Gas Actuated High Voltage Bushing

Gas actuated high voltage bushings have a bore contact mounted for reciprocal movement within a bushing housing. The bore contact moves in response to the expansion of gases generated from the heat of the prestrike arc on close-in of a rod contact with the bore contact. Movement of the bore contact, therefore, depends upon the generation of sufficient gas to fill the bushing at a pressure high enough to move the bore contact into contact with the rod contact. This requires a large volume of gas since the entire bushing interior must be filled.

The gas actuated high voltage bushing of the present invention provides an independent source of gas pressure which is confined within a small space at the end of the bore contact to assure a rapid response to a fault current condition. The bushing includes a snuffer-contact assembly mounted for reciprocal movement within a conductive cylinder located within the bushing housing. A piston head is provided at one end of the assembly which is spaced a short distance from the end of the conductive cylinder. The piston head is connected to the end of the cylinder by a fusible section or rod which will withstand normal load currents but will fuse under fault current conditions. An arcing ring is provided in the snuffer-contact assembly which is connected directly to the fusible section so that the current produced by a prestrike arc will always flow through the fusible section. Whenever the fusible section fuses as a result of a prestrike arc, a rapid gas build up will occur in the small space at the end of the cylinder which will act against the piston head to move the snuffer-contact assembly toward the terminator.

FIG. 1 is a section view of the bushing and terminator according to the invention with the snuffer-contact assembly in the normal position on close-in;

FIG. 2 is a view similar to FIG. 1 showing the snuffer-contact assembly in the fault close position.

The high voltage bushing 10 according to the present invention is used in combination with a terminator 12 to electrically connect a high voltage cable with an electrical device. The terminator 12 includes a probe or rod contact 14 positioned in a tapered recess 16 and an arc follower 15 mounted on the end of the probe 14. Electrical connection is made by inserting the probe 14 and arc follower 15 into an arc snuffer bore contact assembly 18 provided within the bushing 10.

More particularly, the bushing 10 includes a housing 20 which is tapered at 21 to matingly engage the inside surface of the tapered recess 16 in the cable terminator 12. An axially extending bore 22 is provided in one end of the housing 20 and an enlarged bore 24 is provided at the other end. A conductive cylinder assembly 26 is mounted within the housing 20 and is adapted to be connected to an electrical device by a conductive stud 28.

The snuffer-contact assembly 18 is mounted for reciprocal movement within the cylinder assembly 26 from a first or normal position to a second or fault close position. Means are provided for moving the snuffer-contact assembly 18 from the first position to the fault close position. Such means is in the form of a fusible member 32 which increases the pressure of the gas within the cylinder assembly 26 on fusing and forces the assembly 18 toward the fault close position.

The conductive cylinder assembly 26 includes an electrically conductive tubular member 36 having an enlarged cylindrical section 38 positioned in the bore 24 and a small cylindrical section 40 positioned in bore 22. The section 38 is closed at the open end by means of a conductive cap 34. The stud 28 is connected to the opposite side of the cap 34.

The snuffer-contact assembly 18 includes a non-conductive tubular member 44 formed from a glass reinforced plastic and having an arc snuffer or sleeve 46 at one end, a bore contact 30 mounted in the other end and an arcing ring 55 between the snuffer 46 and contact 30. The bore contact 30 includes a piston head 48 having a diameter equal to the inside diameter of the cylindrical section 38 of the member 36. Means are provided for electrically connecting the bore contact 30 to the cylinder 36. Such means is in the form of a louvered band or current interchange member 50 positioned in an annular groove 52 provided in the piston head 48.

The arcing ring 55 is formed of a conductive material such as copper tungsten. The ring 55 is located in front of the bore contact to receive the prestrike arc on close-in of the probe with the bore contact. The open end of the bore contact 30 is closed by means of an insulating disc 54 which is secured to the end of the piston head 48. A recess 56 is provided in the face of the disc 54. The disc 54 has an outer diameter substantially equal to the inner diameter of the cylindrical section 38 to form the face for the piston head 48, the disc 54 being spaced a short distance from the cap 34 when the snuffer-contact assembly 18 is in the first or normal position in the bushing.

Means are provided in the space between the disc 54 and the end cap 34 for generating gas under fault current conditions. Such means is in the form of the fusible member 32 which includes a small hole 33 intermediate the ends to reduce the cross sectional area of the member. The fusible member 32 is connected to the conductive cap 34 by any means such as a threaded section 35 provided on the member 32 which is threaded into a threaded bore 42 in the conductive cap 34. The other end of the fusible member 32 is connected to a conductive disc 58 provided in the recess 56 in the insulating disc 54. The conductive disc 58 is electrically connected to the arcing ring 55 by means of insulated wires 60.

It should be noted that on close-in of the probe 14 with the bore contact 30 the prestrike arc will occur between the probe 14 and the arcing ring 55. The current flow resulting from the establishment of the prestrike arc will always be conducted through the fusible section 32. If this current flow is of sufficient magnitude to fuse the reduced cross sectional area of the fusible section 32, the gases generated in the space between the disc 54 and the cap 34 will expand forcing the snuffer-contact assembly 18 to move rapidly toward the probe 14 to connect the bore contact with the probe 14 and extinguish the arc.