Note: Descriptions are shown in the official language in which they were submitted.
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SITE ANALYSIS METHODOLOGY AND
DEVICE FOR TESTING ELECTRIC POWER
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional Application
Serial
Number 60/783,142, filed March 16, 2006, and incorporated herein by reference
in its
entirety. -
REFERENCE REGARDING FEDERALLY SPONSORED RESEARCH OR
DEVELOPMENT
[0002] Not applicable
SEQUENTIAL LISTING
[0003] Not applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0004] The present invention relates generally to analyzing power delivered to
a load
and to a branch circuit, and more particularly to a method of and device for
analyzing the
quality of a power distribution system by measuring power parameters at
specific locations in
the power distribution system.
2. Description of the Background of the Invention
[0005] Electrical power that is supplied to electronic devices may include
potentially
unwanted characteristics. The potentially unwanted characteristics can result
from external
and internal conditions and can be caused by voltage and/or current, each of
which can
exhibit different potentially unwanted characteristics. Extemal conditions
generally appear in
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the form of power surges, spikes, lower power conditions (i.e., brown-outs),
blackouts, etc.
Internal conditions generally include noise, harmonic distortion of an
incoming power
waveform, transient energy from other devices surging on the ground line,
disruption of
power when other devices within the environment power on or off, etc.
[0006] These potentially unwanted characteristics can produce potentially
adverse
effects in a power distribution system such as errors, data loss, poor quality
factor,
overheating, and ciamaged or destroyed circuits. For example, power surges in
the form of
boosts in voltage or current that can occur from electrical equipment being
turned off may
cause errors, mernory loss, overheating, device shutdown, flickering lights,
etc. Spikes
resulting from lightening strikes can cause memory loss and burned circuit
boards. Other
transients and harmonics are unusable by the devices and are usually converted
into heat,
which reduces the efficiency of the device.
[0007] The potentially adverse effects produced by these unwanted
characteristics can
be prevented or minimized using available power conditioning devices. However,
prior
methods of analyzing power distribution systems have not adequately identified
the sources
of unwanted characteristics to permit optimal placement of the power
conditioning devices.
SUMMARY OF THE INVENTION
[0008] In one embodiment, a method of analyzing a power distribution system
that
supplies power to a load and to a branch circuit includes the steps of
connecting electrical
data acquisition equipment to the power distribution system at a location
upstream of the load
and downstream of the branch circuit and sensing data relating to a power
parameter
experienced at the load. The method further includes the step of analyzing the
power quality
of the power distribution system based on the'sensed data by identifying an
unwanted
characteristic.
[0009] In another embodiment, a method of analyzing the power quality of a
power
distribution system within a site includes the steps of connecting electrical
data acquisition
equipment to the power distribution system at a location directly upstream of
a non-linear
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load and sensing data relating to a power parameter by the non-linear load.
The method
further includes the steps of identifying a potentially adverse characteristic
experienced by
the non-linear load and analyzing the potentially adverse characteristic to
determine a source
of the characteristic
[0010] In yet another embodiment, a method of analyzing and improving power
quality in a powei- distribution system includes the steps of collecting power
parameter data
for a power distribution system and analyzing the collected power parameter
data to identify
sources of adverse power quality characteristics. The method further includes
the steps of
developing a recommended solution for improving the power quality in the power
distribution systein and reporting the results of the collecting, analyzing,
and developing
steps.
[0011] Other aspects and advantages of the present invention will become
apparent
upon consideration of the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a block diagxam of a power distribution system at a site;
[0013] FIG. 2 is a flowchart of a method of analyzing the power in a power
distribution system;
[0014] FIG. 3 is a schematic diagram showing the connection of voltage and
current
probes to a plurality of conductors;
[0015] FIG. 4 is a flowchart of another embodiment of a method of analyzing
the
power quality in a power distribution system;
[0016] FIG. 5 is a flowchart of an embodiment of a method of improving the
power
quality at a power distribution system;
[0017] FIG. 6 is an isometric view of a test fixture implementing the
functionality
encompassed by the dashed lines of FIG. 3;
[00181 FI.G. 7 is an end elevational view of the test fixture of FIG. 6;
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[0019] FIG. 8 is an isometric view of a polyphase test fixture; and
[0020] FIG. 9 is an end elevational view of the polyphase test fixture of FIG.
8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] FIG. I shows a typical power distribution system 20 at a site 22 or
physical
structure such as a residence, an office building, or a manufacturing plant. A
utility power
source 24 supplies electric power to the site 22 and is connected to the site
through a meter
26. The electric power is distributed throughout the site from one or more
distribution panels
28 and sub-panels 30. Typically, the panels and sub-panels 28, 30 distribute
electric power
throughout the site 22 through branch circuits 32. Electric devices 34
connected to the
branch circuits 32 act as loads that receive power from the power distribution
system 20.
One or more loads 34 are typically connected to each branch circuit 32, each
of which may
introduce voltage and/or current harmonics and transients back into the power
distribution
system 20. In adclition, the utility power source 24 supplies electric power
to numerous other
sites (not shown),. each of which can affect the power quality in other
portions of the power
distribution systern.
[0022] Typically, the utility power source is a polyphase system that supplies
AC
power to the site 22 through multiple line or live conductors. In some cases,
the site and/or
load receive(s) a single phase from the utility power source and a load 34
receives power
through a single line conductor and is further coupled to neutral and ground
conductors.
Generally, the neutral conductor returns current from the load 34 back into
the power
distribution system 20 and the ground conductor is a safety connection to
ground. Unwanted
characteristics that affect the power quality sent to individual loads 34 and
which further
adversely affect the power distribution system 20 as a whole can arise on and
across the
conductors in both single and polyphase systems. As noted previously, the
unwanted
characteristics can be caused by external and internal sources, such as
lightning strikes,
nearby high frequency antennas, the loads themselves, etc.
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[0023] As an example, the site 22 in FIG. 1 may be a restaurant that includes
a main
panel 28 that distributes power to first and second sub-panels 30A, 30B
through branch
circuits 32A, 32B. The main panel 28 distributes power to a food preparation
area of the
restaurant through. branch circuits 32C, 32D and loads 34A-34E connected to
the branch
circuits 32C, 32D. The loads in the food preparation area may include ovens,
fryers, stoves,
power strips, lights, etc. Further in accordance with the illustrated example,
the first sub-
panel 30A distributes power to a back office area of the restaurant through
branch circuits
32E, 32F and the loads 34F, 34G connected to the branch circuits 32E, 32F. The
loads in the
back office may include a computer, a printer, a desk light, etc. Further, the
second sub-panel
30B distributes power to the front area of the restaurant through branch
circuits 32G, 32H and
loads 34H, 341, wherein the loads may include multiple computers, fluorescent
lighting, etc.
[0024] FIG. 2 shows an embodiment wherein a measurement of power quality in
the
power distribution system at a site is used to identify unwanted or adverse
electrical
characteristics and potential sources of the characteristics. An initial site
survey is
performed, wherein information regarding the site is gathered (block 50). The
initial site
survey includes gathering information regarding the site itself and the
surrounding area. The
site information includes, for example, an inventory of the loads at the site,
locations of past
power problems, future planned changes to the site, the types of materials
used to wire the
site, the age of the wiring, soil conditions, etc. The inventory of the loads
includes general
mechanical information and electrical information. For example, the mechanical
information
may include the inake and model, the number of loads, service history,
engineering changes
of any kind, age, normal operating times, etc. The electrical information may
include, for
example, the type of power used, voltage and current ratings, UL safety
specification listings,
non-linear power supplies, etc. The information regarding the surrounding area
may include
performing a survey of the surrounding area to identify potential external
sources of
unwanted electrical characteristics, e.g., nearby HF antennas and/or other
sources of
interference. In addition, information regarding the business operating at the
site may also be
gathered, for example, production schedules, personnel who are trained to
operate the
equipment at the site, business models, etc. The site and surrounding area
information
gathered during the initial site survey is used to identify key testing
locations and data capture
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times and is also helpful in identifying potentially unwanted characteristics
and potential
sources of the characteristics. In addition, the business information is
helpful in developing a
recommended solution for improving the power quality of the site that is
tailored for the
customer.
[0025] Afler the initial site survey is complete, one or more testing
locations are
identified that are close to the loads (block 52). Typically, the power
parameters at the
panel(s) and sub-panels(s) are more chaotic, meaning that the power quality at
these locations
is affected by multiple influences including disturbances on the various
branch circuits and
distortion or other unwanted characteristics introduced by individual loads
connected
throughout the site. However, it is typically easier to access
wires/conductors at the panel or
sub-panel to connect data acquisition equipment and measure power quality of
the power
distribution system. The present approach preferably initially analyzes one or
more
parameters of electrical power directly at one or more loads by connecting
electrical data
acquisition equipment to the load(s). The analysis of the power distribution
system is
preferably thereafter expanded to site locations further away from the load(s)
and closer to
the panel(s) and sub-panel(s).
[0026] In a specific example, the initial testing locations are at the
electrical plugs for
the loads. In this case, the electrical data acquisition equipment is
connected upstream of the
load and downstream of one or more branch circuits. In some cases, electrical
plug(s) for the
load(s) may not be easily accessible and the nearest testing location is at a
wall socket
coupled to a power strip or extension cord that is further coupled to the
electrical plug(s) for
the load(s). Preferably, subsequent testing locations are at the panel(s) or
sub-panel(s) that
distribute power through one or more branch circuits to one or more load(s).
In another
embodiment, mu:ltiple testing locations between the load(s) and the panel(s)
and sub-panel(s)
are identified. In any event, the testing locations can be tested sequentially
or concurrently
according to the methodology described below.
[0027] After the testing locations are identified, electrical data acquisition
equipment
is connected to the power distribution system at the testing locations (block
54). The
electrical data acquisition equipment is capable of measuring various
electrical parameters of
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the power distribution system. Examples of power parameters that may be
measured include,
but are not limited to: current and/or voltage magnitude, phase, frequency,
harmonic content,
etc., as well as other power parameters such as power factor, power magnitude,
VARS,
and/or any other power parameter. The equipment includes, for example,
oscilloscopes,
voltage and current probes, power meters, etc. In one embodiment, the
equipment includes,
for example, a Dranetz PX-5 Power Recorder, a Tektronix TDS 3024
Oscilloscope,
Tektronix P5210 5,600 volt 50 Mhz Differential Probes, Tektronix A621 High
Current
Probes, and a Fluke 43B Power Quality Analyzer. Preferably, the equipment
samples the
electric power at high speeds-to capture fast transients that are not detected
by equipment that
samples at slower speeds. In addition, the equipment is capable of measuring
and storing
data over long periods of time so that a normal operating cycle of the load
and/or the power
distribution system can be measured and stored.
[0028] After the data acquisition equipment has been connected, electrical
parameter
data are measured and recorded (block 56). In one embodiment, the data include
both
voltage and current across and on the single-phase or polyphase line, neutral,
and ground
conductors. Generally, the data are measured and recorded during normal
operation of the
loads. In another embodiment, the data are measured and recorded outside of
the normal
operation of the load (e.g., before the load is turned on) to collect data
relating to the initial
conditions of the load and/or the power distribution system as a whole. The
initial conditions
data can be used to develop a power tolerance envelope such as a CBEMA curve
that is used
to identify potentially unwanted characteristics. In particular, the CBEMA
curve is a plot of
electrical equipment reliability, with a vertical axis representing the
voltage applied to the
power circuit and the horizontal axis representing the time factor involved,
ranging from
microseconds to seconds to days. Power parameter data that falls outside of
the CBEMA
curve may indicate a potentially unwanted characteristic and are typically
associated with
equipment malfun.ction. Consequently, the data recorded during the normal
operation of the
loads can be plotted on the power tolerance envelope and potentially unwanted
characteristics
can be identified that fall outsider of the envelope.
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[0029] A determination is made (block 58) whether a sufficient amount of data
has
been collected and recorded or if a predefined amount of time has passed such
that there is
some assurance that valid and/or useful data has been obtained. For example,
in one
embodiment, the ctata are collected and recorded over a routine operating
cycle of the load
itself or over an operating cycle of the power distribution system as a whole.
The routine
operating cycle may be defined as the time it takes to collect a predefined
number of data
samples or sensed events or a predefined amount of time. For example, in one
embodiment,
the determination is made whether the data have been collected and recorded
for ten minutes,
two hours, or twelve hours. In another embodiment, the production schedules of
the site
determine the amount of data this is sensed. For example, if a particular load
is in continuous
operation for a four hour production time, then data will be sensed during the
entire four hour
period. The equipment continues measuring and recording the electrical
parameter data until
the data are verified.
[0030] Once the data have been verified, the electrical parameter data are
analyzed
(block 60) to identify harmonics, transients, poor power factor, noise, and/or
other anomalies
that comprise un-vvanted electrical characteristic(s) affecting the power
quality of the power
distribution system. As discussed above, parameter data that fall outside of
the power
tolerance envelope may indicate an unwanted electrical characteristic.
However, in some
cases, even data that falls within the power tolerance envelope may be
identified as an
unwanted characteristic. For example, it the data is a high frequency
characteristic and the
addition of all of the occurrences is potentially adverse then that data may
be identified as an
unwanted characteristic. In addition, in one embodiment, the unwanted
characteristics are
further categorized into certain types based on the duration of the
characteristic. For
example, characteristics on the left of the power tolerance envelope that last
on the order of
microseconds are identified as impulses_ Characteristics that occur in the
middle of the
power tolerance envelope that last on the order of seconds are identified as
waveshape faults
and characteristics that are of longer duration are identified as RMS events
such as voltage
surges or sags. In addition, the types can be further broken down into
impulsive transients,
oscillatory transients, temporary RMS events, and sustained RMS events. The
unwanted
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characteristics are identified and the parameters of the characteristics are
measured and
stored, e.g., amplitude, duration, frequency, type, etc.
[0031] Thereafter, the unwanted characteristics are analyzed to identify
potential
sources of such characteristics (block 62). In particular, the parameters
measured at the time
that the equipment is directly coupled to the load(s) identifies the load(s)
and branch circuits
that are experiencing the unwanted characteristics. The sources of the
unwanted
characteristics can be further identified by analyzing the parameters measured
during the
subsequent time that the equipment is coupled to points upstream of the
load(s). In addition,
the amplitude, frequency, and duration of the unwanted characteristic are used
to identify the
source of the characteristic. For example, the specific inductance and
capacitance values of a
load result in waveforms having components of identifiable amplitude and
duration. Further,
a positive transient tends to indicate an external source and a negative
transient tends to
indicate a load-based source. The sources of harmonics can be difficult to
identify, because
harmonics that are identified typically include the added effects from
multiple sources.
However, the sensing of data at various locations within the power
distribution system is
helpful in identifying the locations at which harmonics are being added.
Thereafter, a
particular harmonic can more easily be traced back to its source.
[0032] In addition, the type of the characteristic, i.e., impulse, waveshape
fault, and
RMS event, also tends to indicate potential sources of the characteristic. For
example,
impulsive transients are typically caused by lightning/electrostatic discharge
and oscillatory
transients are associated with line/load switching, transformer energization,
etc. In addition,
waveshape faults are typically caused by system faults and RMS events are
associated with
motor starting and load variations.
[0033] Ea:ternal sources can be identified using the information gathered
during the
initial site survey and by analyzing the amplitude and frequency spectra of
the unwanted
characteristics. Specifically, the frequency of noise can be used to identify
an external
source, for example, nearby antennas that are transmitting at the same
frequency as the noise.
Additional sources of unwanted characteristics may include simple mis-wiring
situations, for
example, exchanging line and neutral conductors or a missing ground conductor.
Such mis-
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wiring situations can be identified by analyzing the initial conditions and/or
the unwanted
characteristics.
[0034] FIG. 3 shows an embodiment of the direct connection of electrical data
acquisition equipment 80 through single-phase line, neutral, and ground
conductors 82, 84,
and 86, respectively, to a load 88. The data acquisition equipment 80 is
connected to
measure and record electrical power parameter data, for example, common mode
voltage
between line and ground, common mode voltage between neutral and ground,
transverse
mode voltage between line and neutral, and line, neutral, and ground current
magnitudes
flowing through the respective conductors. The data acquisition equipment 80
is conf gured
according to the load information gathered during the initial site survey. In
one embodiment,
the equipment includes a Tektronix TDS 3024 Oscilloscope coupled between and
on the
line, neutral, and ground conductors 82-86 and the oscilloscope is set to
measure voltages and
currents. For example, to measure common mode transients between line and
ground, a
differential probe 90 is connected between line and ground 82, 86 and an
oscilloscope
channel 1. Charuiel 1 of the oscilloscope is set to Peak Detect Mode at 250
million samples
per second at 40 r.nicroseconds per division. The oscilloscope amplifier is
set to 100 volts per
division. Similarly, to measure common mode transients between neutral and
ground a
differential probe 90 is connected between neutral and ground 84, 86 and to an
oscilloscope
channel 2. Channel 2 is set to Peak Detect Mode at 250 million samples per
second at 40
microseconds per division. The oscilloscope scale for this channel is set to
10 volts per
division. Transverse mode transients are measured by a channel 3 of the
oscilloscope
between line and neutral by connecting a differential probe 90 between line
and neutral 82,
84. Channel 3 is set to a Peak Detect Mode at 250 million samples per second
at 40
microseconds per division. The amplifier is set to 100 volts per division.
[0035] In addition, line, neutral, and ground transient currents are measured
by
clamping current probes 92 around the line, neutral, and ground conductors 82-
86,
respectively. T'he probes 92 are connected to respective additional channels
of the
oscilloscope, which settings include line triggering, variable sensitivity,
and scaling of 40
microseconds per division. In an embodiment, an infinite persistence display
feature of the
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oscilloscope is used to accumulate all of the voltage and current transients
that occur during
the test period. In another embodiment, the waveforms accurnulated by the
oscilloscope are
saved and/or printed for each of the channels. The above configuration of the
oscilloscope is
able to detect very fast voltage and current transients. However, other
configurations or
oscilloscope settings can be used in other embodiments, e.g., the sensitivity
of the horizontal
and vertical axes can be adjusted depending on the amplitude and duration of
voltage and
current transients and surges.
[0036] In addition, the oscilloscope can be used to analyze harmonics by
setting the
oscilloscope to show a spectral display of the harmonics present on the
current and voltage
waveforms. The oscilloscope can also be set to calculate the instantaneous
power in the case
of transients. In another embodiment, a power meter is connected to the power
distribution
system and is used to measure total harmonic distortion and other power
related
measurements. In another embodiment, the equipment is adapted for use in a
polyphase
system.
[0037] In yet another embodiment shown in FIG. 4, the site is first analyzed
to
identify likely sources of unwanted characteristics. In particular, non-linear
loads, such as
loads including a switched mode power supply, have a relatively low power
factor and
introduce harmonics and noise back into the power distribution system. FIG. 4
shows a
process wherein a site is analyzed to identify non-linear loads. During an
initial step (block
110), electrical data acquisition equipment, such as a power quality analyzer
or an
oscilloscope, is directly connected to one or more loads. More generally, the
data acquisition
equipment may be connected at any point that permits measurement of power
quality at the
load. This may be accomplished by connecting the equipment in the branch
circuit that
includes the load, any other branch circuit, or at or near the panel or sub-
panel e.g., if access
is otherwise limited. Thereafter, the electrical power supplied to the load is
analyzed to
identify characteristics of a non-linear load, for example, the presence of
odd current and
voltage harmonics on line and neutral conductors, a low root-mean-square
current draw, and
voltage distortior.L (block 112). Once the analysis is performed, loads that
exhibit one or more
such non-linear characteristics can be identified as non-linear loads (block
114). Once the
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non-linear loads are identified, the process of FIG. 2 may be utilized to
identify unwanted
electrical characteristics and potential sources of the characteristics,
wherein the non-linear
loads are the identified test locations.
[0038] FIG. 5 shows yet another embodiment, wherein recommended solutions to
power quality problems in a power distribution system are provided to a
customer seeking
power quality advice. The process typically begins by collecting data
regarding the power
quality of the power distribution, system (block 130). In one embodiment, the
data are
captured at test locations near each of the load(s) without regard to the
possible linearity or
non-linearity of the load(s) similar to the embodiment of FIG. 2. In another
embodiment, the
process of FIG. 4 is performed, wherein non-linear loads or circuits are first
identified to
identify test locations. The collected data are analyzed, wherein power
quality problems,
such as harmonics and transients, are analyzed and used to identify potential
sources of the
power quality problems (block 132). Thereafter, a recommended solution is
developed for
improving the power quality in the power distribution system based on the
identified sources
(block 134). In an embodiment, the recommended solution includes recommending
placing
power conditioniiig devices upstream of the identified sources in a position
to block voltage
and current transients, reduce harmonic distortion, and/or improve power
factor. In another
embodiment, the recommended solution includes connecting and grouping
identified sources
to different branch circuits, for example, to improve power quality. This
reconfiguration of
the sources can also be implemented using power conditioning devices upstream
of the
sources. Subsequently, the results of the above steps are reported to the
customer (block
136). In one embodiment, a written report is assembled including the above
noted
information. For example, the written report includes an identification of the
power quality
problems discovered and a discussion of the problems in non-technical terms.
The written
report also includes a section discussing the business impact of the power
quality problems
and recommended changes to fix the power quality problems. The customer or a
technician
not otherwise associated with the customer may then implement some or all of
the
recommendations (block 138).
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[0039] It should be noted that one or more of the processes and blocks iri the
embodiments of FIGS. 2, 4, and 5 may be performed either manually or by
appropriate
software.
[0040] The processes of FIGS. 2, 4, and 5 may be implemented at the restaurant
22 of
FIG. 1. For example, during an initial site survey, information regarding the
restaurant 22 is
gathered, for example, the various loads 34 at the site can be identified
and/or particular loads
can be further identified as non-linear loads. In addition, prior problem
areas can be
identified and the surrounding environment can be analyzed to identify
potential external
sources of unwanted power quality characteristics.
[0041] Next, test locations are identified and data acquisition equipment is
connected
at the test locations and the data acquisition equipment is set to measure and
record power
parameters for a period of time, as noted above. The information gathered
during the initial
site survey is used to identify an allowable time-frame to connect the
equipment. For
example, if the loads are in use starting at 7 in the morning, then the data
acquisition
equipment may need to be connected before that time to avoid interrupting the
operation of
the loads. Preferably, the initial test locations are close to or directly
connected to the loads
34A-34I. Further, test locations are identified upstream from the loads, for
example along the
branch circuits 32A-32H or at the panel 28 and sub-panels 30A, 30B. However,
in some
situations, there may not be enough equipment or accessibility to test at each
load.
Consequently, the initial test locations may be located at past problem areas,
at non-linear
loads, or at positions upstream from one or more loads and closer to the panel
28 and sub-
panels 30A, 30B. For example, in one embodiment, the power supplied from sub-
pane130A
has been identified as a past problem area and loads 34H and 34D have been
identified as
non-linear loads. Consequently, data acquisition equipment is directly
connected to the loads
34 D, 34F, 34G, 34H; to branch circuits 32A, 32B, 32D, 32E, 32F, 32G and to
the sub-panels
30A, 30B and the panel 28. If there is not enough data acquisition equipment
then the loads
34 D, 34F, 34G, 34H are first analyzed.
[0042] After the power parameter data has been initially recorded, the data
are
analyzed to ident.ify potential unwanted characteristics, such as, harmonics,
transients, poor
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quality factor, or other anomalies. The identification of the unwanted
characteristics is used
to identify potential sources of the characteristics. In particular, the
location of an unwanted
characteristic and the potential source of the characteristic may correspond
to the location of
the data acquisition equipment. In the example above, if a transient or
harmonic is recorded
at a certain time of day by data acquisition equipment connected to branch
circuit 32A and is
not recorded by data acquisition equipment connected to branch 32D, then the
potential
source of the unwanted characteristic is likely a load connected to branch
32A. Thereafter,
the data acquired from the individual loads 34F, 34G can be analyzed to
further isolate the
potential source of the unwanted characteristic. Further, the parameters of
the unwanted
characteristic(s), e.g., amplitude, frequency, duration, etc., are also
analyzed to determine, for
example, if the potential source results from one or more internal or external
condition(s),
such as a source of EMI or a switched-mode power supply or some other type of
non-linear
load.
[0043] Following the identification of the potential sources of the unwanted
characteristics, a recommended solution can be developed that is focused on
eliminating
and/or minimizing the characteristics caused by the potential sources. The
recommended
solution can be provided in the form of an oral communication or a written
report to the
customer that contains all of the relevant information. Thereafter, the
recommended solution
can be partially or fully implemented to improve the power quality at the
restaurant 22.
[0044] Referring now to FIGS. 6 and 7, a test fixture 150 used in the testing
of
electrical power at a load is shown. The test fixture 150 facilitates the
connection of data
acquisition equipment to the circuit and the normal functioning of the load
during data
acquisition. The test fixture 150 includes a main body 152 having a first end
154 and a
second end 156. A female three-prong receptacle 158 is disposed at the first
end 154 of the
main body 152 and a male three-prong plug 160 is disposed at the second end
156 of the
main body. The test fixture 150 further includes two sets of wires 162, 164
extending
outwardly from the main body 152. As seen schematically in FIG. 3, the dashed
line 166
represents the functionality of the test fixture 150, wherein the male three-
prong plug 160 of
the test fixture is inserted into a power receptacle, and a load is plugged
into the female three
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prong receptacle 158 of the test fixture. Three current sensors are disposed
within the main
body 152 and are connected to the first set of three wires 162 and three
voltage sensors are
disposed in the main body and are connected to the second set of three wires
164. In one
embodiment, the second set of wires 164 is three pairs of wires, wherein each
pair of wires
acts as a differential voltage sensor that is connected to the data
acquisition equipment. In
another embodiment, the second set of wires 164 is three single wires that are
connected
differentially to form the differential voltage sensors. The current sensors
detect the
magnitudes of currents flowing in line, neutral, and ground conductors. The
voltage sensors
detect line-to-neutral, line-to-ground, and neutral-to-ground voltages (common
mode or
transverse mode voltages, as desired). The two sets of wires 162, 164 are
connected to
suitable data acquisition equipment that records and/or displays the various
parameters that
are sensed by the current and voltage sensors.
[0045] FIGS. 8 and 9 show a polyphase test fixture 170 similar to the test
fixture of
FIGS. 6 and 7, but adapted for use in a three-phase power system that includes
three current
carrying conductors, a neutral conductor, and a ground conductor. The
polyphase test fixture
170 includes a main body 172 having a first end 174 and a second end 176. A
female
receptacle 178 is disposed at the first end 174 of the main body 172 and a
male plug 180 is
disposed at the second end 156 of the main body. The polyphase test fixture
170 further
includes two sets of wires 182, 184 extending outwardly from the main body
172. The wires
182, 184 are connected to current sensors and voltage sensors disposed on or
in inductive
communication with the conductors in a manner similar to the test fixture of
FIGS. 6 and 7.
The number of wires in each set of wires 182, 184 can vary depending on the
power
parameters being sensed. In other embodiments, the polyphase test fixture 170
is adapted for
use in a two-phase power system or other polyphase power systems with or
without a neutral
conductor.
INDUSTRIAL APPLICABILITY
[0046] This invention is useful in analyzing the power quality in a power
distribution
system by sensing power parameters initially at one or more loads, and
subsequently or
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concurrently sensing power parameters at other points of the power
distribution system
upstream of the loads.
[0047] Nutnerous modifications to the present invention will be apparent to
those
skilled in the art in view of the foregoing description. Accordingly, this
description is to be
construed as illustrative only and is presented for the purpose of enabling
those skilled in the
art to make and use the invention and to teach the best mode of carrying out
the same. The
exclusive rights to all modifications that come within the scope of the
appended claims are
reserved.
