Note: Descriptions are shown in the official language in which they were submitted.
METHOD AND SYSTEM FOR CONTROLLING MULTIPLE PUMP JACKS
TECHNICAL FIELD:
[0001] The present disclosure is related to the field of electric controllers
for operating pump
jacks, in particular, a pump jack controller that can operate multiple pump
jacks with reduced
electrical consumption from an electric power grid by using electricity
generated by the pump
jacks when they are operating in a negative torque mode.
BACKGROUND:
[0002] A pump jack is the above ground drive for a reciprocating piston pump
in a well. It is
used to mechanically lift liquid, such as oil, out of the well if there is not
enough bottom hole or
formation pressure for forcing the liquid to flow up to the surface. Pump
jacks are commonly
used for onshore wells. A pump jack converts the rotary mechanism of a drive
motor to a
vertical reciprocating motion to drive the pump shaft and displays a
characteristic nodding
motion.
[0003] Modern pump jacks are powered by a prime mover, which commonly
comprises an
electric motor. The prime mover runs a set of pulleys that, in turn, drive a
pair of cranks,
generally fitted with counterweights to assist the motor in lifting the heavy
string of the rod line
running into the ground. The cranks raise and lower one end of a beam, which
is free to move
on an A-shaped frame. On the other end of the beam is a "donkey-head", so
named due to its
appearance. The donkey-head moves up and down as the cranks rotate.
[0004] An induction or asynchronous motor is an alternating current ("AC")
motor in which all
electromagnetic energy is transferred by inductive coupling from a primary
winding to a
secondary winding, the two windings separated by an air gap. In both induction
and
synchronous motors, the AC power supplied to a stator disposed in the motor
creates a
magnetic field that rotates in time with the frequency of the AC power. A
synchronous motor's
rotor turns at the same rate as the stator field. In contrast, an induction
motor's rotor rotates at a
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CA 3074187 2020-02-28
slower speed than the stator field. The induction motor stator's magnetic
field is, therefore,
changing or rotating relative to the rotor. This induces an opposing current
in the induction
motor's rotor, in effect, the motor's secondary winding when the latter is
short-circuited or closed
through an external impedance. The rotating magnetic flux induces currents in
the rotor
windings in a manner similar to currents induced in a transformer's secondary
windings. These
currents, in turn, create magnetic fields in the rotor that react against the
stator field. Due to
Lenz's Law, the direction of the magnetic field created will be such as to
oppose the change in
current through the windings. The cause of the induced current in the rotor
windings is the
rotating stator magnetic field, so to oppose this effect the rotor will start
to rotate in the direction
of the rotating stator magnetic field. The rotor accelerates until the
magnitude of the induced
rotor winding current and torque balances the applied load. Since rotation at
synchronous speed
would result in no induced rotor current, an induction motor always operates
slower than
synchronous speed.
[0005] For the motor to run, the speed of the physical rotor must be lower
than that of the
stator's rotating magnetic field (N), or the magnetic field would not be
moving relative to the
rotor conductors and no currents would be induced. As the speed of the rotor
drops below
synchronous speed, the rotation rate of the magnetic field in the rotor
increases, inducing more
current in the windings and creating more torque. The ratio between the
rotation rate of the
magnetic field, as seen by the rotor (slip speed), and the rotation rate of
the stator's rotating field
is called "slip". Under load, the speed drops and the slip can increase enough
to create
sufficient torque to turn the load. For this reason, induction motors are
sometimes referred to as
asynchronous motors. An induction motor can be used as an induction generator
by running the
motor at a speed higher than the synchronous speed of the stator magnetic
field. In other
words, by running the motor at negative slip.
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[0006] Slip, s, is defined as the difference between synchronous speed and
operating speed, at
the same frequency, expressed in revolutions per minute ("RPM"), or in percent
or ration of
synchronous speed. Thus:
ns ¨
s=
17
where 17s is the synchronous speed of the stator magnetic field; and rir is
the rotor mechanical
speed.
[0007] Therefore, as the motor operates to lift the donkey-head, the motor
consumes electrical
power from an electrical power grid. In doing so, potential energy is created
in lifting the donkey-
head. As the donkey-head falls, the potential energy can be converted to
kinetic energy as the
motor can operate as a generator to generate electricity. This generated
electricity can be put
back onto the electrical power grid.
[0008] Underwriters Laboratories standard no. UL1741 is an accepted standard
for grid
interconnection with an electrical utility for inverter-based micro-generation
technology, such as
used in wind-generated electricity technology.
[0009] US Patent No. 10,250,168 issued to the Applicant discloses a pump jack
controller that
export electricity generated by a pump jack motor to an electric power grid.
What is not known
in the prior art, however, is a system and method to utilize the electricity
generated by one of a
plurality of pump jacks located at a common site to at least partially power
other pump jacks at
the common site to minimize the overall draw of electricity from an electric
power grid.
[0010] It is, therefore, desirable to provide a pump jack controller system
and method to
harness the potential energy generated in operating a pump jack and convert
that potential
energy into electricity that can be used to at least partially power other
pump jacks.
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SUMMARY:
[0011] In some embodiments, a pump jack controller is provided that can
harness the potential
energy created in operating a pump jack into AC electric power that can be put
back onto an AC
electric grid such that the pump jack can operate as a micro electric
generator.
[0012] Broadly stated, in some embodiments, a pump jack controller can be
provided for
converting waste energy created during the operation of one of a plurality of
pump jacks into
electrical energy that is then supplied back to other pump jacks of the
plurality of pump jacks,
each of the plurality of pump jacks operatively coupled to and operated by an
electric induction
motor, each of the plurality of pump jacks comprising a donkey-head and a
counterweight
operatively coupled thereto wherein each of the donkey-head and the
counterweight rise and
fall when each pump jack is operated by their electric induction motor, the
pump jack controller
system comprising: a plurality of motor drive units ("MDU"), one for each of
the plurality of pump
jacks, each MDU comprising a direct current ("DC") input and an alternating
current ("AC")
output, the AC output operatively coupled to one of the electric induction
motors, the MDU
configured to invert DC power supplied to the DC input into AC power that is
outputted from the
AC output to power the electric induction motor, the MDU further configured to
rectify AC
electric power generated by the electric induction motor into generated DC
power that is
outputted from the DC input when either of the donkey-head and the
counterweight is falling
thereby causing the motor to be in a negative torque operating condition; a DC
bus operatively
coupled to the DC input of each of the plurality of MDUs; and a generator
drive unit ("GDU")
comprising a DC output and an AC input, the DC output operatively coupled to
the DC bus, the
GDU configured to rectify a source of supplied AC electric power from the
power grid coupled to
the AC input into DC power that is outputted onto the DC bus, the GDU
configured to regulate
and maintain a preset DC bus value on the DC bus, the GDU further configured
to invert the
generated DC power into generated AC power that is outputted from the AC input
back to the
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power grid when the generated DC power supplied to the DC bus by the MDU
exceeds the
preset DC bus value.
[0013] Broadly stated, in some embodiments, a method can be provided for
converting waste
energy created during the operation of one of a plurality of pump jacks into
electrical energy that
is then supplied to other pump jacks of the plurality of pump jacks, each of
the plurality of pump
jacks operatively coupled to and operated by an electric induction motor, each
of the plurality of
pump jacks comprising a donkey-head and a counterweight operatively coupled
thereto wherein
each of the donkey-head and the counterweight rise and fall when each pump
jack is operated
by the electric induction motor, the method comprising the steps of: receiving
a pump jack
controller system and operatively coupling the system to the plurality of pump
jacks, the system
further comprising: a plurality of motor drive units ("MDU"), one for each of
the plurality of pump
jacks, each MDU comprising a direct current ("DC") input and an alternating
current ("AC")
output, the AC output operatively coupled to one of the electric induction
motors, the MDU
configured to invert DC power supplied to the DC input into AC power that is
outputted from the
AC output to power the electric induction motor, the MDU further configured to
rectify AC
electric power generated by the electric induction motor into generated DC
power that is
outputted from the DC input when either of the donkey-head and the
counterweight is falling
thereby causing the motor to be in a negative torque operating condition, a DC
bus operatively
coupled to the DC input of each of the plurality of MDUs, and a generator
drive unit ("GDU")
comprising a DC output and an AC input, the DC output operatively coupled to
the DC bus, the
GDU configured to rectify a source of supplied AC electric power from the
power grid coupled to
the AC input into DC power that is outputted onto the DC bus, the GDU
configured to regulate
and maintain a preset DC bus value on the DC bus, the GDU further configured
to invert the
generated DC power into generated AC power that is outputted from the AC input
back to the
power grid when the generated DC power supplied to the DC bus by the MDU
exceeds the
preset DC bus value; supplying the source of supplied AC electric power to the
system to power
CA 3074187 2020-02-28
the electric induction motors to operate the plurality of pump jacks;
producing generated DC
power with the electric induction motors when one or more of the electric
induction motors is in
a negative torque condition when either of the donkey-head and the
counterweight is falling,
wherein the generated DC power is outputted from the DC input of the MDU
associated with the
electric induction motor that is in the negative torque condition onto the DC
bus; and powering
one or more of the plurality of pump jacks with the generated DC power when
the generated DC
power comprises a DC voltage that exceeds the preset DC bus value.
[0014] Broadly stated, in some embodiments, the controller can further
comprise a low-pass
filter unit disposed between the AC input of the GDU and the source of
supplied AC electric
power.
[0015] Broadly stated, in some embodiments, each of the plurality of MDUs can
further
comprise a first inverter-based motor drive unit.
[0016] Broadly stated, in some embodiments, the DC bus can comprise a filter
capacitor.
[0017] Broadly stated, in some embodiments, the GDU can comprise a second
inverter-based
motor drive unit.
[0018] Broadly stated, in some embodiments, the source of supplied AC electric
power can be
connected to the electric power grid.
[0019] Broadly stated, in some embodiments, the source of supplied AC electric
power can
comprise 3-phase AC electric power.
[0020] Broadly stated, in some embodiments, the preset DC bus value can be in
excess of a
root-mean-square voltage value of the supplied AC electric power multiplied by
the square root
of 2.
[0021] Broadly stated, in some embodiments, the GDU can further comprise a PID
control for
regulating and maintaining the preset DC bus value on the DC bus.
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BRIEF DESCRIPTION OF THE DRAWINGS:
[0022] Figure 1 is a block diagram depicting one embodiment of a controller
for use with a
pump jack.
[0023] Figure 2 is a simplified block diagram depicting the controller of
Figure 1.
[0024] Figure 3 is a front elevation view depicting the controller of Figure 1
installed in a
cabinet.
[0025] Figure 4 is an electrical circuit schematic depicting a general circuit
model of the
controller of Figure 1 including an Active Front End.
[0026] Figure 5 is an electrical circuit schematic depicting the Active Front
End of Figure 4.
[0027] Figure 6 is a block diagram depicting another embodiment of the
controller of Figure 1
for use with a plurality of pump jacks.
[0028] Figure 7a is a block diagram depicting a pump jack in operation with
the controller of
Figure 1.
[0029] Figure 7b is a block diagrams depicting a plurality of pump jacks in
operation with the
controller of Figure 6.
[0030] Figure 8 is a block diagram depicting one embodiment of the controller
of Figure 6 in a
field trial using three 50 horsepower FL6 pump jacks.
[0031] Figure 9 is a block diagram depicting the three pump jacks of Figure 8
powered by
variable frequency drive systems.
[0032] Figure 10 is a block diagram depicting the three pump jacks of Figure 8
powered by
across the line starting systems.
[0033] Figure 11 is a block diagram depicting the three pump jacks of Figure 8
powered by the
controller of Figure 6.
[0034] Figure 12 is a table depicting data collected during the operation of
the pump jacks
powered by variable frequency drive systems shown in Figure 9, across the line
starting
systems shown in Figure 10 and the controller shown in Figure 11.
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[0035] Figure 13 is an X-Y graph depicting the data of Figure 12.
DETAILED DESCRIPTION:
[0036] In some embodiments, a pump jack controller is provided that can
harness the potential
energy created in operating a pump jack into AC electric power that can be put
back onto an AC
electric grid such that the pump jack can operate as a micro electric
generator.
[0037] Referring to Figure 1, a block diagram of one embodiment of pump
controller 10 is
shown. In some embodiments, controller 10 can be connected to alternating
current ("AC")
electric power grid 12 via electric connections 14. In this illustration,
connections 14 represent a
3-phase AC electric power connection, as well known to those skilled in the
art although it is
equally obvious to those skilled in the art that a single phase power
connection or a poly-phase
power connection can be substituted.
[0038] In some embodiments, controller 10 can comprise low pass filter unit 16
further
comprising a first port and a second port. The first port can be operatively
coupled to electric
connections 14. In some embodiments, filter unit 16 can comprise a third-order
low-pass filter
further comprising an inductor-capacitor-inductor configuration as well known
to those skilled in
the art. Filter unit 16 is shown in more detail in Figure 4. In a
representative embodiment,
inductors 36 can comprise an inductance value in the range of 0.11 to 5.2 mH,
and capacitors
38 (also labelled as Cl, C2 and C3) can comprise a capacitance value in the
range of 1.5 to
192 pF. The values of inductors 36 and capacitors 38 can also be selected by
those skilled in
the art, depending on the size of motor 32 to be controlled by controller 10.
In some
embodiments, controller 10 can be configured to operate electric motors
producing power in the
range of 5 to 700 horsepower. Filter unit 16 has specific heat dissipation
characteristics, in the
range of 70 to 1650 watts so as to maintain temperature stability within 4 C
of ambient
temperature.
[0039] In some embodiments, pump controller 10 can comprise front end 110,
which can further
comprise of filter unit 16, GDU 20 and DC bus 24. Pump controller 10 can
further comprise
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motor controller system 100 that can further comprise MDU 28 supplying AC
power to filter
reactor 31 over power connections 30.
[0040] Referring to Figures 1 and 2, the second port of filter unit 16 can be
connected to
generator drive unit ("GDU") 20 via electrical connections 18. In some
embodiments, GDU 20
can comprise an inverter-based motor drive unit that can be used to rectify a
source of supplied
AC electric power, such as from electric grid 12, into DC power. For the
purposes of this
specification, GDU 20 is also referred to as an "Active Front End" or "AFE".
[0041] As shown in Figure 5, GDU 20 can comprise a number of switching devices
40
configured to invert DC power into AC power, as known to those skilled in the
art. Each device
40 can comprise a solid state device 39 bypassed by a diode 41. Solid state
devices 39 can
comprise any suitable device for providing an electrical switching function
such as transistors,
field effect transistors ("FETs"), MOSFETs, insulated gate bipolar transistors
("IGBTs"), silicon
controlled rectifiers ("SCRs"), triacs or any other equivalent functioning
solid state device as
known to those skilled in the art. By operating GDU 20 "in reverse", that is,
supplying the source
of supplied AC electric power to AC output connections of a motor drive unit,
diodes 41 can
rectify the supplied AC electric power into DC power that can be outputted
from the DC input of
the motor drive unit. In a representative embodiment, GDU can include a motor
drive unit as
manufactured by Elettronica Santerno Spa of Castel Guelfo, ITALY, model no.
SINUS PENTA
0005 thru 0524.
[0042] Referring back to Figure 1, GDU 20 can be coupled to DC bus 24 via DC
power
connections 22. In some embodiments, DC bus 24 can comprise a filter capacitor
as shown in
Figure 5. In some embodiments, the filter capacitor can comprise a capacitance
value in the
range of 3,300 to 40,000 pF. The capacitance value of the capacitor disposed
in DC bus 24 can
depend on the size of motor 32 being controlled by controller 10. In some
embodiments, the
capacitance value can increase as the size of motor 32 increases.
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[0043] In some embodiments, DC bus 24 can be connected to motor drive unit
("MDU") 28 via
DC power connections 26. Similar to GDU 20, MDU 28 can comprise an inverter-
based motor
drive unit. In some embodiments, MDU 28 can comprise the same motor drive unit
as disposed
in GDU 20. MDU 28 is configured to be fed or powered by the DC bus 24 of GDU
20. GDU 20 is
setup with a PID control to regulate and maintain a preset DC bus value. This
DC bus value is
considered a setpoint DC value calculated as a value in excess of the root-
mean-square
("RMS") voltage value of the AC electric power supplied to GDU 20 multiplied
by the square root
of two.
[0044] In some embodiments, MDU 28 can be connected to motor 32 via AC power
connections 30. In some embodiments, motor 32 can comprise an induction or
asynchronous
electric motor. In some embodiments, controller 10 can further comprise
reactor filter 31
disposed between MDU 28 and motor 32 to provide low-pass filtering of the AC
power supplied
to motor 32, as well known to those skilled in the art.
[0045] Referring to Figure 3, one embodiment of controller 10 is shown
installed in cabinet 34,
including GDU 20, MDU 28, filter unit 16 (including generative interface 17)
and filter reactor 31.
[0046] Referring to Figure 6, another embodiment of controller 10 is shown. In
some
embodiments, controller 10 can comprise of front end 110 operatively coupled
to electric power
grid 12, wherein DC bus 24 can be operatively coupled to a plurality of motor
controller systems
100, each of which provides electric power to a pump jack motor 32, via DC
power connections
26 from DC bus 24 to the MDU 28 of each motor controller system 100.
[0047] Referring to Figure 7a, pump jack 42 is shown being operated by motor
32, which is
controlled by controller 10 supplied by power from electric grid 12. As well
known to those
skilled in the art, pump jack 42 comprises donkey-head 44 pivotally attached
to support frame
47, wherein donkey-head 44 is operatively coupled to counterweight 43 via
connecting rod 45.
In Figure 7a, motor 32 is operating to rotate counterweight 43 downward which,
in turn, raises
donkey-head 44 upward as it pivots on supporting frame 47.
CA 3074187 2020-02-28
[0048] In Figure 7b, motor 32 of pump jack labelled "A" operates to rotate
counterweight 43
upwards which, in turn, lowers donkey-head 44 downwards. Depending on the
conditions of the
well and the type of oil (light or heavy) being extracted, motor 32 can be
placed in an "over-
speed" or "negative torque" operating condition when donkey-head 44 is falling
or when
counterweight 43 is falling. In other words, either of donkey-head 44 or
counterweight 43 falling
can cause an over-speed condition in motor 32 depending on whether pump jack
42 is pump
heavy or counterweight heavy, respectively. In either case, the energy
expended or released by
donkey-head 44 or counterweight 43 falling is energy that is otherwise wasted.
It is when motor
32 is operating in an over-speed condition caused by the release of this waste
energy that
motor 32 can operate as a generator. As motor 32 operates as an AC power
generator, MDU 28
can rectify the AC power generated by motor 32 into generated DC power that
can be outputted
onto DC bus 24. When the DC voltage of the generated DC power rises above a
predetermined
set point or threshold, the generated DC power can then be used to supply DC
power to pump
jacks labelled "B" and "C" via DC power connections 26. In this situation, the
generated DC
power can be used to offset and/or reduce the amount of electric AC power
drawn from electric
grid 12 that otherwise would be needed but for the generated DC power
generated by one or
more pump jack operatively coupled to a plurality of pump jacks. As a result,
when a plurality of
pump jacks each having motor controller systems 100 operatively coupled to a
common DC bus
to provide DC power to the MDU 28 of each pump jack, DC power generated by a
pump jack
operating in an "over-speed" or "negative torque" operating condition can
provide DC power to
other pump jacks resulting in a reduced combined AC power draw from electric
grid 12 and,
thus, reducing the cost of the electric power operating costs of the plurality
of pump jacks.
FIELD TRIAL RESULTS
[0049] Referring to Figures 8 to 13, one embodiment of controller 10 was
tested in a field trial
using three FL6 pump jacks, each powered by a 50 horsepower NEMA induction
electric motor.
In the field trial, the operation of controller 10 was compared to two prior
art methods: powering
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each pump jack with a variable frequency drive ("VFD") system, referred to as
"Step 1" in the
following disclosure; and powering the pump jacks with across the line
starting systems,
referred to as "Step 2" in the following disclosure. The operation of
controller 10 with the pump
jacks in the field is referred to as "Step 3" in the following disclosure.
[0050] Figure 8 is a block diagram illustrating how controller 10 was
configured with the electric
grid and the pump jacks in the field trial. Figure 9 illustrates Step 1 of the
field trial, wherein
each pump jack 42 is powered by VFD unit 120, as well known to those skilled
in the art. Figure
illustrates Step 2 of the field trial, wherein each pump jack 42 is powered by
across the line
starter 130, as well known to those skilled in the art. The objective of the
field trial was to
perform a controlled energy usage study to compare these three types of
powering schemes
directly to a power utility (SaskPower) billing metrics and power usage
recording methodology.
For Step 1, using VFDs to power the pump jacks, the strokes per minute ("SPM")
production
speed of each pump jack was set to the required production rate for the site,
which was
maintained across all three steps of the field trial. For Step 2, the motor
for each pump jack was
re-sheaved as close as possible to match the SPM rate of Step 1. For Step 3,
controller 10 was
introduced to operate the VFDs to power the pump jacks. An ltrone Sentinel
model SS4SL
power meter was used to acquire the electrical power usage data for the field
data. This power
meter is Measurement Canada approved and is a utility-grade, four-quadrant
power meter as
used by SaskPower to measure power usage by its customers in the Province of
Saskatchewan
in Canada.
[0051] The scope of the field trial proceeded based on the following steps:
1. Install a provisioned and calibrated Itrone power meter.
2. Verify production of a candidate well site pad that is consistent for a 30
to 40 day trial
period.
3. Validate what a correct SPM rate applicable for the trial.
4. Arrange for the 3-step sections of pump jack speed control of:
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a. Step 1 - VFDs only; set the SPM
b. Step 2 - Across the line starter; motors sheaved to match Step 1 SPM
c. Step 3 - Install controller 10; re-sheave motors back to Step 1 VFD SPM
rate and
run the VFD at the same SPM as Step 1
5. Once the Itron meter is installed, poll with the Itron data acquisition
software to
validate all parameters are operational and the Itron meter is operational
and error-free
6. Start the power study
7. Once Step 3 has run for the set amount of time (6 days), poll the Itron
meter with the
Itron data acquisition software and export the data to evaluate the operation
performance, modelling and return on investment payback.
[0052] The field trial commenced on March 9, 2019 and finished on April 9,
2019. Referring to
Figure 12, a table of the power data collected from the Itron power meter is
shown for all three
Steps of the field trial. An X-Y graph comparing the collected data of the
three Steps over the
time period of the trial is shown in Figure 13. The summary of the data is
shown in the following
table.
Parameter Step 1 Step 2 Step 3
Power Factor (PF) 0.98 0.84 1.00
kVA 61.45 72.00 31.83
kW 60.21 60.65 31.83
Load: VFD operation 3 x Starter operation 3 x DCX & VFD
operation
NEMA 6 50hp NEMA B 50hp 3 x NEMA B 50 hp
TABLE 1: FIELD TRIAL DATA SUMMARY
[0053] As shown in TABLE 1, Step 3 utilizing controller 10 (denoted as DCX in
the table)
resulted in an optimal power factor of 1.00 and the lowest power draw of kilo-
volts-amperes
("kVA") and kilowatts ("kW') of the three steps of the field trial.
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[0054] In terms of operating costs measured, the following table illustrates a
side-by-side
comparison of the costs of Steps 1, 2 and 3 in the trial.
Item Step 1 Step 2 Step 3
Yearly Cost $39904.77989 $40295.96039 $21100.89495 kWh (8760
hours)
of Operation
$9882.253904 $11580.3307 $5120.133585 kVA (12 months)
Yearly Carbon $121.7893882 $122.9832711 $64.39993139 per kWh
Tax
Sub-total: $49908.82318 $51999.27373 $26285.42847 kWh + kVA
Basic Monthly $737.88 $737.88 $737.88
Charge
Yearly Sub- $50646.7 $52737.15 $27023.31
total:
CA GST: $2532.34 $2636.86 $1351.17
Sask. PST: $3038.80 $3164.23 $1621.40
Yearly Total: $56,217.84 $58,538.24 $29,995.87
TABLE 2: YEARLY COST SUMMARY OF 3 STEPS OF FIELD TRIAL
[0055] In reviewing the data of the field trial, it is apparent that operating
three pump jacks with
the use of controller 10 as described above has resulted in a significant
reduction of electric
power consumed from the electric utility that, in and of itself reduces the
electric power
operating costs of the pump jacks. In addition, the use of controller 10
results in the power
drawn from the electric utility at a perfect power factor of 1.00, which also
results in a reduction
of cost of the electric power delivered by the utility. Further, the reduction
of electric power
consumed from the utility also results in a reduction in the carbon footprint
of the pump jacks as
less electricity generated by the utility is required to operate the pump
jack, which also has the
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beneficial reduction in the carbon tax payable in respect of the electric
power consumed from
the utility to operate the pump jacks. Last, but not least, is a reduction in
the federal goods and
services tax ("GST") and provincial sales tax ("PST") payable to the utility
that further reduces
the overall operating costs in operating the three pumps using the systems and
methods
described herein as compared to conventional prior art methods to operate pump
jacks.
[0056] Although a few embodiments have been shown and described, it will be
appreciated by
those skilled in the art that various changes and modifications can be made to
these
embodiments without changing or departing from their scope, intent or
functionality. The terms
and expressions used in the preceding specification have been used herein as
terms of
description and not of limitation, and there is no intention in the use of
such terms and
expressions of excluding equivalents of the features shown and described or
portions thereof, it
being recognized that the invention is defined and limited only by the claims
that follow.
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