US2838717A - Control system - Google Patents

Description

June w, 1958 H. A. BREEDING ETAL 2,838,717

' CONTROL SYSTEM Filed Dec. 30, 1955 g 3 1 l A; o l J Inven'ior-s:

Harold A. Breeding Ermzs+ C. MQLr'H' by, Thrzir Afior-nay United States Patent CONTROL SYSTEM Harold A. Breeding, Hendersonville, N. C., and Ernest C. Marti, Chagrin Falls, Ohio, assignors to General Electric Company, a corporation of New York Application December 30, 1955, Serial No. 556,729

13 Claims. (Cl. 317--22) ()ur invention relates to control systems for series lighting circuits.

In series lighting circuits, a number of lamps are connected in series with one another and supplied with a substantially constant current from a substantially constant potential source through the agency of a translating device which converts a constant voltage supply into a constant current supply. The most commonly employed translating device for accomplishing this result is a floating coil variable impedance transformer although various networks such as the monocyclic square may be used. Such a device, in its attempt to maintain constant current output, will generate extremely high output voltages when the continuity of the series lighting circuit supplied thereby is interrupted. Such high voltages may damage the circuit components of the system and are a definite shock hazard to anyone coming in contact with the circuit.

In order to avoid these high open circuit voltages, it has heretofore been proposed to de-energize the series lighting circuit in response to open circuits caused by apparatus failures other than lamp failures. Lamp failures have been provided for by connecting across each lamp a cutout which, upon a lamp failure, completes a circuit about the defective lamp. If an open circuit is caused by a lamp failure, it is desirable to maintain energization of the series lighting circuit until the cutout connected across the defective lamp can function to short circuit the lamp and re-establish the series circuit. For open circuits, due to causes such as the breaking of an overhead wire forming part of the series circuit, it is desirable to de-energize the circuit quickly, and if possible,-before the wire falls to the ground. Usually, a delay period of from one to one and one half seconds between the occurrence of an open circuit and the operation of a circuit breaker for de-energizing the lighting circuit is sutficient to give the protection desired and sufficient time within which the lamp cutouts may function to short circuit defective lamps. Such a protective systcm is shown and described in United States Letters Patent 2,324,875, Justin Peterson and Frederick A. Weigel,

granted July 20, 1943.

Open air arcs, incandenscent lamps, and various forms of vapor lamps may be used in such lighting circuits. The employment of straight series connected vapor lamps may result in the failure of cutouts associated with operative lamps or, if a cutout fails to operate, in an indication of an open circuit when in fact current has ceased to flow in the series lighting circuit because one or more arcs have become extinguished due to a voltage dip in the source of supply and cannot be re-struck at the usual ignition voltages because of the heated condition of the lamps. This situation will be appreciated from a consideration of the operation of a mercury vapor lamp having a gas filling such as argon in order to facilitate are striking and the subsequent vaporization of the mercury filling of such a lamp. Such a mercury vapor lamp may become extinguished if a 25% subnormal operating voltage exists for a period of time as short as four cycles of the source of supply. Once heated such a mercury vapor lamp requires a much higher starting voltage than is suitable for starting it in its cold condition. Such a mercury arc lamp may require from 200 to 300 volts for are striking when cold whereas when heated due to a prior operation thereof it may require several thousand volts for are striking. Due to the ionizable gas filling in these lamps and its low pressure when the lamp is cold, the 200 to 300 volts required for are striking may drop to as low as 20 volts upon ignition of the arc and thereafter increase after about five minutes to an operating value of about volts when the pressure in the lamp has increased to about one atmosphere due to the vaporization of the mercury therein. Ordinarily, about 25 such lamps are connected in a series lighting circuit and supplied with about 3.2 ampercs by a constant current transformer having an open circuit voltage of about 6300 volts. Each lamp in such circuit may be provided with a short circuiting cutout which is intended to breakdown at a lamp voltage of from 450 to 600 volts. Consequently, if a series lighting circuit includes straight series connected mercury lamps of the type above described and these lamps have been brought to their operating temperature before they become extinguished due to a dip in line voltage, any attempt to re-ignite them may result in premature cutout failures indicative of lamp failures whereas in fact the difficulty is due to the high striking voltage required to rc-ignite them in their heated condition resulting from previous operation.

it is an object of our invention to prevent a protective de-energization of a series lighting circuit immediately following an interruption in the current flow therein and to provide for such protective de-energization if energization of the circuit produces no current flow therein.

It is another object of our invention to provide for the re-energization of a series lighting system a predetermined time interval after the interruption of current flow therein has caused its de-energization so that previously ignited lamps may cool sufficiently to facilitate are striking at lower applied voltages.

It is also an object of our invention to provide a series are lighting system which is de-energized both after a short interval following its energization without current flow and immediately upon the interruption of a current flow once established and which is re-energized after a time interval sulficient for the arc lamps therein to cool to normal starting conditions once current has flowed in the circuit and given an indication that the open circuit condition may be due to arc extinguishment and not due to some mechanical failure requiring attention and repair.

It is a further object of our invention to provide a control system for a series lighting circuit in which protection is provided against overvoltage occurring due to mechanical failures in the system and in which a delay period is imposed for re-energizing the system after each de-energization thereof in response to interruption of current flow therein to prevent premature cutout failures occurring across lamps having a high starting voltage when heated due to their previous operation.

For a better understanding of our invention, together with other and further objects thereof, reference should be had to the following description taken in connection With the accompanying drawing, and its scope will be pointed out in the appended claims.

In the accompanying drawing, Fig. 1 is a diagrammatic illustration of the circuit elements and their interconnection in an electrically reset system embodying our invention; and Fig. 2 is a diagrammatic representation of a like system embodying a mechanically reset component.

type which converts a substantially constant voltage supply into a substantially constant current supply for the vapor lamps 9 which are connected in direct series circuit with one another in the lighting circuit 1. These lamps may be of the mercury type above described and have like operating characteristics. They have been indicated by Xs and only four have been shown although it is to be understood that the circuit may include any reasonable number of these lamps and the extension of the circuit for this purpose has been indicated by the dotted lines which complete the lighting circuit as illustrated in the drawing. Each lamp is provided with a cutout which may form part of the lamp structure or be associated with the socket for the lamp. In the drawing, one of these cutouts has been illustrated at it) connected in shunt to one of the lamps 9 and it will be understood that each of the lamps will normally be provided with such a cutout. One suitable type of cutout comprises a dielectric film or barrier which breaks down when the voltage applied thereto by electrodes in engagement with the film exceeds a predetermined value. Upon breakdown of the dielectric film of the cutout, a circuit is completed in shunt to a defective lamp so that the continuity of the series circuit and the ignition of the remaining lamps in this circuit is not interrupted.

The energization of operating winding 8 of contactor 7 is controlled by two timing means which are selectively energized by a series relay 11 having an operating winding 12, normally open contacts 13 and normally closed contacts 14. V The operating winding 12 of this series relay is connected to be responsive to current flow in the lighting circuit. In the arrangement illustrated, this has been accomplished by energizing it through a series insulating transformer 15 having its primary winding 16 connected in the series lighting circuit and its secondary winding 17 connected to its operating winding 12. In view of the fact that the vapor lamps have at times a tendency to generate a direct current component of current flow in the lighting circuit, a condenser 18 has been connected in series with the lamps to prevent the flow of this current. In order to increase the sensitivity of series relay 11, a condenser 19 has been connected in series circuit with its winding 12. It will be understood that the arrangement is such that upon current flow in the lighting circuit, series relay 11 will be energized to close its normally open contacts 13 and open its normally closed contacts 14 and that upon no current how in the lighting circuit or upon an interruption of the current flow therein, this relay will assume the position illustrated in the drawing opening its normally open contacts 13 and closing its normally closed contacts 14.

One of the above-noted timing means, which acts as a protective device, is controlled through the normally closed contacts 14 of series relay 11. This timing means comprises a thermal switch 20 and a lock-in relay 21. The other above-noted timing means, which constitutes a recycling device, is controlled through the normally open contacts 13 of series relay 11 and comprises a time delay reclosing relay 22 and a holding relay 23 associated therewith. The first timing means operates to disconnect the constant current transformer from its supply conductors in response to an interruption in the lighting circuit due to some apparatus failure other than a lamp failure, and the second timing means operates to disconnect the primary of the constant current transformer from its supply conductors when current flow in the lighting circuit is interrupted after having once been established therein. Under the control of this second timing means, the primary of the constant current transformer will again be connected to the source of supply a predetermined time after the interruption of current how in the lighting circuit so that the lamps therein may be re-ignited after a suitable cool period following their extinguishment and the opening of the lighting circuit which may have resulted from a dip in line voltage or other circuit disturbance. If, however, the opening of the lighting circuit has been the result of some circuit failure, such as a broken conductor, the arrangement is such that after the second timing means has recycled in order to re-energize the circuit, the absence of current flow therein will then operate the first timing means to disconnect the primary of the constant current transformer from its source of supply in a manner requiring a resetting operation thereof before the lighting circuit can again be energized by connecting the primary of the constant current transformer to its source of supply.

Thermal switch 20 has normally closed contacts 24 and normally open contacts 25 which are controlled by a thermal element 26 which acts on a bimetal switch member 27 which constitutes a common contact for both contacts 24 and 25. This thermal switch is so constructed as to operate within a second or a second and a half after its thermal element has been energized so that within this period of time its contacts 24 are opened and its contacts 25 are closed. In order to limit arcing at its contacts, bimetal switch member 27 may have a snap action in its movement from one position to the other to control the making and breaking of circuits through its contacts 24 and 25.

Lock-in relay 21 has an operating winding 28, normally closed control contacts 29, normallyclosed reset contacts 3t! and normally open lock-in contacts 31.

Time delay reclosing relay 22 has an operating winding 32 normally closed contacts 33 and an adjustable delay mechanism 34 which permits its contacts 33 to be opened immediately on the energization of its winding 32 but which delays the closing of these contacts by a time period having a duration of the order of 7 to 10 minutes although longer delay times maybe used. In the an rangement illustrated, the delay mechanism 34 has been indicated as of the dash pot type although obviously other mechanisms may be employed for imposing a time delay in the closing of contacts 33 of this relay.

The holding relay 23 associated with the time delay reclosing relay 22 has an operating winding 35, normally open contacts 36 and normally open contacts 37.

Control power for operating the components of the control circuit is supplied through a switch 38 which connects the control circuit with energizing conductors 39. These energizing conductors are connected to the secondary 46 of a control transformer 41 having its primary winding connected across supply conductors 5. These supply conductors may be energized at 2400 volts from a 60 cycle source of supply and the control transformer may be constructed to provide a control voltage of the order of 200 to 220 volts. The control switch 38 has been illustrated as a hand operated switch although it is to be understood that in many instances it will be the switching means of a time switch or of a photoelectric relay which may be employed for turning the series lighting circuit on or off in accordance with a desired program.

The interconnection of the above-described components into the system of Fig. 1 will now be described in connection with the operation of the system.

The lighting circuit 1 may be energized by closing control switch 38. Closure of this switch connects the operating winding 8 of contactor 7 across energizing conductors 39 through the normally closed contacts 33 of time delay reclosing relay 22 and normally closed control contacts 29 of lock-in relay 21. Contactor 7 consequently closes its contacts 6 and connects primary winding 4 of constant current transformer 3 to supply conductors 5 for energization from the source of supply. Constant current transformer 3 is thus energized and through its secondary winding 2 and the load conductors connected thereto supplies energization to lighting circuit 1. If, due to a line fault or circuit fault other than a defective lamp, no current flows in the lighting circuit, series relay 11 will not be energized and will remain in the position illustrated in the drawing with its normally closed contacts 14 closed and its normally open contacts 13 open. Consequently, thermal switch will be energized from conductors 39 through the normally closed contacts 14 of series relay 11 through a circuit including the normally closed contacts 33 of time delay reclosing relay 22, the normally closed contacts 24 of thermal switch 20, its thermal element 26, resistor 43, normally closed contacts 14 of series relay 11 and normally closed resetting contacts of lock-in relay 2.1. After a time delay period of one to one and one half seconds, thermal switch 20 will close its contacts 25 energizing winding 28 of lock-in relay 21 from conductors 39 through a circuit including the normally closed contacts 33 of time delay reclosing relay 22. When relay 21 picks up, it completes its own holding circuit across conductors 39 through its normally open contacts 31. it also opens its normally closed control circuit contacts 29 and tie-energizes winding 8 of contactor 7 which thereupon opens its contacts 6 to deenergize the lighting circuit 1. It also opens its reset contacts 39 to tie-energize thermal switch 20 which thereupon opens its contacts 25 and closes its contacts 24 for a SIlbSQUIllZ operation Since lock-in relay 21 remains energized, through its contacts 31, the operating winding 8 of contactor 7 cannot again be connected for energization until operating winding 28 of lock-in relay 21 is de-energized by opening control switch 38. Upon de-energization, lock-in relay 21 returns to the position illustrated in the drawing and this relay under the control of thermal switch 20 is again conditioned for another protective operation such as has been described.

If as a result of the energization of lighting circuit 1 by closing control switch 38, current flows in the lighting circuit, series relay 11 will be energized and close its normally open contacts 13 and open its normally closed contacts 14. The opening of normally closed contacts 14 ale-energizes the protective timer 2021 which cannot consequently operate as above described. Closing of normally open contacts 13 of series relay 11 will cause holding relay 23 to close its contacts 36 and 37 by connecting its operating winding across conductors 39 through normally closed control contacts 29 of lock-in relay 21 and normally closedcontacts 33 of time delay reclosing relay 22. Closure of contacts 36 of holding relay 23 will connect the operating Winding 32 of time delay reclosing relay 22 across conductors 39 through the normally open contacts 13 of series relay 11, which are now closed, normally closed contacts 29 of lock-in relay 21 and the now closed normally open contacts 37 of holding relay 23. Thereafter, if for some reason current ceases to flow in lighting circuit 1, series relay ill will become deenergized closing its normally closed contacts 14 and opening its normally open contacts 13. The opening of contacts 13 of series relay 11 de-energizes windings 32 and 35 of time delay reclosing relay 22 and holding relay 23. Relay 23 immediately opens its contacts 36 and 37 but contacts 33 of relay 22 will not close until timing mechanism 34 permits them to close from 7 to 10 minutes after the deenergization of relay 22. This results in the de-energization of operating winding 8, of relay 7 and the consequent removal of power from the lighting circuit by the opening of contacts 6. During this timing period of relay 22, the timing of thermal switch 20 is prevented by the opening of its operating circuit at contacts 33 of relay 22 and at contacts 37 of relay 23. After'the time interval imposed by relay 22, contacts 33 thereof will close to energize operating winding 8 of contactor 7 by connecting it across conductors 39 through switch 38, contacts 33 of relay 22 and contacts 29 of relay 21. Contactor 7 will thus close its contacts 6 and secure another energization of the lighting circuit 1 through constant current transformer 3. The time period imposed by relay 22 before the lighting circuit 1 can again be energized is sufiicient to permit lamps 9 in the lighting circuit to cool down so that they may be restarted at their cold starting voltages. If, however, upon re-energization of lighting circuit 1 no current flows therein, then protective timer 20-21 will operate to disconnect the lighting circuit from its source of supply and require resetting before the lighting circuit can be energized again.

Thus, recycling of the circuit provides for re-ignition of the direct series connected lights when their extinguishrnent resulted from a dip in line voltage or a similar line disturbance, the circuit being automatically re-energized after a sufiicient time delay to prevent premature cutout failures occurring across lamps having a high starting voltage as a result of their heated condition resulting from previous operation. On the other hand, any fault causing an open circuit which produces clangerously high open circuit voltages, causes the lighting circuit to be de-energized after a short time delay in response to the operation of protective timer 20-21. One advantage of this circuit is that the time delay reclosing relay 22 is not inserted into the circuit until the lamps have started. Therefore, any fluttering of contacts in the circuit or any other primary circuit disturbances will not cause misoperation of the circuit. Furthermore, once the lamps have started, any primary circuit disturbances which will not put the lamps out will not cause recycling and consequently recycling of the system is limited to only the necessary number of operations and is strictly dependent on the stability of the lamps under the conditions of the circuit. A further advantage of this circuit is that the protective timer 2G-21 will operate to prevent excessive voltages in the lighting circuit in the event that a failure of current to flow therein is due to a fault that requires correction before re-energizing the lighting circuit.

From the operations above described, it will also be apparent that a failure of the power supply will impose the necessary time delay before an attempt is made to restart the lamps, since such restarting operation cannot occur until contacts 33 of the time delay reclosing relay 22 has completed the control circuit for the operating winding 3 of the contactor 7.

The control system shown in Fig. 2 is substantially the same as that shown in Fig. 1 with the exception that a timer 44 requiring manual resetting has been substituted for the electrical reset timer 20-21 of Fig. 1. Consequently, in Fig. 2 like reference numbers have been employed to identify parts therein corresponding with parts previously described in connection with Fig. 1.

Thermal switch 44 is a toggle switch having an operating lever 45 provided with a handle and pivoted upon a pin 46, a trip member 47 pivoted upon this pin and a contact operating arm 48 also pivoted on this pin. A toggle spring 49 connected between operating lever 45 and contact arm 48 moves this contact arm into an upward position so that a contact 50 mounted on this arm engages a contact 51 within a shield 52 when the operating lever and its handle are moved to an upper position. Trip member 47 is held in position by a thermostatic element 53, the free end of which engages a trigger 54 on trip member 47. At normal temperatures the thermostatic element catches trigger 54 and holds trip member 47 stationary against the pressure of rod 55 which is urged downwardly by a spring 56'. When the thermostatic element is heated by current flowing through trip member 47 about pin 46 in a ciockwise direction.

The trip member in turn engages a tripping lug 57 on arm 48 and carries this arm in a clockwise direction against the pull of spring 49 to open contacts 50, 51. Switch 44 is reset by first moving lever 45 counterclockwise, the lever being provided with a projection 58 which engages and carries trip member 46 along with it. The trip member is so moved until trigger 54 is engaged by thermostatic element 53. Trip member 47 is then held in its normal position by the thermostat. Lever 49 is thereafter moved clockwise to its uppermost position, the over-center spring 49 being moved past pivot 46 and arm 49 being raised to close the circuit of contacts 50, 51.

Thermostatic element 53 is heated by current supplied by a secondary winding 59 of a transformer 69. The circuit may be traced from one terminal of winding 59 through the thermostatic element 53 and contacts 50, 51 to the other terminal of this winding. The primary winding 61 of transformer 60 is connected across energizing conductors 39 through switch 38, contacts 33 of time delay reclosing relay 22, an adjustable resistor 62 and contacts 14 of series relay l1. Resistor 62 provides a timing adjustment for thermal switch 44. When switch 44 is tripped by thermostatic element 53, contacts 50, 51 open the circuit of the thermostat and the handle of lever 45 of switch 44 releases contacts 63 to open the circuit of the operating winding 8 of contactor 7 in the same manner as control contacts 29 of lock-in relay 21 of Fig. l. The thermalswitch 44 and its operating circuits are the same as those shown in the above-referred to United States Letters Patent 2,324,875 which may be considered for further detailed information relative thereto.

In view of the several operations described above in connection with Fig. 1, it is believed to be quite obvious that the same operations will occur when using the circuit of Fig. 2 with the exception, of course, that thermal switch 44 must be reset by adjusting its linkage at the location of this switch whereas the corresponding timing mechanism 26-21 of Fig. 1 can be reset electrically at a remote location by opening and again closing control switch 38.

Systems embodying our invention provide the overvoltage protection required in series lighting circuits and at the same time also prevent premature cutout failures occurring across lamps having a high restarting voltage while still hot from a previous operation which was interrupted due to circuit disturbances resulting in an extinguishment of one or more lamps in the lighting circuit. In other words our system prevents a protective de-energization of a series lighting circuit immediately following an interruption in the current ilow therein and provides for such protective de-energization if energization or re energization of the circuit produces no current flow there- While we have described above only two preferred em bodiments of our invention by way of illustrating the same, many modifications will occur to those skilled in the art, and we, therefore, wish to have it understood that we intend in the appended claims to cover all such modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. A control system comprising: supply conductors; load conductors; switching means for controlling the connection of said supply conductors with said load conductors; a control circuit, the closing and opening of which respectively operates said switching means to connect and disconnect said load conductors with said supply conductors; first timing means for opening said control circuit a predetermined time interval after its energization when no current exists in said load conductors; second timing means responsive to an interruption in current flow in said load conductors for opening said control circuit 8 and again closing it after a predetermined time; and means for opening and closing said control circuit independently of but subject to the control of each of said timing means.

2. A control system including load conductors; supply conductors; a contactor having normally open contacts and'means including a winding for operating said contacts; means including said normally open contacts of said contactor for connecting said lead conductors with said supply conductors; first timing means for energizing said winding of said contactor and for in. rrupting the energization of said winding of said contactor a predetermined time interval after its energizatiou when no current exists in said load conductors; and second timing means for completing the energizing circuit for said winding of said contactor while current flows in said load conductors, for interrupting said energizing circuit upon interruption of current flow in said load conductors, and for again completing said energizing circuit a predetermined time period thereafter.

3. A control system including load conductors; supply conductors; a contactor having normally open contacts and means including a Winding for operating said contacts; means including said normally open contacts of said contactor for connecting said load conductors with said supply conductors; first timing means energized concurrently with the energization of said winding of said contactor and responsive to a condition of no current flow in said load conductors for interrupting and maintaining interrupted the energization of said winding of said contactor after a predetermined time interval; and a second timing means for completing the energizing circuit for said windnig of said contactor while current flows in said load conductors, for interrupting said energizing circuit upon interruption of current flow in said load conductors, and for again completing said energizing circuit a predetermined time period thereafter.

4. A control system comprising supply conductors; load conductors; a contactor having normally open contacts and means including a winding the energization of which closes said contacts; means including said contacts of said contactor for connecting said load conductors to said supply conductors; a series relay having normally closed contacts, normally open contacts, and means including an operating winding for actuating said contacts; means for connecting the operating winding of said series relay to be responsive to current flow in said load conductors; first timing means including the normally closed contacts of said series relay in their closed position for de-energizing and maintaining de-energized said operating winding of said contactor in response to no current flow in said load conductors a predetermined time interval after said operating winding of said contactor has been energized; and second timing means including the normally open contacts of said series relay for maintaining energization of said winding of said contactor upon closure of said last mentioned contacts and for de-energizing said winding of said contactor for a predetermined time interval upon opening of said last mentioned contacts.

5. A control system comprising supply conductors; load conductors; a contactor having normally open contacts and means including a winding .the energization of which closes said contacts; means including said contacts of said contactor for connecting said load conductor to said supply conductors; a series relay having normally closed contacts, normally open contacts, and means including an operating winding for actuating said series relay contacts; means for connecting the operating winding of said series relay to be responsive to current flow in said conductors; first timing means including the normally closed contacts of said series relay in their closed position for de-energiz ing said operating winding of said contactor in response to no current flow in said load conducotrs a predetermined time interval after said operating winding of said contactor has beenenergized; and second timing means including the normally open contacts of said series relay 9 for maintaining the energization of said winding of said contactor upon closure of said last mentioned contacts and for de-energizing said winding of said contactor for a predetermined time interval upon opening of said last mentioned contacts.

6. A control system comprising a constant current translating device having input and output terminals; load conductors connected to the output terminals of said device; a contactor having normally open contacts and means including a winding for operating said contacts; supply conductors connected to the input terminals of said device through said contacts of said contactor; a control circuit in series with said winding of said contactor; means including a switch in said control circuit for connecting said control circuit to said supply conductors and for controlling the energization of said winding of said contactor through said control circuit; firsttiming means for energizing said winding of said contactor and responsive to a condition of no current flow in said load conductors for interrupting said control circuit independently of said switch a predetermined time interval after energization of said contactor winding; and second timing means for completing said control circuit while current flows in said load circuit, for interrupting said control circuit independently of said switch upon an interruption of current flow in said load conductors, and for again completing said control circuit after a predetermined time interval.

7. A control system comprising a constant current translating device having input and output terminals; load conductors connected to the output terminals of said device; a contactor having normally open contacts and means including a winding for operating said contacts; supply conductors connected to said input terminals of said device through said contacts of said contactor; a control circuit in series with said winding of said contactor; means including a switch in said control circuit for connecting said control circuit to said supply conductors and for controlling the energization of said winding of said contactor through said control circuit; first timing means energized concurrently with the energization of said winding of said contactor and responsive to a condition of no current flow in said load conductors for interrupting said control circuit independently of said switch after a predetermined time interval; and second timing means for completing said control circuit while current flows in said load circuit, for interrupting said control circuit independently of said switch upon an interruption of current flow in said load conductors, and for again completing said control circuit after a predetermined time interval.

8. A control system comprising a constant current translating device having input terminals and output terminals; load conductors connected to said output terminals of said device; supply conductors; a contactor having normally opened contacts connected between said supply conductors and said input terminals of said translating device and means including a winding for actuating said contacts; a timing relay having normally closed contacts and means including an operating winding and a delay mechanism for immediately opening said contacts upon energization of said winding and thereafter upon de-energization of said winding closing said contacts after the lapse of a predetermined time interval determined by said delay mechanism; a holding relay having means including an opertaing winding, normally open contacts connected in shunt to said normally closed contacts of said timing relay, and normally open contacts connected in circuit with said operating winding of said timing relay in shunt to the operating winding of said holding relay; means including a second timing relay having normally closed control contacts, normally closed reset contacts, and an operating circuit for opening both of said control and reset contacts after a predetermined time interval following energization thereof; a series relay having normally closed contacts controlling the energization of said operating circuit of said second timing relay, normally open contacts controlling the energization of said operating windings of said first timing relay and of said holding relay, and means including an operating winding connected to be responsive to current flow in said load conductors for actuating said series relay contacts; a control circuit including the normally closed control contacts of said first timing relay, the operating winding of said contactor and the normally closed control contacts of said second timing relay; and means for controlling the energization of said control circuit to control the energization of said operating winding of said contactor.

9. A control system comprising a constant current translating device having input and output conductors; supply conductors; load conductors connected to said output conductors of said translating device; a contactor having normally open contacts and means including a winding for operating said contacts; means including said contacts of said contactor for controlling the connection of said input conductors of said translating device with said supply conductors; a series relay having normally open contacts, normally closed contacts and means in cluding a winding for operating said series relay contacts; means for connecting said winding of said relay in series circuit relation with said load conductors; a timing relay having normally closed contacts and means including an operating winding and a time delay mechanism for instantaneously opening the contacts of said timing relay when its said operating winding is energized and for delaying the closure of said contacts for a predetermined interval determined by its said time delay mechanism upon de-energization of its said operating winding; a holding relay having means including an operating winding, normally open contacts connected in shunt with said normally closed contacts of said timing relay, normally open contacts which connect the winding of said timing relay in shunt to said holding relay winding; control conductors, means including a switch for connecting said control conductors to said supply conductors; a thermal switch having normally closed contacts in circuit with a thermal element and normally open contacts which are closed by a predetermined heating of said thermal element which also opens its normally closed contacts; and a lock-in relay having: normally closed control contacts connecting said winding of said contactor in circuit with said normally closed contacts of said timing relay across said control conductors and connecting said winding of said holding relay across said control conductors in circuit with said normally closed contacts of said timing relay and said normally open contacts of said series relay; normally closed reset contacts connected in circuit with said normally closed contacts of said series relay, said thermal element, said normally closed contacts of said thermal switch and said normally closed contacts of said timing relay across said control conductors; and normally open lock-in contacts connected in shunt across said normally open contacts of said thermal switch, said lock-in relay having means including a winding for operating its said contacts, and said lock-in relay winding being con nected across said control conductors through said normally opened contacts of said thermal switch and said normally closed contacts of said timing relay.

10. A control system for operating switching means for controlling the connection of supply conductors with load conductors comprising: a control circuit, the closing and opening of which respectively operates said switching means to connect and disconnect said load conductors with said supply conductors; first timing means effective after a predetermined time interval for opening and holding open said control circuit when no current exists in said load conductors; second timing means effective immediately after an established current in said load conductors ceases to exist for opening said control circuit and preventing operation of said first timing means 1 l and effective a predetermined time interval thereafter for reclosing said control circuit and permitting-operation of said first timing means. V a 1 V 11. A control system for operating switching means for controlling the connection of supply conductors with load conductors comprising: a control circuit, the closing and opening of which respectively operates said switching means to connect and disconnect said load conductors with said supply conductors; first timing means effective a predetermined time interval after said control circuit is energized for opening and holding open said control circuit when no current exists in said-load conductors; second timing means effective when current ceases to exist in said load conductors for opening said control circuit and preventing operation of said first timing means fora predetermined time interval thereafter.

12. A control system for operating switching means for controlling the connection of supply conductors with load conductors comprising: a control circuit, the closing and Opening of which respectively operates said switch ing means to connect and disconnect said load conductors with said supply conductors; first timing means effective a predetermined time interval after being energized for opening and holding open said control circuit; sec ond timing means for opening said control circuit and de-energizing said first timing means immediately upon de-energization of said second timing means and for retiming means a predetermined time interval thereafter; means for supplying energization to said control circuit and to each of said timing means; and means for interrupting said energization to said first timing means only when current exists in said load conductors and for interrupting said energization to said second timing means only when no current exists in said load conductors.

13. A control system for operating switching means for controlling the connection of supply conductors with load conductors comprising: a control circuit, the closing and opening of which respectively operates said switching means to connect and disconnect said load conductors with said supply conductors; first timing means including a delay circuit efieetive a predetermined time interval after being closed to cause said first timing means to open and hold open said control circuit; second timing means for opening said control circuitand said delay circuit immediately upon de-energization of said second timing means and for reclosing said control circuit and said delay circuit a predetermined time interval thereafter;

means effective only during a condition of no current existing in said load conductors for holding open said delay circuit to prevent the operation of said first timing means and for maintaining said second timing means deenergized.

No references cited.

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