EP2005200A2

EP2005200A2 - Site analysis methodology and device for testing electric power

Info

Publication number: EP2005200A2
Application number: EP07753314A
Authority: EP
Inventors: Michael W. Januszewski; Leonard E. Webster
Original assignee: Leveler LLC
Current assignee: Leveler LLC
Priority date: 2006-03-16
Filing date: 2007-03-16
Publication date: 2008-12-24
Also published as: WO2007109156A9; JP2009531005A; AU2007227438A1; CA2646062A1; WO2007109156A3; WO2007109156A2; ZA200807965B

Abstract

A method of analyzing a power distribution system that supplies power to a load and to a branch circuit, the method includes connecting electrical data acquisition equipment to the power distribution system at a location upstream of the load and downstream of the branch circuit, sensing data relating to a power parameter experienced at the load, and analyzing the power quality of the power distribution system based on the sensed data by identifying an unwanted characteristic.

Description

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 REGARDINGFEDERALLY 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. External conditions generally appear in 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 damaged 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, memory 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 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 power 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 system 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 diagram 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;

[0018] FIG. 7 is an end elevational view of the test fixture of FIG. 6; [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. 1 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 addition, 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 system.

[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. [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, 3OB 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 3OB 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 make 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 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] After 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, hi 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, multiple 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 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 malfunction. 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. [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 data 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 unwanted 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 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] External 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- 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 configured 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. Channel 1 of the oscilloscope is set to Peak Detect Mode at 250 million samples per second at 40 microseconds 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. The 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 oscilloscope is used to accumulate all of the voltage and current transients that occur during the test period. In another embodiment, the waveforms accumulated 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 distortion (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 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 conditioning 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). [0039] It should be noted that one or more of the processes and blocks in' 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 3OA, 3OB. 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-panel 3OA 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 30A₅ 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 identify potential unwanted characteristics, such as, harmonics, transients, poor 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 32 A. 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 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 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 concurrently sensing power parameters at other points of the power distribution system upstream of the loads.

[0047] Numerous 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.

Claims

WE CLAIM:

1. A method of analyzing a power distribution system that supplies power to a load and to a branch circuit, the method comprising 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; sensing data relating to a power parameter experienced at the load; and analyzing the power quality of the power distribution system based on the sensed data by identifying an unwanted characteristic.

2. The method of claim 1 , further comprising performing the steps of connecting electrical data acquisition equipment to the power distribution system at one or more other locations upstream of one or more other loads connected to the power distribution system, and performing the steps of sensing and analyzing at the one or more other locations.

3. The method of claim 2, further comprising connecting electrical data acquisition equipment to the power distribution system at one or more locations further upstream from the loads and downstream from a location wherein multiple branch circuits converge, and performing the steps of sensing, analyzing, and identifying at the one or more locations.

4. The method of claim 3, wherein the step of sensing at each of the locations is performed concurrently.

5. The method of claim 2, further comprising identifying a potential source of the unwanted characteristic by analyzing the unwanted characteristic and the locations where the electrical data acquisition equipment are connected.

6. The method of claim 1, wherein the data include voltage and current across and on a plurality of conductors, and further wherein the unwanted characteristic includes a harmonic, transient, low power quality, or other anomaly in the power distribution system.

7. The method of claim 1, further comprising sensing data during a normal operating cycle of the load.

8. The method of claim 1, further comprising connecting the electrical data acquisition equipment to the power distribution system through a test fixture, wherein the test fixture includes a body, a male receptacle disposed at a first end of the body, a female receptacle disposed at a second end of the body, voltage sensors disposed within the body coupled to detect voltage across a plurality of conductors, and current sensors disposed within the body coupled to detect current flowing through the plurality of conductors.

9. A method of analyzing the power quality of a power distribution system within a site, comprising the steps of: connecting electrical data acquisition equipment to the power distribution system at a location directly upstream of a non-linear load; sensing data relating to a power parameter by the non-linear load; identifying a potentially adverse characteristic experienced by the non-linear load; and analyzing the potentially adverse characteristic to determine a source of the characteristic.

10. The method of claim 9, further comprising performing the steps of connecting, sensing, identifying, and analyzing for other non-linear loads connected to the power distribution system.

11. The method of claim 10, further comprising identifying a non-linear load connected to the power distribution system by connecting data acquisition equipment at a location upstream of a load and sensing non-linear load characteristics including odd current harmonics, a low RMS current draw, and/or voltage distortion, wherein the load is identified as a non- linear load if one or more of the non-linear load characteristics are sensed.

12. The method of claim 10, further comprising connecting electrical data acquisition equipment to the power distribution system at one or more locations further upstream from the non-linear loads and downstream from a location wherein multiple branch circuits converge, and performing the steps of sensing, identifying, and analyzing at the one or more locations.

13. The method of claim 12, wherein the step of sensing at each of the locations is performed concurrently.

14. The method of claim 9, wherein the data include voltage and current across and on a plurality of conductors, and further wherein the potentially adverse characteristic is a harmonic, transient, low power factor, or other anomaly in the power distribution system.

15. The method of claim 9, further comprising sensing data during a typical operating cycle of the non- linear load.

16. A method of analyzing power quality in a power distribution system, comprising the steps of: collecting power parameter data for a power distribution system; analyzing the collected power parameter data to identify sources of adverse power quality characteristics; developing a recommended solution for improving the power quality in the power distribution system; and reporting the results of the collecting, analyzing, and developing steps.

17. The method of claim 16, further comprising identifying one or more test locations that are located near loads and collecting data at the test locations using data acquisition equipment, wherein the collected data includes voltage and current across and on a plurality of conductors.

18. The method of claim 16, wherein the step of analyzing includes identifying harmonics and transients and determining power factors of the power in the power distribution system, and wherein the harmonics, transients, and power factors are analyzed to identify the sources.

19. The method of claim 16, wherein the recommended solution includes isolating the sources of the adverse power quality characteristics using power conditioning devices that substantially eliminate voltage and current transients, reduce harmonic distortion, and improve power factor.

20. The method of claim 16, further comprising performing an initial survey of the power distribution system.