US2820927A - Anti-inrush sensing device - Google Patents

Description

r Jan. 21, 1958 R. STEINER 2,820,927

ANTI-:NRUSH SEN SING DEVICE Filed May 28, 1956 I 2 Sheets-Sheet 1 3,6 Fig. 1

INVENTOR. RUDOLF STEINER BY I TTORNEYS R- STEINER ANTI-'-INRUSH SENSING DEVICE Jan. 21, 1958" 2 Sheets-Sheet. 2

Filed May 28, 1956 kamkkbb INVENTOR RUDOLF STEINER United States Patent ANTI-INRUSH SENSING DEVICE Rudolf Steiner, Van Nuys, Calif.

Application May 28, 1956, Serial No. 587,914

8 Claims. (Cl. 317-49) (Granted under Title 35, U. S. Code (1952), sec. 266) This invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The invention relates to an anti-inrush sensing device, and more particularly to an anti-inrush sensing device for use with electrical circuit breakers.

In electrical systems, the steady state conditions for various circuit factors are frequently the exception rather than the rule. Certain allowances are made for the socalled normal variations of the voltage or current that can be tolerated without damage to wiring, power sources, and equipment. If these variations exceed specific limits, up and/or down, situations detrimental to the proper functioning or the safety of the system may develop and devices must be provided which either limit the deviations or disconnect the faulty element from the system. Undercurrent protection devices are less important as a rule, and therefore application of these devices in electrical power systems find somewhat less utility. Over-current protection devices, on the other hand, or those designed for response upon over-voltage or over-current deserve first consideration.

Various over-current devices are in existence. It is generally required of such a device not only that it distinguish between a dangerous sustained overload and a transient overload, but that it also is insensitive to such a transient overload, more commonly known in the popular language of the trade as a nuisance type of overload. These transient overloads, characteristically of short duration, are harmless, and various means have been devised to preclude circuit openings during nuisance overloads. Typical of such devices has been the utilization of time delay response elements in a variety of complex electromechanical, and electrical and hydraulic constructions, which include, for the time delayresponse characteristic, such members as oil dash pots, induction type rotatably driven disks in which the duration of the time delay is determined by the amount of rotation of the disk, or the series-parallel combination of electrical RLC elements. A further type employs a relay arrangement based upon the principle that transient or nuisance overloads are predominately either of negative or positive polarity. A common disadvantage of the aforementioned protective devices is that their response to dangerous overload currents is frequently too slow-acting, and generally there are more mechanical components than are desirable for good design and reliability of performance. Further, if hydraulic fluids are involved, additional difiiculties may arise due to the effects of the environments in which these devices may be employed.

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The anti-inrush sensing unit contemplated by the instant invention substantially overcomes the various deficiencies of the aforementioned protective devices, The inventive device utilizes in a simple and compact construction the inductive character of a pair of coils which are of substantially differing values of inductance to preclude operation in response to the fast-rising or nuisance type of current or voltage overload. One coil is essentially an aircoil inductance, while the other is enclosed by an iron-core magnetic circuit. An embodiment of two such inductive coils in a parallel circuit arrangement is used to discriminate against surge or inrush currents of the nuisance type so as to preclude circuit openings, while in the event of dangerous sustained overload currents the tripping arm of the inventive device is efiective to open a circuit breaker or other protective mechanism, since the inductive effect of the iron-core coil is rapidly reduced by the presence of magnetic core saturation and/ or a rapidly decreasing rate of change of current. Therefore, an embodiment of the anti-inrush sensing element according to the inventive principle substantially overcomes the deficiencies of the prior art by enabling a simple compact construction requiring a minimum of electro-mechanical components, thus contributing to a high degree of reliability of performance. In addition, this anti-inrush sensing device is more universal in application than the existing devices of the prior art, since the inventive device is applicable to power circuits employing either alternating or direct current.

An object of the present invention is the provision of an anti-inrush sensing device which will distinguish between a dangerous sustained overload current and a transient overload current.

Another object is to provide an anti-inrush sensing device having an adjustable core to permit calibration of the magnetic circuit in compliance with specific, unforeseen circuit parameters.

A further object of the invention is the provision of an anti-inrush sensing device which will discriminate against fast-rising nuisance overload currents, but will respond to dangerous overload and fault conditions by actuating an armature having a trip arm.

A final object of the present invention is the provision of an anti-inrush sensing devicew hich has universal application, being adapted to either alternating or direct current. Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing in which like reference numerals designate like or corresponding parts throughout the figures thereof and wherein:

Fig. 1 is a simplified view partially broken away, showing a preferred embodiment of the anti-inrush sensing device of the instant invention.

Fig. 2a illustrates a graphic representation of a typical magnitude of inrush current upon initial application of a load to a D. C. power circuit relative to its subsequently assumed steady state value.

Fig. 2b illustrates a graphic representation of a typical inrush current which may appear on a line and is capable of developing into a dangerous fault during regular operation.

Fig. 3 is a schematic representation of one circuit embodiment of the anti-inrush sensing device showing the manner in, which" the respective coils may be connected for aiding-fluxa Fig. 4 is a schematic representation of an alternate cir cuit embodiment of the anti-rush sensing device showing the manner in which the respective coils may be connected for opposing flux.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in the functional embodiment of Fig. 1 an upper coil encircled by a substantially closed magnetic circuit consisting of an upper supporting frame 25, including a verticalmember 12 and a horizontal member 14, which may be formed integrally with member 12 orbe fixedly secured thereto by any suitable fastening, an adjustably positioned core-16, anair gap 18, and an armature20, which'is confied into an area ofinfluence adjacent the. pole face of'core 16 by adjustable stop-22 and lock nut 24, both of which are secured to a stationary portion of frame 23 which may conveniently be a part of. a housing for the inventive The elements comprising the magnetic circuit of the upper coil 10 areof highly permeable material such device.

as soft iron, or'the like, and may preferably be a laminated type of construction. A spring 26 fixedly secured to upper frame 12 by means of a rivet 35'or other suitable means biases the armature 20, tension on which is 'ad-' justable by means of screw 28 threadably engaged in the armature and locked with locking nut 30. The armature pivots about pin 32 when the armature'is attracted to the pole face of core 16, and the movement of tail piece of the armature assembly is effective to interrupt a circuit breaker or other protective mechanism. The lower coil 40 is an air-core inductance, the lower supporting frame 19for this coil being of a non-ferrous material such as brass, or the like. be joined to its companion member, the upper supporting frame 25, by means of a suitable fastener such as a screw 21, as shown. Permeable core 16 is threadably engaged with a relatively slenderadjusting screw 36 having. nonmagnetic properties, and is fixedly secured with pin 44. A non-magnetic collar 42 may be provided, as shown, as a lower limit stop locked in position with set screw 43 on adjusting screw 36, which itself is threadably engaged in lower frame 19 and locked with lockingnut 38. Hence, the highly permeant core 16 is restricted in its travel, preventing entry thereof into the air-core inductance 40 when rotation of screw 36 resultsin vertical movement of the core within the'tubular non-ferrous coil bobbin.45' on,

which coils 10..and 40 are wound. Horizontal members 46 are inflexible non-ferrous separators provided for PUT-1 poses of insulation and may conveniently be fiber washers.

It should be noted that although there is a small amount of leakage flux. originating frjomthe lower coil whichis permeable material ,to, give the device different leakage flux characteristics.

To, appreciate or, better, understand the principle of operation of the anti-inrush sensing .device,.it is desirable to refer initiallyto.Fig.,2a.and;.Fig,-2b.., First,: it is believed to be self-evident that, the. instant invention constructedf'as shown. insFig; 1 will, respond .to a gradual, in:

creasein current to a point above the upper responselimit designated in Figs. v.2a,,and, 2b .by,roman..numeral I by generatinga.suificiently .strongfiunto; close the armature;

The lower supporting frame 19 may 34-which conveniently may be formed as an integral part 4 20, noting that the amount of inductance in the respective coilsis not-a significant factor when the rate of increase in current represented by the slope of the current wave is small. Hence, a shallow current curve representative of this condition is not illustrated in Figs. 2a and 2b. Conversely, Figs. 2a and 2b constitute illustrations of typical transient or nuisance current overloads characterized by a high constant rate of change of current indicated by the steep slope of the curves. There are various circumstances in which the normal course of operation may cause quite excessive over-currents to flow, as shown, though for a comparatively short period of time. Two typical representatives of such occurrences are the current surges or inrushes experienced upon initially connecting a tungsten-filament lamp load to a line, or when starting an electric motor. In each case, the-current may rise to 6 to 10 times thenormal, ratedoperatingcurrent. Such a condition is illustrated by the curve III in Fig. 2a. Similar conditions caused by circumstances other than those reiterated above, may occurduring thetoperation of an equipment, as portrayed by the curve IV in Fig. 2b. Contrary tothese nuisance overloads,.dangerous overload and fault conditions can develop from what initially appears to be a temporary nuisance overload. This condition is represented by the dotted curve V in Fig. 2b. In this instance,- the current' initially rises substantiallyin thesame manner asif it were anormal surge of short duration;

however, it keeps on increasing past the crest C'until the magnitude of this current; is only prevented from reaching an infinite value'throughthe physical and electrical properties of-the circuit at which the slope decreases substan tially to zero. It becomes clear that both the crest of theharmless surge and the entire trace of the dangerous.

overload current are well beyond and above the upper response limit I of "the over-current sensing meansrof the instant invention, and it further becomes clear. that. a close relationship exists amongthe initial. trend of a,

nuisance overload and a dangerous overload. In fact, the first portion of both these manifestations is, identical. It finally becomes apparentthat. the decision in regard to what transpires (nuisance or dangerous overload) can only be made in retrospect,.when it becomes apparent at point C whether the current will fall along the solid trace IV or continue to. rise along. thev dotted traceV.

It is the'characteristics peculiar to these manifestationsof transient overload conditions illustrated in Figs. 2a and- 2b upon whichthe principle of operation of .theinventive anti-inrush sensing device depends. In, contrast. to thegradually developing overloadvcondition referred to abovewherein inductance was not a significant factor, the. rela-. tive inductance of the respective coils of theinstant in ventionis a critical factor in its operation in, response to these rapidly developing transient overloads. A fundamental property of an inductance is ,thattheinduced.elec

tromotive force is equalftothe inductance times-therate of change of current, or stated more-precisely 3 The steep slope of the.current surge ,up to point C ,or, the

substantially constant: rate ofchange .of ,current permitted1to increase sufficiently to generate afluxlarge,

enough to .close armature 20in response to a, dangerous overload, and thus, thedevice functions in a manner comparable to that in which it responds to an overload curin essence,

producing a self-induced rent developed more gradually along a shallow slope to the upper limit response I, as described above. As in the case of a dangerous overload, the steep slope presented by a current wave front in the case of a harmless surge or transient overload generates in coil 10 a self-induced E. M. F. of sufiicient magnitude to prevent any increase in flux across the gap, thus precluding response of the armature to these nuisance type current overloads, while conversely, the abrupt reversal of slope of curve IV at point C to a steep negative slope characteristic of a transient nuisance overload is accompanied by a reversal in the sense of the self-induced counter E. M. P. which merely perpetuates the relatively very small current fiowing in coil 10 insufficient to effect operation of armature 20 in response to a transient overload. Consequently, inductance of the coil 10 is effective to discriminate against nuisance overload currents by virtue of its reaction to a rate of change of current which is an inherent characteristic of any surge or transient current.

The actual operation of the inventive device can best be described with reference to Fig. 3 which illustrates a schematic representation of parallel aiding circuit connections of the anti-inrush sensing element. As shown in the functional embodiment of Fig. l, the arrangement shown is composed of two coils, an upper iron-core inductance 10, and a lower air-core inductance 40, which together comprise the binary actuating means of the inventive overload sensing device. Armature 20 is shown resting in its normal quiescent position biased against stop 22 by spring 26 affording a greatly exaggerated showing of air gap 18. The incoming line 11 is shown connected at junction 15 to coils l and 40, in turn connected at point 17 to the common outgoizg line 13. The parallel connection of coils 10 and 40 as depicted in Fig. 3 permits the fluxes to combine in an additive or like sense, the schematically representative leakage flux common to both coils is indicated by the direction of arrows to be in the same sense as 5,, and the schematically representative fluxes, respectively, of the upper and lower coils. To illustrate the operation of the device, assume as an example, that the two common lines 11 and 13 are capable of carrying 10 amperes continu ously,-where as each coil 10 and 40, respectively, being wound of an identical number of turns of like wire, carries one-half of the total, i. e., 5 amperes continuously. Thus, during a steady state current condition, the total of amperes will divide evenly, and armature 20, calibrated by means of its spring 26' to remain in the open position shown, will not respond to the coil current of 5 amperes. On gradually increasing loads which exceed the upper response level I, the total current will separate equally in the previously described manner, however, the lines of magnetic flux emanating from the pole face of core 16 will now attract the armature sufficiently to overpower biasing spring 26'. Consequently, the armature tail piece 34 will rotate with the armature and engage tripping or other release means and cause the automatic interruption of the the circuit in series with which the lines 11 and 13 were originally connected.

On sudden surges, inrushes or the like, of comparatively short duration, the incoming total current will no longer be divided evenly among the coils 10 and 40, for the inductance of the iron-core equipped coil is much greater than that of the air-core coil. Thus, a large portion of the total current will flow through coil 40. A strong field results from the flow of current through coil 40, but because it is physically remote from armature 20 and not surrounded by a magnetic circuit, little effect will be produced by the increase in leakage flux on thearmature 20. If, however, the apparently temporary current surge should develop into a vicious fault, in which case the self-induced counter E. M. F. of coil 10 falls to zero, the armature 20 will be attracted, after a few milliseconds, by the combined effect of the remote field of coil 4% and the now increasing field o of coil 10.

A useful modification of the basic arrangement is illustrated, schematically, in Fig. 4. Contrary to the circuit embodiment described above, coil 40 is wound in the opposite sense with respect to coil 10 as indicated by the wiring symbols. Aside from this difference, all other circuit and construction elements used previously are again employed and hence the showing in Fig. 1 is equally applicable to this embodiment. The operation of this unit is comparable to that pictured in Fig. 3, except that on surge or inrush currents, not only does the major portion of the current flow through coil 49 but the magnetic fluxes and created thereby, will be opposed to flux induced by coil 10, as indicated by the relative directions of the schematically representative flux lines in Fig. 4. The leakage flux 1: will under these conditions, detract from the total flux that is emanating from the pole face of core 16, and therefore, more time will elapse before the net flux required to attract the armature 2G with sufficient force to overpower the biasing spring 26' is developed than that needed previously for the aiding flux connection of Fig. 3. A need for such an embodiment of the instant invention may arise on starting of electric motors having inrush currents of comparatively longer duration than, for example, tungsten-filament lamp load starting currents. It should be noted that dangerous overloads will, as in the other embodiment, cause displacement of the armature in response to the flux generated either by the over-energized coil 10 or by the physically remote, reverse-wound coil 40, or the comhined effect of both. Since only soft iron, or a metal of similar characteristics is used for the parts of the magnetic circuit, the reversal of the magnetic polarity has no bearing on the operation of the device characterizing the instant invention.

It is apparent from the foregoing description of the alternative embodiment of the anti-inrush sensing device that a wide variation of time delay characteristics are possible, by providing for a leakage flux gb which is of an intensity comparable to the desired time delay. The construction in Fig. 1 provides for one type of embodiment, but other configurations providing for different intensities of leakage flux 5,, are well within the skill of those in the art. For example, an element constituting a permeant path to intensify the leakage flux may be provided between the core at the lower end of coil 40, as shown in Fig. 1, and a point adjacent the free end of armature 20, or alternatively by forming the lower supporting frame 19 of a permeable material. In this respect, it should be pointed out that the leakage flux as shown for the aiding flux connection in Fig. 3 is not essential for that particular mode of operation. The represented leakage fiux is inherent in the construction of the illustrative functional embodiment, and its presence is advantageously utilized in the alternative construction, as described in relation to Fig. 4.

Although the invention has been described from a point of view of application to direct current circuits, the principles evolved will hold true, in essense, for application of the anti-inrush sensing device to alternating current circuits having frequencies from 25 through approximately 1000 cycles per second. The illustrative curves of Fig. 2a and Fig. 2b, under alternating current operation, are readily representative of qualitative root-mean-square values of current. Further, so far as the magnetic circuit is concerned, its physical characteristics will depend on the contemplated application of the sensing unit. While the conditions for direct and 25 through 60 cycle alternating current will be comparable within reason, those for higher frequency alternating current applications will require special consideration, inasmuch as the impedance of a coil varies directly with the applied frequency, and hence, is a significant factor when contemplating operation in a frequency range beyond the usual power frequencies.

An embodiment of the anti-inrush sensing device acof a dangerous sustained overload current, an armature connected to a suitable trip arm is effective to interrupt a circuit breaker or other protective mechanism. Its construction-provides for incorporating such desirable features as an adjustable core, variable armature biasing pressure, and a variable air gap, all of which contribute to the adaptability of the sensing device in various applications by permitting calibration of the magnetic circuit in compliance with specific circuit parameters. The anti-inrush sensing device is further unique in that it is of universal utility, being capable of operating in both direct and alternating current circuits.

It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention and that numerous modifications or alterations may bemade therein without departing from the spirit and the scope of the invention as set forth in the claims.

What is claimed is:

l. ln an electrical power system having a main power line for supplying excitation to a load, an overload sensing device comprising, in combination, a first relatively high inductance means, a second relatively low inductance means, said inductance means being interconnected electrically in'parallel and thence connected directly in series with a load to form binary actuating means of said sensing device, and armature means pivotally mounted adjacent said first high inductance means for movement between an open position and a closed position, said armature means being insensitive, to transient or surge overload currents through said inductance means, but responsive to sustained overload currents through said inductance means, thereby actuating said armature means to the closed position.

2. An overload sensing device comprising, in combination,'a first relatively high inductance means, and a second relatively low inductance means, said first and said second inductancemeans'being electrically connected in shunt and disposed on a common axis for magnetic flux interaction, and an-arrnature with permeable supporting means therefor, forming a substantiallyclosed.magnetic circuit with said first high inductance means, said armature being movable between an open position and a closed position, saidarmature being insensitive to transient or surge overload currents through said inductance means, but responsive tosustained overload currents through said inductance means, thereby actuating the armature to the closed position 3; An anti=inrush sensing device comprising, in com v bination,- afirst inductance means, a second inductance means; said inductance means being electrically connected in parallel, permeablecore means adjustably movable withinthe core ofsaid first inductance means, andjan armature with an elongatedpermeable' supporting means therefor, forming a'substantially closed magneticcircuit with said permeable core means, said armature being.

movable betweena normally-open position and a closed position, and insensitive to-transient or'surge overload currents through said inductance means, but responsive to sustained overload currents through said-' inductance means, thereby actuating'said armature to the closed position.

4; Ananti-inrush sensing device comprising, in combination, afirst relatively high-inductance means, a second relatively-low inductance means, said inductance means being connected electrically in parallel, said first high inductance means including apermeable core means armounted for movement between an open and a closed POSIUOH, permeable supporting means for said armature means, and biasing means effective to maintain saidannature; meansin' its normally open position, said armature means and said'permeable supporting means forming a substantially closed magnetic circuit with said core means, said armature means being insensitive to transient or surge overload currents through said inductance means, but responsive to sustained overload .currents through said inductance means bymovement to its closed position.

5.-An-anti-inrushsensingdevice comprising, in com bination; a first relatively high inductance means, a second relatively low inductance means, said Iinductance means being electrically interconnected in parallel, said second lowinductance means being disposed adjacent to and on a commonaxis withsaid first inductance means, and unilaterally magnetically coupledfwith said first inductance means, an armature and permeable supporting means therefor, said armature being rotatably mounted for movement between an open and a closed position,

biasing means effective to maintain said armature in its normally open position, andJa trip arm means connected to said armature and capable of releasing a circuit breaker or other protective-mechanism, said first high inductance means including a permeable core adjustable for limited travel along'the core of said first high inductance means, said permeable coreand said armature and the permeable supporting means therefor comprising elements of a substantially closed magnetic circuit, said second 'low inductance means, having an air-core and including a supporting frame of non-magnetic material, said armature being insensitive to transient, or surge overload currents through said inductance means, but, responsive to. sus tained overload currents through said inductance means by movernent 'to its closed position, effectinga displace-j ment of said trip-armmeans.

6. An anti-inrush=sensing device comprising; in combination, a first relatively high-inductance means, a second relatively low inductance means, said inductance means being electricallyinterconnected in parallel, said second low inductance means being disposed adjacent to and on a common axis with said first high'inductance means and unilaterally magnetically coupled with said first high inductance means, anarmature and permeable supporting means therefor, said armature being rotatably mounted for movement between an open and a closed position, biasing means effective to maintain said armsture in its normally open'position, and a trip arm means connected to said armature and capableof releasing a circuit breaker or other protective mechanism, said first high inductance means including a permeable core means adjustable for limited movement along the core. of said first high inductance means,- said second low inductance means having an-air-core and-including a magnetically permeable'supporting frame, said permeable core means being adjustablyconnected by non-magneticmeans to one end of said permeable supporting frame, said armature being insensitive to transient or surge overload currents through said inductance means, but responsive to sustained overload currents through said inductance means by movementto its closed position, effecting displacement of said trip arm means.

7. An overload sensing device comprising, in combination, a first relatively highinductancemeans, a second relatively low inductance means, said first and said second inductance means being; disposed mutually adjacent on a common axis and electrically connected for magnetic coupling in a concurrent aiding sense, and an armature with permeable supporting means therefor forming a substantially closed magnetic circuit with said first relatively highjinductance-means, said armature being movable be tweenan open position and a closed position, said arma! ture being insensitive to transient or surge overload cub rents through said inductance means, but responsive to sustained overload current through said inductance means.

8. An overload sensing device comprising, in combination, a first relatively high inductance means, a second relatively low inductance means, said first and said second inductance means being disposed mutually adjacent on a common axis and electrically connected for magnetic coupling in an opposing sense, and an armature with permeable supporting means therefor forming a substantially closed magnetic circuit with said first high in- 10 ductance means, said armature being movable between an open and a closed position, said armature being insensitive to transient or surge overload currents through said inductance means, but responsive to sustained overload current through said inductance means.

References Cited in the file of this patent UNITED STATES PATENTS 1,873,087 Wensley Aug. 23, 1932 FOREIGN PATENTS 217,065 Switzerland Sept. 30, 1941

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