US2261712A - Circuit breaker - Google Patents

Description

NOV. 4, 1941. J, BEHF-INGER 2,261,712

CIRCUIT BREAKER Filed NOV. l5, 1940v WITNESSES: INVENTOR Patented Nov. 4, 1941 CIRCUIT BREAKER Joseph Behringer, Berlin-Treptow, Germany, assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application November 15, 1940, Serial No. 365,821

In Germany November 25, 1939 6 Claims.

The present invention relates to high-voltage circuit breakers, and, more specifically, to a circuit breaker whose movable contact-making member is provided in the form of a rod that is actuated with the aid of another rod that is made of insulating material. A circuit breaker of this particular type is especially well adapted to be structurally combined with a hollow column-type insulator for supporting its parts, the most advantageous arrangement being obtained in this case when said rod of insulating material is located inside the hollow insulator.

When a hollow column-type insulator is used for the purpose just outlined, the arrangement has to be such that if a high overvoltage--for instance, in the form of a surge-wave-should reach the breaker, there will occur a flashov'er along the outer surface of the insulator before the dielectric stress in the interior of the latter can increase to a magnitude high enough to result in a `dielectric breakdown along the surface oi' said rod of insulating material, the lower end of this rod of insulating material being preferably linked to an operating mechanism. whose metal parts are connected to ground.

When the movable switching rod, arranged in the manner just outlined, is operated within the hollow support insulator in the course of the process of opening the breaker, the internal ilashover distance (along the surface of said rod of insulating material) becomes shorter. In view thereof, it has been heretofore proposed to fill the hollow insulator with an insulating liquid, in order to prevent endangering the breaker structure as a result of this shortening of the internal ashover distance. The dielectric strength inside the hollow insulator can be further increased by mounting inside this insulator, at the lower end of the switching rod when this rod is in the off position, a grading cap for making the distribution of the electric field at this point more uniform. In addition, the grounded flange belonging to the supporting structure of the breaker mechanism can be so shaped that it will have on the dielectric stresses an equalizing effect similar to that of a grading cap. But all these measures are not sufficiently effective Ito 'enable the designer to drastically reduce the overall height of the breaker structure.

The present invention discloses how the overall height of a breaker structure of the kind just referred to can be reduced to a quite considerable extent without resorting to complicated measures. In accordance with the present invention, there is provided inside the support insulator that is being used as a base or support for the insulator containing the interrupter assembly a grading cap to which voltage is applied only (Cl. 20G-48) when the breaker is in the off position; when the breaker is in the closed position, this grading cap acquires a floating potential somewhere between the line-potential and the ground-potential. This grading cap must be so supported that it will be insulated from all other breaker parts; it can be suspended, for instance, from the breaker structure with the aid of a tube of insulating material. The arrangement can then be such that when the breaker is in the open position, a spring will establish contact between the switching rod and the grading cap, so that no arcing will occur between these two members when the switching rod approaches its 01T position. On the other hand, when the switching rod is in the on position, its lower end must be located at such a distance from the grading cap that the flow of capacitive current from the switching rod to the grading cap cannot give rise to a discharge inthe form of an arc-over. The grading cap will then acquire a floating potential somewhere between the line-potential and the ground-potential.

The proposed arrangement offers the advantage that when the breaker is in the closed position, the entire axial distance inside the hollow post-type insulator is available for establishing the required dielectric strength (the entire axial distance in question being the distance from the upper iiange of the support insulator down to the point inside this insulator where the grounded parts of the operating mechanism are linked to the insulating rod to which the switching rod is connected). In this connection, it should be realized that at the presentday stage of the art, it is not yet possible to build circuit breakers for very high voltages (for instance, for kv. and more) whose overall heights are kept so low as to make shipments of these breakers on standard flat railroad cars possible; on the contrary, it is still necessary to ship such breakers on expensive, special railroad cars having a platform whose distance from the rail-top level is as small as possible, cars that are utilized only for shipping very heavy pieces of freight. This difference between the overall height of the breaker and the maximum permissible height determined by the clearance proles which the railroads have adopted for their rail lines-a difference which, although its absolute value may be rather small, will make it necessary to use such a special railroad car for ship-ping a breaker as long as it cannot be reduced to zero-can be eliminated by designing said breakers in accordance with the present invention, so that it becomes possible to ship the breakers on standard flat railroad cars.

In addition, application oi the present invention makes it possibleV to make one further step in improving the breaker-design, insofar as this invention discloses that the breaker structure can be so arranged that the members (such as levers) of the operating mechanism will only extend into the interior of the hollow insulator when the breaker is in the closed position, whereas, when the breaker is in the open position, said members will be located outside the hollow insulator. In other words, although live parts having the potential of the switching rod will extend downward as far as the insulated grading cap when the breaker is in the open position, all members of the operating mechanism will be in this case in their lowest position, outside the hollow post-type insulator, and in this position they are electrically protected by the grounded flange mentioned above, which is preferably so shaped as to have an equalizing effect similar to that of a gra-ding cap on the dielectric stresses. Since there is always a possibility that a disconnecting switch may fail to function properly, it is recommended, in view hereof, to design the operating mechanism of the breaker in such a manner that none of its guiding members will be mounted inside the hollow support insulator, and to permit the presence of grounded movable members of saidmechanism inside this insulator only when the breaker is in the closed position. If, therefore, it should not be possible to do without stationary guiding members (sliding surfaces) for the rod of insulating material to which the switching rod is connected, such guiding members would have to be made of some insulating material.

The advantages that can be secured by applying the present invention-the principal advantage being the considerable reduction in overall height of the breaker structure that is obtainable in this mannerare especially great in those instances where the hollow column-type support insulator in which the insulated grading cap is located is filled with oil or with an insulating compound.

Other objects and advantages will become apparent from the following description of a breaker structure illustrated in a single figure of the drawing which exemplifies a breaker arrangement conceived in accordance with the present invention and which shows the high-voltage breaker of the invention in the closed position.

The high-voltage current is supplied to the breaker shown through a terminal I secured to a metal fiange 2 located in the intervening space between two hollow insulators 3 and 4 that are placed one above the other. In insulator 3 is mounted an interrupter assembly comprising, for instance, a switch chamber 5, while the other insulator 4 accommodates the actuating parts. The switching chamber 5 for example may be of the resilient expansion type and encloses a stationary contact assembly 6 at its upper end. A coacting switching or contact rod 1 is operable through the chamber 5 and is slidably connected to the flange 2 by spring pressed contacts 8 disposed in a suitable casing mounted upon the flange, as shown. The current then flows through a contact rod 1 through the stationary contact assembly 6, and finally leaves the breaker at the terminal 9. Consequently, when the breaker is in the closed position, the terminals I and 9 carry both the high supply-line voltageamounting, for instance, to 100 kv.-and the full potential-difference existing between the terinal I and ground.

Inside the lower insulator 4 is mounted a curved metal grading cap I 0 with rounded-off edges which is preferably composed of sections of a sphere, and is provided for the purpose of making the distribution of the electric field more uniform. It is a feature covered by the present invention that the line-voltage is applied to this grading cap only when the breaker is in the open position; when the breaker is in the closed position, the grading cap acquires a floating potential somewhere between the line-potential and the ground-potential. In order to enable the grading cap I0 to acquire said potentials, it is supported by means of a tube II made of an insulating material that may have a fibrous or a laminated structure. pended from the flange 2 located between the two insulators. Since the dielectric stresses to be taken up by said tube of insulating material are essentially perpendicular to the direction of its laminations, the use of such a tube is feasible even when the voltages in question are exceptionally high.

The grading cap I0 can be mounted within the tube II of insulating material and can then be fastened to this tube by screws or bolts I2, so that it will be readily removable. The screws or bolts can also be used for fastening the springs I3 which, for instance, may be disposed inside the grading cap I0. The arrangement is such that the springs I3 will not interfere with the motion of an operating rod I4 of insulating material that establishes the connection between the contact rod 1 and the breaker operating mechanism. The rod I4 of insulating material is operable inside the tube II of insulating material to actuate the contact rod 1 to open and closed positions and has considerable clearance from the inner wall of the insulating tube II. When the breaker approaches the open position, the springs I3 come into contact with and are spread apart by a metal sleeve (or some other similar part) I5, fastened to the lower end of the contact rod 1, and has a diameter larger than the diameters of the rod 1 and the rod I4 of insulating material. Thus when the breaker is in the closed position, the grading cap I0 is charged by a capacitive current and acquires a oating potential somewhere between the line potential and the ground potential but when the breaker is in the open position, the grading cap I0 becomes electrically connected with the breaker terminal I, so that its potential is raised to that of the line without any occurrence of sparking between the contact rod 1 and the grading cap I0.

The springs I3 can be provided in the form of curved blade-springs, spiral or helical springs, or may consist of a plurality of individually bent strips of metal and can be arranged like sliding contacts, surrounding the rod I4 of insulating material in a manner such as to leave sufficient clearance for the switching motions of said rod.

The hollow insulator 4 in which the grading cap I0 is located is preferably filled with an insulating liquid but may be filled with a solidified, or with a granulated or pulverized insulating material in order to increase the dielectric strength still further.

The contact rod 1 can be actuated by means of a rocker arm 2| carried by a rock shaft I6 and which may be coupled either directly or indirectly with the operating rod I4 of insulating material. The shaft IB is operatively mounted in a grounded metal casing I1 which also serves to support the hollow insulator 4. The rod I4 can be guided with the aid of a cross-head I8 that is The tube II can be susrigidly attached to it, which may be provided on both sides with slots that can loosely engage and slide along two guide-rails I9 made of an insulating material and having a rectangular or a dovetail-shaped cross-section. This arrangement for the operating members is such that no metal parts of the drive will be positioned inside the hollow insulator 4 when the breaker is in the open position, and only when the breaker is in the closed position will grounded metal parts of the actuating mechanism be located inside the insulator 4. Moreover, when the breaker is in the open position, the grounded metal parts of the actuating mechanism will be electrically protected by a grounded metal flange supported by the casing II and having a configuration to provide an electrostatic grading cap or shield.

The present invention is applicable to any high-voltage switching device, and more particularly to high-voltage circuit breakers. of applying the invention to an expansion-type breaker as above described, it is equally feasible to apply it to a gas-blast breaker that receives the required quantities of compressed gas from an outside source, or to a self-generated gas blast breaker in which the extinguishing gases are liberated from a solid insulating material, preferably provided in the form of tubular members. Furthermore, the invention can be applied to any other type of breaker, single-pole or multi-pole, v

or to a type in which the extinction of the arc is brought about or facilitated by a magnetic field.

The various features covered by the present invention represent valuable improvements in the circuit breaker art, not only when applied in combination, but also when they are applied individually.

I claim as my invention:

1. In a high voltage circuit breaker, a casing of insulating material one end of which is maintained at ground potential, circuit interrupting means including separable contacts disposed within said casing adjacent the other end thereof, an electrostatic stress grading member disposed within said casing between said contacts and ground, and means electrically connecting one of said contacts with said stress grading member when said contacts are in the open circuit position, said stress grading member being' so arranged that when said contacts are in the closed circuit position said member is disconnected from said contact and acquires a floating potential between line potential and the ground potential.

2. A high voltage circuit breaker having a hollow supporting insulator one end of which is maintained at ground potential, separable contact means in said insulator including a contact rod, an operating rod of insulating material disposed within said insulator for actuating said contact rod to open and closed positions, a potential grading member disposed within said hollow insulator between said contact rod and ground, and means for electrically connecting said contact rod to said grading member when said contact rod is in its open circuit position, said grading member being disconnected from said contact rod when said rod is in the closed circuit position and caused to acquire a potential intermediate the potential of said contact member and ground.

3. A high voltage circuit breaker as set forth in claim 2, characterized by the feature that the grading member is supported by an insulat- Instead ing tube within the hollow insulator, which tube surrounds said operating rod and insulates the grading member from other breaker parts.

4. A high voltage circuit breaker having a hollow supporting insulator one end of which is maintained at ground potential, separable contact means in said insulator including a contact rod, an operating rod of insulating material disposed within said insulator for actuating said contact rod to open and closed positions, a potential grading member disposed within said hollow insulator between said contact rod and ground, metallic operating mechanism disposed adjacent the grounded end of said hollow insulator and connected to the lower end of said operating rod, said mechanism having only portions thereof extending into said hollow insulator when the breaker is in the closed position and being wholly outside said hollow insulator when the breaker is in the open circuit position, and a metallic grading shield disposed between said operating mechanism and said potential grading member for equalizing the dielectric stresses between said member and the operating mechanism.

5. In a circuit breaker, a grounded metallic base, a hollow support insulator carried by said base, a metallic closure for the upper end of said insulator, circuit interrupting means carried by said metallic closure, said circuit interrupting means including a contact movable through said closure to open and closed positions, operating mechanism disposed in said base, an insulating operating rod extending from said mechanism through said hollow insulator and operatively coupled to said movable contact to actuate the latter, a tubular insulator suspended from said metallic closure and disposed in surrounding spaced relation with respect to said operating rod, a generally spherical potential grading member carried by said tubular insulator, and means operative upon moving said contact to open circuit position for connecting said contact to said potential grading member, said potential grading member causing a more uniform distribution of electrical stresses between said contact and said grounded metallic base.

6. In a circuit breaker, a grounded metallic base, a hollow support insulator carried by said base, a metallic closure for the upper end of said insulator, circuit interrupting means carried by said metallic closure, said circuit interrupting means including a contact movable through said closure to open and closed positions, operating mechanism disposed in said base, an insulating operating rod extending from said mechanism through said hollow insulator and operatively coupled to said movable contact to actuate the latter, a tubular insulator suspended from said metallic closure and disposed in surrounding spaced relation with respect to said operating rod, a generally spherical potential grading member carried by said tubular insulator, and means operative upon moving said contact to open circuit position for connecting said contact to said potential grading member, and a grounded potential grading member disposed within said hollow insulator between said operating mechanism and said rst potential grading member for more uniformly distributing the dielectric stresses between said contact and said grounded base.

JOSEPH BEHRINGER.

Images