground switch having a lightweight blade (e. g ., aluminum tubing) connected to a piston of a piston-cylinder. The cylinder contains an electrically firable propellant cartridge, the firing circuit for which contains a normally open switch.
When a sensor detects a predetermined condition in a high-voltage system, the normally open switch is closed to fire the cartridge. Firing of the cartirdge pressurizes the piston-cylinder to rapidly move the piston. Rapid piston movement rapidly pivots the blade on an electrically grounded hinge into engagement with a mating contact connected to the high-voltage system.
The system is thus grounded.
McMorris, U.S. Patent 2,305,436, describes a fuse device, which 5 includes a fusible element in electrical series with an inductor, the series combination being in electrical parallel with a spark gap. The fusible ele-ment is surrounded by an explosive charge ( e . g ., gunpowder) contained within a cardboard housing. The inductor physically surrounds the spark gap and the cardboard housing. One side of the fusible element is elec-10 trically and physically connected to one electrode of the spark gap. Actingbetween the one electrode and a terminal of the device is a spring, which also is a current path between the one electrode and the terminal. All ele-ments are in an insulative housing closed by a porcelain disk cemented thereto near the terminal. If the device is subjected to a prolonged surge, 15 the spark gap first breaks down and conducts because of the voltage developed across the inductor. Subsequently, the gap ceases conduction and current flows through the inductor and the fusible element, blowing the fusible element to detonate the explosive charge. Detonation of the charge fractures the cement joint between the disk and the insulative 20 housing, permitting the spring to e~pel the terminal from the latter.
In U.S. Patent 1,917,315 to Murray, a high tension fuse includes a hollow tube having a pair of low mass plungers therewithin. It is not clear if the plungers are insulative or conducting. A fusible element runs the length of the rube through the plungers and has a "blowing point"
25 between the plungers. A quantity of gun cotton may be on one of the plungers near the blowing point. When a fault current occurs in a circuit to which the fusible element is connected, gas generated by the fusing of the blowing point, and by detonation of the gun cotton effected by such fusing, drives the plungers apart. The plungers carry with them portions 30 of the fusible element passing therethrough.
Curry, in U.S. Patent 2,491,956, discloses a circuit interrupter having a high resistance path in electrical shunt with a low resistance path.
_ 9 _ The low resistance path includes, in series, a terminal, a bimetallic element, a first movable contact on the element, a second movable contact normally engaged by the first movable contact, a movable contact rod mounting the second movable contact, and a sliding contact continuously electrically con-5 nected to the contact rod. The contact rod and the second movable contactare biased for movement away from the first movable contact by a spring.
This bias is normally resisted by a fusible strain wire. The high resistance path includes, in series, the terminal, the strain wire, a portion of the contact rod, and the sliding contact. Excessive current flow through the 10 interrupter heats the bimetallic element, causing it to flex and disengage the first movable contact from the second movable contact. This, in turn, transfers the current to the strain wire, which fuses, permitting the spring to move the contact rod and the second movable contact away from the first movable contact. Such movement elongates the arc between the movable 15 contacts in an arc-extinguishing environment to interrupt the excessive current .
None of the above references discloses devices intended for cur-rent-limiting circuit interruption. Moreover, some of them (Hellgren, Filbert, and Perry and Frey) are either low-voltage devices or are " close 20 only" switches or grounding switches. In Biermanns et al, only the heat energy of a chemical charge is utilized; in McMorris, detonation of an ex~
plosive charge is primarily utilized to disintegrate a housing so that a spring may expel a terminal; Curry uses no chemical charge or explosive at all. In Murray, the electrical connection between two plungers is first 25 broken, following which the plungers move apart. As will soon be apparent, the present invention involves, in part, movement apart of two contacts, following the inception of which movement, normal electrical interconnection therebetween is broken by the movement. Lastly, all of these prior art devices are complicated, are unsuitable for high-voltage circuit interruption, 30 are of doubtful operability, or all of these.
Accordingly, an object of the present invention is the provision of a high-voltage fuse having a high continuous current rating. A further ~2g~
object of the present invention is a high-voltage fuse having the following proper-ties: convenient, expeditious and economical manufacture; reliable operation;
simplification and minimization of parts; minimization of inductance; and reliable formation of a gap in the main conductive path which ensures current commutation 5 to a fusible element. Another object of the present invention is the provision of a switch for use in the main conductive path, in which switch a pair of normally electrically interconnected contacts are moved apart by ignition of a charge in a chamber defined by at least one of the contacts, the movement breaking the elecrical interconnection therebetween.
SUMMARY OF THE INVENTION
With the above and other objects in view, the present invention relates to a high-voltage circuit protecting device utilizing a switch. The switch functions to open a first current path of the device and includes a pair of normally elec-15 trically interconnected contacts. The contacts are relatively movable apart along afixed line of direction. Movement of the contacts apart breaks the normal elec-trical interconnection therebetween to open the first current path. When the contacts are electrically interconnected, at least one of them defines an enclosed chamber. The chamber may be selectively pressurized to rapidly move the con-20 tacts. Preferably, though not necessarily within the chamber is contained an ignit-able chemical charge or power cartridge which, upon ignition, rapidly evolves high-pressure gas. The evolution of the high-pressure gas acts on the chamber to rapidly drive and move the contacts apart. In this way, the switch does not depend upon the mere fracturing (or blowing apart) and peeling back of portions of the main 25 current path, as is the case with some prior art devices, but rather positively drives and moves the contacts apart ensuring that a large gap is opened therebetween.
~2~60 The device is an interrupting device, similar to a current-limiting fuse, which includes the switch. The device includes a second current path in shunt with the first current path. Movement apart of the contacts opens the first current path, commutating or transferring current flowing therein to the second current 5 path. The second current path contains a fusible element and helically and co-axially surrounds the first current path. This surrounding relationship not only decreases to a minimum the inductance of the overall device, but further minimizes the number of directional changes which the commutated or transferred current experiences, keeping the current flowing in the same direction in the second cur-10 rent path as it flowed in the first current path. Further, the surrounding relation-ship renders the fuse convenient to fabricate and aæemble. Facilities may be provided for isolating the fusible element from the evolved high pressure gas during and after movement apart of the contacts.
In a specific preferred embodiment of the device, a first insulative 15 housing completely encloses the ignitable chemical charge, both current paths, the particular medium, and the isolating facilities. Terminals at either end of the first current path are fixed to and extend beyond the first housing, the terminals being connectable to a high-voltage electrical circuit. Each contact is continuously electrically connected to its respective terminal. The isolating facility includes a 20 second insulative housing within the first housing, which second housing encloses the contacts, the ignitable chemical charge, and the first current path. The housings define therebetween an annular compartment in which the current-limiting fuse, including its fusible element and the particular arc~uenching medium, is contained.
BRIEF DESCRIPTION OF THE DRAWING
FIGURE 1 depicts an exterior view of a high-voltage device in accordance with the principles of the present invention; the device is mounted between a pair of insulators, one of which is partially sectioned 5 to generally depict a sensing and triggering unit contained therein;
FIGURE 2 is a side elevation, partially sectioned view of a sim-plified switch and current-limiting fuse depicting certain details of the novel features thereof, the fuse-switch combination being a specific form of the device shown in FIGURE 1;
FIGURE 3 is a side elevational, partially sectioned view showing an alternate version of the switch and the current-limiting fuse shown in FIGURE 2; and FIGURE 4 is a side elevational, partially sectioned view of a portion of a switch structure alternative to that shown in FIGURES 2 and 3.
DETAILED DESCRIPTION
Referring first to FIGURE 1, there is shown a general exterior view of a novel high-voltage device 10 in accordance with the principles of the present invention. The novel device 10 may include a high-voltage 20 use 12 and a novel high-voltage switch 14 therefor, both contained within an elongated insulative housing 16. The ~use 12 may be either a current-limiting or a non-current-limiting fuse 12, although the former is preferred.
The housing 16 may contain a plurality of leakage-distance-increasing skirts 18, as is well known, and may be made of porcelain or other suitable 25 insulative material ~ such as molded cycloaliphatic epoxy resin . The housing 16 may surround, and be attached to, an inner housing 19 (FIGURES 2 and 3), preferably made of glass-fiber-wound epoxy.
Extending from the left end of the housings 16 and 19 is a first terminal 20 which is connected to various elements therewithin, in a manner 30 to be described below. Extending from the right end of the housings 16 and 18 is a second terminal 22 which is also connected to elements within the housings 16 and 19.
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The terminal 20 is detachably connectable, in any convenient fashion, to a mounting facility 24 which may be formed integrally with, or otherwise suitably connected to, a cable- or line-attachment facility 26.
One cable or line (not shown) of a circuit (not shown) to be protected by the device 10 is attached in any convenient manner to the facility 26. The mounting facility 24 and the cable-attachment facility 26 are supported by, and are attached to, a support insulator 28 formed of porcelain or other convenient insulative material, such as cycloaliphatic epoxy resin. The insulator 28 may contain a plurality of leakage-distance-increasing skirts 30, and is supported on a common base 32 which may be a structural steel or the lilce.
The other terminal 22 may take any convenient configuration, the inverted L-shape depicted in FIGURE 1 being one example thereof. The terminal 22 is detachably engagable by a mounting facility 34. If the terminal 22 takes the generally circular cross-section depicted in FIGURE 1, the mounting facility 34 may comprise a plurality of contact fingers 36 (only two are shown), spring biased into intimate engagement with the terminal 22 by one or more garter springs 38. The mounting facility 34 may be molded-in as an integral part of an insulator 40 which may be made of porcelain, a cycloaliphatic epoxy resin, or other suitable insulative material.
Also contained within the insulator 40 may be a conductor 42 which is con-tinuously connected to the fingers 36, as at 37, and which is connectable to another cable or line (not shown) of the circuit (not shown) being pro-tected by the device 10.
Also contained within the insulator 40 may be a sensing and triggering unit 44. The sensing and triggering unit 44 generates appro-priate output signals on output conductors 46, for a purpose to be des-cribed below, in response to the condition of the current in the conductor 42, which may be sensed by a current transformer 48. The unit 44 and the transformer 48 may be integrally molded into the insulator 40. The current transformer 48 and the sensing and triggering unit 44 are inter-connected by appropriate leads 50. The output conductors 46 of the ~3~2~
sensing and triggering unit 44 may pass through a portion 41 of the insul-ator 40 to an appropriate detachable clamp member 52 surrounding the terminal 22. The output conductors 46 may enter the interior of the housings 16 and 19 through the terminal 22 which may be hollow or bored 5 for this purpose. The insulator 40 may contain a plurality of leakage-distance-increasing skirts 54 and is attached to the common mounting base 32. The present invention also contemplates the unit 44 and /or the transformer 48 being in a location other than within the insulator 40. For example, the lmit 44 may be within the housing 16 or in a separate housing 10 (not shown) attached to or formed integrally with the housing 16. In this latter event, the structure of the terminal 22, the mounting facility 34, and the insulator 40 may well vary from that depicted in FIGURE 1.
The insulators 28 and 40, on the one hand, and the device 10, on the other hand, are shown in FIGURE 1 as having, respectively, verti-15 cal and horizontal orientations. Any of these components may be mountedin any other desired orientation, as should be obvious. The unit 44 and the transformer 48 may be reusable; only the fuse 12 and the switch 14 require replacement following operation of the device 10.
Referring now to FIGURE 2, there is shown a cross-sectional 20 view of a simplified version of the high-voltage switch 14 and the high-voltage fuse 12, in accordance with the principles of the present inven-tion, and which together comprise the high-voltage device 10.
The switch 14 includes a pair of contacts 100 relatively movable apart along a fixed line of direction. The contacts 100 are normally posi-25 tioned so as to be electrically interconnected by a conductive metallicconnection. The metallic connection may take numerous forms, exemplary of which are: direct physical engagement of the contacts 100; close proximity of the contacts 100 with a small space therebetween, the space including a quantity of conductive material; or separation of the contacts 30 100, with one or more conductive members attached between the contacts 100. ~Vhen the contacts 100 are normally positioned so as to be electrically interconnected by the metallic connection (whatever its form), at least one ~zg46c~
of them (or a portion thereof, or a member thereon) defines, or contributes to the definition of, an enclosed chamber 104. The chamber 104 may be pressurized to drive the contacts 100 farther apart than they are in their normal positions.
Parting movement of the contacts 100 breaks the normal electrical interconnection 5 by rendering discontinuous the conductive metallic connection. Depending on the voltage and current with which the switch 14 is used, the breaking of the normal electrical interconnection between the contacts 100 may or may not interrupt such current. For example, as is well known, if the voltage is sufficiently high, rendering discontinuous the normal metallic connection may result in the formation 10 of an arc between the contacts 100; until the arc is extinguished, current continues to flow in the switch 14, even though the metallic connection has been broken. If an arc forms, it develops an arc voltage which may be viewed as an impedance to current flow. If an arc does not form, there is between the contacts 100 a gap having a very high (nearly infinite) impedance to current flow.
The normal series combination of contact-interconnection-contact has a low resistance or impedance and a high current-carrying capacity. This series combination is shunted by a higher impedance conductive path, through which little current normally flows. When the contacts 100 move apart to break the normal electrical interconnection therebetween, current is commutated or transferred to ZO the shunt path, which has a lower impedance to current flow than either the arc or the gap between the contacts 100 if no arc forms. If extinguishment or suppression of any arc that may form is desirable, the arc may be made to form in the vicinity of an arc-extinguishing medium, including ablative solids (such as boric acid) or fluids (such as SF6). As is well known, such media either extinguish or suppress the 25 arc, or both.
The contact-interconnection-contact series combination is referred to herein as a "first current path." The shunt path is referred to herein as a "second current path." Considering the switch 14 by itself, and not in conjunction with the second current path, the phrase "opening the first current path" refers to the parting movement of the contacts 100 and the concomitant breaking of the normal metallic connection therebetween, without regard to whether an arc forms or, if one does form, whether it is ex-tinguished or not. Considering the combination of the switch 14 and the second current path, the commutation of current from the first current 5 path to the second current path may be viewed as the result of "breaking the interconnection" or of "opening the first current path. " Thus, both phrases may also refer to the breaking of the metallic connection and the resulting current commutation to the shunt path; neither phrase is intended to imply that current flow in the switch 14 is necessarily interrupted by 10 movement apart of the contacts 100 for, as noted earlier, an arc may well form. Of course, following current commutation and the cessation of current flow in the switch 14, no current will again flow thereafter in the switch 14, regardless of what occurs in the shunt path, if the dielectric strength of the gap between the parted contacts 100 is sufficiently high.
In FIGURE 2, the switch 14 is seen to include a pair of contacts 100, which may be similar, generally cylindrical bodies of copper or other highly conductive material. The contacts 100 may be normally positioned to be physically engaged along an annular interface 102, in which position the contacts 100 are electrically interconnected and, therefore, electrically 20 continuous. Interconnection of the contacts 100 may also be achieved by a conductive medium (not shown) at the interface 102 or by one or more conductive members (not shown) attached therebetween rather than by the depicted interfacial engagement. If such is the case, the conductive medium or members may be breakable, frangible, or tearable upon movement apart 25 of the contacts 100. At least one of the contacts 100, portions thereof, or a member thereon defines an enclosed chamber 104 when the contacts 100 are electrically interconnected. In the embodiment of FIGURE 2, the chamber 104 is generally cylindrical and is centrally located, although such is not required. The chamber 104 of FIGURE 2 is made up of two similar 30 blind holes or apertures 106 formed in the facing portions of the contacts 100. Various facilities for normally preventing relative movement of the ~2~
contacts 100 may be provided. For example, the contacts 100 may be jointly held in their normal position, at or near the center of the housings 16 and 19, by soldering or brazing the interface or by appropriate fingers (not shown) or other holding or motion-preventing members which engage the contacts 100 as appropriate.
To iterate, as used herein, the phrase "electrically interconnected, "
as it refers to the contacts 100, means the following:
(1) The contacts 100 are electrically continuous, either (a) be-cause of their physical engagement along the interface 102, or (b) because of the conductive medium or members (not shown) attached therebetween, 10 whether or not the contacts 100 are physically engaged; and
PRESSURE-OPERATED HIGH-VOLTAGE CIRCUIT PROTECTING
DEVICE WITH HIGH CONTINUOUS CURRENT RATING
BACKGROUND OF THE INVENTION
Field of the Invention The present invention relates to an improved high-voltage device having a high continuous current rating. More specifically, the present invention relates to an improved high-voltage circuit-protection device, and to current-limiting or non-current-limiting high-voltage fuses, which constitute a portion of the improved device, both fuses more conveniently achieving a higher continuous current rating than possessed by known fuses and are reliable in operation, convenient and economical to manufacture, and partially reusable, thereby reducing replacement and maintenance costs. The present invention also relates to an improved switch which also constitutes a portion of the improved device.
Brief Discussion of the Prior Art Fault currents (used herein to mean all undesirable over-currents) impress rather stringent thermal and mechanical stresses on high-volta~e electric systems and on apparatus used in such systems. The severity of the thermal stresses is known to be generally proportional to the product of (I) the square of the fault current, and (2) time - i.e., 12t. The severity of the mechanical stresses is generally proportional to the square of the pe~k or crest value achieved by the fault current. Thermal stresses are generally manifested in the burning down of, or in other thermal damage to, lines, cables, and equipment attached to electrical systems. The mechanical stresses are manifested in the deformation of bus work and switches and in damage to items, such as transformers or reactor coils, due to the extremely high magnetic forces generated by the fault current.
~ . ., ~",i ~z~
Circuit breakers and circuit switchers are well known devices for protecting high-voltage electrical systems and apparatus connected therein.
These devices have high continuous current ratings, as well as substantial fault-current interrupting capabilities. Expulsion fuses, which are also 5 used for high-voltage circuit protection, have somewhat lower continuous current ratings than breakers and circuit switchers. To the present, none of these devices, regardless of continuous current rating, possess the consistent ability to limit in all cases both fault current peaks and IZt to low values. That is, while these devices do interrupt current, they are 10 usually not able to limit current peaks or I2t until interruption occurs.
Thus, if such devices do happen to limit current peaks or I2t to low values, it is because interruption occurs by happenstance a very short time after initiation of the fault current. For these devices to be rendered consistently capable of interrupting fault currents very shortly after initi-15 ation thereof is an expensive proposition. Accordingly, although thesedevices may well protect the overall high-voltage system from severe, widespread damage, some damage may nevertheless result to either the system or to the apparatus therein due to the fact that the fault current peaks and I t may achieve substantial magnitudes.
Current-limiting fuses of the so-called silver-sand variety and other current-limiting devices are well known expedients for limiting the magnitude of fault currents . See the following commonly assigned U . S .
Patents: 4,063,208 to Bernatt; 4,057,775 to Biller; 4,035,753 to Reeder;
4~028,656 to Schmunk and Tobin; 4,011,537 to Jackson and Tobin; and 25 4,010,438 to Scherer. Unlike circuit breakers, expulsion fuses, and circuit switchers, current-limiting fuses both interrupt fault currents and peak fault current and limit I2t to tolerable levels. These tolerable levels of peak fault current and I2t are lower than the values achievable with circuit breakers, expulsion fuses, and circuit switchers. These lower 30 values of peak fault current or I2t are often termed the "let-through current" or, simply, "let through. " Current-limiting fuses, therefore, are designed to (1) interrupt fault currents, and (2) limit the peak fault current and I2t to tolerable magnitudes, thereby minimizing thermal and mechanical stresses. However, as is well known, current-limiting fuses, particularly at higher voltages, have low continuous-current ratings which impose limitations on the applicability thereof.
As electrical systems have expanded, and electric consumption has increased, continuous current in such systems has also increased.
Because of the low continuous-current rating of conventional silver-sand current-limiting fuses, such fuses have limited applicability in the systems.
The low continuous-current rating of current-limiting fuses is apparently 10 inherent; known current-limiting fuses cannot meet both requirements of low let-through and high continuous-current rating without some modifica-tion or the addition of special apparatus. Further, fault current levels have begun to exceed the capability of existing switchgear. If, in order to avoid the occurrence of increased fault currents, electrical systems are 15 arranged so that th~ey contain individual sections having low available fault currents, or if current-limiting reactors, high impedance transformers, or the like are used, certain disadvantages may nevertheless result. For example, sectionalizing and the use of current-limiting reactors are un-economical and may render voltage regulation difficult to achieve. These 20 techniques also usually produce an over-abundance of idle reserve in the electrical system. Thus, unless an economical and reliable current-limiting fuse having a high continuous-current rating becomes generally available, the only solution -- a costly one -- to solve the problem of increased fault-current levels is to replace existing switchgear with gear having 25 higher fault and overcurrent withstand capabilities and higher interrupting capabilities .
Accordingly, the fault-limiting properties of current-limiting fuses are so desirable that they have been, and remain, the subject of great interest.
Approximately twenty years ago, a device, sometimes referred to as an ~Is-Limiter, " was developed by Calor-Emag Corporation (now a llZg4fi~
division of Brown 13overi, West Germany). The Is-Limiter is constructed with a high-continuous-current-capacity main conductive path which is electrically paralleled with a more or less standard current-limiting fuse.
The current-limiting fuse may be of the well known silver-sand type having 5 a silver fusible element surrounded by a fulgurite-forming arc-quenching medium, such as silica or quartz sand. The main conductive path of the Is-Limiter includes a so-called "bursting bridge" which, upon detonation of a chemical charge contained therewithin in response to a fault current, renders the main conductive path discontinuous and rapidly transfers or 10 commutates the current flowing through the main conductive path to the current-limiting fuse.
The bursting bridge is comprised of a pair of tube sections, each open at one end and containing longitudinal slots over the majority of their length. The open ends of the tube sections are joined along a 15 brazed, weak interface to enclose the chemical charge. Detonation of the chemical charge breaks the weak interface, blowing up the bursting bridge and bending fingers defined between the slots of each tube section out and back in a "banana peel" configuration; this renders discontinuous the main conductive path. See U.S. Patent 2,892,062 to Bruckner, et al.
20 This discontinuity in the main conductive path transfers or commutates the current to the current-limiting fuse, which current is then interrupted in a conventional manner common to silver-sand current-limiting fuses. The chemical charge is detonated by means of a pulse transformer, or other electronic device, contained in one of two insulators which mounts the 25 combintation of the current-limiting fuse and the main conductive path, each housed in its own individual insulative housing.
When the bursting bridge is blown apart, an arc forms between the tube sections. The arc voltage is, sometime thereafter, sufficiently high to commutate the current to the fusible element so that interruption 30 in the current-limiting fuse may occur. If not properly fabricated, the bursting bridge may not fully open. Further, it has been found that the gap between the bent-back fingers of the tube sections may be ionized by hot ignition products, mostly gaseous, due to detonation of the chemical charge. Such ionization permits the arc to persist and lowers the arc voltage, thus slowing or preventing commutation of the current to the 5 current-limiting fuse. It has also been found, however, that the dielectric strength across the gap recovers, or at least increases rather quickly, after about 200 microseconds. Therefore, the fusible element of the cur-rent-limiting fuse portion of the Is-Limiter must be so designed and con-structed as to (a) overlap the "dead time" of the bursting bridge until the 10 200 microsecond time passes, and then (b) limit and interrupt the current.
Following the initial 200 microseconds, voltage stress across the gap has been found to be rather low, due to the lower resistance of the fusible element as compared to that of the gap. Thus, the Is-Limiter is a current-limiting device combining a fast-acting switch having a high continuous-15 current capability but poor current-interrupting capability, with an elec-trically parallel current-limiting fuse having a low continuous-current capability but high current-limiting and interrupting capability.
Several disadvantages of the Is-Limiter should be noted. First, the current-limiting fuse and the main conductive path form two scparate 20 elements in their own separate housings. This arrangement is not only somewhat clumsy and difficult to manipulate during replacement or initial placement, but increases material costs due to the duplication of certain elements, such as housings, end ferrules, conductors, and the like.
Second, commutation of the current flowing through the main current path 25 to the current-limiting fuse may be slower than it might otherwise be, because the inductance of the main conductive path and current-limiting fuse combination is relatively high. Third, there is a practical limitation to the gap that can be formed by the bursting bridge. Specifically, only so much chemical charge may be confined within a practical volume of the 30 bursting bridge to ensure that the fingers defined by the slots in the two tube sections are sufficiently blown outwardly and bent backwardly. That 112~0 is, the tube sections may be greatly elongated and filled with a chemical charge of larger size so that its detonation bends back fingers of increased length. Both the increased size of the charge and the length of the fingers, however, require a larger housing of higher burst strength, adding to the cost and inconvenience of the overall device. Fourth, as already noted, some coordination between the operation of the current-limiting fuse of the Is-Limiter and the dielectric recovery of the gap formed between the tube sections is necessary. Due to the vagaries of fault-current conditions in high-voltage circuits, this coordination may prove difficult to achieve.
A complete discussion of the Is-Limiter may be found in the follow-ing documents: "A Current-Limiting Device for Service Voltages Up to 34.5 kV" by Keders and Leibold, Paper A76 436-6, presented at the IEEE
PES Summer Meeting, Portland, Oregon, July 18-23, 1976; I'Limiting Fault Currents Between Private and Public Networks" by Blythe, The Electrical Review (Great Britain), October 5, 1973; "Fault Levels Too High?" an English language publication put out by Calor-Emag Corporation as Leaflet No. 1197/6E; "The Application of Is--Limiters in Three-Phase Systems " by Bdotger, a publication of the Calor-Emag Corporation, circa August 1967; and "The Economic Benefits of Using Is-Limiters" by Heilmann, a publication of the Calor-Emag Corporation, circa February 1963.
Other types of circuit interruptcrs utilizing the blowing apart of a conductor by an explosive charge are disclosed in the following: U.S.
Patents 466,761 to Wotton; 1,856,701 to Gerdien; 2,175,250 to Burrows et al; 2,54~,112 to Kaminky; 2,551,858 to Stoelting et al; 3,400,301 to Misare; 3,851,219 to Kozorezov et al; 3,958,206 to Klint; and French Patent 2,262,393 to Grebert.
Some general improvement of devices similar to the Is-Limiter has been effected, as described by Pflanz, Clark, and Laboni, in "A New Approach to High-Speed Current Limitation, " presented in the Symposium Proceedings, New Concepts in Fault-Current Limiters and Power Circuit Breakers, printed in a special report of the Electrical Power Research Insti-tute, Paper EPRI EL-276-SR, in April 1977.
In the Pflanz et al device, a fusible element is embedded in and surrounded by a fulgurite-forming particulate medium, such as silica sand, 5 to form a current-limiting fuse apparently of more or less standard design.
The fusible element is electrically paralleled with a large-cross-section copper conductor which constitutes a main current path. The fusible ele-ment and the conductor are contained in a common insulative housing. The large-cross-section conductor is surrounded by, and has wound around it, lO a so-called "linear charge" which, upon detonation, cuts through the large-cross-section conductor to create a plurality of gaps therein. The forma-tion of these gaps commutates the current normally flowing through the conductor to the fusible element for current-limiting interruption of a fault current. Detonation of the linear charge is initiated by a sensor/
15 initiator, which is described only as a "fuse primary charge," responsive to either current flowing through the large-cross-section conductor or to the output of a current transformer. According to Pflanz et al, the sensor and initiator may be either contained within the common housing for the device or externally thereof. As should be apparent, the Pflanz et al 20 device operates substantially the same as Is-Limiter except that plural gaps are formed in the main current conductor prior to current-limiting circuit interruption by the current-limiting fuse. The Pflanz et al device suffers at least two of the shortcomings of the Is-Limiter. Specifically, although numerous gaps are formed in the main conductive path, the length of these 25 gaps is nevertheless limited by the ability of the linear charge to render the large-cross-section conductor discontinuous. There is a practical limit to the dimensions these gaps may achieve; apparently, the gap dimensions are quite small. Thus, it would seem that the possibility exists for re-striking of arcs in the small gaps, should the arc voltage in the current-30 limiting fuse reach high levels. Second, although the Pflanz et al devicesubstantially decreases the inductance of the overall device, as compared to l~Z~61~
the Is-Limiter, by placing the fusible element and the main conductive path in the same housing, reduction of such inductance has not been optimized.
Other devices related to the Is-Limiter and the Pflanz et al device, either by their use of chemical charges or by their parallel arrangement of cur-rent paths, are also known. A summary follows.
It is known to ignite or detonate a chemical charge with heat caused by a fault current, the exothermic ignition of the charge melting or breaking a member. The member normally restrains movement of an element; melting or breaking of the member permits a stored-energy source or spring to perform work, such as moving the element to operate a cir-cuit breaker operating lever. See U.S. Patent 1,917,315 to Biermanns et al .
It is broadly known to move a contact and close a circuit by the detonation of a chemical charge. In U.S. Patent 3,184,726 to Hellgren, detonation of a pyrotechnic mixture pressurizes a housing and a bellows forming part thereof to move the end of the bellows. The bellows end ultimately engages a grounded contact to ground a circuit which includes the housing therein.
In U.S. Patent 2,721,240 to Filbert, detonation of an explosive charge everts or deforms a ductile, conductive diaphragm. Eversion or deformation of the diaphragm causes it to engage and electrically inter-connect a pair of separated contacts, thus completing a circuit there-between .
Perry and Frey, in an article entitled "Ultra-High Speed Ground Switch Application and Development" (AIEE Paper No. 62-1109, presented in Denver, Colorado, in June 1962), describe a ground switch having a lightweight blade (e. g ., aluminum tubing) connected to a piston of a piston-cylinder. The cylinder contains an electrically firable propellant cartridge, the firing circuit for which contains a normally open switch.
When a sensor detects a predetermined condition in a high-voltage system, the normally open switch is closed to fire the cartridge. Firing of the cartirdge pressurizes the piston-cylinder to rapidly move the piston. Rapid piston movement rapidly pivots the blade on an electrically grounded hinge into engagement with a mating contact connected to the high-voltage system.
The system is thus grounded.
McMorris, U.S. Patent 2,305,436, describes a fuse device, which 5 includes a fusible element in electrical series with an inductor, the series combination being in electrical parallel with a spark gap. The fusible ele-ment is surrounded by an explosive charge ( e . g ., gunpowder) contained within a cardboard housing. The inductor physically surrounds the spark gap and the cardboard housing. One side of the fusible element is elec-10 trically and physically connected to one electrode of the spark gap. Actingbetween the one electrode and a terminal of the device is a spring, which also is a current path between the one electrode and the terminal. All ele-ments are in an insulative housing closed by a porcelain disk cemented thereto near the terminal. If the device is subjected to a prolonged surge, 15 the spark gap first breaks down and conducts because of the voltage developed across the inductor. Subsequently, the gap ceases conduction and current flows through the inductor and the fusible element, blowing the fusible element to detonate the explosive charge. Detonation of the charge fractures the cement joint between the disk and the insulative 20 housing, permitting the spring to e~pel the terminal from the latter.
In U.S. Patent 1,917,315 to Murray, a high tension fuse includes a hollow tube having a pair of low mass plungers therewithin. It is not clear if the plungers are insulative or conducting. A fusible element runs the length of the rube through the plungers and has a "blowing point"
25 between the plungers. A quantity of gun cotton may be on one of the plungers near the blowing point. When a fault current occurs in a circuit to which the fusible element is connected, gas generated by the fusing of the blowing point, and by detonation of the gun cotton effected by such fusing, drives the plungers apart. The plungers carry with them portions 30 of the fusible element passing therethrough.
Curry, in U.S. Patent 2,491,956, discloses a circuit interrupter having a high resistance path in electrical shunt with a low resistance path.
_ 9 _ The low resistance path includes, in series, a terminal, a bimetallic element, a first movable contact on the element, a second movable contact normally engaged by the first movable contact, a movable contact rod mounting the second movable contact, and a sliding contact continuously electrically con-5 nected to the contact rod. The contact rod and the second movable contactare biased for movement away from the first movable contact by a spring.
This bias is normally resisted by a fusible strain wire. The high resistance path includes, in series, the terminal, the strain wire, a portion of the contact rod, and the sliding contact. Excessive current flow through the 10 interrupter heats the bimetallic element, causing it to flex and disengage the first movable contact from the second movable contact. This, in turn, transfers the current to the strain wire, which fuses, permitting the spring to move the contact rod and the second movable contact away from the first movable contact. Such movement elongates the arc between the movable 15 contacts in an arc-extinguishing environment to interrupt the excessive current .
None of the above references discloses devices intended for cur-rent-limiting circuit interruption. Moreover, some of them (Hellgren, Filbert, and Perry and Frey) are either low-voltage devices or are " close 20 only" switches or grounding switches. In Biermanns et al, only the heat energy of a chemical charge is utilized; in McMorris, detonation of an ex~
plosive charge is primarily utilized to disintegrate a housing so that a spring may expel a terminal; Curry uses no chemical charge or explosive at all. In Murray, the electrical connection between two plungers is first 25 broken, following which the plungers move apart. As will soon be apparent, the present invention involves, in part, movement apart of two contacts, following the inception of which movement, normal electrical interconnection therebetween is broken by the movement. Lastly, all of these prior art devices are complicated, are unsuitable for high-voltage circuit interruption, 30 are of doubtful operability, or all of these.
Accordingly, an object of the present invention is the provision of a high-voltage fuse having a high continuous current rating. A further ~2g~
object of the present invention is a high-voltage fuse having the following proper-ties: convenient, expeditious and economical manufacture; reliable operation;
simplification and minimization of parts; minimization of inductance; and reliable formation of a gap in the main conductive path which ensures current commutation 5 to a fusible element. Another object of the present invention is the provision of a switch for use in the main conductive path, in which switch a pair of normally electrically interconnected contacts are moved apart by ignition of a charge in a chamber defined by at least one of the contacts, the movement breaking the elecrical interconnection therebetween.
SUMMARY OF THE INVENTION
With the above and other objects in view, the present invention relates to a high-voltage circuit protecting device utilizing a switch. The switch functions to open a first current path of the device and includes a pair of normally elec-15 trically interconnected contacts. The contacts are relatively movable apart along afixed line of direction. Movement of the contacts apart breaks the normal elec-trical interconnection therebetween to open the first current path. When the contacts are electrically interconnected, at least one of them defines an enclosed chamber. The chamber may be selectively pressurized to rapidly move the con-20 tacts. Preferably, though not necessarily within the chamber is contained an ignit-able chemical charge or power cartridge which, upon ignition, rapidly evolves high-pressure gas. The evolution of the high-pressure gas acts on the chamber to rapidly drive and move the contacts apart. In this way, the switch does not depend upon the mere fracturing (or blowing apart) and peeling back of portions of the main 25 current path, as is the case with some prior art devices, but rather positively drives and moves the contacts apart ensuring that a large gap is opened therebetween.
~2~60 The device is an interrupting device, similar to a current-limiting fuse, which includes the switch. The device includes a second current path in shunt with the first current path. Movement apart of the contacts opens the first current path, commutating or transferring current flowing therein to the second current 5 path. The second current path contains a fusible element and helically and co-axially surrounds the first current path. This surrounding relationship not only decreases to a minimum the inductance of the overall device, but further minimizes the number of directional changes which the commutated or transferred current experiences, keeping the current flowing in the same direction in the second cur-10 rent path as it flowed in the first current path. Further, the surrounding relation-ship renders the fuse convenient to fabricate and aæemble. Facilities may be provided for isolating the fusible element from the evolved high pressure gas during and after movement apart of the contacts.
In a specific preferred embodiment of the device, a first insulative 15 housing completely encloses the ignitable chemical charge, both current paths, the particular medium, and the isolating facilities. Terminals at either end of the first current path are fixed to and extend beyond the first housing, the terminals being connectable to a high-voltage electrical circuit. Each contact is continuously electrically connected to its respective terminal. The isolating facility includes a 20 second insulative housing within the first housing, which second housing encloses the contacts, the ignitable chemical charge, and the first current path. The housings define therebetween an annular compartment in which the current-limiting fuse, including its fusible element and the particular arc~uenching medium, is contained.
BRIEF DESCRIPTION OF THE DRAWING
FIGURE 1 depicts an exterior view of a high-voltage device in accordance with the principles of the present invention; the device is mounted between a pair of insulators, one of which is partially sectioned 5 to generally depict a sensing and triggering unit contained therein;
FIGURE 2 is a side elevation, partially sectioned view of a sim-plified switch and current-limiting fuse depicting certain details of the novel features thereof, the fuse-switch combination being a specific form of the device shown in FIGURE 1;
FIGURE 3 is a side elevational, partially sectioned view showing an alternate version of the switch and the current-limiting fuse shown in FIGURE 2; and FIGURE 4 is a side elevational, partially sectioned view of a portion of a switch structure alternative to that shown in FIGURES 2 and 3.
DETAILED DESCRIPTION
Referring first to FIGURE 1, there is shown a general exterior view of a novel high-voltage device 10 in accordance with the principles of the present invention. The novel device 10 may include a high-voltage 20 use 12 and a novel high-voltage switch 14 therefor, both contained within an elongated insulative housing 16. The ~use 12 may be either a current-limiting or a non-current-limiting fuse 12, although the former is preferred.
The housing 16 may contain a plurality of leakage-distance-increasing skirts 18, as is well known, and may be made of porcelain or other suitable 25 insulative material ~ such as molded cycloaliphatic epoxy resin . The housing 16 may surround, and be attached to, an inner housing 19 (FIGURES 2 and 3), preferably made of glass-fiber-wound epoxy.
Extending from the left end of the housings 16 and 19 is a first terminal 20 which is connected to various elements therewithin, in a manner 30 to be described below. Extending from the right end of the housings 16 and 18 is a second terminal 22 which is also connected to elements within the housings 16 and 19.
~12~4~
The terminal 20 is detachably connectable, in any convenient fashion, to a mounting facility 24 which may be formed integrally with, or otherwise suitably connected to, a cable- or line-attachment facility 26.
One cable or line (not shown) of a circuit (not shown) to be protected by the device 10 is attached in any convenient manner to the facility 26. The mounting facility 24 and the cable-attachment facility 26 are supported by, and are attached to, a support insulator 28 formed of porcelain or other convenient insulative material, such as cycloaliphatic epoxy resin. The insulator 28 may contain a plurality of leakage-distance-increasing skirts 30, and is supported on a common base 32 which may be a structural steel or the lilce.
The other terminal 22 may take any convenient configuration, the inverted L-shape depicted in FIGURE 1 being one example thereof. The terminal 22 is detachably engagable by a mounting facility 34. If the terminal 22 takes the generally circular cross-section depicted in FIGURE 1, the mounting facility 34 may comprise a plurality of contact fingers 36 (only two are shown), spring biased into intimate engagement with the terminal 22 by one or more garter springs 38. The mounting facility 34 may be molded-in as an integral part of an insulator 40 which may be made of porcelain, a cycloaliphatic epoxy resin, or other suitable insulative material.
Also contained within the insulator 40 may be a conductor 42 which is con-tinuously connected to the fingers 36, as at 37, and which is connectable to another cable or line (not shown) of the circuit (not shown) being pro-tected by the device 10.
Also contained within the insulator 40 may be a sensing and triggering unit 44. The sensing and triggering unit 44 generates appro-priate output signals on output conductors 46, for a purpose to be des-cribed below, in response to the condition of the current in the conductor 42, which may be sensed by a current transformer 48. The unit 44 and the transformer 48 may be integrally molded into the insulator 40. The current transformer 48 and the sensing and triggering unit 44 are inter-connected by appropriate leads 50. The output conductors 46 of the ~3~2~
sensing and triggering unit 44 may pass through a portion 41 of the insul-ator 40 to an appropriate detachable clamp member 52 surrounding the terminal 22. The output conductors 46 may enter the interior of the housings 16 and 19 through the terminal 22 which may be hollow or bored 5 for this purpose. The insulator 40 may contain a plurality of leakage-distance-increasing skirts 54 and is attached to the common mounting base 32. The present invention also contemplates the unit 44 and /or the transformer 48 being in a location other than within the insulator 40. For example, the lmit 44 may be within the housing 16 or in a separate housing 10 (not shown) attached to or formed integrally with the housing 16. In this latter event, the structure of the terminal 22, the mounting facility 34, and the insulator 40 may well vary from that depicted in FIGURE 1.
The insulators 28 and 40, on the one hand, and the device 10, on the other hand, are shown in FIGURE 1 as having, respectively, verti-15 cal and horizontal orientations. Any of these components may be mountedin any other desired orientation, as should be obvious. The unit 44 and the transformer 48 may be reusable; only the fuse 12 and the switch 14 require replacement following operation of the device 10.
Referring now to FIGURE 2, there is shown a cross-sectional 20 view of a simplified version of the high-voltage switch 14 and the high-voltage fuse 12, in accordance with the principles of the present inven-tion, and which together comprise the high-voltage device 10.
The switch 14 includes a pair of contacts 100 relatively movable apart along a fixed line of direction. The contacts 100 are normally posi-25 tioned so as to be electrically interconnected by a conductive metallicconnection. The metallic connection may take numerous forms, exemplary of which are: direct physical engagement of the contacts 100; close proximity of the contacts 100 with a small space therebetween, the space including a quantity of conductive material; or separation of the contacts 30 100, with one or more conductive members attached between the contacts 100. ~Vhen the contacts 100 are normally positioned so as to be electrically interconnected by the metallic connection (whatever its form), at least one ~zg46c~
of them (or a portion thereof, or a member thereon) defines, or contributes to the definition of, an enclosed chamber 104. The chamber 104 may be pressurized to drive the contacts 100 farther apart than they are in their normal positions.
Parting movement of the contacts 100 breaks the normal electrical interconnection 5 by rendering discontinuous the conductive metallic connection. Depending on the voltage and current with which the switch 14 is used, the breaking of the normal electrical interconnection between the contacts 100 may or may not interrupt such current. For example, as is well known, if the voltage is sufficiently high, rendering discontinuous the normal metallic connection may result in the formation 10 of an arc between the contacts 100; until the arc is extinguished, current continues to flow in the switch 14, even though the metallic connection has been broken. If an arc forms, it develops an arc voltage which may be viewed as an impedance to current flow. If an arc does not form, there is between the contacts 100 a gap having a very high (nearly infinite) impedance to current flow.
The normal series combination of contact-interconnection-contact has a low resistance or impedance and a high current-carrying capacity. This series combination is shunted by a higher impedance conductive path, through which little current normally flows. When the contacts 100 move apart to break the normal electrical interconnection therebetween, current is commutated or transferred to ZO the shunt path, which has a lower impedance to current flow than either the arc or the gap between the contacts 100 if no arc forms. If extinguishment or suppression of any arc that may form is desirable, the arc may be made to form in the vicinity of an arc-extinguishing medium, including ablative solids (such as boric acid) or fluids (such as SF6). As is well known, such media either extinguish or suppress the 25 arc, or both.
The contact-interconnection-contact series combination is referred to herein as a "first current path." The shunt path is referred to herein as a "second current path." Considering the switch 14 by itself, and not in conjunction with the second current path, the phrase "opening the first current path" refers to the parting movement of the contacts 100 and the concomitant breaking of the normal metallic connection therebetween, without regard to whether an arc forms or, if one does form, whether it is ex-tinguished or not. Considering the combination of the switch 14 and the second current path, the commutation of current from the first current 5 path to the second current path may be viewed as the result of "breaking the interconnection" or of "opening the first current path. " Thus, both phrases may also refer to the breaking of the metallic connection and the resulting current commutation to the shunt path; neither phrase is intended to imply that current flow in the switch 14 is necessarily interrupted by 10 movement apart of the contacts 100 for, as noted earlier, an arc may well form. Of course, following current commutation and the cessation of current flow in the switch 14, no current will again flow thereafter in the switch 14, regardless of what occurs in the shunt path, if the dielectric strength of the gap between the parted contacts 100 is sufficiently high.
In FIGURE 2, the switch 14 is seen to include a pair of contacts 100, which may be similar, generally cylindrical bodies of copper or other highly conductive material. The contacts 100 may be normally positioned to be physically engaged along an annular interface 102, in which position the contacts 100 are electrically interconnected and, therefore, electrically 20 continuous. Interconnection of the contacts 100 may also be achieved by a conductive medium (not shown) at the interface 102 or by one or more conductive members (not shown) attached therebetween rather than by the depicted interfacial engagement. If such is the case, the conductive medium or members may be breakable, frangible, or tearable upon movement apart 25 of the contacts 100. At least one of the contacts 100, portions thereof, or a member thereon defines an enclosed chamber 104 when the contacts 100 are electrically interconnected. In the embodiment of FIGURE 2, the chamber 104 is generally cylindrical and is centrally located, although such is not required. The chamber 104 of FIGURE 2 is made up of two similar 30 blind holes or apertures 106 formed in the facing portions of the contacts 100. Various facilities for normally preventing relative movement of the ~2~
contacts 100 may be provided. For example, the contacts 100 may be jointly held in their normal position, at or near the center of the housings 16 and 19, by soldering or brazing the interface or by appropriate fingers (not shown) or other holding or motion-preventing members which engage the contacts 100 as appropriate.
To iterate, as used herein, the phrase "electrically interconnected, "
as it refers to the contacts 100, means the following:
(1) The contacts 100 are electrically continuous, either (a) be-cause of their physical engagement along the interface 102, or (b) because of the conductive medium or members (not shown) attached therebetween, 10 whether or not the contacts 100 are physically engaged; and
(2) When the contacts 100 are so electrically continuous, at least one contact (or a portion thereof or a member thereon) defines the chamber 104.
Facilities are provided to selectively pressurize the chamber 104 15 to drive the contacts 100 apart. In FIGURE 2, the chamber 104 contains a quantity of an ignitable chemical charge, which preferably takes the form of a so-called power cartridge 108, which effects such selective pressuriza-tion .
The power cartridge 108 may assume any convenient configuration.
AS iS well known, the power cartridge 108 may constitute a so-called pres-sure cartridge which is capable of gencrating energy for any system re-quiring work. Such cartridges 108 usually include a unit, hermetically sealed or otherwise, containing smokeless powder (not shown) or the like and a fusible bridge wire (not shown), the heating or fusing of which 25 ignites the powder. Power cartridges are ignitable by low currents flowing through the bridge wire, typically in the 5-ampere range. Such cartridges 108 are available from Quantic Industries, Inc. of San Carlos, California, and Holex, Inc, of Hollister, California. Previously noted U.S. Patents
Facilities are provided to selectively pressurize the chamber 104 15 to drive the contacts 100 apart. In FIGURE 2, the chamber 104 contains a quantity of an ignitable chemical charge, which preferably takes the form of a so-called power cartridge 108, which effects such selective pressuriza-tion .
The power cartridge 108 may assume any convenient configuration.
AS iS well known, the power cartridge 108 may constitute a so-called pres-sure cartridge which is capable of gencrating energy for any system re-quiring work. Such cartridges 108 usually include a unit, hermetically sealed or otherwise, containing smokeless powder (not shown) or the like and a fusible bridge wire (not shown), the heating or fusing of which 25 ignites the powder. Power cartridges are ignitable by low currents flowing through the bridge wire, typically in the 5-ampere range. Such cartridges 108 are available from Quantic Industries, Inc. of San Carlos, California, and Holex, Inc, of Hollister, California. Previously noted U.S. Patents
3,851,219 and 3,400,301, and French Patent 2,262,393 describe the general use of such cartridges in fuses or fuse-like devices. The following previously cited articles also provide additional background on the use of power cartridges: "A Current-Limiting Device for Service Voltages Up to 34.5 kV" by Keders and Leibold, Paper A76 436-6, presented at the IEEE
PES Summer Meeting, Portland, Oregon, July 18-23, 1976; "Limiting Fault Currents Between Private and Public Networks, " by M. C. Blythe in The Electrical Review (U.K.), October 5, 1973; and "Fault Levels Too High?"
leaflet number 1197/6E of Calor-Emag Electrizitats - Aktiengessellschaft, Ratingen, West Germany.
The output conductors 46 of the sensing and triggering unit 44 are appropriate connected to the bridge wire (not shown) of the power 10 cartridge 108 for ignition thereof at an appropriate time, as hereinafter described .
Each contact 100 may contain a second cylindrical blind aperture or hole 110 which telescopically, intimately, slidingly engages a cylindrical conductive member 112 fabricated of copper or other good conductor. The 15 members 112 may be mounted in any convenient fashion to, or may be formed integrally with, conductive end ferrules 113 which close the housings 16 and 19. The ferrules 113 may include flanges 114 trapped between the housings 16 and 19. The ferrules 113 are continuously, electrically con-nected to respective ones of the terminals 20 and 22. The sliding engage-20 ment between the members 112 and the apertures 110 constrains each con-tact 100 to move in a fixed line of direction, which is horizontal in FIGURE
2. As the contacts 100 move, they remain in continuous, sliding electrical engagement with their members 112. Additional elements, such as sliding contact structures, flexible conductors, frangible conductors, or peelable 25 conductors (not shown) may be mounted between the contacts 100 and their respective members 112. The current-carrying ability of the contacts 100, the members 112, and the interface 102 may be made quite high by appro-priate selection of the materials and the effective cross-sectional area thereof.
The piston-cylinder relationship of the members 112 and the 30 contacts 100 may lead to a pressure build-up in the apertures 110 when the contacts 100 move. Accordingly, the walls of the contacts 100 may contain one or more relief vents 115 communicating with the apertures 110 for preventing this pressure build-up.
_ 19 _ 1~%~4Ç~C~
The switch 14 may be enclosed in an insulative housing 116 within, and coaxial with, the housings 16 and 19. The housing 116 may be sup-ported by flanges 117 on support members 118 formed integrally with, or attached to, the members 112. The housing 116 may be glass-fiber-wound epoxy with high burst strength and mechanical rigidity to resist the pres-sure of the ignition products of the power cartridge 108.
When the sensing and triggering unit 44 receives an output on the leads 50 from the current transformer 48 indicating that a fault current is flowing in the circuit which includes the terminals 22 and 26, an appro-priate pulse or signal (i.e., appropriate as to magnitude, duration, and timing with respect to the fault current) is transmitted on the output con-ductors 46 to the power cartridge 108. This pulse ignites the power cartridge 108, causing the rapid evolution and build-up of high pressure gas within the enclosed chamber 104. This pressure build-up causes the contacts 100 to part along the interface 102 as they are driven and move rapidly away from each other. When the contacts 100 move apart, the electrical interconnection therebetween is broken and the first current path is opened. The first current path includes, in series, the terminal 20, the left ferrule 113, the left-hand member 112, the left contact 100, the interface 102, the right contact 100, the right member 112, the right ferrule 113, and the terminal 22. The motion-preventing members previously referred to (but not shown) which hold the contacts 100 in their normal positions may also prevent motion of the contacts 100 until sufficient pressure builds up in the chamber 104 to ensure parting along the interface 102 and rapid movement apart of the contacts 100. Moreover, the exterior of the contacts 100 and the shape of the chamber 104 may be configured so as to ensure the interfacial parting of the contacts 100 without significant dissipation of the energy tending to move the contacts 100 apart.
The contacts 100 may be configured, or made of a material suf-ficiently malleable or flexible, so as to deform upon reaching the end of their opening movement. Specifically, the flanges 117 may define annular depressions 120 into which the ends of the contacts 100 are forced due to the rapid evolution of the high pressure gases by the power cartridge 108.
The movement of the contacts 100 apart may be sufficiently rapid to cause their respective ends to be forced and jammed into these depressions 120, thus preventing their subsequent movement back toward each other.
Other ways of preventing movement of the contacts 100 following their separation are discussed in greater detail below.
The housing 1~ 6 not only electrically isolates the contacts 100 and their associated elements from electrical structure between the housings 116 and 19, as discussed below, but also may be relied on to prevent the igni-10 tion products (ionized or un-ionized hot gases) of the power cartridge 108 from reaching the remainder of the volume enclosed by the housings 16 and 19.
Surrounding the housing 116 is the fuse 12 which may be either of the non-current-limiting or the current-limiting variety, although the 15 latter is particularly contemplated by the present invention and represents a preferred embodiment. It is also preferred that the fuse 12 coaxially surrounds the housing 116 and all of the elements contained therewithin, and when the fuse 12 is the preferred current-limiting fuse, it may co-axially and helically surround the housing 116.
Referring again to FIGURE 2, the fuse 12 may include a fusible element 122 wound about an appropriate support 124 which may be attached to or formed integrally with the housing 116. The fusible element 122 may be a wire or a rihbon, the latter being either helically flat-wound or edge-wound about the support 124. A more detailed description of such a fusible 25 element 122 and the support 124 may be found in commonly assigned U. S.
Patent 4,057,775 to Biller. An annular volume or compartment 126 defined between the housings 16 and 116 is filled with a fulgurite-forming, particu-late arc-quenching medium such as silica or quartz sand 128 which sur-rounds the fusible element 122. Respective ends of the fusible element 122 30 are attached to respective conductive members 112 in any convenient fashion (not shown). Accordingly, the fusible element 122 coaxially surrounds the contacts 100 and a part 112-100-102-112 of the first current path 20-113-112-100-102-100-112-113-22, as well as the fixed line of direction of movement apart of the contacts 100. Also, the fusible element 122 defines a second current path in shunt with the contacts 100 and with any gap opened therebetween, following 5 ignition of the power cartridge 108.
As used herein, "surround" means that the first current path is at least partially encircled by the second current path. The second current path may be envisioned as lying partially or entirely on the surface of an imaginary volume, such as a cylinder, which totally encompasses the first current path, 10 with the points of connection between the paths being angularly spaced from each other about the major axis of the volume; if the points of connection are not angularly spaced, then the second current path encircles the first current path at least once.
The separation or movement apart of the contacts 100 has been 15 previously described. These contacts 100 move along the fixed line of direction, as guided by the members 112, following the detection of a fault current or overcurrent by the sensing and tripping unit 44 which detonates the power car-tridge 108. As the contacts 100 separate, the above described first current path is opened thereby. This commutates or transfer the current flowing in the first 20 current path to the second current path, that is, in the case of FIGURE 2, to the fusible element 122. Because of the wide separation or gap potentially achiev-able between the contacts 100 due to their ability to move apart, the dielectric strength of the gap therebetween reaches quite high values quite quickly and the commutated current is ultimately interrupted by operation of the fuse 12.
25 Current commutation to the fusible element 122 may, if desired, be ensured by suppressing or extinguishing any arc tending to form, or forming, between the contacts 100; by ensuring that the voltage of such an arc ~should it form) is elevated; or by opening additional gaps in the first current path 20-113-112-100-102-100-112-113-22. Where the fusible element 122 is a part of the preferred current-limiting fuse 12, circuit interruption is effected in a 5 current-limiting mode. To be completely accurate, if the sensing and triggering unit 44 ignites the power cartridge 108 so that current is commu-tated to the fusible element 122 before a first fault-current loop reaches its peak, the device 10 indeed acts in a "current-limiting" mode. If one or more fault-current loops occur before current commutation to the fusible 10 element 122, the device 10 is more properly said to operate in an "energy limiting" mode.
To iterate, as used herein, the phrases "breaking the electrical interconnection" and "opening the first current path" mean:
(1) The conductive metallic connection -- the interfacial engage-15 ment 102, the conductive material (not shown) between the contacts 100, or the conductive members ( not shown) -- is broken or rendered disintegral, whether or not current through the switch 14 is interrupted at that time;
and, in cases where the switch 14 is used with the second current path;
(2) The current is commutated to the second current path 20 following breaking of the conductive metallic connection, whether or not anarc forms between the contacts 100.
The structure of the device 10 according to the present invention should be contrasted with the earlier described prior art devices. First, the coaxial arrangement of the various parts is quite convenient from a 25 manufacturing standpoint, leading to economies in manufacture and labor and rendering the device 10 quite reasonable in cost. Second, the contacts 100 being movable apart, successful operation of the device 10 does not depend on the contacts 100 merely being disintegrated and peeled back to create a gap therebetween; the contacts 100 may move apart just about any 30 slected distance to effect a very large gap therebetween. This large gap ensures that current is commutated to the second current path constituted by the fusible element 122. In addition, movement apart of the contacts 100 ~:~2~
occurs as rapidly as the peeling back of various portions of bursting bridge structures of prior art devices. Third, the inductance of the device 10 has been decreased to an absolute minimum. Specifically, not only are the switch 14 and the fuse 12 contained within the same housings 16 and 19, thereby 5 decreasing the length of the electrical connection therebetween, but also the current, in being commutated from the first current path to the second cur-rent path, is not required to make a great number of turns and flows in the second current path in the same direction as it flows in the first current path. This decreases the inertia of the current flow which might otherwise 10 cause it to resist changes in its direction and is manifested by the device 10 having alow inductance. Current flows in the second current path in the same direction as it flows in the first current path, thereby experiencing minimal (or no) electromagnetic forces which tend to discourage its flow in the second current path.
Referring now to FIGURE 3, a modified device 10 similar to that shown in FIGURE 2 is depicted. To the extent that the same structure is shown in FIGURES 2 and 3, the same reference numerals have been used.
In FIGURE 3, the contacts 100 take the form of main contact mem-bers 200 which define the enclosed chamber 104 therebetween. As before, 20 the chamber 104 houses the power cartridge 108. Rather than telescopically sliding upon the members 112, the contacts 100 contain at their outer ends, remote from the interface 102, a plurality of contact fingers 202. Sliding contact portions 204 of the fingers 202 slidingly, electrically engage the members 112 and fix the direction of movement of the contact members 200.
25 One or more garter springs 206 may surround the fingers 202 in the vicinity of the contact portions 204 to maintain and ensure good sliding electrical contact between the portions 204 and the members 112. In the embodiment of FIGURE 3, the flanges 118 define the annular depression 120, but the side walls of the depression 120, rather than being flat as in FIGURE 2, 30 contain one or more protruding ridges 2080 The ridges 208 are so spaced, and the radial extent of the depressions 120 is such that the contact por-tions 204 of the fingers 202 protrude thereinto, near and at the end of the Q
parting movement of the contacts 100. Entry of the contact portions 204 into the depressions 120 causes the ridges 208 to engage the garter springs 206, thus ensuring that the contacts 100 cannot move back, or bounce back, toward each other following their separation. The ridges 208 may 5 be replaced by depressions (not shown) into which the garter springs 206 may conformally fit following full opening of the contacts 100.
Referring now to FIGURE 4, an alternative arrangement, which prevents movement or bouncing of the contacts 100 back together following their full opening, is shown. This arrangement may be used in the embodi-10 ments of either FIGURE 2 or FIGURE 3. Specifically, not only do thedepressions 120 have one or more protruding ridges 208 for engagement with the garter springs 206, but also the depressions 120 contain a sloped or slanted wall portion 210 opposite the ridges 208. Upon full parting move-ment of the contacts 100, the garter springs 206 are engaged by the ridges 15 208, and the slanted walls 210 act as a ramp which outwardly deforms the contact portions 204, bending them slightly and wedging them within the depressions 120. This action ensures the inability of the contacts 100 to move back toward each other for any reason after full separation thereof.
Various changes may be made in the above described embodiments 20 of the present invention without departing from the spirit and scope there-of. Such changes as are within the scope of the claims that follow are intended to be covered thereby. For example, whether the electrically interconnected contacts 100 are normally physically engaged or not, either one or both may carry a piston (not shown) coacting with either an aper-25 ture in the other contact or elsewhere to define the chamber 104. Ignitionof the power cartridge 108 moves the piston (not shown) to move the contact 100 carrying it. Both contacts 100 need not be movable; one may be stationary. Moreover, rather than being normally interconnected by engagement along the interface 102 or by separate conductive material or 30 conductors (fragible or otherwise), one contact 100 may include contact fingers (not shown, but similar to the fingers 202) which normally fit within the contact walls of an aperture in the other contact 100. These contact fingers may be so constructed or spring-loaded that a fault cur-rent in the first current path flexes the fingers inwardly away from the aperture walls to permit free relative movement of the contacts 100.
It should be apparent that the high conductivity first current path, including the contacts 100 and the members 112, eliminates the neces-sity of the second current path carrying high-level currents. Whether the fusible element 122 is found in a current-limiting or non-current-limiting fuse 12, the continuous current rating of the device 10 is both high and almost solely dependent on the first current path.
PES Summer Meeting, Portland, Oregon, July 18-23, 1976; "Limiting Fault Currents Between Private and Public Networks, " by M. C. Blythe in The Electrical Review (U.K.), October 5, 1973; and "Fault Levels Too High?"
leaflet number 1197/6E of Calor-Emag Electrizitats - Aktiengessellschaft, Ratingen, West Germany.
The output conductors 46 of the sensing and triggering unit 44 are appropriate connected to the bridge wire (not shown) of the power 10 cartridge 108 for ignition thereof at an appropriate time, as hereinafter described .
Each contact 100 may contain a second cylindrical blind aperture or hole 110 which telescopically, intimately, slidingly engages a cylindrical conductive member 112 fabricated of copper or other good conductor. The 15 members 112 may be mounted in any convenient fashion to, or may be formed integrally with, conductive end ferrules 113 which close the housings 16 and 19. The ferrules 113 may include flanges 114 trapped between the housings 16 and 19. The ferrules 113 are continuously, electrically con-nected to respective ones of the terminals 20 and 22. The sliding engage-20 ment between the members 112 and the apertures 110 constrains each con-tact 100 to move in a fixed line of direction, which is horizontal in FIGURE
2. As the contacts 100 move, they remain in continuous, sliding electrical engagement with their members 112. Additional elements, such as sliding contact structures, flexible conductors, frangible conductors, or peelable 25 conductors (not shown) may be mounted between the contacts 100 and their respective members 112. The current-carrying ability of the contacts 100, the members 112, and the interface 102 may be made quite high by appro-priate selection of the materials and the effective cross-sectional area thereof.
The piston-cylinder relationship of the members 112 and the 30 contacts 100 may lead to a pressure build-up in the apertures 110 when the contacts 100 move. Accordingly, the walls of the contacts 100 may contain one or more relief vents 115 communicating with the apertures 110 for preventing this pressure build-up.
_ 19 _ 1~%~4Ç~C~
The switch 14 may be enclosed in an insulative housing 116 within, and coaxial with, the housings 16 and 19. The housing 116 may be sup-ported by flanges 117 on support members 118 formed integrally with, or attached to, the members 112. The housing 116 may be glass-fiber-wound epoxy with high burst strength and mechanical rigidity to resist the pres-sure of the ignition products of the power cartridge 108.
When the sensing and triggering unit 44 receives an output on the leads 50 from the current transformer 48 indicating that a fault current is flowing in the circuit which includes the terminals 22 and 26, an appro-priate pulse or signal (i.e., appropriate as to magnitude, duration, and timing with respect to the fault current) is transmitted on the output con-ductors 46 to the power cartridge 108. This pulse ignites the power cartridge 108, causing the rapid evolution and build-up of high pressure gas within the enclosed chamber 104. This pressure build-up causes the contacts 100 to part along the interface 102 as they are driven and move rapidly away from each other. When the contacts 100 move apart, the electrical interconnection therebetween is broken and the first current path is opened. The first current path includes, in series, the terminal 20, the left ferrule 113, the left-hand member 112, the left contact 100, the interface 102, the right contact 100, the right member 112, the right ferrule 113, and the terminal 22. The motion-preventing members previously referred to (but not shown) which hold the contacts 100 in their normal positions may also prevent motion of the contacts 100 until sufficient pressure builds up in the chamber 104 to ensure parting along the interface 102 and rapid movement apart of the contacts 100. Moreover, the exterior of the contacts 100 and the shape of the chamber 104 may be configured so as to ensure the interfacial parting of the contacts 100 without significant dissipation of the energy tending to move the contacts 100 apart.
The contacts 100 may be configured, or made of a material suf-ficiently malleable or flexible, so as to deform upon reaching the end of their opening movement. Specifically, the flanges 117 may define annular depressions 120 into which the ends of the contacts 100 are forced due to the rapid evolution of the high pressure gases by the power cartridge 108.
The movement of the contacts 100 apart may be sufficiently rapid to cause their respective ends to be forced and jammed into these depressions 120, thus preventing their subsequent movement back toward each other.
Other ways of preventing movement of the contacts 100 following their separation are discussed in greater detail below.
The housing 1~ 6 not only electrically isolates the contacts 100 and their associated elements from electrical structure between the housings 116 and 19, as discussed below, but also may be relied on to prevent the igni-10 tion products (ionized or un-ionized hot gases) of the power cartridge 108 from reaching the remainder of the volume enclosed by the housings 16 and 19.
Surrounding the housing 116 is the fuse 12 which may be either of the non-current-limiting or the current-limiting variety, although the 15 latter is particularly contemplated by the present invention and represents a preferred embodiment. It is also preferred that the fuse 12 coaxially surrounds the housing 116 and all of the elements contained therewithin, and when the fuse 12 is the preferred current-limiting fuse, it may co-axially and helically surround the housing 116.
Referring again to FIGURE 2, the fuse 12 may include a fusible element 122 wound about an appropriate support 124 which may be attached to or formed integrally with the housing 116. The fusible element 122 may be a wire or a rihbon, the latter being either helically flat-wound or edge-wound about the support 124. A more detailed description of such a fusible 25 element 122 and the support 124 may be found in commonly assigned U. S.
Patent 4,057,775 to Biller. An annular volume or compartment 126 defined between the housings 16 and 116 is filled with a fulgurite-forming, particu-late arc-quenching medium such as silica or quartz sand 128 which sur-rounds the fusible element 122. Respective ends of the fusible element 122 30 are attached to respective conductive members 112 in any convenient fashion (not shown). Accordingly, the fusible element 122 coaxially surrounds the contacts 100 and a part 112-100-102-112 of the first current path 20-113-112-100-102-100-112-113-22, as well as the fixed line of direction of movement apart of the contacts 100. Also, the fusible element 122 defines a second current path in shunt with the contacts 100 and with any gap opened therebetween, following 5 ignition of the power cartridge 108.
As used herein, "surround" means that the first current path is at least partially encircled by the second current path. The second current path may be envisioned as lying partially or entirely on the surface of an imaginary volume, such as a cylinder, which totally encompasses the first current path, 10 with the points of connection between the paths being angularly spaced from each other about the major axis of the volume; if the points of connection are not angularly spaced, then the second current path encircles the first current path at least once.
The separation or movement apart of the contacts 100 has been 15 previously described. These contacts 100 move along the fixed line of direction, as guided by the members 112, following the detection of a fault current or overcurrent by the sensing and tripping unit 44 which detonates the power car-tridge 108. As the contacts 100 separate, the above described first current path is opened thereby. This commutates or transfer the current flowing in the first 20 current path to the second current path, that is, in the case of FIGURE 2, to the fusible element 122. Because of the wide separation or gap potentially achiev-able between the contacts 100 due to their ability to move apart, the dielectric strength of the gap therebetween reaches quite high values quite quickly and the commutated current is ultimately interrupted by operation of the fuse 12.
25 Current commutation to the fusible element 122 may, if desired, be ensured by suppressing or extinguishing any arc tending to form, or forming, between the contacts 100; by ensuring that the voltage of such an arc ~should it form) is elevated; or by opening additional gaps in the first current path 20-113-112-100-102-100-112-113-22. Where the fusible element 122 is a part of the preferred current-limiting fuse 12, circuit interruption is effected in a 5 current-limiting mode. To be completely accurate, if the sensing and triggering unit 44 ignites the power cartridge 108 so that current is commu-tated to the fusible element 122 before a first fault-current loop reaches its peak, the device 10 indeed acts in a "current-limiting" mode. If one or more fault-current loops occur before current commutation to the fusible 10 element 122, the device 10 is more properly said to operate in an "energy limiting" mode.
To iterate, as used herein, the phrases "breaking the electrical interconnection" and "opening the first current path" mean:
(1) The conductive metallic connection -- the interfacial engage-15 ment 102, the conductive material (not shown) between the contacts 100, or the conductive members ( not shown) -- is broken or rendered disintegral, whether or not current through the switch 14 is interrupted at that time;
and, in cases where the switch 14 is used with the second current path;
(2) The current is commutated to the second current path 20 following breaking of the conductive metallic connection, whether or not anarc forms between the contacts 100.
The structure of the device 10 according to the present invention should be contrasted with the earlier described prior art devices. First, the coaxial arrangement of the various parts is quite convenient from a 25 manufacturing standpoint, leading to economies in manufacture and labor and rendering the device 10 quite reasonable in cost. Second, the contacts 100 being movable apart, successful operation of the device 10 does not depend on the contacts 100 merely being disintegrated and peeled back to create a gap therebetween; the contacts 100 may move apart just about any 30 slected distance to effect a very large gap therebetween. This large gap ensures that current is commutated to the second current path constituted by the fusible element 122. In addition, movement apart of the contacts 100 ~:~2~
occurs as rapidly as the peeling back of various portions of bursting bridge structures of prior art devices. Third, the inductance of the device 10 has been decreased to an absolute minimum. Specifically, not only are the switch 14 and the fuse 12 contained within the same housings 16 and 19, thereby 5 decreasing the length of the electrical connection therebetween, but also the current, in being commutated from the first current path to the second cur-rent path, is not required to make a great number of turns and flows in the second current path in the same direction as it flows in the first current path. This decreases the inertia of the current flow which might otherwise 10 cause it to resist changes in its direction and is manifested by the device 10 having alow inductance. Current flows in the second current path in the same direction as it flows in the first current path, thereby experiencing minimal (or no) electromagnetic forces which tend to discourage its flow in the second current path.
Referring now to FIGURE 3, a modified device 10 similar to that shown in FIGURE 2 is depicted. To the extent that the same structure is shown in FIGURES 2 and 3, the same reference numerals have been used.
In FIGURE 3, the contacts 100 take the form of main contact mem-bers 200 which define the enclosed chamber 104 therebetween. As before, 20 the chamber 104 houses the power cartridge 108. Rather than telescopically sliding upon the members 112, the contacts 100 contain at their outer ends, remote from the interface 102, a plurality of contact fingers 202. Sliding contact portions 204 of the fingers 202 slidingly, electrically engage the members 112 and fix the direction of movement of the contact members 200.
25 One or more garter springs 206 may surround the fingers 202 in the vicinity of the contact portions 204 to maintain and ensure good sliding electrical contact between the portions 204 and the members 112. In the embodiment of FIGURE 3, the flanges 118 define the annular depression 120, but the side walls of the depression 120, rather than being flat as in FIGURE 2, 30 contain one or more protruding ridges 2080 The ridges 208 are so spaced, and the radial extent of the depressions 120 is such that the contact por-tions 204 of the fingers 202 protrude thereinto, near and at the end of the Q
parting movement of the contacts 100. Entry of the contact portions 204 into the depressions 120 causes the ridges 208 to engage the garter springs 206, thus ensuring that the contacts 100 cannot move back, or bounce back, toward each other following their separation. The ridges 208 may 5 be replaced by depressions (not shown) into which the garter springs 206 may conformally fit following full opening of the contacts 100.
Referring now to FIGURE 4, an alternative arrangement, which prevents movement or bouncing of the contacts 100 back together following their full opening, is shown. This arrangement may be used in the embodi-10 ments of either FIGURE 2 or FIGURE 3. Specifically, not only do thedepressions 120 have one or more protruding ridges 208 for engagement with the garter springs 206, but also the depressions 120 contain a sloped or slanted wall portion 210 opposite the ridges 208. Upon full parting move-ment of the contacts 100, the garter springs 206 are engaged by the ridges 15 208, and the slanted walls 210 act as a ramp which outwardly deforms the contact portions 204, bending them slightly and wedging them within the depressions 120. This action ensures the inability of the contacts 100 to move back toward each other for any reason after full separation thereof.
Various changes may be made in the above described embodiments 20 of the present invention without departing from the spirit and scope there-of. Such changes as are within the scope of the claims that follow are intended to be covered thereby. For example, whether the electrically interconnected contacts 100 are normally physically engaged or not, either one or both may carry a piston (not shown) coacting with either an aper-25 ture in the other contact or elsewhere to define the chamber 104. Ignitionof the power cartridge 108 moves the piston (not shown) to move the contact 100 carrying it. Both contacts 100 need not be movable; one may be stationary. Moreover, rather than being normally interconnected by engagement along the interface 102 or by separate conductive material or 30 conductors (fragible or otherwise), one contact 100 may include contact fingers (not shown, but similar to the fingers 202) which normally fit within the contact walls of an aperture in the other contact 100. These contact fingers may be so constructed or spring-loaded that a fault cur-rent in the first current path flexes the fingers inwardly away from the aperture walls to permit free relative movement of the contacts 100.
It should be apparent that the high conductivity first current path, including the contacts 100 and the members 112, eliminates the neces-sity of the second current path carrying high-level currents. Whether the fusible element 122 is found in a current-limiting or non-current-limiting fuse 12, the continuous current rating of the device 10 is both high and almost solely dependent on the first current path.
Claims (6)
1. A high-voltage circuit protecting device, which comprises:
a first current path which has a low resistance to current flow and which is connectable between opposed points of a high-voltage circuit;
a helical second current path which has a higher resistance to current flow than the first current path and which surrounds the first current path in a generally coaxial manner;
a fusible element in the second current path;
means for connecting the second current path in electrical shunt with the first current path; and means for commutating current flowing in the first current path to the second current path, which commutating means includes a pair of normally electrically interconnected contacts for normally carrying current in the first current path, the contacts being relatively movable apart along a fixed line of direction to break the electrical interconnection therebetween and to open the first current path, at least one of the interconnected contacts defining an enclosed chamber, and means for pressurizing the chamber to rapidly drive the contacts apart.
a first current path which has a low resistance to current flow and which is connectable between opposed points of a high-voltage circuit;
a helical second current path which has a higher resistance to current flow than the first current path and which surrounds the first current path in a generally coaxial manner;
a fusible element in the second current path;
means for connecting the second current path in electrical shunt with the first current path; and means for commutating current flowing in the first current path to the second current path, which commutating means includes a pair of normally electrically interconnected contacts for normally carrying current in the first current path, the contacts being relatively movable apart along a fixed line of direction to break the electrical interconnection therebetween and to open the first current path, at least one of the interconnected contacts defining an enclosed chamber, and means for pressurizing the chamber to rapidly drive the contacts apart.
2. A device as in Claim 1, wherein:
the second current path surrounds the fixed line of direction along which the contacts move apart in a generally coaxial manner.
the second current path surrounds the fixed line of direction along which the contacts move apart in a generally coaxial manner.
3. A device as in Claim 1, wherein:
the pressurizing means is a power cartridge which rapidly evolves high pressure gas upon ignition thereof.
the pressurizing means is a power cartridge which rapidly evolves high pressure gas upon ignition thereof.
4. A device as in Claim 3, wherein:
the power cartridge is in the chamber.
the power cartridge is in the chamber.
5. A device as in Claim 1, which further comprises;
a first, outer insulative housing which encloses the contacts and both current paths;
a pair of terminals carried by the first housing, the terminals being respectively connected to the ends of the first current path and being respectfully connectable between opposed points of the high voltage circuits;
a second, inner insulative housing within a first housing which encloses the contacts and isolates them from the fusible element, an enclosed volume being defined between the housings; and a mass of particulate arc-quenching material within the enclosed volume and surrounding the fusible element.
a first, outer insulative housing which encloses the contacts and both current paths;
a pair of terminals carried by the first housing, the terminals being respectively connected to the ends of the first current path and being respectfully connectable between opposed points of the high voltage circuits;
a second, inner insulative housing within a first housing which encloses the contacts and isolates them from the fusible element, an enclosed volume being defined between the housings; and a mass of particulate arc-quenching material within the enclosed volume and surrounding the fusible element.
6. A device as in claim 5, wherein the housings are generally coaxial;
the pressurizing means is a power cartridge which rapidly evolves high pressure gas upon ignition thereof, the second housing isolating the fusible element and the arc-quenching material from the gas; and the second current path surrounds the fixed line of direction along which the contacts move apart in a generally coaxial manner.
the pressurizing means is a power cartridge which rapidly evolves high pressure gas upon ignition thereof, the second housing isolating the fusible element and the arc-quenching material from the gas; and the second current path surrounds the fixed line of direction along which the contacts move apart in a generally coaxial manner.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US97265078A | 1978-12-21 | 1978-12-21 | |
| US972,650 | 1978-12-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1129460A true CA1129460A (en) | 1982-08-10 |
Family
ID=25519953
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA341,244A Expired CA1129460A (en) | 1978-12-21 | 1979-12-05 | Pressure-operated high-voltage circuit protecting device with high continuous current rating |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1129460A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0133632A1 (en) * | 1983-08-09 | 1985-03-06 | S & C ELECTRIC COMPANY | Improved high-speed, multi-break electrical switch |
-
1979
- 1979-12-05 CA CA341,244A patent/CA1129460A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0133632A1 (en) * | 1983-08-09 | 1985-03-06 | S & C ELECTRIC COMPANY | Improved high-speed, multi-break electrical switch |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry | ||
| MKEX | Expiry |
Effective date: 19990810 |