Note: Descriptions are shown in the official language in which they were submitted.
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This application is a Division of Canadian
Application Serial No. 220,790, filed February 24, 1975.
This invention relates to instrument -transformers
and more particularly to dry-type instrument transformers
with potential taps and to connector modules mating with
such potential taps.
In the metering and control art it is well known
to use instrument transformers such as potential
trans~ormers and current transformers to isolate high
voltage circuits and provide a means of transforming
voltage or currents to values that are convenient to
measure or use in control circuits~ In the metering art,
it is often desirable to interconnect current transformers
and potential transformers to obtain desired values for
metering. In such interconnecting, it is necessary to
provide a potential connection between the high voltage
terminal of the current transformer and the high voltage
terminal of the potential transformer. With present day
dry-type instrument transformers the connection between
such high voltage terminals is often made by means of
clamp type connections which must be tapped or otherwise
shielded to eliminate dangerous potentials. With the
advent of dead-front connections and pad mounted equipment,
it is considered desirable to provide dry-type irlstrument
transformers with potential taps whereby such transformexs
may be interconnected for metering applications while still
maintaining the dead-front connections. Also, for mounting
in enclosed spaces, it is desirable to provide ground shield5
or coatings on the surfaces of the dry-type instrument
tranS~ormerS to eliminate any high volt~e gr~dient on
such sux~aces. As Will be apparent~ such ~round shields
Will reduce the danger of electrical shock and allow smaller
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metering enclosures.
It is therefore a primary object of this
invention to provide potential taps for dry-type instrument
transformers.
A further object of this invention is to provide
potential taps for dry-type instrument transformers which
are recessed in the insulation body of such instrument
transformers.
A still further object of this invention is to
provide potential taps recessed into the insulation body of
dry-type instrument transformers and a connector module
which will make dead-front electrical connection with such -~
potential taps.
A still further object of this invention i5 to
provide elbow-type connector modules having electrical
conductors for mating with recessed potential taps o~ dry-
type instrument transformers.
A still further object of this invention is to
provide dry-type current and potential transformers, each
having recessed potential taps and a pair of elbow
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connector modules for interconnecting the transformers for
metering application.
Briefly, in one form this invention comprises
dry-type instrument transformers having a well in the
insulation body of such transformers. The well provides a
potential ~ap and recessed within the well is an electrical
terminal which is connected to the high voltage winding
of the instrument transEormer. A connector module is -
provided for inser-tion into the well and making electrical
connection to the recessed terminal within such ~ell~ ~
g~ound coating is pro~ided on the surface o~ thé ~nstrument
txan~ormer ~s well ~s on the connector module and such
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coatings are electrically connected when the connector
module is in place in the well.
According to another feature of this invention,
a dry-type current and potential transformer each having
recessed potential taps are interconnected for metering
applications by a pair of connector modules which are
electrically connected together and electrically connected
to the potential taps.
The invention which is sought to be protected
will be particularly pointed out and distinctly claimed in
the claims appended hereto. However, it is believed that
; this invention and the manner in which its objects and
advantages are obtained as well as other objects and
advantages thereof will be more fully understood by
reference to the following detailed description of a
preferred embodiment, particularly when considered with the
accompanying drawings.
Figure 1 is a perspective view of a current
trans~ormer and a potential transformer interconnected for
2Q a meteriny application according to the preferred form o~
this invention;
Figure 2 is a top ~iew on a reduced scale of the
curxent trans~ormer and potential transformer o~ Figure 1
showing the connector modules in an exploded view from the
trans~ormers;
Figure 3 is a partial sectional view on an
.
, enlaxged scale taken along the line 3-3 o Figure 1 showin~ -
'' the preferxed embodiment of the potential tap and a portion ; ~ -
' of the connection module o~ this invention;
- 3~ Figure 4 is a plan view of a sleeve member used
in the potential tap according to the preferred embodiment '~
of this invention;
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Figure 5 is a ~iew similar ~ Figure 4 showing
the use of a reinforcement according to this invention;
Figure 6 is a partial sectional view showiny the
ground shield and its grounding according to the preferred
embodiment of this invention; and
Figure 7 is a plan view oE the preferred form of
connector module according to this invention.
This invention disclosed dry-type instrument
transfQrmers suitable for interconnection in metering
10 applications with dead-front type connections. In referring
to the drawing~, like numerals will be used to indicate
like parts throughout the various views. Considering first
Figures 1 and 2, a dry-type current transformer 10 and a
dry-type potential transformer 12 are shown interconnected
by connector modules 14 and 16, respectively, in a metering
applicationO The cable 18 interconnects modules 14 and 16 in
the manner shown. The current transformer 10 is shown as
provided with standard elbow connector modules 20 and 22 to
provide primary energization of curxent transformer 10. Such
20 elbow connector modules are shown for example, in U.S. patent
; 3,763,461 issued October 2, 1973 to General Electric Company.
A potential tap 24 is provided in current transformer 10
connected internally to the primary or high voltage winding or
terminal (not shown), which is energized by the el~ow 22, as
is indicated by dotted lines 26 in Figure 2. As will be under-
stood, male connector 28 of connector module 14 electrically
connected to the conductor of potential tap Z4 of the
current transformer 10 while the male connector 30 of
.
connector module 16 electrically connects to the conductor
of potential tap 32 of potential transformer 12 as will
be more fully discussed hereafter. The conductor of
potential tap 32 is connected to the high voltage winding
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(not shown) of potential ~ransformer 12. When used ~or
metering line to ground, the grounded neutral terminal of
potential transformer 12 is connected to the baseplate 34
by ground strap 36, as shown. Obviously, a second potential
tap can be provided in potential transformer 12 when it is
desired to meter line to line.
In the preferred embodiment, the surfaces of
both the current transformer 10 and the potential
transformer 12 are provided with a low resistance conductive
ground shield. Preferably, a low resistance conductive
elastomer such as EPDM is used. The elastomer is sprayed
on the surfaces of the transformers and is then cured to
form a strong bond with such surfaces and also to develop
its maximum physical properties. In Figure 6 the conductive
ground shield or coating is indicated as 38, while the
transformer insulation is shown as 40. The shield 38 is
effectively grounded by bonding to a large area of the
baseplate, such as baseplate 34, as shown in Figure 6.
The preferred form of potential tap is best seen
in Figure 3 of the drawings. While the descxipti~n ~ill be
related to potential transformer 12, it will be ~nderfit30d
that the potential tap 24 of current transformer 10 is
of like construction. As shown in Fi~ure-3. a tapered well
42 is foxmed in insulation 40, which forms the body o~
potential transformer 12. In the pre~erred embodi~ent
shown, the well 42 is ~ormed by an epoxy sleeve 44 which
is pre-molded (see Figure 4) and then molded into the
insulation 40 of potential transformer 12. The epoxy
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sleeve 44 is preferred since it provides dimensional
stability to the well 42. Obviously, the well 42 could
be molded directly in the insulation 40 if desired.
However, as above noted, the epoxy sleeve 44 is preferred.
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The epoxy sleeve 44 is preferably molded with a groove
46 which aids in locking the sleeve 44 in the insulation
40 as is clearly apparent from Figure 3. When sleeve 44
is used, the exterior surface down to groove 46 is coated
with a conductive coating 48 to reduce electrical stress
between insulation 40 and sleeve 44. A female terminal 50 ~-
is provided in potential txansformer 12 at the base of the
well 42. As will be understood, the terminal 50 is
connected to the high voltage winding (not shown) of the
potential transformer 12. A depression 52 is formed in the
inner end o~ sleeve 44, the depression 52 receiving the end
of ~emale terminal 50, as shown. In the preferred form, a
conductive coating 54 is applied to such depression to help
reduce the voltage stress in this area.
In a modi~ied form of sleeve 44, a metal rein-
forcing member 56 is provided on the outer surface as
shown in Figure 5. Reinforcing member 56 is in the form of
a metal ring fitting tightly over the outer suxface of
slee~e 4~. The ring 56 ma~ be of any desired metal, although
brass is presently preferred. The ring 56 prevents
cracking o~ the end o~ sleeve 44 when the transformer is
subjected to rough handling.
A special elbow connector module 60 is used with
the potential tap as can be seen from Figure 3. The elbow
connector module 60 is best shown in Figure 7 of the
drawings. The elbow connector module 60 is molded from an
elastomeric material such as EPDM. It is provided with a
male con~uctor 62 which makes electrical contact with the
female terminal 50 as is shown in Figure 3. In the
pre~erred form, the elbow module 60 is provided with a
tapered insulated male member 64 which closely surrounds
the male conductor 62. As is apparent fxom Figure 3, the
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insulating member 64 fits tightly in well 42 providing
a substantially watertight seal. Conductor 62 is provided
with a locking ring 66 which locks into the female
terminal 50. Also pro~ided is an indicating member 68
formed on the insulating member 64 which will fit against
the outer edge of well ~2 when the conductor 62 is properly
seated in female terminal 50. As is shown, a ground coat
70 covers the outer surface of elbow module 50 and extends
slightly below the indicating member 68. This will ensure
a good conducting contact with the ground coat 38 on the
transformer. The elbow 60 also includes a conducting insert,
a cable entrance, a pulling eye and the like. However,
these elements are standard with elbow modules of the
prior art (see for example U.S. patent 3,539,972 issued
November 10, 1970 to ~ueteet al~ and will not be further
described.
From the above, it will be apparent that by means
of this invention there is provided dry-type instrument
transformers which may be readily interconnected in meter~
ing applications to provide dead-front ~ype connections.
~ile there has been shown and described the present
preferred embodiment of the invention, it will be apparent
to those skilled in the art that various modifications may
be made without departing from the spirit and scope of the
invention, especially as defined in the appended claims.
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