GAS-BLAST LOAD-BREAK SWITCH

Abstract: In a gas-blast load-break switch, a nozzle (21) is configurated so as to have a cylindrical trunk part (21a) and a bottom part(21b); the cylindrical trunk part (21a) has enough large inner diameter to withstand a recovery voltage generated between the fixed arc contact (16) and the movable arc contact (15) in breaking current, and thereby an inner surface of the nozzle (21) is isolated from the arc space, so that undesirable creating discharge on the nozzle (21), flashover through the nozzle (21) or the reignition outside the nozzle (21) is prevented.

Description: The present invention relates to a gas-blast load-break switch wherein an insulation gas extinguishes an arc thereby to break a current as a load disconnecting switch or a gas-blast circuit breaker. FIG. 5 is a cross-sectional view showing a conventional puffer type gas-blast load-break switch disclosed in the Japanese published patent application Sho 53-133771, from which the present invention starts. FIGs. 6 and 7 are an enlarged partial cross-sectional views of FIG. 5 at the time of current-breaking. In FIG. 5, a fixed side shield 3 which is held by a first insulation spacer 2 is provided at an inner upper side of a cylindrical gas-tight earthed tank 1. A second insulation spacer 4 which is provided on the middle part of the earthed tank 1 is connected to a movable side shield 6 via a connector 5. The movable side shield 6 is fixed to a supporter 8, which is held by an insulation cylinder 7. A piston 9 which is one member of an insulation gas supply unit is fixed on the supporter 8. A cylinder 10 is provided around the piston 9 in a manner slidable thereon in up-down direction of the figure, and a puffer chamber 11 is formed by a space sectioned by the cylinder 10 and the piston 9. A fixed finger 12 whose lower end is fixed to the piston 9 is provided around the cylinder 10, and the cylinder 10 is slidable in the up-down direction against the fixed finger 12. A cylindrical piston rod 13 having a through-passage therein is inserted slidably into the center of the piston 9 and is upwardly projected out of the cylinder 10. The insulation gas supply unit comprises the piston 9, the cylinder 10, the fixed finger 12 and the piston rod 13. The piston rod 13 has a movable arc contact 15 on an upper end thereof for connecting to a fixed arc contact 16 fixed by its upper end to the fixed side shield 3. The movable arc contact 15 is disposed on the same axis as the fixed arc contact 16. A nozzle 17 which is made of an insulating material is screwed into a shield 14, which is fixed on the cylinder 10, in a manner to surround a lower end of the fixed arc contact 16 and the movable arc contact 15 with a given gap inbetween. An inner surface of this nozzle 17 is formed so that arc-extinguishing insulation gas 19 is conducted to arcs 18 which are formed between the fixed arc contact 16 and the movable arc contact 15 at the time of current-breaking. Next, operation of the above-mentioned puffer type gas-blast load-break switch is described. When this gas-blast load-break switch is to break a load current, for instance the load current of a reactor (not shown) from a closed state where an inner surface of the movable arc contact 15 is engaging with an outer surface of the fixed arc contact 16, an insulating rod 20 is lowered therefor. Accompanying with the lowering of the insulating rod 20, the movable arc contact 15, the nozzle 17 and the cylinder 10 are lowered, respectively. Thereby, the movable arc contact 15 is disconnected from the fixed arc contact 16, and the arcs 18 are formed between the movable arc contact 15 and the fixed arc contact 16. At that time, the insulation gas 19 compressed by the piston 9 is conducted to an inner space of the nozzle 17. Thereafter, the insulation gas 19 branches out into two passages, upwards toward the fixed arc contact 16 and downwards into the central hole of the piston rod 13 as shown in FIG. 6. Thereby, the arcs 18 are extinguished by mainly cooling effect of the insulation gas 19 blasted thereto. In breaking the current for a reactor, at the moment of breaking, a recovery voltage, which has one hundred and dozens micro seconds duration of wave front and has about "2E" (E is the normal negative peak value of voltage to ground) peak voltage, is impressed across the movable arc contact 15 and the fixed arc contact 16. Therefore, though the insulation gas supply unit blasts the insulation gas 19, reignitions are repeated between the movable arc contact 15 and the fixed arc contact 16. When insulation between the movable arc contact 15 and the fixed arc contact 16 comes to be able to withstand the recovery voltage corresponding to the aforementioned "2E", interruption of current is completed. FIG. 8 is a graph showing a relation between an inter-pole distance and a flashover voltage of the conventional gas-blast load-break switch, wherein a curve I which shows the relation between the movable arc contact 15 (FIG. 6) and the fixed arc contact 16 (FIG. 6) is represented at some inter-pole distances by plotting averages of scatterings "A" of the reignition voltages at the time of current-breaking. Another curve II shows a relation of the flashover voltage, which makes flashover hence to form an arc 30 between the fixed side shield 3 outside the nozzle 17 and the shield 14 as shown in FIG. 5, versus the inter-pole distance thereof. Since there are no gas-flows of the insulation gas 19 outside the nozzle 17, once the flashover occurs, the arc 30 cannot be extinguished by this gas-blast load-break switch. Therefore, to avoid such state, the puffer type gas-blast load-break switch is designed so that the curve II has higher flashover voltages than the highest scatterings of curve I, which shows the relation between the inter-pole distance and the flashover voltage inside the nozzle 17, at the same inter-pole distances. However, in the above-mentioned conventional puffer type gas-blast load-break switch, when the reignition occurs as shown in FIG. 7, such disposition that an inner surface of the nozzle 17 comes close to an arc space between the fixed arc contact 16 and the movable arc contact 15 brings an undesirable creeping discharge (flashover) 31 along the inner surface of the nozzle 17, and a tracking which brings deterioration of insulation is made thereon. Once the tracking is made on the nozzle 17, the scatterings "A" of the flashover voltage in the curve I of FIG. 8 become large, and thereby the flashover voltages represented by the curve II come within the region of the scatterings "A" of the curve I. Then the flashover (making the arc 30 of FIG. 5) occurs with a certain probability, and thereby inducing such a state that the current cannot be interrupted. Furthermore, as shown in FIG. 7, since the nozzle 17 is exposed in a high potential field, a flashover (making an arc 32) through the nozzle 17 occurs between the fixed arc contact 16 and the shield 14. Thereby, the arc 18 flows to the shield 14 which is disposed apart from gas-flows of the insulation gas 19, thereby inducing such a state that the current cannot be interrupted. The object of the present invention is to offer an improved gas-blast load-break switch which is capable of preventing the creeping discharge on the nozzle, flashover through the nozzle and the reignition outside the nozzle thereby achieving an excellent breaking ability. The invention is given in the claim. The invention will now be described in more detail by the following description to be taken in conjunction with the accompanying drawing, in which: FIG. 1 is a cross-sectional view showing an embodiment of a puffer type gas-blast load-break switch in accordance with the present invention; FIG. 2 is an enlarged partial cross-sectional view of FIG. 1 at the time of current-breaking; FIG. 3 is an enlarged partial cross-sectional view of FIG. 1 after breaking current; FIG. 4 is a graph showing relations between inter-pole distance and flashover voltage of the embodiment shown in FIG. 1; FIG. 5 is the cross-sectional view showing the conventional puffer type gas-blast load-break switch; FIG. 6 is the enlarged partial cross-sectional view of FIG. 5 at the time of current-breaking; FIG. 7 is the partial enlarged cross-sectional view of FIG. 5 showing undesirable state of current-breaking; and FIG. 8 is the graph showing relations between inter-pole distance and flashover voltage of the conventional puffer type gas-blast load-break switch shown in FIG. 5. FIG. 1 is a cross-sectional view showing an embodiment of a puffer type gas-blast load-break switch according to the invention. FIGs. 2 and 3 are enlarged partial cross-sectional views of FIG. 1 at the time of current-breaking and after breaking current, respectively. In FIG. 1, a fixed side shield 3 which is held by a first insulation spacer 2 is provided at an inner upper side of a cylindrical gas-tight earthed tank 1. A second insulation spacer 4 which is provided on the middle part of the earthed tank 1 is connected to a movable side shield 6 via a connector 5. The movable side shield 6 is fixed to a supporter 8, which is held by an insulation cylinder 7. A piston 9 which is one member of an insulation gas supply unit is fixed on the supporter 8. A cylinder 10 is provided around the piston 9 in a manner slidable thereon in up-down direction of the figure, and a puffer chamber 11 is formed by a space sectioned by the cylinder 10 and the piston 9. A fixed finger 12 whose lower end is fixed to the piston 9 is provided around the cylinder 10, and the cylinder 10 is slidable in the up-down direction against the fixed finger 12. A cylindrical piston rod 13 having a through-passage therein is inserted slidably into the center of the piston 9 and is upwardly projected out of the cylinder 10. The insulation gas supply unit comprises the piston 9, the cylinder 10, the fixed finger 12 and the piston rod 13. The piston rod 13 has a movable arc contact 15 on an upper end thereof for connecting to a fixed arc contact 16 fixed by its upper end to the fixed side shield 3. The movable arc contact 15 is disposed on the same axis as the fixed arc contact 16. A nozzle 21 which is made of an insulating material is screwed into a shield 14, which is fixed on the cylinder 10, in a manner to surround a lower end of the fixed arc contact 16 and the movable arc contact 15 with a given gap inbetween. An inner surface of this nozzle 21 is formed so that arc-extinguishing insulation gas 19 is conducted to arcs 18 which are formed between the fixed arc contact 16 and the movable arc contact 15 at the time of current-breaking. Next, operation of the above-mentioned puffer type gas-blast load-break switch embodying the present invention is described. When this gas-blast load-break switch is to break a load current, for instance the load current of a reactor (not shown) from such a closed state that an inner surface of the movable arc contact 15 is engaging with an outer surface of the fixed arc contact 16, an insulating rod 20 is lowered therefor. Accompanying with the lowering of the insulating rod 20, the movable arc contact 15, the nozzle 21 and the cylinder 10 are lowered, respectively. Thereby, the movable arc contact 15 is disconnected from the fixed arc contact 16, and the arcs 18 are formed between the movable arc contact 15 and the fixed arc contact 16. At that time, the insulation gas 19 compressed by the piston 9 is conducted to an inner space of the nozzle 21. Thereafter, the insulation gas 19 branches out into two passages, upwards toward the fixed arc contact 16 and downwards into the central hole of the piston rod 13 as shown in FIG. 2. Thereby, the arcs 18 are extinguished by mainly cooling effect of the insulation gas 19 blasted thereto. In breaking the current for the reactor, at the moment of breaking, a recovery voltage, which has one hundred and dozens micro seconds duration of wave front and has about "2E" (E is the normal negative peak value of voltage to ground) peak voltage, is impressed across the movable arc contact 15 and the fixed arc contact 16. Therefore, though the insulation gas supply unit blasts the insulation gas 19, reignitions are repeated between the movable arc contact 15 and the fixed arc contact 16. When insulation between the movable arc contact 15 and the fixed arc contact 16 comes to be able to withstand the recovery voltage corresponded to the aforementioned "2E", interruption of current is completed. Hereupon, as shown in FIG. 2, the nozzle 21 has a cylindrical trunk part 21a and a bottom part 21b having a hole 21c thereon. An inner diameter of the cylindrical trunk part 21a is formed large up to a predetermined position so that the inner surface of the nozzle 21 can withstand an electric field of recovery voltage at the time of current-breaking between the fixed arc contact 16 and the movable arc contact 15, and an inner diameter of the hole 21c in the bottom part 21b is formed smaller than that of the cylindrical trunk part 21a in order to surround the fixed arc contact 16. Thereby, the inner surface of the nozzle 21 is sufficiently isolated from an arc space between the fixed arc contact 16 and the movable arc contact 15. In the above-mentioned puffer type gas-blast load-break switch, as shown in FIG. 2, since the inner surface of the nozzle 21 is isolated from the above-mentioned arc space at the time of current-breaking for the reactor, the arcs 18 are formed only between the fixed arc contact 16 and the movable arc contact 15. After that, as shown in FIG. 3, an inter-pole distance "a" withstands the recovery voltage, and thereby interruption of current is completed. FIG.4 is a graph showing a relation between inter-pole distance and flashover voltage of the embodiment, wherein a curve I which shows the relation between the movable arc contact 15 (FIG. 2) and the fixed arc contact 16 (FIG. 2) is represented at some inter-pole distances by plotting averages of scatterings "B" of the reignition voltages at the time of current-breaking. Another curve II shows a relation of the flashover voltage, which makes flashover hence to form an arc 30 between the fixed side shield 3 outside the nozzle 17 and the shield 14 as shown in FIG. 1, versus the inter-pole distance thereof. In comparison with FIG. 8 which shows the conventional relation between the inter-pole distance and the flashover voltage, FIG. 4 of the present invention clarifies that the scatterings "B" of the reignition voltages are smaller than the scatterings "A" of FIG. 8. Therefore, the maximum reignition voltage included in the maximum value of the scatterings "B" does not come above the curve II. That is, the reignitions occur only between the fixed arc contact 16 (FIG. 2) and the movable arc contact 15 (FIG. 2). In other words, no reignition occurs outside the nozzle 21 (FIG. 1) between the fixed side shield 3 (FIG. 1) and the shield 14 (FIG. 1).

Claims: A gas-blast load-break switch comprising: a gas-tight tank (1); a fixed arc contact (16) fixed in said tank (1); a movable arc contact (15) which is held in said tank (1) to be movable in the same axis as an axis of said fixed arc contact (16), for selectively connecting with and disconnecting from said fixed arc contact (16); insulation gas supply means (9, 10, 12, 13) which is held in said tank (1) for blasting an insulation gas (19) to an arc 18) which is formed by disconnecting said fixed arc contact (16) from said movable arc contact (15); and a nozzle (21) which is made of an insulating material and is held in said tank (1) for conducting said insulation gas (19), characterized in that said nozzle (21) is formed by a cylindrical trunk part (21a) with an inner cylindrical surface having: an inner diameter of a predetermined size sufficient to withstand a recovery voltage generated between said fixed arc contact (16) and said movable arc contact (15) during the breaking of a current therebetween and a bottom part (21b) having a hole (21c) of a diameter smaller than said inner diameter and larger than said fixed arc contact (16) in a direction transverse to said axis for surrounding a contact portion of said fixed arc contact (16), said inner cylindrical surface has a predetermined length in the direction of said axis such that the contacting part of said fixed arc contact (16) remains within the cylindrical trunk part (21a) of nozzle (21) at the point where that inter-pole distance (a) between the fixed (16) and movable (15) arc contacts is reached, at which this inter-pole distance (a) of the arc contacts (15, 16) withstands the recovery voltage and thereby interruption of current is completed.

Inventors: SASAMORI, KENZI-ITAMI SEISAKUSHO MITSUBISHI DENKI
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1988
Main classification: H01H33
IPC codes: H01H33