High Voltage Switch With Preinsertion Resistor Connected In The Circuit Through Graphite Corona Balls

Abstract

Conducting arms connected in parallel with the switch blades of a center break disconnecting switch through pre-insertion resistors have graphite corona balls at their distal ends to provide arcing surfaces that are unimpaired when impinged by arcs and relatively light weight to minimize inertia.

Description

This invention constitutes an improvement over the construction disclosed in application Ser. No. 768,825, filed Oct. 18, 1968, now U.S. Pat. No. 3,576,414, issued Apr. 27, 1971.

As pointed out in the above application it is desirable to limit the inrush current in a circuit on energization thereof. This is particularly the case when a capacitor bank is energized from a high voltage circuit or a high voltage electric power transmission line having relatively high capacitance is energized. If the inrush current is not limited, transient disturbances in the system may be generated which may cause flashover, insulation breakdown and the like. Further, the closure of the circuit in air may develop objectionable noise incident to formation of arcs on completion of the circuit.

According to the above application a center break switch construction is modified to insert a resistor in the circuit while the switch is being closed for limiting the inrush current and to short circuit the resistor when the switch is in the closed position. For this purpose a resistor assembly is mounted in upstanding relation on each switch blade adjacent its pivot axis. A conducting arm extends from the upper end of each resistor assembly toward the other arm with the arrangement being such that a spark gap is formed between the arms during closure of the switch blades in series with the resistor assemblies which is shorter than the gap between the distal ends of switch blades. When the arms, moved conjointly with the switch blades, reduce the length of the arc gap therebetween sufficiently to permit it to arc over, current begins to flow in the circuit which is limited by the voltage drop across the arc and by the resistor assemblies while the arc is maintained until it is short circuited by engagement of the switch blades at their distal ends. For a balanced construction, two resistor assemblies are used. However, the resistance can be embodied in a single resistor assembly. At their distal ends in the switch closed position the resistor inserting arms are spaced from each other. The arms extend angularly from the vertical plane of the respective switch blade on the side facing the direction of closing movement of the switch blades.

The distal ends of the conductor arms, as originally constructed, were provided with corona balls formed of aluminum to distribute electrostatic stress and to minimize weight and thereby the inertia of the moving parts. Actual field experience showed that the flashover distance between the corona balls increased after the initial closing operation because the surfaces of the balls were roughened since globules of aluminum were melted out due to the heat of the arc that was struck therebetween. As a result the circuit closing operation was impaired.

Accordingly, among the objects of this invention are: To maintain unimpaired the surfaces of the corona balls after repeated circuit closing operations; to employ for this purpose a material no heavier than aluminum which does not melt when subjected to an electric arc in air; to employ graphite for the corona balls; and to minimize transfer of the arc from the corona balls to the supporting conductor arms by providing rounded surfaces on the former adjacent the juncture with the latter.

In the drawings:

FIG. 1 is a top plan of one pole of a polyphase disconnecting switch and circuit interrupter assembly provided with resistor insertion means having arc resisting corona balls embodying the present invention. FIG. 2 is a view, in side elevation, of the construction shown in FIG. 1, certain parts being broken away in order to illustrate certain internal details of construction.

FIG. 3 is an elevational view, at an enlarged scale of the distal end of one of the resistor inserting conductor arms and the corona ball thereat, certain parts being broken away in order to show the internal details of construction.

FIG. 4 is a sectional view taken generally along line 4--4 of FIG. 3.

Referring now to FIGS. 1 and 2 of the drawings, the reference character 10 designates, generally, one pole of a polyphase switch and interrupter assembly provided with resistance inserting means. For three phase application it will be understood that three poles are employed.

The pole 10 includes a frame base 11 that can be constructed of welded rolled steel angle sections with suitable bracing. At the left end there is mounted a stationary insulator stack 12. Also mounted on the frame base 11 are first and second rotatable insulator stacks 13 and 14. Suitable bearings are provided for mounting the lower ends of the insulator stacks 13 and 14 about vertical axes on the frame base 11. The height of the insulator stacks 12, 13 and 14 varies, depending upon the voltage of the system in which the pole 10 is connected. For relatively low voltage application each insulator stack may comprise a single insulator, such as a porcelain insulator. For higher voltages a number of separate insulators having metallic fittings at their ends are bolted together endwise in order to accommodate the voltage used.

As shown in FIG. 2 shafts 15 and 16 extend downwardly from the rotatable insulator stacks 13 and 14 and each carries an operating arm 17 and 18. Mechanism is provided for rotating the operating arms 17 and 18 and thereby shafts 15 and 16 in opposite directions. This mechanism includes links 19 and 20 which are connected at one end to the respective operating arms 17 and 18. At their other ends the links 19 and 20 are connected respectively to crank arms 21 and 22 that extend from a crank shaft 23. On rotation of the crank shaft 23 through slightly more than 180.degree. from the position shown in FIG. 2, the links 19 and 20 are actuated to effect rotation of the shafts 15 and 16 and thereby of the first and second rotatable insulator stacks 13 and 14 respectively. The frame base 11 is suitably enclosed to protect the operating mechanism from the weather. This includes ice shield plates, one of which is indicated at 27.

The stationary insulator stack 12 at its upper end carries a line terminal 30 to which one end of a circuit interrupter, indicated generally at 31, is connected. The other end of the circuit interrupter 31 is mounted on a metallic mechanism housing 32 which has a bearing and contact extension 33 projecting from and journaled on the upper end of the first rotatable insulator stack 13. A suitable linkage within a housing 34 mechanically interconnects the first rotatable insulator stack 13 and the mechanism within the metallic housing 32 for operating the circuit interrupter 31. Mounted on the upper end of the first rotatable insulator stack 13, movable therewith and straddling the bearing and contact extension 33, is a bifurcated mounting bracket 35. The mounting bracket 35 includes a bottom clamp fitting 36 having thereabove a cooperating top clamp fitting 37 connected thereto by bolts 38. The clamp fittings 36 and 37 have clamping engagement with a switch blade 39 the distal end 40 of which is arranged to have contact engagement with the distal end 41 of a switch blade 42 which is mounted on and is movable with the second rotatable insulator stack 14. The mounting of the switch blade 42 on the second rotatable insulator stack 14 is similar to the mounting of the switch blade 39 on the first rotatable insulator stack 13. The mounting arrangement for the switch blade 42 includes a bifurcated mounting bracket 43 that is secured to and rotates with the second rotatable insulator stack 14. The mounting bracket 43 includes a bottom clamp fitting 44 and a cooperating top clamp fitting 45 interconnected by bolts 46 for holding the clamp fittings 44 and 45 in clamping engagement with the switch blade 42. A line terminal 47 extends laterally from between the arms of the bifurcated mounting bracket 43 and is suitably journaled therebetween.

In FIG. 1 the switch blades 39 and 42 are shown by broken lines in the switch open position. On rotation of the crank shaft 23 in the manner previously described the switch blades 39 and 42 are swung from the closed position, shown by full lines, to the open position. On reverse rotation of the crank shaft 23 the switch blades 39 and 42 are rotated in the directions indicated by arrows 49 and 50, respectively, to swing the distal ends 40 and 41 into contact engagement with each other to complete a circuit between the line terminals 30 and 47 through the circuit interrupter 31 which, after having opened the circuit during the initial rotation of the crank shaft 23 in a switch opening direction, is reclosed while the switch blades 39 and 42 are being swung to their full open positions as shown by broken lines in FIG. 1.

It is during the final closing movement of the switch blades 39 and 42, while their distal ends 40 and 41 are approaching each other, that, unless prevented, an arc is formed between these distal ends which is accompanied by substantial current flow since the resistance otherwise between the line terminals 30 and 47 is relatively low. This current flow, particularly in the case of closing in on a high capacitance load, may be substantial and may be accompanied by objectionable noise.

In accordance with the invention of the above application provision is made for momentarily increasing the resistance between the line terminals 30 and 47 during the circuit closing operation of the switch 10. FOr this purpose, as shown more clearly in FIG. 2, resistor assemblies 53 and 54 are employed. They extend upwardly from the top clamp fittings 37 and 45 and thereby are offset inwardly from the pivot axes 25 and 26 in the direction of the other axis. At their upper ends the resistor assemblies 53 and 54 carry tubular aluminum conductor arms 55 and 56 which are secured to the upper ends of the resistor assemblies 53 and 54 by clamp members 57 and 58. The distal ends 59 and 60 of the conductor arms 55 and 56 are offset so that they overlap with substantial mechanical clearance such that there is little likelihood of their being encased jointly in ice or sleet or, if they are so encased, the ice can be readily ruptured for circuit opening purposes. Corona balls 61 and 62 are carried by the distal ends 59 and 60 at their extremities.

As shown more clearly in FIG. 1 the arms 55 and 56 extend angularly from the vertical plane of the respective switch blade 39 and 42 on the side thereof facing the direction of closing movement. The reason for this arrangement is to provide a shorter spark gap between the corona balls 61 and 62 on the conductor arms 55 and 56 than is present between the distal ends 40 and 41 of the switch blades 39 and 42 as they are pivoted toward the switch closed position. As a result arcing takes place initially between the corona balls 61 and 62 on the distal ends 59 and 60 of the conductor arms 55 and 56 and current flow takes place through the resistor assemblies 53 and 54 until they are short circuited on engagement of the distal ends 40 and 41 of the switch blades 39 and 42 as they are pivoted into the switch closed position.

In accordance with this invention the corona balls 61 and 62 are formed of purified graphite. Preferably purified graphite is employed since it is about 0.82 times as dense as aluminum and does not melt when it is subjected to an electric arc. Tests have shown that alternating current arcs with a crest current in excess of 10,000 amperes do not pit or mar its surface. Also load current arcs of about 350 amperes flowing for 15 cycles of 60 Hz do not harm the surfaces of the corona balls 61 and 62 when they are formed of graphite. Each of the corona balls 61 and 62 is formed with a reduced diameter end portion 63, FIG. 3, that is telescoped within the tubular distal end 60 of the respective conductor arm 56. Pins 64 in drilled holes in the distal end 60 and the reduced diameter end portion 63 hold the corona ball 62 firmly in place.

Each of the corona balls 61 and 62 also has a hemispherical distal end portion 65 the radius of which may be 11/2 inches. It merges into an intermediate cylindrical section 66 which terminates in a rounded section 67 having a radius of about five-sixteenths inch. The rounded section 67 reduces the likelihood that the arc struck from the hemispherical distal end 65 or the intermediate cylindrical section 66 will transfer to the distal end 60 of the conductor arm 56.

In operation, as the first and second insulator stacks 13 and 14 are pivoted about their vertical axes 25 and 26 from the switch open position toward the switch closed position, the corona balls 61 and 62 on the conductor arms 55 and 56 approach within sparking distance of each other and current begins to flow as soon as an arc is drawn but it is limited because of the series connection with the resistor assemblies 53 and 54. As the insulator stacks 13 and 14 continue to be pivoted toward the switch closed positions, current continues to flow but, as indicated, it is limited with the result that a minimum of disturbance in the system results accompanied by a minimum of attendant noise. Because of the circuit that is established through the resistor assemblies 53 and 54 a minimum of arcing takes place between the distal ends 40 and 41 of the switch blades 39 and 42. As a result there is a minimum of erosion thereof. Since the switch blades 39 and 42 and the conductor arms 55 and 56 are pivoted at high speed toward the switch closed position, current flow takes place through the resistor assemblies 53 and 54 for only a correspondingly limited time which is determined by the time that elapses beginning with the initial sparking between the corona balls 61 and 62 on the conductor arms 55 and 56 until they are short circuited by contact engagement between the distal ends 40 and 41 of the switch blades 39 and 42. Since the corona balls 61 and 62 are formed of graphite, their surfaces remain unimpaired after repeated circuit closures and the sparking distance therebetween remains unchanged.

Claims

What is claimed as new is:

1. A resistor inserting switch construction having a pair of parallel spaced apart insulators pivotally mounted at one end about the respective longitudinal axis, each having a switch blade at its other end movable therewith for contact engagement at its distal end with the other switch blade on conjoint pivotal movement of said insulators, said switch construction being characterized by a first conductor arm mounted on, electrically connected to one of said switch blades, extending therealong and movable unitarily therewith, a resistor assembly mounted on and electrically connected at one end to the other of said switch blades and movable unitarily therewith, a second conductor arm mounted on, movable with, and electrically connected at one end to the other end of said resistor assembly and extending toward said first conductor arm to complete a conductive path by arcing in the atmosphere between the distal ends of said arms through said resistor assembly in advance of completion of a conductive path through said switch blades as they are swung toward contact engagement at their distal ends, said distal ends of said arms terminating in corona balls formed of purified graphite substantially unaffected by the arc formed therebetween on operation of said switch blades toward switch closed position.

2. The resistor inserting switch construction according to claim 1 wherein each of said corona balls has a hemispherical distal end, an intermediate cylindrical section, and a support section telescoped with the respective conductor arm.

3. The resistor inserting switch construction according to claim 2 wherein said intermediate section terminates in a rounded section whereby transfer of said arc to the respective conductor arm is minimized.

4. The resistor inserting switch construction according to claim 3 wherein said hemispherical end has a radius of about 11/2 inches and said rounded section has a radius of about five-sixteenth inch.

5. The resistor switch construction according to claim 2 wherein pins extend radially through said distal ends of said arms into drilled holes in the support section of the respective corona ball to hold the same in place.