US2439930A - Differential relay and restraint magnet therefor - Google Patents

Description

April 20, 1948. a. v. HOARD DIFFERENTIAL RELAY AND RESTRAINT MAGNET THEREFOR Filed Ot. 10, 1942 INVENTOR B677 l/Haard ATTORNEY Patented Apr. 20,1948

DIFFERENTIAL RELAY AND RESTRAINT MAGNET THEREFOR Bert v. Hoard, Portland, one, assignor to West inghonse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 10, 1942, Serial No. 461,577

My present invention relates to an improved type oi. electromagnet, which may be constructed in any one or several diflerent forms, with slightly different characteristics; and the invention also has relation to a particular differential altemat lug-current relay utilizing one or a plurality of these electromagnets in an apparatus and system which is particularly useful in differential busprotection involving a large number of feeders, and for other uses.

My improved electromagnet or electro-responsive device consists of a, cylindrical magnetic core surrounded by a coil and having two flat polepieces, one at each end the core and coil, the pole-pieces extending out from the core and terminating in tapering ends; the movable part of the relay or other electro-responsive device being in the form of a thin fiat rectangular magnetizable armature spaced from the coil in parallel relation thereto, and movable toward and away from the coil, between the two tapered ends of the polepieces. The tapering of the ends of the pole- 24 Claims. (Cl. 175-294) Among the objects and advantages obtainable by my invention may be mentioned simplicity of manufacture, a high torque with a small weight or inertia, which means a high speed of operation, a high torque with a small volt-ampere requirement, which means high eiiiciency and a small burden on the potential or current-transformer which supplies the device with energy, constancy of magnetic pull at all positions of the movable armature, or any other characteristic of the pull with respect to the position or movement of the armature, and responsiveness to either the first power or the square of the magnetizing-current, depending upon the nature of the core which is utilized. In the differential-relay embodiment, my invention makes it possible to differentially protect an eight-circuit bus or other multi-ter-' minal apparatus, with a single relay per phase, and with a very simple system of wiring connecgo tlons, accomplishinga variable fatio difierential pieces makes it possible to maintain a constant pull on the armature at all positions of the armature, or to maintain a radually increasing or decreasing pull, as the armature moves in either direction. By an alternative construction which makes provision for progressive saturation in the core, the relay or electro-responsive device can be made to develop a force or pull which is practically exactly proportional to the first power of the magnetizing current, over a wide range of current-values from zero to over 120 amperes, as contrasted with the force proportional to the square of the current, which is developed in most current-responsive devices.

My new electromagnet or electro-responsive device is extremely compact, and lends itself admirably to being associated either with other deg my invention consists in the apparatus, parts,

combinations, circuits, systems and methods hereinafter described and claimed and illustrated in the accompanying drawing, wherein:

Figure 1 is a plan view of a variable-ratiodiii'erential relay embodying my invention,

Fig. 2 is an elevational view thereof, with parts broken away to illustrate the construction,

vices of the same nature, or with diflerent kinds 4o ofrelay-elements, with one or more or the novel electromagnet-devices utilized as restraint-elements, for example.

In particular, my present invention hasreference to a saturating type of current-responsive relay having two parts, an operative-iorce-producing part which responds linearly to the current up to a certain value of current, after which the response falls off due to saturation, and a restraint-force-producing part comprising a plurality of my novel electromagnets utilized as restraint-elements responding linearly to the current in individual feeders, with the totalized bus-- current being supplied to the Operating-coils of the operating part of the current-responsive relay.

be utilized as alternatives of the construction Fig. 3 is a diagrammatic view of the circuitconnections for the difierentlal relay shown in Figs. 1 and 2, with diagrammatic representations explanatory oi the construction and operation of the several parts of the relay.

Figs. 4 and 5 are detail views of different poleplece shapes for the electromagnet, which may be utilized to obtain difler'ent torque-response characteristics with respect to the position or movement of the movable armature, and

Figs. 6 and 7 are detail side views of different forms of electromagnet-constructions whlchmay shown in Figs. 1, 2 and 3.

The diiferential relay shown in Figs. 1 and 2 consists essentially of two diil'erent parts, associated with a vertical shaft [0' carrying a movable contact-arm ll cooperating with stationary contacts I! which are connected in the relaycontrolled circuit IS. The upper part of the relay consists of eight (or other number) of my special electromagnets Ml to M8, arranged (as shown) in two tiers l 4 and I, one above the other.

The bottom part of the relay consists of a special" high-speed induction-disk element 18, of a type which is specifically described, and which is claimed, in my copending application Serial No. 456,901, filed September 1, 1942, for High-speed relays, now Patent No. 2,379,905, issued July 10,

The eight magnet-structures Ml to M8 of Figs. 1 and 2 are all alike, and they are also shown in side-elevational view in Fig. 3. As shown in Fig. 3, they are utilized as restraint-elements responsive to the currents in individual feeders Fl to F8, which are connected to a, common bus B; while the actuating or operating-torque of the relay is provided by the disk-type current-responsive element l6 which is energized in response to the summation or total of all of the feeder-currents as supplied by the respective current-transformers CTI to GT8.

Each of the electromagnets, such as the electromagnet M4, comprises a core which is made up of a thin-walled steel or other magnetizable tube 20 which is tapped throughout its length, thus making a series of notches along the face of its bore or inner diameter. Iron or other magnetizable screws 2| and 22 enter the tapped tube 20, from the respective ends thereof, and thus provide an additional iron area near the ends of the tube, the central portion of the tube beinghollow, and not filled with magnetizable material. The ta ped tube 20 is surrounded by an energizing-coil 28 for the electromagnet. Abutting against the respective ends of the tapped tube 20, are two fiat pole- pieces 24 and 25, which extend out away from the core 20 and from the coil 28, and which terminate in diagonally cut ends 28, as shown in plan view in Fig. 1. The pole- pieces 24 and 25 may be held in place by the screws 2| and 22, respectively, and one of these screws, as 22, may also be utilized to mount the device on a stationary supporting-plate 21, as shown in Fig. 2. Preferably, the pole- pieces 24 and 25 should be slotted, as shown at 24' and 25' to reduce theeddy-current losses resulting from the alternating flux in the core 20.

The movable element of" each electromagnet, such as the electromagnet M4, consists of an armature 28 which is in the form of a thin flat rectangular piece of magnetic material, mounted on' an arm 29 carried by the shaft l0, at right angles to the shaft. The armature 28 extends between the two tapered ends 28 of the two pole- pieces 24 and 25, with small airgaps 8| between the respective ends of the armature 28 and the inner surfaces of the pole- pieces 24 and 25, respectively. The armature 28 is disposed in a plane substantially parallel to the core 20, and the core 20 is vertical, or parallel to the shaft in which constitutes the pivot-point for the armature-arm 29, so that the armature 28 moves in a direction toward and away from the core 20 and its magnet-coil 23.

The bottom half of the relay shown in Figs. 1 and 2 constitutes the current-responsive membar [6 which provides the operating torque for turning the shaft III in a direction necessary to make the relay respond, as by closing its contacts il-I2. The current-responsive operating-element I6 comprises a disk 88 which is carried by the shaft [0, at right angles thereto, and is actuated upon by two multipoiar stator-portions 84 and '35, respectively, one abovethe disk 83 and the other below the disk 88.

The upper multipoiar structure 34 comprises four pole-pieces, each having a vertical tubular 4 magnetlzable pole-shank 88 extending parallel to the shaft [0. Each pole-shank 88 terminates, at its bottom end in a segmental magnetizable poleface portion 4| which is spaced from the upper surface of the disk 38 by an airgap 42. Each pole shank 88 terminates, at its upper end, in a ringshaped magnetizable yoke-member 48 which joins the upper ends of all four of the pole-shanks 88 of the upper multipoiar structure 84. The parts Just described can be held in assembled position,

.and also mounted on a horizontal support-plate 44, by means of bolts 45 which pass thro gh Poles 46 in the yoke-member 48, and also pass through the tubular pole-shanks 88, screwing into the pole-face pieces 4| of the respective poles of the upper multipoiar structure 84.

The lower multipoiar structure is similar, except that the tubular pole-shank portions 88" are thicker, and the energizing-coils 48' are larger, consisting of more turns suitable for voltage-responsive energization as distinguished from the current-coils of the upper multipoiar structure. In the lower multipoiar structure, also, the yoke-member 43' is a solid disk, as distinguished from the ring-structure 48 of the upper multipolar member.

-ly saturable autotransformer 50.

The several pole-pieces of the upper and lower multipolar structures 84 and 85 are displaced with respect to each other in substantially quadrature space-relationship, as indicated in Figs. 1 and 2, and also as diagrammatically illustrated, in a development view, in Fig. 3.

I As shown in Fig. 3, the current-coils 48, and the voltage-type coils 40 of the operating-element 48 are energized from a special, progressive- The transformer 50 has an iron core 5|, one portion of which is provided with a taperingly reduced cross-section as indicated at 52, so as to produce progressive saturation, starting at low values of the exciting-current which traverses the transformer-winding 53. Thus, as the transformercurrent gradually increases from zero, the narrowest portion of the restricted section 52 firstsaturates, and this saturation creeps along for a greater and greater distance, as the excitingcurrent increases. The autotransformer has a high-current intermediate tap 54 which is utilized to energize the current-windings 40, and a lowcurrent terminal 55 which energizes the voltagetype current-responsive coils 48' through a phase-adjusting resistor 55.

In the operation of the apparatus and circuitconnections shown in Figs. 1, 2 and 3, attention will be directed, first, to the electromagnets, such as the electromagnet M4. The movable armature 28 has its ends presented (through airgaps) to the triangular or tapered portions 28 of the two pole- pieces 24 and 25 of the electromagnet. Because of the triangular or tapered configuration of these pole-piece ends, the flux flowing from each pole-piece to the end of the armature 28 is larger, on the side of the armature which is presented toward the magnet-core 28, than on the side of the armature furthest away from said core. The flux on the core side tends to pull the armature toward the core, with a force proportional to the square of this flux, while the flux on the opposite side tends to pull the armature away from the core, or toward the pointed tips of the ends of the pole-pieces, with a force which is again proportional to the square of the flux. Because of the tapered shape of each poleforce which is approximately proportional to the square of the flux-density, times the difference between the cross-sectional areas of the effective airgaps on the two sides of the armature 28' that is, on the side towards the. core 28, and on the side away from the core 28, making due allowancefor the fringing of the flux in the airgap, on each side of the armature 28.

If the tapering of the end-portion 28 of the pole pieces 24 and 25 is uniform, as shown in Fig. l, and if the effective radius of the turningmoment operating on the armature-supporting arm 28 does not materially change throughout the range of movement of the armature 28, then the total effective operating-moment which tends to draw the armature 28 toward the core 28 will be constant at all positions of the armature 28, for any given strength of energization of the magnet-coil 23. If the efiective turning-moment operating on the armature-supporting arm 28 changes during the movement of the armature 28, this change in turning-moment can be compensated for by suitably shaping the pole-pieces, as shown in Figs. 4 and 5.

It will be readily understood that if it is desired to have a larger force, which remains substantially constant over a smaller distance of movement of the armature 28, the tapering of the tapered ends 26 of the pole-pieces can be made more sharp than the tapering shown in Fig. 1, so that the airgap-sectlon increases at a faster rate, as the armature moves toward the core of the magnet. If it should be required that the torque should increase, as the armature moves toward the core, the shape of the pole-pieces should be modified so that the rate of increase of the airgap-section increases, as the armature approaches the core, as shownat 26' in Fig. 4. If it should be required that the torque should decrease, as the armature is attracted toward the core, the pole-piece shape should be modified so that the rate of change of the airgap-section, or the rate of change of this width of each pole-piece, shall decrease, as the armature approaches the core, as shown at 26" in Fig. 5.

In any event, it will be noted that the electromagnet M4 is simple to make, and that it provides a means whereby the operating-force produced by the magnet shall be either substantially independent of the armature-position, or

mils, or less, and about 60 mils, another important advantage accrues, as a result of the fringing of the flux at the airgaps 8!, as diagrammatically indicated at I! in the electromagnets shown in Fig. 3. From this figure, it will be seen that the fringing, or spreading out of the flux as it leaves the respective ends of the armature 28 and enters the tapered polepieces, on both the core side of the armature 28 and the opposite side of the armature, produces the same effect as if the armature were several times thicker than it is, but without the fringing of the magnetic flux. Thus the fringing causes the airgap-area to become several times, or at least four or five times, the iron area presented by the respective ends of the thin armaturemembers 28.

Since the magnetic forces operative upon-the armature are proportional to the square of the total flux, and since the amount of fiux is proportional to the effective airgap area, it will be noted that this fringing of the flux, which produces at least a fourfold increase in the airgaparea, produces a corresponding increase in the amount of the magnetic pull or attraction, thus producing a larger force, in comparison to the mass or inertia of the armature, than would be the case without fringing. This effect has two important advantages, in that it increases the operating-force, and hence the sensitivity of the electro-responsive device, for any given voltampere burden on the potential or currenttransformer which supplies energy to the device,

in accordance with any other predetermined torque-characteristic with respect to armatureposition.

The rectangular-shaped magnetizable armature-piece 28 should have as small a cross-section as possible, so as to decrease the mass or inertia of the movable element, particularly in electromagnet-structures where a high speed of operation is desirable, which means a large ratio of operating-force to inertia. Thus, the relay or electromagnet would be designed so that the cross-section of the main part of the armaturepiece 28 will just begin to approach saturation,

at the full rated voltage of the magnet-coil 23,

if the electromagnet is utilized as a voltage-responsive device, or to approach saturation at the maximum expectable current therein, or at any smaller predetermined current-value, if the electromagnet is utilized as a current-responsive device.

When the armature-piece 28 is made of a sheet of iron or steel having a thin thickness, such as the thickness of one ordinary lamination, which is 15 mils, or a thickness of, say, between 15 and it also increases the ratio of force to inertia, which means an increased speed of operation.

In cases where still greater operating forces are desired, it is feasible to increase the effective thicknesses or cross-sections of the extreme ends of the armature-piece 28, without changing the sectional area of the main portion of the armature-piece. In this manner, the airgapsection can be increased, without materially increasing the mass or inertia of the armature. A convenient manner of carrying this idea into execution is indicated in the armature-piece 2B of Fig. 6, wherein the ends of the armature are .bent over, as indicated at 60 in Fig. 6. This modified form of construction of the armature, with bent-over ends 68, may be utilized in any of the embodiments of my invention.

Thus far, I have been specifically discussing the torque-characteristics of the electromagnet M4 with reference to the armature-position and the armature-inertia, without reference to the effectiveness of the energization or magnetization of the electromagnet.

Reference to Fig. 3 will show that the screwthreads which are tapped into the thin walled steel tube 20 which is utilized for the core of the electromagnet produce a plurality of wedgeshaped sectional areas, or an iron-section which progressively increases and decreases along the length of the core, at least along the central portion of the tapped core-tube 20, which is not filled with the iron screws 2| or 22. By a thinwalled, tapped, tube 20, in this case, I thus mean a tube in which the walls are thin enough so that the threads which are tapped into the tube will be fairly deep, as compared to the thickness of the tube-walls, so that a fairly large proportionate decrease in the effective section shall be produced by the threads. I also contemplate that the threads shall be triangular-shaped, rather than square-shaped, or of any other shape. It is apparent that the notches produced 7 by the screw-threads will produce portions of the tube walls, at spaced points along the length 01' the tube, which will progressively saturate, with increasing magnetizing current, until the thickest section is saturated. The design is such that the saturation commences at a small value or the energizing-current, and progresses in its extent, as the energizing-current increases.-

The exact characteristics of the saturationefiects in the magnets Ml to M8 can conveniently be determined by the length or the iron screws 2| and 22' which enter the tube 20 from the respective ends thereof. In one particular electromagnet, tests have shown that when each screw enters about 25% of the tube length, the

flux increases so slowly in response to increases in the exciting-current, that the square of the flux, which determines the magnetic pull developed by the electromagnet-structure, responds substantially rectilinearly to the current, for all current-values from zero to 120 amperes, thus producing a response to the first power or the current, as distinguished from a response to the square of the current, which would be obtained if no saturation were present. The saturationefiects can be strengthened by having each screw enter only a shorter distance, say about of the tube length, whereas, if each screw enters a greater distance of the tube-length, say about 40%, the magnetic torque is approximately double the value which it would have when the screw enters the tube about 10% of the total tube-length, although the current-responsive curve is not quite as straight for all currentvalues as when each screw enters about 25% of the tube-length. This constitutes a simple method of controlling the torque of the electromagnet, although the torque can also be controlled by changing the number of turns on the coil 23.

The tapered eiTect of the progressively saturable iron section, which is produced by the screw-threads tapped into the thin-walled steel tube 20, may be produced in other ways. Thus, in Fig. 6, the core 20 is produced by machining down the outer diameter of the tubular or cylindrical core 20', to produce a single reduced-section point Bl near the center of the core, which gradually increases in diameter or cross sectional area toward the ends of the core. In this manner, by properly choosing the rate at which the coreseotion increases from its .most restricted point, substantially the same saturatlon-efiects can be obtained as have already been described, thus producing an electro-responsive device which produces an operating torque which is either linearly responsive to the first power of the current, or responsive in accordance with some other predetermined function.

In many applications of my electro-responslve device, such as M4, the rectilinear, or first-power response is important. tions, however, it is desirable to have the more sual-type of response, in which the force varies as the square of the current. In such a case, the core 20 may be made tohave a sufilcient thickness so that it will not saturate, as shown in Fig. 7, in which case the core may be a solid cylinder, rather than a tube, or if it is a tube, it will have 4 thick, non-saturable walls, and the inner bore of the tube could be either smooth or tapped, so long as the tapped screw-threads did not reduce the core-section: sufiiciently to produce saturation.

In the particular application of my novel electromagnet-structure which'is shown in Figs. 1, 2

In many other applica-- and 3, the rectilinear response 01 each electromagnet to the first power or the exciting-current is quite important, because the electromagnets Ml to M8 are utilized to develop restraint-torques which are responsive to the currents in the respective feeders or terminals Fl to F8 of an alternating-current bus B, in a diflerential busprotecting relay in which an operating-force is produced in accordance with the vectorlal sum,.

or instantaneous totals. of the currents flowing into the bus at all of its terminals or feeders Fl to F8, regardless of whether those feeders are normally power-supplying feeders or load-feeders. .By making the individual restraint-torques responsive to the first power or the currents in the respective feeders or terminals, the sum-total of all the restraint, for any given total current, will be the same regardless of the distribution of that current along the several terminals or feeders Fl to F8, whereas, if the restraint-torque were responsive to the square of the currents in the respective feeders, the total amount of restraining torque of all eight electromagnets would be eight times more, if all of the current were carried by a single feeder, than if the total-current were divided equally among the eight feeders.

In the differential relaying device shown in Figs. 1, 2 and 3, it is desirable that the operatingforce, by which is meant the force tending to actuate the relay in opposition to the back-pull of the restraining forces, shall also be responsive to the first power of the current (or other electrical quantity to which the relay is difierentially responding), but it is also desirable that the operating-force-response shall fall off, at certain excessive current-values, so that the operating force becomes non-linearly responsive to the current at these high current-values, thus giving my differential relay the well-known variableratio response-characteristic.

In Figs. 1, 2 and 3, the current-responsive opcrating-element 16, which is shown at the botcrating-element it of the relay, the induction disk forces are made to be responsive to substantially the first power of the current, rather than responding to the second power of the current, or to the product of the fluxes produced in the upper and lower magnet- structures 34 and 35, times the cosine of the angle between them, as

. in ordinary induction-type instruments.-

The falling oil of the first-power current-response of the operating-torque, at heavy currentvalues, is attained, in Figs. 1 to 3, by building the upper magnet-structure 34 with magnetic crosssections which are sumciently small to produce saturation, commencing with any desired current-value, this being illustrated in Fig. 2, by

showing the pole-piece tube 38 of the upper magnet-structure 34 as being s aller, in thickness or cross-section, than the corresponding pole-shaped tube 33' of the lower magnetic structure 35, and also by showing the upper yoke-member 63 as being ring-shaped, so as to have a smaller effective sectional areawith respect to circumferentially flowing fluxes, as compared to the solid or diskshaped construction of the lower yoke-member 48'. 4

As a result of the structure and combination which I have just described, the differential relay of Figs. 1, 2 and 3 develops an operating-torque, tending to make the relay respond and close its contacts "-42, with a substantially rectilinear response to the first power of the total current flowing into the bus B, summated over all of its terminals F! to F8, for current-values up to the point where the upper magnetic structure 34 of the operating-element l8 begins to saturate, at which time the current-response will fall off, and the operating-torque will thereafter increase considerably more slowly than the current-increases beyond this saturating point.

The normal linear response to current is obtained by the progressive saturation of the current-transformer 50 which feeds the operatingelement I8, and at about the time when the upper set of poles 38 begins to saturate, the currenttransformer 80 saturates rapidly. Simultaneously with the decrease in the rate of change of the magnitude in the fluxes, during continued increases in the current, as a result of saturation, I also obtain a. decrease in the angle between the upper and lower fluxes, in the poles 38 and 38' of the operating-element it, due to the saturation of the upper poles 38, which still further reduces the torque produced by the operatingeiement I8. Consequently, during and after the flnal saturation of the current-transformer 50, practically no increase in torque occurs, in the operting-eiement IS, with increasing bus-current.

On the other hand, the several restrainingmagnets Ml to M8 develop restraining-forces which are substantially rectilinearly responsive to the first power of the respective terminal-currents, for all current-values. Thus the proportion or ratio of the total restraining-force to the operating-force is constant up to the point when saturation begins to occur in the upper magnetstructure of the operating-element l8, while beyond this point the ratio of restraint-torque to operating torque becomes larger, because of the falling off of the operating torque with respect to very large currents. This produces the variable-ratio effect which is so desirable in many types of differential relays.

When a fault occurs on the bus B, the summation, or vectorial sum, of all of the currents entering the bus through all of its terminals Fi to F8 will be equal to the fault-current, and the relay is made so that the operating-force which is developed, under such conditions, will be sum- I ciently strong to actuate the relay, even though the upper magnet-structure 34 of the operatingelement It is strongly saturated under those conditions. In other words, the operating element I 8 develops a greater operating-force, even under saturation-conditions, than the sum of the proportional to the current in its feeder, so that the sum-total of the eight restraining-forces is very large, while the operating force developed by the operatingelement i8 will be theoretically zero, because the instantaneous or vectorial sum of the eight said currents will be zero, there being no fault on the bus B, so that all current which enters the bus must leave the bus.

However, it is well known that the currenttransformers CTI to GT8 will not, in general, be absolutely perfectly matched with respect to each other, even at normal load-current values, while, under abnormal current-flow conditions of faultmagnitude, the current-transformers CT! to GT8 will inevitably saturate, in any actual commercial embodiment, and they will begin to saturate at diiferent current-values, and in diflerent degrees or' saturation-characteristics, so that the vectorial sum of the secondary currents on the eight current-transformers CTI to GT8 will not be equal to zero, in the average case, but will indicate the presence of a fictitious summation-current which is not really present in the bus-terminals TI to T8, but which is actually present in the operating-element l8 of the differential relay. Because of this fictitious fault-current in the operating-element it of the relay, resulting from saturation of the line-current transformers CTI to 0T8 during so-called through-fault conditions, or fault-conditions outside of the protected bus B, the operating element I6 is designed to produce saturation in its upper magnet-structure 34, so that it will not develop an operatingforce suflicient to overcome the restraint of the eight restraining magnets Ml to M8 under such conditions. The introduction of saturation in the upper magnet-structure 34 of the operatingelement It makes it possible to increase the sensitivity of the diflerential relay with respect to its response to faults on the protected bus B, without introducing erroneous responses to true-fault conditions.

The combination of an electromagnet-type restraint-device or devices, and an induction-type operating-force-producing element is particularly advantageous, in differential relay-devices which are utilized to protect transformers, where heavy asymmetrical magnetizing-currents flow into the transformer upon the flrst instant of application of power thereto, as well as being advantageous in the general case, in which fault-currents, in general, are apt to be asymmetrical in nature, during the first few half-cycles of a fault, because of the occurrence of the fault at different times in the voltage-wave of the line-voltage, and at different phase-relations between the faultcurrent and the line-voltage. The result of these asymmetrical currents, whether transformermagnetizingcurrents or fault-currents, is to produce the same effect as if a fairly large direct current were superimposed upon the alternatingcurrent component of the asymmetrical current, this direct-current starting out with a large value and dwindling to zero after a few cycles, depending upon the conditions of the circuit.

In my novel differential relay, it will be observed that the restraining-torque, which prevents faulty relay-operation, is responsive to the instantaneous magnitudes of the current, that is, to the direct-current component plus the instantaneous value of the alternating-current component, at any moment, whereas the operatingcurrents, which tend to produce a relay-response, being dependent upon the development of eddycurrents in an induction-disk or the equivalent, are responsive, selectively, practically to only the the actual structure of the electromagnet-element, and in respect to the combination which constitutes the differential-relay structure and system, I wish it to be understood that many changes in specific embodiments, and permutations of different features, involving omissions as well as substitutions or additions, may be made as will be obvious to those skilled in the art. I desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their language.

I claim as my invention:

1. An electromagnet-structure comprising a magnetizable core-member, an energizing-coil means surrounding the core-member, a hat polepiece at each end or the core-member, each ilat pole-piece having a tapered end extending out away from one side of the core-member, a movable armature comprising a, fiat rectangular piece of magnetic material disposed between the two tapered ends of the two pole-pieces and separated therefrom by airgaps, said rectangular armature-piece being substantially parallel to the core and to the coil-means, and means for movably supporting said armature piece to move toward and away from said core and said coilmeans between the tapered ends oi. the polepieces, whereby the tapering 01' said pole-piece ends causes the magnetic flux to draw the armature-piece toward said core and said coil-means.

2. The invention as defined in claim 1, characterized by the armature-piece having thickened ends presenting a greater cross-sectional area to the airgaps than the cross-sectional area oi the rest of the armature-piece.

3. The invention as defined in claim 1, characterized by the armature-piece being sufilclently thin to cause the magnetizable material thereof to be approaching saturation under an operating condition of the device, and also to cause fiuxfringing to increase the efiective airgap-sectlon to at least four times the section oi the magnetizable armature-piece.

4. The invention as defined in claim 1, characterized by said magnetizable core-member h'aving a section which varies at different points along the length of the core so as to provide progressive saturation as the coil-energization increases.

5. The invention as defined in claim 1, characterized by said magnetizable core-member having a section which varies at diil'erent points alon the length of the core in such manner and degree as to produce an operating-force, on the armature, which varies substantially in accordance with the first power or the energizing-current in the coil-means, throughout a material operatingrange of current-values.

6. The invention as defined in claim 1, characterized by said magnetizable core-member comprising a thin-walled magnetizable tube tapped so as to provide a notched bore in such manner as to provide progressive saturation in the tube, on increased coil-energization.

7. The invention as defined in claim 1, characterized by said magnetizable core-member comprising a thin-walled magnetlzable tube tapped so as to provide a notched bore in such manner as to provide progressive saturation in the tube, on increased coil-energization, and a magnetizable screw extending partway into the tapped tube from at least one end thereoi, leaving a region beyond the inner end of the screw where the tube-material progressively saturates.

8. A multi-torque alternating-current lectroresponsive device comprising a first torque-producing part and a second torque-producing part, said first torque-producing part comprising at least one electromagnet-structure oi the type defined in claim 1, and said second torque-producing part-comprising an induction-type electrorespcnsive device.

9. A difierential relay for a multi-terminal electrical device to be protected, said relay comprising a cumulative electro-responsive operatingmeans for all of. the terminals to be protected, and a plurality of electro-responsive restrainingmeans, a restraining-means being provided for each one of the plurality of terminals to be protected; characterized by said operating-means being of a type which develops, in the relay. an operating-force responsive, at times. substantially to the first power of a summation of the terminalcurrents of the device to be protected, and each restraining-means being of a type which develops, in the relay,'a restraint-force responsive substantially to the first power of its own individual terminal-current.

10. An alternating-current differential relay for a multi-terminal altemating-current device to be protected, said relay comprising a cumulative alternating-current operating-means for all of the terminals to be protected, and a plurality oi. electro-responsive restraining-means, a restraining-means being provided for each one of the plurality of terminals to be protected; characterized bysaid operating-means being of a type which develops, in the relay, an operating-force selectively responsive to the alternating-current component of the vectorial sum of the terminalcurrents, to the substantial exclusion of any direct-current component thereof, and each restraining-means being of a type which develops, in the relay, a restraint-force responsive to both the direct-current component and the alternating-current component of its own individual terminal-current.

11. An alternating-current differential relay for a multi-terminal alternating-current device to be protected, said relay comprising a cumulative altemating-current operating-means for all of the terminals to be protected, and a plurality of electro-responsive restraining-means, a restraining-means being provided for each one of the plurality of terminals to be protected; characterized by said operating-means being of a type which develops, in the relay, an operating-force responsive substantially to the product 01 two out-of-phase' alternating fluxes times a function of the phase-angle between them, and each restraining-means being of a type which develops a restraint-force responsive substantially to the square of the instantaneous value of a single flux; in combination with flux-producing means, associated with said operating-means, for producing two out-of-phase alternating fluxes each of which is responsive, at times, substantially to the square root of the vectorial sum of the terminal-currents, and flux-producing means, associated with each 01 the restraining means, for producing a flux 13 which is responsive substantially to the square root of the particular terminal-current individual to that restraining-means.

12. A diiierential relay for a multi-terminal electrical device to be protected, said relay comprising a cumulative electro-responsive operating-means for all of the terminals to be protected, and a plurality of electro-responsive restrainingmeans, a restraining-means being provided for each one of the plurality of terminals to be protected; characterized by said operating-means being of a type which develops, in the relay, an operating-force responsive, at times, substantially to the first power of a summation of the terminalcurrents of the device to be protected, and each restraining-means being of a type which develops, in the relay, a restraint-force responsive substantially to the square of the instantaneous value of a single flux; in combination with flux-producing means, associated with each of the restrainingmeans, for producing a flux which is responsive substantially to the square root of the particular terminal-current individual to that restrainingmeans.

13. An alternating-current diflerential relay for a multi-terminal alternating-current device to be protected, said relay comprising a cumulative alternating-current operating-means for all of the terminals to be protected, and a plurality of electro-responsive restraining-means, a restraining-means being provided for each one of the plurality of terminals to be protected; characterized by said operating-means being of a, type which develops, in the relay, an operating-force responsive substantially to the product of two out-of-phase alternating fluxes times a function of the phase-angle between them, and each restraining-means being of a type which develops a restraint-force responsive substantially to the first power of its own individual terminal-current; in combination with flux-producing means. associated with said operating-means, for producing two out-of-phase alternating fluxes each of which a is responsive, at times, substantially to the square root of the vectorial sum of the terminal-currents.

14. An alternating-current differential relay for a multi-terrninal alternating-current device to be protected, said relay comprising a cumulative alternating-current operating-means for all of the terminals to be protected, and a plurality of electro-responsive restraining-means, a restraining-means being provided for each one of the plurality of terminals to be protected; characterized by said operating-means being of a type which develops, in the relay, an operating-force responsive substantially to the product of two out-of-phase alternating fluxes times a function of the phase-angle between them, and each restraining-means being of a type which develops a restraint-force responsive substantially to the square of the instantaneous value of a single flux; in combination with flux-producing means associated with said operating-means, and flux-producing means associated with each of the restraining-means, each of said flux-producing means including a progressively saturable magnetizable-core portion having I cross-sections which increase progressively, for a certain distance along the length of that core-portion. from a minimum sectional area that begins to saturate at a very low value of the magnetic flux.

15. A differential relay for a multi-terminal electrical device to be protected, said relay comprising a cumulative electro-responsive operating-means for all of the terminals to be protected,

and a plurality of electro-responsive restrainingmeans, a restraining-means being provided for each one of the plurality of terminals to be protected; characterized by said operating-means being of a type which develops, in the relay, an operating-force responsive, at times, substantially to the first power of a summation of the terminalcurrents of the device to be protected, and each restraining-means being of a type which develops, in the relay, a restraint-force responsive substantially to the square of the instantaneous value of a single flux; in combination with fluxproducing means, associated with each of the restraining-means, including a progressively saturable magnetizable-core portion having crosssections which increase progressively, for a certain distance along the length of that core-portionffrom a minimum sectional area that begins to saturate at a very low value of the magnetic flux.

16. An alternating-current differential relay for a multi-terminal alternating-current device to be protected, said relay comprising a cumulative altemating-current operating-means for all of the terminals to be protected, and a plurality of electro-responsive restraining-means, a restraining-means being provided for each one of the plurality of terminals to be protected; characterized by said operating means being of a type which develops, in the relay, an operatingforce responsive substantially to the product of two out-of-phase alternating fluxes times a function of the phase-angle between them, and each restraining-means being of a type which develops a restraint-force responsive substantially to the first power of its own individual terminal-current; in combination with flux-producing means, ,associated with said operating-means, including a progressively saturable magnetizable-core portion having cross-sections which increase progressively, for a certain distance along the length of that core-portion, from a minimum sectional area that begins to saturate at a very low value of the magnetic flux.

17. An alternating-current difierential relay for a multi-terminal alternating-current device to be protected, said relay comprising a cumulative alternating-current operating-means for all of the terminals to be protected, and a plurality of electro-responsive restraining-means, a restraining-means being provided for each one of the plurality of terminals to be protected; characterized by said operating means being of a type which develops, in the relay, an operating-force responsive substantially to the product 01' two out-of-phase alternating fluxes times a function of the phase-angle between them, and each restraining-means being of a type which develops a restraint-force responsive substantially to the first power of its own individual terminal-current; in combination with flux-producing means, associated with said operating-means, comprising transformer-means including a progressively saturable magnetizable-core portion having crosssections which increase progressively, for a certain distance along the length 01 that core-portion, from a minimum sectional area that begins to saturate at a very low value of the magnetic flux.

18. An electro-responsive device, comprising a flux-producing means including a progressively saturable magnetizable-core portion having crosssections which increase progressively, for a certain distance along the length of that core-portion, from a minimum sectional area that begins of the flux produced by said flux-producing means; characterized by said transformer-means including a progressively saturable magnetizablecore portion having cross-sections which increase progressively, for a certain distance along the length of that core-portion, from a minimum sectional area that begins to saturate at a very low value of the magnetic flux.

20. An electro-responsive device, comprising a flux-producing means including a magnetizable core-portion comprising a thin-walled magnetizabletube tapped so as to provide a notched bore in such manner as to provide progressive saturation in the tube, that begins to saturate at a very low value of the magnetic flux, and a force-producing means of a type which is substantially dependent upon the square of the flux produced by said flux-producing means.

21. The invention as defined in claim 20, in

combination with a magnetizable screw extending partway into the tapped tube from at least one end thereof, leaving a region beyond the inner end of the screw where the tube-material progressively saturates.

22. An alternating-current electro-responsive device of a type which develops a force responsive substantially to the product of two out-of- Dhase alternating fluxes times a function of the phase-angle between them, in combination with an alternating-current control-source, and fluxproducing means for producing, in said electroresponsive device, two out-of-phase alternating fluxes each of which is responsive, at times, substantially to the square root of a current of said control-source.

23. An altemating-current electro-responsive device of a type which develops a force responsive substantially to the product 01. two out=of-phase alternating fluxes times a function of the phaseangle between them, in combination with fluxproducing means for producing two out-of-phase alternating fluxes in said electro-responsive device, said fiux-producing means including a progressively saturable magnetizable-core portion having cross-sections which increase progressively, for a certain distance along the length of that core-portion, from a minimum sectional area that begins to saturate at a very low value of the magnetic flux.

24. An alternating-current electro-responsive device of a type which develops a force responsive substantially to the product of two out-of-phase alternating fluxes times a function of th phaseangle between them, in combination with fluxproducing means for producing two out-of-phase alternating fluxes in said electro-responsive device, and transformer-means for supplying energizing-current to said flux-producing means, said transformer-means including a progressively saturable magnetizable-core portion having crosssectlons which increase progressively, for a certain distance along the length of that core-portion, from a minimum sectional area that begins i010 saturate at a very low value of the magnetic BERT V. HOARD.

REFERENCES (CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 928,516 Hellmund July 20, 1909 1,193,678 Fowle Aug. 8, 1916 1,222,431 McCarthy Apr. 10, 1917 1,236,177 Jacobs Aug. 7,1917 1,273,940 Smith July 30, 1918 1,503,090 Carichofl July 29, 1924 1,610,744 Carichofl Dec. 14, 1926 1,648,674 Carichofi Nov. 8, 1927 1,740,536 Breisky Dec. 24, 1929 1,906,027 Wahl Apr. 25, 1933v 1,907,804 Hausman et al. May 9, 1933 2,110,673 McConnell Mar. 8, 1938 2,110,676 Prince Mar. 8, 1938 2,240,677 Sonnemann et al. 1 May 6, 1941 2,246,548 Sonnemann June 24, 1941 2,303,442 Draper Dec. 1, 1942 2,318,359 Bellows May 4, 1943

Images