Note: Descriptions are shown in the official language in which they were submitted.
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MODULAR CORE, SELF-POWERED POWERLINE SENSOR
FII?LD OF INVLNTION
This invention relates to a modular core, self powered powerline sensor and
more
particularly to such a sensor which is capable of effciently extracting power
from
powerlines having extremely low level line currents.
BACKGROUND OF INVENTION
Monitoring a.c. powerlines, in both overhead and underground and primary and
secondary applications, is a useful practice for electric utility companies in
order to
anticipate outages which occur due to faulty equipment and overloads on a.c.
powerlines
and which result in loss of service for potentially a (urge number of
customers. The
potential for an outage and for the loss of the greatest number of customers
is incre<rsed
during peak periods when power usage is at a maximum and delivery of
continuous power
is most critical. Outages caused by faulty and overloaded lines, transformers
and other
equipment are expensive to repair, dangerous for utility company employees and
costly to
the electric utility company in terms of income lost for lost service and in
terms of damage
to the utility's reputation. The effects of an unexpected outage as a result
of a faulty or
overloaded powerline are exacerbated if the powerline is underground.
Replacing a.
damaged underground line requires more man hours and increased safety
precautions due
to the fact that the majority of work required occurs underground in cramped,
sometimes
wet, and always less than ideal conditions. As a result, repairing such a
damaged
underground line is even more costly, time consuming and dangerous.
Thus, a.c. powerline sensors which sense electrical conditions, such as power,
voltage and current are very useful to electric utility companies in
monitoring a.c.
CA 02241837 2002-O1-07
powerlines and associated equipment such as transformers and switches, in
order to better
anticipate the likelihood of an unexpected outage occurring due to faulty and
overloaded
equipment. If the electric utility companies are able to monitor the
conditions on the
powerlines, they are better able to perform maintenance on and replacement of
powerlines
which are likely to become de-energized as a result of an overload or fault,
thereby
lowering the number of unexpected outages. By replacing and maintaining such
equipment the utility company can significantly decrease outage time to the
customer.
The costs associated with repair or replacement of damaged cables will also be
decreased:
the cost of replacing or repairing damaged cables may be significantly greater
in
comparison to normal scheduled maintenance or replacement because of the
overtime pay
involved.
Conventional commercial powerline sensors, however, typically require an
invasive electrical connection to the power circuit that is being monitored.
This type of
installation is expensive for the utility company, potentially dangerous for
the installer and
can cause a service interruption for the customer. Due to these limitations,
powerline
sensors have not been widely used in the electric utility industry.
One sensor described in I1.S. Patent No. 5,892,430 and assigned to the
assignees of
the instant invention, overcomes the deficiencies of the prior au systems.
That sensor
utilizes a thin but relatively wide core layer of high permeability
fewomagnetic material
which is wrapped about the insulating rubber layer of an a.c. powerline in a
completely
non-invasive manner. A plurality of windings are wound about the core layer so
that they
are substantially parallel to the direction of the a.c. powerline. The a.c. in
the powerline is
used to induce a current in the windings to power the sensor and a controller
and to sense
the current in the a.c. powerline as well as to measure a non-referenced
voltage level. That
sensor is very low in profile and is therefore capable of being easily
installed in restrictive
volumes and on very closely spaced lines. Moreover, it operates without an
invasive
contact to the powerline and is therefore safely, easily and quic(~ly
installed. That sensor
does, however, have shortcomings.
First and foremost, it does not efficiently extract power from the a.c.
powerline. In
order to get the most efficient extraction of power, the core layer should be
toroidal in
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shape, with the thickness of the core layer cross-section approximately equal
to its width.
However, to maintain a low profile that sensor has a core layer cross-section
which is
significantly wider than it is thick. This results in a sensor which does not
efficiently
extract power from the powerline and therefore is not capable of extracting
sufficient
power to operate on powerlines with low line currents. In order to extract
more power,
the width of the core layer must be increased, but at the same time to
maximize
efficiency, the cross-section thickness must be commensurately increased. To
achieve the
power requirement desired, the thickness of the core layer cross-section must
be increased
to a point where its low profile configuration is no longer maintained and
therefore is no
longer capable of being installed in restrictive volumes and on closely spaced
lines.
Additionally, the width of the core layer of that sensor makes it somewhat
inflexible and difficult to install on portions of powerlines which have
radical curvatures.
SUMMARY OF INVENTION
It is therefore an object of this invention to provide a modular core, self
powered
powerline sensor that senses conditions in or about an a.c. power line in a
completely
non-invasive manner.
It is a further object of this invention to provide such a modular core, self
powered powerline sensor which efficiently maximizes the extraction of power
from the
. a.c. powerline while maintaining a low profile configuration.
It is a further object of this invention to provide such a modular core self
powered
powerline sensor which is capable of extracting power from powerlines with
extremely
low line currents.
It is a further object of this invention to provide such a modular core, self
z~ powered poweriine sensor which is very ilexibie.
It is a further object of this invention to provide such a modular core, self
powered powerline sensor that is powered by low power drawn directly from the
a.c.
powerline in a completely non-invasive manner.
It is a further object of this invention to provide such a modular core, self
powered powerline sensor that is capable of transmitting sensed conditions in
and about
the a.c. powerline over the powerline itself.
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It is a further object of this invention to provide such a modular core, self
powered powerline sensor that is capable of transmission to and reception of
communications from a remote base station over the a.c. powerline in a
completely non-
invasive manner.
It is a further object of this invention to provide such a modular core, self
powered powerline sensor that is quickly, easily and safely installed without
interrupting
or affecting power service to the customer.
It is a further object of this invention to provide such a modular core, self
powered powerline sensor that may be installed on various size powerlines.
It is a further object of this invention to provide such a modular core,
powerline
sensor that may be installed on closely spaced cables in restrictive volumes.
It is a further object of this invention to provide such a modular core, self
powered powerline sensor that has a low profile, is compact in size and is
light weight.
It is a further object of this invention to provide such a modular core, self
i5 powered powerline sensor that is mechanically supported by the a.c.
powerline.
It is a further object of this invention to provide such a modular core, self
powered powerline sensor that is inexpensive and disposable.
This invention results from the realization that a very low profile, self
powered
powerline sensor that can efficiently extract sufficient power to operate even
from an a.c.
. powerline having an extremely low line current can be achieved by providing
a core
containing a plurality of Iow profile modular core elements disposed about the
a.c.
powerline, each having a number of windings which extract power from the a.c.
powerline, wherein the windings of each of the modular core elements are
interconnected,
providing a means for sensing a condition in or about the a.c. powerIine and
controller
means, powered by the windings and responsive to the means for sensing, for
receiving a
signal indicative of the condition sensed.
This invention features a modular core, self powered powerline sensor. The
current extraction device of the sensor includes a plurality of modular core
elements for
disposing about an a.c. powerline. There is a winding layer to be energized by
the a.c.
powerline, including a plurality of windings disposed about each modular core
element.
The windings of each modular core element are interconnected. The current and
voltage
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sensor and other means for sensing a condition in or about the a. c. powerline
are powered
by the windings if they require power. A controller, also powered by the
windings, is
responsive to the means for sensing and receives (and transmits) a signal
indicative of the
condition sensed.
5 In a preferred embodiment the modular core elements of the current
extraction
devices are preferably toroidal in shape, Iow in profile and they may be
formed of highly
magnetically permeable ferromagnetic material. The width of the core elements
may
approximately equal their cross-section thickness. The modular core elements
may
contain gaps therein which may be urged apart for enabling the powerline
sensor to be
installed on and removed from the a.c. powerline. The windings of each modular
core
element may be interconnected electrically in series or in parallel and the
windings may
be energized by non-contacting transformer action with the a.c. powerline.
The voltage sensor includes a capacitor for capacitively sensing the voltage
on the
a.c. powerline, including first and second spaced plates located proximate the
a.c.
powerline and a dielectric disposed between the plates. The dielectric may be
air. The
first and second spaced plates may be coaxially disposed about the a.c.
powerline. The
current sensor is an inductor and includes a plurality of windings disposed
about the first
and second spaced plates and a separating material. Other sensors may be used
to sense a
plurality of other conditions in or about the a.c. powerline.
~ The controller means may include means for transmitting the signal
indicative of
the sensed condition over the a. c. powerline. The means for transmitting may
transmit
the signal to a remote base station. The means for transmitting may include a
communications core element disposed about the a.c. powerline and a plurality
of
windings disposed about the communications core element for coupling the
signal to the
a.c. poweriine through non-contacting transformer action. The controller means
may
include means for transmitting the signal indicative of the sensed condition
over the a.c.
powerline and the means for transmitting may be interconnected with the
capacitor to
capacitively couple the signal to the a.c. powerline. The controller means may
include
means for receiving communications from a remote base station and the means
for
receiving may be interconnected to the capacitor to capacitively couple the
communications from the powerline. The controller means may include means for
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receiving communications from a remote base station transmitted over the a.c.
powerline.
The means for receiving may include a communications core element disposed
about the
a. c. powerline and a plurality of windings disposed about the communications
core
element for coupling from the a.c. powerline the communications from remote
base '
station. The controller means may include means for transmitting the signal
indicative of
the sensed condition over the a.c. powcrline and means for receiving
communications
transmitted from a remote base station, wherein the means for transmitting and
means for
receiving are interconnected to the capacitor to capacitively couple signals
transmitted by
the controller means to the a.c. powerline and capacitively couple signals
from the a.c.
powerline transmitted by the remote base station. The controller means may
further
include means for receiving communications from a remote base station and the
plurality
of windings on the communications core element may couple the communications
from
the a.c. powerline through non-contacting transformer action. The controller
means may
include means for statistically manipulating the received signals indicative
of the sensed
condition over a predetermined time period to establish a nominal condition
level and
means for detecting variances from said nominal level. The sensed condition
may be
voltage. The means for statistically manipulating may include means for
averaging the
signals received over the predetermined time period.
. I~ISCLOSUItE OF PREFERRED EMBODIIVIENT
Other objects, features and advantages will occur to those skilled in the art
from
the following description of a preferred embodiment and the accompanying
drawings, in
which:
Fig. lA is a three dimensional view of a modular core, self powered powerline
sensor according to this invention;
Fig. 1B is a schematic view depicting the interconnection of the windings
about
the modular core elements of Fig. 1; '
Fig. 1C is a three dimensional view of the sensing device of the modular core,
self powered powerline sensor as shown in Fig. lA;
Fig. 2 depicts the modular core, self powered powerline sensor of Fig. 1 with
a
protective covering wrapped thereabout and electronics components disposed
between the
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protective covering and the windings of the sensor;
Fig. 3 is a schematic block diagram of the sensor of Fig. I and a base station
both
coupled to an a.c. poweriine; and
Fig. 4 is a flow chart of the software that may be used by the microcontroller
of
Fig. 3 in order to construct a time based nominal level for a sensed condition
in or about
the a.c. powerline to determine variances from the nominal condition in or
about the a.c.
powerline.
There is shown in Fig. 1A modular core, self powered powerline sensor 10
according to this invention disposed about a.c. powerline 12. PowerIine I2
includes
conductive strands (or a single core) 14 and an insulating rubber Iayer 16.
The a.c.
powerline 12 shown is a cable of the type typically used in underground
secondary power
distribution applications; however, this is not a necessary limitation of this
invention, as
sensor 10 may be utilized in overhead, secondary voltage applications and in
overhead
and underground primary voltage applications with insulated or uninsulated
cable.
Power Extraction
Sensor 10 includes low profile, modular core elements 18, 20 and 22 which are
disposed about powerline 12 by urging apart gaps 19, 21 and 23 therein to
install the core
elements on powerline IZ and then allowing them to resiliently return to their
original
position to secure the core elements in place. The core elements are formed of
a highly
magnetically permeable ferromagnetic material such as steel and are typically
coated with
insulating material.
Core elements i8, 20 and 22 are toroidal in shape and have cross-section
thicknesses T which are approximately equal to their widths W, typically
approximately
1/2 inch. Thus, as described in the Background of Invention, they are
approximately
configured for the most efficient power extraction from a.c. powerline 12.
Also as
described in the Background of Invention, with single core systems, in order
to improve
the amount of power extraction from the a.c. powerline the width of the core
must be
increased and its cross-section thickness must be commensurately increased to
maintain
efficiency. But, since the cross-section thickness is increased to maintain
efficiency, the
profile of the sensor becomes very large and prohibits its application in
restrictive
volumes and on closely spaced lines. According to this invention, the core is
comprised
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of a number of modular core elements, in this case three (3). This maintains
the
efficiency of the sensor by making the cross-section thickness of the core
elements
approximately equal to their widths, and by using a number of core elements
the cross-
section thickness of the sensors can be limited to maintain a low profile
while power
extraction is increased.
The sizing of core elements I8, 20, and 22 for optimized power extraction is a
combination of minimizing losses while maximizing coupling between the
plurality of
windings on the core (the secondary windings) and the powerline cable passing
through
the center of the core (the primary winding).
The three fundamental losses observed in practice are the losses due to the
resistance of the secondary windings, losses due to magnetic leakage
inductance, and the
losses due to eddy currents induced in the core material. Other losses exist
and can
impact performance to a greater or lesser extent depending on design details.
However,
the three losses described above have been the major losses observed.
In tested embodiments of the sensor, the cores have included designs
fabricated
from tape wound magnetic steel material. By tape wound, it is meant that the
cores are
built up by winding a continuous strip of steel in a spiral manner, creating a
toroidal
shape, much like a roll of common tape. The advantage of this fabrication
approach is
that it is relatively easy and inexpensive, and it permits the use of magnetic
steel which is
~ preferentially oriented to have the highest magnetic permeability aligned
along the length
of the steel strip. When such an oriented steel strip is wound into a toroidal
shape, the
highest magnetic permeability is approximately located along the circular path
of the body
of the toroidal core. Thus, the highest magnetic permeability path is aligned
with the
path of magnetic flux generated by the flaw of current along the primary
conductor
passing through the center of the toroidal core. If a tape wound core is
fabricated from
magnetic material which is coated with an electrically insulating coating then
that material
will result in a core structure which effectively limits the flow of eddy
currents along
paths directed radially outward from the center of the primary winding through
the core.
Such a structure, however, does not tend to limit the flow of eddy currents
along paths in
the core which are parallel to the primary winding, and the eddy currents
induced in the
core by the primary winding currents, will tend to be along these parallel
paths.
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Neglecting other issues, if the toroidal core can be electrically separated
into multiple
side-by side cores to make breaks in the core eddy current paths parallel to
the primary
windings, then these eddy currents will be substantially reduced along with
the losses
' (inefficiencies) associated with them.
S The cross-section of the cores can be optimized to minimize losses and
maximize
coupling between primary and secondary windings. A typical core has an inside
radius
Rl outer radius R2 and width W. The core cross-section thickness, T, is the
difference
between RI and R2 or:
T = RZ - RI ( 1 )
Coupling between the primary and secondary windings can be characterized by
flux
linkage in the core. Secondary winding resistance and leakage inductance can
be
characterized by the length of each secondary wrap on the core or the length
of the core
cross-section perimeter (2T + 2W). By maximizing flux linkage and minimizing
the core
cross-section perimeter, core sizing can be optimized. For the ranges of sizes
anticipated
for the sensor, the optimized core sizing calls for ratios of W to T (W/T)
which
approximately range form 1 to 3. As described, the tested embodiments of the
sensor
have utilized three cores 18, 20, and 22 each with W/T ratios of approximately
one.
A winding layer including windings 24, 26 and 28 is formed by wrapping a wire,
such as a twenty-eight (28) gauge magnet wire, about each core element 18, 20
and 22 in
a number of turns and interconnecting the windings of each core element in
series as
shown in Fig. 1B. Alternatively, the windings may be connected in parallel.
The a.c.
power in powerline 12 induces a current in windings 24, 26 and 28 by non-
contacting
transformer action. A suitable ratio of windings is chosen such that a desired
current will
be induced in the windings when a.c. powerline 12 is energized. The number of
turns in
the windings determines the ratio between the current induced in the windings
and the
current in a.c. powerline 12 up to the point at which the core elements 18, 20
and 22
contain an induced flux density which is at or below their level of
saturation. A typical
number of windings for each core element is 75 for extracting sufficient power
to operate
sensor 10 with line currents as low as 20 amperes. By increasing the number of
core
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elements or windings or both, sensor 10 can be made to extract more power and
therefore
operate with even lower a.c. line currents.
SensingyVoltage
Sensor 10 further includes voltage and current sensing device 36, Figs. 1A and
1C. Voltage is sensed by capacitor 37 having a first, inside surface conductor
38 closely
spaced from insulating layer I6 of a.c. powerline I2 and outside surface
conductor 40
spaced from inside conductor 38. Both conductors are coaxially disposed about
a.c.
powerline 12 and contained therebetween is a dielectric 42, such as air or a
foam core.
Capacitor 37 is used to sense voltage capacitively coupled from a.c. powerline
12 which
is proportional to the powerline 12 voltage and, as described below, as a
receiver for
capacitively coupling high frequency powerline communications from powerline
12.
Because capacitor 37 is coaxially disposed about powerline 12 it tends to
cancel the
effects of power in powerlines other than powerline 12 which may be closely
spaced to
powerline 12.
To further reduce noise and/or undesired effects from external fields, for
example
from adjacent powerlines or other sources of electromagnetic fields, inside
surface
conductor 38 is electrically connected to additional coaxial plates 39 and 41
which are
spaced outside of plate 38 in the same manner as plate 40 and with the same
dielectric
between plates 39 and 38 and plates 38 and 4I. Additional plates 39 and 41
each have
~ approximately one half of the surface area of outer coaxial plate 40 and are
electrically
connected to inner coaxial plate 38 as shown. Therefore, any external signal
will tend to
be picked up equally by both inner coaxial plate 38 and outer coaxial plate 40
and not be
present in a differential measurement between inside surface conductor 38 and
outside
surface conductor 40. There may be only one coaxial plate, e.g. plate 39 which
has the
same surface area as outer plate 40. Alternatively, there may be three coaxial
plates,
each with one third the surface area of outer plate 40. In general, if there
are n plates,
the surface area of each plate is n of the surface area of outer plate 40.
Sensing Current
Disposed about capacitor 37 is an inductor 43 having a number of current
measurement windings 44 wound about toroidal shaped separating material (e.g.
foam)
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45. Current from a. c. powerline 12 induces a current flow in windings 44
proportional to
the current flowing in a.c. powerline I2. Because inductor 43 is wound about
separating
material 45 which contains air or foam material, it does not become saturated
as does a
typical iron core. Therefore the sensed current is more linear which makes it
more
accurate and easier to interpret.
Separating material 45 acts as a form for windings 44 and the material thereof
has
a low magnetic permeability like air. Separating material 45 can have a higher
permeability but care must be taken to include gaps or to control the magnetic
permeability so that the material of form 45 does not become magnetically
saturated and
the current sensed by inductor 43 becomes less than Linear and more difficult
to interpret.
A non-linear current measurement could be sensed by inductor 43 and
interpreted
accurately, however, this would require somewhat greater complexity in other
elements of
the sensor.
Voltage and current sensing device 36 also includes a gap 46 formed therein
for
installing on and removing it from a.c. powerline 12. Although the voltage
sensor device
(capacitor 37) and the current sensor device (inductor 43) of voltage and
sensing device
36 are shown disposed about powerline 12 at the same location, this is not a
necessary
limitation of present invention. They may be disposed adjacent to each other,
or even
spaced from each other.
. Communications
Communications device 48 is comprised of communications core element 50 and a
plurality of windings 52 wound about core element 50 for non-invasively
transmitting
communications from sensor 10 to a.c. powerline 12 by non-contacting
transformer
action. It is preferred, to use communications device 48 as a high frequency
communication transmitter and to use the capacitor 37 of sensor 36 as a high
frequency
communications receiver, in addition to being used as a voltage sensor.
Although either
' could be used to transmit or receive, or both. Thus, the non-invasive
coupling of
communicating signals to and from a powerline according to this invention can
generally
be described as reactive coupling to encompass both capacitive and inductive
coupling
techniques.
Sensor 10 typically includes a protective covering 62, Fig. 2, which provides
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electrical insulation. Covering 62 is normally formed of rubber and is affixed
to the
windings by means of self vulcanizing tape, adhesive, or by some other
suitable means.
Retaining ties 63 and 64 removably secure powerline sensor 10 in place about
a.c.
powerline 12. Covering 62 performs the additional functions of effectively
sandwiching a
number of electronics components 66 mounted on flexible printed circuit board
68
between it and the surface of the windings. An electrical connection between
the
windings (Fig. 1B) and the electronics components is accomplished by
electrical
connections not visible in this figure but shown schematically in Fig. 3.
Electronics
components 66 include various types of sensors for sensing essentially any
phenomenon,
e.g. temperature, pressure, radiation, moisture etc., a power supply powered
by windings
24, 26 and 28 (Fig. 1) energized by non-contacting transformer action with
a.c. powerline
12, a microcontroller and various other components which are discussed in more
detail
below with regard to Fig. 3.
Although all of the electronics components depicted in Fig. 2 are shown
secured to
flexible circuit board 68, this is not required, as sensors could be disposed
off circuit
board 68 and sandwiched between protective covering 68 and the windings, or,
sensors
could even be placed on the exterior of protective coating 62 to sense certain
types of
phenomenon about the exterior of protective covering 62.
Modular core self powered powerline sensor 10 is schematically depicted in
. system 100 of Fig. 3. Power for modular core, self powered powerline sensor
10 is
derived from a.c. powerline 12, which may be a single phase powerline which
may be
alone or part of a multiphase power transmission or distribution system, by
means of
windings 24, 26 and 28 which in this figure are depicted as a single winding
for clarity.
These windings are connected to power supply I02, which is disposed on
flexible circuit
board 68, by means of lines i03 and I04. Power supply 102, which may be an
a.c. to
d.c. regulator integrated circuit, provides SV d.c. to microcontroller 106 and
it also
provides t I2V and +5V outputs which may be utilized by one or more of the
sensors
or other electronics components.
Microcontroller 106 may be an 8-bit embedded-controller with an analog to
digital
converter. Sensors 108-112 are shown interconnected to microcontrolier 106,
however,
various numbers of sensors can be utilized. Sensors 108 through 110 are
disposed on
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flexible circuit board 68 while sensors 111 and 112 are disposed on the
exterior of
protective covering 62, Fig. 2. Only one sensor, sensor 112, is powered by
power
supply 102, as the remaining sensors do not require external power to operate.
These
sensors provide an analog or digital signal to microcontroller 106
representative of the
particular condition sensed in or about a.c. powerline 12. In addition to
those sensors,
there are also shown capacitor 37 which operates as a voltage sensor and
inductor 43
which acts as a current sensor.
Capacitor 37 is interconnected by lines 114 and 115 to signal conditioner 116
which performs amplification and filtering of the sensed signal to match the
input
requirements of microcontroller 106. The signal from voltage sensor 37 is a
capacitively
coupled voltage which is indicative of the instantaneous voltage on a. c.
powerline 12.
Voltage sensor 37 does not provide an absolute voltage reading to
microcontroller 106
since there is no reference voltage. An average or nominal voltage level,
however, can
be determined by monitoring the instantaneous voltage Levels supplied by
capacitor 37
over a period of time and a variation from the nominal voltage level can be
resolved from
the instantaneous input from capacitor 37 after the nominal level is
established.
Microcontroller 106 can perform other statistical manipulations of the non-
referenced
voltage input signal, such as weighting, and can determine deviations from
these other
types of statistical determinations.
. Current sensing is performed by inductor 43 which has induced therein a
current
proportional to the a.c. Line current in powerline 12. The induced current is
then
provided to current pickup signal conditioner I17 which amplifies and filters
the signal
before providing it to microcontroiler 106.
Sensors 108-110 are located on flexible circuit board 68 and sensors I11 and
112
are located on the exterior or protective covering 62. These sensors can
sense, for
example, temperature, pressure, gas, moisture, radiation or light (visible or
infrared). In
fact, a sensor for sensing virtually any phenomenon could be utilized. Certain
sensors,
such as a temperature sensor or a radiation sensor may be installed directly
on flexible
circuit board 68: other sensors such as sensors 111 and 112 which may sense,
for
example, gas and light, would only operate if located on the exterior of
protective
covering 62.
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Sensors 108-lI2 and voltage and current sensor 36 continuously sense various
conditions in and about a. c. powerline 12 and provide microcontroller 106
with analog or
digital signals representative of these sensed conditions. The signals
provided by the
sensors are converted to digital signals, if necessary, by microcontroiler 106
which then
generates communications data indicative of the sensed conditioned and that
data is
provided over line 118 to powerline carrier electronics 120 which encodes the
data.
Powerline carrier electronics 120 then provides the encoded data to output
driver 122
which is used to transmit a low voltage, high current pulse to windings 52 of
communications device 48 to non-invasively couple the transmission from
microcontroller
106 of sensor 10 to a.c. powerline 12 through non-contacting transformer
action. For
localized readout of the condition of the powerline, storage device 129 may be
connected
to lines 118 and 119. Storage device 129 is located at some convenient
location
proximate the powerline.
Alternatively, as shown in phantom, the output from driver 122 may be provided
over lines 124 and 125 to inside and outside surface conductor 38 and 40,
respectively, of
capacitor 37, Fig. I. In that configuration the signals transmitted from
microcontroller
106 are capacitively coupled to a.c. powerline 12 and driver 122 must be
configured to
provide a high voltage, low current output pulse. Presently it is preferred to
configure
driver 122 to drive windings 52 of communications device 48. Driver 122 may be
a high
. voltage amplifier (inverting or non-inverting).
The data transmitted from microcontroller 106 contains an identification code
which identifies powerline sensor 10 and an identification code for each
particular
individual sensor (108-l I2 and 37 and 43) on powerline sensor 10, indicating
the type of
data that is being transmitted. That is, the transmission includes information
about the
origin of the transmission (many powerline sensors can be utilized in various
locations on
an electric utility company's distribution system) and information about the
type of data
being transmitted; i.e. whether it be data regarding voltage, current,
temperature,
radiation, etc. The transmission and identification code and data of interest
can occur on
a regular basis, on a time basis, when particular threshold values are sensed,
or according
to any desired criterion. The communications code may follow a selected formal
communications system specification or protocol. The protocol may be based on
the OS1
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(Open Systems Interconnect) reference model for communications developed by
the ISO
(International Organization for Standardization) Geneva, Switzerland. Any
other
communications code that would be suitable for powerline communications could
also be
utilized.
5 The data transmitted from sensor 10 is received by remote base station 126.
Base
station 126 is interconnected to powerline I2 by means of direct electrical
connections
127 and 128 connected to powerline 12' which is a part of the powerline
distribution or
transmission system and is typically either ground, neutral, or a powerline of
a different
phase than powerline 12' (in a multiphase system). The connection to the
powerline,
10 however, could be accomplished by means of non-contacting transformer
action or
capacitive coupling as described above with regard to sensor 10. For example,
inductor
43' could be used to provide a connection to the powerline by non-invasive
inductive
coupling and/or capacitor 37' could be used to provide non-invasive capacitive
coupling.
The transmitted data is provided to computer 132 through a standard powerline
carrier
15 modem 130 that matches the communications module of sensor 10. Base station
126 is
also capable of transmitting data from computer 132 through powerline carrier
modem
130 to a.c. powerline 12. Then, for example, base station 126 could poll
modular core,
self powered poweriine sensor 10 and any another powerline sensors on the
system for
sensor information on demand instead of passively awaiting transmissions from
the
. powerline sensors. Moreover, the powerline sensors could be reprogrammed
from base
station 126.
Encoded communications transmitted from remote base station 126 are preferably
received by capacitor 37 by means of the capacitive coupling from a.c.
powerline I2.
These high frequency communications signals are provided to high pass filters
I34 and
I36, are allowed to pass therethrough and are provided to powerline carrier
electronics
120. Powerline carrier electronics 120 decodes the communications signals and
then
forwards them to microcontroller 106 on line 119.
Alternatively, windings 52 of communications device 48 could be used to
receive
the communications from remote base station 126. This is accomplished by
providing
lead lines 138 and 139 {depicted in phantom) which interconnect windings 52 to
high pass
filters 134 and I36.
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16
It should be noted that although it is preferred to use non-invasive poweriine
communications between sensor 10 and base station 126, this is not a necessary
limitation
of this invention. Direct contact powerline communication or non-powerline
communications, such as RF, phone line modem, cable TV, cellular phone,
infrared, '
fiber optic cable, microwave, or ultra-sonic communications could be utilized.
Microcontroller 106 performs analog-to-digital conversion of sensed
conditions,
manipulates and updates the memory locations which store previous sensed
conditions,
performs numerical operations such as determining a moving time average, etc.,
keeps
track of the time for synchronization purposes, and controls the
communications between
modular core self powered powerline sensor 10 and base station 126.
Microcontroller 106 can provide base station 126 with actual instantaneous
values
of particular sensed conditions, i. e. actual temperature or radiation
readings. However, it
can also provide base station 126 with an indication that a particular
condition being
sensed has varied from a nominal level and the amount of such variance. As
discussed
briefly above, this type of data transmission is required with voltage sensing
because there
is no reference level to which the sensed voltage can be compared to determine
an
absolute voltage. Therefore, the voltage sensed is compared with a nominal
level and the
variance of the sensed voltage from the nominal level is determined and
transmitted to
base station 126. The nominal level may be an average voltage level, or, other
types of
. statistical manipulation may be performed on the sensed voltage data, such
as weighting,
and be compared to a nominal level to determine variances from the nominal
level.
Moreover, although this process is not required to be performed with all types
of sensors
(since many sensors provide an absolute value of the condition being sensed),
it may be
used with any condition sensed. In fact, it may be more useful to provide the
variance
from the nominal level of the condition sensed rather than providing the
actual absolute
value sensed. This is so because in many instances the conditions that are
being
monitored are not monitored for the actual value, but rather they are being
monitored for
a variance from some nominal -value.
In order to detect and transmit variances from a nominal level of a sensed
condition, microcontroller 106 operates according to flow chart I50, Fig. 4.
At step 152
the modular core, self powered powerline sensor is installed and a condition
or conditions
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17
(e.g. voltage, current, temperature, radiation, etc.) are continuously,
instantaneously
obtained at step I54. At step 156 a time based average of the instantaneous
values or any
other type of statistical manipulation, such as weighting, of the sensed
condition over time
period t is conducted to determine a nominal level for that condition on the
a.c.
powerline. At this point the initial calibration is complete, in that the
nominal level for
the desired type of statistical manipulation has been determined. The
calibration process
can take anywhere from several seconds, to weeks or even months to obtain an
accurate
nominal level reading. After the initial calibration process is complete, at
step 158 the
instantaneous value obtained at step I54 is compared to the nominal level.
After the
initial nominal level is determined, it is continually recalculated from new
instantaneous
sensor data. At step 160 it is determined if the instantaneous value varies
from the
nominal level, and if it does a signal indicating that there is a variance and
the extent of
that variance is transmitted to the remote base station at step 162. Whether
or not a
variance was detected, the system returns to step 154 where another
instantaneous value is
obtained and the process continues until the sensor is removed from the a.c.
powerline or
a determination of the particular condition being sensed is no longer
required.
Although specific features of this invention are shown in some drawings and
not
others, this is for convenience only as each feature may be combined with any
or all of
the other features in accordance with the invention.
. Other embodiments will occur to those skilled in the art and are within the
following claims:
What is claimed is:
