Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SPECIFICATION
Back r~und of the Invention
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The present invention relates generally to current
sensing devices for electrical systems, and more particularly
to automatically resettable alternating current fault indi-
cators.
Various types of fault indicators have been con-
structed for detecting electrical faults in power distribution
systems, including clamp-on type fault indicators, which clamp
directly over cables iD the systems, and test point type fault
indicators, which are mounted over test points in cables or
associated connectors of the system. Such fault indicators
may be either of the manually reset type,.wherein it is necessar.
that the indicators be physically reset, or of the self-
resetting type, wherein the indicators are reset upon restor-
ation of line current. Examples of such fault indicators are
found in products manufactured by E.O. Schweitzer Manufacturing .
Company of Mundelein, Illinois, in U.S. Patents 3,676,740;.
3,816,816; 3,906,477; 4,034,360; 4,063,171; 4,068,529 and
4 234,847 of the present inventor, and in U.S. Patents Nos.
4,438,403 and 4.t458,198 of the present inventor entitled
respectively "Fault.Indicator Having a Remote Test Point at
Which Fault Current is Indicated by Change in Magnetic Field",
and "Fault Indicator with Bidirectional Indicator Winding".
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Detecti~n of faulk currents in self-resetting fault
indicator~ may be accomplished by means of magnetic switch
means, such as a magnetic reed switch positioned in close prox-
imity to the conductor being monitored. Upon occurrence of an
abnormally high fault-associated magnetic field around the
conductor, the reed switch actuates a trip circuit which pro-
duces current flow in a trip winding to position an appxopriate
indicator member, such as a rotatably mounted indicator flag
visible from the exterior of the indicator, to a trip or fault-
indicating position. Upon restoration of current in the con-
ductor, a reset circuit is actuated to produce current flow in
a reset winaing to reposition the indicator flag to a reset or
non-fault indicating position. The invention described in the
aforementioned U.S. Patent 4,438,403 pro-
vides an improvement in such fault indicators, in that it pro-
vides a simplified circuit for uQe in conjunction with a single
bidirectional magnetic winding in place of separate trip and
reset winaings.
To mlnimize the power required by the trip and reset
circuits in repositioning the indicator between reset and trip
positions it is desirable that the indicator flag have minimal
mass and minimal travel between positions. To these ends a
rotatably mounted segmental-type indicator flag consisting of
two indicating segments arranged on opposite sides of the axis
of rotation of the-flag has been utilized. The trip and reset
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circuits of the fault indicator are only required to rotate
this flag go D ~ in contrast to the trip and reset circuits of
a conventional disc-type indicator which must rotate the indi-
cator disc through 180.
One drawback of previous 90 segmental-type indicator
flag assemblies has been the relatively greater space require-
ments and complexity of such assemblies compared to 180 disc-
type assemblies. This has made it difficult and unnecessarily
costly to incorporate these segmental-type assemblies in the
smaller indicator housings preferred in many monitoring appli-
cations. The present invention is directed to a new and im-
proved actuator assembly which allows 90 segmental-type indi-
cator flag systems to be provided in compact housings with
space and cost requirements comparable to those of 180 disc-
type systems.
Accordingly, it is a general object of the present
invention to provide a new and improved fault indicator.
It is a more specific object of the invention to pro-
vide a fault indicator having a more efficient and compact indi-
cator flag assembly for indicating the occurrence of a fault
current.
It is another object of the invention to provide a
fault indicator having an improved 90 segmental-type indicator
flag assembly which is compact and economical to manufacture.
Summary of the Invention
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A fault indieator for indicating the oecurrenee of
a fault eurrent in an electrical conductor ineludes a housing,
and status indicating means comprising an indicator flag rotat-
ably mounted within the housing, the indicator flag having first
and third positions corresponding to a reset state, and seeond
and four positions eorresponding to a fault-indieating state,
these positions being consecutively spaced gO about the axis
of rotation of the indieator flag. A flag aetuator magnet having
first, second, third and fourth magnetic poles of alternating
magnetie polarity spaced 90 around the axis of rotation is
rotatably eoupled to the indieator flag. A magnetic pole pieee
having first, second,third and fourth magnetic pole segments
extending from a common loeation to predetermined loeations is
arranged within the housing in magnetie eommunieation with re-
speetive ones of the first, seeond, third and fourth poles of
the flag aetuator magnet. Cireuit means ineluding a first mag-
netie winding on the first pole segment and a seeond magnetie
winding on the seeond pole segment are provided for eonditioning
the first and third magnetie pole segments to a first magnetie
polarity, and the seeond and fourth magnetie pole segments to
an opposite magnetie polarity during normal eurrent flow in the
eonduetor, and for reversing the polarities of the pole segments
upon occurrence of a fault current in the conduetor whereby the
indieator flag is eaused to rotate from one of the first and
third positions to one of the seeond and fourth positions upon
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occurrence of a fault current.
Brief Description of the Drawings
The features of the present invention which are be-
lieved to be novel are set forth with particularity in the
appended claims. The invention, together with the further ob-
jects and advantages thereof, may best be understood by refer-
ence to the following description taken in conjunction with the
accompanying drawings, in the several figures of which like re-
ference numerals identify like elements, and in which:
Figure 1 is a perspective view of a fault indicator
constructed in accordance with the invention mounted on an
electrical distribution cable.
Figure 2 is an enlarged perspective view of the fault
indicator of Figure 1 with the housing thereof partially broken
away to illustrate the internal construction of the indicator.
Figure 3 is a front elevational view of the fault
indicator of Figure 1.
Figure 4 is a perspective view of the flag actuator
assembly of the fault indicator of Figure 1.
Figure 5 is a cross-sectional view of the flag actuator
assembly taken along line 5-5 of Figure 4.
Figure 6 is an exploded perspective view of the mag-
netic pole piece and bobbin incorporated in the flag actuator
assembly of Figure 4.
Figure 7 is an electrical schematic diagram of the
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fault indicator of Figures 1-3.
Figures 8a and 8b are diagrammatic views of principal
components of the fault indicator in a reset state.
Figures 9a and 9b are diagrammatic views similar to
Figures 8a and 8b, respectively, showing the principal components
of the fault indicator in transition between a reset state and
a tripped state.
Figures lOa and lOb are diagrammatic views similar to
Figures 8a and 8b, respectively, showing the principal components
of the fault indicator in a tripped state.
Figures lla and llb are diagrammatic views similar to
Figures 8a and 8b, respectively, showing the principal components
of the fault indicator in transition between a tripped state and
a reset state.
Figure 12 is a perspective view, partially in section,
of a prior art flag actuator assembly for use in fault indicators.
escription of_the Preferred Embodiment
~eferring to the Figures, and particularly to Figure
1, a fault indicator 10 incorporating the invention is shown
installed on an electrical cable 11. Cable 11, which may com-
prise part of an electrical distribution system, includes in
accordance with conventional practice a central conductor 12
surrounded by an insulating sheath 13. The physical dimensions
of the cable vary as a function of the current and voltage
capacity of the cable in a manner well known to the art.
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The fault indicator 10 is seen to comprise a
generally cylindrical housing 14 attached at its rear end (as
viewed in Figures 1-2~ to cable 11 by means of a mounting clip
15. Clip 15, which may be formed of a spring steel wire or the
S like includes two parallel-spaced portions formed to engage
cable 11 opposite housing 14. The clip member 15, which is
anchored within housing 14 by an epoxy filler or other suitable
means, includes a pair of coil portions which bias the spring
clip against cable 11, thereby securely mounting the fault indi-
cable housing to the cable.
To facilitate installation and positioning of
the fault indicator a closed-loop hook member 16 is provided on
the bottom (as viewed in Figure 1) of housing 14. This hook may
be engaged with a lineman's tool or the like when installing the
indicator on the powered cable. A pair of viewing windows 17
and 18 on the front surface of the indicator housing enable a
user ~o readily ascertain the status of cable 11.
Referring to Figure 2, housing 14 is seen to be
formed of plastic or other electrically non-conductive material.
~ transparent plastic end cap 20 is bonded by appropriate means
to the front end of the housing. A disc-shaped mask meMber 21
is provided behind end cap 20 to form viewing windows 17 and 18.
Appropriate indicia (not shown) may be provided on this mask
member to assist in identification and operation of the fault
indicator. A filler 22 of epoxy or other suitable material may
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be provided to seal the rear end of the housing.
Within housing 14 the principal electrical com-
ponents of the fault indicator are mounted on a disc-shaped
circuit board 23 mounted within the housing perpendicular to the
axis of the housing and in a location intermediate the end
thereof. Electrical contact is established between the elec-
trical components mounted on circuit board 23 and clamp member
15 by an appropriate connection behind the circuit board. In
addition, electrical connection is established between hook
member 16 and the fault idnicator circuitry by a direct connec-
tion within housing 14 to the front surface of the circuit board.
To provide for sensing of a fault current in conductor 12, the
fault indicator includes a magnetic switch 24 mounted to the
rear surface of circuit board 23. Upon occurrence of a fault
current this reed switch closes to energize circuitry which con-
ditions the indicator to a fault indicating magnetic state.
The occurrence of a fault current in conductor
12 is indicated to a lineman or other observes by means of an
indic~tor flag 25 rotatably mounted on a shaft 26 within housing
14. The indicator flag includes indicator segments 26a and 26b
on either side of the axis of rotation. To minimize the mass
of the indicator flag, these flag segments preferably each ex-
tend less than 90 around the axis of rotation. When aligned
as shown in Figure 2, the flag segments are masked by mask rnember
21 and are not visible to an o~server. However, upon occurrence
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of a fault condition, the indicator flag rotates 90 such that
the indicator segments are visible through windows 17 and 18.
The indicator segments are preferably colored red, or another
highly-visible color, to clearly indicate a fault occurrence
when viewed through the windows.
Actuation of flag member 25 between the reset
and fault indicating positions is accomplished by an annular
flag actuator magnet 27 which is rotatably coupled to flag mem-
ber 25 by shaft 26. Shaft 26 is maintained in alignment with
the axis of indicator housing 14 by means of a bearing surface
in a disc-shaped divider wall 28, which also provides a reset-
indicating surface viewable through viewing windows 17 and 18
when the indicator flag is in its reset position. This surface
is preferably colored white, or some other color contrasting
with the color of the indicator flag seyments, to clearly indi-
cate a reset condition when viewed through the windows.
Actuator magnet 27, which may be formed of a mag-
netic material having a high coercive force, such as ceramic,
is formed to provide four magnetic poles of opposite polarity,
with opposite maynetic polarities at 90 intervals along the
circumference of the magnet. Actuator magnet 27, and hence
indicator flag 25, are biased to the position shown in Figures
1-3 when the fault indicator is in a non-tripped or reset con-
dition by means of a flag actuator assembly 30, which includes
four magnetic pole segments in magnetic communication with flag
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actuator magnet 27. The flag actuator assembly 30 is mounted
to the front surface of circuit board 23 such that the four
magnetic poles o~ the actuator assembly extend to positions ad-
~acent the magnetic poles of actuator magnet 27. A magnetic
shield 31 comprising a plurality of parallel magnetically con-
ductive sheets is provided between the actuator assembly and
the circuit board to shield the actuator assembly from the mag-
netic field which accompanies occurrence of a fault current in
conductor 12.
Referring to Figures 4-6, the flag actuator assem-
bly 30 is seen to comprise, in accordance with the invention,
a generally cross-shaped magnetic pole piece 32 formed of a
magnetic material having a relatively low coercive force, such
as chrome steel. As best shown in Figure 6, pole piece 32 com-
prises four magnetic pole segments 33-36 each having an initial
portion which extends in a plane generally perpendicular to the
axis of indicator housing 14 and flag member 25, and a subse-
quent end portion which extends forward generally parallel to
the axis and terminates with respective magnetic poles 40-43 in
close proximity to the circumference of flag actuator magnet 27
(Figure 2). The pole piece 32 is preferably formed as a one
piece element by conventional forming techniques.
Magnetization of pole piece 32 is accomplished
by a pair of magnetic windings 44 and 45 located on pole seg-
ments 33 and 35, respectively. These windings are preferably
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wound on a bobbin 46 which may be formed of a non-magn~tic
plastic material by conventional molding techniques. ~obbin
46 preferably includes a first core portion 47 for receîving
winding 44, a second core portion 48 for recei~ing winding 45,
and a channel portion 4g for receiving the initial portions of
pole se~ments 33 and 35.
The unique construction of pole piece 32 and
bobbin 46 allows the two elements to be separately manufactured
and then joined during a subsequent assembly operation. Bobbin
46 may be permanently secured to the pole piece by a layer 50
(Figure 5) of epoxy or other suitable material aeposited within
channel 49 after pole piece 32 has been inserted. After replace-
ment of the epoxy layer, wïndings 44 and 45 may be formed by
rotating the assembled pole piece and bobbin assembly along
axis A-A (Figure 4) in a conventional coil winaing machine as
the windings are wound on winding cores 47 and 48.
To conserve winding space, it is preferably that
windings 44 and 45 be untapped bidirectional winaings to which
current îs supplied in one direction to establish a fault-indi-
cating status in pole piece 32, and to which current is applied
in the opposite direction to establish a reset-indicating con-
dition. This mode of operation is described in the previously
identified U.S. Patent No. 4,438,403. Also windings 44
and 45, which are wound in opposite directions to provide the
same magnetic polarity at magnetic poles 40 and 42, may be ad-
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vantageously eonnected in series by a eonnection 51 (Figure 4).
The remaining ends of the series-eonnected windings may then
be conneeted through conductors 52 and 53 to the indicator
eircuitry. An appropriate eireuit for energizing windings 44
and 45 thus connerted is shown in Figure 7.
Alternatively, a separate trip and reset winding
may be provided in place of each of windings 44 and 45, with a
corresponding penalty in spaee and cost of manufacture. Various
circuits for energizing such separate trip and reset windings
are well-known to the art.
During normal circuit operation the poles of
pole pieee 32 are biased to the magnetic polarities indicated
in Figures 8a--8b. As a result, the opposite polarity poles of
flag aetuator magnet 27 are attraeted to position the indieator
flag 25 as shown, with the indicator segments 26a and 26b thereof
vertieally aligned and out of view of windows 17 and 18. Thus,
all that is seen is the white reset-indieating surface of divider
2~.
On the occurrence of a fault current in conductor
12, whieh may, for example, exceed 400 amperes, pole piece 32
is remagnetized to the magnetie polarities shown in Figures 9a-
9b and 10a-lOb by momentary energization of the series-connected
magnetie windings 44 and 45 cn pole sections 33 and 35 of the
pole piece, as shown. As a result, the poles of flag actuator
magnet 27 are repelled by adjacent like-polarity poles of the
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pole piece and the indicator flag is caused to rotate 90 to
the tripped position shown in Figures 9a and 9b. In this
position, the red indicator segments 26a and 26b of the indicator
flag are visible through windows 17 and 18 and a lineman viewing
the fault indicator is advised that a fault current has occurred
in conductor 12.
The indicator flag remaing in the fault indicating
position until the poles of pole piece 32 are subsequently re-
magnetized to the magnetic polarities shown in Figures lla-llb
and 8a and 8b by momentary energization of magnetic windings
44 and 45 in the reverse direction. As a result, the flag ac-
tuator magnet, and hence the indicator flag 25, are caused to
rotate from the tripped position shown in Figures lOa and lOb
through the intermediate position shown in Figures lla and llb
to the reset position shown in Figures 8a and 8b, and the fault
indicator is conditioned to respond to a subsequent fault
current.
To provide for predictable rotation of the flag
actuator magnet in the clockwise direction shown, and to pre-
clude the possibility of a balanced on-center stalled condition
in which no rotation would take pl.ace, the magnetic poles assoc-
iated with pole segments 33 and 35 are displaced slightly along
the circumference of the flag actuator magnet. Consequently,
an on-center stalled condition is not possible, since the opposing
repelling force of the displaced poles exerts a turning moment
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on the flag actuator magnet~ The actual displacement may be
slight, and may be conveniently accomplished by additional pole
segment portions 54 and 55 ~Figure 6) which extend along the
circumference of the actuator magnet in a direction opposite
to the desired direction of rotation.
Energization of the series-connected magnetic
windings 44 and 45 by current in one direction upon occurrence
of a fault current during either portion of the alternating
current cycle in conductor 12, and energization of the windings
10 by current in the opposite direction upon restoration of current
in conductor 12, is accomplished by means of circultry contained
within the indicator housing 14. Referring to the schematic
diagram shown in Figure 7, the two untapped series~connected
windings 44 and 45 of fault lndicator 10 are connected by con-
15 ductors 52 and 53 to the fault indicator circuitry, which may
be mounted on circuit board 23 (Figure 2). Operating power for
this circuitry is obtained by means of a bridge rectifier net-
work 60 consisting of diodes 61-64. One input terminal of this
network, formed at the juncture of the anode of diode 61 and the
20 cathode of diode 64, is connected to the wire mounting spring
15, which provides capacitive coupling to conductor 12. The
other input terminal, formed at the anode of diode 62 and the
cathode of diode 63, is connected to ground through the projecting
hook 16, which functions as a counter-poise in a manner well
25 known to the art to provide a reference potential lower than
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that of conductor 12. With this arrangement, high voltage
alternating current carried in conductor 12 is capacitively
coupled to bridge rectifier network 60, resulting in the pro-
duction of a pulsating unidirectional current at the output
terminals of the network.
The positive polarity output terminal of the
bridge rectifier network, formed at the cathodes of diodes 61
and 62, is connected to the series-connected windings 44 and
45 through conductor 53, and to one terminal of a first capacitor
65. The negative polarity output terminal of the bridge rec-
tifier network, formed at the juncture of the anodes of diodes
63 and 64, is connected to the remaining terminal of capacitor
65, and through a forward biased diode 66 and a resistor 67 to
one terminal of a second capacitor 68. The other terminal of
capacitor 68 is connected to the remaining terminal of the
series-connected windings 44 and 45 through conductor 52. With
this arrangement, capacitor 65 is charged directly, and capacitox
68 is charged through windings 44 and 45, diode 66 and resistor
67, by the pulsating unidirectional current developed by bridge
rectifier network 60 during normal current flow in conductor 12.
To provide for periodic energization of windings
44 and 45 during normal current flow in conductor 12, the re-
maining end terminal of the windings is connected through a
silicon controlled rectifier 70 to the negative polarity ter-
minal of capacitor 65. Periodic conduction through SCR 70 is
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obtained by connecting the gate electrode of that device to the
positive polarity output terminal of the bridge rectifier 60
through a voltage divider network comprising a pair of resistors
71 and 72 and a bilateral diode 73. SCR 70 is periodically
triggered into conduction when the voltage developed across
bilateral diode 73 as a result of capacitor 65 being charged
by bridge rectifier 60 reaches the threshold level of the diode.
In operation, under normal current flow conditions,
the voltage developed across capacitor 65 as the capacitor is
charged by bridge rectifier network 60 progressively increases
with time, until the threshold breakdown voltage of bilateral
diode 73 is reached, at which time SCR 70 is triggered and
capacitor 65 discharges through windings 44 and 45. This causes
a current flow in a first direction in the windings, with the
result that a reset-indicating magnetic state is estahlished
in pole piece 32.
Capacitor 68 is charged by bridge rectifier net-
work 60 through diode 66 and windings 44 and 45. Diodes 66 pre-
vents capacitor 68 from being discharged through SCR 70 upon con-
duction of that device leaving the capacitor available for ener-
gizing the windings in a reverse direction in response to a
fault current conditionO
In practice, the breakdown voltage of bilateral
diode 73 may be in the order of 34 volts, and the time required
for that portion of the voltage across capacitor 65 applied by
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resistor 71 and 72 ~o reach this threshold level with a typical
voltage level of 4,400 volts on conductor 12 may be approximately
four minutes. The voltage level with conductor 12 is not critical
to the operation of the reset circuit, and has only the effect
of changing the repetition rate of the reset cycle.
Windings 44 and 45 are energiæed in a second and op-
posite direction upon occurrence of a fault current in conductor
12 by discharge of capacitor 68 through a second SCR 74 having
its cathode connected to the negative polarity terminal of the
capacitor, and its anode connected to the first end terminal
of the windings. Conduction is established through SCR 74 by
closure of the contacts of reed switch 24, which is connected
between the positive polarity te~ninal of capacitor 68 and the
gate electrode of SCR 74 by a network comprising a resistor 75,
a capacitor 76, a bilateral diode 77, and a resistor 78. Reed
switch 24 is positioned within housing 14 in sufficiently close
proximity to conductor 12 such that the contacts of the switch
close upon occurrence of a fault current in the conductor.
Upon occurrence of a fault current, the positive pol-
arity terminal of capacitor 68 is connected through the contacts
of reed switch 24 and the circuit comprising resistors 75, 78,
bilateral diode 77 and capacitor 76 to the gate electrode of
SCR 74, causing that device to be rendered conductive. This
_ causes capacitor 68 to discharge through SCR 74, energizing
windings 44 and 45 in the reverse direction. The resulting
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magnetic ~lux reverses the magnetic sense of the pole piece and
causes th~ pole piece to assume the magnetic polarities shown
in Figures 9a-9b and lOa-lOb.
To preclude the possibility of windings 44 and 45
being simultaneously actua~ed by currents of opposite direction
by simultaneous conduction through SCR 74 and SCR 70, a pre-
determined time delay in conduction through SCR 74 is preferably
provided following occurrence of a fault current in conductor
12. This is accomplished by resistor 75 and capacitor 76, which
together form an RC time constant network in the gate circuit
of SCR 74. ~pon closure of the contacts of reed switch 24 it
is necessary that capacitor 76 charge through resistor 75 to
the threshold voltage of bilateral diode 77 before sufficient
gate electrode current is supplied to SCR 74 to initiate con-
duction through that device. Resistor 78 serves in a conven-
tional manner as a current drain for the gate electrode. A
further detailed discussion of the operation of the circuit of
Figure 7 may be found in U.S. Patent No. 4,438,403.
Thus, in operation windings 44 and 45 are supplied
with unidirectional current in one direction from a first cur-
rent storage device, capacitor 65, and in the oppsoite direction
from a second storage device, capacitor 68. Capacitor 65 is
connected to one terminal of the magnetic windings, and cap-
acitor 68 is connected to the other terminal. A first switch
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device, SCR 70, periodically completes the discharge circuit
for capacitor 65 to the windings during reset conditions. A
second switch device, SCR 74, completes the discharge circuit
for capacitor 68 to the windings upon occurrence of a fault
current.
The two current storage capacitors 65 and 68 are sim-
ultanéously charged by a charging circuit which includes the
line powered bridge rectifier source 60. Capacitor 65 is
charged directly and capacitor 68 is charged through the series-
connected windings 44 and 45, isolation diode 66 and resistor
67. Diode 66 provides isolation for the trip circuit upon oper-
ation of the reset circuit.
While the novel indicator system of the invention has
been shown in conjunction with series-connected hidirectional
magnetic windings and the bidirectional actuator circuit of
Figure 7 t which combination is most advantageous because of its
efficiency and compactness, it will be appreciated that the in-
vention may be utilized instead with separate reset and trip
windings on each of pole segments 33 and 35. In this case, a
total of four windings would be required, and actuating circuitry
such as that shown and described in the previously identified
U.S. Patent would be utilized.
By reason of the compactness and simplicity of the
actuator assembly 30, the fault indicator 10 may be housed in
a compact housing such as housing 14. Previous actuator assem-
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blies intended for 90 indicator flag-type indicating systems,
such as the assembly 80 shown in Figure 12, required substan-
tially more space. This precluded housing the fault indicator
in a compact housing such as housing 14. Moreover, such pre-
vious actuator assemblies utilized a pole piece which was con-
structed with at least three separate elements; two U-shaped
elements 81, 82 and a central core element 83. These elements
could not be constructed as a single one-piece element because
of the necessity of installing the winding 84 on the central
segment prior to installation of the U-shaped pole sections.
In contrast, in applicant's invention the winding bobbin is
installed on a one-piece pole piece and the windings are sub-
sequently wound on the bobbin by merely rotating the assembly
along the axis A-A shown in Figure 4. Thus, the invention
realizes a significant savings in the cost of manufacture of
the actuator assembly.
While a particular embodiment of the invention has
been shown and described, it will be obvious to those skilled
in the art that changes and modifications may be made without
departing from the invention in its broader aspects, and, there-
fore, the aim in the appended claims is to cover all such changes
and modifications as fall within the true spirit and scope of
the invention.
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