US2769053A

US2769053A - Time delay switch

Info

Publication number: US2769053A
Application number: US356450A
Authority: US
Inventors: Edward J Weinfurt
Original assignee: McGraw Electric Co
Current assignee: McGraw Electric Co
Priority date: 1953-05-21
Filing date: 1953-05-21
Publication date: 1956-10-30
Anticipated expiration: 1973-10-30

Description

Oct. 30, 1956 E. J. WEINFURT 2,769,053

TIME DELAY SWITCH Filed May 2l, 1953 5 Sheets-Sheet ll N 6 M7 B\Me1m Unrr\l\ 4 I3 l2 2./ 3 lo-f |"7 w A/4 v /f A l5 x5 j' Smzvzssmcxsssxm u "mf Fie.

I8 l 2|" v ZI f l l lv I Smmmm 3:22:11 e lef' A INVENToR. EDWARD J. Wemr-un-r F`\Gr, 2.- By

Oct. 30, 1956 E. J. WEINFURT 2,769,053

` TIME DELAY SWITCH Filed May 2l, 1955 5 Sheets-Sheet 2 INVENTOR. DwAao J. Wam-'um' AfvoaNf- Y' Fca. 3

Oct. I30, 1956 E. J. WEINFURT 2,759,053

TIME DELAY SWITCH Filed May 21, 1953 5 Sheets-Sheet 3 INVENTOR. EDWARD .J WemFuA-r A-r-roau Y Oct. 30, 1956 E. J. WEINFURT 2,769,053

TIME DELAY SWITCH Filed May 2l, 1955 5 Sheets-Sheet 4 my* A INVENTOR. E. bwAno J. WemFuR'r BY M@ Oct. 30, 1956 E. .1. WEINFURT TIME DELAY SWITCH 5 Sheets-Sheet 5 Filed May 21, 1953 INVENTOR. EDWARD J. wams-um 7 mw oo N. I, la .e F m M @Iiilh .F w, www 3L f L .AMW 2 3 United States Patent O TIME DELAY SWITCH Edward J. Weinfurt, West Allis, Wis., assignor to Mc- Graw Electric Company, Milwaukee, Wis., a corporation of Delaware Application May 21, 1953, Serial No. 356,450

1 Claim. (Cl. 20G- 88) This invention relates to a time delay switch particularly useful with mercury vapor lamps.

Mercury vapor lamps are frequently connected in a series circuit. The lamps have a relatively low internal resistance due to the relatively low pressure when the lamp is cold. When the lamps are first started, therefore, only a relatively safe voltage is required to strike or initiate the arc. During the normal operation of the lamps the pressure rises but the arc is not interrupted as there is continuous ionization. However, when the circuit is interrupted the lamp is extinguished and consequently ionization ceases but the pressure remains for several minutes and the internal resistance of the lamp is relatively high. The arc cannot now be restarted and if an attempt is made to start the mercury vapor lamp by increasing the voltage, it will result merely in a destructive flash-over. If iilm cut-outs are provided in shunt t each of the lamps, one or more of these film cut-outs will be punctured if the circuit is opened and subsequently reclosed before the lamps have had time to cool down.

This invention is designed to provide a time delay switch particularly useful. with mercury vapor lamps or other equipment requiring a time delay after it has once been in operation and one of the main objects of the invention is to provide such a switch which is constructed so that the switch when tirst placed in operation is biased towards closed position and remains closed but if the switch has been in operation a short time it is biased open but not sufficiently to cause opening of the switch.

A further object is to provide a time delay switch which had a further characteristic that after it has carried the load current and has been opened that it will not close for a material length of time, for instance, several minutes, or in other words for a greater length of time than that required for the mercury vapor lamps to cool down.

In greater detail further objects of this invention are to provide a time delay switch which utilizes both the action of an electromagnet and of a thermal element, and in which these two members are so correlated that when the holding magnet is in switch closed position it will remain in such position although the thermal element when heated biases the switch towards open position, and which when opened after carrying the load current and while the thermal element is still heated will remain open and cannot close until the thermal element has cooled down.

A further object is to provide a time delay switch which has the above characteristics and which is eminently suited for a series system of mercury vapor lighting and which is so constructed that it will cause the high voltage circuit to be interrupted at a circuit interrupter in the event that open circuit should occur in the series system.

An embodiment of the invention is shown in the accompanying drawings in which:

Figure l is a diagrammatic view showing the switch when employed in one type of circuit.

Figure 2 is a view showing the switch when used with another type of circuit.

Figure 3 is a sectional view with parts broken away showing the switch in normal position when not in use and when cold and showing in dotted lines the position of the thermal element when heated.

Figure 4 shows the switch open with the thermal element still heated before it has had an opportunity to cool down.

Figure 5 is a sectional view with parts broken away on the line 5 5 of Figure 3.

Figure 6 is a sectional view with parts broken away on the line 6 6 of Figure 3.

Figure 7 is a fragmentary sectional view on the line 7-7 of Figure 3.

Figure 8 is a fragmentary sectional view on the line 8-8 of Figure 3.

In both Figures l and 2, the switch has been shown in a very diagrammatic manner.

In Figure l, the switch is indicated generally by the reference character 1 and comprises a bimetal unit indicated generally by the reference character 2. This bimetal unit has a portion thereof heated by means of current passing through one element thereof but which, for simplicity of disclosure, is shown diagrammatically as being heated by means of the heater 3 supplied from the secondary 4 of a stepdown transformer 5. As the description proceeds, the bimetal unit, as actually constructed will be fully described. The primary 6 of the transformer 5 is fed from the mains 7 and the operation of the switch is controlled by a main control switch 8. The mains 7 are preferably low voltage mains such as the usual mains furnishing current to dwellings and so forth. A source of high voltage indicated generally at 9 is controlled by means of a circuit interrupter indicated generally at 10. This circuit interrupter comprises the movable contacts 11 which are permanently biased open and which are closed when the operating coil 12 is energized thus drawing the plunger 13 upwardly and closing the circuit interrupter.

The high voltage line passes through a constant current static type transformer indicated at 14 and to a series of mercury vapor lamps indicated at 15. Each of the mercury vapor lamps is bridged or shunted by means of a film cut-out indicated generally by the reference character 16. The film cut-out has a sutciently high break-down voltage to withstand a voltage which is in excess of the starting voltage of the individual lamp across which it is bridged, but, obviously, not sutlicient to withstand the full value of the voltage across the high voltage mains.

The switch indicated generally at 1 is provided with a magnet coil 17 which tends to hold the switch in closed position when the series system is energized.

Normally the bimetal unit, as will be understood as the description proceeds further, is biased closed when it is cold. When it is heated it is biased open but is held closed against this opening bias by means of the previously energized coil 17.

If after the system has been in operation for a time necessary to heat the bimetal sufficiently, an opening should occur in any part of the series mercury vapor lighting circuit, the bimetal unit indicated generally at 2 will be released and will move upwardly thus opening the circuit of the closing coil or holding coil 12 of the circuit interrupter 10.

Also it is to be noted that the switch 10 cannot be closed unless the control switch 8 is closed.

if, for example, the circuit should be interrupted andv so that if an attempt to restart the mercury vapor lamps is made, voltage will not be applied to the mercury vapor lamps until the mercury vapor lamps have had sufcient time to cool down. In this way, puncturin-g ofthe film cut-outs 16 is prevented. On the other hand ifA it were possible to immediately close the series circuit through the mercury vapor lamps before they had cooled down, the film cut=outs would be punctured due to theexcessive voltage across one or more of the lamps. It is a wellknown fact that when the lamps are Vhea-ted the pressure rises and the striking voltage for initiating the arc is thus extremely high, more than enough to puncture the hlm Cut-outs and suicient to cause flash=-over with 4consequent damage to the lamps or other equipment. However, as will be seen from the preceding description, this characteristic of mercury vapor lamps has been taken care of.

Figure 2 shows substantially the same construction as that previously described and the same reference characters will be used wherever possible to indicate the same parts.

The differences between the systems shown in Figure lzand that shown -in Figure 2 resides in the fact that Figure 2 shows a protective relay indica-ted generally by the reference character 18. This protective relay indicated by reference character 18 has two switch elements or means indicated at 19 and 20 which are normally closed. The switch 19 is held open whenever the magnet coil 21 is energized, such coil being connected in the high voltage circuit of the mercury vapor lamps 15. The switch 19 controls the energization of the magnet coil 21 which controls the switch Ztl. Whenever the coil 21 is energized the switch 20 is urged to move in a direction against a time delay means 22. The time delay means 22 is provided to prevent false operation of the protective relay as a result of a transient or momentary fault. It will be seen therefore from reference to Figure 2 that normally the switch unit or bimetal unit generally indicated at 2 is closed and t-he switches 19 and 2@ are closed. When the control switch 8 is closed the coil 21 is momentarily energized but as soon as the lamps light the coil 21 is energized and the circuit to the coil 21 is broken before the switch can be opened.

In the form of the invention shown in Figure 2, on the occurrence of an interruption after the delay period, the bimetal unit 2 opens faster than the switch 20 and the effect is just the same as thoughy the switch 8 had been opened. It is to be noted that the bimetal heating circuit isV also interrupted. Thus, after the time delay bimetal unit 2 recloses, if power is again available at 9 the lamps make a normal start, but if the power at 9 is still ott, the switch 19 stays closed, the coil 21 is energized, if power at 7 is still available, and the switch opens, and the circuit interrupter 11 opens. The bimetal u-nit 2 does not rehe'at because the switch 20 is open and the lamps are disconnected until manually restarted.

In Figures 3 through 8 the actual physical st-ructure of the switch which is the subject matter of this invention is shown. The switch is normally housed within a me-tai casing 23 provided with a removable cover or top 24 from which the sw-itch is suspended. The switch consists of a lower insulating base por-tion 25 and an intermediate insulating portion or transverse member 26. The mem-ber 26 carries the elect-romagnet 27 whose coil is the coil 17 previously described. This electromagnet is pro` vided with an armature 2S which when the switch is in closedposition as `shown in Figure 3 is held against the electromagnet 27. The bimetal unit, indicated generally by the reference character 2, consists of an operating bimetal member 29 and a compensating bimetal member 30 which latter corrects for ambient temperature variations. The

members

29 and 39 are rigidly joined at their outer ends by means of the insulating members 31 which are' rig-id with vthe

members

2,9 and 30. The member 29, it will be seen from reference to Figure 7, consists of a pair of arms whose terminals 3 2 are connected to the secondary 4 of the transformer 5. The transformer 5 as will be seen from Figure 6 is carried by the lower or base plate 25. The inner end of the bimetal member 30 is connected by means of a link 33, see Figures 3 and 4, with the movable element 34 of a snap switch which has a switch arm indicated at 35. The arms 'or

elements

34 and 35 are joined by means of tensionsprings 36, see Figures 3, 4 and 6. The inner ends or adjacent ends of the

members

34 and 35 are seated in notched arms 37 of,v a pivotal support. The upper limit of stroke of the iin'k 33 is limited by' the upper stop 37 and the lower limi-t is determined by means of the lower adjustable stop 38,- see Figures' 3 and 4. The movable Contact is indicated at 39 and is carried by the arm 35 and cooperates with a stationary contact indicated by the reference character 40 carried by the contact 41. An operating handle 42", see Figure 5, is secured to a shaft 42 carried in the head or top 24 of the casing. This handle rocks a lever 43 carried by the shaft 42. The lever 43 is connected by means of a link 44 with the pivot pin 45 which joins the links 46 to the armature 2S.

Links

44 and 46 are formed of insulat-ing material and it is to be noted that the link`44 is slotted so as to allow independent motion of the links 46 butthe construction is such as to cause operation' of the links 46 when lthe shaft 42 is manually rotated.

It is to be noted thatr the insulating platforms or transverse members r25 and 26 are supported by insulating pillarksn47 andl 4S which in turn are supported from the top 24 s o that the entire switch may be lifted from the casing when the top is removed. The top is held clamped to the Acasing by any suitable means, not shown. it is to be understood also that suitable bushings extend through the top4 and carry the outwardly extending connecting conductors of the switch in accordance with the usual construction for this, type of apparatus. Also it is to be understood that it is preferable to provide a shielding insulating sheet 49 immediately inwardly of the casing 23, see Figures 3 and 4.

It can now be explained that, as previously stated, the diagrammatic showing of Figures l and 2 of the time delay switch indicated generally at 1 does not actually show the physical structure of this time delay switch which physical structure is shown in the remaining Figures 3 through 8.

The operation ofthe apparatus is as follows:

j Normally the switch is in closed position as shown in Figure 3. The dotted lines show the position of the bimetal unit indicated generally at 2 when the bimetal unit has its member 29 heated due to passage of current through its arms, such current being furnished by the secondary of the transformer 5. When the bimetal unit is heated the parts distort to the dotted line position shown in Figure 3 and bias the switch towards open position so that the link 33 is urged upwardly or biased upwardly by means of the bimetal unit. This upward motion of the` link, however, is resisted by the downward pull upon the armature 28 exerted by the electromagnet due to e'nergization of its coil 17.

It is to be noted that the bimetal ymember 29 is rigidly secured at 32. When it is heated up it carries the insulating member 31 downwardly and tilts it as may be seen by comparing the solid line showing of Figure 3 with the dotted line showing in such figure and also with the full line showing in Figure 4. The tilting of the mmber 31 duek to the heating of the member 29'causes the lefthand end of the bimetal member 30 to be biased upwardly.

However, when the circuit is interrupted in any of the ways previously described, the electromagnet is deenergized and the switch moves to open position as shown in Figure 4. The switch cannot now be closed until the thermal unit has cooled down. These units are so designed that the time delay provided before closing is permitted and is more than sutiicient to allow the I nercury vapor lamps to cool.

If desired, the protective relay 18 may require manual resetting after having once been opened or may be set from the circuit interrupter in any of the usual ways.

The action of the apparatus whether connected in the circuit shown in Figure 1 or in the circuit shown in Figure 2 may be briey summarized as follows. The magnet coil 17 is a series coil in series with the lamps. Normally, the position of the bimetal members and of the snap switch when the circuit is open and the bimetal members are cold is as shown in Figure 3, with the switch closed and the armature in its down position. When the circuit is closed the magnet 27 is energized and holds the armature down and consequently holds the snap switch closed. However, the bimetal actuator strip or operating strip 29 heats up and biases the switch towards open position and the armature towards its up position. The armature, however, holds the switch closed as long as the series coil 17 has current flowing through it in series with the lamp circuit. If the lamp circuit should be opened for any reason whatsoever or if the high voltage supply should be interrupted the series coil 17 will be deenergized. When this occurs the bimetal operating member 29 which is already biased toward its up position moves upwardly thus raising the armature 28 and causing the snap switch to open as shown in Figure 4. if an attempt is made to restart the lamps no current will flow in the lamp circuit and consequently no current will flow in the series coil 17 because the bimetal controlled snap switch 34, 3S is in open position. The bimetal snap switch will remain in open position until the bimetal has had suicient time to cool. When it is cooled the parts will move to the position shown in Figure 3 and the circuit through the lamps can be reestablished.

It will be seen that a very simple type of time delay switch has been provided which is eminently suited for use with mercury vapor lamps arranged in a series system. Also it is to be noted particularly that the switch is so arranged that it can be used in such a system where film cut-outs are provided in shunt with each of the mercury vapor lamps without any danger of puncturing the films in the normal operation of starting and stopping the system.

Although this invention has been described in considerable detail, it is to be understood that such description is intended to be illustrative rather than limiting, as the invention may be variously embodied and is to be interpreted as claimed.

I claim:

A normally closed electric switch having a time delay in closing after carrying load current, said switch comprising Contact means, thermal means, over-center spring means operatively connected to said contact means for causing opening or closing of said contact means when moved across a predetermined point, said thermal means being operatively connected to said spring means and arranged to move said spring means back and forth across said point to open and close said contact means when said thermal means is heated and cooled, respectively, and an electromagnet operatively connected to said spring means for preventing said spring means from moving across said point to open said contact means when said electromagnet is initially energized and when said thermal element becomes heated during the time said electromagnet is energized.

References Cited in the file of this patent UNITED STATES PATENTS 1,399,226 Rhodes Dec. 6, 1921 1,782,937 Perry NOV. 25, 1930 1,929,552 Hanel Oct. 10, 1933 2,181,606 Parks NOV. 28, 1939 2,263,225 Sparrow Nov. 18, 1941 2,307,776 Grant et al. Jan. 12, 1943 2,629,034 Harrold Feb. 17, 1953