US2636934A - Dual action magnetic relay with variable air gap - Google Patents

Description

April 28', 1953 T. 5. A. SILLERS 2,636,934

' DUAL ACTION MAGNETIC RELAY WITH VARIABLE AIR GAP Filed Dc. 29, 1950 FIG! INVENTOR 0 Mme-NT THOMAS G.A.SILLERS ATTORNEY Patented Apr. 28, 1953 DUAL ACTION MAGNETIC RELAY WITH VARIABLE AIR GAP Thomas G. A. Sillers, Wauwatosa, Wis., assignor to Allis-Chalmers Manufacturing Company,

Milwaukee, Wis.

Application December 29, 1950, Serial No. 203,294

3 Claims.

This invention relates to improvements in automatic circuit protective devices and more particularly to a new and improved delayed action overcurrent electromagnetic relay.

The usual type of electromagnetic relay has a characteristic fast action which is not adapted to certain circuit arrangements, such as are involved in switchgear circuit breaker practice. This type of application requires a relay with a time delayed action. The period of time during which electric equipment can be subjected to abnormal conditions, such as currents or short circuit currents, is ordinarily variable depending upon the character er intensity of such abnormal conditions. In some cases it is desirable to permit the electric system to remain intact for a period. of time that varies with the value of an abnormal condition. At high values of overload currents or short circuit currents, it is desirable that the circuit be interrupted after a time interval which is comparatively small but which, nevertheless, insures freedom from interruption due to momentary disturbances.

Power distribution systems are frequently protected by a number of serially connected circuit breakers which operate in a predetermined sequence. Each serially connected breaker is adjusted to trip at a difierent predetermined interval of time, thereby sequentially isolating segments of the electric circuit in accordance with the location of the disturbance, the length of time the disturbance continues, or the character of the disturbance. Heretofore, time delay relays have been used to sequentially trip serially connected circuit breakers but these relays have not been capable of accurate settings for such short time intervals as are desirable for clearing circuit faults with a minimum of burning of connections and connected apparatus.

In accordance with the invention claimed, a new and improved delayed action overcurrent electromagnetic relay is provided for circuit breaker operation which has a given currenttime characteristic for currents up to a predetermined value and a different current-time characteristic for currents above that predetermined value.

In the preferred embodiment of the invention, the magnetic relay embodies an armature which actuates a switch operating rod. The rod is retarded by a pair of suction disks from moving into switch actuating position in a time varying inversely of the current traversing the winding of the relay. For currents below a predetermined value the armature is disposed adjacent the relay core structure to provide an air gap of a predetermined size, and for currents above a certain value the armature is actuated to another position to provide a smaller air gap. armatures second position, the flux induced in the iron core structure is greater than it would have been had the air gap retained the length it had in the armatures first position, and consequently, the inverse time characteristic has been changed to permit the time delay relay to operate in a shorter time for currents above the predetermined value.

It is, therefore, one object of the present invention to provide a delayed action overcurrent electromagnetic relay in which the relay has a given current-time characteristic for overload currents up to a predetermined value and a different current-time characteristic for currents above that predetermined value.

Another object of this invention is to provide a delayed action magnetic relay with dual inverse time relationships which provide for adjustments of the point of changeover from one relationship to the other.

A further object of this invention is to provide a new and improved delayed action relay which is adjustable for operation at predetermined current values with predetermined periods of time delay.

Objects and advantages other than those set forth will be apparent from the following description when read in connection with the accompanying drawing in which:

Fig. l is a diagrammatic view of a circuit breaker and a delayed action overcurrent electromagnetic relay therefor embodying the present invention; and

Fig. 2 is a graph of the current-time characteristics of the electromagnetic relay illustrated in Fig. l and a graph of current-time characteristics of a prior art circuit breaker tripping device. v

. Referring more particularly to the drawing by characters of reference, Fig. 1 illustrates an electric circuit 6 provided with a circuit interrupter or breaker l and a time delay overcurrent electromagnetic relay 8 for controlling its actuation at predetermined overloads. The relay comprises a magnetizing winding 9 connected to one phase conductor of the electric circuit 8. Wind:- ing 9 may be connected in series with the associated phase conductor, or may be connected therewith through a current transformer, as is well known. The relay further comprises a core structure I0 and an armature ll. Armature II is In the i of cylindrical form and is provided with a central opening I2 adapted to be closed at one end thereof by a nut l3. A threaded core Hl extending through the central portion of the nut and within the armature H is coaxially aligned with the armature to form a part thereof. The armaure is disposed adjacent core structure it to form therewith a magnetic circuit having a given air gap.

The armature ii, nut l3 and core M are provided with aligned openings loosely receiving a rod I5 adapted to actuate the circuit breaker switch arm 48. The rod i5 is provided with a flange portion is adapted to fit loosely within armature ii and to close the upper end of armature H when the relay is in the position illustrated in Fig. 1. The lower end of the rod is threaded into a nut 2B which is, in turnbsuitably secured to one of a pair of suction disks. Nut 29 may be pinned to rod iii to lock it in place, if so desired. A resilient means such as a spring H5 is arranged within armature ll about rod id ,ior opposing movement of armature ii relative to rod 15.

A rigid cylinder 22 surrounds the lower end of armature l l and is suitably secured to core structure it and acts as a guiding means or bearing for the armature. Flange is of rod l5 acts as a guiding means for the upper end of armature H and a rigid cylinder 23 suitably secured to core structure it acts as a guiding means or ing for the upper portion of rod 55.

The suction dislrs are arranged in an oil with the upper disk 2 3 secured to rod 25 and the lower disk 25 secured to the bottom of a container 25 which houses the oil.

Circuit breaker i as illustrated in the drawing comprises stationary arcing contact 2d and mov able arcing contacts 36. The movable arcing contacts 33 are connected to a rod 3! which is actuated to circuit open position by a toggle mechanism 32.

The toggle mechanism 32 comprises a link 33 which is pivotally mounted at 35 and a link which is pivotally mounted at a point 355 on rod 35. A spring 3? biases toggle mechanism 32 to circuit open position. Link 33 carries a lug 38 which is engaged by a catch 3%. Catch it is mounted on one end of pivotally mounted lever arm i8 and is held in its operative position against a stop to by means of a spring i l. Lever arm i8 is actuated by rod 6 5 when it is actuated to switch opening position by armature H.

In Fig. 2 curve ABC illustrates a time-current curve of the usual prior art current responsive relay. The curves ABD, A'EG, and A"FIE-I illus trate the time-current curves of the electromagnetic relay illustrated in Fig. 1 with diiferent adjustments. These curves are plotted, having as abscissa current and having as ordinate time. All of the curves are plotted on the basis of the relay being set for tripping only on values of current above 106% load. Fig. 2 illustrates diagrammatically'the manner iii-which the device shown in Fig. 1 operates and is not intended to set any-limits within which this invention must be restricted.

In operation, the circuit breaker l being closed as indicated in Fig. 1, current flows through the arcing contacts as, to and the magnetizing winding 9. For all line currents below a predetermined value the parts of the relay remain in the position indicated. Upon the occurrence of a line current through magnetizing winding 9 of a certain overload value below a predetermined value, armature l I after a predetermined delay moves rod l5 and actuates arm 18 to trip the circuit breaker 1.

Operation of the relay illustrated in Fig. 1 for overload currents below a predetermined value may be illustrated by curve ABC, shown in Fig. 2. This type of inverse time delay is characteristic of the prior art relay structures wherein the time delay is inversely proportional to the current flowing through the magnetizing winding for the full overload current range of the relay.

In order to permit the relay to operate faster for overload currents above a predetermined value the relay illustrated in Fig. 1 is provided with an armature which is capable of moving relative to the switch actuating rod :35 from a first position to a second position. In the second position of armature i I, the air gap between the armature and the upper part of the core structure is smaller and the magnetizing flux introduced in the core structure is greater per unit of current. flowing through the magnetizing winding than it would have been if the armature remained in its first position. Consequently, the inverse time relation between switch actuation and the value of the current flowing through the magnetizing winding has been changed.

The inverse time relation for a given relay setting for currents above a predetermined overload value is represented by curve BD. There fore, the relay illustrated in Fig. l operates for all overload currents below a predetermined value on the curve AB and for all overload currents above a predetermined value on the curve BID. The diiierence of ordinates between curves EC and ED for any given overload current is representative of the time gained in tripping the circuit breaker by use of this invention in preference to the prior art structures represented by curve ABC.

The actual. mechanical operation of the relay illustrated in i is as follows:

For all overload currents below a mode-ten mined current value represented by the point B on the curve sec, at a given setting. the current flowing thro the magne, ing winding 2: will introduce a -nagnetizi-ns firs in core strut ture which will attract armature it in switch actuating direction. immature H is opposed from moving iv the spring means it which bears against flange l8 and nut i3, the suction 2iand iii The hrust exer d by armature ii on rod it through spring it depends on the value of the current in coil il. After a predetermined period of time, llS thrust causes the suction disks to separate. V the armature ll will actuate rocl it into position to trip the circuit breaker i.

For all overload currents shave the gored-star.- rnined value represents 1 'nt E on the curves illustrated in Fig, 2, ara. re it will be actuated by the magnetizing current flowing through winding 9 to move upward relative to rod it toward the upper of core structure it agains the opposing force of spring 6%. The movement of armature ii is. stopped temporarily the upper portion of core id strikes against flange is of rod iii to interlock the armature and th rod. for moveniaet a u: In so moving from its original to the position Where core it strikes flange or rod is, armature ii has decreased the size or the air gap bfiween the armature i i and the core structure it. Th magnetizing flux now introduced in. the core structure it for the same overload current whi h actuated armature I I to its second position is stronger than it was when the armature was in its original or first position. Consequently, now the movement of rod toward lever [8 against the biasing force of the suction disks 24 and 25 will vary in a new inverse time relationship represented by curve BD.

Thus, the relay illustrated in Fig. 1 has a certain time delay for overload currents below a predetermined value and a much smaller time delay for overload currents over this predetermined value. For exceptionally high overload current, the relay operates almost instantaneously.

The electromagnetic relay 8 may be adjusted so that it may have a number of inverse time ratios for currents above any predetermined overload current. In this manner the same type of relay may be used to protect any number of serially connected circuit breakers which are arranged to operate in a predetermined sequence. Each relay is adjusted to trip at a different predetermined interval of time.

This adjustment is accomplished by screwing armature ll up or down in the threaded core l4. By moving armature II toward flange 18, the air gap when armature H is in its second position is reduced and the breaker will be tripped in a shorter time interval than it would have been formerly. Movement of armature H away from flange l9 increases the air gap when the armature is in its second position and thereby increases the time delay for a predetermined overload current. Adjustment of the tension on spring I6 also may be provided for further variations of the time current characteristics.

Curves A'EG and AFH represent the inverse time relation of relay 8 for two representative settings of the relay wherein the armature H was moved to increase the air gap for the armature in its second position.

Thus, a plurality of relays of the type illustrated may be adjusted to trip at different predetermined intervals of time, thereby sequentially causing isolation of faulty circuits.

Although but one embodiment of the present invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent;

1. A time delay relay comprising a core structure, an armature disposed adjacent said core to form therewith a magnetic circuit having a given air gap, a magnetizing winding for producing a magnetic flux in said magnetic circuit, a rod to be actuated by said armature, means for retarding the movement of said rod in a time varying inversely of the value of the current traversing said winding, resilient means acting between said armature and said rod for opposing movement of said armature relative to said rod,

said armature moving relative to said rod from a first position to a second position when the current traversing said winding reaches a predetermined value, said movement of said armature relative to said rod varying said air gap to vary the inverse time relation between rod movement and the value of said current, and means for interlocking said armature and said rod in said second position for further movement as a unit.

2. A time delay relay comprising a core structure, an armature disposed adjacent said core to form therewith a magnetic circuit having a given air gap, a magnetizing winding for producing a magnetic flux in said magnetic circuit, a rod extending through said armature and operated thereby, means for retarding the movement of said rod in a time varying inversely of the value of the current traversing said winding, resilient means within said armature about said rod and acting between said armature and said rod for opposing movement of said armature relative to said rod, said armature moving relative to said rod from a first position to a second position when the current traversing said winding reaches a predetermined value, said movement of said armature relative to said rod varying said air ap to vary the inverse time relation between rod movement and the value of said current, and cylindrical means around said rod and within said resilient means for interlocking said armature and said rod in said second position for fur ther movement together as a unit.

3. A time delay relay comprising a core structure, an armature disposed adjacent said core to form therewith a magnetic circuit having a given air gap, a magnetizing winding for producing a magnetic flux in said magnetic circuit, a rod to be actuated by said armature, means for retarding the movement of said rod in a time varying inversely of the value of the current traversing said winding, resilient means act-ing between said armature and said rod for opposing movement of said armature relative to said rod, said armature moving relatively to said rod from a first position to a second position when the current traversing said winding reaches a predetermined value, thereby reducing the size of said air gap to vary the inverse time relation between rod movement and the value of said current, and a flange secured to said rod for interlocking said armature and said rod in said second position for further movement as a unit in gap closing direction.

THOMAS G. A. SILLERS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,383,432 Simon July 5, 1921 1,810,591 Atwood June 16, 1931 2,439,165 Graves Apr. 6, 1948 2,451,962 Lindstrom Oct. 19, 1948

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