Tools – Wrench – screwdriver – or driver therefor – With elongated hot line stick
Reexamination Certificate
2001-03-14
2002-09-24
Meislin, D. S. (Department: 3723)
Tools
Wrench, screwdriver, or driver therefor
With elongated hot line stick
C294S019200
Reexamination Certificate
active
06453776
ABSTRACT:
TECHNICAL FIELD
This invention pertains to a tool for venting the cuff area of a separable loadbreak connector to reduce the likelihood of flashover upon separation of the connector's male/female components
BACKGROUND
High voltage cables to padmount transformers, reactors, and other underground power distribution apparatus make use of several types of removable connectors referred to as “separable insulated connectors”. The requirements and constructional dimensions of such connectors are specified in ANSI/IEEE Standard 386, Separable Insulated Connector Systems for Power Distribution Systems Above 600 V. Connectors that can be removed while the apparatus remains energized are referred to as “loadbreak connectors”. The advantage of a load-break connector is that it permits minimizing the number of customers who will be without power while maintenance is in progress by selectively de-energizing individual pieces of apparatus rather than a whole section of line.
FIG. 1
depicts one type of loadbreak connector
10
for electrically conductively coupling cable
12
to apparatus
14
. Connector
10
consists of female elbow portion
16
, male bushing insert
18
and bushing well
20
. As is well known to persons skilled in the art, other types of loadbreak connectors (not shown) may utilize a non-field-replaceable integral bushing instead of a bushing insert; or, a female component such as a parking stand and feedthrough mated to a male elbow; or, an alternative male type cuffed component such as a cap; or, alternative male-female tee connector components. In all cases, the male component has a cuff such as cuff
44
shown in FIG.
1
. Elbow portion
16
includes a grounding wire
21
, an operating eye
22
, and a test point
24
having a removable cap
26
. A compression lug
28
within elbow portion
16
is mechanically and electrically conductively coupled between cable
12
and probe
30
. Bushing well
20
is mounted on apparatus
14
such that connection pin
32
extends within tapered cavity
34
of bushing well
20
. A mating tapered portion
36
of bushing insert
18
having a threaded aperture
38
is fitted within cavity
34
, and connection pin
32
is threaded into aperture
38
. The opposed tapered portion
40
of bushing insert
18
is fitted within mating tapered aperture
42
in elbow portion
16
and sealed by fitting cuff
44
over shoulder
41
of bushing insert
18
, such that probe
30
makes electrical contact with connection pin
32
through aperture
38
and other internal connecting mechanisms (not shown). In operation, internal portions of loadbreak connector
10
including compression lug
28
, probe
30
, tapered portions
36
and
40
, aperture
38
and pin
32
are at high voltage relative to the external housing or shield portions
46
,
48
of loadbreak connector
10
, which remain at ground potential.
Loadbreak connector
10
is conventionally opened (by a qualified, trained operator) by coupling an insulated tool known as a “hotstick” (sometimes alternatively called a “hammer stick”, “impact stick”, lever stick”, “universal grip-all” or “shotgun stick”), to operating eye
22
then pulling on the hotstick to separate elbow portion
16
from bushing insert
18
. As elbow portion
16
begins to move away from bushing insert
18
, partial vacua are created inside aperture
42
until elbow portion
16
has moved sufficiently far away from bushing insert
18
to allow such partial vacua to vent to the ambient air. Such partial vacua can be detrimental to the strength of the high voltage insulation in loadbreak connector
10
. More particularly, weakening of the insulation, either directly or indirectly attributable to such partial vacua, is thought to be responsible for high voltage flashovers which sometimes occur along the operating interface comprising tapered portion
40
of bushing insert
18
and the mating tapered aperture
42
in elbow portion
16
. Besides posing a safety hazard to personnel working with loadbreak connectors, flashovers can cause considerable equipment damage and consequential equipment outage time. It is accordingly desirable to eliminate or minimize these partial vacua so as to eliminate or minimize potential flashovers.
The prior art has addressed the problem of partial vacua and flashovers in a variety of ways. One approach, exemplified by U.S. Pat. No. 5,957,712 Stepniak (believed to be marketed under the trademark Elastimold™ by Thomas & Betts Corporation, Hackettstown, N.J.) has been to provide slots in the shoulder of the bushing insert to vent a cavity formed between the elbow cuff and the transition shoulder portion of the bushing insert with ambient air. According to Stepniak, this avoids a decrease in pressure within the connection region and avoids a decrease in the dielectric strength of the air therein, thus preventing flashover. Alternatively, the elbow portion of Stepniak's connector includes an insulative layer covering a portion of the probe to increase the distance between the energized electrode and ground; or, an insulative layer is provided within the elbow's aperture.
Another prior art approach, exemplified by U.S. Pat. No. 5,857,862 Muench et al. has been to provide a semi-conductive insert which includes an additional volume of air which surrounds energized portions of the connector's elbow or cap. During separation, the semi-conductive insert stretches, increasing the volume of the interior space between the elbow (or cap) and the bushing. According to Muench et al., the additional volume of air lessens the reduction in pressure during separation so that the dielectric strength of the air surrounding energized portions of the elbow (or cap) is maintained at a higher level. The increased dielectric strength of the air is said to significantly reduce the possibility of a flashover occurring during separation of the elbow (or cap) from the bushing.
Yet another prior art approach, exemplified by U.S. Pat. No. 5,846,093 Muench, Jr. et al. has been to line the elbow with an elastic insulator. When the elbow and bushing are connected, a cavity is formed there-between. A rigid member prevents the connector from stretching substantially when the elbow and bushing are disconnected. According to Muench, Jr. et al., because the connector is prevented from stretching, the air pressure in the elbow-bushing cavity remains relatively high during disconnection. The dielectric strength of the air in the cavity, which is a function of pressure, is said to also remain high, so that the possibility of flashover is substantially eliminated.
U.S. Pat. No. 5,655,921 Makal et al. addresses the flashover problem in a variety of ways. In one aspect, exposed conductive portions of the male connector are supplemented with insulated portions such that energized points on the energized connector are placed a greater distance away from the nearest ground plane on the complementary connector. The additional insulation is said to compensate for reductions in dielectric strength of the air occurring during separation of the male connector from the female connector. The bushing's semi-conductive ground shield (i.e. depicted at
46
,
48
in the case of loadbreak connector
10
shown in
FIG. 1
) is also supplemented by an insulating sleeve, which is said to effectively remove a common ground plane to which an arc might tend during a flashover. In another aspect, a substantial airtight seal is prevented between elastomeric seals of the female connector and the probe of the male connector. The connection being thus vented, the available volume of air surrounding the energized components of the connector assembly is increased. The probe portion of the elbow is configured to prevent substantial sealing between the connector components. An annular reduced diameter recess is located between the probe's metal rod and its arc follower (i.e. the tip portion of probe
30
shown in
FIG. 1
) and is elongated to prevent substantially airtight sealing between the elbow and bushing during the initial stages of the loadb
Beattie Jay Earle
Skoropad Walter David
Meislin D. S.
Oyen Wiggs Green & Mutala
Saskatchewan Power Corporation
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