US2201595A - System for arcless interruption of alternating current - Google Patents

Description

May 21, 1940.

W. F. SZABO SYSTEM FOR ARGLESS INTERRUPIION Oi ALTERNATING CURRENT Filed April 3, 1936 2 Sheets-Sheet 1 igz NVENTOR. zcjg/aw W ATTORNEY.

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SYSTEM FOR ARCLESS :[NTERRUPTI0N OF ALTERNATING CURRENT May 21, 1940.

Filed April 3, 1936 2 Sheets-Sheet 2 fig.4

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Patented May 21, 1940 UNITED STATES- PATENT OFFICE SYSTEM FOR ARCLESS INTERRUPTION F ALTERNATING CURRENT Application April 3, 1936, Serial No. 72,569

' 24 Claims. (Cl. 175-294 This invention relates to a control system whereby a contactor interposed in an alternating current circuit may be made to open its contacts when the current passing therethrough is at or near the zero point of its cycle.

When a contactor is used to interrupt alternating currents of high values, very rapid deterioration of the contacts may occur because of the arcing which takes place.

If the (separation of the contacts occurs when the instantaneous value of the currentis at or near its maximum, an arcwill form which may continue for a period of several cycles before it is finally ruptured.

A relation exists between the intensity of arcing at the contacts and the instantaneous value of the current at the time of separation of the contacts so that the maximum amount of arcing will occur when the current is at its peak value, and

so the least amount, if any, will occur when the instantaneous value oicurrent is zero. 1

Broadly, it is therefore an object of this invention to secure an arcless interruption of an alterhating current circuit. as Previous methods have been employed to obtain the physical separation of the contacts at the time of the zero point of the current wave. However, those known involve complex mechanical structures which incorporate moving parts actuated in synchronism with the current cycle.

An object of the present invention is to provide means -ior interruption of the circuit when the instantaneous value of the current therein is sub- Y stantially zero, and without the use of mechanically operating devices timed in accordance with the cycle, and for physically moving the'contacts without the use of such mechanically operated timing devices.

A further object of this invention is to provide 40 a controlling means which is'simple in its operation and-adjustment, and which may be constructed at low cost.

A further specific object is to provide a circuit arrangement having means for altering phase re-.

lationships of currents and voltages which efi'ect the operation of a magnetically actuated device or its equivalent opening the main circuit contacts.

Other objects of this invention will become apparent from the following description.

In the drawings- 1 Fig. 1 is a graphic illustration showing the as.

tive phase relationship between the current in the coil actuating a contactor and the current controlled thereby.

, Fig. 2 is a wiring diagram of a phase shifter.

Fig. 3 is a wiring diagram of my control system illustrating its application to a work circuit.

Fig. 4 is a wiring diagram of a modified form of my control system. Fig. 5 is a wiring diagram 5 showing the application of my control system to a plurality of contactors.

In the drawings, the same characters are used to designate like or the same parts.

Although my invention may be adapted for use 19 in any alternating current circuit, I have chosen for purposes of explanation an embodiment applied to a single-phase load energized by a threephase source.

The energization of coil I0 is controlled by a contacting means I6, such as a push button, which may be interposed in the conductor H. In most magnetically operated contactors, a definite time interval occurs between the interruption of the coil current and the opening of the main contacts. Factors which affect this interval are contact spring pressure, gravity, amount of air gap in the magnetic circuit, thickness of the contacts, and wipe of the moving contacts with respect to the stationary contacts. This time interval, here- 5 inafter referred to as the drop-out time, is substantially constant and may be used to determine and control the time when the main circuit will be interrupted.

It is recognized, however, that worn-out and 30 thin contacts will start to open earlier than will those which are new and thick. But with a contactor having worn-out contacts, the spring pressure afiorded by springs, such as I5, is likewise reduced because of'smaller compression existing 35 when thin contacts are used over that which would exist in the use of thicker contacts. Thus, the two factors, thickness of contacts and spring pressure, although variable, tend to counterbalance each other and do not effect to any appreciable 4o amount the drop-out time.

If the coil current be interrupted prior to the instant when the current through the main contacts is passing through the zero point of its cycle by an amount of time equal to the drop-out time 5 of the contractor, then the main contacts will open at or near said zero point, resulting in arcless interruption.

This may be clearly seen by referring to Fig. 1, where current through the main contacts l3 and 50 I4 is shown as a sine wave, curve A, and where curve B represents the sine wave. of the current through the coil l0.

For the purpose of explanation, assume that it takes a period of time equal to one-third of a 55 cycle for the main contacts II and H to separate after interruption of the coil current, by operation of push button I6, and further assume that the phase of the current B is 120 electrical degrees in advance of the phase of current A. From the assumptions made, an interruption of the current B at a point such as D will cause the contactor to open its contacts 120 electrical degrees or one-third of a cycle later, represented as the point E on the current curve A, and which is the zero point of the sine wave. Separation of the contacts at this point gives arcless interruption of the current.

High inductance of an operating coil circuit of a contactor causes the arc which may be formed by the opening of this circuit to be generally extinguished when the instantaneous value of the current passing therethrough is zero. Therefore, if the contacts of the push button I are separated when the instantaneous value of the current in the coil circuit is not zero, an arc will be established across the contacts of the push button It which will continue until the current passing through said coil reaches a zero point of its sine wave. This are may be extinguished at the instant when the next zero point is reached after the physical separation of the contacts, or it may remain for several cycles, being extinguished, however, whenthe current in the circuit is passing through a zero point of the cycle. When the arc is extinguished, the current will cease to flow through the coil l0, resulting in its deenergization and the subsequent separation of the contacts II from the contacts I4.

It is therefore immaterial when the push button It is operated to open the coil circuit in view'of the continued energization of the coil until the current in the established arc reaches the zero point of the cycle. For instance, push button I8 might be opened when the current in the coil circuit was at a value such as C on curve B. However, current would continue to flow through the coil until a zero point such as D was reached.

Because of the fact that the current through the coil III is thus normally interrupted when it reaches the zero point of its cycle, and the fact i ample, if a contactor has a drop-out time of one-quarter cycle, the phase relation of curve B with respect to curve A may be shifted onetwelfth of a cycle ,so that the zero point D on curve B would occur ahead of point Elinstead of as shown. Curve F represents this phase shift and H the zero point.

In order to shift the phase relationship of the current in the two circuits, that is, the coil circult and the work circuit, some type of phase shifter may be used. Such a suitable phase shifter is illustrated in the drawings. The supply lines L1 and L: are shown connected to an inductance coil or auto-transformer 20 through variable connectors 2i, and conductors ll and 4|, providing a means for connecting the terminals of the auto-transformer 20 to any pair of the 3-phase supply lines L1, L2 and Lo. The cbil I I is shown having one of its terminals 24 connected to the supply line La and the other of its terminals 23 connected to one of a series-0t taps.

by curve A.

I to I, of the auto-transformer 20, and in this instance shown connected to the mid-tap 4.

As shown in Fig. 4, wherein parts previously described are denoted by like but primed numerals, the load circuit 3! and the circuit including the coil I. may be each connected to a difi'erent source of power indicated by conductors Li and L2 and conductors P respectively, provided that a definite time relationship exists be tween the frequencies of the two sources. This definite time relationship is such that uniform intervals occur between the zero values of the respective currents.

. Referring to Fig. 2, if it is desired to shift the phase of the current in the coil III, the conv ductor 22 connecting the terminal 23 of the coil to the auto-transformer 2| may be connected to a different tap. This causes the phase 01' the voltage across coil II to be shifted, which results in a corresponding shift in the phase of the current through the coil. Any number of taps may be provided on the coil of the auto-transformer to give any amount of phase shift varying between zero and 60.

With the apparatus as shown in Fig. 2, the voltage across the coil II is not constant. If the terminal "on the coil ll be connected to tap I or to tap I, the voltage will equal line voltage between L1 and L0 or between La and L1,

respectively. But if the terminal be connected at the mid-point, represented as'tap l, the voltage is equal to 86.6% of the line voltage.

Because of this drop in voltage, it is preferable to employ an additional auto-transformer 26 which is connected to one of the supply lines through conductor 42 and variable connector 2i, and which is connected to coil I. through conductors I1 and". Terminal points I to l, complementary to taps I to 1 of auto-transformer 20, are connected to the auto-transformer 26 through a series of taps II. This combination maintains the voltage across the coil II substantially constant so as to secure proper operation of the contactor.

Any type of variable connector 21 may be used for connecting the taps of the phase shifting auto-transformer II to the taps of the autotransformer 28. from the point connecting taps I to I to a point where it connects taps I to 1', it is possible to obtain six changes of phase relationship in increments of 10 with no change in the voltage across coil II.

By the provision of variable connectors such as 2|. the conductors I, II and 4! may be connected to the supply lines L1, in and L: in any desired combination for the purpose of obtaining further phase shifting. It is therefore possible by this device to shift the current represented by curve B, Fig. l, with respect to the current representedby the curve A in increments of 10 frorna point where the currents represented by the curves are in phase through a phase'shift or change equal to 360, at which point the currents are again in phase.

In operation of my device, assume that the drop-out time of contactor I is 35 of a second or equal to 90 electrical degrees. of a BO-cycle current. Further assume that the current in the coil II, represented by curve B, Fig. i, is 120 in advance of current in :work circuit ll, represented The current represented by the curve F is in the desired phase relationship with respect to the current represented by curve A, since the time in electrical degrees from the Point H to By moving the connector 21 the point E is 90 electrical degrees, and is equal to the drop-outtime of the contactor. There fore, it is desired to change the phase of current through the coil Ill from curve B to curve F.

By the movement of the variable connector 21 from an assumed previous position such as taps I and l' to a position connecting taps l and 4', a change in phase of the current in the coil II will equal about or A of a cycle.

The currentin the coil I0 is then about 90 ahead of the current in the work circuit 30. This difierence in phase between the two currents permits the contactor to interrupt the work circuit 30 at the zero point of the cycle of the current passing therethrough.

It is thus seen that since the drop-out time is a substantially constant factor, it is possible to adjust the phase oi the current in the operating coil so as to consistently obtain the opening of the contactor when the instantaneous value of the current therethrough is substantially at zero, thus resulting in arcless interruption. A change in the drop-out time, as by the use of a different contactor, would require merely an adjustment to be made at the phase shifter by the movement of one or more of the connectors 21 and 2! The drop-out time of a particular contactor may not be equal to a definite multiple of 10 electrical degrees, but if the phase of the coil current be shifted to the nearest iii-degree interval, it has been found that sufllcient accuracy of timing is obtained.

Although I have'shown and described my invention as controlling the operation of a doublepole contactor, it is to be understood that the apparatus will function in the same manner with a single-pole contactor. As shown in Fig. 5, for example, a single-pole contactor 50 may be connected into each conductor of a polyphase power circuit and the operating coils 5! each energized through a different phase-shifting device 0. A push button 52 is arranged to simultaneously open or close the coil energizing circuits. The phase shifting devices are so adjusted that each contactor opens its respective circuit at or near the zero point of the current cycle, even though the power circuits through the contactors are out of phase. v

Having thus described my invention, what I claim is: w

1. In combination with a source of polyphase current, a load circuit arranged to be energized I thereby, a contactor for connecting one phase means for opening the control circuit at a pre-' determined point in the cycle of the current in oi the source to the load circuit, a control circuit including a coil for operating said contactor, said control circuit including an inductance coil connected across one phase of said source and having an intermediate tap connected .to a terminal of said contactor coil, another terminal of the contactor coil being connected to the source, and a the control circuit, said intermediate tap being so positioned that upon opening of said control circuit at said predetermined point said contactor opens'when' the current in the load circuit is at or near the zero point 01 its cycle. is v 2. In a control system having a source of power, a translating device connected to said source, and a means for disconnecting the device from the source when the current therethrough is substantially at the zero point of its cycle, comprising: a power-operated contactor having an operating means, a circuit for energizing saidoperating means irom said source including a phase shifting means for adjusting the phase relationship of the .current through the operating means with the current through the translating device so that the time difierence in phase relationship is equal to the drop-out time of said contactor, and means for opening said circuit only when the current therethrough is at a predetermined point of its cycle.

3. In a device for controllinga load circuit, a source of polyphase current, a polyphase load circuit, a plurality of contactors for connecting the load circuit to the source, coils respective to the contactors for operating'said contactors, and control circuits respective to said coils-for energizing said coils from said source, each of said control circuits including an inductance coil connected across a phase of said source each of said inductance coils having an intermediate tap connected to a terminal of its respective contactor coil, the other terminal of such contactor coil being connected to said source whereby interruption of each control circuit causes its respective contactor to open its contacts when the value of the current therethrough is substantially zero.

4. In a device for controlling a load circuit, a source of three-phase current, a load circuit, a contactor for connecting the load circuit tothe source, a coil for operating said contactor, and a control circuit for energizing said coil from said source, said control circuit including an induc--' tance coil connected across a phase of said source and to a terminal of said contactor coil, the other terminal of said coil being connected to said source whereby the phase of the current in the load circuit and the phase of thecurrent in the coil circuit are constrained in a predetermined relationship.

5. In a control system, a source of alternating current, a load circuit, a contactor for connecting the load circuit to said source, another source of alternating current having a phase relationship with that of said first named source such that uniform intervals of time occur between the instants of zero values of current from one source and the instants of zero values of current from the other source, a magnetic means for operating said contactor and including a coil for controlling the opening of said contactor, said coil being "electrically connected to said second named source, and-phase shifting means operatively con! nected with both of said soiirces to shift the phases of the two currents with respect to each other to predetermine the duration of said uniform intervals of time to permit opening of the contactor at approximately the zero point of the cycle of the current from said first-named source.

6. In a control system, a source of alternating current, a load circuit, a contactor for connecting the load circuit to the source, a coil for operating said contactor, a source of polyphase current having a frequency so proportional to that of said first named source that the intervals of so that interruption of the current in the coil circuit when its value is substantially zero will" cause said contactor to open its contacts when the value of the current theretbrough is substantially zero.

'7. In combination, an alternating current power circuit, a circuit interrupter, an alternating current operating circuit having inductive reactance, a winding operatively associated with the interrupter and operating circuit, and operable when energized to hold the interrupter in circuit closed condition with respect to the power circuit, means 'i'or physically interrupting the operating circuit and permitting arcing at the point of and consequent upon said interruption, the inductive reactance of said operating circuit being sufiicient to cause the cessation oi. the current therethrough only at a zero point of its cycle whereby arcing at the point of interruption ceases and the operating circuit and associated winding are finally deenergized thereby onlywhen saidcurrent is at said zero point of its cycle, means for opening the interrupter in a predetermined drop out time after cessation of flow of current through said operating circuit, and means for establishing a predetermined phase relationship'between the currents in said circuits so that deenergization oi the operating circuit occurs a suilicient time before a zero point of the cycle ,of the current in the power circuit is reached to cause opening of the inter rupter at a zero point of the cycle of the power v circuit.

8. A- system for interrupting an alternating current power circuit at or near the zero point of the current cycle, comprising an interrupting.

means, an operative winding for holding 'said means in a, circuit closed position when energized, and for releasing said means when deenergiaed to permit said means to interrupt said alternating current power circuit, means for returning the interrupting means to circuit cloud position, an

' alternating current operating circuit connected to the operative winding for energizing the same upon energization of the circuit, a switch normally closing the control circuit and operable to physically break the control circuit while permitting arcing at .the point of and upon said breaking, whereby the flow of current in the circuit and through the operative winding is maintained through the are after breaking by the switch, said winding having suillcient inductive reactance to arrest the flow of current therethrough only at a zero point oi. the cycle of the control circuit current, whereby the are is extinguished and the control circuit finally deenergized only at thev zero point oi said ourrent, and means to cause the. zero point oi said current to occur a sumcient time before the aero point'oi' the alternating current in said power circuit to permit said interrupting means to interrupt said power circuit at the instant 0! nero current therethrough.

9. A system for interrupting an alternating current power circuit at or near the zero point of the current cycle, comprising an interrupting means, an alternating current control circuit for holding said interrupting means in circuit closed position when energined, and for releasingsaid interrupting means when deenergiaed topermit said interrupting means to interrupt saidaiter nating current power circuit, means for returning the interrupting means to circuit closed position, a switch normally closing the control circuit and operable to the control circuit amiable while permitting arcing at the point of and consequent upon said breaking, whereby the control circuit is maintained through the are after breaking by the switch, said control circuit having suilicient inductive reactance to arrest the flow of current therethrough only at a zero point of the cycle of the current, whereby the arc is extinguished and the circuit flnaily deenergized only at the zero point of said current, and means to cause the zero point of said current to occur a suiiicient time before the zero point of the alternating current in said power circuit to permit said interrupting means to interrupt said power circuit at the instant ot zero current therethrough. a

10. A system for interrupting an alternating current power circuit at or near the zero point of the current cycle, comprising an interrupting means, an electrically operable means for holding said interrupting means in a predetermined po sition when said position permitting said alternating current to flow through said a said electrical operating means having suilicient inductive reactance to arrest the flow 01 current therethrough only at a zero point of the cycle of the current, whereby the arc is extinguished and the circuit flinally deenergized only at the zero point oi! said current, and means to cause the zero point of said. current to occur a sufilcient time before the zero point of'the alternating current in said power circuit to permit said interrupting means to interrupt said power circuit at the instant oi! zero current therethrough. V

11. The combination with a circuit interrupter for an alternating current circuit, an alternating current operating circuit including means dependent upon the energization of the operating circuit for operating the circuitinterrupter, and controlling means operative for controlling the energimtion of the operating circuit at a predetermined point in the cycle of the current supplying the operating circuit, ot'means for constraining the phases '01. the currents in said circuits in a predetermined relation to each other,

' whereby the interrupter is. rendered operative consequent upon a change in the energization of the operating circuit ivy-said controlling means to interrupt the current through the interrupter at a predetermined point in its cycle.

12. The comb with an alternating ctr-- rent power circuit and a circuit interrupter having an operating'winding associated therewith,

operating circuit at a predetermined point in the 6701601 the v current insaid operating circuit, otmeanstor thephaseoithecurrentinsaidopera circuitsothatitbearsa definite relation to the phase of the current in said power circuit to permit opening of the circuit interrupter at a predetermined point in the cycle or the current in the power circuit consequent upon a change in the energizatioii 01' said operating winding by saidcontrolling means.

13. The combination with an alternating current circuit and a circuitinterrupterhaving an operating winding associated therewith, a separate source of alternating current for energizing said winding, and controlling means operative for controlling the energization of the operating winding at a predetermined point in the cycle of the current in said separate source of alternating current, of means for constraining the phases of the currents in a predetermined relation to each other, whereby the interrupter is rendered operative consequent upon .a change in the energizationnof the operating winding by said controlling means to interrupt thecurrent through the interrupter at a predetermined point in its cycle.

14. In a. control system, a source of current, a load circuit, a contactor for connecting the load circuit to said source, means for operating said contactor including a coil, and phase shifting means electrically interconnecting said source and said coil and adapted to shift the phase or the current through the coilin relation to the phase of the current through the load circuit to permit opening of the contactcr at approximately the zero point of the cycle or the load current.

15. In a. control system, a source of current, a load circuit, a contactor for connecting the load circuit to said source, a coil for operating said contactor, means for energizing said coil, a phase-shifting means, said means effecting an adjustment of the phase relationship of the current through the coil with respect to the current through the load circuit, and means for inter- -rupting the coil current at a predetermined point in its cycle so that an interruption of the current through the coil by said last means causes the contactor to interrupt the current through the load circuit substantially at the zero point of the cycle of the load current.

16. In a control system for an electrically operated translating device, a source of power, a magnetically-operated contactor for connecting and disconnecting the translating device to the source of power and having an operating coil for controlling the opening of the contactor, and a phase-shifting means electrically interconnecting said source and said coil for adjusting the phase relationship of the current through the coil with respect to the current through the translating device so that the time diiference in the phase relationship is equal to the dropout time of said contactor.

17. In a control system, a source of current, a load circuit, a contactor for, connecting the load circuit to said source, a coil connected to said source and operative for closing said contactor, means for opening said contactor, a phase shifting means adapted to shift the phase of the current through the coil in relation to the phase or the current through the load circuit, means for interrupting the coil current at a predetermined point in its cycle so that an inter ruption of the current through the coil by said last means causes opening of the contactor by the opening means at approximately the zero point of the cycle of the load current, and means for maintaining substantially a predetermined voltage across said coil.

18. In a control'system, a source of current,-

a load circuit, a contactor for connecting the the phase position of the current through the coil with respect to the current through the load circuit in a predetermined relationship, means for interrupting the coil current at a predetermined point in its cycle so that an interruption of the current through the coil causes an interruption of the current through the load circuit substantially at the zero point of the cycle of the load current, said phase-shifting means including means to maintain a substantially constant voltage across said coil.

19. In a device for controlling a load circuit, a source of polyphase current, a load circuit, a contactor for connecting the load circuit to the source, a 'coil for operating said contactor, a control circuit for energizing the operating coil from the source, said control circuit including an inductance coil, means for variably connect ing said inductance coil to said source and to a terminal of the operating coil, the other terminal of the operating coil being connected to the source, means for interrupting the flow of current in the control circuit at a predetermined point in its cycle, whereby the contactor opens its contacts when the value of the current there through is substantially zero, and a means included in said control circuit to maintain a substantially constant voltage across said coil.

coil with respect to the current through the con.-

tactor associated with such coil so that an interruption oi the flow of current through each coil at a predetermined point in its cycle causes interruption of the current through its associated contactor at substantially the zero point of the cycle of the current through such contactor.

21. In a control system, a source of alternating current, a load circuit, a contactor movable to one position for connecting the load circuit to said source and to another position for disconnecting the load circuit from said source, a coil for operating said contactor to one of said position's, phase-shifting means deriving electrical energy from said alternating current source and conducting the said electrical energy to said coil, said means altering the phase relationship between the input energy and the output energy and maintaining the zero values of the coil current in a timed relationship with the zero values of the load current, and means for deenergizing' .said coil at a predetermined point in the cycle of the coil current, said deenergization permitting operation of said contactor to control the load circuit at a zero point in the cycle o1. the load current.-

22. In a control system, a source of alternating current, a load circuit, a plurality of con- I intervals of time may be preselected between the instants of zero values of the current from one source and the instants of zero values or the current from the other source, aplurality or operating coils for the contactors connected to said other source, said coils being associated with said contactors respectively, a plurality of phaseshitting means, said phase-shifting means being associated with said coils respectively, each of said phase shifting means permitting an adjustment oi the phase relationship of the current through its-associated coil with respect to the load current through the contactor associated with such coil to preselect the respective values of said intervals of time, and means for interrupting the current through each coil at a predetermined point in its cycle, so that an interruption of the current through each coil causes an interruption of the load current through the contactor associated therewith substantially at the zero point of the'cycle of said load current.

23. In a control system, a source of alternating current, a load circuit, a contactor movable to one position for connecting the load circuit to said source and to another position for disconnecting the load circuit from said source, a magnetic means for maintaining said contactor inone of said positions, means for energizing said magnetic means in a manner to produce an alternating flux in a timed relationship with the load current, adjustable phase shitting meansoperatively associated with load circuit and the magnetic means for varying the timed relationship between the alternating flux and the load current to permit the contactor to move to one or its positions at a definite point in the cycle of the load current.

4- In a control system for an electricallyoperated translating device, a magneticallyoperated contactor for connecting and disconnecting the translating device to a source 01' alternating current and having an operating coil for controlling the opening of the contactor, and a phase-shitting means adapted to electrically interconnect said source and said coil and operative, when so interconnecting, to permit the coil to create an alterating flux in timed relation with the load current, said phase-shifting means being adapted to shift the phase of the current through the coil in relation to the phase of the current through the translating device so that the time diflerence in the phase relationship between said alternating current and the flux created by said coil is proportional to the drop-out time of said contactor.

WILLIAM F. SZABO.

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