U.S. patent number 3,887,888 [Application Number 05/347,460] was granted by the patent office on 1975-06-03 for high current switch.
This patent grant is currently assigned to Arrow-Hart, Inc.. Invention is credited to John Bayles, Randall C. Bremer, George E. Gauthier, Frank J. Nascimbeni, Robert J. Petitjean.
United States Patent |
3,887,888 |
Bayles , et al. |
June 3, 1975 |
High current switch
Abstract
An electric switch of the sort capable of carrying high amperage
currents, especially under short circuit conditions is provided
with a ferromagnetic U-shaped yoke piece around the contacts and an
armature mounted on the movable contact carrier in position to be
attracted by the magnetic force created in the yoke when current
flows through the contacts. The fixed and movable contact members
act like a one-turn electromagnetic coil especially under severe
short circuit conditions to hold the contacts together against
electromagnetic forces which otherwise would cause contact
separation under such conditions. Rocking of the movable contact on
the fixed contact is prevented by a leaf spring which acts in
closed circuit position of the contacts and in cooperation with the
holding means on short circuit conditions.
Inventors: |
Bayles; John (East Dover,
VT), Bremer; Randall C. (East Granby, CT), Gauthier;
George E. (Farmington, CT), Nascimbeni; Frank J. (Avon,
CT), Petitjean; Robert J. (Simsbury, CT) |
Assignee: |
Arrow-Hart, Inc. (Hartford,
CT)
|
Family
ID: |
23363790 |
Appl.
No.: |
05/347,460 |
Filed: |
April 4, 1973 |
Current U.S.
Class: |
335/195; 200/250;
335/16 |
Current CPC
Class: |
H01H
1/54 (20130101); H01H 1/50 (20130101) |
Current International
Class: |
H01H
1/54 (20060101); H01H 1/00 (20060101); H01H
1/50 (20060101); H01h 077/08 () |
Field of
Search: |
;335/195,16 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Broome; Harold
Attorney, Agent or Firm: Davis, Hoxie, Faithfull &
Hapgood
Claims
We claim:
1. An electric switch comprising a pair of fixed contact members
and a bridging contact member movable into and out of engagement
with said fixed contact members, a pair of members of
ferro-magnetic material for each pair of fixed and movable contact
members forming a loop through which extends at least one contact
supporting member of each pair thereof, one magnetic member of each
pair thereof being secured to said bridging contact member, said
magnetic members providing a flux concentrating path for
electro-magnetic flux around said loop-penetrating
current-conducting members whereby on occurrence of a short circuit
in the electric circuit including said contacts, said one magnetic
member is attracted toward the other magnetic member and said
contacts are held in engagement by a force proportional to the
current flow through said contact members, and operating means
carrying said bridging contact member, and anti-rocking means
carried by said operating means acting on said bridging contact
member in switch-closed position to prevent rocking of the
contacting surfaces of said bridging member on the contacting
surfaces of said fixed contact members in switch-closed position on
a short circuit condition.
2. In a switch as claimed in claim 1 having means biasing said
bridging contact member into engagement with said fixed contact
members in closed circuit position.
3. A switch as claimed in claim 1 wherein said anti-rocking means
engages said bridging contact member at spaced positions defining a
plane and exerts an anti-rocking force on said bridging contact
member.
4. A switch as claimed in claim 1 wherein said anti-rocking means
comprises a leaf spring which engages said bridging contact member
along parallel lines transverse to the length of the bridging
contact member.
5. A switch as claimed in claim 4 wherein said spring has slots
running along its length, and pins mounted in said bridging member
extending through said slots at their adjacent ends.
Description
This invention relates to electric switches and more particularly
to high current electric switches having full load ratings as high
as 600 amperes but which under abnormal conditions, such as short
circuit conditions may have to carry as high as 20,000 ampere RMS
or even in excess of that.
Switches of the sort to which this invention relates are used in
connection with emergency supply equipment and in other usages
where under short circuit conditions very high amperages are
developed. Currents as high as 5,000 amperes may develop under some
short circuit conditions, while under more severe and extraordinary
conditions, currents as high as 20,000 amperes or in excess of that
may occur.
In prior art devices a pair of fixed contacts were bridged by a
movable contact that was held in closed circuit condition by a
spring pressure against the movable or bridging contact.
Ordinarily, the fixed contact members and the bridging contact
members as well as the contact surfaces themselves are massive and
are held closed by relatively heavy springs which impose
considerable pressure on the bridging contact to hold it in
engagement with the fixed contacts.
On the occurrence of the short circuit current in the neighborhood
of 5,000 amperes RMS, contact pressure of the spring holding the
bridging contact in engagement with the movable contact can be
overcome by magnetic forces of repulsion developed between the
stationary and movable contacts. When the spring bias is overcome,
the contacts tend to separate. Contact separation under short
circuit conditions always results in arcing. This sometimes has
resulted in a violent explosion in instances of a large fault. In
less severe cases there may be merely a melting of small amounts of
contact material, with the result that when the "short" was
cleared, by a fuse or other protective device, the contacts would
snap back together and the molten material would cool. This caused
very firm welding of the contacts together.
The present invention overcomes the above difficulties by
utilization of two mechanisms which work together. In one mechanism
the very heavy amperage current flow on short circuits is utilized
to hold the contacts together, overcoming the effort of such
currents to separate the contacts. The second mechanism is a
mechanical arrangement to prevent rocking motion of the contacts in
switch-closed position and hence tending to prevent any arcing
between the fixed and movable contacts under ordinary or moderately
severe short circuit conditions.
According to the present invention, magnetic forces generated by
the very large over-current conditions are utilized by the addition
of a stationary ferromagnetic member half surrounding the
stationary contact and an armature on the movable contact. The
attractive forces are generated by the passage of current through
what is in effect a single-turn coil which passes through the
magnetic structure constituted by the magnet and the armature. The
stationary magnetic member and the armature need not touch but they
cooperate to form a broken loop which provides a concentrated flux
path that is particularly effective under heavy short circuit
conditions.
One object of the invention is to provide means associated with the
fixed and movable contacts which provide on the one hand forces
generated in proportion to the increase of current flow which tend
to hold the movable contact in engagement with the fixed contact
and on the other hand, to prevent rocking of the movable contact on
the fixed contact and hence any tendency toward arcing at the point
of contact engagement.
Other objects and advantages of the invention will appear as the
invention is described in connection with the accompanying
drawing.
In the drawings:
FIG. 1 is a longitudinal section view through a switch embodying
the invention with the switch contact in open position.
FIG. 2 is a view similar to FIG. 1 with a part of the switch in
longitudinal section but with the contacts in closed circuit
position.
FIG. 3 is a transverse section view along line 3--3 of FIG. 2.
FIG. 4 is a perspective view of the new magnet structure which
tends to keep the movable and fixed contacts in engagement.
FIG. 5 is a fragmentary plan view of the bridging contact of the
structure illustrated in FIGS. 1 and 2 showing the novel
anti-rocking spring.
FIG. 6 is a fragmentary view showing in section the mounting of the
bridging contact on the operating member.
Referring to the drawings, an insulating base 10 of the elongated
rectangular form has an elongated channel shaped recess formed in
one face of it for receiving the current carrying parts. In the
contral part of the recess, there is an aperture through which
passes an electromagnetically operated member for causing the
reciprocation of the hereinafter described bridging contact
structure. One possible type of operating mechanism is disclosed in
the H. E. Schleicher U.S. Pat. No. 2,802,919.
At opposite ends of the base are identical thick
fixed-contact-carrying plates 20 of generally rectangular form. On
top of each plate 20 lies a heavy duty terminal plate 22 which
extends beyond the end of the base and on which may be mounted, if
desired, a terminal clamp (not shown) by means of which conductor
cables may be connected to the switch. The terminal plates 22 and
fixed contact plates 20 may be secured to the base by bolts 24
passing through the base and through the plates with nuts 26
threaded on the protruding ends. On the inner end of the contact
supporting plate 20 and on the upper upwardly facing surface
thereof are fixed contact blocks or faces 28 which preferably are
of silver or other common or suitable contact metal or alloy which
may be flat, as illustrated, or curved convexly.
For bridging the contacts 28 a movable contact member is provided
which in the higher rated devices preferably has arcuate spaced
intermediate portions 32. Extending in opposite directions from the
arcuate portions 32 parallel to and over the fixed contact plates
20 are ends 33 on the under and inner surface of which are mounted
movable contacts 34. The movable contacts may be buttons, or
rectangular plates as shown. The faces of the movable contacts 34
which engage the fixed contacts may be arcuate about a longitudinal
axis as shown in FIG. 3.
To bias the movable contacts against the fixed contacts in
switch-closed position (FIG. 2), a coiled compression spring 35 is
positioned between the two arcuate intermediate parts 32. It
presses at one end against the middle of the bridging contact
member and at its other end against the middle of a thin
rectangular flat resilient plate 38 of spring metal. Plate 38
extends over the arcuate parts 32 and is secured in place by a
dish-shaped or concave metal washer 36 and a securing screw 37,
which passes through the washer and threads into a tapped hole in a
cylindrical connector member 37a. Connector 37a extends coaxially
through the coiled spring 35 and loosely through the center of the
bridging contact member and is secured with its lower end abutting
a molded insulating member 30 by a screw bolt 37b. The bolt 37b
passes through a central bore in member 30, and into a tapped hole
in the lower end of connector 37a and thus secures the insulation
member 30 to the connector 37a so that they act as a unit.
The insulation member 30 may be of any suitable shape or form and
may be adapted to be secured to conventional operating mechanism
(not shown) such as in electromagnetically actuated mechanism of
conventional form or any other operating mechanism. Conventionally,
when the electromagnetic or other operating mechanism is energized
or operated, the bridging contact assembly will be moved downwardly
until the movable contacts 34 engage fixed contacts 28. Further
downward movement of operating member 30 will cause spring 35 to be
compressed and strongly press the bridging contact member, its
contacts 34 maintained firmly biased against the fixed contacts
28.
In this structure, the magnetic forces acting on the bridging
contact when an overload due to short circuit conditions occurs,
tends to overcome and in extreme cases does overcome the bias of
the compression spring 35 and causes the movable contacts to
separate from the fixed contacts a distance depending upon the
degree of overload or overcurrent. Contact separation under short
circuit conditions results routinely in arcing between the movable
and fixed contacts. This arcing can cause a violent explosion or
merely a melting of the contacts. If the contacts melt on momentary
separation incident to the short circuit, the short may be cleared
by a fuse or other protective device somewhere in the circuit. If
the contacts then snap back together, the molten metal will cool,
welding the fixed and movable contacts firmly and permanently
together. This can happen in a very small interval of time due on
the one hand to the extremely high current flow of the short
circuit and on the other hand, due to the quick, almost
instantaneous, reaction of the switch biasing spring.
The problem of contact separation on short circuit overload
conditions is overcome by the present invention by the provision,
adjacent each fixed contact, of metallic U-shaped members, each
constituting a field piece or magnet, designated in the drawings
generally by the numeral 40. The members 40 are preferably made of
material of high magnetic permeability (referred to generically as
ferromagnetic material) which will not saturate in the presence of
fault currents with the design of air gap present, in order that as
currents increase, the magnetic force tending to keep the contacts
closed will increase. One suitable material is cold rolled steel,
but other materials having high permeability in the area of 8000
gausses, such as iron or other steels may be used. The members 40
each have parallel side plates 42 embracing each of the fixed
contact members 20 on opposite sides thereof with a transverse
plate portion 44 connecting the side arms 42 and lying under the
fixed contact members 20 in recessed portions of the base under the
fixed contact members. The magnet members 40 are not rigidly held
by the fixed contact members but are permitted to have a slight
amount of movement for adjusting themselves to an armature member
46 which cooperates therewith.
The armature 46 also is made of ferromagnetic metal in the form of
a flat rectangular plate secured by screws or otherwise on the flat
top surface of the extending ends 33 of the bridging contact
member. The armature plate extends transversely over the contact
members 33 and over the top edges of the side plates 42 of the
magnet, as may be seen in FIG. 3. The length of the armature plate
preferably equals the overall dimension of the magnet 40 and the
armature width preferably equals the width of the magnet arms 42,
as may be seen in FIG. 4.
A liner member 45 of U-shape made from thin sheet insulation lies
within the magnet 40 under the fixed contact 20 so that the magnet
is not in direct electrical contact with the fixed contact member.
The height of the side plates 42 is such that when the magnet is
assembled as shown in FIG. 3, the top edges of the side plates 42
do not touch the armature when the bridging contact is in
switch-closed position as shown in FIG. 3. This spacing ensures
engagement of the fixed and movable contacts. As the switch
contacts wear away in use, the armature will come closer and closer
to the arms of the magnet. When the armature 46 finally engages the
magnet arms 42, the switch contacts 28 and 34 will have reached the
end of their useful life.
The magnetic attraction of the armature 46 to the magnet 40 is
created by the electromagnetic flux around the fixed and movable
contact members as current flows through them. The fixed and
movable contact members thus act like one turn of an
electromagnetic coil. Since the electromagnetic flux around the
contacts increases in proportion to the square of the current
passing through them, the attractive force exerted on the bridging
contact member will become very great under short circuit current
conditions, thus preventing the bridging contact member from
allowing separation of the movable from the fixed contacts.
Under some short circuit conditions when the electromagnetic forces
in the prior art switch devices were insufficient to overcome the
bias of the spring 35, the electromagnetic force was nevertheless
sufficient to weaken the pressure of the movable contact against
the fixed contact. The movable contacts then tended to rock on the
fixed contact about an axis extending longitudinally of the switch.
When the movable contacts are convexly curved along an axis in that
direction, the rocking tendency is enhanced, although the curvature
was provided for entirely different reasons, namely, adjustment of
the movable contact to the fixed contacts as they engage and for
increased pressure between the contacts along the line of
engagement. The reason for the rocking is not exactly known and was
not noted in prior art devices, but is thought to be caused
possibly by variations in the force relationships in the magnetic
assembly as the polarity of the alternating current changes. The
rocking causes some minor arcing at the contact surfaces. Although
the arcing is not as serious as the short circuit arcing, it is
desirable to avoid it.
In order to overcome this rocking tendency, the flat leaf spring 38
is provided preferably made in strip form from stiff spring sheet
metal. The spring is mounted beneath the convex surface of the
washer 36 and extends longitudinally over the bridging contact
member and is adapted to press on the outward or top surface of the
arcuate portions 32 thereof. The anti-rocking spring 38 is kept in
proper longitudinal orientation and from turning about the axis of
the securing screw 37 by two pins 39 extending upwardly from a
mounting in each of the two portions 32 of the bridging contact
member. The pins 39 extend through aligned slots 38s extending
longitudinally of the leaf spring 38. The pins 39 are located in
the ends of the slots 38s nearest the center of the spring. The
slots prevent binding of the spring as the bridging contact between
switch-open and switch-closed positions. In switch-open position,
the leaf spring 38 is not in engagement with the arcuate portions
32 of the bridging contact member; but upon movement toward
switch-closed position, after the movable contacts 34 engage the
fixed contacts 28 and the bridging contact member can move no
further, the leaf spring is carried into engagement with the parts
32 of the bridging contact member by continued movement in
switch-closing direction of all but the bridging member itself. The
leaf spring 38 thus becomes slightly stressed and will exert a
small amount of pressure or bias of the movable contacts against
the fixed contacts. By reason of the spring being flat and engaging
the top surface of the parts 32 of the bridging contact member in
parallel lines that are coplanar with the plane of the spring 38
(as may be seen in FIG. 3) and the pins 39 engaging with the sides
of slots 38s, the rocking tendency of the movable contacts 34 on
the fixed contacts 28 is overcome.
The anti-rocking just described is claimed per se in our divisional
application Ser. No. 540,003, filed Jan. 10, 1975, entitled
"Anti-Rock Preventing Means for Electric Switch Contacts."
In addition to the anti-rocking function of the leaf spring 38,
this spring prevents contact bounce as tends to occur when one of
the movable contacts engages its fixed contact before the other. To
that end, location of the pins 39 in the inner ends of slots 38s is
desired. The slots 38s in the leaf spring thus enable lengthwise
bowing of the bridging contact member, whilst applying constant
pressure along parallel lines at spaced positions along the
bridging contact member on opposite sides of the axis of the main
biasing spring 35. The operating member 30 has a flat upper or
outer end on which rests the middle of the bridging contact member
whose lower or inner surface is likewise flat.
Still further there is a tendency of the bridging contact to tilt
or teeter longitudinally about the screw 37 and connector member
37a. This tilting is restricted by the location of the pins 39 in
the proximate ends of the slots 38s. The pins engage the spring as
the tilting tends to increase. This engagement in cooperation with
the engagement of the bridging member with the connector member or
port 37a restricts the tilting.
From the foregoing, it will be clear that arcing due to contact
separation or weakening of the pressure of the movable contacts
against the fixed contacts incident to different short circuit
conditions is overcome by this invention due on the one hand to
utilization of the electromagnetic forces generated during the high
current conditions (such as are created by extraordinary short
circuiting) to increasingly press the bridging and fixed contacts
together, and on the other hand, by using a supplementary leaf
spring in cooperation with the bridging contact member to prevent
rocking of the movable contacts on the fixed contacts under lesser
short circuit conditions.
Many modifications within the scope of the invention will occur to
those skilled in the art. Therefore, the invention is not limited
to the specific form and dimensions of the invention as described
in the preferred embodiment illustrated.
* * * * *