CONTACT ASSEMBLY AND VACUUM SWITCH INCLUDING THE SAME
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority from and claims the benefit of U.S.
Patent Application Serial No. 13/589,687, filed August 20, 2012, which is
incorporated by reference herein.
BACKGROUND
Field
The disclosed concept pertains generally to circuit interrupters and,
more particularly, to circuit interrupters employing a vacuum envelope such as, for
example, a vacuum interrupter. The disclosed concept even more particularly pertains
to contact assemblies used in vacuum interrupters.
Background Information
Circuit interrupters provide protection for electrical systems from
electrical fault conditions such as, for example, current overloads, short circuits and
abnormal voltage conditions. Typically, circuit interrupters include a spring powered
operating mechanism which opens electrical contacts to interrupt the current through
the conductors of an electrical system in response to abnormal conditions.
Circuit interrupters, such as, for example, power circuit breakers for
systems operating above about 1,000 volts, typically utilize vacuum interrupters as the
switching devices. For the higher voltages, or for a more compact arrangement, each
vacuum interrupter is housed in a separate pod molded of an electrically insulative
material, such as a polyglass. These molded pods, in turn, are bolted to a metal box
containing the operating mechanism. The metal box is grounded to isolate the
operating mechanism from the line voltage of the power circuit. Manual controls for
the operating mechanism are accessible at the front face of the metal box. See, for
example, U.S. Pat. No. 6,373,358.
Vacuum circuit interrupter apparatus include separable main contacts
disposed within an insulating housing. Generally, one of the contacts is fixed relative
to both the housing and to an external electrical conductor which is interconnected
with the circuit to be controlled by the circuit interrupter while the other contact is
movable. In the case of a vacuum circuit interrupter, the movable contact assembly
usually comprises a stem of circular cross-section having the contact at one end
enclosed within a vacuum chamber and a driving mechanism at the other end which is
external to the vacuum chamber. An operating rod assembly comprising a push rod,
which is fastened to the end of the stem opposite the movable contact, and a driving
mechanism provide the motive force to move the movable contact into or out of
engagement with the fixed contact.
Typically, each of the contacts is secured to the associated stem via a
hub on the stem and a corresponding hole on the contact which mates with the hub. A
braze washer, provided between the mating parts of each contact and associated stem,
brazes the components together during a vacuum cycle in a vacuum furnace. In order
to ensure a reliable braze joint, weight (typically 1 to 2 pounds) is applied to hold the
joint between the contact and the stem together during the brazing operating. For a
full furnace load, this can amount to 50 to 100 pounds of extra weight in the furnace.
There is room for improvement in electrical switching apparatus, such
as vacuum
interrupters.
There is also room for improvement in the methods employed for
manufacturing vacuum interrupters.
SUMMARY
These needs and others are met by embodiments of the disclosed
concept which are directed to a contact assembly, a vacuum switch including a
contact assembly, and a method of assembling a contact assembly.
As one aspect of the disclosed concept, a contact assembly for use in a
vacuum switch is provided. The contact assembly comprises an electrode stem and a
contact coupled to an end portion of the electrode stem via a threaded fastener which
threadingly engages a threaded portion of the electrode stem.
The contact may be further coupled to the electrode stem via a braze
material.
The threaded fastener may comprise a shoulder screw.
The threaded fastener may be formed from a material having a lower
thermal expansion than a number of materials from which either the electrode stem or
the contact is formed, such that during the brazing cycle the joint self-tightens.
The threaded fastener may be formed from one of a stainless steel
material or a Nickel-Iron material.
As another aspect of the disclosed concept, a vacuum switch is
provided. The vacuum switch comprises a vacuum envelope, a fixed contact
assembly disposed partially within the vacuum envelope and a movable contact
assembly disposed partially within the vacuum envelope and movable between a
closed position in electrical contact with the fixed contact assembly and an open
position spaced apart from the fixed contact assembly. At least one of the fixed
contact assembly and the movable contact assembly comprise an electrode stem and a
contact coupled to an end portion of the electrode stem via a threaded fastener which
threadingly engages a threaded portion of the electrode stem.
The contact may be further coupled to the electrode stem via a braze
material.
The threaded fastener may comprise a shoulder screw.
The threaded fastener may be formed from a material having a lower
thermal expansion than a number of materials from which either the electrode stem or
the fixed contact is formed, such that during the brazing cycle the joint self-tightens.
The threaded fastener may be formed from one of a stainless steel
material or a Nickel-Iron material.
The vacuum switch may be a vacuum interrupter.
The other one of the fixed contact assembly and the movable contact
assembly may comprise a second electrode stem and a second contact coupled to an
end portion of the second electrode stem via a second threaded fastener which
threadingly engages a threaded portion of the second electrode stem.
The second threaded fastener may comprise a second shoulder screw.
As yet another aspect of the invention, a method of assembling a
contact assembly having an electrode stem and a contact for use in a vacuum switch is
provided. The method comprises disposing the contact on a portion of the electrode
stem and coupling the contact to the electrode stem via a threaded fastener.
Coupling the contact to the electrode stem via a threaded fastener may
comprise coupling the contact to the electrode stem via a shoulder screw.
The method may further comprise providing a braze material between
the contact and the portion of the electrode stem prior to coupling the contact to the
electrode stem via the threaded fastener.
The method may further comprise brazing the contact to the electrode
stem by subjecting the coupled contact and the electrode stem to a vacuum cycle in a
vacuum furnace.
BRIEF DESCRIPTION OF THE DRAWINGS
A full understanding of the disclosed concept can be gained from the
following description of the preferred embodiments when read in conjunction with the
accompanying drawings in which:
Fig. 1 is a cross-sectional view of a vacuum switch disposed in a closed
position in accordance with an embodiment of the disclosed concept.
Fig. 2 is a cross-sectional view of the fixed contact assembly of the
vacuum switch of Fig. 1.
Fig. 3 is a cross-sectional view of the movable contact assembly of the
vacuum switch of Fig. 1
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As employed herein, the term "number" shall mean one or an integer
greater than one (i.e., a plurality).
As employed herein, the statement that two or more parts are
"connected" or "coupled" together shall mean that the parts are joined together either
directly or joined through one or more intermediate parts. Further, as employed
herein, the statement that two or more parts are "attached" shall mean that the parts
are joined together directly.
As employed herein, the term "vacuum envelope" means an envelope
employing a partial vacuum therein.
As employed herein, the term "partial vacuum" means a space (e.g.,
within a vacuum envelope) partially exhausted (e.g., to the highest degree practicable;
to a relatively high degree; to a degree suitable for use in a vacuum switching
apparatus application) by a suitable mechanism (e.g., without limitation, an air pump;
a vacuum furnace).
The disclosed concept is described in association with vacuum
interrupters, although the disclosed concept is applicable to a wide range of vacuum
switches.
The disclosed concept provides for an improved method of assembling
contact assemblies for use in vacuum switches. The disclosed concept further
provides for improved contact assemblies for use in vacuum switches.
Referring to Fig. 1, a vacuum switch, such as a vacuum interrupter 2, is
shown. The vacuum switch 2 includes a vacuum envelope 4, a fixed contact assembly
6 disposed partially within the vacuum envelope 4, and a movable contact assembly 8
disposed partially within the vacuum envelope 4 and movable between a closed
position (as shown in Fig. 1) in electrical contact with the fixed contact assembly 6
and an open position (partially shown in phantom in Fig. ) spaced apart from the
fixed contact assembly 6.
Referring to Fig. 2, the fixed contact assembly 6 includes an electrode
stem 10 and a fixed contact 12. The fixed contact 12 is at least initially coupled to,
and pressed against, an end portion 14 of the electrode stem 10 via a threaded
fastener, such as shoulder screw 16, which threadingly engages a threaded portion 8
of the electrode stem 10. Although shown as a shoulder screw 16 in the illustrated
example embodiment, it is to be appreciated however that other suitable threaded
fasteners may be employed without varying from the scope of the present invention.
Before coupling the fixed contact 2 to the electrode stem 10, a braze material, such
as braze washer 20 is provided between the electrode stem 10 and the fixed contact
12. After the fixed contact 12 is coupled to the electrode stem 0 via the shoulder
screw 16, the assembly 6 is then subjected to a vacuum cycle in a vacuum furnace
(not shown) that brazes the fixed contact 12 and the electrode stem 10 together. By
utilizing the shoulder screw 6 to initially couple and press the fixed contact 12 to the
electrode stem 10, the need for weights or other temporary fixing mechanisms
aligning and pressing the fixed contact 12 against the electrode stem 10 together
during the brazing process is eliminated.
In order to ensure that shoulder screw 16 tightly couples the fixed
contact 2 to the electrode stem 10 during the vacuum cycle in the vacuum furnace,
shoulder screw 6 is preferably formed from a material having a lower thermal
expansion than the materials from which either of the fixed contact 2 or the electrode
stem 10 are formed. Due to the different thermal expansions between the contact 12,
electrode 10 and the screw 16, the braze joint is squeezed together during the brazing
cycle.
In an example embodiment of the disclosed concept, the shoulder
screw 16 is formed from stainless steel material (e.g., without limitation SST416)
while the fixed contact 2 is formed from Copper-Chrome and the electrode stem
is formed from Oxygen Free High Conductivity (OFHC) Copper. In another example
embodiment of the disclosed concept, the shoulder screw 16 is formed from Nickel-
Iron material.
Referring to Fig. 3, the movable contact assembly 8 is generally
assembled in a similar manner as the fixed contact assembly 6. Movable contact
assembly 8 includes a movable electrode stem 22 and a movable contact 24. The
movable contact 24 is at least initially coupled to, and pressed against, an end portion
26 of the movable electrode stem 22 via a threaded fastener, such as shoulder screw
28, which threadingly engages a threaded portion 30 of the movable electrode stem
22. Although shown as a shoulder screw 28 in the illustrated example embodiment, it
is to be appreciated however that other suitable threaded fasteners may be employed
without varying from the scope of the present invention. Before coupling the
movable contact 24 to the movable electrode stem 22, a braze material, such as braze
washer 32 is provided between the movable electrode stem 22 and the movable
contact 24. After the movable contact 24 is coupled to the movable electrode stem 22
via the shoulder screw 28, the assembly 8 is then subjected to a vacuum cycle in a
vacuum furnace (not shown) that brazes the movable contact 24 and the movable
electrode stem 22 together. By utilizing the shoulder screw 28 to initially couple the
movable contact 24 to the movable electrode stem 22, the need for weights or other
temporary fixing mechanisms aligning and pressing the movable contact 24 against
the movable electrode stem 22 during the brazing process is eliminated.
In order to ensure that shoulder screw 28 tightly couples the movable
contact 24 to the movable electrode stem 22 during the vacuum cycle, shoulder screw
28 is preferably formed from a material having a lower thermal expansion than the
materials from which either of the movable contact 24 or the movable electrode stem
22 are formed. In an example embodiment of the disclosed concept, the shoulder
screw 28 is formed from stainless steel material (e.g., without limitation SST416)
while the movable contact 24 is formed from Copper-Chrome and the movable
electrode stem 22 is formed from Oxygen Free High Conductivity (OFHC) Copper.
In another example embodiment of the disclosed concept, the shoulder screw 28 is
formed from Nickel-Iron material.
While specific embodiments of the disclosed concept have been
described in detail, it will be appreciated by those skilled in the art that various
modifications and alternatives to those details could be developed in light of the
overall teachings of the disclosure. Accordingly, the particular arrangements
disclosed are meant to be illustrative only and not limiting as to the scope of the
disclosed concept which is to be given the full breadth of the claims appended and
any and all equivalents thereof.

What is Claimed is:
1. A contact assembly (6, 8) for use in a vacuum switch (2), the
contact assembly comprising:
an electrode stem (10, 22); and
a contact (12, 24) coupled to an end portion (14, 26) of the electrode
stem via a threaded fastener (16, 28) which threadingly engages a threaded portion
(18, 30) of the electrode stem.
2. The contact assembly (6, 8) of claim 1 wherein the contact (12, 24)
is further coupled to the electrode stem (10, 22) via a braze material (20, 32).
3. The contact assembly (6, 8) of claim 1 wherein the threaded fastener
(16, 28) comprises a shoulder screw.
4. The contact assembly (6, 8) of claim 1 witerein the threaded fastener
(16, 28) is formed from a material having a lower thermal expansion than a number of
materials from which either the electrode stem (10, 22) or the contact (12, 24) is
formed.
5. The contact assembly (6, 8) of claim 1 wherein the threaded fastener
(16, 18) is formed from one of a stainless steel material or a Nickel-Iron material.
6. A vacuum switch (2) comprising:
a vacuum envelope (4);
a fixed contact assembly (6) disposed partially within the vacuum
envelope; and
a movable contact assembly (8) disposed partially within the vacuum
envelope and movable between a closed position in electrical contact with the fixed
contact assembly and an open position spaced apart from the fixed contact assembly;
wherein at least one of the fixed contact assembly and the movable
contact assembly comprises a contact assembly as recited in claim .
7. The vacuum switch (2) of claim 6 wherein the contact (12, 24) is
further coupled to the electrode stem (10, 22) via a braze material (20, 32).
8. The vacuum switch (2) of claim 6 witerein the threaded fastener (16,
28) comprises a shoulder screw.
9. The vacuum switch (2) of claim 6 wherein the threaded fastener (16,
28) is formed from a material having a lower thermal expansion than a number of
materials from which either the electrode stem (10, 22) or the fixed contact (12, 24) is
formed.
10. The vacuum switch (2) of claim 6 wherein the other one of the
fixed contact assembly and the movable contact assembly comprises:
a second electrode stem (10, 22); and
a second contact (12, 24) coupled to an end portion (14, 26) of the
second electrode stem (10, 22) via a second threaded fastener (16, 28) which
threadingly engages a threaded portion (18, 30) of the second electrode stem (10, 22).
11. The vacuum switch (2) of claim 10 wherein the second threaded
fastener (16, 28) comprises a second shoulder screw.
12. A method of assembling a contact assembly (6, 8) for use in a
vacuum switch (2), the contact assembly having an electrode stem (10, 22) and a
contact (12, 24), the method comprising:
disposing the contact on a portion of the electrode stem; and
coupling the contact to the electrode stem via a threaded fastener (16,
28).
13. The method of claim 12 wherein coupling the contact to the
electrode stem via a threaded fastener (16, 28) comprises coupling the contact to the
electrode stem via a shoulder screw.
14. The method of claim 12 further comprising providing a braze
material (20, 32) between the contact and the portion of the electrode stem prior to
coupling the contact to the electrode stem via the threaded fastener.
15. The method of claim 14 further comprising brazing the contact to
the electrode stem by subjecting the coupled contact and the electrode stem to a
vacuum cycle in a vacuum furnace.