Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: ELECTRICAL PLUG
TECHNICAL FIELD
The present invention relates to an electrical plug.
The invention has been primarily developed for medium to high voltage and/or
medium to high current multi-core power supply cables such as those used in
the
underground mining industry and will be described hereinafter with reference
to that
application. However, it will be appreciated that the invention is not limited
to that
particular field of use.
Known electrical plugs for power supply cables used in underground mines have
1 o generally included an axially extending cylindrical body which is
configured at one
end for insertion into a complimentary receptacle having a number of connector
pins.
The other end of the body is configured to receive a mufti-core cable. Within
the body
the ends of the cable cores are electrically connected to respective internal
contacts
which, in turn, selectively electrically engage with the connector pins within
the
15 receptacle.
As it is necessary to insulate the ends of the various cores in the mufti-core
cable
from each other the body generally includes a one piece moulded insulator
which
surrounds the internal contacts and allows them to contact only a respective
connector
pin. An example of a known electrical plug is illustrated in Figures 1 and 2
and will
2o be described below in more detail.
The known plugs are particularly disadvantageous as they are heavy and the
insulator is prone to damage and is difficult to replace without at the same
time
replacing all the internals df the body. In a mine environment where operating
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conditions are harsh the known plugs are particularly undesirable as they are
expensive to maintain in safe working condition.
DISCLOSURE OF THE INVENTION
It is an object of the present invention, at least in the preferred
embodiment, to
overcome or substantially ameliorate this disadvantage of the prior art.
According to a first aspect of the invention there is provided an electrical
plug
including:
a body extending between a first end and a second end which are respectively
configured for insertion into a corresponding receptacle and receiving an
electrical
1 o cable having one or more cores; and
at least one tubular insulator, the or each insulator having a connector for
receiving at one end the respective ends of the one or more cores and at the
other end a
respective connector pin within the receptacle to allow releasable electrical
connection
between the cores and the connector pins.
15 Preferably, the plug includes:
a first and a second plate respectively located at or adjacent the first end
of the
body and intermediate the first and second ends of the body, both plates
having a
plurality of apertures which align with respective ones of said insulators;
and
retention means extending between said plates for captively retaining the
2o insulators therebetween.
Preferably also, the retention means includes a member extending through the
cavity. More preferably, the member is a phase barner. Even more preferably,
the
member is tensioned.
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In a preferred form, the or each tubular insulator is cylindrical.
Alternatively,
the or each insulator has a square cross section.
Preferably, in circumstances where a plurality of insulators are used they are
equally angularly spaced within the cavity.
Preferably also, the or each insulator is surrounded by a respective
additional
tubular insulator. More preferably, the or each insulator is separated from
the
additional insulator by an air gap.
In a preferred form the connectors are disposed wholly within the respective
tubular insulators.
t 0 According to another aspect of the invention there is provided an
electrical plug
including:
a body extending between a first end and a second end which are respectively
configured for engagement with a complementary electrical plug and receiving
an
electrical cable having one or more cores;
~ 5 one or more connectors for receiving at respective first ends the one or
more
cores and at respective second ends a connector formation associated with the
complementary plug to allow releasable electrical connection between the cores
and
the connector formations; and
one or more insulating sheaths extending about respective ones of the one or
20 more connectors for electrically isolating the connectors from each other.
Preferably, the connectors are metallic and the sheaths are plastics sleeves.
In
other embodiments the sheaths are defined by a layer of ceramic material which
is
deposited on the outside of the connector.
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Preferably also, the body includes a solid conductive core. More preferably,
this
core is generally cylindrical and includes a plurality of spaced apart
parallel axially
extending passages through which the respective insulating sheaths extend.
More
preferably, the core is earthed. Even more preferably, the core is metallic.
BRIEF DESCRIPTION OF~'HE DRAWINGS_
Some preferred embodiments of the invention will now be described, by way of
example only, with reference to the accompanying drawings in which:
Figure 1 is an end view of a known electrical plug;
Figure 2 is a cross section taken along line 2-2 of Figure 1;
Figure 3 is an end view of an electrical plug according to the invention;
Figure 4 is a cross section taken along line 4-4 of Figure 3;
Figure S is an end view of an alternative electrical plug according to the
invention;
Figure 6 is a cross section taken along line 6-6 of Figure 5;
t 5 Figure 7 is an exploded cross sectional view of the plug of Figure 6;
Figure 8 is an end view of another electrical plug according to the invention;
Figure 9 is a cross section taken along line 9-9 of Figure 8; and
Figure 10 is a cross sectional view of an adaptor for the plug of Figure 8;
Figure 11 is an exploded cross sectional view of the plug of Figure 9.
2o MODES FOR CQR_RYINCT OUT THE INVENTION
Reference is made to the prior art electrical plug 1 of Figures 1 and 2. The
plug
includes a generally cylindrical body 2 extending between a first end 3 and a
second
end 4 which are configured respectively for insertion into a corresponding
receptacle
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(not shown) and receiving a multi-core electrical cable (not shown). As is
well known
to those in the art, mufti-core cables generally include three equally spaced
apart
medium or high voltage mains conductors and one or more pilot cores for
carrying
communication signals. Body 2 includes a single piece moulded interior
insulator 5
s which extends from end 3 and terminates at end 6, which lies intermediate
ends 3 and
4. Insulator 5 surrounds two differently sized sets of three connectors 7 and
8 which,
at one end, receive the cores of the cable and, at the other end, receive the
connector
pins that are located within the receptacle. Accordingly, electrical
connection is
selectively provided between the cores in the cable and the connector pins
within the
1 o receptacle. One such receptacle is described and illustrated in Australian
Patent
Application No. 21600/95, the disclosure of which is incorporated herein by
way of
cross reference.
The end of the cable is received in an aperture 9 at end 4 of body 2 and
subsequently secured by clamping means 10. The cores of the cable are
separated in
t 5 internal chamber 11 and inserted into respective cylindrical bores 12 in
insulators 5
and secured to connectors 7 or 8, as appropriate.
Connectors 7 and 8 each include at one end a thimble 13 for receiving the free
end of a respective cable core, as is known to those skilled in the art. The
end of the
core is soldered or otherwise connected to thimble 13. Each connector also
includes,
2o at its other end, a socket 14 for receiving a respective connector pin
located within the
receptacle. That is, the connector pins are received into engagement with
respective
sockets 14 when plug 1 is inserted into the receptacle. The respective pairs
of thimble
13 and contact 14 are maintained in abutting electrical engagement by bolts
15.
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Insulator S also encases a phase barrier 16 which is a centrally located metal
structure having three legs which extend radially outwardly between adjacent
mains
conductors. Barrier 16 is earthed via lead 17 and reduces the risk of phase to
phase
faults. In alternative embodiments barrier 16 includes a different number of
legs.
Referring now to Figures 3 and 4, there is illustrated an electrical plug 21
according to the invention. The features of plug 21 which correspond with
those of
plug 1 are denoted by corresponding reference numerals.
Plug 21 includes six equally angularly spaced axially extending tubular
insulators 22 which, best shown in Figure 4, have a central internal annular
ridge 23
1 o against which thimble 13 and socket 14 are collectively secured by the
operation of
bolt 15. It will be appreciated that thimble 13 and socket 14 provide the same
function
as described above with respect to prior art plug 1.
Although in this embodiment insulators 22 are made from polyester, other
insulating materials are used in other embodiments, for example, rubber,
reinforced
15 resin or ceramics. Moreover, in very high voltage applications each
insulator 22
extends within a co-axially disposed additional insulator (not shown) to
ensure greater
electrical isolation between the cores and connectors 7 and 8. Preferably, the
internal
diameter of the additional insulator is sufficiently greater than the external
diameter of
insulator 22 to provide an air gap therebetween.
2o Each insulator 22 includes at opposed ends annular shoulders 25 and 26 for
abutting a complementary formation to retain the insulators in a fixed
configuration
with respect to body 2. At end 3 of body 2, that complementary formation is
defined
by the combination of a circular apertured plate 27 and an annular lip 28
which
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inwardly extends from end 3. Plate 27 includes a plurality of apertures which
receive
the ends of insulator 22, whereby plate 27 abuts against shoulder 2S.
At the other end of insulators 22, the complementary formation is defined by a
circular plate 29 which includes apertures corresponding to those in plate 27.
These
apertures in plate 27 interact similarly with shoulders 26 of the insulators.
Both plates 27 and 29 are secured to body 2 by way of circumferentially spaced
rivets 30. Moreover, these plates are structural members and provide
additional
strength to plug 21 and, accordingly, increase the useful lifetime of the
product.
Moreover, plug 21 provides this additional strength while being lighter than
the prior
t o art plug 1.
In this embodiment barrier 16 is also a structural member being engaged at
opposed ends 31 and 32 by respective plates 27 and 29. The plates are forced
toward
each other and into clamping engagement with insulators 22 by the action of
bolts 33
which are threadedly engaged within complimentary bores in barrier 16.
In other embodiments only the cores in the cable carrying supply voltages are
within insulators 22, the pilot lines being of sufficiently low voltage that
the
intermediate air gap is adequate to prevent arcing therebetween.
In some embodiments, once the cable is installed within cavity 11, that cavity
is
filled with an expandable compound via a filling aperture (not shown). The
2o compound stress relieves the cable termination and reduces the possibility
of water
ingress from outside the cable and plug, or through water entrapment within
the cable
(a function of the cable manufacturing process).
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Plate 27 is produced from a metal or hard plastics material and, accordingly,
is
resistant to damage from inadvertent contact with other objects. In the event
plate 27
is damaged it can be easily replaced.
Reference is now made to an alternative electrical plug 41 according to the
invention which is illustrated in Figures 5, 6 and 7. Where appropriate
corresponding
features have been denoted by corresponding reference numerals. More
particularly,
plug 41 includes a body 2 which extends between a first end 3 and a second end
4.
These ends 3 and 4 are respectively configured for engagement with a
complementary
electrical plug (not shown) and receiving an electrical cable (not shown)
having four
1 o cores. Plug 41 also includes four spaced apart connectors 42 for receiving
at
respective first ends 43 the cores and at respective second ends 44 a
connector
formation associated with the complementary plug to allow releasable
electrical
connection between the cores and the connector formations. Four insulating
sheaths
45 extend about respective connectors 42 for electrically isolating connectors
42 from
~ s each other.
Connectors 42 are metallic and, as plug 41 is intended for low to medium
voltage applications, sheaths 45 are plastics sleeves. In higher voltage
applications,
sheaths 45 are defined by a layer of ceramic material which is deposited on
the outside
of connectors 42. This arrangement effectively eliminates any air gap between
the
2o connectors 42 and the respective surrounding insulating sheaths 45 and
thereby
prevents corona discharge about those connectors.
Body 2 includes a generally cylindrical solid conductive nose cone 46 which
extends along an axis 47 and which has four spaced apart parallel axially
extending
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passages through which sheaths 45 extend. In this embodiment cone 46 is both
metallic and earthed. Accordingly, cone 46 functions not only as a mechanical
support for plug 41 but also as a phase barrier.
Cone 46 includes, at one end, shoulders 48 which extend across the periphery
of
the adjacent passages to provide an abutment for one end of sheaths 45. Cone
46 also
includes, at its other end, a removable end cap 49 which also extends across
the
periphery of the passages to provide an abutment for the other ends of sheaths
45. The
combination of shoulders 48 and cap 49 captively retains sheaths 45 within
cone 46.
In this embodiment, cap 49 is retained to cone 46 by a bolt 50 which is offset
1 o from the passages. In other embodiments different attachment means are
used.
Body 2 includes a hollow cylindrical housing 51 which extends along axis 47
between a first end 52 and a second end 53 which are respectively threaded
internally
and externally. End 52 also includes an abutment formation 55 for receiving a
coupling nut 56. Moreover, cone 46 includes an abutment formation 57 and an
external thread 58. When thread 58 is engaged with end 52, as shown in Figure
6, nut
56 is captively retained between formations 55 and 57 for rotation about axis
47. Nut
56 includes an internal thread 59 for selectively engaging with a
complementary
thread of the electrical plug or receptacle.
End 53 is received within the complementary internally threaded end 65 of a
2o backnut 66. Sandwiched between end 53 and backnut 66 is a rubber grommet 67
and
a washer 68. As will be appreciated by those skilled in the art, as the
threaded
engagement between backnut 66 and end 53 is increased, grommet 67 is
compressed
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and therefore moves into a more intimate sealing and clamping engagement with
the
cable extending into housing S 1.
Another electrical plug 71 according to the invention is illustrated in
Figures 8
to 11 where, for convenience, corresponding features are denoted by
corresponding
reference numerals. In this embodiment plug 71 includes connectors 72 having
four
spaced apart axially extending pins 73 for engaging within complementary
apertures
of an adjacent plug, such as plug 41. Connectors 72 are housed within sheaths
4S and,
as such, are insulated from each other. Moreover, the connector and sheath
combinations are located within respective axial passages of a generally
cylindrical
conductive former 75. Former 75 is threaded to a tubular first and second body
portions 76 and 77 and functions similarly to nose cone 49.
Plug 71 also includes a second tubular body portion 81 which extends between a
first end 82 and an axially spaced apart second end 83. End 83 is, in use,
captively
engaged with a respective backnut 84, washer 85 and grommet 86, similarly to
end 53
of housing 51.
Former ?S includes a shoulder 91 adjacent one end, and an end cap 92 adjacent
the other end, for providing opposed abutments for sheaths 45. These abutments
retain sheaths 45 and connectors 42 within the passages in former 7S.
Preferably, cone 46 and former 75 are cast from copper and machined to include
2o the respective passages.
A plug produced in accordance with the preferred embodiments of the invention
offers a more durable and cost effective product which provides the necessary
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insulation between the cores at a weight significantly less than corresponding
prior art
plugs. By way of example, plug 21 is approximately 20% lighter than prior art
plug 1.
Although the invention has been described with reference to a particular
example it will be appreciated by those skilled in the art that it may be
embodied in
many other forms.
