Note: Descriptions are shown in the official language in which they were submitted.
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LOAD BREAK SWlTCH
WlTH SAFETY MECHANISM
DESCRIPTION
This invention relates to safety features for
switches, and particularly for ground enclosed, load-
break switches adapted for use in medium voltage power
distribution systems in the range about 1 to about 36 10
kilovolts (kv) for interrupting currents of up to about
1 kiloampere (ka).
Load break switches used in medium voltage power
distribution range circuits generally include a pair of
electrodes, one being stationary and the other movable
to open and close the circuit. As commonly used in
three-phase systems, three or multiples of three
switches are mounted in a common grounded metal
enclosure.
One type of load break switch for power distribution
systems is gas insulated switches that employ a gas for
both insulation and interruption. Sulfur-10
hexafluoride (SE6), either alone or mixed with other
gases such as nitrogen, is used. The gas is used to
rapidly extinguish the arc formed as the switch is
opened. In a typical three phase configuration, a
grounded metal enclosure surrounds three, or multiples
of three9 switches. Each individual switch typically
comprises an unsealed cylindrical housing of a plastic
such as reinforced epoxy resin. A grounded metal
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housing filled with sulfur hexafluoride surrounds the
interrupters with substantial clearance to prevent
arcing.
A problem with pressurized gas filled switches is
that the pressure within the enclosure can degrade to an
unsafe level at which the arc developed upon opening the
switch might not be quenched, resulting in rapid heating
and vaporization of the contacts, and in some instances,
an explosion. A pressure gage can be provided, but this
does not prevent opening the switch and it constitutes
an additional source of leakage.
An additional problem with sealed switches is that a
malfunction within the switch can cause uncontrolled
arcing, heating and consequent vaporization of metalic
contacts. This increases the internal pressure of the
switch and creates a safety hazard of a possible explo-
sion of the switch.
In view of these problems, there is a need for a
pressurized switch that is not a safety hazard when the
gas pressure within the switch is either too high or too
low and does not incorporate unnecessary sources of
leakage.
In accordance with the present invention, there is
provided a switch comprising: (a) a sealed housing;
(b) a pressurized insulating gas in the housing; (c) a
bellows sealingly mounted to the housing; (d) an
actuating arm having an operative position in which the
arm is capable of opening and closing the switch, the
act~ating arm being sealingly mounted to the bellows and
extending into the housing through the bellows; (e) low
pressure biasing means for biasing the bellows in oppo-
sition to the gas pressure in the housing, wherein when
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the force of the gas on the bellows is greater than the
force of the low pressure biasing means on the bellows,
the arm is in its operative position; and (f) locking
means for rendering the arm inoperative, the locking
means being positioned so that when the force of the low
pressure biasing means on the bellows is greater than
the force of the gas on the bellows, the bellows is
moved by the low pressure biasing means and the arm is
moved into a locked position.
Preferably, movement of the bellows in response to the
operation of the locking means results in a contraction
of the bellows.
The low pressure safety mechanism comprises low
pressure biasing means such as a spring for biasing the
bellows in opposition to gas pressure within the
housing. As long as the force of the gas on the bellows
is greater than the force of the low pressure biasing
means on the bellows so that the bellows is not
contracted, the arm remains in its operative position.
Locking means are provided to render the arm inoperable.
The locking means are positioned so that when the force
of the low pressure biasing means on the bellows is
greater than the force of the gas on the bellows, the
bellows is contracted, and the arm is moved into engage-
ment with the locking means. In this locked position,
preferably the arm cannot be moved to either open or to
close the switch. This prevents the operator from
moving the arm, thereby creating an arc, when there is
inadequate gas pressure within the housing for quenching
an arc. Thus the single bellows provides a seal for
motion of the arm opening and closing the switch as well
as for motionoperating a pressure safety mechanism.
Preferably the bellows deflects in rocking mode when
the arm opens and closes the switch.
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Advantageously, the switch comprises (a) high
pressure biasing means for biasing the bellows in oppo-
sition to gas pressure within the bellows for preventing
expansion of the bellows unless the force of the gas on
the bellows is greater than the force of the high
pressure biasing means on the bellows; and (b) puncture
means for piercing the bellows when the bellows expands
against the high pressure biasing means.
In accordance with another aspect of the present
invention, there is provided a switch comprislng (a) a
sealed housing; (b) a pressurized insulating gas in the
housing; (c) a bellows sealingly mounted to the
housing; (d) an actuating arm for opening and closing
the switch, the arm being sealingly mounted to the
bellows and extending into the housing through the
bellows; (e) high pressure biasing means for biasing
the bellows in opposition to gas pressure within the
bellows for preventing expansion of the bellows unless
the gas pressure in the bellows increases above a prede-
termined high level; and (f) puncture means for piercing
the bellows when the bellows expands against the force
of the high pressure biasing means.
The high pressure safety mechanism may cleverly take
advantage of features of the low pressure mechanism.
The high pressure mechanism comprises a high pressure
biasing means that acts on the bellows in opposition to
gas pressure within the housing for preventing expansion
of the bellows unless the gas pressure increases above a
predetermined high level. When the force of the gas
pressure on the bellows is greater than the force of the
high pressure biasing means on the bellows, the bellows
is expanded, and engages puncture means that pierce the
bellows. This reduces the gas pressure in the housing
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so that the low pressure safety mechanism takes effect
and moves the arm into the locked position, so that the
switch can be neither opened nor closed.
Preferably the switch includes a pressure indicator
so the operator can know whether the switch is operative
or is at too low pressure. This indicator can comprise
a cover over the actuating arM, and a normal pressure
indicia and a low pressure indicia on the arm at a posi-
tion on the arm external of the bellows. The normal
pressure indicia preferably is closer to the bellows
than is the low pressure indicia. The cover advan-
tageously includes a window so that only one of the
pressure indicia is visible at a time. When the arm is
in its operative position, the normal pressure indicia
can be seen through the window. When the arm is in its
locked position, only the low pressure indicia is
visible through the window. This alerts the operator
that the switch needs to be replaced or repaired.
Thus, according to the present invention, a switch
is provided that alerts the operator when the switch is
unsafe to use, and also prevents the operator from
moving the contacts when the gas pressure within the
switch is too low or too high.
The present invention is directed to a switch in
which a pressurized gas is used. However, it is par-
ticularly, though not exclusively, adapted for load-break
switches used in medium voltage power distribution
systems in the range of about 1 to about 36 kilovolts
for interrupting currents of up to about 1 kiloampere.
Thus, although the present invention will now be
described in considerable detail with re~ard to such a
switch by way of example, 1~ is to be appreciated that
the prese;.~ safety mechanism can be used with other
switches.
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The switch of the present invention advantageously
has features of the switch described in our
International Patent Application Publication No. W0
84/04201.
The switch preferably has a grounded enclosure
comprising a metal housing of a generally cylindrical
configuration. The term "generally cylindrical" is used
herein to mean that the housing is substantially
cylindrical but not necessarily of circular cross-
section. Although less preferred, oval and similar
cross-sections can be employed, if desired. The housing
can be grounded by connecting it by an appropriate con-
ductor to ground. The housing is hermetically sealed
and thus is gas-tight, as well as submersible in water
without damage. This makes the switch suitable for
underground applications where flooding is a possibility
or in environments not compatible with air insulation.
In this specification, a hermetic seal is defined as a
gas-tight seal effective to limit the total leakage from
a pressurized enclosure into the atmosphere to less than
-6 cc/sec measured at atmospheric pressure.
The switch contains within the housing an insulating
gas maintained under positive pressure, i.e. greater
than 1 atmosphere absolute. The gas is preferably
sulfur hexafluoride (also referred to herein as SF6).
The gas pressure utilized in a particular switch depends
on the voltage and current ranges of the switch, its
size and the presence of a puffer mechanism, or other
gas blast device used. The gas pressure is in the range
of greater than I atmosphere to aboul 5 atmospheres
absolute, and preferably from about 1.5 to about 5
atmospheres absolute, for S~6 insulated switches in the
15-36k~ range. There is normally a substantial range of
safe operating pressure in a given application of the
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switch. The hermetically sealed housing permits
pressures in this range to be maintained for periods in
excess of twenty years.
A pair of bushings are mounted in the housing.
Each bushing comprises a metal conductor within and
protruding through an insulator, i.e. a plastic such as
epoxy or a ceramic material. A metal mounting flange is
molded into the plastic and is welded to the wall of the
ground enclosure of the switch. The metal conductor of
the bushing extends through the bushing for conducting
electricity into the switch. The conductor can be a rod
of a suitable metal, generally copper or aluminum.
Where aluminum is used, preferably the aluminum exten-
sion is enclosed where the contacts engage in a metal
more appropriate for arcing or sliding contact.
Preferably bushings are installed coaxially at the
ends of the substantially cylindrical housing with the
bushing conductors extending axially through the housing
end. This permits an inline circuit configuration not
requiring power cable loops and allows a small diameter
housing suitable for high levels of pressurization to be
used.
The interruption of high power circuits requires the
dissipation of substantial amounts of heat by the
switch. The primary mode of heat dissipation is by con-
duction from the switch contacts through the conductors
to the external power cable. Secondarily, heat is con~
ducted from the conductors through the bushings into the
housing. It is important, therefor, to keep the length
of the conductors short. The inner length of the con-
ductor, i.e. that portion of the conductor extending
into the body of the switch, depends primarily on the
contact stroke used. The conductors must be suf-
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ficiently long to make physical and electrical contact
with the contact assembly when it is in its first, or
closed, position and must accommodate the movement of
the contact assembly into its second or fully open posi-
tion. The additional length of the conductor within the
portions of the bushings internal to the housing depends
upon the surface distance required along the insulating
material of the bushings to prevent arcing to the
housing. ~ecause the insulating gas within the housing
can be maintained at high pressure, both a short contact
stroke and a short internal bushing length can be used.
The contact assembly is capable of assuming a first
position in which it is physically and electrically con-
nected with the conductors of each bushing. In this
first closed position, the contacts of the assembly must
be capable of carrying continuous current. According to
its rating, the switch is capable of conducting con-
tinuous current up to at least 200 amperes in the lowest
rating and up to at least 1000 amps (or 1 kA) and
possibly higher. The contact assembly is also capable
of assuming a second position in which it is separated
from a first conductor of one of the bushings to inter-
pose a gas insulated gap in the circuit path thereby
interrupting current flowing through the switch. The
switch is capable of opening under normal current load
and closing into high fault currents of such as 12,000
amps, 25,000 arnps, or even higher in accordance with
standard short circuit ratings.
The contact assembly generally moves in an axial
direction. As it moves into or out of contact
with the first bushing conductor direction. As an arc
forms between the contact assembly and the conductor.
As discussed in more detail below the arc is quenched
by the pressurized insulating gas.
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Preferably the contact assembly comprises a plura-
lity of elongated, electrically conductive contact rods
arranged in a hollow cylindrical configuration. The
contact rods are preferably of a highly conductive
material such as copper. The contact rods are main-
tained in a cylindrical configuration by being mounted
in a holding means providing a radial slot for each rod.
The holding means can be an axially slidable piston used
for pumping insulating gas as described below, where the
piston is made of an insulating material such as molded
plastic. The radial slot configuration retains the con-
tact rods in a cylindrical configuration spaced from one
another, and notches in the contact rods engage the
slots for axial location of the contact rods by the
piston. The slots in the holding means can be provided
by appropriately configured washers as discussed in more
detail below.
The contact assembly is preferably provided with a
guide for maintaining the contact assembly in proper
axial alignment with the other components~ This
guide can be a cylinder for the piston.
The piston preferably has a relatively open spider
configuration to allow the insulating medium to cir-
culate in the housing. The housing can contain a puffer
assembly, for example in a gas insulated interruptor
device, to force a flow of arc quenching gas across the
gap formed between the first conductor and the contact
assembly when the circuit is opened or closed. A puffer
device can be conveniently incorporated into the design
of the piston, if desired. The piston comprises a rela-
tively solid cylindrical block having a number of holes
or passageways drilled through it. When the contact
assembly is moved from its first to its second position
the insulating gas is forced through the holes and
, ................. .
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directed to the gap formed between the first electrode
and the contact assembly. In such embodiments of the
invention the conductive rods of the contact assembly
can be mounted on the aligning means so that the sur-
faces of the rods in contact with the first electrode
are positioned relatively close to the holes through the
aligning means.
The contact assembly comprises a spring associated
with the contact rods such that when the assembly is in
its first position, that is in contact with each of the
conductors, the contact rods exert a maximum inward con-
tact force on the conductors. This assures low contact
resistance and high heat transfer across the closed con-
tacts. The springs can be, for example, leaf springs
mounted on each of the conducting rods. Other springs
such as a spiral or garter spring mounted around the
conducting rod assembly, individual radial springs
mounted on each rod, or any other means which provides
an inward force on the conducting rods can be used.
To open the switch the contact assembly is moved
from the first to the second position, that is the
piston is moved so that the contact rods no longer con-
tact both conductors. The assembly can be moved by
means of a linking arrangement connected with the piston
which is activated by a handle or actuator located
external to the housing. As described more fully below
with reference to the accompanying drawings, opening of
the switch, that is moving the switch to its second
position, causes the contact rods to move away from the
first electrode. An arc between the leading edges of
the contact rods is extinguished by the insulating gas.
The inward force applied to the contact rods causes the
rods to be pushed inward against a spacer as soon as the
contact rods are no longer in contact with the first
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conductor. The spring is associated with the contact
rods in such a manner that when the contact rods are
forced inwardly against the spacer upon disengagement
with the first conductor, the ~orce on the opposing ends
of the contact rods against the second conductor is
greatly reduced. The contact rods remain in contact
with the second conductor so that current resulting from
the arc between the leading edge of the rods and the
first conductor is transferred to the second conductor.
The contact assembly is drawn away from the first con-
ductor a sufficient distance to provide a gap such that
the arc between the first conductor and the contact rods
does not regenerate after it has been quenched. The
reduced force on the rods at this end of the assembly
reduces wear on the rods and the second conductor.
Generally, it has been found that when the contact
assembly is used in a load-break switch in a 200 ampere,
25 15kV circuit, the piston can have a relatively open
"spider" configuration. When used in a 600 ampere, 15kV
circuit a puffing mechanism is preferably provided.
For the puffing mechanism to be effective, the flow
of insulating gas must continue after the contacts have
separated a distance sufficient to prevent regeneration
of the arc until a subsequent current reversal occurs.
Because synchronization of contact opening with line
frequency is not practical, the flow of quenching gas
must continue for at least half a cycle to insure
quenching flow after the contacts have separated beyond
the arc regeneration distance. Because it is also
desired to minimize the heat generated by the arc,
quenching should be completed within a short time inter-
val. The switch of the present invention can be
operated with a short contact stroke with corresponding
low contact velocity within a time frame dictated by the
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above considerations. Since the low contact velocity
greatly reduces the kinetic energy necessary for
operating the switch, light weight construction of the
moving parts is possible, so that a very low power
actuator can be used.
B~J making all of the components other than the con-
tact assembly of an appropriate insulating medium, it is
possible to produce a ground enclosed compact switch in
which the ground enclosure is less than 6 inches in
diameter.
A piston operating in a cylinder can guide the con-
tact assembly in versions of the invention in which a
puffer or gas blasting mechanism is employedO A puffer
mechanism provides a flow of insulating gas to the
region where the arc forms to "blow out" the arc. In
such versions, the body of the piston is relatively
solid and is provided with appro-priately positioned
holes extending through the piston to direct a flow of
insulating gas to the gap between the contacts so as to
quench the arc formed as the contact assembly is moved.
A puffer mechanism used in an embodiment of this inven-
tion is illustrated in Fig. 7 discussed in more detail
below.
It is preferred to insert a solid tubular member or
liner of an appropriate insulating medium or material
between the contact assembly and the housing in the
vicinity of the arcing zone. The tubular member pre-
ferably is positioned adjacent the wall of the housing
and if desired can be bonded thereto. If the tubular
member is bonded to the metal wall, the interface bet-
ween the two components should be void free. It is pre-
ferred to position the tubular member such that there is
an annular gap between the member and the wall. The
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tubular member can extend the entire length of the
housing, if desired. The thickness of the insulating
material depends, to a certain extent, on the voltage
use of the switch. In general the tubular member should
be from about 0.1 inch (2.5 mm) to about 0.5 inch (13
mm) thick. The tubular member is preferably of an acry-
lic, epoxy, or similar plastic. The tubular member can
serve as a cylinder for guiding the piston of the con-
tact assembly.
The switch can be equipped with electrodes for
capacitive detection at relatively low voltage both high
voltage energization of the switch conductors and the
open or closed position of the contacts. This is
possible with the tubular insulating liner positioned
coaxially within the housing separated therefrom by a
small gap or annular space for capacitive division of
alternating current voltages of the conductors. The
insulating liner can have conductive bands deposited in
contact with the annular space, axially positioned
proximate to each coaxial contact. The conductive bands
can be connected to hermetically sealed terminals on the
housing. Voltage measurements of the terminals can be
made locally or remotely, the measurements corresponding
to the contact voltages when the switch is connected in
a distribution system.
For example, if the housing is approximately three
inches (76mm) in diameter, the conductive bands are
approximately 2.9 inches (74mm) in diameter and the con-
tacts are approximately 0.5 inches (13mm) in diameter, a
voltage of 15kV at either contact results in a voltage
of approximately 225 volts being coupled to the
corresponding conductive band; therefore, tne presence
of a high voltage at either contact can be detected by
conventional equipment connected to the corresponding
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terminals. Should the voltages measured at the ter-
minals indicate that one contact is energized while the
other is not, a further indication of the contact
assembly being in the open position is provided.
In case the contacts are shown by these measurements
to be in the same condition (both energized or both une-
nergized) a high frequency current source can be con-
nected to one of the terminals to determine the position
of the contact assembly. The high frequency excitation
of one conductive band is coupled to the corresponding
conductor, through the contact assembly to the other
conductor, thence to the other conductive band where it
can be measured by a conventional frequency discrimi-
nating voltmeter. When the contacts are in the closed
position, the transfer of excitation from one conductor
to the other is direct; however, when the contacts are
in the open position the resulting very low series capa-
citance between the conductors prevents significant high
frequency excitation from being passed to the other con-
ductor thence to the other conductive band. The degree
of high frequency coupling can be measured under
controlled operating conditions for calibration of the
measurements. These measurements are meaningful in the
switch of the present invention because the capacitance
between the contacts is relatively low compared to the
capacitance between the conductive bands and the respec-
tive contacts.
The switch is provided with means for moving the
contact assembly from its first position to its second
position. A preferred means comprises a rocking bellows
or diaphragm mechanism positioned on the side wall
towards one end of the housing. Operation of a lever or
arm extending through the bellows results in moving the
contact assembly from its first to its second position
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and back again as desired. Operation of the arm
deflects the bellows by lateral and/or pivoting motion
in a direction substantially normal to the axis of
expansion of the bellows. This mode of deflection of
the bellows is referred to herein as "rocking".
The use of bellows having rocking mode deflection in
the high voltage switch provides several advantages.
The rocking bellows can be operated without substan-
tially changing the volume enclosed by the bellows as
the contact assembly moves from its first position to
its second position. This eliminates work which other-
wise would be done compressing the insulating gas by
conventional axial movement of the bellows. The rocking
bellows enables the bellows to be located off the center
line axis and thereby permits the unimpeded linear
orientation of the conductors. Such linear orientation
of the conductors, made possible by the use of a rocking
bellows in this manner, permits the switch to be readily
installed as discussed more fully below. Further, the
linear orientation of the conducting path within the
switch assembly advantageously affects the magnitude and
direction of magnetic forces arising from a short cir-
cuit. The metal enclosure provides useful shielding
tending to reduce the magnetic forces resulting from
external current loops under short circuit conditions.
The use of a rocking bellows adds to the long life
of the switch since there are no gas leak paths that
would be present if O-ring or sliding seals were used.
Use of the rocking bellows reduces the size and cost
of the bellows required, that is, the number of con-
volutions required of the bellows and also the life of
the bellows is also improved because its actuating velo-
city is reduced, that is, only the relatively small
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velocities near the pivot are imparted to the bellows
and not the high contact velocity. Since the stresses
in the bellows are directly related to the velocity to
which it i3 operated at high speeds, this innovation
reduces stresses and increases the life and reliability
of the device.
The rocking bellows can also be used to operate a
safety interlock by axial deflection in case of abnormal
pressure within the switch. A low pressure bias can be
applied in opposition to the pressure within the housing
to compress the bellows, should the pressure within the
housing fall too low. The term "compress", used in this
context, means that the volume of gas within the switch
enclosed by the bellows is reduced, whether the bellows
is mounted as shown in the drawings or is inverted.
Conversely, "expand" is the opposite of "compress". A
high pressure bias can be applied in opposition to the
pressure within the housing to allow the bellows to
expand should the pressure within the housing become too
high. Over the normal range of pressure within the
switch, the bellows can be prevented from expanding or
contracting by a suitable stcp. The arm can be locked,
preventing movement of the contacts, should the bellows
be contracted as a result of abnormally low pressure.
The bellows can be punctured to release the gas, should
the bellows be expanded as a result of abnormally high
pressure. The combination of rocking mode deflection
for movement of the contacts and axial deflection for
safety interlock allows the single bellows to her-
metically seal these independent motions without intro-
ducing an additional potential source of` leakage.
The compact size and light weight of the switch
shown in the Figures enables it to be readily inserted
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into a distribution network. The switch can be con-
nected directly into a power cable, for example by a
conventional splice or by conventional separable joints
or connectors. Such separable joints and connectors are
typically of a molded elastomeric material adapted to
receive, for example, a power cable and bushing to form
an electrical connection between them. The relative
ease with which the switch can be inserted in the
distribution network is illustrated by the fact that the
switch can be attached directly to a transformer by
means of an elbow connector. Elbow connectors are com-
mercially available and an example of a typical elbow
connector can be found in U.S. Patent No. 3,559,141 to
Hardy.
A switch in accordance with the present will now be
described, by way of example, with reference to the
accompanying drawings, in which:
Figure 1 is a side elevation view of a switch having
features of the present invention, the switch including
a contact assembly and an actuator;
Figure 2 is a detailed vertical sectional view
the contact assembly portion of the switch of Fig. l;
Figure 3 is a lateral sectional view o~ the switch
of Fig. 1 taken along line 3-3 in Fig. 2;
Figure 4 is another lateral sectional view of the
switch of Fig. 1 taken along line 4-4 in Fig. 2;
Figure 5 is a detailed vertical sectional view of
the actuator of the switch of Fig. 1, the actuator
including a water-tight cover; and
Figure 6 is a lateral sectional view of the switch
of Fig. 1 taken on line 6-6 in Fig. 5.
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Referring to Figs. 1-5, switch 205 includes a metal,
cylindrical housing 210 at ground potential. A supply
bushing 212 and a load bushing 214 are mounted at oppo-
site ends of the housing. The bushings 212 and 214 each
have a ring 215 molded in place. The rings 215 are
welded to the housing 210 to form a hermetic seal bet-
ween the supply bushing 212, the load bushing 214 and
the housing 210. A .supply current rod 216 extends
through the supply bushing 212 and a load current rod
218 extends through the load bushing 214. The current
rods 216 and 218 each have a threaded hole 211 for
engaging a fitting (not shown) or for use as a solder
cup to join a power cable 217 of an external distribu-
tion networkO
With reference to Figs. 2, 3, and 4, a contact
assembly 219 is axially slidably mounted within the
housing 210. The contact assembly 219 comprises a
plurality of cylindrically disposed contact rods 220
mounted concentrically within a piston 222. When the
piston 222 is in a closed position (a) a first end 221
of the contact rods 220 engages an arcing contact 226,
which is fastened to the load current rod 218. The con-
tact rods 220 disengage from the arcing contact 226 when
the piston is in an open position (b). In the drawings,
the parts are shown in the closed position by solid
lines; the open position is shown by phantom lines. A
second end 227 of the contact rods 220 is at all times
slidably engaged with a transfer contact 224, which is
fastened to the supply current rod 216 within a counter-
bore 228 in the supply bushing 212. The counterbore 228
permits the combination of the contact 224 and the
supply bushing 212 within the housing 210 to be made
shorter for improved heat conduction while maintaining a
sufficiently great surface distance over the supply
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bushing 212 to prevent arcing from the transfer contact
224 to ground potential. The piston 222 is provided
with a plurality of axial holes 230 therethrough to
accommodate flow of insulating gas produced by the
displacement of the gas by motion of the piston 222 bet-
ween the first and second positions. A piston cup 231
is fastened to the outside of the piston 222 and holds a
nozzle 232 surrounding the arcing contact 226 when the
piston is in the first position. The piston cup 231 has
a plurality of axial holes 233 all covered by a check
valve 234 to control the flow of gas as described below.
The check valve 234 is retained by a valve pin 235.
A blast shield 238 is located on the load current
rod 218 and held in place by a retaining ring 240. The
blast shield 238 is concave toward the arcing contact
226 for protecting the load bushing 214 from arcing.
An insulating liner 242 surrounding the contact
assembly 219 is radially centered within the housing 210
by an 0-ring 244 proximate to the supply bushing 212 to
provide an annular space 245 between the housing 210 and
the insulating liner 242. The piston cup 231 with the
piston 222is guided by the inside of the insulating
liner 242.
The contact rods 220 are aligned to the piston 222by
a pair of finger washers 246 which are centered incoun-
terbores 247 on opposite sides of the piston. Each of
the contact rods 220 is biased inwardly by a leaf spring
2l18. Each of the contact rods 220 and leaf springs 248
have notches 249 to engage a slot 250 in the finger
washers 246. A sleeve spacer 252 is clamped to a
threaded spacer 254 by a screw 256. The spacers 252 and
254 are axially located by engagement of the finger
washers 246 with the spacers 252 and 254 within a
cylinder 251 formed by the contact rods 220.
B~
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The main purpose of the sleeve spacer 252 is to
control the contact force between the contact rods 220
and the transfer contact 224 when the contact rods 220
are disengaged from the arcing contact 226. When the
contact rods disengage from the arcing contact, the con-
tact rods are driven against the sleeve spacer 252 by
the leaf springs 248. The shift in the axial position
of the reaction force against the contact rods from the
arcing contact 226 to the sleeve spacer 252 results in
reduction in the force of the contact rods on the
transfer contact 224, thereby reducing the magnetude of
the contact force at the transfer contact when the con-
tact rods 220 are disengaged from the arcing contact
226. The amount of this outward bias depends on the
length of the sleeve spacer 252. A relief 257 is pro-
vided in each contact rod 220 localizing the pressure on
rod 220. It is acceptable to tolerate a much lower con-
tact force on the transfer contact 224, because heating
is not a problem within the very short time interval
that is required to move the contacts from their open to
closed position, i.e. a matter of 10 to 20 milliseconds.
Another purpose of the spacers 252 and 254 is to retain
the contact rods 220 and the leaf springs 248 within the
slots 250 to facilitate handling of the contact assembly
219 prior to final assembly within the housing 210.
Preferably clearance is provided between the sleeve
spacer 252 and the contact rods 220, the clearance
being sufficient to allow for some misalignment of the
arcing contact 226 with the contact assembly 219 and for
normal ero~ion of the contacts.
This piston 222 is driven from the open position (a)
to the closed position (b) by a pair of links 258, which
are pivotably connected to the piston by a pair of
piston pins 259. The piston pins 259 can also serve to
fasten the piston cup 231 to the piston 222.
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- 21 - MP931
Preferably the piston 222, the cup 231, the links
258 and the piston pins 259 are all made of an insu-
lating material. By avoiding the use of unnecessary
conducting materials in the vicinity of the contact
assembly 219, the grounded housing 210 can be smaller in
diameter without being subjected to arcing. Conductive
materials within the contact assembly 219 are arranged
within a diameter approximating the diameter of the
supply bushing 212 and the load bushing 214 resulting in
a nearly optimum ratio of energized to grounded coaxial
diameters for reducing the maximum electric field
strength within the housing 210. In addition, the use
of only insulating materials where there is sliding con-
tact, especially between the piston cup 231 and the
insulating liner 242, avoids contamination of the insu-
lating gas within the switch 205 by conductive wear par-
ticles.
~ ith reference to Figs. 5 and 6, the links 258 are
connected to a yoke 260 by a pair of yoke pins 262. A
crank or actuating arm 264 is welded to the yoke 260 and
extends through a rocking bellows 266, the bellows 266
being soldered to the arm 264 to form a hermetic seal.
The bellows 266 is soldered to a bellows support 268,
which is welded to the housing 210. The arm 264 sli-
dably engages a bridge rocker 270, which is pivotably
mounted to a rocker stand 272 welded to the housing 210.
The pivotable mounting of the bridge rocker 270 to the
rocker stand 272 forms a fulcrum 273 for the arm 264.
The fulcrum 273 passes through the rocking bellows 266
for suf`ficient freedom of the arm 264 with only slight
strain of the rocking bellows ~ ~. ~otation of the
crank through an angle of about 32 degrees results in
movement of the piston 222 by the links 258 between the
closed position (a) and the open position (b).
-. .;
11 ~531lE~'~
- 22 - MP931
An overcenter mechanism 274 is used to pivot the
bridge rocker 270 to operate the arm 264. The over-
center mechanism 274 can be enclosed within a water
tight-cover 276 fastened to the housing 210 by a pair of
conventional clamps 278 with a gasket 279 between the
cover 276 and the housing 210. A conventional handle
280 strad~les the cover 276 and is coupled to the over-
center mechanism 274 through the cover 276 by a pair of
coupling shafts 282 equipped with O-ring seals 284. The
gasket 279 and the O-ring seals 284 exclude water and
foreign matter from the interior of the cover 276 which
is maintained nominally at atmospheric pressure.
The coupling shafts 282 are each fastened to a slot
283 in the handle 280 by a screw 285 and a washer 287.
Fach of the coupling shafts 282 is held in axial align-
ment by a coupling retainer 289 fastened to the cover276 by a screw 291.
The overcenter mechanism 274 comprises a U-shaped
detent arm 286 pivotably mounted to the rocker stand 274
in line with and driven by a slot 293 in each of the
coupling shafts 282. A striker 288 is pivotably mounted
to the rocker stand 272, engaging slots 290 in the
bridge rocker 270 and biased by an overcenter spring 292
away from a detent shaft 294, which is fixed to the
detent arm 286. The travel of the detent arm 286 and
the bridge rocker 270 is limited by a detent stop 295,
which is fastened to the rocker stand 272.
In some applications of the switch 205~ the water-
tight cover 276 enclosing the overcenter mechanism 274
need not be provided. In that case, the handle 280 can
be adapted to be fastened directly to the detent arm 286
as shown in Fig. 1.
~i3~8~
- 23 - MP931
Sulfur hexafluoride, or other insulating gas, is
introduced into the switch 205, with the cover 276
removed, through an extension 296 and iniet passage 298
in the crank 264. After the introduction of the desired
amount of gas to the switch 205, a hermetic seal is
generated by bending the exension 296 to produce a fold
300.
The arm 264 is biased toward the interior of the
housing 210 by a low pressure spring 302 acting through
a spring washer 304. The elevated pressure within the
switch biases the rocking bellows 266 away from the
housing 210, compressing the low pressure spring 302
until the arm 264 engages a stop washer 306, which is
biased against the bridge rocker 270 by a high pressure
spring 308. If a leak develops in the switch, the low
pressure spring 302 overcomes the reduced pressure
within the rocking bellows 266 to displace the arm 264
toward the supply bushing 212. In that event, the arm
264 is in a locked inoperative position and the piston
222 is locked into either the first or second position
by a stop 310 engaging the yoke 260. The stop 310 is
fixably mounted to a collar 312 welded to the housing
210, the collar 312 surrounding the supply bushing 212.
Normal pressure within the housing 210 causes the yoke
260 to be positioned away from the stop 310 to permit
operation of the piston 222 between the first and second
positions.
In the event that an abnormally high pressure deve-
lops within the housing 210, the outward bias of the
rocking bellows 266 overcomes the high pressure spring
308 and the stop washer 306 is forced away from the
bridge rocker 270. This causes the rocking bellows 266
to be punctured by a blade 314 and/or a point 316 fixed
to the bridge rocker 270. This safety feature prevents
~5 3~
- 24 - MP931
an explosion of the switch, should there be an abnormal
generation of gas within the switch. Should the rocking
bellows 266 become punctured by the blade 314 and/or the
point 316, the resulting low pressure condition causes
the piston 222 and arm 26~ to become locked as before
described.
A side window 318 is provided in the cover 276 for
visual indication of the pressure within the housing
210. A cap 320 mounted on the arm 264 has colored low
and normal indications visible one at a time through the
side window 318. When the proper pressure level exists
within the housing 210, the "normal" indication is
visible through the side window; when a low pressure
condition allows the crank to be depressed to lock the
yoke by the stop 310 the "low" indication is visible
through the side window~ If the rocking bellows 266
becomes punctured by the blade 314 or the point 316 as a
result of an abnormally high pressure within the switch,
the stop 310 becomes engaged by the yoke 260 as a result
of the ensuing low pressure condition and the "low"
indication will be visible through the side window.
Alternatively, a plurality of indicia of khe
"normal" and "low" pressure conditions can be provided
the indicia sirnultaneously visible through a window
array for increasing the visibility of the indication.
A visual indication of the position of the contact
assernbly 219 is provided through a top window 322 in the
cover 276. A position indicator 324 having appropriate
"open" and "closed" labels is connected to the cap 320
and biased against the top window by a clip 326.
Remote indications of pressure and contact position
conditions can be provided by means of conventional
~s~
- 25 - MP931
switches (not shown) which can be actuated by the cap
320 and the position indicator 324 respectively.
A molecular sieve 328 is retained within a holder
330 by a screen 332. The insulating liner 242 holds the
screen in place to retain the molecular sieve with the
holder against the load bushing 214. The small size of
the switch 205 results in a high ratio of surface area
to volume within the housing 210; therefore, a substan-
tial concentration of undesirable moisture from the
internal surfaces can be present after the switch 205 is
sealed. The molecular sieve 328 attracts moisture from
within the housing 210 and gas contaminates generated by
wear and/or arcing within the switch. The insulating
liner 242 is held against the screen by a liner stop
334, which is fastened to the collar 312. An auxilliary
molecular sieve 329 can be retained under the collar 312
by a pair of tabs 335 on the liner stop 33l1.
33~
A bracket ,,l~ is welded to the housing to permit the
switch 205 to be located by a channel 336 fastened to
the bracket ~ by a pair of screws 338. The channel
336 can be used to support the switch 205 and/or locate
additional switches according to this invention parallel
to the switch 205, for example, to form an assembly of
three single-phase switches. A bar 340 extending
through the handles 280 of the switches 205 can operate
each of the switches simultaneously to disconnect the
phases in a 3-phase configuration. The screws 338 can
be used to electrically connect the housing 210 to
ground. A shield lead 342 from each of the power cables
217 is clamped under a corresponding screw 338.
The switch 205 is equipped with electrodes for capa-
citive detection at relatively low voltage both high
voltage energization of the switch conductors and the
~2S~
- 26 - MP931
open or closed position of the contacts. The insulating
liner has a first conductive band 350 and a second con-
ductive band 352 deposited in contact with the annular
space 245 axially positioned proximate to the arcing
contact 226 and the transfer contact 224 respectively.
On the conductive bands 350 and 352 are soldered
corresponding first and second spring clips 3511 and 356
engaging first and second terminals 358 and 360. The
first and second terminals 358 and 360 are insulatingly
hermetically sealed within respective first and second
nipples 362 and 364 by corresponding f'irst and seeond
bushing plugs 366 and 368. The first and second nipples
362 and 364 protrude~the housing 210 and are her-
metically fastened thereto with solder. F`irst and
second threaded caps 370 and 372 engaging respective
first and second nipples 366 and 368 ean be provided for
protecting the terminals 358 and 360 when not in use.
Whether used singly or in combination the switeh 305
is sufficiently light and compaet to be supported by the
power cables 217 connected to the supply current rod
216 and the load current rod 218, if desired.
In operation, movement of the handle 280 away from
the housing 210 eauses the detent arm to rotate,
eompressing the overcenter spring 292 until the detent
arm 286 is in line with the striker 288. Continued
operation of the handle results in rapid rotation of the
bridge rocker 270 by the striker 288 to generate a snap
aetion of the piston 222 and the contact assembly 219
from (a) the closed position to (b) the open position
regardless of the speed of operation of the handle 280.
Conversely, movement of the handle 280 toward the
housing 210 causes the piston 222 and the eontact
assembly 219 to snap from (b) the open position to (a)
the closed position regardless of the speed of operation
of the handle 280.
~Z~3~8~
- 27 - MP931
When the contact assembly 219 snaps from (a) the
closed position to (b) the open position, the ends 221
of the contact rods 220 are displaced from contact from
the arcing contact 226. This results in an arc being
drawn between the contact rods 220 and the arcing con-
tact 226 when a load current is present in the switch
205. The rapid motion of the piston 222 generates a
flow of insulating gas through the holes 230 in the
piston 222, the gas being directed around the first ends
221 of the contact rods 220 and through the nozzle 232
to quench the arc. The flow of gas increases the
pressure within the piston cup 231, holding the check
valve 234 closed against the piston cup confining all
gas flow to the nozzle 232.
The increased pressure within the piston cup 231
caused by the flow of insulating gas through the nozzle
232 tends to stabilize the velocity of the contact
assembly 219 to assure a continued flow of insulating
gas through the nozzle 232 during a current reversal
following separation of the contact rods 220 from the
arcing contact 226 a distance sufficiently great to
preclude arc regeneration. The volume of insulating gas
downstream of the nozzle 232 within the housing 210,
including the volume of the annular space 245, being
larger than the rernaining volume of insulating gas
within the housing 210t provides for expansion of insu-
lating gas having been heated by the arc without
excessivly increasing back pressure at the nozzle.
The equalization of gas pressure within the housing
210 downstream of the nozzle 232 and within the annular
space 245 causes some flow of insulating gas through the
molecular sieve 328. Wear particles and vaporization
products present in the insulating gas are directed
. .
:~2~:i3~8~
- 28 - MP931
toward the molecular sieve 328 where they are trapped as
a result of gas flow through the molecular sieve 328 and
because of the attracting properties of the molecular
sieve 328.
Additional wear particles and vaporization products
are attracted to the auxilliary molecular sieve 329.
When the switch 205 is operated to connect a 1Oad by
movement of the contact assembly 219 from (b) the second
position to (a) the first position, the check valve 234
opens by sliding on the valve pins 235 away from the
holes 233 in the pistGn cup 231, thereby relieving
pressure in front of the advancing piston cup 231 to
allow a more rapid snap movement of the contact assembly
219 from (b) the second position to (a) the first posi-
tion for preventing arcing as the first ends 221 of the
contact fingers 220 engage the arcing contact 226.
When the arcing contact 226 or the transfer contact
224 ar energized with an alternating current voltage, a
corresponding voltage can be measured at the
corresponding first or second terminals 358 or 360. A
voltage of 15KV at either the arcing contact 226 or the
transfer contact 224 results in a voltage of approxima-
tely 225 volts being coupled to the corresponding first
or second conductive band 350 ir 352, thus the presence
of a high voltage at either contact can be detected by
conventional equipment connected to the corresponding
terminals 358 and 360. Should the voltages measured at
the first and second terminals 358 and 360 indicate that
one contact is energized while the other is not, a
further indication of the contact assembly 219 being in
the open position is provided.
In case the arcing contact 226 and the transfer con-
tact 224 are shown by these measurements to be in the
:~53~34
- 29 - MP931
same condition (both energized or both unenergized) a
high frequency current source can be connected to one of
the first or second terminals 358 or 360 to determine
the position of the contact assembly 219 as described
above.
~. .. .
