US2071857A - Broad range time limit relay - Google Patents

Description

l R. M. SMITH BROAD RANGE TIME LIMIT -RELAY Filed 001;. 13, 1931 2 Sheets-Sheet 1 Feb. 23, 1937.

WITNESSESI Feb. 23, 1937. R M SMITH BROAD RANGE TIME LIMIT RELAY Filed Oct. 13, 1931 2 Sheets-Sheet 2 I I Isaak/1 Per 'em Current ma zoo nu 40a su /ooo Per em Current ATTO Patented Feb. 23, 1937 UNITED sTATEs PATENT OFFICE BROAD RANGE TIME LMT RELAY Roy M. Smith, North Arlington, N. .1., assignor to Westinghouse Electric d: Manufacturing Com pany, a corporation oi' Pennsylvania Application October 13, 1931, Serial No. 568,827

7 Claims.

with a modified or partially inverse form of such time characteristic. This preference for induction-disc type relays is due mainly to the superior accuracy and permanence oi calibration made possible by the induction principle, and any relay which departs from this principle of operation must necessarilyeiect a superior protection and incorporate Aadditional novel and advantageous characteristics. i

Referring to the known types of induction relays, it may be noted that the usual preference has been for a at time-current-characteristic curve, whereby the operating time of the relay is made to be independent of the magnitude of the short-circuit current. 'I'he main reason for this 1 preference was due to the fact that relatively little was known concerning an accurate method of calculating short-circuit currents, and this didiculty has only been surmounted in very recent years. The introduction and popularization of symmetrical component methods of calculating unbalanced fault currents has made it possible to determine quite accurately the conditions obtaining during fault conditions. g

In accordance with the introduction of a suitable method for calculating short-circuit currents, attempts have been made to use the inverse portion of existing time-current-characteristiccurves, but the general adoption of such relay characteristics has been diilicult in view of the fact that all possible time-current-characteristic curves of induction type relays have an inverse portion of quite restricted range.

The use of deiini'te time, or over-current relays having a. dennite time-current-characteristic curve, results in a very serious disadvantage in that the application oi such relays to a section- .alized powersystem requires that the timing of the relays must be properly cascaded with the result that those relays nearest to the generating source or sources have to be set for a prohibitively (Cl. 20D-97) long denite time of operation. This disadvantage has resulted in an increased demand for an inverse tlme-current-characteristic curve in a relay.

Furthermore, the tendency in the relaying of all electric systems is toward quicker clearing times, as is evidenced by the recent development of e'xtremely high speed protective relays, and the objection to cascaded relay settings is at once apparent. j

It is an object of the present invention, therefore, to provide a protective relay incorporating a time-current-characteristic curve which may be made inverse over substantially the entire operating range. i

Another object of the present invention is to provide a reliable relay which may be utilized either as a denite time remlay or an inverse time relay, as desired.

Another object of the present invention is to provide a relay having a suitable actuating means therefor, and means for .imparting an inverse time characteristic to the relay through substantially the entire operating range thereof.

A further object of the present invention is to provide a relay having a time-current-characteristic curve such that the ratio of the current increment and the time decrement maybe made substantially constant throughout the entire operating range of the relay.

A further object of the present invention is to provide an accurately responsive relay of a flexible character such that any desired inverse time-current-characteristic curves may be obtained in accordance with any particular system conditions.

Further objects and advantages of the present invention will become readily apparent to those skilled in the art by reference to the following description of one embodiment of the present invention.

In the drawings:

Figure 1 is a perspective view of a relay4 de- -signed in accordance with the principles of the the proper mounting of the relay elements. The

- main operating element 2, of the relay, comprises an operating winding 3 mounted on a suitable bracket member 4, the bracket member 4 being held in xed position with reference to the base I by means of a screw 6. The operating winding 3 is adapted to be held in position by means of vertical plate member portions 1 and 8 associated with the bracket member 4.

A suitable iron core 9 is associated with the Winding 3 and is adapted to be moved laterally with respect to thewinding 3 in accordance with the degree of energization of such winding. The core 9 is secured to a pivotal contact member I I, which is pivotally mounted between horizontal plate members I2 and |3 associated with the bracket member 4.

'I'he pivotal contact member is provided with a suitable contact |4, which is adapted-to coact with, and bridge, stationary contact members I6 which are secured to an insulating block I1 and the block I1 is secured to the vertical plate member 'I by means of screws I8.

'Ihe pivotal contact member is provided with a downwardly extending' arm I9 which isy also adapted to be moved laterally with the solenoid coil 3 in accordance with the degreeof energization of such coil.

A spring 2| has one end thereof fastened to the vertical plate member 1 by means of Aan adjustable screw 22 and lock nuts 23, and the other end thereof associated with the downwardly extending arm portion I9 by means of an adjustable screw 24 and lock nuts 26. The spring 2| is, practically, as long as possible in order to provide a substantially' constant spring force through the entire travel required of the pivotal contact member II before the contact I4 effects the bridging of stationary contacts I6.

A second spring 21 is adapted to be connected to the lower end of the downwardly extending arm portion I9 by means of an adjustable screw 28 and lock nuts 29. 'I'he other end of the spring 21 is connected to one end of a rotatably mounted bar member 3|, and the spring 21 is made relatively short and strong in order to effect an appreciable normal tension. The bar member 3| is positioned on a rotatably adjustable shaft 32,

which is mounted for rotation between horizontal bracket members 33 and 34 of a bracket assembly 36 comprising the bracket members 33, 34 and vertical aligning members 31 and 38. The horizontal and vertical bracket members are secured together by means of cap screws 39. The rotatable shaft 32 is adjustably positioned with vrespect tothe bracket members 33 and 34 by means of adjustable screw bearings 33 and 34', respectively, and the bracket assembly 36 is secured to a base mounting 46 by means of screws 4|. The base mounting 40 is adapted to be secured to the base by any suitable means, not shown.

A ratchet-wheel 42 is mounted on the shaft 32 and is adapted to be rotated in accordance with the rotation of the shaft 32. Associated with the ratchet-wheel 42 are two diametrically opposed pawls 43 which are secured to a gear 44 included in a suitable reduction gear train, shown schematically in Fig. 2 as including gear 45. 'I'he pawl and ratchet-wheel assembly is so arranged that the gear 44 is adapted to be moved in accordance with the rotation of the shaft 32 only when the pivotal contact member is being actuated in a direction to effect the bridging of stationary contacts I6 by means of the contact I4.

When'the shaft 32 and associated bar member 3| are rotated in a clockwise direction, or in a direction to separate the contacts I4 and I6, the pawl and ratchet assembly is ineffective to move the gear 44 and its associated gear train.

A non-magnetic disc element 46 is mounted securely on a spindle 41, and the spindle 41 is `mounted for rotation between upper and lower bearing structures 48 and 49, respectively. The

upper bearing structure .48 is associated with the horizontal bracket member 33 included in the bracket assembly 36, and the lower bearing structure 49 is adapted to be associated with a raised portion 5| of the base mounting 40.

- The discA member 46 and the spindle 41 are associated with the gear train, including the gear 44, and are adapted to be rotated in accordance with the counter-clockwise movement of the shaft 32. A permanent magnet assembly 52 is assoc'iated with the disc member 46 and is secured to the base mounting 40 by means of screws 53. The permanent magnet assembly 52 may be of any usual construction, and is-shown as including two ordinary C-magnet structures rigidly secured together by means of clamp 54 and screws 56. A usual means for varying the damping flux of the permanent magnet assembly 52 is also provided, and is represented as including a laminated nut 51 and set screw 58. i

When the shaft 32 is rotated in a counterclockwise direction, the pawls 43 engage the ratchet 42, and the resultant movement of the gear train, including the gear 44,` effects the movement of 'the disc element 46 between the poles of the permanent magnet assembly 52. The provision of the disc element 46 and the permanent magnet assembly effects a damping of the movement of the shaft 32, and such damping may be varied by changing the position of the permanent magnet assembly 52 with respect to the disc element 46 and/or by moving the laminated nut 51 in a vertical direction.

However, when the shaft 32 is rotated in a clockwise direction, the pawls 43 are disengaged from the ratchet 42 with the result that the gear 44 is not moved in accordance with the rotation of the shaft 32 and ratchet 42. It follows, therefore, that the disc member 46 is not rotated between the poles of the permanent magnet assembly 52, and no damping of the movement of the shaft 32 results.

An initiating element 59, comprising a solenoid winding 6| and a solenoid core 65, is adapted to be securely positioned with respect to the base The winding element 6| .is mounted on a suitable bracket member 62 and is adapted to be secured in proper position by means of vertical bracket members 63 and 64 associated with the bracket member 62. The bracket member 62 is secured to the base by means of screw 66 in a similar manner to the position of the bracket member 4 associated with the main operating element 2.

A pivotal member 61 is pivoted between horizontal bracket members 68 and 69 associated with thebracket member 62. and is secured to the solenoid core for horizontal movement therewith. A block member 1| is secured to the vertical bracket member 63 by means of suitable screws 12 and is made similar to the insulating block I1 associated with the main operating element 2 in order to provide substantial symmetry in the appearance of the elements' 2 and 59.' A'

stop member 13 is secured to the block member 1I by means of screw 14 and is adapted to limit the position of the pivotal member 61 when the winding 6I of the initiating element 59 is deenergized.

The pivotal member 61 is provided with a downwardly extending portion or arm 16, and the member 61 is adapted to be normally held against the stop member 13 by means of a spring member 11. One end of the spring member 11 is adapted to be adjustably secured to the vertical bracket member 1 of the main operating element 2 by means of screw member 18 and lock nuts 19. The other end of the spring member 11 is adapted to be adjustably secured to the downwardly extending portion 16 of the pivotal member 61 by means of screw 8| and lock nuts 82. The spring member 11 is made relatively short, in comparison with the spring member 2|, and spring member 11'is also provided with a very high initial tension.

An adjustable screw -83 and lock nuts 84 are associated with the lower extremity of the downwardly extending arm portion 16 of the pivotal member 61, and the end of the screw is adapted to coact with the pivotal bar member 3|. By adjusting the position of the screw 83, the initial position of the bar member 3| and pivotal contact member II may be predetermined, and such -screw 83, associated with the pivotal member 61,

and the spring member 11 effectively limits the.,

`munten-clockwise rotation of the bar member 3| when the energizing winding 6I of the initiating element 59 is deenergized.

A terminal block 86 is'secured to the base I by means of screws 81, and is provided with a plurality of taps 88 associated with the energizing winding 3, such that the position of the contact screw 89 predetermines the number of effective turns included in the energizing winding 3 and/or the degree of energization of the winding 3. A second terminal block 9| is secured to the base I by means of screws 92, and -is adapted to be associated with the energizing winding 6I of the initiating element 59. This terminal block 9| is provided with suitable taps 93, associated with the winding 6 I, and the contact screw 94 is adapted to be associated with any such taps in order to effect a predetermined effective energization of the winding 6I of the initiating element 59.

Assuming the main operating element 2 of the present relay to be energized in accordance with the current flowing in a transmission or distribution system, and the initiating element 59 to .be made responsive to a predetermined magnitude of current existing in such line or system, under normal current conditions, the position of the respective relay elements is as follows.

The energizing winding 3 of the operating element 2 is energized and acts to effect the movement of the solenoid core 9 and associated pivotal contact member II in a direction to ef fect the bridging of stationary contacts I6 by means of contact member I4. The movement of the pivotal contact member I I in the direction to set of the pivotal contact member |I.

Assuming .that a definite predetermined magnitude of over-current exists, such that the energizing winding 6| of the initiating element 59 is effectively energized to move the solenoid core 65 and associated pivotal member 61 against the normal tension of the spring 11, the screw 83 is moved out of engagement with the rotatable bar 3|, and the pivotal contact member I I is adapted to be moved in a direction to bridge the stationary contacts I6 by means of contact member I4. The forces effective to control the movement of the pivotal contact member II and associated contact I4 comprise the force acting on the solenoid core 9, which may be made proportional to a desired exponential function of the energizing current for the energizing winding 3, the constant force effected by the 'spring member 2| and the damping force eiected by the rotation of the disc member 46 between' the poles of the permanent magnet assembly 52. The tension of the spring 21 is substantially unchanged .for low and medium values of current in the energizing winding 3,-and this spring is' only provided for the purpose of permitting an added displacement between the contact member I I and the rotatable bar member 3| under conditions of high current energization ofthe Winding 3.

Assuming that the over-current condition no longer exists, or that the contacts I6 have been bridged by the Contact I4 to effect the deenergization of the relay elements, the energizing winding 6I, of the initiating element 59, is effectively deenergized with the result that the spring 11 effects the movement of the pivotal member 61 and associated downwardly extending arm 16 to the normal position thereof. This action of the Lspring 11 forces the screw 83 against' the rotatable bar 3|, and effects the rotation thereof in a clockwise direction, thereby effecting a quick re- During the reset operation of the relay elements, the rotatable bar 3| is being rotated in a clockwise direction with the result that the pawls 43 are disengaged fromtheratchet 42, and the gear 44 is not rotated in accordance with the rotationof the bar 3| and' shaft'32, and no damping by means of the disc member 46 and permanent magnet assembly 52 is provided in the reset opera-4 tion of the relay.

From the foregoing description of one embodiment of the present invention as depicted'in Figs. 1 and 2, it should be noted that the stationary contacts I6 are adapted to be bridged lby the contact I4 by a torque equal to an exponential function of the energizing current plusthe constant force exerted by the spring 2| minus the damping force exerted by the movement of the disc member 46 between the poles of the permanent magnet assembly 52.

In Fig. 3, curves A, B, CD and E are illustrative of the time-current curves of the usual induction type current-responsive relay, and it may be noted that these curves have an inverse portion of quite restricted range. .These curves are plotted, having as abscissa per cent current, and having as ordinate time in seconds. All of the curves are also plotted on the basis of lthe relay being set for tripping only on values of current above 100% load. The various curves A, B,

:sol

C, D and E are obtained,in the usual-type inducdamping effective to restrain actuation of the relay contacts.

With this type of curve, it will be noted that for low values of over-current, namely up to 200% current, the timing of. the relay may not be determined with any degree of accuracy, in view of the asymptotic nature of the curves with respect to the time ordinate. For such low values of over current, the time required for the relay contacts to close becomes prohibitively long and, in practice, it has been found impracticable to utilize such low settings of these relays. It may also be noticed that these curves become asymptotic with respect to the current abscissa, thereby providing a substantially definite time characteristic in the actuation of the relay contacts, with the result that such relays are not capable of distinguishing between heavy over-currents.

'As referred to hereinbefore, attempts have been made to utilize the inverse portion of the existing time-current curves of the usual induction relay, and such attempts have met with partial success, but only for very limited ranges of over current. The relay of the present invention is very flexible in character and, as will be explained hereinafter, the various constants and adjustments of the relay may be varied to eifect a time-current characteristic curve of almost any desired inverse form.

Referring to the curve B of a usual inductiontype relay, the relay of the present invention is assumed to effect a time-current curve, similar to curve B, for values below 250% current, andv is shown as extending down to the current abscissa at substantially 925% current. This new curve F may be obtained from the relay of the present invention, assuming the constant force spring 2| to be removed.

The main operating element or driving element 2, of the relay, is of the solenoid type', and this electromagnet is designed to have characteristics such that the pull thereof will not increase materially as the plunger, or armature, is` permitted to move by the Atiming mechanism or damping element. Much of the design of electromagnet solenoids is of an empirical nature, although much design data is availablen relating to solenoid type. electromagnets. It follows, therefore, that the electromagnet `2 may be so designed as to elTect a time-current curve, which is similar to curve B for currents up to 250%, and the slope of this curve may be varied within a broad range by changing the characteristics of the solenoid. This characteristic curve portion is obtained by means of the driving element 2, and the timing or damping mechanism, effected by the disk 46 and permanent magnet assembly 52 together with the constant force spring 2| are not utilized.

For higher values of current energization of the driving element 2, the pull of the solenoid element effects a stretching of the spring 21, and the time required for the contacts I4 and I6 to close will be materially shortened, inasmuch as the full time of the time element is not utilized. If the proportions are correctly made between the pull of the electromagnet 2, spring 21 and the timing mechanism, including the disk 46 and the permanent magnet assembly 52, it will be possible to denitely x a point where the contacts will close substantially instantaneously without waiting for the time element to move or be effective. This feature constitutes the essence of the present invention, inasmuch' as the straightening out of the lower part of the curve, and effecting an instantaneous time of operation, as indicated by curve F, is not possible in any present type of over-current induction relay.

The use of the spring 21 obvlates the necessity for increasing the operating force of the drlv.- ing element 2 beyond values which are easily obtainable, and the stretching ofthe spring 21 permits the closing of the contacts Il and I6 without Waiting for the full time of the timing mechanism or damping element.

The provision of the substantially constant force spring 2| serves to bend the upper part of the curve in such manner as to effect the closing of the contacts I4 and I6 after a definite time,

assuming the driving,r element 2 to be deenergizedI and the actuating element 59 to be ineffective to restrict the movement of the contact Il. It follows, therefore, that by employing both the substantially constant force spring 2| and the spring 21, the upper part of the curve B. may be straightened out in such manner Vto intersect the4 time ordinate, while the lower part of the curve B is made to' intersect the current abscissa, by virtue ofthe action of the spring 21. The various constants of the present relay may be varied in such manner to eiect a straight line time-current characteristic, and examples of such characteristic curves are indicated by the curves G, H, I, J and K.

The curves G, H, I, J and K are illustrated as being parallel, and they are shown as originating at the 100% current point. Obviously, however, these curves extend to the zero current point, thereby permitting the use of the relay on values of current below 100%, without altering the slope of the curve in any manner. These different straight line curves are obtained by varying the position of the screw |53v and/or by changing the adjustment of the substantially constant-force spring 2|, and by adjusting the actuating element 59, such that the contact` I4 and associated timing mechanism are permitted to be. actuated in accordance with the combined pull of the spring 2| and the solenoid electromagnet 2.

v'Ihe slope of the time-current characteristic curve may also be varied, as illustrated in Fig. 4,

' by changing the amount of pull or force exerted by the electromagnet driving element 2. The curves L, M, N, O, P, Q and R, .illustratedin this gure, are obtained by adjusting the substantially constant forcespring 2| in such manner that the contacts I4 and I6 will be permitted to close in 10 seconds, when the main operating element 2 is deenergized and when the actuating element 59 is adjusted for 100% current. 'I'he curve L is obtained in this manner and, obviously, since the spring 2| exerts asubstantially constant force, the curve L denes an absolute deflnite time of operation of the relay. 'I'he remaining curves M, N, O, P, Q and R ,are obtained by increasing the energization of the main operating element 2 and by maintaining the same initial tension of the spring 2|. This increased energization of the energizing winding is eiected by changing the tap setting thereof, for example,

' spring 2| for the particular time desired, and

the relay may be actuated in accordance withy any predetermined value of current by means of the actuating element 59. When the relay is used as a definite time relay, the main operating element or driving element 2 is completely deenergized. The slope of the time-current-characteristic 4curve may be altered, if desired, by maintaining a constant setting of the screw 83 .and spring 2,] and `by varying the energization of the main operating element 2. Here again, the relay may actuated for any predetermined value of current by means of the actuating element 59. 'I'he parallel straight line curves, as shown in Fig. 3, may be obtained by imparting a predetermined energization to the main operating element 2'and by changing the setting of the screw 83 and/or the amount of tension or force exerted by the spring 2|.

'I'he relay of the present invention is, therefore, capable of effecting a very broad range of characteristics and may be adjusted for either straight line or modified inverse time-current characteristics. 'I'his relay effects a substantially constant ratio of current increment to time decrement and may be admirably adapted for any protection application where current protection is required., The time-current characteristic may be made to intersect the time ordinate and to become asymptotic with respect to the current abscissa, if desired, by eliminating the spring 21 and effecting a non-resilient connection between the driving element and the timing mechanism,

or time-current-characteristic curves similar to curve F may be obtained by utilizing the spring 21 and eliminating the use of the substantially A constant force spring 2l. Obviously, anydesired modified form of inverse time characteristic may be obtained in the present relay with a minimum of trouble.l A

The advantages of this relay, incorporating the straight line or modified inverse time current characteristics, should be obvious to one skilled in the .protective relaying art.- and it is deemed unnecessary to point out in detail wherein the application of such relay is far superior to the application of any existing relays, induction or other- Wise.

'I'he actuating element 59 of the present relay may also be of any desired type, and may be made responsive to voltage, impedance of an associated system, etc. Broadly speaking, the present invention relates to a broad range relay wherein the time characteristic may be made to be either a straight line curve, or modified inverse form of such curve. This relay may also be utilized as a definite time relay, as desired, and the simple schematic illustration of the component parts of the relay, as shown in Fig. 2 ofthe drawings, should provide a complete and accurate description of the theory of operation of the relay and, Y

obviously, the various desired .characteristic curves may easily be obtained by balancing the characteristics of the springs 2l, 21, the characteristics of the operating element 2 and any suitable timing mechanism.

In view of the basic improvement in relay characteristics made possible by a relay designed in Vaccordance with the foregoingdescription, in

timing device having a movable element operable with a displacement dependent upon time, a. contact operating member movable toward a contact operating position and resiliently restrained by said element, current-responsive electromagnetic means for exerting an operating force dependent upon current upon said contact operating member, and biasing means tending to move said contact operating member toward said position and effective to accelerate operation of said `contact members at low current values.

2. In an overcurrent relay, contact members, a timing device having a movable element operable from an initial position with a displacement dependent upon time, a contact operating member movable toward a contact-operating position and resiliently restrained by said element, currentresponsive electromagnetic means for exerting an operating force `dependent upon current upon said contact operating member, biasing means tending to move said contact operating member toward said position and effective toaccelerate operation of said contact members at W current values, and means effective upon deenergization of said'relay for returning said movable element `to said initial position without time delay.

3. In a relay, the combination including contact means, energizing means associated therewith for effecting the actuation thereof, damping means, means resiliently coupling said damping means to said energizing means, and actuating means including means associated with said damping means for rendering said damping means ineective for one direction of movement of said contact n means. y

4. In combination in a relay, contacts, actuating means therefor, means for applying a substantially constant force for biasing said actu- .ating means to contact closing position, means for applying thereto, in aiding relation, a second force which is substantially an exponential function of the energizing current, means for applying a damping force opposing said first and sec- 4ond, forces, and starting means for preventing operation of said actuating means under normal conditions and for initiating operation of said actuating means in response to said forces under predetermined abnormal conditions.

5. In combination in a relay, contacts, actuating means therefor, means for applying a substantially constant force for biasing said actuating means to contact closing position, means for applying thereto, in aiding relation, a second force which is substantially an exponential function of the energizing current, starting means for preventing operation of said actuating means under normal conditions and for initiating operation of said actuating means in response to said forces under predetermined abnormal conditions, and

timing means connected with said actuatingl means for maintaining a substantially constant time-current derivative over substantially the entire range of vcurrents by which said relay may be operated.

6. In combination in a relay, contacts, actuating means therefor, means for applying a substantially constant force for biasing said actuating means to contact closing position, electromagnetic means for applying thereto, in aiding relation, a. second force which is a function of the energizing current in said electromagnetic means, damping means and resilient coupling means between said' actuating means and said damping means arranged to permit substantially instantaneous operation of said actuating means in restantiaily constant force for biasing said actuating means to contact closing position, electromagnetic means for applying thereto, in aiding rela- 10 tion, a second force which is a function of theI energizing current in said electromagnetic means.

damping means, resilient coupling means between said actuating means and said damping means arranged to permit substantially instantaneous operation of said actuating means in response to a predetermined value of said second force, and to introduce the timing action of said damping means for lesser values of said second force, and initiating means forholding the damping means until the energizing current exceeds a predetermined value.

vROY M. SMITH.

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