US2557681A - Time-delay power relay - Google Patents

Description

June 19, 1951 J. IOSTLIND ETAL TIME-DELAY POWER RELAY 2 Sheets-Sheet 1 Filed Dec. 12, 1949 5 E R06 5 mm mm mm u 7 m k4 QM M f w Patented June 19, 1951 2,557,881 TIME-DELAY POWER RELAY Joel Ostlind, Oakland, and William L. Werner, Palo Alto, Calif.

Application December 12, 1949, Serial No. 132,604 7 Claims. (Cl. 175-375) for sequential operations, such as may be connected in cascade to provide for the operation of groups of street-lighting circuits.

At the present time street lighting is largely provided by lamps of the incandescent type. The difference between the cold resistance and the hot resistance in such lamps is very large, the hot resistance being many times that which the lamps exhibit when cold. Ordinarily all of the lamps in a single city are lighted at dusk, and if all are lighted at the same time the initial surge of current, lasting until the lamps have come up to approximately their final temperature, may be such as greatly to overload the circuits, throwing undue strain upon the generating equipment and the protective devices appurtenant thereto. Accordingly, it is much better if the distribution system for such lighting be divided into groups or sections which are excited successively, so that the transient currents or surges consequent upon the excitation of one group may have an opportunity to die away before the next section is excited. If the entire system is divided into a suiiicient number of groups an carry a current hearing this ratio to the steady value it would amount to a very serious overload indeed.

Sequential tions from a minated at the station, or, in the alternative, a large number of separate control lines being required. If, on the other hand, the excitation of one section can be made to accomplish the delayed excitation of a succeeding section, and this, in turn, cause the delayed excitation of the next section in the series, an extensive subdivision accomplished at a reasonnetwork.

Such operations as just mentioned presuppose that the control relays be mounted in exposed positions; on the poles supporting the light, in manholes, or the like. This implies that in many cases the operating relay be exposed to extreme variations in temperature, and it is well known operate perfectly at degrees Fahrenheit or thereabout-may not operate satisfactorily under sub-zero ambient temperature conditions, or that their lives may be seriously shortened by operating under such conditions.

With these facts in mind, among the objects 01' this invention are to provide a relay which will successfully make and break circuits carrying substantial amounts of power; to provide a relay which will control such circuits and which will delay their operation in so controlling them by predetermined amounts which may vary between a very few seconds and a minute or even several minutes; to provide a type of relay which may be operated in cascade, utilizing a control current of the same voltage and frequency characteristics as that in the circuits to be controlled; to provide a relay which will operate under extremes Of temperature with complete reliability; and to provide a relay which will withstand many -thousand cycles of operation, under such extremes of temperature, without electrical or mechanical failure.

In its broad aspect, this invention comprises a power switch of the mercury-tube type, wherein the make and break operations are accomplished by tilting the tube so that the fluid mercury either bridges or does not bridge a gap between two contacts sealed into the tube. The drive mechanism for the relay comprises a motor, preferably a synchronous motor of the type familiar in electric clocks, which, in the most ordinary applications of our invention, is provided with the usual step-down gear. The motor is of the self-starting type and is provided with means for establishing two opposing electromagnetic fields, so that one tends to rotate the common. armature and shaft structure in a clockwise di-- rection while the other tends to cause rotation in a counterclockwise direction. ()ne of these fields is excited from a control circuit, while the other is connected for excitation from the controlled circuit when the latter is closed through the mercury switch.

Rotation of the motor tilts the switch-tube to make or break the circuit. For short delays the mounted for direct operation by the motor shaft. Where longer delays are required there is preferably mounted upon the motor shaft a cam, conveniently in the form of a disk having a portion Of its periphery cut away so as to form a slot or gap. The width of this gap determines the time delay of the relay; it may be very narrow, in which case the delay will be very short, or it may extend around asunder 'nearly the entire periphery of the disk leaving merely a projecting tooth in which case a delay as long as 59 seconds (assuming a one-minute period of rotation for the shaft) will be the result. The faces at'the edges of the slot engage a tiltable support which holds the mercury tube, rotation of the disk in one direction tilting the support and tube in such sense as to close the contacts, while rotation in the other tilts it back to open the contacts. To operate the relay current is supplied to the motor field which rotates the shaft in the proper direction to tilt the mercury switch to the closed position. Rotation in this sense continues until the cam disk engages the tiltable structure and closes the switch, energizing the line to be controlled and the other motor field structure which is bridged across this line. This tends'to rotate the armature structure in the opposite direction, balances the torque produced by the control field and brings the device to rest. The fields remain in this balanced condition until the voltage is removed from the control winding, whereupon the second winding assumes control, tilts the switch into the open position, and deenergizes the motor.

It will be apparent that the controlled line for one relay may become the controlling line for another, which may have either the same or a different delay constant depending upon the formation of the cam disk. As many relays as may be desired can therefore be connected in cascade, closing successive circuits at successive predetermined intervals.

Mercury switches of the type here considered have relatively long lives and will stand a large number of cycles of operation when carrying the loads for which they are designed. We have found, however, that when failure does occur as a result of continued use, the failure is caused by the flaking off of minute chips of glass from the interior of the tube. This flaking or sloughing action takes place very gradually and is apparently caused by intense local heating of the glass envelope due to the arcing or sparking which occurs, usuallyat the time of the break, but which may also occur at the time that the circuit is closed. Actually it appears that the sparking which occurs upon the make action is more destructive than that occurring at the break, even though it occurs less frequently and is apparently less severe.

It has been found, moreover, that the action referred to is much more serious at low temperatures than it is at high.

The reason for the phenomena just mentioned appears to lie in the nature of glass. Glass is frequently referred to as a supercooled liquid the reason being that when a true glassis cooled from a liquid state there is no point at which it can be definitely said that solidification occurs. The cooling curve of the material is practically continuous, no discontinuities occurring as in the case of a crystalline substance wherein energy is liberated upon the transition from a liquid to a solid phase. Moreover, the viscosity curve of glass indicates it to be one of the most rigid and elastic substances known, but its rigidity increases with decrease in temperature. Local heating, causing expansion of the glass, is therefore very much more destructive when the glass is at greatly reduced temperatures than it is when it is relatively warm, not only because of the mere difference in temperature but also because the glass has more give" when it is warmer.

A very important part of this invention, therefore, is the fact that there is provided, adjacent to and preferably surrounding the mercury tube, a heating winding of relatively high resistance which is bridged across the operating. contacts and which carries current when the switch is open, thereby maintaining the glass at a temperature which is materially above the ambient temperature. To accentuate this, the relay is preferably surrounded by a complete enclosure.

When the mercury switch is openthe temperature is therefore maintained by the heatin coil. When the switch is closed the heating coil is shorted out by the mercury itself, but since the latter is carrying a relatively heavy load, the heat generated would be of the same order of magnitude, or even higher, so that it will maintain the glass in its more malleable condition. Furthermore, when the relay is closed, additional heat is generated in both of the actuating coils and this is retained by the enclosure. The total temperature rise under both conditions will be generally of the same order of magnitude, although somewhat higher, usually, during the closed condition of the switch. This is not disadvantageous, however, as it keeps the glass in its most malleable condition at the time of severest sparking, occurring at the break.

The invention will be more clearly understood from the following description of a preferred embodiment, taken in connection with the accompanying drawings, wherein:

Figure 1 is a plan view of a. relay embodying this invention, with the cover removed;

Figure 2 is a front elevational view of the relay,

the cover and base being shown in section;

Figure 3 is an end elevation of the relay mechanism, the base and cover and the connection between the motor and switch rocker being shown in section;

Figure 4 is a wiring diagram showing a plurality of sections of a lighting distribution system actuated by relays in cascade and showing the wiring of the relay and heating coils.

Figure 5 is a front elevation of a modified form of relay of this invention which may be used where time delays of from one to two seconds only are required.

The embodiment of the relay of this invention illustrated in the first three figures comprises a baseplate i whereon there is mounted the frame 3 of, the relay motor mechanism. In this case the frame comprises an L-shaped strip, the Ver tical arm of the L being of a length which extends from the baseplate i to the full height of the structure so that a surrounding enclosure or cover 5, when in place, rests upon the top of the frame. The horizontal branch of the L is secured to the baseplate, and is provided, at its end, with a short vertical riser 1. A. motor mechanism, generally indicated by a reference character 9, is mounted upon studs ii and it respectively, the lower of these studs being supported between the riser portion 1 and the vertical arm of the L-shaped frame 3, while the upper one is secured to the vertical arm alone.

The two field structures of the motor, comprising the cores l5 and I5 and the windings I7 and H are mounted on the studs just described. The armature structure of the motor is enclosed in a cylindrical housing 19. This structure is not illustrated in detail as it comprises essentially simply two clock motors of known type mounted in bucking relationship, and various types of such motors are well known and are commercially its slot-like character comparable to a single-tooth gear. The relative available. The usualstep-down gear case 2|, of

the same type as is used in most clock motors, is mounted on the end of the housing IS. The gearing within this housing. reduces the speed ofthe projecting shaft 23 by any desired ratio; in this case to a speed of one revolution per minute when one of the motor fields is supplied with 60-cycle current. r

The lower of the two studs supporting the motor, 1. e., stud H, projects forward of the support frame 3 to form a stationary shaft 25 on I i which 'is mounted a bearing bushing 21. The

lower end of a vertical arm 29 of a T-shaped rocker is secured to this bushing. The horizontal arm 3| of the rocker is provided with spring clips 33 for holding a mercury switch-tube or capsule 35 of known type. a I

The vertical arm 29 of the rocker is slotted, as shown at the reference character 31, to permit the passage of the motor also provided with a pin 38 (which may be formed by bending a tab out of the material of the rocker itself) projecting outwardly at its median line between the shaft 23 and rocker bearing 21.

Anoperating disk or cam 39 is secured on the end of the shaft 23. Theperiphery of this disk is cut away or slotted as shown at the reference character 40, and the time delay of the relay is shaft. The arm 29 is determined by the width of this slot, which may be varied as .desired, as has already been stated. In the present instance the slot is shown of such proportions as would give a delay of approximately six seconds with a shaft speed of one revolution per minute. It should be clear that any portion of the periphery may be cut away in this manner, or to almost the entire periphery of the disk, in which case the cutaway portion loses and the disk becomes more position of the parts as shown in Figure 2 is one which would never be assumed in actual operation but which is shown in the drawing for purpose of clarity. As shown in the drawing the rocker 29 would be in unstable equilibrium and this position would be assumed only when one or the other of the two edges of the slot 40 were in contact with the pin 38 on the rocker arm. Clockwise motion of the cam disk 39 causes the right hand edge of the slot to engage the pin and tilt the rocker to the left, causing the mercury in the tube 35 to bridge the two contacts connecting two leads 43 and 45 (which are shown only in part) and thus making the circuit. Counterclockwise rotation of the cam disk will move the rocker in the opposite direction, breaking the circult. The instability of the rocker arm when it is nearly in the position shown is increased by the fluidity of the mercury, which, as the device is otherwise neariy in balance, starts to flow in the direction of motion and speeds up the make or break operation.

A terminal block 49 is providedon the forward portion of the base plate and the power and control leads 5| and 53 are connected to this block. The switch leads 43 and 45 connect with the power lead 5i, but this figures in order to prevent confusion in the drawings, the actual connections being indicated in the circuit diagram of Figure 4.

Surrounding the switch-tube 35 is the heating coil 55. This coil is wound of fine resistance wire insulated by heat-resisting material such as asbestos or Fiberglas. The coil terminates at the same contacts as the leads 43 and 45, also as indicated in the circuit diagram. In the paris not shown in the first three opposing torque, will ticular relays shown in the drawings the coil 55 is designed to dissipate about six watts, having 2440 ohms resistance when built for operation on a 120 volt circuit or nearly a thousand ohms if designed for operation on 240 volts. When the switch is closed the dissipation by the heating element is of the order of one one-hundredth of a watt, while a 30 amp. current through the mercury generates about 3.6 watts. To this, however, must be added the heat generated in the coils of the motor so that actually the heat liberated within the casing is very nearly the same under both conditions.

The operation of the device can best be appreciated by considering the circuit diagram of Figure 4. The control leads 53 connect to the coil l1 and nothing else. Excitation of this coil causes clockwise operation of the motor of relay A, tilting the switch tube 35 into the position shown, and closing the circuit between the input leads '5! to the switch. These leads are in series with the lighting circuit 51 tribution network 59, exciting coil I1, relay A to rest. At the same time control circuit 533 of relay B is energized, starting this motor in turn in the clockwise direction so that eventually the switchtube 353 will close and the operation repeat. Relay A will remain closed until the control voltage is removed from the leads 53, at which time coil ll, no longer balanced by an take control and open the relay, thus, in turn, removing the control voltage from coil 53B and again the operation will repeat, as many circuits as desired being opened or closed in succession after the required delays.

The relays just described are exceptionally reliable in operation even under extreme changes of operating voltage and unbalance between control and operating circuits. Tests have shown that the device will work satisfactorily with full voltage on the coil H, i. e., 120 volts, even though the control voltage across coil ll be dropped to less than volts. Similarly, operation was still satisfactory with a control voltage on coil ll of volts and a controlled circuit voltage of 90 or less. When the voltages of both coils were reduced together, satisfactory operation could still be obtained through about the same range of voltages.

which is a branch of a disthus lighting the lamps 6|,

Because of the use of the heating coil opera- 7 tion under extreme conditions is still satisfactory; the device has been cycled repeatedly at temperatures of minus one hundred degrees Fahrenheit, the freezing temperature of mercury being minus forty. Furthermore, the life of the device, using the heating coil is indefinitely long. Operated at normal ambient temperatures the life of the device even without the use of the coil and considering a cycling operation of once per day as normal for this type of use, indicates a life expectancy of approximately forty years. The etching or flaking off of the inner surface of the tube when used at greatly reduced temperatures without the coil indicated a greatly decreased life under these circumstances, but using the heating coil an approximately equal life may be expected even under these conditions. The durability of the relay indicates that it may be expected to last longer than the circuits on which it is operated.

Where time delays of short duration only are required, 1. e., delays of from one to two seconds, the cam and rocker mechanism may be omitted.

- This modification of the device is illustrated in and thus bringing the motor of the mercury -switch tube.

Figure 5, wherein the motor mechanism itself is identical with that described above and the parts therefore are identified by the same reference characters. In this instance, however, a crank arm 60 is mounted directly upon the motor shaft. This arm carries a clip SI for holding The switch tube in this case is supplied with the heating coil 55 as before.

A stop 63 may be provided for limiting the motion of the crank arm in the counterclockwise or "off position. The reason for the stop is that there is one specific set of conditions wherein the current through the heating coil may become a sneak current which tends to cause rotation of the relay. This condition occurs only when through some accident the load is removed from the work circuit, as, forexample, by the burning out of all the lights in the circuit. Under these circumstances the potential across the work circuit divides between the "off, coil l1 and the heating element, in which case enough cur-' rent may flow through the coil to produce sufiicient torque to actuate the motor in the off" direction when the coil 11 is not excited. The

stop blocks any such motion. When normal load is connected to the work circuit this effect does not occur, since, in a l20-volt, -amp. circuit, the resistance of the load, bridging the coil 11', is of the order of from one-half to four ohms,

and this effectively shorts out the coil l1 so that practically the entire voltage drop takesto take care of the situation where some relay early in the cascade system may fail causing those later in the sequence to turn to the off position. If however, some such difficulty is feared, the relays described are sufficiently inexpensive to' permit two of them being operated iii-parallel with respect to both their control and work circuits, so that should one fail tooperate through switch-tube failure or otherwise the other will carry the current. A slightly less, but often adequate degree of protection may be obtained merely by the use of two mercury switch tubes in parallel, both operated by the same actuating mechanism.

We claim:

1. A time-delay power relay comprising a mercury switch tube, a mounting for said switch tube tiltable in two directions to open or close a circuit through said switch tube depending on the direction of tilt, connections for completing a work circuit through said switch tube, means for tilting said switch tube to control said work circuit comprising a motor having a rotor structure and Number of said electromagnetic fields from a control circult, and connections for exciting the other of said electromagnetic field from said work circuit when completed through said switch tube.

2. A relay in accordance with claim 1 including step-down gearing between said rotor structure and said switch tube mounting.

a 3. A relay in accordance with claim 1 wherein said motor comprises a clock-type self-starting synchronous motor having two opposed field structures.

4. A time-delay relay comprising a self-starting motor having a rotor structure and a pair of opposed field coils excitation whereof tends to turn said rotor in opposite directions, step-down gearing driven by said rotor, awork shaft driven by said gearing, and a cam element on said work shaft; a switch mechanism and a cam follower element thereon, one of said cam and follower elements having spaced faces for engaging a portion of the other, means for connecting a control circuit to the one of said field coils tending to so rotate said cam as to close said switch mechanism, means for connecting said work circuit in series with said switch mechanism, and means-for connecting the other of said field coils across said work circuit.

'5. A relay in accordance with claim 4 wherein said switch mechanism comprises a mercury switch-tube and a tiltable mounting therefor, said cam follower element being so positioned on said mounting as to tilt the same through a position of unstable equilibrium when engaged by said cam element.

6. A relay in accordance with claim 4 wherein said switch mechanism comprises a mercury switch tube having a pair of contacts therein for connection to said work circuit and including a heating coil connected across said contacts so as to be shorted out when said contacts are closed.

'7. A relay in accordance with claim 4 wherein said switch mechanism comprises a mercury switch-tube a rocker on which said switch tube is mounted and a pivotal mounting for said rocker positioned at the bottom thereof, said cam follower comprises a pin projecting from said rocker and said cam comprises a disk having a portion of its periphery interrupted to leave substantially radial faces engaging saidpin.

JOEL OSTLIND.

WILLIAM L. WERNER.

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

UNITED STATES PATENTS Name Date 1,941,920 Wilhjelm Jan. 2, 1934

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