U.S. patent application number 15/174079 was filed with the patent office on 2017-03-23 for electric meter and contact arcing detector, and arcing detector therefor.
The applicant listed for this patent is Advent Design Corporation, doing business as TESCO The Eastern Specialty Company. Invention is credited to Ralph Nicolas Amato, Richard Hughes Hewitt, Thomas Alan Lawton.
Application Number | 20170082674 15/174079 |
Document ID | / |
Family ID | 58227839 |
Filed Date | 2017-03-23 |
United States Patent
Application |
20170082674 |
Kind Code |
A1 |
Lawton; Thomas Alan ; et
al. |
March 23, 2017 |
ELECTRIC METER AND CONTACT ARCING DETECTOR, AND ARCING DETECTOR
THEREFOR
Abstract
An electric meter contact arc detector is mountable to an
electric meter base and may comprise: a de-tuned resonant tank
circuit configured to receive a magnetic field and/or an electric
field from an electrical arc at a stab contact; an electrical
detector detecting signals generated in the de-tuned resonant tank
circuit responsive to the electrical arc at the stab contact; and
an output device indicating detection of an electrical arc. A
disconnect device responsive to the electrical detector and
configured to interrupt an electrical connection to the stab
contact, may be provided. An electrical arc at the stab contact may
thus be detected and may cause an electrical connection to the stab
contact to be interrupted.
Inventors: |
Lawton; Thomas Alan;
(Newtown, PA) ; Amato; Ralph Nicolas;
(Branchville, NJ) ; Hewitt; Richard Hughes;
(Ewing, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Advent Design Corporation, doing business as TESCO The Eastern
Specialty Company |
Bristol |
PA |
US |
|
|
Family ID: |
58227839 |
Appl. No.: |
15/174079 |
Filed: |
June 6, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62221160 |
Sep 21, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02H 1/0015 20130101;
G01R 31/14 20130101; G01R 1/00 20130101; G01R 22/068 20130101; H02H
1/00 20130101; G01R 22/00 20130101; G01R 31/69 20200101; H02J 1/00
20130101; G01R 31/1227 20130101 |
International
Class: |
G01R 31/04 20060101
G01R031/04; G01R 22/00 20060101 G01R022/00 |
Claims
1. An electric meter and contact arc detector comprising: an
electric meter base formed of an electrically insulating material
and having a plurality of stab contacts configured for making
electrical connection to plural contacts of an electric meter
socket; a metering device supported by said electric meter base;
and a contact arc detector supported by said electric meter base,
said contact arc detector comprising: a de-tuned resonant tank
circuit configured to receive a magnetic field and/or an electric
field generated by an electrical arc at a series connection
including one or more of the plurality of stab contacts when the
magnetic field and/or the electric field impinges upon said
resonant tank circuit; an electrical detector to which said
de-tuned resonant tank circuit is coupled for detecting signals
generated in said de-tuned resonant tank circuit responsive to the
magnetic field and/or an electric field generated by an electrical
arc at one or more of the plurality of stab contacts; and a
disconnect device responsive directly or indirectly to said
electrical detector and configured to interrupt an electrical
connection to one or more of the plurality of stab contacts,
whereby an electrical arc at one or more of the plurality of stab
contacts is detected and causes the interruption of an electrical
connection to one or more of the plurality of stab contacts.
2. The electric meter and contact arc detector of claim 1 wherein
said de-tuned resonant tank circuit includes an inductor and a
capacitor in parallel connection.
3. The electric meter and contact arc detector of claim 1 wherein
said de-tuned resonant tank circuit is coupled to a resistance for
de-tuning the resonant tank circuit to broaden the bandwidth
thereof.
4. The electric meter and contact arc detector of claim 1 wherein
said electrical detector has two inputs, a first of the two inputs
thereof being coupled to said de-tuned resonant tank circuit and a
second of the two inputs thereof being connected to a reference
source configured to provide an offset to a detection threshold of
said electrical detector.
5. The electric meter and contact arc detector of claim 1 wherein
said electrical detector includes: a timing network for determining
a duration of an output signal therefrom.
6. The electric meter and contact arc detector of claim 5 wherein
said timing network includes a resistor and a capacitor connected
for determining a time constant.
7. The electric meter and contact arc detector of claim 1 wherein
said electrical detector includes first and second transistors, an
output electrode of each of the first and second transistors being
coupled to an input electrode of the other of the first and second
transistors, wherein turning the first transistor on causes the
second transistor to turn on causing positive feedback to the input
electrode of the first transistor, whereby the first and second
transistors latch into an on condition.
8. The electric meter and contact arc detector of claim 7 wherein
the output electrode of the second transistor is coupled to the
input electrode of the first transistor by a resistor and a
capacitor connected for determining a time constant, whereby the
first and second transistors latch into the on condition for a
predetermined time.
9. The electric meter and contact arc detector of claim 1 further
comprising: an optical coupler or a transistor coupling said
electrical detector to said disconnect device.
10. The electric meter and contact arc detector of claim 1 further
comprising: a metering device including a micro-controller or a
microprocessor, wherein said micro-controller or microprocessor is
responsive to said electrical detector: to cause said disconnect
device to interrupt an electrical connection to one or more of the
plurality of stab contacts; or to cause said disconnect device to
interrupt an electrical connection to one or more of the plurality
of stab contacts after the output of said electrical detector
persists for a predetermined time.
11. An electric meter contact arc detector mountable to an electric
meter base formed of an electrically insulating material and having
a plurality of stab contacts configured for making electrical
connection to plural contacts of an electric meter socket, said
contact arc detector comprising: a de-tuned resonant tank circuit
configured to receive a magnetic field and/or an electric field
generated by an electrical arc at a series connection including one
or more of the plurality of stab contacts when the magnetic field
and/or the electric field impinges upon said resonant tank circuit;
an electrical detector to which said de-tuned resonant tank circuit
is coupled for detecting signals generated in said de-tuned
resonant tank circuit responsive to the magnetic field and/or an
electric field generated by an electrical arc at one or more of the
plurality of stab contacts; and an output device responsive to said
electrical detector and configured to respond to detection of an
electrical arc at one or more of the plurality of stab contacts,
whereby an electrical arc at one or more of the plurality of stab
contacts is detected and causes the output device to respond to
detection of an electrical arc at one or more of the plurality of
stab contacts.
12. The electric meter contact arc detector of claim 11 wherein
said de-tuned resonant tank circuit includes an inductor and a
capacitor in parallel connection.
13. The electric meter contact arc detector of claim 11 wherein
said de-tuned resonant tank circuit is coupled to a resistance for
de-tuning the resonant tank circuit to broaden the bandwidth
thereof.
14. The electric meter contact arc detector of claim 11 wherein
said electrical detector has two inputs, a first of the two inputs
thereof being coupled to said de-tuned resonant tank circuit and a
second of the two inputs thereof being connected to a reference
source configured to provide an offset to a detection threshold of
said electrical detector.
15. The electric meter contact arc detector of claim 11 wherein
said electrical detector includes: a timing network for determining
a duration of an output signal therefrom.
16. The electric meter contact arc detector of claim 15 wherein
said timing network includes a resistor and a capacitor connected
for determining a time constant.
17. The electric meter contact arc detector of claim 11 wherein
said electrical detector includes first and second transistors, an
output electrode of each of the first and second transistors being
coupled to an input electrode of the other of the first and second
transistors, wherein turning the first transistor on causes the
second transistor to turn on causing positive feedback to the input
electrode of the first transistor, whereby the first and second
transistors latch into an on condition.
18. The electric meter contact arc detector of claim 17 wherein the
output electrode of the second transistor is coupled to the input
electrode of the first transistor by a resistor and a capacitor
connected for determining a time constant, whereby the first and
second transistors latch into the on condition for a predetermined
time.
19. The electric meter contact arc detector of claim 11 wherein
said output device includes: an audio or visual indicator, or a
light emitting diode configured to provide an indication that said
electrical detector has detected electrical arcing; or an optical
coupler or a transistor or a metering device directly or indirectly
coupling said electrical detector to a disconnect device configured
to interrupt electrical power to one of more of the plurality of
stab contacts.
20. The electric meter contact arc detector of claim 11 further
comprising: a metering device including a micro-controller or a
microprocessor supported by the electric meter base, wherein said
metering device responds to the output of said electrical detector:
for activating said output device; or for determining a duration of
the output of said electrical detector; or for activating said
output device after the output of said electrical detector persists
for a predetermined time.
Description
[0001] This Application claims the benefit of the priority of U.S.
Provisional Patent Application No. 62/221,160 entitled "ELECTRIC
METER AND CONTACT ARCING DETECTOR, AND ARCING DETECTOR THEREFOR"
which was filed on Sep. 21, 2015, and which is hereby incorporated
herein by reference in its entirety.
[0002] The present invention relates to an electric meter including
a detector of arcing at an electrical contact, and to an electrical
contact arcing detector therefor.
[0003] Revenue-grade socket electric meters, used in approximately
200 million plus locations in the United States, can possibly have
dangerously arcing connections between the meter connections
("stabs") of the electric meter and the socket connections ("jaws")
of the meter socket that connect to it. A condition where the
stab-to-jaw connection is arcing without causing any easily
detectable power problems on the site is dangerous because the
arcing connection can heat up to a point of causing a fire, yet the
arcing connection does not necessarily cause a condition which is
easily detectable by commonly used fault-detection methods, such as
fuses and circuit breakers which respond to over-current conditions
or ground fault detectors which respond to current flowing from a
supply to a safety ground.
[0004] Given the large number of these meters in use, the potential
harm from electrical arcing at connections is widespread, yet at
the same time such high volume usage calls for an extremely low
cost detection device and method so as to be affordable on such a
large scale.
[0005] Such electric meters, which are widely employed to indicate
usage of electrical power by a consumer or customer of an electric
utility supplier, are typically plug-in devices that are plugged in
to a meter socket which is typically mounted in an enclosure on a
building or other structure whereat electrical power is consumed.
The meter socket typically includes plural metal "jaws" which are
female electrical contacts that are embedded or otherwise attached
to an insulating socket base in a standardized pattern. A typical
meter socket for single phase or two phase power can have four jaws
for providing two pairs of electrical connections from the socket
to the meter, one pair for carrying current from the utility supply
to the meter and a second pair for carrying electrical current from
the meter to the electrical panel and wiring of the consumer.
[0006] The electric meter typically includes plural metal "stabs"
which are male electrical contacts that are embedded in or
otherwise attached to an insulating base of the electric meter in
the standardized pattern, so that the electric meter conveniently
plugs into the meter socket and is likewise removable therefrom. A
typical electric meter for single phase or two phase power can have
four stabs for providing two pairs of electrical connections
between the meter and the socket, one pair for carrying current
from the utility supply to the meter and a second pair for carrying
electrical current from the meter to the electrical panel and
wiring of the consumer.
[0007] Typical residences have 100 ampere, or 150 ampere, or 200
ampere electrical service and so substantial electrical current
typically flows through each stab-to-jaw connection. Practically,
the electrical contact between a jaw and a stab departs from the
ideal, e.g., in that complete electrical contact over the intended
surface area may be lacking, e.g., due to misalignment, wear,
relaxation of the metal jaw, dirt and/or corrosion, and the like.
These manifest as, e.g., an increased electrical resistance of the
connection and/or a gap across which the current flows by arcing,
which results in electrical heating at the connection. Under high
current conditions, such heating can increase temperature
sufficiently to lead to fire. Many instances of electrical meter
fires have been reported. (See the web page at:
http://emfsafetynetwork.org/smart-meters/smart-meter-fires-and-explosions-
/).
[0008] While some schemes to detect such contact arcing have been
proposed, those are understood to be complex and therefore tend to
add significant complexity and cost to each electric meter. Patents
and patent applications exist which describe detecting arcing via
detection of RF radio wave emissions, yet those patents require
complicated methods of detection and discrimination. For example,
U.S. Published Patent Application 2014/0327449A1 to Elster
describes arc detection using a sophisticated spread-spectrum radio
transceiver used in remote meter reading systems. U.S. Pat. No.
5,729,145 to Blades describes a complicated system of correlating
RF detection with instantaneous line voltage in order to
discriminate between arcing and other radio noise.
[0009] Applicant believes there is a need for a simpler contact arc
detector that can detect arcing at the stab-to-jaw connections of
an electric meter and signal a need for an action that is, e.g.,
intended to prevent a fire or alert personnel, while being
relatively small, so as to be easily and inexpensively made part of
an electric meter or carried.
[0010] Accordingly, an electric meter contact arcing detector that
may be mountable to an electric meter base having a plurality of
contacts for connecting to plural contacts of an electric meter
socket may comprise: a de-tuned resonant tank circuit configured to
receive a field generated by an electrical arc at a contact; an
electrical detector for detecting signals generated in the de-tuned
resonant tank circuit responsive to an electrical arc; and an
output device responsive to the electrical detector. Thus, an
electrical arc at a contact may be detected and cause the output
device to respond thereto.
[0011] An electric meter and contact arc detector may comprise: an
electric meter base having contacts for connecting to an electric
meter socket; a metering device; and a contact arc detector that
may comprise: a de-tuned resonant tank circuit configured to
receive a field generated by an electrical arc at a contact; an
electrical detector for detecting signals in the de-tuned resonant
tank circuit responsive to an electrical arc; and a disconnect
device configured to interrupt an electrical connection to one or
more of the contacts. Thus, electrical arc at a contact may be
detected and cause interruption of an electrical connection to a
contact.
[0012] In summarizing the arrangements described and/or claimed
herein, a selection of concepts and/or elements and/or steps that
are described in the detailed description herein may be made or
simplified. Any summary is not intended to identify key features,
elements and/or steps, or essential features, elements and/or
steps, relating to the claimed subject matter, and so are not
intended to be limiting and should not be construed to be limiting
of or defining of the scope and breadth of the claimed subject
matter.
BRIEF DESCRIPTION OF THE DRAWING
[0013] The detailed description of the preferred embodiment(s) will
be more easily and better understood when read in conjunction with
the FIGURES of the Drawing which include:
[0014] FIG. 1 is a schematic diagram illustrating elevation views
of an example meter socket and of an example embodiment of an
electric meter including a contact arc detector;
[0015] FIG. 2 is a side view of an example embodiment of an
electric meter including a contact arc detector proximate an
example meter socket, and FIG. 2A is an enlarged view of a stab to
jaw connection;
[0016] FIG. 3 is a schematic diagram of example embodiment of an
electric meter contact arc detector; and
[0017] FIG. 4 is an electrical schematic diagram of an example
embodiment of an electrical circuit of an electric meter contact
arc detector.
[0018] In the Drawing, where an element or feature is shown in more
than one drawing figure, the same alphanumeric designation may be
used to designate such element or feature in each figure, and where
a closely related or modified element is shown in a figure, the
same alphanumerical designation may be primed or designated "a" or
"b" or the like to designate the modified element or feature.
Similar elements or features may be designated by like alphanumeric
designations in different figures of the Drawing and with similar
nomenclature in the specification. As is common, the various
features of the drawing are not to scale, the dimensions of the
various features may be arbitrarily expanded or reduced for
clarity, and any value stated in any Figure is by way of example
only.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0019] The present arrangement detects arcing at an electric
contact utilizing a relatively simple broadband detector circuit
installed within close proximity of the meter stabs, e.g., in use,
the stab-to-jaw connections between the electric meter and a meter
socket. One example embodiment of such a detector circuit is
described herein, and other, perhaps simpler, embodiments may be
possible. Because this detector circuit is so simple, it can be
made very small physically, and thus can be placed in relatively
close proximity to where the arcing may occur, e.g., at the stabs.
With the detector circuit so close to the potential arcing
location, more sophisticated methods of discrimination are not
necessary, because the signal generated by the contact arcing falls
off quite rapidly with increasing distance between the location of
the arc and that of the arc detector circuit.
[0020] This arrangement allows for the detection/discrimination
process to be extremely simple due to physical placement of the
detector close to the location of potential arcing. Thus, the
circuit doesn't require that the emissions from arcing be a radio
wave (using the common definition of a radio wave as being a
disturbance where the respective amplitudes of electric and
magnetic fields are proportional to one another related by the
impedance of free space), although the detector operates over a
range of frequencies generally considered to be in a radio
frequency (RF) band. The close proximity placement of the arcing
detector to the location of potential arcing allows electrical
and/or magnetic energy from the arcing to be coupled into a
de-tuned inductor/capacitor tank circuit, e.g., by simple
transformer action with the inductor and circuit wiring in the case
of coupling via a magnetic field created by the arcing, or by
capacitive coupling with the capacitor and circuit wiring in the
case of coupling via an electric field created by the arcing, or by
other means.
[0021] Typically, the harmful effects of electric meter contact
arcing will take more than 20-30 seconds of continuous arcing to
materialize as a dangerous condition, e.g., in the form of melting
of meter components, and/or of out-gassing and/or burning of meter
components, due to heat created by the arcing. Therefore, this
arrangement utilizes a straight forward timing law, which may be
implemented in any number of different ways, e.g., by a
microcomputer or microcontroller and/or with timing networks,
counters and other appropriate electronic circuits.
[0022] FIG. 1 is a schematic diagram illustrating elevation views
of an example meter socket 10 and of an example embodiment of an
electric meter 20 including a contact arc detector 100, FIG. 2 is a
side view of an example embodiment of an electric meter 20
including a contact arc detector 100 proximate an example meter
socket 10, and FIG. 2A is an enlarged view of an example connection
of a stab contact 22 of an electric meter 20 to a jaw contact 12 of
a meter socket 10. Meter socket 10 includes a typically circular
insulating base 14 in which are embedded or otherwise attached a
plurality of electrical contacts 12 each of which is usually a
female contact member referred to as a jaw 12 because it has plural
flexible contact extensions into which a male contact member 22 may
be inserted. Jaws 12 are typically in a standardized pattern with
standardized spacing. In a typical installation, meter socket 10 is
installed, e.g., in a metal electrical box having a sealable
interface for receiving an electric meter 20 with protection
against weather and security against tampering, that is mounted on
a building or other structure or support.
[0023] Electric meter 20 includes a typically circular insulating
base 24 in which are embedded or otherwise attached a plurality of
electrical contacts 22 each of which is usually a male contact
member 22 referred to as a stab 22 because it has a male contact
member 22 which may be inserted into a female contact member 12.
Stabs 22 are typically in a standardized pattern with standardized
spacing that corresponds to the pattern and spacing of contacts 12
of meter socket 10. In a typical installation, electric meter 20 is
installed into a metal electrical box containing a meter socket 10
and the metal electrical box provides a sealable interface for
protection against weather and for security against tampering with
electric meter 20.
[0024] Electrical contact arc detector 100 is typically and
preferably mounted near the insulating base 24 of electric meter 20
in relatively close proximity to stabs 22, e.g., in a region
generally centrally located within the pattern of stabs 22.
Insulating meter base 24 is typically circular and of substantially
the same size as is socket base 14. Meter base 24 also typically
supports a metering device 30 having a meter readout 32.
[0025] Metering device 30 may be, e.g., an electro-mechanical
metering device 30 driven by the power passing through meter 20 and
having a mechanical dial read out 32 or an electronic readout 32,
or may be, e.g., an electronic metering device 30 having an
electronic readout 32 or having a transmitter for transmitting
metering and/or status information to a utility via a communication
link or network. The latter more modern type of electric meter 30
is typically referred to as a "smart meter" and includes a
microprocessor or micro-controller that digitally monitors and
meters electric power usage and status, and that typically can
actuate a disconnect device, e.g., an electro-mechanical or an
electronic disconnect device, to disconnect the power supply mains
from the utilization wiring and equipment at that location, e.g.,
by interrupting the electrical power connection to one or more of
stabs 22 of meter 20.
[0026] With stabs 22 inserted into jaws 12, the contact extensions
of jaws 12 are urged outwardly, e.g., apart, by stab 22 thereby to
create pressure between jaw 12 and stab 22 for making a better
electrical connection over the area AR of physical contact between
the surfaces of jaw 12 and stab 22. But neither the contact area AR
nor the electrical connection is perfect, e.g., due to surface
imperfections, tarnish, corrosion, foreign matter and the like, and
so electrical arcing will eventually occur in region AR. While the
electric and magnetic fields generated by the electrical current
flowing through the connection of jaws 12 and stab 22 are at the
power line frequency, the electric and magnetic fields generated by
the electrical arcing are over a broad band of frequencies,
including radio frequencies that are at least in part within the
bandwidth of electrical arc detector 100.
[0027] FIG. 3 is a schematic diagram of example embodiment of an
electric meter contact arc detector 100. Therein, the electric and
magnetic fields generated by the electrical arcing (indicated by
the four jagged arrows) impinge upon a resonant electrical circuit
110, e.g., a so-called L-C tank circuit, to produce a voltage which
is coupled via summing node 140 to detector 120, e.g., to the "+"
input thereof. A reference level or offset 160 is applied to the
other input of detector 120, e.g., to the "-" input thereof, to
establish a minimum or threshold level below which detector 120
does not respond and above which detector 120 produces a detection
signal at its output.
[0028] When detector 120 responds to the electric and magnetic
fields generated by the electrical arcing, its output signal may be
applied for two purposes. Firstly, the output signal from detector
120 may directly or indirectly cause a power switch 130, e.g., a
contactor or circuit breaker, to be actuated to disconnect or
interrupt the power supply mains received at one or more of stabs
22, thereby to disconnect electrical power flowing to the utilizing
load and to extinguish the current flow that is producing
electrical arcing.
[0029] The output signal from detector 120 is also applied to
feedback network 150 and through that feedback network 150 to the +
input of detector 120 via summing node 140, thereby to provide
positive feedback to cause detector 120 to remain in the arc
detecting condition, at least temporarily. Feedback network 150
preferably is AC coupled and has a time constant that controls the
time that detector 120 remains in the arc detecting condition so
that its output is of sufficient duration to directly or indirectly
cause power switch 130 to activate and disconnected electrical
power, thereby to remove electrical power from the supply mains, or
to satisfy another utilization condition.
[0030] Alternatively, and usually preferably, the arc detector 100
acts indirectly in that it provides an output signal of sufficient
duration to indicate an occurrence of electrical arcing to the
micro-controller or microprocessor of the metering device 30 of
electric meter 20. That micro-controller or microprocessor would
then, if the extent and/or duration of electrical arcing exceeds a
predetermined limit or threshold, actuate the disconnect switch of
the electric meter 20 if the meter manufacturer and/or utility has
provided and enabled that functionality.
[0031] Because detection circuit 100 is relatively simple and does
not filter out or correlate any false signals, e.g., signals from
AMI transmitters or other RF sources, it is preferred that such
functionality be implemented by the micro-controller or
microprocessor of the metering device 30 of electric meter 20 in
the manner determined by the utility utilizing such meter. It is
noted that different utilities will likely have different limit
and/or threshold criteria for different types of electric meters,
for electric meters from different manufacturers, and for their
determined level of risk and experience relating to electric meters
and their problems, including electrical arcing and possibly fires
resulting from electrical arcing of electric meters.
[0032] Typically, in a smart meter 20, actuation of disconnecting
power switch 130 is detected by the microprocessor or
micro-controller thereof and is communicated by electric meter 20,
e.g., by a transmitter and/or modem associated with metering device
30, to a utility. Power may be reconnected by resetting
disconnecting power switch, e.g., manually at the location of meter
20, by remote control from the utility utilizing the microprocessor
or micro-controller of meter 20, or by the microprocessor or
micro-controller of meter 20 monitoring conditions at meter 20 and
initiating the resetting of switch 130.
[0033] Electrical power for arc detector 100 is provided by power
supply 180 which may take one of many forms. In its simplest form,
power supply 180 may be a battery. In another form, power supply
180 may be or may be part of a power supply that is part of a smart
meter 20 or another electronic meter 20, e.g., that is part of
metering device 30 thereof. Typically, power supply 180 derives
electrical power from the power supply mains received via stabs 22
and may include, among other things, a rectifier, transformer,
and/or DC converter. Even such DC converters may include a back up
battery power source for times when there is an outage or other
loss of power received from power supply mains.
[0034] FIG. 4 is an electrical schematic diagram of an example
embodiment of an electrical circuit of an electric meter contact
arc detector 100. The illustrated detector circuit 100 is
illustrative of an example embodiment of an electrical arc detector
100 of the sort shown and described in relation to FIG. 3. The
electric and/or magnetic fields created by electrical contact
arcing impinges upon the tank circuit formed by capacitor C1 and
inductor L1, an L-C tank circuit, which is physically located
proximate to the site or sites of potential electrical arcing.
[0035] Capacitor C1 and inductor L1 comprise a tank circuit 110 or
resonant circuit 110 which resonates when excited by energy coupled
into it from any nearby alternating magnetic or electric field of
sufficient strength and having a frequency within the appropriate
range, which is substantially higher than the utility power line
frequency, e.g., 60 Hz in the United States and 50 Hz in Europe and
elsewhere. Thus, the tank circuit 110 does not respond to the
utility power line frequency.
[0036] The tank circuit L1-C1 is de-tuned by the resistive load
imposed on it via connection to resistor R3 and/or resistors R7,
R1, R2 so that it's quality factor Q is reduced and its frequency
response or bandwidth is broadened. The DC voltage applied at
capacitor C2 is at a DC voltage level that is set by the adjustable
potentiometer R7 in cooperation with resistors R1, R2 and
diode-connected transistor Q3 to be used (after adjustment) as a
predetermined reference or threshold level for detector circuit 120
which is provided by transistors Q1, Q2 for detecting the electric
and/or magnetic field created by electric contact arcing.
[0037] As ambient temperature changes induce changes in the
base-to-emitter voltages Vbe of transistors Q1 and Q3, the amount
of thermally induced drift in the two transistors Q1, Q3 is
substantially the same if the transistors Q1, Q3 are thermally
coupled, as is preferred, and so the effects of temperature change
are substantially reduced. Ideally transistors Q3 and Q1 are in the
same package, so as to be closely thermally coupled, such as a dual
NPN transistor array that is fabricated on a common substrate. The
constant voltage on capacitor C2 produces an offset voltage which
adds to the signal voltage produced by the tank circuit 110 formed
by C1/L1. In practice, potentiometer R7 is set so that the DC
voltage at capacitor C2 is just below the threshold which causes
transistor Q1 to start conducting.
[0038] Transistors Q1, Q2 of detector 120 are preferably
interconnected so as to function as a latching circuit. Once
transistor Q1 starts to conduct, the base of transistor Q2 is
pulled low by the conduction of transistor Q1 to turn transistor Q2
on, whereby current flows out of the emitter of transistor Q2. The
portion of that current that flows through the series circuit
including resistor R4 and capacitor C3 will provide positive
feedback that will tend to turn transistor Q1 on even further. This
positive feedback action causes transistors Q1 and Q2 to further
turn on until a saturated condition whereby the Q1-Q2 transistor
pair are latched in a fully turned on or saturated condition,
thereby to provide an output signal from detector 120. Once this
conduction commences, it will continue for a time period determined
by time constant determined by the values of resistor R4 and
capacitor C3. Once triggered, transistor pair Q1-Q2 remain ON until
C3 charges completely, thus reducing the feedback current to zero,
removing the drive to transistor Q1 so that transistors Q1-Q2 both
turn off, terminating the output signal from detector 120.
[0039] When transistor Q2 is conducting, an output signal is
generated from electric contact arc detector circuit 100 suitable
for initiating an action, e.g., signaling for operation of a
disconnect switch or interrupter or contactor or circuit breaker,
to reduce the electrical current flowing at the site of the
electrical arcing thereby to reduce the arcing to a safe level or
to extinguish the arcing. Transistors Q1, Q2 thus function as a
detector 120 or as a comparator 120 that compares the voltage
generated across the de-tuned L-C tank circuit 110 to the reference
(or offset) voltage provided by reference source 160.
[0040] The signal output from transistors Q1-Q2 of detector 120 may
be applied via and/or to different utilization devices, of which
two examples are described. In a first example, the turning on of
transistor Q2 causes current to flow through the light emitting
diode (LED) D1 which illuminates to produce light indicating that a
triggering arcing event has occurred, e.g., likely to be arcing at
one or more meter connections. While LED D1 may provide a visual
indication or warning that arcing has occurred, the light produced
thereby may be utilized to impinge upon an opto-electronic device,
e.g., a photo-diode, of an optical coupler coupled for initiating
operation of an interrupt and/or disconnect device 130.
[0041] Alternatively, in another example, output current from
transistor Q2 way be applied to turn on a further transistor Q4
which, e.g., directly is coupled to initiate operation of an
interrupt and/or disconnect device 130.
[0042] The illustrated example circuit 100 of FIG. 4 includes an
on/off switch S1 and a battery BT1 for convenience in testing,
e.g., testing of circuit 100 and or testing of circuit 100 in an
electric meter 20, and one or both thereof would not likely be
included in a commercial embodiment of circuit 100. However, in an
embodiment of detector 100 configured, e.g., as a portable tester
for detecting electrical arcing, then an on/off switch S1 and a
battery power source 180 would be provided in a housing containing
detector 100, and an LED D1 and/or an audible indicator 130 would
be provided, e.g., to provide a visual and/or audible indication
that the presence of electrical arcing had been detected.
[0043] In the illustrated example embodiment, PNP transistor Q2 is
intentionally operated in an "inverted" mode wherein the terminal
thereof normally serving as the emitter serves as its collector and
the terminal thereof normally serving as the collector serves as
the emitter, so that the effective current gain (e.g., beta) of
transistor Q2 is substantially less than that in normal mode
operation. Typically, transistor Q2 when operated in inverted mode
exhibits a current gain of about two, which in combination with the
normal mode current gain of NPN transistor Q1 provides sufficient
gain for the described latching operation of transistors Q1-Q2. A
high beta, such as exhibited in normal mode operation of
transistors Q1 and Q2, could make the Q1-Q2 latching circuit
unstable, e.g., susceptible to oscillating during its turning on
(becoming latched) and turning off (becoming unlatched), however,
that gain could be attenuated at higher frequencies by employing a
small capacitor and/or inductor, e.g., a ferrite bead that slips
onto a wire, such as one of the leads of a transistor or another
electrical component.
[0044] In a typical example embodiment of the detector circuit 100
of FIG. 4, the circuitry is powered by a small 3V DC "coin" cell
battery 180, BT1, so that it could easily be fitted into an
electric meter without having to modify or connect to the meter's
existing electronics. In practice, however, detector circuit 100
would preferably be powered by an existing low voltage DC power
supply 180 that is built into the smart meter 20; the additional
power drawn from that power supply appears to be negligible. An
example parallel LC tank circuit 110 with inductor L1=100 .mu.H and
capacitor C1=820 pF provides a calculated resonance frequency of
about 560 kHz, and preferably has a relatively broad bandwidth,
e.g., preferably in the range of about 10 kHz to several hundred
KHz. The value of de-tuning resistor R3, e.g., 100 kilohms, which
couples the L1-C1 tank circuit 110 output into the base of
transistor Q1 can be determined empirically, e.g., to obtain a
desired bandwidth.
[0045] In one example, the offset voltage 160 was set about 0.6V,
partly to offset a substantial amount of the base-to-emitter
threshold voltage Vbe of transistor Q1, so that the voltage
generated across the L1-C1 tank circuit 110 by the electric and/or
magnetic fields produced by electrical arcing only needed to be
around about 20 mV to trigger the Q1-Q2 detector circuit 120 to
detect the arcing.
[0046] The time duration of the electrical arcing which results in
damage to the electric meter 20 varies greatly between electric
meters of different configurations and types and between those from
different manufacturers, as well as with the material from which
meter base 24, and socket base 14, are made. Some electric meters
can withstand electrical arcing for more than 10 minutes with
minimal damage, and other electric meters can only withstand about
20-30 seconds of electrical arcing before exhibiting visible
melting and out-gassing, e.g., of the meter base. Thus, it is
preferred that time limits for allowable duration of electrical
arcing and delay before initiating a disconnect or interrupt be
incorporated into a microcontroller or microprocessor of the
metering device 30. Typically, a manufacturer or utility can
program the acceptable values for a particular electric meter 20
into the software controlling the microcontroller or microprocessor
of metering device 30 thereof so that, e.g., an electrical arc must
persist for a predetermined time before the disconnect device 130
is activated.
[0047] The timing controlled by the time constant provided by
resistor R4 and capacitor C3 is preferably selected to set the
minimum pulse width duration at the output of detector circuit 100,
120. The minimum pulse width for each detection should be of
sufficient duration to ensure that the
micro-controller/microprocessor in the metering device 30 and/or
the interrupt or disconnect device 130 will properly and reliably
respond to the pulse. Where a visible LED D1 is provided, the
minimum pulse width could be selected so that a human observer,
e.g., service personnel, could see that the LED illuminates
indicating when arcing has occurred.
[0048] An electric meter 20 and contact arc detector 100 may
comprise: an electric meter base 24 formed of an electrically
insulating material and having a plurality of stab contacts 22
configured for making electrical connection to plural contacts 12
of an electric meter socket 10; a metering device 30 supported by
the electric meter base 24; and a contact arc detector 100
supported by the electric meter base 24, the contact arc detector
100 may comprise: a de-tuned resonant tank circuit 110 configured
to receive a magnetic field and/or an electric field generated by
an electrical arc at one or more of the plurality of stab contacts
22; an electrical detector 120 to which the de-tuned resonant tank
circuit 110 is coupled for detecting signals generated in the
de-tuned resonant tank circuit 110 responsive to the magnetic field
and/or an electric field generated by an electrical arc at one or
more of the plurality of stab contacts 22; and a disconnect device
130 responsive directly or indirectly to the electrical detector
120 and configured to interrupt an electrical connection to one or
more of the plurality of stab contacts 22. An electrical arc at one
or more of the plurality of stab contacts 22 may be detected and
cause the interruption of an electrical connection to one or more
of the plurality of stab contacts 22. The de-tuned resonant tank
circuit 110 may include an inductor L and a capacitor C in parallel
connection. The de-tuned resonant tank circuit 110 may be coupled
to a resistance R for de-tuning the resonant tank circuit 110 to
broaden the bandwidth thereof. The electrical detector 120 may have
two inputs, a first of the two inputs thereof being coupled to the
de-tuned resonant tank circuit 110 and a second of the two inputs
thereof being connected to a reference source 160 configured to
provide an offset to a detection threshold of the electrical
detector 120. The electrical detector 120 may include: a timing
network 150 for determining a duration of an output signal
therefrom. The timing network 150 may include a resistor R and a
capacitor C connected for determining a time constant. The
electrical detector 120 may include first and second transistors
Q1, Q2, an output electrode of each of the first and second
transistors Q1, Q2 being coupled to an input electrode of the other
of the first and second transistors Q1, Q2, wherein turning the
first transistor Q1 on causes the second transistor Q2 to turn on
causing positive feedback 150 to the input electrode of the first
transistor Q1, whereby the first and second transistors Q1, Q2
latch into an on condition. The output electrode of the second
transistor Q2 may be coupled to the input electrode of the first
transistor Q1 by a resistor R and a capacitor C connected for
determining a time constant, whereby the first and second
transistors Q1, Q2 latch into the on condition for a predetermined
time. The electric meter 20 and contact arc detector 100 may
further comprise: an optical coupler D1 or a transistor Q4 coupling
the electrical detector 120 to the disconnect device 130. The
electric meter 20 and contact arc detector 100 may further
comprise: a metering device 30 including a micro-controller or a
microprocessor, wherein said micro-controller or microprocessor is
responsive to said electrical detector 120 to cause said disconnect
device 130 to interrupt an electrical connection to one or more of
the plurality of stab contacts 22; or to cause the disconnect
device 130 to interrupt an electrical connection to one or more of
the plurality of stab contacts 22 after the output of the
electrical detector 130 persists for a predetermined time.
[0049] An electric meter contact arc detector 100 mountable to an
electric meter base 24 formed of an electrically insulating
material and having a plurality of stab contacts 22 configured for
making electrical connection to plural contacts 12 of an electric
meter socket 10, and a metering device 30 supported by the electric
meter base 24;, the contact arc detector 100 may comprise: a
de-tuned resonant tank circuit 110 configured to receive a magnetic
field and/or an electric field generated by an electrical arc at
one or more of the plurality of stab contacts 22; an electrical
detector 120 to which the de-tuned resonant tank circuit 110 is
coupled for detecting signals generated in the de-tuned resonant
tank circuit 110 responsive to the magnetic field and/or an
electric field generated by an electrical arc at one or more of the
plurality of stab contacts 22; and an output device 30, 130, D1, Q4
responsive to the electrical detector 120 and configured to respond
to detection of an electrical arc at one or more of the plurality
of stab contacts 22. An electrical arc at one or more of the
plurality of stab contacts 22 may be detected and cause the output
device 30, 130, D1, Q4 to respond to detection of an electrical arc
at one or more of the plurality of stab contacts 22. The de-tuned
resonant tank circuit 110 may include an inductor L and a capacitor
C in parallel connection. The de-tuned resonant tank circuit 110
may be coupled to a resistance R for de-tuning the resonant tank
circuit 110 to broaden the bandwidth thereof. The electrical
detector 120 may have two inputs, a first of the two inputs thereof
being coupled to the de-tuned resonant tank circuit 110 and a
second of the two inputs thereof being connected to a reference
source 160 configured to provide an offset to a detection threshold
of the electrical detector 120. The electrical detector 120 may
include: a timing network 150 for determining a duration of an
output signal therefrom. The timing network 150 may include a
resistor R and a capacitor C connected for determining a time
constant. The electrical detector 120 may include first and second
transistors Q1, Q2, an output electrode of each of the first and
second transistors Q1, Q2 being coupled to an input electrode of
the other of the first and second transistors Q1, Q2, wherein
turning the first transistor on causes the second transistor Q2 to
turn on causing positive feedback to the input electrode of the
first transistor Q1, whereby the first and second transistors Q1,
Q2 latch into an on condition. The output electrode of the second
transistor Q2 may be coupled to the input electrode of the first
transistor Q1 by a resistor R and a capacitor C connected for
determining a time constant, whereby the first and second
transistors Q1, Q2 latch into the on condition for a predetermined
time. The electric meter contact arc detector 100 wherein the
output device 130 may include: an audio or visual indicator D1,
130, or a light emitting diode D1 configured to provide an
indication that the electrical detector 120 has detected electrical
arcing; or an optical coupler D1 or a transistor Q4 or a metering
device 30 directly or indirectly coupling the electrical detector
120 to a disconnect device 130 configured to interrupt electrical
power to one of more of the plurality of stab contacts 22. The
electric meter contact arc detector may further comprise a metering
device 30 including a micro-controller or a microprocessor
supported by the electric meter base 24, wherein the metering
device 30 responds to the output of the electrical detector 120:
for activating the output device 130; or for determining a duration
of the output of the electrical detector 120; or for activating the
output device 130 after the output of the electrical detector 120
persists for a predetermined time.
[0050] As used herein, the term "about" means that dimensions,
sizes, formulations, parameters, shapes and other quantities and
characteristics are not and need not be exact, but may be
approximate and/or larger or smaller, as desired, reflecting
tolerances, conversion factors, rounding off, measurement error and
the like, and other factors known to those of skill in the art. In
general, a dimension, size, formulation, parameter, shape or other
quantity or characteristic is "about" or "approximate"whether or
not expressly stated to be such. It is noted that embodiments of
very different sizes, shapes and dimensions may employ the
described arrangements.
[0051] Although terms such as "up," "down," "left," "right," "up,"
"down," "front," "rear," "side," "end," "top," "bottom," "forward,"
"backward," "under" and/or "over," "vertical," "horizontal," and
the like may be used herein as a convenience in describing one or
more embodiments and/or uses of the present arrangement, the
articles described may be positioned in any desired orientation
and/or may be utilized in any desired position and/or orientation.
Such terms of position and/or orientation should be understood as
being for convenience only, and not as limiting of the invention as
claimed.
[0052] As used herein, the term "and/or" encompasses both the
conjunctive and the disjunctive cases, so that a phrase in the form
"A and/or B" encompasses "A" or "B" or "A and B." In addition, the
term "at least one of" one or more elements is intended to include
one of any one of the elements, more than one of any of the
elements, and two or more of the elements up to and including all
of the elements, and so, e.g., the phrase in the form "at least one
of A, B and C" includes "A," "B," "C," "A and B," "A and C," "B and
C," and "A and B and C."
[0053] As used herein, the terms "connected" and "coupled" as well
as variations thereof are not intended to be exact synonyms, but to
encompass some similar things and some different things. The term
"connected" may be used generally to refer to elements that have a
direct electrical and/or physical contact to each other, whereas
the term "coupled" may be used generally to refer to elements that
have an indirect electrical and/or physical contact with each
other, e.g., via one or more intermediate elements, so as to
cooperate and/or interact with each other, and may include elements
in direct contact as well.
[0054] A fastener as used herein may include any fastener or other
fastening device that may be suitable for the described use,
including threaded fasteners, e.g., bolts, screws and driven
fasteners, as well as pins, rivets, nails, spikes, barbed
fasteners, clips, clamps, nuts, speed nuts, cap nuts, acorn nuts,
and the like. Where it is apparent that a fastener would be
removable in the usual use of the example embodiment described
herein, then removable fasteners would be preferred in such
instances. A fastener may also include, where appropriate, other
forms of fastening such as a formed head, e.g., a peened or heat
formed head, a weld, e.g., a heat weld or ultrasonic weld, a braze,
and adhesive, and the like.
[0055] The term battery is used herein to refer to an
electro-chemical device comprising one or more electro-chemical
cells and/or fuel cells, and so a battery may include a single cell
or plural cells, whether as individual units or as a packaged unit.
A battery is one example of a type of an electrical power source
suitable for a portable or other device. Such devices could include
power sources including, but not limited to, fuel cells, super
capacitors, solar cells, and the like. Any of the foregoing may be
intended for a single use or for being rechargeable or for
both.
[0056] Various embodiments of a battery may have one or more
battery cells, e.g., one, two, three, four, or five or more battery
cells, as may be deemed suitable for any particular device. A
battery may employ various types and kinds of battery chemistry
types, e.g., a carbon-zinc, alkaline, lead acid, nickel-cadmium
(Ni--Cd), nickel-metal-hydride (NIMH) or lithium-ion (Li-Ion)
battery type, of a suitable number of cells and cell capacity for
providing a desired operating time and/or lifetime for a particular
device, and may be intended for a single use or for being
rechargeable or for both.
[0057] The term DC converter is used herein to refer to any
electronic circuit that receives at an input electrical power at
one voltage and current level and provides at an output DC
electrical power at a different voltage and/or current level.
Examples may include a DC-DC converter, an AC-DC converter, a boost
converter, a buck converter, a buck-boost converter, a single-ended
primary-inductor converter (SEPIC), a series regulating element, a
current level regulator, and the like. The input and output thereof
may be DC coupled and/or AC coupled, e.g., as by a transformer
and/or capacitor. A DC converter may or may not include circuitry
for regulating a voltage and/or a current level, e.g., at an output
thereof, and may have one or more outputs providing electrical
power at different voltage and/or current levels and/or in
different forms, e.g., AC or DC.
[0058] The term "utility" is used herein in several ways to include
all of the recognized used and definitions of the term. It may be
used in relation to a company, corporation, government agency or
other entity that supplies and/or controls the supply of a utility,
e.g., electrical power, as well as what is supplied, e.g.,
electricity. The term may also be used in relation to the system,
transmission lines, distribution lines, wires, meters, equipment,
transformers and the like employed in connection with transmitting
and/or delivering the utility to a customer or other user.
[0059] While the present invention has been described in terms of
the foregoing example embodiments, variations within the scope and
spirit of the present invention as defined by the claims following
will be apparent to those skilled in the art. For example, the
output from detector 100, 120 may be coupled to an LED, or to a
utilization device 130, or to both an LED and a utilization device
130. The coupling may be direct, e.g., to an LED D1 that serves as
a visual indicator, or indirectly, e.g., via an LED D1 that is part
of an opto-electronic coupler that itself is directly coupled to a
disconnect device or that is coupled thereto via a micro-controller
or microprocessor of an electric meter 20, e.g., of a metering
device 30 thereof.
[0060] Detector 120 may be implemented by discrete electronic
components as illustrated, or may alternatively employ a comparator
or high-gain amplifier, e.g., in integrated circuit form, or may be
implemented digitally in a micro-controller or microprocessor that
is part of a metering device 30 of an electric meter 20.
[0061] While certain features may be described as a raised or male
feature, e.g., a stab, ridge, boss, flange, projection or other
raised or male feature, such feature may be positively formed or
may be what remains after a recessed or female feature, e.g., a
jaw, groove, slot, hole, indentation, recess or other recessed
feature, is made. Similarly, while certain features may be
described as a recessed or female feature, e.g., a jaw, groove,
slot, hole, indentation, recess or other recessed feature, such
feature may be positively formed as a female feature or may be what
remains after a raised feature, e.g., a stab, ridge, boss, flange,
projection or other raised feature, is made. For example, two
closely spaced male features, e.g., stabs similar to stab 22, could
define a female feature, e.g., a jaw 12, configured to receive a
stab 22 there between.
[0062] Preferably the LC tank circuit 110 of detector 100 is
located within the housing 24, 28 of electric meter 20, which would
typically put the detector tank circuit 110 within about 4 inches
(about 10 cm), or less, of all the stabs 22 of the electric meter
20, as illustrated. Alternately, plural detector tank circuits 110
may be employed, so that a separate dedicated detector LC tank
circuit 110 could be located more closely to each stab 22, e.g., to
each potential arcing location, typically within about 1 inch
(about 2.5 cm), or less, of each stab 22. Such plural detector LC
tank circuits 110 may be connected in series and coupled to a
common detector circuit 120, or may be coupled to separate detector
circuits 120.
[0063] While the typical electric meters described herein usually
have plural stab contacts and the meter sockets described herein
usually have plural jaw contacts, the present arrangement is
equally suitable for use with electric meters and sockets that have
different contact configurations, e.g., an electric meter having
plural jaw contacts, a meter socket having plural stab contacts, or
an electric meter and meter socket each having various combinations
of stabs and jaws, and the terms stab contact and jaw contact in
the claims, whether singular or plural, are expressly intended to
be so construed.
[0064] Each of the U.S. Provisional Applications, U.S. Patent
Applications, and/or U.S. Patents, identified herein is hereby
incorporated herein by reference in its entirety, for any purpose
and for all purposes irrespective of how it may be referred to or
described herein.
[0065] Finally, numerical values stated are typical or example
values, are not limiting values, and do not preclude substantially
larger and/or substantially smaller values. Values in any given
embodiment may be substantially larger and/or may be substantially
smaller than the example or typical values stated.
* * * * *
References