US3598939A

US3598939A - Isolating switch for ultra high voltages

Info

Publication number: US3598939A
Application number: US16030A
Authority: US
Inventors: Gustave E Heberlein; James B Owens
Original assignee: ITE Imperial Corp
Current assignee: ABB Inc USA
Priority date: 1970-03-03
Filing date: 1970-03-03
Publication date: 1971-08-10
Anticipated expiration: 1988-08-10
Also published as: CA906552A

Abstract

An isolating switch having large metallic electrodes presenting substantially smooth surfaces facing one another, with at least one of the electrodes being movable by means of a moving carriage to which it is secured. The electrodes in the open gap position have a relatively high withstand or insulation strength on switching voltage surge, impulse voltage, and with a relatively small gap space. The movement of the carrier to contact both electrodes corresponds to the closed position of the switch while movement of the carriage to break the contact between the electrodes corresponds to the open position. In that latter position, a substantially uniform electrostatic field is produced in the gap between the electrodes. This has the advantage that a simple and reliable disconnecting means for very high voltage lines and apparatus is provided while, at the same time, significantly reduces the size, weight and land requirements of previous disconnect switches because of the improved electrical gradients made possible by the electrode geometry.

Description

Primary Examiner Robert K. Schaefer Assistant E.taminer-H. J. Hauser Attorney-Ostrolenk, Faber, Gerb and Soffen ABSTRACT: An isolating switch having large metallic electrodes presenting substantially smooth surfaces facing one another, with at least one of the electrodes being movable by means of a moving carriage to which it is secured. The electrodes in the open gap position have a relatively high withstand or insulation strength on switching voltage surge, impulse voltage, and with a relatively small gap space. The

the advantage that a simple and reliable disconnecting means for very high voltage lines and apparatus is provided while, at the same time. significantly reduces the size, weight and land requirements of previous disconnect switches because of the improved electrical gradients made possible by the electrode geometry Inventors United States Patent 1508 15 23 404 0 54 4 .4 l 04 M43 7 07 7 /4l. 2 l m 1 24 OH I m m moo 7 h 4 m S "u 3 M T m N H mm W W 7 m mm .rll. m P m s A m 4 C S m H a u m a E m n B n00 T m "4 "m e m w m mmR D n M Ma R D TC H ""4 E H mI "72 m m N45 m Umw H n II 200 '0 .l d Cw Ld 32 U .mF fi a 2 0 6 4 6 U UK 1 1 22 PATENTED Auslolsn 598,938

SHEET 2 OF 3 PATENTEU ms] 0 [9n SHEET 3 OF 3 ISOLATING SWITCH FOR ULTRA HIGH VOLTAGES BACKGROUND OF THE INVENTION This invention relates to electrical switches, and to high voltage air-isolating switches of the disconnect type. More specifically it relates to such switches which are provided with a novel electrode arrangement which substantially minimizes the danger of flashover in the open gap when the switch is in its disconnect position, so as to substantially reduce the open gap dimensions heretofore required.

Disconnecting switches are designed to isolate electrical apparatus and portions of electrical systems from energized lines for the safe handling, maintenance, repair and inspection they require. It is, therefore, of the utmost importance to provide adequate protection for personnel working in the immediate region of this disconnected equipment. Hence, when the switch is open it is necessary that the gap in the open position be adequate to withstand all usual, as well as unusual voltages which are impressed upon it by the system. lf a surge voltage causes the switch open gap to flashover, the lives of personnel may be placed in serious jeopardy.

Such disconnecting switches are customarily designed so that the switch open gap will withstand higher voltages than the insulator columns which support the energized parts from the grounded metal base. As a result, flashover is much more likely to occur between the energized parts and ground, than across the switch open gap. In this manner, the insulator columns provide protection for the switch and operating personnel against switching surge voltages, and impulse voltages. However, this requires the provision of very large open gaps in the switch to insure greater insulation strength or withstand than exists across the insulator column.

In the past, disconnecting switches have been constructed with large open gaps with nonuniform electric field distribution because of the geometry of the switch blade and associated contacts. In some instances, methods were provided to reduce the insulation strength of the insulator columns to ensure higher insulation strength across the open gap than existed down the insulator columns to earth. These methods have included the use of devices such a rod electrodes connected to the base of the insulator columns. These methods, however, have all suffered two critical drawbacks.

The first drawback is that the effective insulation strength or withstand of the insulator column cannot be reduced without limitation. The effective withstand of the column cannot be reduced, for example, to the point where it will not be sufficient under high voltage conditions when the system is in operation. lf the withstand of the insulator column is too low, the system will not be able to function properly or reliably.

The second drawback is that the gap between the switch blades of the disconnecting switch in all of these cases establishes the insulating distances as essentially that between rod electrodes, i.e., behaves like a rod gap, and since the withstand of the insulator column must always be sufficiently high, this gap must of necessity remain large. The necessity of this large gap distance further creates a situation subject to anomalous flashovers rather than the required controlled flashover to ground. With a very large gap behaving like a rod gap, it is very difficult to obtain the required flashover control.

In the same way that voltages of 500 and 700 kilovolts have been recently developed as overlay for 300--345-kilovolt systems, 1,0001,500 kilovolts is presently being developed for future overlay on 500- and 700-kilovolt systems. The formidable factor in such system designs has been to provide sufficiently high switching surge insulation strength. With the successful application of surge control in power circuit breakers and advances in surge diverter design, switching surges can be limited to a sufficiently low level that operating voltages can be increased to l,O-l,500 kilovolts with no greater probability of flashover than on the present 700- kilovolt systems. These 700-kilovolt systems have a switching surge withstand of 1,350 kilovolts, impulse withstand of 2,100

kilovolts, power frequency withstand of 970 kilovolts and with no visible corona at 500 kilovolts to ground. Future 1,500- kilovolt systems may require a switching surge withstand of 2,300 kilovolts, impulse withstand of 2,600 kilovolts, power frequency withstand of 2,000 kilovolts and with no visible corona at 1,300 kilovolts to ground.

In recent times, power plants are being developed using voltages as high as LOGO-1,500 kilovolts. These plants require disconnecting switches having insulator columns with great withstand during operation. The insulator columns may be of the order of 20 feet in order to provide adequate withstand for switching surges of 2,300 kilovolts or so. Under these conditions, the switch open gap using existing switch blade arrangements may be considerably longer (e.g., 25-30 feet) to ensure that flashover will be across the insulator columns rather than across the open gap. By means of the present invention, the switch open gap has been reduced while ensuring no flashover in the open gap position.

This invention provides a new and novel switch open gap whereby the switch open gap is substantially shortened to produce greater control of any flashovers without the necessity of reducing the effective insulation strength of the insulator columns. This invention also permits a substantial savings in yard space resulting from its significantly reduced size, weight and land requirement as compared to prior switch configurations.

This invention solves the problems of the prior art by providing new and novel switch blade electrode arrangements which set up a substantially uniform electrostatic field over a wide but controlled area when the electrodes are in their disconnect position, rather than the concentrated nonuniform electrostatic field previously established by switch blade and electrode arrangements producing rod-type gaps. As will become apparent hereinafter, the present invention represents a modification of that invention disclosed in pending U.S. application Ser. No. 68 1,743, filed Nov. 9, 1967 (BF-48) and assigned to the same assignee as the instant invention. As will also become apparent, the present invention represents a further modification of that invention disclosed in U.S. application Ser. No. 839,456, (EP-64) filed July 7, 1969. As will further be apparent, this invention also incorporates features of the invention disclosed in U.S. application Ser. No. 864,016, (BF-234) filed Oct. 6, 1969.

In one embodiment of the invention, a disconnect switch has a first metallic spherical electrode supported from an insulator column secured to a suspension frame in stationary rela tionship. The disconnect switch also has a second metallic spherical electrode supported from an insulator column connected to a carriage which is movable along the frame by means of wheels, rollers, or similar such apparatus. When the carriage is moved under external direction to connect the two metallic spherical electrodes, the disconnect switch is in its closed position. When the carriage is directed to disconnect the metallic spherical electrodes, the disconnect switch is in its open position, with the separation between the two electrodes defining the switch open gap. With the electrodes in this position, a sphere gap is produced and any potential difference between the two electrodes will set up a substantially uniform electrostatic field. Since the electrostatic field is substantially uniform and over a wide area, the voltage necessary to cause any flashover in the switch open gap will be far greater than is necessary for a rod gap having the same electrode separation and the switch open gap may be decreased substantially.

Accordingly, a primary object of the invention is to provide a novel switch open gap to protect against flashover in the gap in disconnect-type switches.

Another object of the invention is to provide a novel construction for disconnecting switches which permits a decrease in the length ofthe switch open gap of the switch.

A further object of the invention is to provide a novel construction for disconnecting switches which effects a significant reduction in the size. weight, and land requirement of disconnecting switches heretofore known.

An additional object of the invention is to provide a disconnect switch, wherein the switch open gap is substantially shorter than the insulator column and yet ensures against flashover in the switch open gap itself.

These and other objects of the invention will become apparent from a reading of the accompanying description and drawings in which:

FIG. 1 is a portion ofa front elevational view of an embodiment of the disconnect switch of the instant invention;

FIG. 2 is a side elevational view of the embodiment of FIG. 1;

FIGS. 3 is a plan view of a portion of the embodiment of FIG. 1 rotated through an angle of 90; and

FIG. 4 illustrates a possible construction ensuring proper contact when the disconnect switch of the invention is closed and proper positioning of the electrodes at this point of time.

DESCRIPTION AND OPERATION OF THE SWITCH OF FIGS. 1 AND 2 Referring now to FIGS. l4, there is shown a two-insulator disconnect switch assembly including a suspension frame 10, which is preferably of a rigid metallic structure. The frame rests on the ground surface, and is provided with means 11 and 12 which secure the upper portions of a pair of insulator columns 13, 14 to the frame 10 in any desirable manner, such that the insulator columns 13, 14 extend downwardly from the support frame 10 in an inverted, underhung position. As pointed out in pending application Ser. No. 864,016 (E-234) the greater dielectric characteristic associated with mounting the insulator column in an inverted position as compared to a conventional upright mounting, permits the insulator height to be significantly reduced for a given voltage application.

As indicated in FIG. 1, means 11 is secured to the support frame 10 so as to be held in stationary relationship. Means 12, on the other hand, is shown as a carriage, being movable along the frame 10 (within a track therein, for example) by means of a pair of wheels, rollers or the like 15 under the control of a cable and pulley arrangement 16, including pulleys 17, 18, 19, cables and rotatable drum 21. A pair of large

metallic electrodes

22, 23 are secured to the ends of insulators 13, 14, respectively, and are controlled to move towards and away from one another under direction of movement of the rotating drum 21. For example, rotation of an integral crank arm 24 of the drum 21 in a direction to wind the cable 20 onto the drum 21 might have the effect of moving the carriage 12 to the open or dotted position (i.e., to the right while rotation of the crank 24 to unwind the cable 20 from the drum 21 might cause the carriage 12 to move to the closed position of the switch (i.e., to the left).

Conductors 25 and 26 are respectively coupled to these

electrodes

22, 23 in this and other environments, in any suitable manner and connect these electrodes to suitable utilization apparatus (not shown). It is to be understood that while solid, generally spherical electrodes have been shown, the

electrodes

22 and 23 may also be of the shape of toroidal rings, ellipsoids, spheroids, Rogowski curves or any special geometric shape to provide a substantially uniform electric voltage gradient between the adjacent electrode surfaces.

When the switch illustrated in FIG. I is to be closed, the integral handle 24 and drum 21 are rotated in a direction to bring the

electrodes

22, 23 in contact. As previously mentioned, the rotation of the handle 22 in this manner is such as to cause the electrode 23 to be carried by the carriage 12 to the left.

FIG. 4 shows the electric current transfer in the closed position of the

electrodes

22, 23 as being provided by contact finger 27 on the electrode 22 and jaw 29 on the electrode 23. As indicated these members 27, 28 are arranged so that they are shielded by their respective electrode surfaces in both the open and closed position-specifically, so that in the open position, substantially smooth surfaces continue to be faced adjacent to one another to effect the substantially uniform electric voltage gradient and a dispersed electrostatic field in the airgap.

When the switch is to be opened, the integral handle 24 and drum 21 are rotated in a direction to effectuate a movement of the carriage 12 to the right. In one arrangement of the invention, it was found that with electrodes of approximately 6 feet 6 inches in diameter, a movement to present a switch open gap of some 7 feet was found to be sufficient to minimize the possibility of flashover. A rod-type gap, on the other hand, oftentimes requires a spacing of 27 feet and more to prevent against flashover for ultrahigh voltages of comparable amount.

The electric advantage of this sphere gap switch includes better corona control, a more uniform flashover characteristic with less tendency to anomalous flashover, and a greater ease of gap coordination with insulation to ground. The large electrodes employed will further have a grading effect on the supporting insulators and a better voltage distribution to reduce the height of the insulator stacks substantially. This height reduction is further buttressed by the inclusion of the insulator columns in an inverted underhung arrangement as disclosed in application Ser. No. 864,016 (15-234).

In accordance with the present invention, adequate protection for personnel against flashover in the switch open gap is provided by the substantially uniform distribution of the electrostatic field in the gap region. The substantially uniform electrostatic field requires a much higher voltage for flashover than does the concentrated electrostatic field of a rodgap. Furthermore, with a more uniform electrostatic field, the switch open gap may be considerably shortened (to, for example, the 7 feet of one arrangement of the invention) and can be more easily coordinated with the withstand characteristic of the insulator column. It is seen that this switch open gap is considerably shorter than the insulator column and still provides adequate protection against flashover in the gap.

Further protection to personnel working in the switch open gap is provided by the novel electrode arrangement since any flashover between the electrodes and ground will occur in regions not between the insulator columns themselves. The reason for this is that the electrodes in the region between the insulator columns produce a more uniform electrostatic field, while no rodgap between these units is provided. The result of this feature is that any dangerous flashover will necessarily be in a region away from personnel and that the insulator columns will shield the switch open gap from any ionized gases created by flashover between theelectrodes and ground.

It will therefore be seen that the instant invention provides an alternative solution to problems involving flashover than is described in aforementioned U.S. applications Ser. No. 681,743 (EP-48) and Ser. No. 839,456 (BF-64). There, instead of using movable spherical electrodes to effectuate closing and opening of the switch, the first application described the use of a pair of rotating switch blades to place the switch in either one of an opened and closed position, while the second application described the use of a retractable blade to connect and alternatively disconnect the electrodes employed. Thus, although the invention disclosed in the Ser. Nos. 681,743 and 839,456 applications afford the desirable features and advantages set forth therein, the invention of the instant application offers many additional desirable features of its own. These additional features should not be construed, however, as detracting from the attractiveness of those inventions as there too, the advantage of reducing the possibility of flashover with decreased gap dimensions is also provided.

The principal advantages of this invention over air disconnect switches of previous design not only includes its reduced physical size and its high withstand to overvoltages, but also include the fact that its operation is one free of corona. This and other advantages will be well recognized and appreciated by those skilled in the art.

The embodiments ofthe invention in which we claim an exclusive privilege or property are claimed are defined as follows:

1. An electric switch comprising:

a suspension frame; v

first and second metallic switch electrodes operative to produce a substantially uniform electrostatic field therebetween when in a disengaged switch position;

first and second insulator supports respectively upholding 5 said first and second metallic electrodes and secured to the underside of said frame for suspending said electrodes in inverted, underhung arrangement; and

means coupled to said insulator supports and operative to effect relative movement between said supports to cause contact between said first and second electrodes to establish an engaged switch position and to cause withdrawal of said electrodes to break said contact to establish said disengaged switch position.

2. An electric switch as defined in claim ll, wherein one of said insulator supports is secured in a stationary manner with respect to said suspension frame while the other of said supports is adapted to traverse said suspension frame and carry its associated electrode into contact with the electrode associated with said stationary support to establish said engaged switch position and to withdraw said electrode to break said contact to establish said disengaged switch position.

3. An electric switch as defined in claim 1, wherein said first and second metallic electrodes comprise a pair of electrodes operative to present substantially smooth surfaces toward one another when in a disengaged switch position.

4. An electric switch as defined in claim 3, wherein said electrodes are operative to produce a sphere gap condition therebetween when in said disengaged switch position.

5. An electric switch as defined in claim 4, wherein said suspension frame is positioned atop a grounded base and 6 wherein the distance between said electrodes when the switch is in its disengaged position is substantially shorter than the length of said insulator support, and yet the breakdown voltage for flashover is greater between said first and second electrodes than it is from said electrodes to said grounded base across the respective insulator support lengths.

6. A high voltage disconnect switch comprising:

a suspension frame;

first and second metallic switch electrodes for carrying voltages of the order of hundreds of kilovolts and more and operative to produce a substantially uniform electrostatic field between facing surfaces thereof when in a disengaged switch position, with one of said electrodes having an opening in its respective facing surface and with the other electrode having an extension therefrom;

first and second insulator supports respectively upholding said first and second metallic electrodes and secured to the underside of said frame for suspending said electrodes in inverted, underhung arrangement; and

7. An electric switch as defined in claim 6, wherein said electrode opening and said electrode extension are both substantially shielded by said first and second metallic electrodes in both the engaged and disengaged position of the said disconnect switch.

Claims

1. An electric switch comprising: a suspension frame; first and second metallic switch electrodes operative to produce a substantially uniform electrostatic field therebetween when in a disengaged switch position; first and second insulator supports respectively upholding said first and second metallic electrodes and secured to the underside of said frame for suspending said electrodes in inverted, underhung arrangement; and means coupled to said insulator supports and operative to effect relative movement between said supports to cause contact between said first and second electrodes to establish an engaged switch position and to cause withdrawal of said electrodes to break said contact to establish said disengaged switch position.

2. An electric switch as defined in claim 1, wherein one of said insulator supports is secured in a stationary manner with respect to said suspension frame while the other of said supports is adapted to traverse said suspension frame and carry its associated electrode into contact with the electrode associated with said stationary support to establish said engaged switch position and to withdraw said electrode to break said contact to establish said disengaged switch position.

5. An electric switch as defined in claim 4, wherein said suspension frame is positioned atop a grounded base and wherein the distance between said electrodes when the switch is in its disengaged position is substantially shorter than the length of said insulator support, and yet the breakdown voltage for flashover is greater between said first and second electrodes than it is from said electrodes to said grounded base across the respective insulator support lengths.

6. A high voltage disconnect switch comprising: a suspension frame; first and second metallic switch electrodes for carrying voltages of the order of hundreds of kilovolts and more and operative to produce a substantially uniform electrostatic field between facing surfaces thereof when in a disengaged switch position, with one of said electrodes having an opening in its respective facing surface and with the other electrode having an extension therefrom; first and second insulator supports respectively upholding said first and second metallic electrodes and secured to the underside of said frame for suspending said electrodes in inverted, underhung arrangement; and means coupled to said insulator supports and operative to effect relative movement between said supports to cause contact between said first and second electrodes to establish an engaged switch position and to cause withdrawal of said electrodes to break said contact to establish said disengaged switch position.