Note: Descriptions are shown in the official language in which they were submitted.
CA 02365015 2008-10-01
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HYBRID CURRENT AND VOLTAGE SENSING SYSTEM
This application relates to a system for sensing current and/or voltage in a
utility system including a plurality of power lines. In particular, this
invention relates to
a system (and corresponding method) including a central controller which
enables
monitoring of current and/or voltage on a plurality of different power lines
(or phases)
at the same time.
BACKGROUND OF THE INVENTION
[0001] Overhead power lines typically operate in a three-phase system, with
each
phase disposed on the pole or tower in spaced relation to the other two
phases. A
different power line is typically utilized for each different phase. U.S.
Patent No.
5,874,900 discloses an example of a three-phase power line system.
[0002) Utilities desire the ability to monitor the current and/or voltage in
such
power lines. There exists a need in the art for a more efficient system and/or
method
for monitoring current and/or voltage in such power lines. It is a purpose of
this
invention to fulfill this need, as well as other needs which will become
apparent to
those skilled in the art upon reviewing this document.
SUIVIMARY OF THE INVENTION
[0003] Generally speaking, certain example embodiments of this invention
fulfill
one or more of the above-listed needs by providing a method of sensing
current, the
method comprising: providing a current sensing unit for a phase to be
monitored; the
current sensing unit sensing a current of the phase and converting analog
current data to
digital current data; forwarding the digital current data to a potential
sensing unit via at
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least one optical interface; and transmitting the digital current data from
the potential
sensing unit to a control unit via at least one communications interface.
[0004] Other example embodiments of this invention fulfill one or more of the
above-listed needs by providing a system for simultaneously sensing current
and
voltage for a plurality of different phases, the system comprising: a first
line unit or
current sensing unit and a first base unit or voltage sensing unit for a first
power line to
be monitored, wherein said first line unit or current sensing unit and said
first base unit
or voltage sensing unit communicate with one another optically; said first
line unit or
current sensing unit mounted proximate a first end of a first high voltage
insulator and
said first base unit or voltage sensing unit mounted proximate a second end of
said first
high voltage insulator so that said first line unit or current sensing unit
senses current of
said first power line and said first base unit or voltage sensing unit senses
voltage of
said first power line; a second line unit or current sensing unit and a second
base unit or
voltage sensing unit for a second power line to be monitored, wherein said
second line
unit or current sensing unit and said second base unit or voltage sensing unit
communicate with one another optically; said second line unit or current
sensing unit
mounted proximate a first end of a second high voltage insulator and said
second base
unit or voltage sensing unit mounted proximate a second end of said second
high
voltage insulator so that said second line unit or current sensing unit senses
current of
said second power line and said second base unit or voltage sensing unit
senses voltage
of said second power line; a controller in communication with each of said
first and
second line units or current sensing units and each of said first and second
base units or
voltage sensing units; and wherein said controller outputs sampling signals to
each of
said first and second line units or current sensing units and each of said
first and second
base units or voltage sensing units so that current and voltage measurements
from each
of said first and second power lines are in phase with .one another.
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BRIEF DESCRIPTION OF THE INVENTION
[0005] FIGURE 1 is a schematic diagram of a current/voltage monitoring system
according to an embodiment of this invention.
[0006] FIGURE 2 is a block diagram of the line unit and the base unit of the
Fig.
1 embodiment.
[0007] FIGURE 3 is a block diagram of the control or output unit of the Fig. 1-
2
embodiment, wherein the control or output unit is coupled to and in
communication
with each of the line and base units.
DETAILED DESCRIPTION OF CERTAIN EXAMPLE EMBODIMENTS
OF THE INVENTION
[0008] This invention relates to a system and corresponding method capable of
simultaneously monitoring current and/or voltage in a plurality of different
phases (e.g.,
three phases) of a power system such as in the context of a utility operated
system.
While three different phases is referred to herein, this number is for
purposes of
example and the instant invention may be used in monitoring one phase, two
phases, or
more than three phases simultaneously in different embodiments of this
invention. For
purposes of example only and without limitation, certain embodiments of the
instant
invention may be utilized to measure current and/or voltage in different
phases of an
overhead power line system. In certain example embodiments, a central or
common
controller and output unit is in communication with current/voltage monitoring
units for
each of the different phases, and enables all phases to be monitored in a
common
phase/time relationship. For each of the multiple phases, a separate
current/voltage
sensor including both analog and digital circuitry is provided and mounted on
a high
voltage insulator corresponding to that phase. In certain embodiments of this
invention,
the system may be configured to monitor current only, voltage only, or both,
for each of
the plurality of phases.
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[0009] Figure 1 is a schematic diagram of an embodiment of this invention. As
shown in Figure 1, three different phases or power lines 1 are provided, each
on a
different composite high voltage insulator 3 on support 4. High voltage
insulators 3
are known in the art, and often include a series of fins or skirts 5 along
their respective
lengths. At the high potential or top end of each insulator 3, a pair of
terminal
connectors 7 are provided and to each of which a power line 1 is attached. It
is noted
that connectors 7 in Figure 1 are illustrated 90 degrees turned from their
normal
positions, for purposes of simplicity and illustration.
[0010] A current sensing line unit 9 is provided at the high potential end of
each
high voltage insulator 3, for sensing electrical current in the corresponding
power line
1. For example, a current sensing coil 27 (e.g., Rogowski coil) of line unit 9
may be
provided in the form of a ring located around aluminum tube 11 disposed
between the
opposing terminal connectors 7 of each insulator 3, while the circuit board 9a
of line
unit 9 may be provided below connectors 7.
[0011] A voltage sensing base unit 15 is provided at the low or ground
potential
end of each high voltage insulator 3. Voltage sensing base unit 15 is thus
spaced from
the power line 1 to be monitored for each phase. In particular, base unit 15
may be
located a distance "d" from the power line 1 to be monitored, where distance
"d" may
be from about 10-120 inches in different embodiments of this invention. As
will be
appreciated more fully below, each high voltage insulator 3 is hollow and
allows fiber
optic line(s) to run therein which couple the line 9 and base 15 units on each
insulator 3
to one another. As can be further seen in Fig. 1, controller and output unit
17 is in
communication with the current/voltage sensing circuitry for each phase (i.e.,
for each
high voltage insulator 3).
[0012] Referring to Fig. 2, the current sensing line unit 9 for each of the
three
phases includes solar power panel(s) 21, lead acid charger 23, lead acid
battery(ies) 25,
current sensing coil (e.g., Rogowski coil) 27, voltage regulator 29, analog-to-
digital
converter (ADC) 31, and fiber optic interface 33. As can be seen, the solar
powered
battery voltage source at the high potential end of the insulator 3 includes a
plurality
(e.g., three) of lead acid batteries (other battery types may of course
instead be used)
CA 02365015 2001-12-10
connected in series to provide a power source (e.g., 6 volt source). Charger
23 is for
keeping the battery(ies) 25 fully charged via output from panels 21 due to
incoming
sunlight. In certain embodiments, line unit 9 may function for at least 10
days without
sunlight, more preferably at least 30 days without sunlight. The power source
including
elements 21, 23, and 25 for the current sensing line unit 9 is advantageous in
that it
generates power at the high potential end of the insulator 3 for each phase.
Moreover, it
eliminates the need to generate power at the bottom of the power line pole or
support
(from a practical viewpoint, copper wiring cannot be run up through insulator
3 from
the ground potential to the high potential end).
[0013] Still referring to Figure 2, for each phase coil 27 is provided around
the
power line 1 as discussed above for sensing current change therein. Coil 27
(e.g.,
Rogowski coil, or any other suitable current sensing coil) produces a voltage
output
which is proportional (directly or otherwise) to the rate of current change in
the
corresponding power line 1. In example embodiments where a Rogowski coil is
used,
the output voltage waveform may be the cosine (COS) of the current waveform.
Rogowski coils are used in certain embodiments, because they provide linear
and stable
voltage output. The voltage output from current sensing coil 27 is converted
into a
digital value by analog-to-digital converter (ADC) 31 (e.g., to a 16 bit
digital value in
certain example embodiments). In one example embodiment, the waveform may be
sampled 6,956 times per second (based on the sample clock signal received from
controller 17 via base unit 15). This high sampling rate at 16 bits provides
for a very
accurate reproduction of the current waveform. The digital data is buffered
and
transmitted to base unit 15 via fiber optic interface 33 and corresponding
fiber optic
cable(s) 16 that run(s) through the hollow interior of the corresponding high
voltage
insulator 3. The sampling clock (which provides the sampling signal to units 9
and 15
via fiber optic cable(s)) and the conversion rate (which provides the convert
signals to
units 9 and 15 via fiber optic cable(s)) are controlled and output by central
controller
17.
[0014] As shown in Figure 2, voltage sensing base unit 15 includes fiber optic
interface 41 for enabling communication with current sensing line unit 9,
interface 43
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for enabling communication with central controller 17, electromagnetic
radiation
sensing rod 45 for sensing voltage from the corresponding power line 1, analog-
to-
digital converter (ADC) 47, linear regulator 49, isolated voltage source 51,
and
optocoupler interface 53. The base or circuit board of unit 15 receives its
sampling
clock and convert signals from central controller 17 via interface 43 (e.g.,
RS
422interface, or any other suitable interface). The sampling clock and
conversion (i.e.,
convert) rate signals are converted from RS422 to fiber optical signals at 41,
43, and
sent to the circuit board of the line unit 9 via fiber optic cable(s) 16. The
same
sampling clock and conversion signals are also used by unit 15 and potential
sensor 45
therein; so that there is a common or constant time relationship between the
current
waveforms in unit 9 and the potential waveforms in unit 15. The current data
received
by unit 15 from unit 9, and the potential data (i.e., voltage data) generated
by unit 15
are converted to RS422 signal levels at 43, and thereafter sent to controller
17.
[0015] Potential sensor 45 detects/senses the electromagnetic field generated
by
the high voltage in the corresponding power line 1(from which the sensor 45 is
spaced
a distance "d"), and converts the electromagnetic energy into a voltage which
is
proportional (directly or otherwise) to the potential source. This voltage
waveform
output from sensor 45 is converted into a digital value by ADC 47 (e.g., into
a 16 bit
digital value). The waveform is sampled at 6,956 times per second in certain
example
embodiments of this invention. This high sampling rate at 16 bits provides an
accurate
reproduction of the potential waveform. The resulting digital data indicative
of power
line voltage (i.e., "voltage data") is buffered and transmitted to interface
43 via
optocoupler interface 53. From interface 43, the digital data indicative of
power line
voltage (i.e., "voltage data") is sent to central controller 17 as shown in
Figure 2.
[0016] Regarding power, base unit 15 in certain example embodiments may
require an average of about 100 mill amperes. The controller 17 may provide
+12 volts
as shown in Figure 2, which may be converted to +5 volts by regulator 49 for
powering
the isolated potential voltage sensing circuitry, the optical circuitry, and
the interfaces
of unit 15.
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[0017] Figure 3 is a block diagram illustrating how central controller or
output
unit 17 controls and interacts with the current sensing line units 9 and the
voltage
sensing base units 15 for each of the three phases. The block 61a ("phase 1")
in Figure
3 is for communicating with both line unit 9 and base unit 15 for the first
phase (i.e., for
a first power line 1); while the block 61 b("phase 2") in Figure 3 is for
communicating
with both line unit 9 and base unit 15 for the second phase (i.e., for a
second power line
1); and the block 61c ("phase 3") is for communicating with both line unit 9
and base
unit 15 for the third phase (i.e., for a third power line 1). The +12 signals,
sample clock
signals, ground signals, and convert signals from interface blocks 61 (e.g.,
RS422
interfaces) are provided to voltage sensing base unit 15 (see Fig. 2) for each
corresponding phase, with the unit 15 thereafter also sending the clock and
convert
signals to the corresponding current sensing unit 9. Meanwhile, the current
and voltage
signals from units 9, 15 are received by blocks 61.
[0018] As shown in Figure 3, communications between controller 17 and sensors
9, 15 are done via interfaces 61 (e.g., RS422 interfaces, or any other
suitable type of
interface(s)). The same sampling and conversion signals provided by controller
17 are
used by both current sensing line units 9 and voltage sensing base units 15
(in all
phases). This insures a constant phase/time relationship between the potential
and
current waveforms.
[0019] Central controller 17 (e.g., DSP and/or programmable logic circuit)
uses
crystal oscillator 71 for clocking purposes. Each of the three current sensing
line unit 9
inputs (i.e., "current data") and each of the three voltage sensing base unit
15 inputs
(i.e., "voltage data") is monitored by controller 17 for a correct data
format. For
example, if a number (e.g., four) of sequential or consecutive incorrect data
formats are
detected, LED 73 status indicator(s) is illuminated and status relay 75 is
deenergized.
Likewise, each current and potential output amplifier may be monitored for
save
operating limits, and if unsafe condition(s) is/are detected the LED 73 status
indicator(s) is illuminated and status relay 75 deenergized. As can be seen,
in certain
embodiments the system is programmable for monitoring the number of phases
(e.g.,
three) and the number of current and voltage sensors (e.g., six altogether
when three
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phases are being monitored). A programmable filter/threshold detection circuit
may
limit low levels of ground loop current(s) and small voltage fluctuations.
[0020] An example of how controller 17 operates is as follows. Serial data
from
the first phase (first power line) current sensing line unit 9, and serial
data from the first
phase voltage sensing base unit 15 is received by interface 61a. This serial
digital data
is converted from RS422 format, and forwarded to controller 17.
[0021] From controller 17, the first phase voltage data is forwarded to
digital-to-
analog converter (DAC) 91a (e.g., 16 bit DAC). After conversion to analog, the
analog
voltage signal for the first phase is level shifted, gain adjusted (see gain
adjuster 93a),
filtered (see high pass filter 95a), and converted to 120VAC (see amplifier/AC
converter 97a). As can be seen in Figure 3, DACs 91c and 91e handle the
voltage
signals in a similar manner for the other two phases, gain adjusters 93c and
93e handle
gain adjustment in a similar manner for the other two phases, high pass
filters 95c and
95e handle filtering in a similar manner for the other two phases, and
amplifiers/converters 97c and 97e handle AC conversion in a similar manner for
the
other two phases.
[0022] From controller 17, the first phase current data is forwarded to
digital-to-
analog converter (DAC) 91b (e.g., 16 bit DAC). After conversion to analog, the
analog
current signal for the first phase is level shifted, gain adjusted (see gain
adjuster 93b),
filtered (see high pass filter 95b), and amplified/converted to 0 to 1 ampere
(see current
amplifier 97b) to provide output. As can be seen in Figure 3, DACs 91 d and 91
f handle
the current signals in a similar manner for the other two phases, gain
adjusters 93d and
93f handle gain adjustment of the current signals in a similar manner for the
other two
phases, high pass filters 95d and 95f handle current signal filtering in a
similar manner
for the other two phases, and current amplifiers 97d and 97f handle current
amplifying
in a similar manner for the other two phases. In certain embodiments, each
current
sensor may be matched to its gain to provide an initial accuracy of a
predetermined
amount (e.g., 0.3% or any other suitable amount). In certain embodiments, each
phase
may have a manual gain adjustment for field calibration.
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[0023] The aforesaid embodiment(s) illustrate and describe circuitry which is
provided for purposes of example only. Other circuitry, or software
implementations,
may also be used and are intended to be covered by this invention.
[0024] While the invention has been described in connection with what is
presently considered to be the most practical and preferred embodiment, it is
to be
understood that the invention is not to be limited to the disclosed
embodiment, but on
the contrary, is intended to cover various modifications and equivalent
arrangements
included within the spirit and scope of the appended claims.
