A block of bushings of a three-phase rotary switch-disconnector

Abstract

 The invention disclosed is a block of bushings of a three-phase rotary switch-disconnector with a double isolating clearance between the electric contacts, intended for multiple switching of currents in electric circuits that are in a working status, and also for emergency switching-on of electric circuits that are in a fault condition. The block of bushings of a three-phase rotary switch-disconnector is a resin casting in the form of a rotary shaft (2) with three bushings (3a, 3b) fitted with circumferential petticoats (7a, 7b). The bushings (3a, 3b) are arranged along the axis of the rotary shaft and perpendicularly to the axis of the shaft, and the shaft axis divides the body of each of the bushings into two symmetrical parts in which a common conducting rod (4) is located, whose ends protrude outside the bushing body and make a movable element of the current path of the switch-disconnector. The bodies of the bushings (3a, 3b) in a cross-section have the contour in the shape of an ellipse or an ellipse with the vertexes truncated on both sides.

Description

[0001] The present invention relates to a block of bushings of a three-phase rotary switch-disconnector with a double isolating clearance between the electric contacts, intended for multiple switching of currents in electric circuits that are in a working status, and also for emergency connection of electric circuits that are in a fault condition.

[0002] A rotary section switch-disconnector is known from the description of the Italian utility model nr ITMI20000019 and from the catalogue of Italian company IMEQUADRI DUESTELLE SPA which manufactures it. The switch-disconnector is designed for disconnecting electric contacts. The switch-disconnector contains a frame in which a uniform body is rotationally fixed, the body containing a rotary shaft and three bushings spaced evenly and perpendicularly to the axis of rotation of the shaft, each being intended for a single supply phase. At the same time, the axis of rotation of the shaft divides individual bushings into two symmetrical parts. At the ends of each of these parts there are movable electric contacts whose active parts are oriented according to the sense of rotation of the bushings. The switch-disconnector contains two rows of piston insulators fixed to the support frame, which incorporate a cylinder open on one side with a piston sliding inside the cylinder. A piston insulator forms a support for the fixed electric contacts that function together with the movable electric contacts. The contact between the movable and fixed contact members occurs as a result of the revolution of the uniform body around the axis of rotation of the shaft, when the switch-disconnector is being closed. The pistons are coupled with the bushings in pairs, so that during the revolution of the body, during switching-on of the contact, the movement of the piston inside the cylinder causes suction of air into the cylinder. Then, while the contact is being opened, the movement of the pistons causes compression of air and its blow-out in the zone where the electric arc is burning. The piston of each piston insulator is permanently connected with the piston rod which in turn is connected by an articulated joint with the bushing using at least one coupling element installed on the revolving body of the bushings. Each bushing is fitted with circumferential ribs.

[0003] A rotary switch-disconnector type AM made by ABB incorporates a rotary block of bushings made as a resin casting. The block comprises cylindrical bodies of three bushings and a rotary shaft on which the bodies of the bushings are arranged. A conducting rod is immersed in each of the bushing bodies. The conducting rods are arranged along the shaft axis and perpendicularly to the shaft axis in the plane of rotation of the bushings and they are the cores of the bushings. The shaft axis divides each of the conducting rods into two symmetrical halves, and both ends of theses rods protrude outside the bodies of the bushings and are a movable element of the current path of the switch-disconnector. The rotary shaft is fitted with stiffening strips in the shape of the letter "T" which are situated along the shaft axis on the opposite sides of the shaft and are made as an integral part of the resin cast of the block. The bushings are fitted with transverse circumferential petticoats which are arranged on the outer surface of the bushings above the stiffening strips. The ends of the rotary shaft are fitted with three metal inserts with female threads, which are arranged radially in relation to the axis of rotation of the shaft in a plane perpendicular to the axis of rotation. Bearing journals that enable the rotation of the block of bushings are fixed in the inserts.
In the presented solutions the quantity of resin used to make the block of bushings is relatively large, which results in high rigidity of the block and its mechanical strength, but also requires the use of an increased-energy drive to activate the switch-disconnector. Therefore there is a demand for a new construction of the block which would keep the mechanical properties of the existing solutions while at the same time reducing the mass of the whole block, which will allow the use of a drive of a lower energy.

[0004] The block of bushings of a three-phase rotary switch-disconnector according to the invention is made as a resin casting in the form of a rotary shaft with three bushings fitted with circumferential petticoats. The bushings are arranged in series along the axis of the rotary shaft and perpendicularly to the axis of the shaft. The shaft axis divides the body of each of the bushings into two symmetrical parts in which there is located a common conducting rod whose ends protrude outside the bushing body and make a movable element of the current path of the rotary switch-disconnector. The block of bushings of a three-phase rotary switch-disconnector according to the invention is characterized in that the bodies of the bushings in cross-section have the contour in the shape of an ellipse or an ellipse with the vertexes truncated on both sides.

[0005] Preferably, the bushing body incorporates the first element with a fixed cross-section, adjoining the rotary shaft, and the second element of a variable cross-section, adjoining the first element. The longitudinal axes of the first and the second elements are the longitudinal axis of the bushing body and form a single line with the longitudinal axis of the conducting rod.

[0006] Preferably, in cross-section of the bushing body, in the first element with the fixed cross-section, the ratio of the semi-major axis "a" of the ellipse to the semi-minor axis "b" of the ellipse has a fixed set value, and in the second element with the variable cross-section, the ratio of the semi-major axis "a" of the ellipse to the semi-minor axis "b" of the ellipse decreases in relation to the set value for the first element.

[0007] Preferably, the selected value of the ratio of the semi-major axis "a" of the ellipse to the semi-minor axis "b" of the ellipse for the first element of the bushing with the fixed cross-section is within the range of 1.5 to 3.

[0008] Preferably, the set value of the ratio of the semi-major axis "a" of the ellipse to the semi-minor axis "b" of the ellipse for the second element of the bushing with the variable cross-section decreases from the set value for the first element to a value bigger than 1.

[0009] Preferably, on the faces of the bushing body, between the axis of the rotary shaft and the circumferential petticoats, on its first element with the fixed cross-section there are two catches which are situated opposite each other, on the opposite sides of the longitudinal axis of the bushing body.

[0010] Preferably, the catches form an integral part with the bushing body.

[0011] Preferably, the rotary shaft is fitted with coupling elements located at the ends of the shaft in its axis of rotation and having the form of journals anchored in the resin cast of the shaft.

[0012] Preferably, the coupling element has the form of a cylinder with a fixing handle attached to its face, the surface of the handle being the active surface of the coupling element and transmitting the mechanical load to the rotary shaft.

[0013] Preferably, the fixing handle is made in the form of a blade having a shape resembling the letter "C".

[0014] Preferably, the cylinder of the coupling element and its fixing handle are made as a uniform whole.

[0015] The advantage of the block of bushings according to the invention is that it maintains the large mechanical strength while reducing the mass of the whole block. The reduction in the mass of the block offers the possibilities of achieving correspondingly higher rotational speeds during the operation of the rotary switch-disconnector. Owing to the reduction in the mass, also the braking of the block during its operation is easier. Moreover, the smaller number of details necessary for arranging the bearing of the rotary shaft in the support frame makes the installation much easier, and the use of one coupling element which forms the mechanical connection between the drive and the rotary shaft of the block of bushings and which at the same time is an element forming the bearing between the shaft and the frame improves the mechanical strength of the connections. The shape of the fixing handle of the coupling element increases the effective surface that transmits the mechanical load between the coupling element and the rotary shaft.

[0016] The invention is explained in an embodiment in the drawing, where:

fig. 1 shows the rotary block according to the invention in perspective in the first embodiment of the invention,

fig. 2 - a fragment of the bushing from fig. 1 showing the cross-section of the bushing, without showing its connection with the block of bushings,

fig. 3 - the rotary block according to the invention in perspective in the second embodiment of the invention,

fig. 4 - a fragment of the bushing from fig. 3 showing the cross-section of the bushing, without showing its connection with the block of bushings,

fig. 5 - a fragment of the end part of the block in the longitudinal section,

fig. 6 - the coupling element in perspective.

[0017] The bushing block 1 according to the invention is made as a resin casting which incorporates a uniform rotary shaft 2 whose axis is the axis of rotation of the block, and incorporates three bushings 3a or 3b which are arranged in series along the shaft axis and perpendicularly to the shaft axis, and their longitudinal axes lie on one plane. The shaft axis divides the body of each bushing into two symmetrical parts in which there is located a common conducting rod 4. The conducting rod 4 makes the core of the bushing 3a or 3b. The ends of the rod 4 protrude outside the body of the insulator 3a or 3b and they form a movable element of the current path of the switch-disconnector. The bodies of the bushings 3a or 3b are formed of two parts situated symmetrically in relation to the axis of rotation of the shaft 2, each of these parts comprising the first element with the fixed cross-section 5a or 5b with the contour in the shape of an ellipse, adjoining the surface of the rotary shaft 2, and the second element 6a or 6b with the contour in the shape of an ellipse with a variable cross-section decreasing towards the end of the bushing, whereas the elements 6a, 6b adjoin the first elements 5a, 5b respectively. In the first embodiment of the invention the contours of the cross-section of the first element 5a and the second element 6a have the shape of a full ellipse. In the cross-section of the body of the bushing 3a in the first element 5a with a fixed cross-section the ratio of the semi-major axis "a" of the ellipse to the semi-minor axis "b" of the ellipse has a fixed set value, preferably in the range of 1.5 to 3. In the second element 6a with a variable cross-section, the value of the ratio of the semi-major axis "a" of the ellipse to the semi-minor axis "b" of the ellipse decreases in relation to the set value for the first element 5a, preferably from the value set for the first element 5a to a value bigger than 1.

[0018] In the second embodiment of the invention the cross-section area of the first element 5b and of the second element 6b is modified by truncating a fragment of this area near the vertexes of the ellipse with two lines "I" perpendicular to the semi-major axis of the ellipse "2a". In fig. 4 the section between the truncated vertexes of the ellipse has been marked "2a1", the value "a1" being less than the value "a", preferably by 3 to 10% of the value of "a". In the cross-section of the body of the bushing 3b in the first element 5b with a fixed cross-section, the ratio of the semi-major axis "a" of the ellipse to the semi-minor axis "b" of the ellipse has a fixed set value, preferably in the range of 1.5 to 3. In the second element 6b with a variable cross-section, the value of the ratio of the semi-major axis "a" of the ellipse to the semi-minor axis "b" of the ellipse decreases in relation to the set value for the first element 5b, preferably from the value set for the first element 5b to a value bigger than 1. On the elements 6a, 6b of the bushing 3a, 3b there are built resin circumferential petticoats 7a, 7b situated parallel to each other. On the faces of the bodies of the bushings, on the elements 5a, 5b with a fixed cross-section, there are built two resin catches 8 which are situated between the axis of the shaft 2 and the petticoats 7a, 7b opposite each other at a distance of 2b, on the opposite sides of the longitudinal axis of the body of the bushing 3a, 3b. The switch-disconnector piston pull-rods, not shown in the drawing, are rotationally fixed to those catches. The catches 8 make an integral part of the body of the bushings 3a, 3b. The rotating shaft 2 is fitted with stiffening strips 9a, 9b and 9c, made of resin in the block casting process, which are arranged symmetrically on both sides of the shaft and form an integral part of the block. The stiffening strips 9a and 9c are situated between the ends of the shaft 2 and the bushings located in extreme positions along the shaft axis. The stiffening strips 9b are situated on both sides of the bushing located in the center position and they are arranged along the shaft, on its both sides to the bushings situated in the extreme positions. The endings of the strips 9a and 9c on the shaft-end side are made as stiffening brackets 10 situated perpendicularly to the shaft 2 axis and they connect the edge of the strips 9a and 9c with a part of the side surface of the shaft 2. The stiffening strips 9a, 9b and 9c are connected with the bodies of the bushings 3a or 3b by intermediate elements shaped in the form of fastening flanges 11 which on one side adjoin the side surfaces of the bushings 3a, 3b and on the other, the surface of the shaft 2. The intermediate elements are made of resin and they make an integral part of the, block of bushings. At the ends of the rotary shaft 2 there are fixed coupling elements 12 used for fastening and rotating the block of bushings 1 in the support frame of the switch-disconnector, not shown in the drawing, and for transmitting the torque from the drive, not shown in the drawing, to the rotary shaft 2. The coupling elements 12 in the form of a cylinder 13 perform the function of the journal of a slide bearing whose bearing bush is the opening in the support frame of the switch-disconnector, not shown in the drawing. The coupling elements 12 have the shape of a cylinder 13 and they are fitted with fixing handles 14 which are attached to the base of the cylinder 13 and to the fragments of their side surfaces. The fixing handles, are made preferably in the form of a blade having a shape resembling the letter "C". The surfaces of the fixing handles 14 form the active surfaces of the coupling elements 12, through which load from the coupling element 12 is transmitted from to the rotary shaft 2 of the block of bushings 1. The cylinder 13 is made as a uniform whole.

[0019] List of markings In the drawing:

1 - a block of bushings

2 - a rotary shaft

3a, 3b - a bushing

4 - a connecting rod

5a, 5b, - a first element of a bushing with a fixed cross-section

6a, 6b, - a second element of a bushing with a variable cross-section

7a, 7b - circumferential petticoats

8 - catches

9a, 9b, 9c - stiffening strips

10 - a stiffening bracket

11 - a fastening flange

12 - a coupling element

13 - a cylinder

14 - a fixing handle.

Claims

1. A block of bushings (1) of a three-phase rotary switch-disconnector made as a resin casting in the form of a rotary shaft (2) with three bushings (3a,3b) fitted with circumferential petticoats (7a, 7b), the bushings (3a, 3b) being arranged in series along the axis of the rotary shaft and perpendicularly to the axis of the shaft, and the axis of the shaft dividing the body of each of the bushings into two symmetrical parts in which there is located a common conducting rod (4) whose ends protrude outside the body of a bushing (3a, 3b) and make a movable element of the current path of the rotary switch-disconnector, characterized in that the bodies of the bushings (3a, 3b) in cross-section have the contour in the shape of an ellipse or an ellipse with the vertexes truncated on both sides.

2. A block of bushings according to claim 1, characterized in that the body of a bushing (3a, 3b) comprises a first element with a fixed cross-section (5a, 5b), adjoining the rotary shaft (2) and a second element (6a, 6b) with a variable cross-section, adjoining the first element (5a, 5b) respectively, and the longitudinal axes of the first and the second elements are the longitudinal axis of the body of the bushing (3a, 3b) which forms a single line with the longitudinal axis of the conducting rod (4).

3. A block of bushings according to claim 2, characterized in that in cross-section of the body of the bushing (3a, 3b), in the first element (5a, 5b) with a fixed cross-section the ratio of the semi-major axis "a" of the ellipse to the semi-minor axis "b" of the ellipse has a fixed set value, and in the second element (6a, 6b) with a variable cross-section, the ratio of the semi-major axis "a" of the ellipse to the semi-minor axis "b" of the ellipse decreases in relation to the set value for the first element (5a, 5b).

4. A block of bushings according to claim 3, characterized in that the set value of the ratio of the semi-major axis "a" of the ellipse to the semi-minor axis "b" of the ellipse for the first element of the bushing with the fixed cross-section is within the range of 1.5 to 3.

5. A block of bushings according to claim 4, characterized in that the set value of the ratio of the semi-major axis "a" of the ellipse to the semi-minor axis "b" of the ellipse for the second element (6a, 6b) of the bushing with the variable cross-section decreases from the set value for the first element (5a, 5b) to a value bigger than 1.

6. A block of bushings according to claim 2, characterized in that on the faces of the body of the bushing (3a, 3b), between the axis of the shaft (2) and the circumferential petticoats (7a, 7b) respectively, on its first element (5a, 5b) with a fixed cross-section there are two catches (8) which are situated opposite each other, on the opposite sides of the longitudinal axis of the body of the bushing (3a, 3b).

7. A block of bushings according to claim 6, characterized in that the catches (8) form an integral part with the body of the bushing (3a,3b).

8. A block of bushings according to claim 1, characterized in that the rotary shaft (2) is fitted with coupling elements (12) located at the ends of the shaft (2) in its axis of rotation, having the form of journals anchored in the resin cast of the shaft (2).

9. A block of bushings according to claim 8, characterized in that the coupling element (12) has the form of a cylinder (13) with a fixing handle (14) attached to its face, the surface of the handle being the active surface of the coupling element and transmitting the mechanical load to the rotary shaft (2).

10. A block of bushings according to claim 8, characterized in that the fixing handle (14) is made in the form of a blade having a shape resembling the letter "C".

11. A block of bushings according to claim 8, characterized in that the cylinder (13) and the coupling element (14) are made as a uniform whole.

Drawing