Closure resistor assembly for high voltage electrical gear

A closure resistor assembly for high voltage electrical gear. The assembly includes a multiplicity of resistive electrical components aligned in a row along an axis, and a mechanism which exerts a compression force on the electrical components along the axis so as to maintain electrical contact between them. The mechanism for exerting the compression force includes a rigid tube within which the electrical components are stacked, and an energy-storing floating structure placed inside the tube at one end of the row of electrical components. The floating structure is constituted by a first piece disposed between the end of the row of electrical components and a second piece that is mounted in a fixed manner inside the tube, together with a spring that is kept in compression between the first and second pieces. The first piece is also mounted so as to be semi-moving between two abutments that are spaced-apart along the axis D.

The present invention relates to a closure resistor assembly for high
 voltage electrical gear, the assembly comprising a multiplicity of
 resistive electrical components aligned in a row along an axis, and a
 mechanism for exerting a compression force on the electrical components
 along the axis so as to maintain electrical contact between them.
 BACKGROUND OF THE INVENTION
 Such an assembly is designed to be fixed at the end of a break chamber in a
 compressed gas circuit-breaker, for example, in order to reduce the
 effects of high currents during closure of the circuit-breaker by
 inserting the resistor in the electrical circuit of the circuit-breaker.
 Until now, the electrical components forming the closure resistor which are
 in the form of resistor disks, have been stacked inside a metal case
 mounted at the end of the break chamber which is vertical and said row of
 electrical components has generally been mounted in such a manner as to
 extend along the axis of the break chamber. At one end of the stack of
 electrical components, there is placed a spring which is put into
 compression by a cover which is fixed on an end opening of the case.
 For a break chamber that is mounted in a horizontal position, such a
 disposition for the closure resistor takes up space and gives rise to a
 bending moment at the end of the break chamber because of the considerable
 length and the mass of the closure resistor, and difficulties are
 encountered with applying compression to the electrical components inside
 the case because of the risk of the compression spring expanding before
 the cover has been finally fixed to the case.
 OBJECTS AND SUMMARY OF THE INVENTION
 An object of the invention is to remedy those various drawbacks.
 To this end, the invention provides a closure resistor assembly for high
 voltage electrical gear, the assembly comprising a multiplicity of
 resistive electrical components aligned in a row along an axis, and a
 mechanism which exerts a compression force on the electrical components
 along the axis so as to maintain electrical contact between them, wherein
 the mechanism for exerting said compression force comprises a rigid tube
 within which the said electrical components are stacked, and an
 energy-storing floating structure placed inside the tube at one end of the
 row of electrical components, said floating structure being constituted by
 a first piece disposed between said end of the row of electrical
 components and a second piece that is mounted in fixed manner inside the
 tube, together with a spring that is kept in compression between the first
 and second pieces, said first piece also being mounted so as to be
 semi-moving between two abutments that are spaced-apart along the axis D.
 With such an arrangement, the electrical components are compressed along
 the axis D merely by exerting an axially-directed force on the other end
 of the row of electrical components against the force exerted by the
 spring on the first piece, so as to make use of the energy of the floating
 structure without any risk of it being ejected. This pressure can be
 exerted by the cover of a case inside which the tube loaded with
 electrical components is placed.
 In addition, in accordance with the invention, the row of electrical
 components is fixed to the end of the break chamber of electrical gear in
 such a manner as to extend perpendicularly to the break chamber so as to
 reduce the lever arm effect.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 In the FIGURE, the closure resistor assembly comprises a multiplicity of
 resistive electrical components 1 of the resistor block type which are
 aligned in a row along an axis D inside a rigid tube 2 of electrically
 insulating material.
 The tube 2 is placed inside a metal case 3 that is generally cylindrical in
 shape, extending longitudinally along the axis D and designed to be
 mounted to the end of the break chamber of a piece of high voltage
 electrical gear such as a compressed gas circuit-breaker. In the FIGURE,
 the tube 2 is placed between the end wall 4 of the case and a cover 5
 which closes the case in a sealed manner by means of a gasket 6.
 The end 7 of the tube 2 rests in a depression formed in a projection 8 on
 the end wall of the case, thereby holding said tube centered inside the
 case.
 A first electrically-conductive metal plate 9 is placed inside the tube
 against the first electrical component 1A of the stack, in electrical
 contact therewith, and a second metal plate 10 is placed inside the tube
 against the last electrical component 1B of the stack, in electrical
 contact therewith. The two plates 9 and 10 preferably constitute inlet and
 outlet terminals for the current flowing through the closure resistor.
 When the cover 5 closes the case 3, an axial compression force is exerted
 on the two plates 9 and 10 and on the electrical components 1 to maintain
 good electrical contact between them.
 This compression force is produced firstly by an energy-storing floating
 structure mounted inside the tube at the end 7 of the tube which rests on
 the end wall of the case. More particularly, this floating structure is
 constituted by the plate 9, by another plate 11 optionally made of metal
 and disposed inside the tube, being axially spaced apart from the plate 9
 inside the tube, and a compression spring 12 that is kept compressed
 between the plates 9 and 11. The plate 9 which is in contact with the
 first electrical component 1A of the stack is also mounted to be
 semi-moving along the axis D inside the tube relative to the plate 11
 which is fixed in the tube.
 As can be seen in the FIGURE, starting from the end 7 of the tube, the
 bottom face of the plate 11 is in abutment on studs 13 which pass through
 orifices provided in the wall of the tube 2 and which extend into the tube
 beneath the bottom edge of the plate 11. It should be observed that the
 top face of the plate 11 has a kind of central depression within which one
 end of the spring 12 is engaged, this depression serving to center the
 spring 12 on the axis D.
 The plate 9 also has a bottom surface opposite from its surface in contact
 with the electrical component 1A, which bottom surface has a central
 depression in which the other end of the spring 12 is engaged. The plate 9
 is mounted to have limited movement (i.e., be semi-moving) along the axis
 D by being secured to studs 14 passing through respective slots 15
 provided in the tube 2, each slot extending longitudinally along the axis
 D to allow the stud 14 to move a certain distance between two ends which
 are spaced apart along the axis D. As can be seen in the FIGURE, the studs
 14 are inserted into the thickness of the plate 9. The spring is kept
 compressed between the plates 9 and 11 whatever the position of the plate
 9 between the two ends of the slots 15.
 The top face of the plate 10 has a projection 16 with a central recess in
 which one end of a stud 17 is engaged. The bottom face of the cover 5 also
 has a projection 18 with a central recess in which the other end of the
 stud 17 is engaged. The length of the stud 17 along the axis D is adjusted
 in such a manner that when the cover 5 is fixed to the case 3, the plate
 10 is pushed a little way along the axis D so as to displace the plate 9
 between the two ends of the slots 15 so as to make use of the energy of
 the spring 12 and put the stack of electrical components under compression
 due to the compression force from the spring 12.
 With this arrangement, the tube 2 is not subjected to bending since
 substantially all of the compression force is localized in the end 7 of
 the tube. The major portion of the tube 2 therefore serves solely to hold
 the electrical components 1 of the stack, and as a result the tube can be
 of relatively lightweight structure and can be low in cost.
 The number of electrical components in the tube can be greater or smaller
 depending on the desired resistance, but the axial compression to which
 the stack of electrical components is subjected can be determined simply
 by adjusting the length of the stud 17 along the axis D, which can be done
 particularly cheaply.
 With the arrangement of the invention, the stack of electrical components 2
 can be constituted outside the case as follows. Starting with an empty
 tube 2, the plate 9 is initially mounted in the tube with the studs 14
 engaged in the slots 15. Thereafter, the spring 12 is placed between the
 plate 9 and the plate 11. The spring 12 is then compressed between these
 two plates by means of a screw 19 which engages in the thickness of the
 plate 9 and which passes through the plate 11, the screw 19 being operated
 to move the two plates towards each other until it is possible to insert
 the studs 13 through the tube and under the plate 11. The screw 19 is then
 withdrawn so that the plate 9 comes into abutment against the top ends of
 the slots 15. At this stage, the spring 12 between the plates 9 and 11 is
 compressed while still retaining a compression margin. The electrical
 components are inserted into the tube 2 over the plate 9 and thus over the
 floating structure, after which, the tube loaded with the electrical
 components can be put into place inside a case.
 As can be seen in the FIGURE, the fixing flange 20 for fixing the case 3 to
 a break chamber (not shown but extending perpendicularly to the axis D),
 e.g. of a circuit-breaker, is disposed in the middle of the case along the
 axis D so as to enable the case to be fixed in a T-disposition to the end
 of the chamber, thus disposing the closure resistor perpendicularly to the
 chamber. With this disposition, the lever arm exerted by the closure
 resistor on the end of the break chamber is considerably reduced. The
 end-to-end size of the break chamber is also reduced, and it is possible
 to place two or more stacks of electrical components 1 in parallel inside
 the case 3, and this can be done more easily than would have been possible
 if the length direction of the case 3 extended the axial direction of the
 break chamber.
 The resistor assembly arrangement of the invention also provides simple
 access to the electrical components 1 for replacement purposes without it
 being necessary to act within the break chamber of the electrical gear
 that is connected to the resistor.