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Патент USA US3059161

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Oct. 16, 1962
3,059,151
L. w. MARKS
HIGH VOLTAGE CURRENT TRANSFORMER
Original Filed July 18, 1955
2 'Sheets—Sheet 1
[rel/672751;
' Lou/'5 WMar/ra
17m #Zm
Oct. 16, 1962
|_. w. MARKS
3,059,151
‘HIGH VOLTAGE CURRENT TRANSFORMER
Original Filed ‘July 18, 1955
2 Sheets-Sheet 2
United States Patent 0 "ice
2
1
3,059,151
3,059,151
Patented Oct. 16, 1962
is comprised of an open turn of a tubular conductor and
the leads joining the turn are comprised of a longitudi
.
nally split straight tubular conductor.
HIGH VOLTAGE CURRENT TRANSFORMER
Louis W. Marks, Pittstield, Mass, assignor to General .
Electric Company, a corporation of New York
A further object of this invention is to provide means
in a high voltage current transformer for preventing ex
cessive damage due to internal faults.
A still further object is to provide means in a current
transformer for actuating circuit breaker means for iso
lating the current transformer and adjacent power line
sections from power lines in the event of internal failure
in the current transformer and also to isolate adjacent
Original application July 18, 1955, Ser. No. 522,416, now
Patent No. 2,947,958, dated Aug. 2, 1960. Divided
and this application Feb. 11, 1960, Ser. No. 8,123
11 Claims. (Cl. 317—15)
This invention relates to transformers and more in
particular to an improved high voltage current trans
power line sections in the event of faults on such adja
former for circuit breaker relaying and metering. This
cent power line sections.
application is a division of my copending application,
My invention will be better understood from the fol—
Serial Number 522,416, ?led on July 18, 1955, and titled
High Voltage Current Transformer, now United States 15 lowing description taken in connection with the accom
panying drawing, and its scope will be pointed out in the
Patent 2,947,958 which is assigned to the same 'assignee
appended claims.
as this invention.
In the drawings:
FIG. 1 is a cross-sectional view of an “eye-bolt” cur
annular-shaped primary winding disposed in a dielectric
?uid ?lled tank and having leads extending upwardly 20 rent transformer embodying this invention and illustrat
ing typical connections of the current transformer in
through a high voltage bushing to a pair of terminals on
circuit breaker applications,
an upper terminal assembly. One or more annular
FIG. 2 is a perspective view of the primary winding of
shaped secondary windings are interlinked with the pri
Current transformers are frequently comprised of an
mary winding in the transformer tank, the planes of the
secondary windings being perpendicular to the plane of
the primary Winding. The primary winding is generally
25
the transformer of FIG. 1,
FIG. 3 is a perspective view of a modi?ed form of a
portion of the primary winding of FIG. 3,
FIG. 4 is a diagrammatic representation of the cur
rent transformer of FIG. 1,
FIG. 5 is a diagrammatic representation of a modi?ed
nent of the line current without appreciable voltage drop.
In transformers of this type, a tubular electrostatic shield 30 form of the current transformer of FIG. 1,
FIG. 6 is a diagrammatic representation of another
surrounding the primary winding for carrying the charg
modi?ed form of the current transformer of FIG. 1,
ing component of the line current extends upwardly
comprised of one or several turns of conductors, and the
conductors are adapted to carry the heavy power compo
FIG. 7 is a diagrammatic representation illustrating the
internal fault protection means of my invention as ap
leads. A layer of insulating material is disposed about the
electrostatic shield, and a grounding shield surrounds the 35 plied to a “cable-type” current transformer, and
FIG. 8 is a diagrammatic representation illustrating
insulating material and extends upwardly through the
the internal fault protection means of my invention as
bushing to surround the primary winding leads. A layer
applied to a twin “bushing-type” current transformer.
of insulating material is disposed about the electrostatic
Brie?y stated, in accordance with one aspect of my in
shield, and a grounding shield surrounds the insulating
vention, I provide a high voltage current transformer of
material and extends upwardly through a portion of the
the “eye-bolt” type wherein the primary winding is com
bushing. The electrostatic shield, the insulating material,
through the bushing to surround the primary winding
prised of one turn of a tubular conductor and the primary
and the grounding shield separate the primary winding
winding leads connected to the ends of the primary wind
ing and extending upwardly through the transformer bush
ing are comprised of a longitudinally split tubular con
from the secondary windings. The number of turns in the
secondary winding is determined by the particular appli
cation of the transformer.
In transformers of this type considerable di?iculty is
encountered in the winding of the coil inside the electro
static shield, and the cost of such transformers is there
by increased. A further di?iculty materializes when the
transformer is used in circuit breaker applications if 50
an internal electric arc occurs between the primary wind
age to the transformer upon the occurrence of an internal
fault from the primary winding to the grounding shield.
ing and certain portions of the grounding shield. When
used in circuit breaker applications the current transform
er is generally connected such that upon the occurrence
of any fault that might cause vfault currents to circulate in
ductor. The primary winding also acts as an electrostatic
shield and thus carries both charging current and line cur
rent. My invention also provides, in a current trans
former employing two secondary windings wound on an
nular magnetic core means for preventing excessive dam
This protective means is comprised of a grounding cable
connected on one end to the grounding shield and passing
0
through both cores so as to couple inductively to the
secondary windings and thence through a terminal on the
the power lines, the circuit breakers act to disconnect
transformer to ground or to a potential device. The
the power source from the section of line having a fault.
grounding shield is provided with a gap in order to pre
However, in certain cases, if an internal fault occurs in
vent the flow of circulating currents in the shield. As
the transformer there is a possibility that the circuit
breakers would not be actuated properly and the‘ current 60 will be disclosed in more detail later, the protective cir
cuit means will not function properly unless the ground
transformer would thus not be isolated from the power
ing cable is af?xed to certain portions of the grounding
lines.
shield with respect to the gap in the shield.
It is therefore an object of this invention to provide an
Referring now to the drawings, and more in particular
improved high voltage current transformer.
to FIG. 1, therein is illustrated a current transformer 10
It is also an object of this invention to provide a high
having the primary winding 11 and a pair of secondary
voltage current transformer of the “eye-bolt” type wherein
windings 12 and 13 wound on annular magnetic cores.
the electrostatic shield serves the function of the primary
The windings 11, 12 and 13 are annular-shaped, with the
winding.
‘axis of the respective windings 12 and 13 being aligned
Another object of my invention is to provide a simpli
perpendicular to the ‘axis of the primary winding 11. The
?ed construction for the primary winding of a current 70 two secondary windings and their cores are structurally
transformer of the “eye-bolt” type, wherein the winding
interlinked with the primary winding, due to the fact that
8,059,151
3
each secondary winding passes through the hollow portion
of the primary winding. A pair of leads 14 and 15 extend
upwardly from the tank 16 in which the windings are
disposed through an insulating bushing 17, and are con
4
a power line bus from any section having a ground fault
and also for isolating the current transformer in the event
of an internal fault in the transformer. In this circuit
the current transformer 10 is connected in series with a
nected by means of conductors 18 to terminals 19 and
20 respectively positioned on a top terminal assembly 21.
The top terminal assembly 21 is a metallic chamber that
is electrically connected to the terminal 19 and electrical
ly insulated from the lead 20 by means of an insulating
bushing 22. A metallic shield 23 ‘may be provided sur
rounding the terminal 20‘ and electrically connected to
in the bus 40. One end portion 41 of the bus 40 is
connected by way of the contacts of a ?rst remote circuit
breaker 42 to a second portion 43 of the bus 40 and this
second section 43 is connected by way of the contacts of
a local circuit breaker 44 to a third portion 45 of the
the top terminal assembly.
the current transformer. The terminal 18 of the current
The structure of the primary winding may be more
clearly seen in FIG. 2 wherein it is shown that the winding
high voltage bus 40. Current may ?ow in either direction
bus 40, which is connected directly to the terminal 19‘ of
transformer is connected by way of a fourth portion 46 of
the bus 40 through the contacts of a second remote circuit
11 is comprised of a single turn of a tubular conductor 15 ‘breaker 47 to the other end portion 48 of the bus 40. A
. with the ends of the turn being separated by a short gap
remote current transformer 50 on the one end 41 of the
25. The primary winding leads 14 and 15 which are con
bus 40 adjacent the ?rst remote circuit breaker 42 is
nected to the ends of the primary winding are each one
connected in series opposition with the secondary winding
half of a longitudinally split tubular conductor. The pri
12 of the current transformer and the differential current
mary winding assembly may be formed by welding or 20 from these two sources passes through the actuating wind
otherwise electrically connecting a straight tubular con
ings of a local relay 51 and a remote relay 52. The con
ductor to the side of an annular tubular conductor in the
tacts of the remote relay 52 actuate the ?rst remote circuit
plane of the annular conductor, and then splitting the
breaker 42 by conventional means. The winding of an
straight tubular section and the annular tubular section
other current transformer 53 on the other end portion 48
along the plane perpendicular to the plane of the annular 25 of the bus 40 adjacent to the remote circuit breaker 47 is
tubular section and passing through the axis of the straight
tube. As illustrated in FIG. 2 it is preferred that the tube
from which the primary winding leads 14 and 15 are
fabricated has a larger diameter or greater wall thickness
than the. tube from which the winding itself is formed, 30
connected in series opposition with the secondary wind
ing 13 of the current transformer 10 and the differential
current from these two sources passes through the wind
ings of remote relay 54 and the local relay 55. The con
tacts of remote relay 54 actuate the second remote circuit
breaker 47 by conventional means. The contacts of local
relays 51 and 55 are connected to separate coils 56 and
A modi?cation of the primary winding of FIG. 2 is il~
57 respectively of a conventional circuit breaker trip
lustrated in FIG. 3. Here a strip 26 of semi-conducting
mechanism for actuating the local circuit breaker 44 so
material having sufficiently high resistance to prevent the 35 that closing of the ‘contacts of either or both of the relays
bypass of appreciable power current therethrough is in
51 and 55 opens the local circuit breaker 44.
serted in the gap between the ends of the primary winding
The terminal 36 may be connected to ground by way
turn and the leads 14 and 15. The semi-conducting mate
of a switch 58, in which case current passing through the
rial relieves electrostatic stress concentrations that exist in
grounding cable in the event of internal failure in the
the gaps, and thereby reduces the danger of breakdown 40 current transformer induces current in the secondary
in other parts of the transformer. As another alternative
windings 1'2 and 13 to open the circuit breakers in a
the strip 26 may be of a solid insulating material to in
manner to be more fully disclosed in the following
sure mechanical stability of the primary winding, and a
paragraphs. As an alternative, the grounding of the
in order that the leads 14 and 15 have the same conductor
cross sectional area as the primary winding.
coating of semi-conducting material may be provided on
ground cable 35 may also be accomplished by arcing
the edges of the strip 26 or a resistance tape may be wound 45 across a spark gap 59, in the event of internal failure in
on the leads 14 and 15.
the transformer.
Referring again to FIG. 1 the primary self-shielding
In order to more clearly disclose the action of the
winding 11 and primary winding leads 14 and 15 are
current transformer 10 upon the occurrence of various
wrapped in a conventional manner with an insulating ma
terial 30. A grounding shield 31 surrounds the primary
winding insulation material 30 and extends upwardly
through the lower portion of bushing 17. The grounding
shield 31 is provided with a gap 32 surrounding the pri
mary winding at one point in order to prevent the ?ow
of circulating current in the grounding shield.
An annular shield member 33 may be provided sur
rounding the top ends of the primary winding leads 14‘ and
15 in the bushing 17 or the insulated leads 14 and 15
fault conditions, the various conditions and their effect
are hereinafter described.
Assuming a power how in bus 40 from left to right
in FIG. 1, if a ground fault occurs on portion 43 of the
bus, fault current flows in the secondary winding of cur
rent transformer 50 and no fault current flows in the sec
ondary winding 12 of current transformer 10. This re
sults in the closing of the contacts of relays 51 and 52,
due to differential current and therefore the contacts of
the remote circuit vbreaker 42 and the local circuit breaker
may be extended into the top terminal assembly 21. The
44 are opened, thereby isolating the section of line having
60 the ground fault. If the ground fault occurs on line
shield '33 is electrically connected to the lead 14.
A grounding cable 35 is electrically connected to the
section 46, fault current ?ows in secondary winding 13 and
grounding shield adjacent one side of the split 32, passes
no fault current ?ows in the secondary winding of current
downwardly through the secondary winding 13 and core,
transformer 53. This results in the closing of the con
around the bottom of the primary winding, makes a single
tacts of relays 54 and 55, and therefore the opening of
loop around the secondary winding 12 and core is con 65 the contacts of local circuit breaker 44 and remote circuit
nected to a terminal 36 on the transformer wall 16.
It
is to ‘be noted that any current passing through the cable
35 passes through one of the secondary windings in the
same direction as normal current in the primary Wind
breaker 47, thereby isolating the section of line having
the ground fault. If a fault were to occur between line
section 45 and ground, an erroneous signal would occur
causing circuit breakers 42 and 44 to open their con
ings, and passes through the other secondary winding in 70 tacts. Therefore the shield 23 has been positioned sur
the direction opposite to the normal current passing
rounding the line 45, so that no fault can occur between the
through the primary winding 11. Normal current ?ow in
line 45 and ground. A ground fault on the shield appears
the primary winding may be in either direction.
as a ground fault on line section 46.
The current transformer of FIG. 1 is shown connected
Similarly, when power ?ows from right to left along
in a typical circuit breaker application for disconnecting 75 the bus 40 in FIG. '1, a ground fault on line section 46
3,059,151
5
causes the opening of the contacts of circuit breakers
44 and 47, a ground fault on line section 43 causes the
opening of the contacts of circuit breakers 42 and 44, and
6
isolation of power line section 43. In view of this, if
it is not required that the power line section 43 be iso
lated in the event of internal failure in the current trans
former ‘10, the loop of the grounding cable 35 around
the secondary winding 12 may be omitted.
A modification of the arrangement of FIG. 4 as illus
A fault involving protective equipment is serious in
trated in FIG. 5 has the gap 32 in the grounding shield
nature in that it may remove the protection from the cir
31 in the lower portion of the grounding shield between
cuit. Novel features of this transformer protect the sys
the secondary windings 12 and 13. In this modi?ca
tem in the event of internal failure of the protective
current transformer.
10 tion the four regions of possible internal faults are the
region 7%} between the grounding shield 31 above the
The protective action afforded by the grounding lead
secondary winding 13 and the lead 15 or the portion of
35 may more clearly be understood by reference to FIG.
the primary winding 11 adjacent the lead 15, the region
4, which is a diagrammatic representation of the current
71 between the primary winding 11 and the lower por~
transformer of FIG. 1. Breakdown occurring between the
leads 14 and 15 and the primary winding 11 to the ground 15 tion of the grounding shield 31 between the secondary
winding 13 and the gap 32, the region 72 between the
ing shield may be in one of four general areas. A fault
primary winding 11 and the lower portion of the ground
may occur in the region 65 between the grounding shield
ing shield 31 between the gap 32 and the secondary wind
above the gap 32 and the lead 15 or the portion of the pri~
ing 12, and the region 73 between the grounding shield
mary winding 11 adjacent the lead 15, a fault may occur
31 above the secondary winding 12 and the lead 14 or
in the region 66 between the primary winding 11 and the
the portion of the primary winding 11 adjacent the lead
grounding shield above the secondary winding 13 and be
a fault on line section 45 to the shield 23 causes the
opening of the contacts of the circuit breakers 44 and 47.
low the gap 32, a fault may occur in the region 67 be
tween the primary winding 11 and the ‘lower portion of the
grounding shield, or a fault may occur in the region 68
14.
In this modi?cation, if the instantaneous current flow
grounding lead 35 inducing a current proportional to the
twice the fault currentpbeing induced in winding 13. If
fault current in secondary windings 12 and 13, the current
in winding 12 being reverse in respect to the current nor
mally induced therein. If the fault occurs in region 66,
fault current ?owing through grounding shield 31 and the
grounding cable 35 provides a resultant induced current
proportional to twice the fault current in secondary wind
ing 13, and no resultant current in secondary winding 12.
The same effect is produced by a fault in region 67 and
the current ?ow is normally clockwise in primary wind
is counterclockwise in the primary winding 11, a fault
between the grounding shield above the secondary wind 25 in region 70 or 71 results in current proportional to the
fault current being induced in the secondary windings
ing 12 and the lead 14 or the portion of the primary wind
12 and 13, the current induced in winding 12 being in
ing adjacent the lead 14.
the opposite direction of normal current ?ow therein,
‘When the instantaneous direction of current ?ow is
and a fault in regions 72 or 73 results in no current being
counterclockwise in the primary winding 11, a fault in
region 65 results in fault current ?owing through the
induced in winding 12 and a current proportional to
region 68.
ing 11, a fault in regions 70‘ or 71 results in no current
being induced in winding 13 and a current proportional
to twice the fault current being induced in winding 12,
while a fault in regions 72 or 73 results in currents pro
portional to the fault current being induced in both sec
ondary windings 12 and 13 with the current in winding
13 being in the opposite direction to normal ?ow therein.
40 It is readily seen that the modi?cation of FIG. 5 func
When the instantaneous direction of current ?ow is
tions the same as the current transformer of FIGS. 1
clockwise in primary winding 11, a fault in region 65
results in no resultant current being induced in secondary
and 4.
In the modi?cation illustrated in FIG. 6, the ground
cable 35 is connected to the ground shield 31 above the
winding 13 and a resultant current proportional to twice
the fault current being induced in secondary winding 12.
secondary winding 12, and the cable passes downward
If the fault occurs in regions 66, 67, or 68 a resultant
current proportional to the fault current is induced in
both of the secondary windings, but the current in sec
ondary winding 13 is in the opposite directional to nor
through winding 12 downward through the winding 13,
mal flow therein.
the modification of FIGS. 1 and 4.
The protective arrangement of any invention may also
be applied to a cable type current transformer, as illus
trated in FIG. 7. This type of transformer is comprised
basically of a single loop of a cable having a central
conductor 75 surrounded by a grounding shield 76.
Secondary windings 77 and 78‘ wound on generally an
nular-shaped magnetic cores are positioned coaxial with
As previously stated, secondary windings 12 and 13
are connected in series opposition with secondary wind
ings of current transformers 53 and 50 respectively
(FIG. 1). In the case of faults occurring in each of the
regions 65, 66, 67 and 68 the currents in secondary wind
ings 12 and 13 are different from the current in the
secondary windings of current transformers 53 and 51)
respectively, since in the event of current flow from left
and thence to ground. The resulting currents induced
in secondary windings 12 and 13 in the event of internal
faults are the same in this modification as in the case of
each leg of the loop. The grounding cable 79 is fastened’
to the grounding shield 76 above secondary winding 77,
current proportional to the fault current is induced in 60 passes downward through winding 77 and thence down
ward through winding 78 to ground.
the secondary winding of current transformer 50 and
to right in bus 40 upon the occurrence of such a fault a
no current is induced in the secondary winding of current
In FIG. 8 the protective arrangement of my invention
is illustrated as applied to a pair of bushing type current
transformer 53, and in the event of ?ow of current from
right to left in bus 40 upon the occurrence of such a
transformers. This construction may also be used in a
fault a current proportional to fault current is induced in 65 transformer in a single tank, and the primary winding
the secondary winding of current transformer 53 and
may be multiturn. In this modi?cation, the central pri
no current is induced in the secondary Winding of cur
mary lead 80 of one current transformer is connected
rent transformer 50. Therefore, in the event of any in
in series with the central primary lead 81 of the other
transformer. The central lead 80 is surrounded by a
ternal fault in the regions 65, 66, 67 and 68, the con
70 ground shield 82 which is in turn surrounded by a sec
tacts of all three circuit breakers are opened.
A differential current between the secondary winding
13 and the secondary winding of current transformer 53
causes isolation of the current transformer 10, while a
ondary winding 8-3, and the central lead of the other
transformer is surrounded by a ground shield 84 which
is in turn surrounded by a secondary winding 85. A
ground cable 86 is connected to the shield 82 above the
differential current between secondary winding 12 and
the secondary winding of current transformer 50 causes 75 winding 83, passes downward through the windings 83
3,059,151
7
and 85, and thence to ground. A conductor 87 is con
nected between the upper portions of the grounding
shields 82 and 84. As an alternative the conductor may
be connected between the lower portions of the ground
ing shields 82 and 83.
From the foregoing disclosure then, my invention pro
vides means ‘for inducing a current in each of a pair of
secondary windings, such as windings 12 and 13, of a
current transformer that is of different phase or mag
3
said turn, said leads being comprised of a pair of spaced
apart sections of a longitudinally split straight tubular
conductor, insulation material surrounding said turn and
at least the adjacent portions of said spaced apart leads, a
tubular grounding shield surrounding said insulation ma
terial a gap in said grounding shield to prevent circulat
ing currents from ?owing therein, ?rst and second sec
ondary windings wound on annular magnetic cores and
interlinked with said primary winding turn, said ?rst sec
nitude that the current ?owing through the relatively 10 ondary winding linking the portion of said primary wind
ing adjacent said ?rst lead ‘and said second secondary
opposite terminals, such as terminals 19 and 2t) respec
tively, of the current transformer in the event of internal
winding linking the portion of said primary winding ad
fault in the transformer, regardless of the direction of
jacent said second lead, a grounding cable having one
normal current ?ow in the transformer. It will be ob
end connected to said grounding shield, means for
vious that other combinations of the position of the 15 grounding the other end of said cable, said grounding
grounding shield gap and the ground cable may also be
cable passing through each of said secondary windings,
employed and still retain the protective feature. The
said gap and grounding cable being 50 arranged that cur
protective ground cable means may also be employed
rent ?owing in said ?rst secondary winding is proportional
in the case where the primary Winding has more than one
to the current ?owing in said second lead and current
turn. Therefore, my invention provides a current trans 20 ?owing in said second secondary winding is proportional
former having simpli?ed construction and means for ac
to the current ?owing in said ?rst lead regardless of the
tuating external circuit breaker means in the event of
direction of current ?ow in said transformer under nor
internal failure thereof.
mal operating conditions, ‘and current ?ow in said ?rst
It will be understood, of course, that, while the forms
secondary winding is either of a different proportion to
of the invention herein shown and described constitute 25 or is out of phase with the current ?ow in said second
preferred embodiments of my invention, it is not intended
lead and current ?ow in said second secondary winding
herein to illustrate all of the possible equivalent forms
is either of a different proportion or is out of phase With
or rami?cations thereof. It will also be understood that
the current flow in said ?rst lead when an internal fault
the words used are words of description rather than of
exists in said transformer.
limitation, and that various changes may be made with 30
4. In a high voltage current transformer of the eye
out departing from the spirit or scope of the invention
bolt type, a primary winding comprised of an open turn
herein disclosed, and it is aimed in the appended claims
of a tubular conductor, ?rst and second leads connected
to cover all such changes as fall within the true spirit
to the ends of said turn coplanar with said turn and ex
and scope of the invention.
tending upwardly to a pair of terminals, said leads being
What I claim as new and desire to‘ secure by Letters
comprised of a pair of spaced apart sections of a longi
Patent of the United States is:
1. In va high voltage current transformer, a primary
winding comprised of an open turn of a conductor, a
tudinally split straight tubular conductor, insulation ma
terial surrounding said turn and at least the adjacent por
tions of said leads, a tubular grounding shield surround
ing said insulation material, a gap in said grounding shield
to prevent the ?ow of circulating currents therein, ?rst
and second secondary windings wound on annular mag
netic cores and interlinked with said primary winding
pair of leads connected to the ends of said turn, insula
tion material surrounding said primary winding and at
least a portion of said leads, a grounding shield surround
ing said insulation material, a gap in said grounding
shield to prevent circulating currents from ?owing there
turn, said ?rst secondary Winding linking the portion of
in, a grounded cable having one end connected to said
said primary winding adjacent said ?rst lead and said
grounding shield, at least one secondary winding inter 45 second secondary winding linking the portion of said pri
linked with said primary winding turn, said grounded
mary winding adjacent said second lead, a grounding
cable passing through said secondary winding between
cable having one end connected to said grounding shield,
where said one end is connected to said shield and where
means grounding the other end of said grounding cable,
it is connected to ground.
said grounding cable passing through each of said sec
2. In ‘a high voltage current transformer, a primary 50 ondary windings.
winding comprised of an open turn of a conductor, a
5. The current transformer of claim 4 in which said
pair of leads connected to the ends of said turn, insula
grounding cable is connected to the portion of the
tion material surrounding said turn and at least the ad
grounding shield above said ?rst secondary winding,
jacent portions of said pair of leads, a tubular grounding
passes downwardly through said ?rst secondary winding,
shield surrounding said insulation material, a gap in said 55 thence around said primary winding and passing down
grounding shield to prevent circulating currents from
?owing therein, at least one secondary winding wound
on an annular magnetic core and interlinked with said
wardly through said second secondary winding to said
grounding means, and said gap‘ is located between said
?rst secondary winding and the connection between said
primary winding turn, a grounded cable having one end
cable and said shield.
connected to said grounding shield, means for grounding 60 6. The current transformer of claim 4 in which said
the other end of said cable, said grounded cable passing
grounding cable is connected to the portion of said
through at least one of said secondary windings between
grounding shield above said ?rst secondary winding,
where said one end is connected to said shield and where
passes downwardly through said ?rst secondary winding,
it is connected to ground, said gap and grounded cable
thence around said primary winding and passing down
being so arranged that current ?owing in one of said sec 65 wardly through said second secondary winding to said
ondary windings is proportional to the current ?owing
grounding means, and said gap is located in the lower
through one of said leads regardless of the direction of
portion of said grounding shield between said secondary
current ?ow in said transformer under normal operating
windings.
conditions and current ?owing in said one secondary
7. The current transformer of claim 4 in which said
winding is either of a different proportion to or is out 70 grounding cable is connected to the portion of said
of phase with the current ?owing through said one lead
grounding shield above said ?rst secondary winding,
when an internal fault exists in said transformer.
passes downwardly through said ?rst secondary winding,
3. In a high voltage current transformer, a primary
thence around said primary winding and passing down~
winding comprised of an open turn of a tabular con
wardly through said second secondary winding to said
ductor, ?rst and second leads connected to the ends of 75 grounding means, and said gap is located in the portion
3,059,151
10
of said ground shield above said second secondary
ing one end connected to said grounding shield, means
winding.
grounding the other end of said grounding cable, said
grounding cable passing through each of said secondary
windings, sa-id gap‘ and grounding cable being so arranged
that current ?owing in said ?rst secondary winding is
proportional to current flowing in said second lead and
current ?owing in said second secondary winding is pro
portional to the current ?owing in said ?rst lead regard
8. In a high voltage current transformer of the cable
type, a primary winding comprised of a loop of a con
ductor, a grounding shield surrounding said loop, a pair
of secondary windings surrounding said grounding
shield, a grounded cable having one end connected to
said grounding shield, means grounding the other end
less of the direction of current ?ow in said transformer
of said grounded cable, said cable being connected to
said grounding shield above each of said secondary wind 10 under normal operating conditions, and current ?ow in
said ?rst secondary winding is of a different proportion
ings and passing through each of said secondary wind
ings between where said one end is connected to said
shield and where it is grounded.
or is out of phase with current ?ow in said second lead
and current ?ow in said second secondary winding is
either of a different proportion or out of phase with the
9. In a high voltage current transformer, a pair of con
ductors connected in series, each of said conductors 15 current ?ow in said ?rst lead when an internal fault
comprising the primary winding of a separate bushing
type transformer, a grounding shield surrounding each
of said conductors, a secondary winding surrounding
each of said grounding shields, a grounded cable having
exists in said transformer.
11. In a high voltage current transformer of the type
enclosed in a housing, a primary winding comprised of
an open turn of a conductor, an insulation medium in
one end connected to one of said grounding shields above 20 said housing surrounding said primary winding, a ground
the respective secondary winding, means grounding the
other end of said cable, said cable passing through each
ing shield between said housing and primary winding,
ground means including a grounded lead having one end
connected to said grounding shield, at least one second
of said secondary windings between where said one end
ary winding interlinked with said primary winding turn,
is connected to said shield and where it is grounded,
and a conductor connected between one end of said of 25 and said grounded lead passing through said secondary
winding between where said one end is connected to said
said grounding shields and the respective end of said
shield and where it is connected to ground.
other grounding shield.
10. In a high voltage current transformer, 21. primary
References Cited in the ?le of this patent
winding having ?rst and second leads extending there
from, a tubular grounding shield surrounding said pri 30
mary winding and insulated therefrom, a gap in said
grounding shield to prevent the ?ow of circulating cur
rents therein, ?rst and second secondary windings inter
linked with said primary winding, a grounding cable hav
UNITED STATES PATENTS
2,804,577
2,929,963
2,931,951
Roth _______________ __ Aug. 27, 1957
Kaestle _____________ __ Mar. 22, 1960
Wilson _______________ .._ Apr. 5, 1960
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