US3641359A

US3641359A - Monitor circuit for vacuum-type electric circuit interrupter

Info

Publication number: US3641359A
Application number: US95107A
Authority: US
Inventors: Orin P Mccarty
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1970-12-04
Filing date: 1970-12-04
Publication date: 1972-02-08
Anticipated expiration: 1989-02-08

Abstract

This application discloses a protective circuit for monitoring both loss of vacuum and contact wear in a vacuum-type electric circuit interrupter having separable contacts and a vapor shield surrounding the contacts. The shield is so located that a part fixed to the moving contact rod and normally spaced from the shield will closely approach or engage the shield as a result of contact wear. A monitor circuit including the rod-to-shield gap includes current responsive indication or control means.

Description

United States Patent 1 3,641,359

McCarty Feb. 8, 1972 [54] MONITOR CIRCUIT FOR VACUUM- i ,91 ,iTI/Ti8i newer .l ..307/l36 Ux TYPE ELECTRIC CIRCUIT INTERRUPTER Orin P. McCarty, Pittsfield, Mass.

Assignee: General Electric Company Filed: Dec. 4, 1970 App]. No.: 95,107

Inventor:

U5. CL ..307/l36, 317/62 Int. Cl. ..I-I0lh 9/30 Field olSearch ..200/48, 146, 148, 170; 307/92,

I UN

[56] References Cited UNITED STATES PATENTS 3,593,291 9/1968 4 Crpu h. ..307/I3 6 UX Primary ExaminerHerman .I. Hohauser Attorney-J. Wesley Haubner, Frank L. Neuhauser, Oscar B. Waddell and Joseph B. Forman ABSTRACT This application discloses a protective circuit for monitoring both loss of vacuum and contact wear in a vacuum-type electric circuit interrupter having separable contacts and a vapor shield surrounding the contacts. The shield is so located that a part fixed to the moving contact rod and normally spaced from the shield will closely approach or engage the shield as a result of contact wear. A monitor circuit including the rod-toshield gap includes current responsive indication or contml means.

8 Claims, 1 Drawing figure PATENTED EB 8 2 3.641.359

MONITOR CIRCUIT FOR VACUUM-TYPE ELECTRIC CIRCUIT INTERRUP'IER My invention relates to means for monitoring vapor pressure and contact wear inside a vacuum-type electric circuit interrupter, and particularly to current responsive means for substantially continuously monitoring both pressure and contact wear while the interrupter is connected for service in a high voltage power circuit.

As illustrated in U.S. Pat. No. 3,472,981 to McCarty it has been proposed to utilize vacuum interrupting devices as the nonnally closed arcing contactor in stepping-type load tap changers for power transformers, reactors and the like. In such service the arcing contact device is ordinarily immersed in a dielectric fluid and is subject to highly repetitive current interrupting operation. It is therefore most desirable to monitor such a device for fluid leaks and for contact wear by means operable substantially continuously and not requiring interruption of service or other irregular inspection procedure.

Accordingly it is a principal object of my invention to provide simple and inexpensive protective means for substantially continuously monitoring either internal pressure or contact wear or both in a vacuum-type electric circuit interrupter.

It is a further object of my invention to provide common current responsive means external to a vacuum-type circuit interrupting device for simultaneously and substantially continuously monitoring both internal pressure and contact wear.

A typical vacuum-type circuit interrupter comprises a highly evacuated envelope and a pair of relatively movable contacts located within the envelope. When the interrupter is in closed circuit position the contacts are engaged and are thus capable of carrying current through the interrupter. Circuit interruption is effected by separating the contacts to draw an arc therebetween, and when extinguished the arc is prevented from reigniting because of the existing vacuum within the envelope. To ensure that the arc will be extinguished as desired and prevented from reigniting, it is important that the pressure inside the envelope be maintained below a predetermined value and that contact wear be limited to a predetermined maximum.

In carrying out my invention in one preferred embodiment, I utilize a vacuum interrupting device having a pair of contact rods axially aligned for abutting engagement within an evacuated envelope of insulating material. One rod is fixedly mounted and the other is axially movable to engage and disengage contacts at the abutting ends of the rods. The movable rod is sealed to the evacuated envelope through a concentric flexible bellows having one end fixed to the rod. A tubular metallic shield is positioned within the envelope and surrounding the separable contacts. The shield is mounted in an insulating support for electrical isolation from the contacts and extends atone end into proximity with a lateral projection on the moving contact. The movable end of the flexible bellows serves conveniently as such a projection. Gradual erosion of the contacts diminishes the gap between shield and bellows in the contact engaging position of the bellows. The gap is initially so set that it will be reduced to zero or other predetermined minimum dimension after a predetermined maximum permissible amount of contact wear. To provide a signal for alarm or protective action when the gap attains its minimum dimension it is connected'in an electric circuit as a discharge gap or contact switch or both. The potential impressed across the gap is preferably so selected that a predetermined loss of pressure in the envelope, as well as a predetermined diminution of the gap, will permit current to flow from bellows to shield and actuate an alarm or protective device in the circuit.

My invention will be more fully understood and its objects and advantages further appreciated by referring now to the following detailed specification taken in conjunction with the accompanying drawing, the single FIGURE of which is a schematic illustration of a vacuum-type circuit interrupting device shown in axial cross section and including a protective monitor circuit in accordance with my invention.

Referring now to the drawing, l have shown a vacuum-type circuit interrupter which comprises a highly evacuated housing or envelope formed of a tubular insulating shell 10 and a pair of metallic end caps 11 and 12. The end caps 11 and 12 are connected to the tubular shell 10 by hermetic seals 14 and each cap is centrally apertured to permit passage through the cap of a current carrying contact rod. The cap 12 is seated upon a metallic mounting plate 13.

Within the evacuated

envelope

10, 11, 12, a pair of

contact rods

15 and 16 are positioned in axial alignment and provided, respectively, with separable abutting disk-shaped contacts and 16a. The contact rod 15 enters the envelope through a central aperture in end cap 11 and is fixedly mounted on that end cap as by the welds 11a. The contact rod 16 passes through aligned aperture in end cap 12 and plate 13 and is mounted for axial sliding movement between contact engaging and disengaging positions. In the drawing the contacts 15a and are shown in engaged position and it will be understood by those skilled in the art that when the movable contact rod 16 is moved downwardly, as shown in the drawing, the contacts will separably be disengaged. To seal the movable contact rod 16 to the end cap 12 a flexible metallic bellows 17 of generally tubular configuration surrounds the contact rod 16. The bellows 17 is closed at its upper end by a disklike base portion 17a which is hermetically sealed to rod 16 by a weld 17b. The open lower end of bellows 17 is sealed to the end cap 12 by a weld 17c. Because the bellows 17 forms a wall portion of the evacuated envelope the pressure difference between its inner and outer surfaces normally expends the bellows and biases the contact rod 16 to its contact engaging position.

The primary function of the vacuum interrupter is to control the flow of an electric current through a high voltage power circuit in which it is connected. Such a circuit is represented by a conductor 25 shown connected to the fixed contact rod 15 and a conductor 26 connected to the movable contact rod 16. When the contacts 15a and 160 are in engaged position as shown, current can flow between the

conductors

25 and 26 through the

contact rods

15 and 16.

In order to interrupt the circuit between the

conductors

25 and 26 the movable contact rod 16 is driven downwardly against its bias to separate the contacts 15a, 16a. Contact separation establishes an arc between the contacts which are persists until the first natural current zero, assuming an alternating current circuit. The are is prevented from reigniting after current zero by the high dielectric strength of the vacuum within the envelope thereby completing circuit interruption.

For condensing the metallic vapors which are liberated from the contacts by arcing, a tubular metal shield 30 is provided. Metal vapors projected by the are from the gap between the contacts 15a, 16a are intercepted and quickly condensed by this shield 30 during an interrupter operation. During an interrupter operation, as will be explained hereinafter, the metal shield 30 is electrically isolated from both

contacts

15 and 16. The shield 30 is suitably mounted upon an annular metal ring 32 which is hermetically sealed in and extends through the insulating shell 10 of the evacuated envelope.

The annular shield 30 is so positioned that its lower end is adjacent but axially spaced from the disklike base 17a of bellows 17. Since the base 17a of bellows 17 is fixed to and extends laterally from the movable contact rod the gap between shield and bellows base is variable. This gap is minimum when the contacts 150, 160 are engaged, as shown, and diminishes gradually to a limiting small dimension (which may be zero) as the interrupter contacts wear or erode. The shield 30 is so positioned that as a limit it will be engaged to the laterally projecting base end 17a of bellows 17.

In the drawing I have illustrated schematically a suitable actuating mechanism for moving the contact rod 16 between engaging and disengaging position with respect to the contact rod 15. As previously noted, because of the high degree of vacuum within the envelope i.e., on the outer surface of the flexible bellows 17, and the presence of normal atmospheric pressure within the bellows 17 the contact rod 16 is biased into contact engaging position by the pressure difference between the inside and the outside of the bellows. It will of course be understood that if desired this bias may be supplemented or reversed by the addition of suitable springs or the like. In the illustrated embodiment no bias is provided other" than the closing bias of bellows 17.

in order to drive the contact rod 16 to contact disengaging position against its bias I have shown at the lower end of the rod a slidable actuating member 35 loosely connected to the rod 16 by interengaging

annular shoulders

36 and 37 and biased to contact opening position by a driving spring 38. To move the actuating member 35 against its bias and thereby permit the movable contact rod 16 to move to engaging position under its own bias I provide a

toggle

40, 41 positioned between the actuating member 35 and a fixed pivot 42.'The

toggle

40, 41 is driven to extended position (as shown) by a rotatable cam 43. As shown the cam 43 is so shaped that a slight further clockwise movement suddenly releases the

prop

40, 41 for collapse by the driving spring 38. For opening and closing operation of the vacuum interrupter l have shown the cam 43 driven by a motor 50 which is energized from a suitable source of control power, shown as a battery 51, and normally controlled by a switch 52. For a purpose to be described hereinafter the motor 50 may be disabled and operation of the vacuum interrupter prevented by actuation of a relay 53 having normally closed contacts 54in series circuit relation in the motor circuit.

it will of course be evident to those skilled in the art that if desired other switch actuating mechanisms may be used, but I find it especially desirable in the application of my invention to use an overtravel type actuator, such as the member 35, which begins its opening movement prior to movement of the movable contact.

When a vacuum interrupter is utilized as the arcing contactor in a transformer load tap changing apparatus, such as that shown in US. Pat. No. 3,472,981 to McCarty et al., it is normally subjected to very frequent opening and closing operation and may be located in a hazardous atmosphere, as by immersion in oil. As pointed out in the McCarty et al. patent such oil-immersed location makes it advisable that the internal pressure in the evacuated envelope be monitored substantially continuously to detect any abnormal pressure increase. The high operating frequency of tap changing duty makes it further desirable that automatic mean be provided for indicating or responding to excessive contact erosion. In some applications it is desirable to disable the vacuum interrupting device in response to contact wear of a predetermined maximum amount. 1

In order to provide automatic monitoring of both of the foregoing conditions I apply across the variable gap between the movable end of flexible bellows l7 and the proximate end of metallic shield 30 a high potential derived through a transformer 55 having a primary winding connected to the power circuit conductor 25 and a secondary winding connected between the shield supporting ring 32 and the mounting plate 13. The potential applied across the shield-to-bellows gap must be sufficiently low so that no significant discharge is present across minimum gap spacing greater than the minimum limit so long as pressure inside the evacuated envelope is in a normal range, but sufficiently high to initiate a discharge across even the maximum gap spacing when the pressure inside the envelope is above the normal range. By way of example, such a monitoring voltage may suitably be of the order of 5,000 volts.

It is likely that with monitoring voltage sufficiently high to monitor internal pressure discharge across the shield-to-bellows gap (as its minimum is reduced by contact wear) will occur at some limiting distance prior to actual engagement of these parts, as for example when the movable end of the bellows in its contact closing position progresses by contact wear to the position shown by the dotted line 56. if desired, of

course, the monitoring voltage may be sufficiently low to require engagement between the shield and bellows before the secondary winding of transformer 55 conducts current. Such lower voltage is appropriate if it is desired to monitor only contact wear and not loss of vacuum. in this case the monitoring voltage may be from any available source of control volt age and may be alternating or unidirectional.

While I have shown the movable end of bellows 17 as one terminal of the monitor gap, it will be evident to those skilled in the art that any suitable electrically conductive lateral extension on the movable contact rod 16 may be utilized for this purpose.

In order to indicate flow of signal current in the secondary winding of the monitoring transformer 55 l have shown the secondary connected to supply current through-a transformer 60 to a normally'open contrOl relay 6]. The contacts 61a of relay 61 are connected to complete a circuit from the control power source 51 to an alarm device, shown as a bell 62, and to a protective device, shown as the motor disabling relay 53. It will be evident that the signal current may be utilized as desired, for either indication or control, or both. With the relay 53 shown by way of example it will be evident that energization of the relay will open the circuit of motor 50 and prevent further actuation of the interrupter contact 16.

It is important to the operation of some vacuum interrupting devices that the metallic shield 30 be electrically isolated from the contact 15a, 16a, at least during circuit interrupting operation. To ensure such isolation l have provided a control switch 70 in the secondary clrcuit of the monitoring transformer 55. The switch 70 is biased to open position but normally held closed by a portion 71 of the actuating member 35 when in the contact closing position shown. it will be evident that when the member 35 is released to open the vacuum interrupter contacts the control switch 70 will be opened before the vacuum interrupter contacts 15a, 16a are separated. Thus the monitor voltage between the shield 30 and contact rod 16 is removed before an arc is drawn and during interruption the shield is electrically isolated from the interrupter contacts. A monitoring circuit of this type is more fully described and is claimed in US. Pat. No. 3,403,297 to Crouch.

It will now be observed that in operation monitoring voltage from the secondary winding of the transformer 55 is applied across the bellows-to-shield gap inside the vacuum interrupter envelope at all times when the interrupter contacts are in engagement. Thus in all circuit applications where the interrupter is used as a normally closed switching device, as in power circuit breaker applications and in load tap changing apparatus of the type previously referred to, my single monitoring circuit, which includes the bellows-to-shield gap within the interrupter envelope, serves to monitor substantially continuously both loss of vacuum and contact wear. If in any particular application it is desired to utilize this circuit only for monitoring contact wear it is possible to utilize a low monitor voltage and to set the initial shield-to-bellows gap so that contacting engagement between the shield and the bellows is necessary to initiate the flow of signal current in the monitor circuit.

While I have shown and described a particular embodiment of my invention by way of illustration, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in itsbroader aspects; I therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What 1 claim as new and desire to secure by Letters Patent of the United States is:

1. In a protective system for a vacuum-type electric circuit interrupter comprising an evacuated .envelope having cooperable fixed and movable contacts therein, a movable contact rod carrying said fixed contact and extending through the wall of said envelope, said rod being slidable axially between contact engaging and disengaging positions, a tubular metal shield fixedly mounted within said envelope and surrounding said contacts. said shield being mounted for electrical isolation from said contacts, an electrically conductive projection on said movable contact rod adjacent but axially spaced from one end of said shield, the gap between said shield and said projection being minimum when said contact rod is in its contact engaging position, said minimum gap diminishing as said contacts erode in current interrupting operation, means for impressing an electric potential across said gap, and signal means responsive to flow of current between said shield and projection for substantially continuously monitoring contact wear and vacuum sealing in said circuit interrupter.

2. in a protective system for a vacuum-type electric circuit interrupter comprising an evacuated envelope having cooperable fixed and movable contacts therein, a movable contact rod carrying said fixed contact and extending through the wall of said envelope, said rod being slidable axially between contact engaging and disengaging positions, a tubular metal bellows closed at one end and surrounding said rod, said bellows having said one end hermetically sealed to said rod and its other end sealed to said wall, a tubular metal shield fixedly mounted within said envelope and surrounding said contacts, said shield being mounted for electrical isolation from said contacts, said one end of said bellows being adjacent but axially spaced from one end of said shield and movable with said contact rod so that the variable gap from bellows to shield is minimum when said contact rod is in contact engaging position, said minimum gap diminishing as said contacts erode in current interrupting operation, and single means for substantially continuously monitoring contact wear and vacuum sealing in said circuit interrupter comprising means for applying an electric potential across said gap.

3. In a protective system for a vacuum-type electric circuit interrupter comprising an evacuated envelope having cooperable fixed and movable contacts therein, a movable contact rod carrying said fixed contact and extending through the wall of said envelope, said rod being slidable axially between contact engaging and disengaging positions, a tubular metal bellows surrounding said rod and having a disklike clo sure at one end, said bellows being hermetically sealed at its closed end to said rod and at its other end to said wall, a tubular metal shield fixedly mounted within envelope and surrounding said contacts, said shield being mounted for electrical isolation from said contacts, said closed end of said bellows being adjacent but axially spaced from one end of said shield and movable with said contact rod so that the variable gap from bellows to shield is minimum when said contact rod is in contact engaging position, said minimum gap diminishing as said contacts erode in current interrupting operation, means for applying an electric potential across said gap when said contacts are engaged, and means for removing said electric potential during separation of said contacts.

4. The apparatus of claim 3 in combination with means biasing said contact rod to contact engaging position, lost motion actuating means for disengaging said contacts including a driving member movable prior to contact separation, said means for removing electric potential being actuated by said driving member prior to contact separation.

5. The apparatus of claim 3 wherein said electric potential is sufficiently low that no significant discharge is present across said minimum gap when greater than a predetermined limiting dimension and the pressure inside said envelope is in a normal range, said potential being sufficiently high that discharge across said gap will occur at its maximum dimension when said pressure is above said normal range, and signal means connected in series circuit relation with said gap and operable in response to flow of current between said shield and bellows.

6. The apparatus of claim 4 in combination with said signal means includes means responsive to flow of current across said gap for disabling said actuating means.

7. The apparatus of claim 2 in combination with signal means operable in response to flow of current between said shield and bellows.

8. In a protective system for a vacuum-type electric circuit interrupter comprising an evacuated envelope having cooperable fixed and movable contacts therein, a movable contact rod carrying said fixed contact and extending through the wall of said envelope, said rod being slidable axially between contact engaging and disengaging positions, a conductive lateral projection on said movable contact rod, a tubular metal shield fixedly mounted with said envelope and surrounding said contacts, said shield being mounted for electrical isolation from said contacts, said lateral projection being normally spaced from one end of said shield to provide a gap between said shield and projection which is a minimum when said movable contact rod is in contact engaging position, said gap diminishing by wear as said contacts erode in current interrupting operation and said projection being positioned at the limit of such wear to engage said shield, current responsive signal means, and means operable upon engagement of said shield and projection to energize said signal means.

Claims

1. In a protective system for a vacuum-type electric circuit interrupter comprising an evacuated envelope having cooperable fixed and movable contacts therein, a movable contact rod carrying said fixed contact and extending through the wall of said envelope, said rod being slidable axially between contact engaging and disengaging positions, a tubular metal shield fixedly mounted within said envelope and surrounding said contacts, said shield being mounted for electrical isolation from said contacts, an electrically conductive projection on said movable contact rod adjacent but axially spaced from one end of said shield, the gap between said shield and said projection being minimum when said contact rod is in its contact engaging position, said minimum gap diminishing as said contacts erode in current interrupting operation, means for impressing an electric potential across said gap, and signal means responsive to flow of current between said shield and projection for substantially continuously monitoring contact wear and vacuum sealing in said circuit interrupter.

3. In a protectivE system for a vacuum-type electric circuit interrupter comprising an evacuated envelope having cooperable fixed and movable contacts therein, a movable contact rod carrying said fixed contact and extending through the wall of said envelope, said rod being slidable axially between contact engaging and disengaging positions, a tubular metal bellows surrounding said rod and having a disklike closure at one end, said bellows being hermetically sealed at its closed end to said rod and at its other end to said wall, a tubular metal shield fixedly mounted within said envelope and surrounding said contacts, said shield being mounted for electrical isolation from said contacts, said closed end of said bellows being adjacent but axially spaced from one end of said shield and movable with said contact rod so that the variable gap from bellows to shield is minimum when said contact rod is in contact engaging position, said minimum gap diminishing as said contacts erode in current interrupting operation, means for applying an electric potential across said gap when said contacts are engaged, and means for removing said electric potential during separation of said contacts.