US3161822A

US3161822A - Electric integrating apparatus for integrating a variable electric quantity

Info

Publication number: US3161822A
Application number: US219274A
Authority: US
Inventors: August L Streater
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1962-08-24
Filing date: 1962-08-24
Publication date: 1964-12-15
Anticipated expiration: 1981-12-15

Description

Dec. 15, 1964 A. ELECTRIC INTEGRATIN A VARIABLE Filed Aug. 24, 1962 L. STREATER G APPARATUS FOR INTEGRATING ELECTRIC QUANTITY 2 Sheets-Sheet l INVENTOR. Aueusr L. 6 REATER,

Dec. 15, 1964 A. 1.. STREATER RATING APPARAT ELECTRIC INTEG US FOR INTEGRATING A VARIABLE ELECTRIC QUANTITY 2 Sheets-Sheet 2 Filed Aug. 24, 1962 /N VENTOR.

BY e/0 R, E v R M J R 5% T T S A U United States Patent 3,161,822 ELECTRIC HJTEGRATKNG APPARATUS FOR INTE- GRATING A VARIABLE ELECTRIC QUANTITY August lL. Sireater, Broomail, Pa, assignor to General Electric Company, a corporatien oi New York Fiied Aug. 24, I962, Ser. No. 219,274 11 Claims. (Cl. 32423) My invention relates to electric metering, or integrating, apparatus for totalizing a variable electric quantity such as current, voltage or power over a time interval comprehending possible discontinuity of the quantity. More particularly the invention relates to a system and apparatus for integrating the arcing currents of an electric circuit breaker over an extended interval of time as a measure of total interrupting duty, and thus a measure of contact erosion.

Heretofore it has been the established practice in maintaining circuit breakers designed for overload or fault interruption duty to check contact erosion from time to time by visual inspection. With the advent of fully sealed interrupting units such as vacuum interrupters, visual inspection has become impractical and may in some cases be impossible without destruction of the interrupting unit. Available studies of contact erosion indicate that erosion is proportional to the integral of I dt where I is average arcing current and n is greater than 1 and less than 2. It is evident therefore that a current measuring and integrating device having a non-linear current response controllable within these limits by selection of available design parameters and having a sufiiciently rapid response to give accurate indication within the very short arcing intervals characteristic of modern circuit interrupters will provide a measure of contact erosion.

Accordingly it is a general object of my invention to provide an inexpensive, accurate and reliable device which will conveniently give a measure of circuit breaker arcing current and integrate the arcing duty over a time interval.

It is another object of my invention to provide are current integrating means for an electric circuit breaker having a rapid response and an integrating characteristic controllable by design to match approximately the contact erosion characteristic of a circuit interrupting device over an extended time interval.

It is a more specific object of my invention to provide a new and improved electric arc current integrating apparatus utilizing an electromagnetic pump of the conducting liquid type.

In carrying out my invention in one preferred embodiment, I utilize an electromagnetic pump of the conducting liquid type in which a column of conducting liquid is disposed in a transverse magnetic field, and current is passed through the liquid transversely of the column and substantially perpendicular to the direction of the field. Such a device, when energized in proportion to the magnitude of a current to be measured, drives the liquid along the column, suitably in a conduit, and at a flow rate proportional to a function of the energizing current. I energize the pump only during arcing intervals of a circuit breaker the arcing current of which is to be integrated. By accumulating or otherwise integrating the volume of liquid driven past a predetermined point during arcing intervals, I provide a measure of current integrated over these intervals and thus a measure of contact erosion in the circuit breaker. In an illustrative embodiment integration is carried out by preventing reverse flow in the conduit when the pump is deenergized and accumulating the liquid in a suitable chamber or vessel. The current response can be made linear or non-linear depending upon the mode of pump excitation, the degree of pump field saturation and the flow losses in the fluid system. By suitable selection of these parameters I can approximately match total liquid accumulation and total contact erosion.

My invention will be better understood and its various objects and advantages further appreciated by referring now to the drawings in which:

FIG. 1 is a diagrammatic representation of an electromagnetic pump integrating apparatus shown partially in perspective and connected to measure arcing currents of an electric circuit interrupter, and

FIG. 2 is a similar diagrammatic representation illustrating another embodiment of my invention in which the electromagnetic pump is provided with a shunt field winding energized from arcing voltage.

Referring now to the drawing, particularly to FIG. 1, I have illustrated diagrammatically an electric current interrupting device CB of the vacuum type having a pair of separable contacts 1 and 2 relatively movably mounted and partially enclosed within a sealed envelope 3. While the contacts 1 and 2 are shown in their engaged position, the movable contact 2 is slidable longitudinally through a vacuum tight bushing 2a and is biased to open position by means of a tension spring 4. A latch lever 5 pivotally mounted and biased by a spring 6 to latching position is arranged to engage an annular projecting shoulder 7 at the outer end of the contact 2 to maintain the contacts in the engaged position shown.

In order to measure and integrate arc currents between the circuit breaker contacts 1 and 2, I provide a conducting liquid system comprising a conduit it connected at one end to a supply source or reservoir 11 and having its discharge or outlet end connected to suitable liquid-accumulating means. As shown, the accumulating means comprises a discharge chamber 12 connected through an overflow tube 12a to an accumulating vessel or gauge 13. The conduit 10, supply reservoir 11 and discharge chamber 12 are filled with a conducting liquid 14 such as mer cury, and a check valve 15 is provided at some suitable point, such as between the conduit 16 and the discharge chamber 12, to prevent reverse flow of the liquid and thus maintain the discharge chamber completely filled at all times.

It will, of course, be evident to those skilled in the art that the check valve 15 may be located at any convenient point between the supply reservoir and the accumulator. If desired the discharge chamber may itself be used as the accumulator, but I find it more convenient to measure the overflow from this chamber than the liquid input to it.

t an intermediate point along the length of the conduit It), there is provided an electromagnetic pump P comprising an electromagnet 16 having a magnetizable core 17 and a field winding 18. The core 1'? is suitably C-shaped as shown to provide a pair of spaced-apart pole pieces 17a, 17b disposed closely adjacent the conduit 10 on opposite sides thereof. Thus when the electromagnet 16 is excited, it provides between the pole pieces 17a and 1711 a magnetic field oriented in a direction transversely across the column of conducting liquid contained in that section of the conduit lying in the gap between the pole pieces. Finally the electromagnetic pump includes a pair of current-conducting

electrodes

20 and 21 disposed on opposite sides of the conduit 10 within the gap between the magnet pole pieces and along an axis mutually perpendicular to both the direction of the magnetic field and the longitudinal axis of the conduit. The conduit 10 is preferably formed of electrically insulating material, the electrodes 2% and 21 passing through the walls of the conduit into electric contacting engagement with the contained column of conducting liquid.

It will be understood that when current is passed transversely through the conducting liquid between the electrodes 2t] and Z1 and the electromagnet field winding 18 is energized, the resulting electromagnetic force will drive, or pump, the liquid 14 along the conduit 18 in a direction depending upon the directions of current flow through the liquid and in the field winding. In the illustrated embodiment of the invention, these directions of current flow are so selected that liquid is pumped from the res ervoir 11 toward the discharge chamber 12. The rate of liquid flow is proportional to a function of the currents in the liquid and the magnetic field winding. Accordingly the volume of liquid pumped past any predetermined point in an incremental interval of time dt is proportional to the product of a function of current and time and is thus a measure of current integrated over a desired interval.

In the illustrated embodiments of the invention the full volume of the liquid pumped into the discharge chamber 12 over any predetermined period of time overflows from the chamber through the overflow tube 12a and into the accumulating vessel 13 which is calibrated in any suitable terms representative of the integrated current, such as ampere-seconds or'ampere-squared seconds. Conveniently the accumulating vessel of gauge 13 may be calibrated in terms of percent of maintenance-free life of the circuit interrupter contacts I and 2, so that the level of mercury in the gauge 13 will provide a quick and simple indication of remaining contact life. It will now be evident to those skilled in the art that integration of the volume of liquid pumped in the course of several pumping intervals may be carried out by means other than direct accumulation of the conducting liquid itself. In application S.N. 248,998, filed by l. Barkan and T. A. Burns on January 2, 1963, and assigned to the same as signee as the present application, there is shown one indirect liquid flow integrator wherein recurrent flow of conducting liquid into the discharge chamber reverses, or resets, to a predetermined initial level after each discrete arcing interval and a secondary overflow liquid is utilized to integrate forward flow ofthe conducting liquid.

In order to provide energization of the electromagnetic pump in accordance with the magnitude of current flowing through the circuit breaker contacts 1 and 2 and only for those intervals while an arc is being drawn between the contacts, I provide a current transformer 25 coupled to a power current conductor 25a and a pair of control switches 26 and 27 actuated by opening movement of the circuit breaker contact 2. The power conductor 25a is connected to the contact 2 and thus carries the current passing through that contact, the control current in the secondary winding of the current transformer 25 thus being proportional to the power current. The control switches 26 and 27 are shown for the purpose of illustration as cam-actuated contacts operated by the movable contact 2 of the circuit breaker CB, the contacts 29 of the switch 26 being closed and the contacts 3% of the switch 2'7 being open when the main circuit breaker is in closed position. Through these contacts 29 the sec ondary winding of the current transformer 25 is connected to energize an overcurrent trip coil 28 of the circuit breaker CB. The same secondary winding is also arranged for connection to the electromagnetic pump P through the switch contacts 36 which are closed immediately upon opening movement of the circuit breaker contact 2. In the embodiment of the invention illustrated at FIG. 1, the electromagnetic pump is energized in series circuit relation, the electrodes 2% and 21 being connected in series with the pump field winding 18 across the current transformer 25 when the contacts 38 are closed. To ensure that in the transition from one position to the other the control switches 26 and 27 do not leave the current transformer secondary winding open momentarily, a suitable contact overlap is provided to delay opening of the contacts 29 until after the contacts 30 are closed.

When the electromagnetic pump is energized with the electrodes Ztl and 21 in series circuit relation with the field winding 18, as shown at FIG. 1, it will be evident that the instantaneous driving pressure applied against a static column of mercury in the conduit 16 is proportional to the square of the instantaneous energizing current from the current transformer 25 so long as the magnetization of the core 17 remains in a linear range below saturation. If, of course, the core 17 is excited beyond its point of saturation (or if it is separately excited from some constant voltage supply source), the driving pressure is proportional to the first power of the current between the electrodes 2t: and 21. Thus with the series connection shown, the driving pressure may be controlled by desi n to be proportional to I where n is greater than 1 and less than 2. Of course when the conducting liquid is in motion as a result of pumping action, the driving pressure is reduced by losses due to inertia of the liquid column, friction against the conduit walls and turbulence in the fluid system. By proper design these losses can be so determined that the rate of flow is proportional to current within the limits indicated, i.e., I and preferably matches approximately the relation of arc current to contact erosion. The integral of I dt over an extended time interval is then proportional to total contact erosion over the interval considering a series of time intervals during which arcing current flows between the contacts, the total liquid pumped through the conduit during these time intervals is the summation of the integrals T J di for the individual time intervals, where T is the period of time over which the current I flows in a given interval.

It will be evident that in operation with the main circuit breaker contacts I and 2 closed, current is flowing through the line conductor 25a, and the trip coil 28 is excited in proportion to the magnitude of that current. The trip coil of course is so designed that it will not actuate the latch 5 until some predetermined magnitude of excessive or overload current occurs. The control switches 26 and 27 are in the position shown with the contacts open, so that the electromagnetic pump remains deenergized. Assuming that sufiicient pumping action has previously occurred to completely fill the discharge chamber 12 of the integrating device, the check valve 15 will be closed so that the discharge chamber 12 remains full and on the point of overflow.

If now an overload current of sufficient magnitude occurs to trip the latch 5, the circuit breaker contact 2 will open under the influence of its bias spring 4. As soon as opening movement begins, an arc exists between the contacts 1 and 2 and the initial opening movement shifts the control switches 25 and 27 to a position closing the contacts 30. Thus substantially simultaneously with the initiating of arcing, energization is applied to the electromagnetic pump P from the secondary winding of the current transformer 25 and mercury is pumped through the conduit 10 toward the discharge chamber 12 at a flow rate proportional to a function of the magnitude of the arc current. As soon as electromagnetic pumping begins, the discharge chamber 12 begins to overflow into the accumulating vessel 13 thereby to add to the accumulated mercury in the vessel 13 a volume of mercury proportional to the integral of a function of the current flowing during the arcing interval. It will be understood, of course, that as soon as arcing between the main circuit breaker contacts 1. and 2 ceases, the current transformer 25 and thus the electromagnetic pump P is deenergized. At this point the check valve 15 seats to prevent reverse flow of mercury in the conduit 10 and maintain the discharge chamber 12 completely full in readiness for the next pumping operation. Reclosure of the main circuit breaker contact 2 reverses the position of the control switches 26 and 27 to restore the contacts 29 and 36} to the positions shown in FIG. 1.

Referring now to FIG. 2, I have shown another embodiment of my invention which differs from that at FIG. 1 primarily in that the field winding 18 of the electromagnetic pump is energized from the arc voltage existing between the main circuit breaker contacts 1 and 2 rather than in series circuit relation with the

electrodes

20 and 21. The

electrodes

20 and 21, however, are energized at FIG. 2 from the secondary winding of the current transformer 25 in the same manner as at FIG. 1. With this arrangement, it is unnecessary to provide any switching means responsive to circuit breaker opening movement to energize the electromagnetic pump, since no arcing voltage exists and the field Winding 18 remains deenergized except when the contacts 1 and 2 are separated. In this respect, when the contacts 1 and 2 are in engagement, there is a very low impedance path through the interrupter and hence no appreciable voltage across the contacts or across the winding 18, which is in parallel with the contacts 1, 2. Accordingly, therefore, the winding 18 is shown connected permanently across the contacts 1 and 2, and the

electrodes

20 and 21 are shown permanently connected across the secondary winding of the current transformer 25 in parallel circuit relation with the trip coil 28. It is of course true that with this arrangement the field exciting winding 18 of the electromagnetic pump remains energized after an arc is extinguished. However, at this time pumping action of the electromagnetic pump ceases because upon interruption of the main power current, the current transformer 25 is effectively deenergized and current flow between the

electrodes

20 and 21 is efiectively discontinued. With respect to the deenergization of current transformer 25 under these conditions, it will be understood that the impedance of winding 18 is so high that no significant amount of current flows through the line 25a when an open circuit exists between the then-separated interrupter contacts 1 and 2. It will be evident that while the field exciting winding 18 is not connected in series circuit relation with the

electrodes

20 and 21, the pumping action of the electromagnetic pump is still proportional to the function of the current between the

electrodes

20 and 21, and by suitable determination of design parameters may thus be made proportional to a function of the arcing current and hence to contact erosion.

While I have described several preferred embodiments of my invention by way of illustration, many modifications will occur to those skilled in the art, and I therefore wish to have it understood that I intend in the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

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

1. In combination, an electric circuit interrupting device including a pair of separable contact members between Which an arc may be drawn, integrating means responsive to current traversing said contacts during a series of spaced time intervals for providing an indication proportional to the summation of the integrals T f I dt for the individual time intervals, where I is a function of the current I traversing said contacts and T is the period of time over which the current I fiows in a given interval, and means responsive to relative position of said contacts for rendering said integrating means operable only when said contacts are separated, said integrating means being operable to add to the previouslyexisting indication in response to currents traversing said contacts during a given interval irrespective of whether the current during said given interval is less than during a preceding interval that said integrating means responded to.

2. In combination, an electric circuit interrupting device including a pair of separable contact members between which an arc may be drawn, electroresponsive integrating means arranged for energization in response to current traversing said contacts during a series of spaced time intervals for providing an indication proportional to a function of said current integrated over the total of said time intervals, and means controlled by the relative position of said contacts for disabling said integrating device whenever said contacts are in engagement, said integrating means when not disabled being responsive to currents traversing said contacts during a given interval to add to any previously-existing indication irrespective of whether the current during said given interval is less than that during a preceding interval that said integrating means responded to.

3. In combination, an electric circuit interrupting device including a pair of separable contact members between which an arc may be drawn, electroresponsive integrating means having a pair of input circuits and responsive to the product of two electrical input quantities received through said input circuits during spaced time intervals for integrating the product of said input quantities over the total of said time intervals, means coupling one said input circuit for variable energization in proportion to the magnitude of current traversing said contacts, and means for eflfectively energizing the other said input circuit only when said contacts are separated.

4. In combination, an electric circuit interrupting device including a pair of separable contact members between which an arc may be drawn, electroresponsive integrating means having a pair of input circuits and responsive to the product of two electrical input quantities received through said input circuits during spaced time intervals for integrating the product of said input quantities over the total of said time intervals, means coupling one said input circuit for variable energization in proportion to the magnitude of current traversing said contacts, and means for effectively energizing the other said inputcircuit in response to voltage between the said contacts.

5. In combination, an electric circuit interrupting device including a pair of separable contact members between which an arc may be drawn, electroresponsive integrating means having a pair of input circuits and responsive to the product of two electrical input quantities received through said input circuits during spaced time intervals for integrating the product of said input quantities over the total of said time intervals, means coupling both asid input circuits for variable energization in proportion to the magnitude of current traversing said contacts, and means controlled by relative position of said contacts for disabling one said input circuit when said contacts are in engagement.

6. An electric current integrating device responsive to current flowing during a series of spaced time intervals for integrating a function of said current over the total timeof said intervals, said integrating device comprising a conduit connected at one end to a source of electrically conducting liquid and having a discharge outlet, electromagnetic means operable in response to said current for driving said liquid through said conduit in one direction at a flow rate proportion to said function of the current to be integrated over a time interval, liquid accumulating means positioned adjacent said discharge outlet to receive liquid discharged therefrom throughout any interval of liquid flow in said one direction, and means for integrating the volume of liquid so discharged over a plurality of flow intervals, and means for enabling said electromagnetic means to drive liquid through said conduit in response to current flow during a given time interval even though the current during said given time interval is less than that during a preceding interval that said electromagnetic means responded to.

7. An electric current integrating device responsive to current flowing during a series of spaced time intervals for integrating a function of said current over the total time of said intervals, said integrating device comprising a conduit connected at one end to a source of electrically conducting liquid and having a discharge outlet, electromagnetic means for driving said liquid through said conduit in one direction at a flow rate proportional to said function of the current to be integrated over a time interval, means operative in the absence of liquid flow for maintaining said liquid in a static position to discharge through said outlet immediately upon initiation f flow, and liquid accumulating means positioned adjacent said discharge outlet to receive liquid discharged therefrom throughout any interval, and means for preventing the accumulated liquid from blocking the electromagnetic means from driving liquid through said conduit during subsequent'intervals even though the current during a subsequent interval is less than that during a preceding interval.

8. An electrical current integrating device responsive to current flowing during a series of spaced time intervals for integrating a function of said current over the total time of said intervals, said integrating device comprising a conduit connected at one end to a source of electrically conducting liquid and having a discharge outlet, electromagnetic means for driving said liquid through said conduit and toward said outlet at a flow rate proportional to said function of a current to be integrated over a time interval, means preventing reverse flow of said liquid, and calibrated liquid-accumulating means positioned to collect and measure the volume of liquid discharged from said outlet throughout one or more liquid flow intervals, and means for preventing the collected liquid from blocking the electromagnetic means from driving liquid through said conduit during subsequent intervals even though the current during a subsequent interval is less than that during a preceding interval.

9. In a current-integrating arrangement for providing an indication of the arc-erosion occurring in an electric circuit interrupter during a series of arcing intervals, a conduit connected at one end to a source of electrically conducting liquid and having a discharge outlet, electromagnetic means responsive to current flow through said circuit interrupter and operable when effectively energized to drive liquid through said conduit in a forward direction toward said outlet at a flow rate proportional to a function of the current flow through said circuit interrupter, control means for efiectively energizing said electromagnetic means in response only to the flow of arcing current through said interrupter, accumulating means responsive to forward liquid flow to measure the total volume of liquid discharged from said outlet, and means for enabling said electromagnetic means to drive liquid through said conduit in response to current flow during a given arcing interval even though the current during said arcing interval is less than during a preceding interval that said electromagnetic means responded to.

10. In a current integrating arrangement for providing an indication of the arc-erosion occurring in an electric circuit interrupter during a series of arcing intervals, a conduit connected at one end to a source of electrically conducting liquid and having a discharge outlet, means for conducting through said liquid transversely of said conduit an electric current proportional in magnitude to the current passing through said interrupter, and electromagnet positioned to generate a magnetic flux directed transversely of said conduit and substantially perpendicular to the direction of the current flowing through said liquid, means responsive to the flow of arcing current through said interrupter for exciting said electromagnet thereby to drive said liquid through said conduit in a forward direction toward said outlet and at a flow rate proportional to a function of the are current, accumulating means responsive to forward liquid flow to measure the volume of liquid discharge from said outlet throughout one or more flow intervals, and means for enabling said electromagnetic means to drive liquid through said conduit in response to current flow durin a given arcing interval even though the current during said given arcing interval is less than during a preceding interval that said electromagnetic means responded to. i

11. In combination, an electric circuit interrupter having separable contacts and overload responsive tripping means operable when energized to effect separation of said contacts, integrating means responsive to arcing current between said contacts when separated, comprising: a conduit connected to a source of electrically conducting liquid and having a discharge outlet, means for conducting through said liquid transversely of said conduit an electric current proportional to the current traversing said contacts, an electromagnet positioned to generate a magnetic flux directed transversely of said conduit and substantially perpendicular to the direction of flow of current through said liquid, means responsive to operation of said tripping means for exciting said electromagnet thereby to drive said liquid through said conduit at a flow rate proportional to the magnitude of arcing current between said contacts, means for preventing reverse flow of said liquid, and calibrated accumulating means positioned adjacent said discharge outlet to collect and measure the volume of liquid discharged from said outlet during intervals of arcing between said contacts, and means for enabling said electromagnetic means to drive liquid through said conduit in response to current flowing during a given arcing interval even though the current during said given arcing interval is less than during a preceding interval that said electromagnetic means responded to.

Oxley Dec. 11, 1900 Carlson Apr. 10, 1962

Claims

1. IN COMBINATION, AN ELECTRIC CIRCUIT INTERRUPTING DEVICE INCLUDING A PAIR OF SEPARABLE CONTACT MEMBERS BETWEEN WHICH AN ARC MAY BE DRAWN, INTEGRATING MEANS RESPONSIVE TO CURRENT TRAVERSING SAID CONTACTS DURING A SERIES OF SPACED TIME INTERVALS FOR PROVIDING AN INDICATION PROPORTIONAL TO THE SUMMATION OF THE INTEGRALS