US2779899A - Time delay control system - Google Patents

Description

Jan. 29, 1957 T. c. LENNOX 2,779,899

TIME DELAY CONTROL SYSTEM Filed July l, 1954 United States Patent TIME DELAY CONTROL SYSTEM Thomas C. Lennox, Pittsfield, Mass., assgnor to General Electric Company, a corporation of New York Application July 1, 1954, Serial No. 440,751

9 Claims. (Cl. 317-141) This invention relates to a time delay control system of a type particularly suited for controlling the setting of a spring driven electrical switching mechanism of the step type.

Step `type switching mechanisms are widely used in connection with step voltage regulators in which a voltage is adjusted by stepping a contact member from one voltage tap to another. In order to prevent unnecessary operation of the regulating mechanism under rapidly iluctuating load conditions, it has been customary for some years to provide a time delay means between the primary control device and the regulator proper. Lennox Patent 2,220,769, which is assigned to the same assignee as the present invention, illustrates a time delay control system of the type in use prior to the present invention. The embodiment of Patent 2,220,769 actually used commercially is shown in Fig. 2 of the patent wherein the forward and reverse motors of a time delay relay are actuated in response to an auxiliary relay which is in turn energized by a sensitive voltage regulating relay responsive to small iluctuations in the line voltage.

The auxiliary relay, which is of the instantaneous type, has its coils connected directly to the contacts of the voltage regulating relay and consequently, closes or opens its contacts every time a contact closes or opens on the voltage regulating relay. Such a system necessitates a substantial holding or compounding effect on the voltage regulating relay in order that excessive motion and chattering of the auxiliary relay be avoided. This has proved diicult to achieve in practice and therefore efforts have been directed for some time toward the production of a circuit which would omit the auxiliary relay.

It is one of the objects of this invention to provide a time delay control system in which the use of an auxiliary relay energized in response to closing of the voltage regulating relay contacts is avoided.

Another object of the invention is to provide a time delay control system in which the time delay relay winding control motor is initially energized by a circuit passing through contacts of a voltage regulating relay.

It is a further object of the invention to provide a time delay control system which includes two resistorcapacitor networks as control elements.

Briefly stated, in accordance with one of its aspects, the time delay control system of this invention comprises a transformer having a tap connection on the secondary winding, a time delay relay having a motor provided with a forward operating winding and a reverse operating winding, each winding having a main operating circuit through a normally closed contact and an auxiliary operating circuit through a normally open contact, the auxiliary operating circuit being connected to the transformer secondary winding tap connection, a series capacitor common to the main operating circuits, a parallel capacitor common to the auxiliary operating circuits, a resistor common to all operating circuits, a voltage regulating relay with two contacts selectively operable to complete one of the main operating circuits, the circuit 2,779,899 Patented Jan. 29, 1957 rice elements being correlated whereby the operating circuits are tuned in series to operate the motor through the main operating circuits and in parallel to operate the motor through the auxiliary operating circuits, and a set of main control contacts on the time delay relay, the main con? trol contacts being actuated by the time delay relay motor after a predetermined time of rotation in either direction.

The features of the invention which l believe to be novel are set forth with particularity in the appended claims. My invention, itself, both as to its organization and use, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompartying drawing which is a diagrammatic view of a step type voltage regulator apparatus incorporating one embodiment of the time delay control system of this invention.

The drawing shows a pair of power lines 10 and 11 which provide incoming power and lines 10 and 11' which Ifurnish power on the load side of the device. The power line 11 is connected to one end of a shunt winding 12 of a step type voltage regulator in a manner well known in the art. The power line 10 is connected to the mid-tap of a switching reactor 13 through which it is connected to the series winding 14 of the voltage regulator in a manner to be more fully explained hereinafter. The load line 11 is connected to the line 11 at the point where the line 11 is connected to the shunt winding 12 and is in effect a continuation of the line 11. The line 1G is connected to the line 10 through the series winding 14 of the voltage regulator, The series winding 14 is provided with a plurality of taps 15 each of which is connected `to a single one of a plurality of circumferentially arranged conducting segments 16. The two ends of the switching reactor 13 are connected respectively to concentric conducting rings 18 and 19 which are positioned radially inwardly of the conducting seg- `ments 16. A rotatable contact arm 20 is pivotally mounted at the center of the circle described by the conducting rings 18 and 19 and by the conducting segments 16.

In order 'to maintain electrical contact between the lower end of the switching reactor 13, with respect to the view shown in the drawing, and the contact segments 16, the contact arm 20 is provided at its right-hand edge, with respect to the view shown in the drawing, with a pair of contact brushes 21 and 22 which are conductively connected together. The contact 21 maintains contact with the radially inner conducting ring 18 while the contact 22 maintains contacts with the conducting segments 16 which are connected to the taps 15 of the series winding 14. Thus, the lower end of the switching reactor 13 is connected through the inner conducting ring 18, contacts 21 and 22, conducting segments 16, and taps 15 to the series winding 14.

In order to provide electrical Contact between the upper end of the switching reactor 13, with respect to the view shown in the drawing, and the contact segments 16, the left-hand edge of the contact arm 20 is provided with a pair of contact members 23 and 24 which are conductively connected together and respectively maintain contact with the outer conducting ring 19 and the contact segments 16. Thus, the upper end of the switching reactor 13 is connected to the series winding 14 through the conducting ring 19, contacts 23 and 24, conducting segments 16, and taps 15. The contacts 21 and 22 carried by the contact arm 20 are insulated from the contacts 23 and 24.

When the position of the contact arm 2i) is such that the contact arm Ztl and contacts 21, 22, 23, and 24 are in contact with only a single one of the conducting segments 16, the respective contacts 21, 22, 23, and 24 are all at the same electrical potentials since they are shortcircuited by the particular conducting segments 16 with which the contact arm 20 is in alignment.

In this case, the current divides between the two halves of the switching reactor 13, theA two halves of the winding being in parallel electrical relation with each other. However, if the position on the contact armf20 is such that it bridges a pair of adjacent conducting segments 16, as shown in the view in the drawing, then each end of the switching reactor V13 is connected across a different tap of the series winding 14. When this occurs, the switching reactor 13 acts as an auto-transformer and the voltage derived is half-.way between the voltages of the adjacent taps to which the respective opposite ends of the switching reactor 13 are connected.

The switching arm 20 is driven by a shaft 25 which is actuated by a spring-driven Geneva gear mechanism which will now be described.

A motor 26 drives a pinion 27 which engages a gear 28 mounted on a shaft 29 on'one end of which is mounted a Geneva gear driver 40 which is in driving engagement with a Geneva gear 32 mounted upon the same shaft 25 as the switching arm 20 whereby rotation of the Geneva gear rotates the switching arm 20 in unison.

Included in the illustrated embodiment is an arrangement for reversing the polarity connections of the series winding 14 when the switch arm 20 passes through its neutral position. For this purpose, a reversing switch 41 is provided in series with the line The reversing switch 41 is movable into engagement with either of contacts 42 and 43, these contacts being connected to opposite ends of the series winding 14. A pin member 44 is attached to the Geneva gear 32 in a position such that as Geneva gear 32 passes through the neutral position corresponding to the position at which the switch 41 should be moved from contact 42 to contact 43 or vice versa, the pin 44 engages the slot in a segment 45 of the Geneva gear 32 and causes a rapid motion of a reversing shaft 46 upon which is xedly mounted a link 47 connected to the segment 45. Since the switch 41 is also mounted upon the shaft 46, the motion of the shaft 46 causes the. switch member 41 to move from the contact 42 to the contact 43 and vice versa. f

The direction of rotation of the motor 26 depends upon which of its windings 26a and 26b is energized. The energizing circuit for each of the windings 26a and 2611 passes through a limit switch 48 actuated by a pin .49tcarried` by a gear which makes one complete revolution for every two complete revolutions of shaft 25. The limit switch 48 prevents the rotation of the switch arm from going too far in either direction.

The step voltage regulator with its control gearing described in the preceding paragraphs is conventional in all respect. The novel time delay control system for actuating the motor 26 will now be described in detail.

A power winding 50 inductively coupled to the shunt winding 12 supplies power for operating the time delay control system except for a voltage regulating relay 51 which is arranged to be energized on small differences in voltage from a current transformer 52 through a conventional variable control network 53 which is also connected to the power winding 50 by means of conductors 54 and 55 and variable resistor 56.

A voltage from the power winding 5,0 is impressed upon a primary winding 57 of a transformer 61. The transformer 61 has a secondary winding with a tap position 60 which divides the winding into a section 58 and a section 59. Voltage from the transformer 61 is used to operate a forward winding 62 and a reverse winding 63 of a motor 64 which is an element of a time delay relay 65. The motor 64 rotates a pinion 66 which in turn rotates a gear 67 having a pair of knobs 68 and 69 protruding therefrom which selectively engage contact arms which close contacts 70 and 71 to complete circuits through the limit switch 48 for the energization of the winding 26a and 2611 of the motor 26. The contacts 70 and '71 close only after the gear 67 has rotated for a time interval of the order of 30 seconds. The gear 67 is equipped with a radially extending groove member 72 engaged by a biasing spring 73 when the gear is in the neutral position illustrated. The radial member 72 may be turned out of the neutral position illustrated only by the application of a high starting torque and serves to prevent the operation of the motor 64 due to the presence of a spark suppression system to be described hereinafter. A cam element 74 of the time delay relay 65 rotates in unison with the gear 67. When the gear 67 is rotated, the cam 74 will either open a contact 75 and close a contact 76 or open a contact 77 and close a contact 78, energization of the motor winding 62 affecting the contacts 77 and 78 and energization of the motor winding 63 affecting the contacts 75 and 76.

With the gear 67 in the position illustrated, the initial energization of the operating windings 62 and 63 of the motor 64 takes place from the secondary winding of the transformer 61 through a series capacitor 79, contacts 89 or 81 of the voltage regulator relay 51, the normally closed contacts 75 or 77 of the time delay relay 65, the windings 62 or 63, a resistor 82, and back to the secondary winding of the transformer 61. The two circuits thus described are the main operating circuits of the motor windings 62 and 63 and the particular circiut selected depends upon which of the contacts 80 and 81 is closed. A spark suppression circuit for the contacts 80 and 81 is provided by the network consisting of a pair of resistors 83 and a pair of capacitors 84.

Auxiliary circuits for energization of the winding 62 and 63 of the motor 64 are provided by a circuit which includes a parallel capacitor 85 connected at the tap 60 of the secondary winding of the transformer 61.

Normally, the time delay control circuit operates at l20i'vwolts and 6() cycles. The operating coil 63 advances the setting of the voltage regulator and the operating` coil 62 lowers this setting. When the motor 64 has operated for a sufficient time the output contacts 70 or 71, depending upon which direction the motor was turned, close to connect the regulator motor 26 to the source of power. rnrnediately upon the start of a timing cycle either the contact 78 or the contact 76 closes and remains closed until the relay has returned to the neutral position illustrated.

The time delay system operates with the full voltage on the appropriate winding 62 of the time delay relay 65 and with substantially no voltage on the other winding (63) when the contact 80 is closed regardless of whether contact 78 is open or closed. Conversely, with both contacts 80 and 81 open, full voltage will be imposed for run-back on the winding 62 if the contact 76 is closed, in which case the contact 75 will be open. These conditions will lbe obtained provided the elements described have the correct values of resistance and capacitance as hereinafter specified.

The coilsV 62 and 63 are mounted on the stationary magnetic structure of the time delay relay and are highly inductive. When alterna-ting voltage is applied to one of them, the resulting current will lag the voltage by some angle qs, so that cos o represents the power factor of the current. If the impedance of the windings 62 or 63 is Z, the resistance in the resistor 852 is equal to the capacitance of capacitor 85 will equal Sin t ZarfZ i and the capacitance of capacitor 79 will equal 21rfZ SlIl 11 lf the normal voltage required for operation of the windings 62 or 63 equals E, the secondary Winding 58 of the transformer 61 willv be wound for E cos o, and the winding 59 will be wound for l-cosqb While it is well within the province of one skilled in the art to design circuit elements correlated to provide the desired operation, the following quantities are given as typical of a particular installation. Those skilled in the art will appreciate that other correlated quantities may be readily determined.

E: 120 volts Z: 1500 ohms Resistor 82:3000 ohms Capacitor S5=approximately 1.5 microfarads Capacitor 7 9=approximately 2 microfarads Voltage of secondary winding 58:60 volts Voltage of secondary winding 59:240 volts The above correlated arrangement is such that the windings 62 or 63 will oe resonant if in series with the capacitor 79 or in parallel with the capacitor 85. Consequently, when the contact 80 of the voltage regulator relay 51 closes the circ-uit through the capacitor 79, winding 62 and resistor S2 act as a pure resistance and the equivalent resistances are such that the junction between the winding 62 and resistor 82 is at the same potential as the tap 6d. Thus, no voltage appears between these two junctions, and the capacitor 85 which joins them receives no voltage. When the operation of the time delayrelay 65 in response to energization of the winding 62 causes the closing of the contact 78, no voltage is applied to the winding 63 and the relay continues to run forward by means of the winding 62 until the motor 26 is energized. When the contacts 80 and 81 are open, and the contacts 78 remain closed, the condition described above no longer exists and the voltage of the winding 59 is applied to a circuit consisting of the capacitor S5 and the winding 63 in parallel connected in series with the resistor 82, and the impedances are such, due to the resonance of the capacitor 8S and the winding 63, that the required normal voltage appears across the winding 63 and the relay runs back toward its neutral position under full power, no voltage being applied to the winding 62 because the contacts 80 and 76 are both open.

A comparable action to that described above takes place when the contact S1 closes to complete an initial main operating circuit through the winding 63.

T here is shown on the drawing a supplementary circuit consisting of capacitors S4 and resistors 83. These spark suppression elements are of high impedance compared to those previously described. However, the small current bypassed through this network when both contacts 8i) and Si of the voitage regulating relay 51 are open could cause the continued operation of the time delay relay 65 by a slight excitation of the windings 62 or 63, thereby promoting hunting of the device, were it not for the presence of the radial element 72 on the gear 67. When the gear 67 reaches the neutral position illustrated, the spring 73 engages the groove of the element 72 and the current produced by the spark suppressor network does not apply sui'iicient torque to the motor 64 to overcome the frictional engagement of the spring 73 with the elements 72.

The time delay control system of this invention not only permits the holding of a narrower voltage band on the regulator but avoids the mechanical vibration or chatter caused by the presence of an auxiliary relay in the circuit. in addition to this, it is not necessary to pro vide a holding coil in the voltage regulating relay in accordance with the previous practice.

While the present invention has been described With reference to particular embodiments thereof, it will be understood that the time delay control system may he applied to other apparatus than step voltage regulators and that numerous modifications may be made by those skilled in the art without actually departing from the invention. Therefore, I aim in the appended claims to cover all such equivalent vaniations as come within the true spirit and scope of the foregoing disclosure.

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

l. ln a time delay control system: a transformer having a tap connection on the secondary winding; a time delay relay having a motor provided with a forward operating winding and a reverse operating winding, each winding having a main operating circuit through a normally closed contact and an auxiliary operating circuit through a normally open contact, the auxiliary circuits being connected to said transformer secondary winding tap connections; a series capacitor common to said main operating circuits; a resistor common to all operating circuits; a voltage regulating relay with two contacts selectively operable to complete one of said main operating circuits; said circuit elements being correlated whereby said operating circuits are tuned in ser-ies to operate said motor through said main operating circuits and in parallel to operate said motor through `said auxiliary operating circuits; and a set of main control contacts on said time delay relay, said contacts being actuated by said time delay relay motor after a predetermined time of rotation in either direction.

2. A time delay system as claimed in claim l wherein the voltage regulating relay contacts have a high impedance spark suppression resistor-capacitor network connected in series therewith.

3. A time delay system as claimed in claim 2 wherein the time delay relay is equipped with a stop means tending to hold said relay in a neutral position, said stop means preventing operating of the relay motor in the absence of a completed main operating circuit through contacts of the voltage regulating relay.

4. ln a time delay control system: a transformer having a tap connection on the secondary winding; a time delay relay having a motor provided with a forward operating winding and a reverse operating winding, each winding having a main operating circuit through a normalty closed contact and an auxiliary operating circuit through a normally open contact to said transformer secondary winding tap connection; a series capacitor cornmon to said main operating circuits; a parallel capacitor common to said auxiliary operating circuits; a resistor common to all operating circuits; a voltage regulating relay with two contacts selectively operable to complete one of said main operating circuits; said circuit elements being correlated to provide resonance in said motor windings under all conditions wherein said operating circuits are completed; and a set of main control contacts on said time delay relay, said contacts being actuated by said time delay relay motor after a predetermined time of rotation in either direction.

5. ln a time delay control system: a transformer with a secondary winding having a rst terminal, a second terminal, and a tap connection to said winding at a point between said terminals; a time delay relay having a motor provided with a forward operating winding, a normally closed contact in a first operating circuit to said forward winding, a normal open contact in a second operating circuit to said forward winding, a reverse operating winding, a normally closed contact in a third operating circuit to said reverse winding, and a normally open contact in a fourth operating circuit to said reverse winding; avoltage regulating relay having a pair of contacts for selectively completingl an operating circuit to said forward andreverse windings through said first and third operating circuits; a first capacitor in a circuit connecting said first terminal through the contacts of said voltage regulating relay; a resistor in a circuit connecting said forward and reverse windings to said second terminal; a second capacitor connected in parallel with said forward and reverse windings through said second and fourth operating circuits and to the said tap connection; the position of said tap connection being correlated with said resistor, forward and reverse windings, and first and second capacitors whereby said windings are resonant when connected in series with said first capacitor and in parallel with said second capacitor; and a set of main control contacts on said time delay relay, said contacts being actuated by said time delay relay motor after a predetermined time of rotation in either direction.

6. An automatic control system for a step voltage regulator comprising a time delay relay having a motor provided with a forward rotation operating winding and a reverse rotation operating winding, a transformer with a secondary winding having a first and second terminal and tap point between said terminals, a voltage regulating relay having a voltage raising circuit closing position for causing connection of said forward rotation winding to said transformer secondary and having a voltage lowering circuit closing position for causing connection of said reverse rotation winding to said transformer secondary, said regulating relay having an intermediate circuit opening position, a normally closed Contact of said time delay relay through which the operating circuit of said forward rotation operating winding is connected, a normally closed contact of said time delay relay through which the operating circuit of said reverse rotation operating winding is connected, a first capacitor connected in the circuit leading from the first terminal of the secondary winding of said transformer through the contacts of said voltage regulating relay, a resistor connected in the circuit leading from lsaid forward and reverse rotation operating windings to the second terminal of the secondary winding of said transformer, a second capacitor connected to the transformer secondary winding tap, a pair of normally open contacts which close upon the opening of said normally closed contacts to place said second capacitor selectively in parallel with one of said rotation operating windings, the circuit elements being correlated whereby said rotation operating windings are resonant when connected in series with the said first capacitor and when connected in par allel with the said second capacitor, and a set of time delay main control contacts for regulator operating means arranged to be actuated by said time delay relay motor after a predetermined time of rotation in either direction.

7. in a time delay control system: a transformer hava tap connection on the secondary winding; a time delay relay having a motor provided with a forward operating winding and a reverse operating winding, each winding having a main operating circuit through a normally closed contact and an auxiliary operating circuit through a normally open contact, the auxiliary circuits being connected to said transformer secondary winding tap connection; a series capacitor common to said main operating circuits, a resistor common to all operating circuits; a voltage regulating relay with two contacts selectively operable to complete one of said main operating circuits; said circuit elements being correlated whereby said operating circuits are tuned in series to operate said motor through said auxiliary operating circuits; said series capacitor, resistor and tap connection being selected such that insufficient voltage appears across one of said operating windings through said auxiliary circuit to operate said motor when the other of said operating windings is energized through said main operating circuit by way of said voltage regulating relay contacts, and a set of main control contacts on said time delay relay, said contacts being actuated by said time delay relay motorafter a predetermined time 'of rotation in either direction.

8. In a time delay control system: a` transformer having a tap connection on the secondary winding; a time delay relay having a motor provided with a forward operating winding and a reverse operating winding, each winding having a main operating circuit through a normally cioscd contact and an auxiliary operating circuit through a normally open contact, the auxiliary circuits being connected to ysaid transformer secondary winding tap connection; a series capacitor common to said lmain operating circuits; a resistor common to all operating circuits; a voltage reguiating relay with two contacts selectively operable to complete one of said main operating circuits; said circuit elements being correlated whereby said operating circuits are tuned in series to operate said motor through said main operating circuits and in parallel to operate said motor through said auxiliary operating circuits; means for closing the normally open contact of one of said operating windings a predetermined time after the energization of the other of said windings through said voltage regulating relay contacts, said lseries capacitor, resistor, and tap connections being selected such that insuflicient voltage appears across said .one operating win-ding through said auxiliary circuit to operate lsaid motor when said other operating winding is energized through said main operating circuit by way of said voltage regulating relay contacts, and a set of main control contacts on said time delay relay, said contacts being actuated by said time delay relay motor after a predetermined time of rotation in either direction.

9. ln a time delay control system, a transformer with a secondary winding having first and second terminals and a tap terminal intermediate said first and second terminals, a time delay relay having a motor with a forward operating winding and a reverse operating winding, a normally closed contact in series with each of Isaid operating windings, a pair of contacts for selectively connecting said operating windings to said first and second terminals by way of said normally closed contacts, a normally open contact in series with each of said operating windings, circuit means connecting said first and tap terminals to said operating windings by way of said normally open contacts, cam means on said motor operative after a predetermined time after energization of one of said operating windings by said selective contacts to open the normally closed contact and close the normally open contact in series with the other operating winding, a first capacitor inseries in the circuit connecting said second terminal to said operating windings, a resistor in series with the circuit connecting said first terminal to said operating windings, a second capacitor connected in parallel with said operating windings by way of said normally open contacts, said first capacitor being of such a value to provide series resonance with said operating windings, said first capacitor, resistor and tap being selected such that the voltage between said second and tap terminals is substantially equal to the series voltage of the combination of said rst capacitor and said one operating winding when said one oper-ating winding is connected to said second terminal, said second capacitor being of such a value to provide parallel resonance with said operating windings in order to provide sufficient potential from said tap connection to operate said motor, and a set of main control contacts on said time delay relay, said contacts being actuated by said time delay relay motor after a predetermined time of rotation in either direction.

References Cited in the file of this patent UNITED STATES PATENTS

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