Abstract:
A method of monitoring variations is carried out within an electrical energy meter containing means therein for metering a quantity of electrical energy generated by a supplier and transferred via a power supply line to a load. The method includes a first step of sensing a line voltage transferred via the power supply line to the load during the energy measurement time interval. The method also includes the step of detecting a variation in a magnitude of the sensed line voltage relative to an acceptable voltage level, wherein the variation exceeds a first variation threshold. The method then includes the step of capturing a first waveform of the sensed line voltage corresponding to the time when the variation is detected. Finally, the method includes the steps of detecting a subsequent reduction in the variation of the magnitude of the sensed line voltage such that the variation is equal to or less than the first variation threshold and capturing a second waveform of the sensed line voltage corresponding to the time when the subsequent reduction in the variation is detected.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     Cross reference is made to U.S. patent application Ser. No. 09/226,957, filed Jan. 8, 1999, which is assigned to the assignee of the present invention. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to electricity meters such as used by commercial, industrial, or residential customers of power utility companies and, more particularly, to a revenue accuracy meter having various operational capabilities such as power quality measurement and/or energy management. 
     BACKGROUND OF THE INVENTION 
     Utility power distribution generally starts with generation of the power by a power generation facility, i.e., power generator or power plant. The power generator supplies power through step-up subtransmission transformers to transmission lines. To reduce power transportation losses, the step-up transformers increase the voltage and reduce the current. The actual transmission line voltage conventionally depends on the distance between the subtransmission transformers and the users or customers. Distribution substation transformers reduce the voltage from transmission line level generally to a range of about 2-35 kilo-volts (“kV”). The primary power distribution system delivers power to distribution transformers that reduce the voltage still further, i.e., about 120 V to 600 V. 
     For background purposes, and future reference herein, an example of a power utility distribution system as described above and understood by those skilled in the art is illustrated in FIGS. 1A and 1B of the drawings. Power utility companies, and suppliers thereto, have developed systems to analyze and manage power generated and power to be delivered to the transmission lines in the primary power distribution system, e.g., primarily through supervisory control and data acquisition (“SCADA”). These primary power distribution analyzing systems, however, are complex, expensive, and fail to adequately analyze power that is delivered to the industrial, commercial, or residential customer sites through the secondary power distribution system. 
     Also, various systems and methods of metering power which are known to those skilled in the art are used by commercial, industrial, and residential customers of power utility companies. These power metering systems, however, generally only measure the amount of power used by the customer and record the usage for reading at a later time by the utility power company supplying the power to the customer. A revenue accuracy meter is an example of such a metering system conventionally positioned at a customer site to receive and measure the amount of power consumed by the customer during predetermined time periods during a day. 
     Conventionally, electric power is delivered to industrial, commercial, and residential customers by local or regional utility companies through the secondary power distribution system to revenue accuracy type electricity meters as an alternating current (“AC”) voltage that approximates a sine wave over a time period and normally flows through customer premises as an AC current that also approximates a sine wave over a time period. The term “alternating waveform” generally describes any symmetrical waveform, including square, sawtooth, triangular, and sinusoidal waves, whose polarity varies regularly with time. The term “AC” (i.e., alternating current), however, almost always means that the current is produced from the application of a sinusoidal voltage, i.e., AC voltage. 
     In an AC power distribution system, the expected frequency of voltage or current, e.g., 50 Hertz (“Hz”), 60 Hz, or 400 Hz, is conventionally referred to as the “fundamental” frequency, regardless of the actual spectral amplitude peak. Integer multiples of this fundamental frequency are usually referred to as harmonic frequencies, and spectral amplitude peaks at frequencies below the fundamental are often referred to as “sub-harmonics,” regardless of their ratio relationship to the fundamental. 
     Various distribution system and environmental factors, however, can distort the voltage waveform of the fundamental frequency, i.e., harmonic distortion, and can further cause spikes, surges, or sags, and other disturbances such as transients, time voltage variations, voltage imbalances, voltage fluctuations and power frequency variations. Such events are often referred to in the art and will be referred to herein as power quality disturbances, or simply disturbances. Power quality disturbances can greatly affect the quality of power received by the power customer at its facility or residence. 
     These revenue accuracy metering systems have been developed to provide improved techniques for accurately measuring the amount of power used by the customer so that the customer is charged an appropriate amount and so that the utility company receives appropriate compensation for the power delivered and used by the customer. Examples of such metering systems may be seen in U.S. Pat. No. 5,300,924 by McEachern et al. titled “Harmonic Measuring Instrument For AC Power Systems With A Time-Based Threshold Means” and U.S. Pat. No. 5,307,009 by McEachern et al. titled “Harmonic-Adjusted Watt-Hour Meter.” 
     These conventional revenue accuracy type metering systems, however, have failed to provide information about the quality of the power received by a power customer at a particular customer site. Power quality information may include the frequency and duration of power quality disturbances in the power delivered to the customer site. As utility companies become more and more deregulated, these companies will likely be competing more aggressively for power customers, particularly heavy power users, and therefore information regarding the quality of the power received by the power customer is likely to be important. 
     For example, one competitive advantage that some utility companies may have over their competitors could be that their customers experience relatively few power quality disturbances. Similarly, one company may promote the fact that it has fewer times during a month that power surges reach the customer causing potential computer systems outages at the customer site. Another company may promote that it has fewer times during a month when the voltage level delivered to the customer is not within predetermined ranges which may be detrimental to electromagnetic devices such as motors or relays. Previous systems for measuring quality of power in general, however, are expensive, are bulky, require special set up and are not integrated into or with a revenue accuracy meter. Without a revenue accuracy metering system that measures the quality of the power supplied to and received by the customer, however, comparisons of the quality of power provided by different suppliers cannot readily be made. 
     One solution to the above described problems is proposed by U.S. Pat. No. 5,627,759 to Bearden et al. (hereinafter the “Bearden patent”), which is assigned to the assignee of the present invention and incorporated herein by reference. The Bearden patent describes a revenue accurate meter that is also operable to, among other things, detect power quality events, such as a power surge or sag, and then report the detection of the power quality event to a utility or supplier. 
     One of the useful features of the meter disclosed in the Bearden patent is waveform capture. The meter of the Bearden patent is operable to obtain waveform information regarding the voltage and/or current waveform at about the time a power quality event is detected. Such a feature is advantageous because the captured waveform may be analyzed to help determine potential causes of the event, the severity of the event, or other pertinent data. While the waveform capture feature disclosed by the Bearden patent contributes to the usefulness of the meter, the increased sophistication of power consumers has created a need for further information retrieval capabilities in power quality measurement devices. 
     In particular, it has been found that much may be learned about a power quality event by analyzing the voltage waveform when the power quality event ends, as well as when it begins. Moreover, it has been found that power quality events can often include one or more “sub-events”. For example, consider a power quality event in the form of a voltage sag wherein the line voltage falls from 120 volts to 100 volts for five minutes, and then falls to 85 volts for two hours, and then returns to 100 volts for an hour, and then returns to 120 volts. It is useful to gather information about such sub-events for analysis of the power distribution system. 
     One solution would be to implement a power quality device that captures all the voltage waveform data at all times. However, capturing all such data is impracticable. In particular, in order to be of use, the voltage waveform data must be captured, or in other words, stored in non-volatile memory for subsequent retrieval and analysis. The totality of waveform data for any significant length of time over one second is substantial. For example, at a sampling rate of 32 samples per cycle, one seconds worth of data for a single voltage waveform constitutes 1920 samples of data per second. For poly-phase meters wherein both voltage and current are sampled, the number of samples is four to six times that number. 
     It is thus apparent that the storage of ongoing waveform data cannot be achieved in non-volatile memory contained within the meter for any significant period of time. Moreover, it is impracticable for the meter to communicate such data to a remote device having greater memory capability. In particular, the communication of such amounts of data requires a substantial amount of constantly available communication bandwidth, which is not cost-effective nor practical. 
     What is needed, therefore, is a power measurement device which is coupled with a revenue accurate meter and has the capability to obtain waveform information for multiple phenomena within a power quality event. In particular, there is a need for such a device that obtains waveform information for both the beginning and the end of a power quality event, as well as for a device that obtains waveform information for a plurality of sub-events within a particular power quality event. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the above needs, as well as others, by providing a system and method for use in a revenue accurate meter that detects a variation in the line voltage level from a normal voltage level, capturing the line voltage waveform corresponding to the time when the variation was detected, detecting a reduction in the variation of the line voltage level from the normal voltage level, and capturing the waveform corresponding to the time the reduction of the variation was detected. By capturing waveforms both at the time that the voltage varies from the norm and the time that the voltage returns to the norm, the present invention obtains further detailed information about a power quality event than that available in the prior art. Moreover, by capturing waveforms corresponding to the times that the voltage variation is detected and the time that the reduction in the variation is detected, storage and/or communication of the captured waveform data is practicable. Such data may then be analyzed at a later time and/or at a remote location to obtain information regarding the disturbance that caused the line voltage variation. 
     An exemplary method according to the present invention is carried out within an electrical energy meter containing means therein for metering a quantity of electrical energy generated by a supplier and transferred via a power supply line to a load of a customer during an energy measurement time interval. The exemplary method is a method of monitoring variations in the metered quantity of electrical energy. 
     The method includes a first step of sensing a line voltage transferred via the power supply line to the load during the energy measurement time interval. The method also includes the step of detecting a variation in a magnitude of the sensed line voltage relative to an acceptable voltage level, wherein said variation exceeds a first variation threshold. The method then includes the step of capturing a first waveform of the sensed line voltage corresponding to the time when said variation is detected. Finally, the method includes the steps of detecting a subsequent reduction in the variation of the magnitude of the sensed line voltage such that the variation is equal to or less than the first variation threshold and capturing a second waveform of the sensed line voltage corresponding to the time when the subsequent reduction in the variation is detected. 
     An exemplary apparatus according to the present invention is an electrical energy meter for obtaining data regarding line voltage variations in real-time. The electrical energy meter includes a voltage digitizing circuit, a current digitizing circuit, a metering circuit and a power quality circuit. The voltage digitizing circuit is operable to obtain analog line voltage information and generated digital line voltage information therefrom. The current digitizing circuit is operable to obtain analog line current information and generate digital line current information therefrom. The metering circuit is operable to receive the digital line voltage information and the digital line current information and generate metering information therefrom. 
     The power quality circuit is operable to: receive the digital line voltage information and obtain magnitude information therefrom, the magnitude information representative of the magnitude of the line voltage; detect a variation in the magnitude of the line voltage relative to an acceptable voltage level wherein said variation exceeds a first variation threshold; capture a first waveform in the form of a first set of digital line voltage information corresponding to the time when said variation is detected; detect a subsequent reduction in the variation of the magnitude of the line voltage such that the variation is equal to or less than the first variation threshold; and capture a second waveform in the form of a second set of digital line voltage information corresponding to the time when the subsequent reduction in the variation is detected. 
     The exemplary method and apparatus described above provide the above mentioned advantages of capturing waveform information for a voltage waveform at both the beginning of a power quality event and the end of a power quality event. In alternative embodiments, the method and apparatus may be configured to detect a second variation that is greater than the first variation, and capture a waveform corresponding to the time when the second variation is detected. Such a method and apparatus would then be capable of capturing waveform data on sub-events within a power quality event. 
     The above features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B schematically illustrate an environmental view of a revenue accuracy meter having power quality measurement according to the present invention; 
     FIGS. 2A and 2B schematically illustrate a revenue accuracy meter having power quality measurement arranged in communication with a power generator and a power customer according to the present invention; 
     FIG. 3 schematically illustrates a revenue accuracy meter having power quality measurement arranged in communication with various data communication links according to the present invention; 
     FIG. 4 illustrates a revenue accuracy meter having power quality measurement according to the present invention; 
     FIGS. 5A and 5B schematically illustrate a flow chart of a digital signal processor circuit of a revenue accuracy meter having power quality measurement according to the present invention; 
     FIG. 6 schematically illustrates a power quality measurement circuit of a revenue accuracy meter according to the present invention; 
     FIGS. 7A,  7 B, and  7 C illustrates the operations of a power quality circuit within the revenue accuracy meter of FIG. 3 in accordance with the present invention; 
     FIG. 8 schematically illustrates a revenue accuracy meter having power quality measurement and energy management according to a second embodiment of the present invention; and 
     FIG. 9 schematically illustrates an apparatus for providing control parameters to the revenue accuracy meter of FIGS. 3 and 4 in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
     As illustrated in the schematic environmental view of FIGS. 1A and 1B, utility power distribution  20  generally starts with generation of the power by a power generation facility  21 , i.e., power generator or power plant. The power generator  21  supplies power through step-up subtransmission transformers  21   b  to transmission stations  23 . To reduce power transportation losses, the step-up transformers  21   b  increase the voltage and reduce the current. The actual transmission line voltage conventionally depends on the distance between the subtransmission transformers  21   b  and the users or customers, i.e., commercial, industrial, or residential  37 ,  38 . Distribution substation transformers  25 ,  26 ,  27  reduce the voltage from transmission line level generally to a range of about 2-35 kilo-volts (“kV”). The primary power distribution system  31  delivers power to distribution transformers  28 ,  28   a  that reduce the voltage still further, i.e., about 120 V to 600 V. 
     Conventionally, power utility companies and suppliers have developed systems to analyze and manage power generated and power to be delivered to the transmission lines in the primary power distribution system  31 , e.g., primarily through supervisory control and data acquisition (“SCADA”) at a remote operations center  22  such as illustrated. These operation centers  22  generally communicate with the generation facilities  21  and the substations  24 ,  25  through conventional data communication terminals  21   a ,  24   a ,  25   a . Because problems currently arise in the secondary power distribution system  36 , i.e., from the distribution substation to the customers, with respect to analyzing power that is delivered to the industrial, commercial, or residential customer sites through the secondary power distribution system  36 , a revenue accuracy meter  40 , or a plurality of revenue accuracy meters  40  is provided having power quality measurement according to the present invention and preferably is positioned as illustrated (FIGS. 1A-1B) in the secondary power distribution system  36  to provide a remote terminal or node in the overall system  20  for troubleshooting or diagnosing problems, identifying emergency situations, and systematically analyzing information from specific customer sites. 
     Due to the deregulation of the power delivery industry and the consequent brokering of power at the transmission level, it is also advantageous to implement revenue accurate meters  40  having power quality measurement according to the present invention within the transmission system  31  and/or generation system  21 . 
     FIGS. 2A,  2 B,  3 , and  4  schematically illustrate a revenue accuracy meter  40  having power quality measurement arranged in communication with a power generator  80  such as a utility power company and a power customer  60  according to the present invention. A revenue accuracy meter  40  according to the present invention is an electricity meter or an alternating current static watt-hour meter used for billing functions, i.e., billing meter. These revenue power or electricity meters preferably are solid state meters that at least meet American National Standards Institute (“ANSI”) 12.16, International Electrotechnical Commission (“IEC”) 687/1036 standard, similar improved or revised standards, or the like, as understood by those skilled in the art. As illustrated, the revenue accuracy meter  40  for measuring the amount and quality of electrical power received by a power customer  60  preferably has a housing  40   a  and a communications interface which preferably includes a plurality of data communication ports  41 ,  42 ,  43 ,  44  positioned in the housing  40   a  (see FIGS.  3  and  4 A). The housing  40   a  is configured as is well known in the art to connect the meter  40  to the power lines through, for example, a meter socket. 
     Although four data communication ports  41 ,  42 ,  43 ,  44  are illustrated, a revenue accuracy meter  40  according to the present invention preferably has at least two data communications ports. At least one of the plurality of data communication ports  41 ,  42 ,  43 ,  44  is arranged for data communications with a power customer  60 , e.g., a power customer port  41 , and at least one of the plurality of data communication ports  41 ,  42 ,  43 ,  44  is arranged for data communications with a power generator, e.g., power generator ports  42 ,  43 ,  44 . 
     The particular embodiment of the ports  41 ,  42 ,  43 ,  44  illustrated, however, advantageously provides real time data communications with a plurality of the various groups or departments of a utility company  80  such as marketing  82 , operations  83 , engineering  84 , and/or billing/finance  85  (FIG.  2 B). For example, power quality data such as that discussed below in connection with FIGS. 6,  7 A,  7 B, and  7 C may be utilized by the customer service or the marketing group  82  receiving data from a revenue accuracy meter  40  according to the present invention by monitoring power outage, sags/surges, and excessive harmonics. This information can then be relayed, i.e., by sequential calls, to a head office, key account representatives, and/or customers  60 . Such power quality data may be utilized by operations  83  to monitor voltage/current, KW/KVAR, disturbances, and/or harmonics received by customers  60  through the meter  40  and to monitor transformers, i.e., temperature, capacitors, and other control functions in the power distribution system  20 . 
     The engineering group or department, for example, may utilize the meter  40  and the data received therefrom for monitoring total harmonic distortion, for captured waveform analysis, for spectral analysis, as well as studying and analyzing outages and sags/surges from a diagnostic approach. The billing or finance group  85 , in turn, may conduct load or rate research based upon information provided from the meter  40  about power quality and power usage. As understood by those skilled in the art, the billing group  85  of the power generator  80 , for example, can conduct TOU metering, real-time pricing, transformer loss, compensation, load profile, meter installation integrity, meter wiring verification, load curtailment, and/or various other functions. Also, these various groups of the power generator  80  can also responsively interact with the substation controller  86  such as in multi-drop meter applications or to communicate with remote terminal units (“RTUs”), printers, or the like. Further, the power generator  80  can provide various auxiliary inputs to the meter  40  such as transformer oil temperature data, feeder subloads, redundant metering data, status alarms, pressure data, and/or other information as desired. 
     The customer, on the other hand, can receive on-line data such as engineering units, energy cost, subload data, alternate utility data, and other totals or specific information as needed. Preferably the meter  40  also has customer programmed relay control with security, utility alarming, demand prediction, and energy management capabilities. Additionally, as also illustrated in FIGS. 2A and 8A, a revenue accuracy meter  40  according to the present invention further has an energy management controller  90  electrically connected to the second receiver and the second transmitter for controlling power usage responsive to predetermined command signals received from the power customer through the power customer port of the communications interface. Likewise, the customer may provide auxiliary inputs  62  to the meter  40  such as alarms, status, production parameters, non-electrical utility data, load curtailment data, subload data, as well as other data as desired. The meter  40  may also be monitored or utilized by the customer at a customer central station  61  as illustrated. The data communication ports also provide inter or intra-customer communication, i.e., customer to utility or other customer and communication within customer facility or locations. 
     Either separate from the energy management controller  90  or in conjunction therewith, a meter  40  according to the invention preferably further has an access restricter, not shown, coupled in electrical communication with the power generator port for providing restricted access between the power customer port and the power generator port. This security access preferably is resident in one of the controllers of the meter  40 . This access restriction means or access restricter preferably is software programmed as understood by those skilled in the art so that access is provided to either the power customer or the power generator by a command signal representative of a user password or a data access key. This, in turn, provides a wall for security between meter functions used by a customer  60  and meter functions used by a power generator or other third party  80 . 
     Although, as understood by those skilled in the art, the communication interface of a revenue accuracy meter  40  may include any means for communicating data to and from the meter  40 , such as using a probing device, an optical device, or a remote device for interfacing with the meter  40 , the communications interface of a revenue accuracy meter  40  preferably includes one or more transceivers, e.g., universal asynchronous receiver/transmitter (“UART”), positioned within the housing  40   a  of the meter  40  and arranged to receive and transmit data signals through the data communication ports  41 ,  42 ,  43 ,  44 . 
     Referring now to FIG. 3 in particular, the exemplary embodiment of the meter  40  includes an analog sensor circuit  51 , a digital signal processing circuit  45 , a circular buffer  52 , a microprocessor  48 , a non-volatile memory  53 , a time standard source  54 , a communication interface circuit  55 , a display  56 , a clock circuit  57  and the ports  41 ,  42 ,  43  and  44 . 
     The analog sensor circuit  51  is a circuit that connects to the utility power lines and is operable to generate signals including analog line voltage information and analog line current information for each of the phases in a polyphase power system. In the exemplary embodiment described herein, the analog sensor circuit  51  is operable to obtain analog line voltage information, VA, VB and VC, and analog line current information, IA, IB and IC for three phases of a three phase electrical system. To this end, the analog sensor circuit may suitably include voltage divider circuits, current shunts, current transformers, embedded coils, and/or other well known voltage and current multiple outputs sensing technology. 
     The digital signal processing (“DSP”) circuit  45  and the microprocessor  48  together comprise a metering circuit that is operable to receive line voltage and line current information from the analog sensor circuit  51  and generate metering information therefrom. In particular, the DSP circuit  45 , in addition to a DSP, includes one or more analog to digital signal converters that receive the analog line voltage information and analog line current information and generate digital line voltage information and digital line current information therefrom. The DSP circuit  45  and microprocessor  48  are furthermore suitably programmed to receive the digital line current information and digital line voltage information from the analog to digital converters and generate metering information therefrom. The metering information includes watts, VAR and VA quantities representative of energy consumed by the customer. Further detail regarding the operation of the metering circuit is described below in connection with FIGS.  5 A and SB. 
     The DSP circuit  45  and the microprocessor  48  also together comprise a power quality circuit operable to capture waveforms in accordance with the present invention. Further detail regarding the operation of the power quality circuit is described below in connection with FIGS. 6,  7 A,  7 B, and  7 C. 
     It will be noted that the architecture of the metering circuit and power quality circuit describe above is given by way of example only. Those of ordinary skill in the art may readily devise alternative architectures that incorporate the principles of the metering circuit and power quality circuit described herein. For example, the use of a combination of a DSP circuit and a microprocessor as the metering circuit and power quality circuit is given by way of example only. A single processor may suitably be used for either or both of such circuits. Such a single processor may require relatively high processing speeds to accomplish revenue quality metering and therefore may not be as cost effective as the architecture discussed herein. Alternatively, those of ordinary skill in the art may employ metering circuits and/or power quality circuits according to the present invention that incorporate three or more processors, or that incorporate different types of controllers and processors. Such architectures would provide at least some of the advantages of the present invention. 
     The power quality circuit of the meter  40  further includes the circular buffer  52 . The circular buffer  52  is a circuitous memory structure within at least a portion of a memory device, preferably RAM. The circuitous memory structure stores digital line voltage and/or digital line current values in the sequence in which they are received. Once the circular buffer  52  is full, each new value entered replaces the oldest value in the buffer. In the present invention, the circular buffer  52  may suitably be an allocated portion of the internal RAM of the DSP circuit  45 . However, the circular buffer  52  may alternatively comprise an external RAM or even RAM that is internally or externally coupled to the microprocessor  48 . 
     Returning to the exemplary embodiment of the meter  40  illustrated in FIG. 3, the non-volatile memory  53  may suitably be a flash memory non-volatile RAM, EEPROM, or other non-volatile memory. Non-volatile RAM and flash memory are preferable because the footprint of such memories per unit of memory is significantly smaller than the footprint of EEPROM. However, EEPROM can be advantageous when battery back-up or other back up power sources are impractical or unreliable. Preferably, the non-volatile memory  53  has 4 to 8 megabytes of memory. 
     The time standard source  54  is a source of externally-generated precision time standard information. For example, the time standard source  54  may suitably be a GPS receiver operable to obtain precision time standard information via satellite. Alternatively, the time standard source may be an IRIG or WWV time standard receiver. An example of a time standard source that may be incorporated into the meter  40  is the model GPS-PCI card available from TrueTime, Inc. 
     The clock circuit  57  is a circuit well-known in the art that is operable to generate clock/calendar information in an ongoing manner. In general, the clock circuit  57  may suitably include a crystal oscillator circuit and appropriate logic gates and counters for generating clock/calendar information based on the crystal oscillator circuit. Such circuits are well known. The clock circuit  57  is coupled to the microprocessor to provide the clock/calendar information thereto. The clock circuit  57  is further operably connected, through the microprocessor  48 , to receive the externally generated precision time information from the time standard source  54 . The clock circuit  57  is operable to adjust its clock/calendar information based on the received externally generated precision time information. In accordance with the exemplary embodiment described herein, the time standard source  54  provider precision time information in the form of pulse, i.e. one pulse per second. Thus, the clock circuit  67  is “recalibrated” each time it receives a pulse. 
     The display  56  is an LCD or other display circuit operable to display data provided by the microprocessor  48 . The display  56  and/or the microprocessor  48  includes any necessary drivers for converting the microprocessor data into signals that cause the LCD or other display medium to display the information contained in the data. Such circuits are well known. 
     The communication interface circuit  55  cooperates with the communication ports  41 ,  42 ,  43 , and  44  to effectuate communication between the meter  40 , through the microprocessor  48 , and external devices, including remotely located external devices. To this end, the communication interface circuit  55  may include one or more additional processors that assist in providing such communications. 
     The ports  41 ,  42 ,  43  and  44  preferably include an RS-232 interface port and/or a 20 milliampere (“mA”) current loop, an optical port, and two of either an internal modem, a direct interface, a protocol converter, or an RS-485 port. The internal modem is arranged for communicating with utility customer or power customer auxiliary inputs and outputs. The direct interface (“I/F”) is arranged to connect to an external modem which may provide either additional or duplicative data to the processors  45 ,  48 . The protocol converter and the RS-485 port are likewise arranged to provide data communication to the operations center  22  (see FIG. 1) as well as the local area network (“LAN”) of the utility company or industrial consumer. The optical port preferably is arranged for data communication through a power generator port to laptop computers or the like. The current loop provides secure data communication and, preferably, is arranged for data communication with the auxiliary inputs  81 ,  85  from the utility  80 , such as an encoder, printer, RTU, various software or hardware tools, personal computer, remote data display, or the like. The external modem and the LAN are connected in electrical communication with the desired group  82 ,  83 ,  84 ,  86  of the utility or power generator  80  as illustrated. 
     The elements of the meter  40  described above of FIG. 3 are advantageously configured to reside within a single housing that is operable to be mounted on select ones of standard meter sockets, as illustrated in FIG.  4 . 
     FIGS. 5A and 5B show in further detail the operation of the metering circuit and the power quality circuit of the meter  40  of FIG.  3 . In particular, the DSP circuit  45  portion of the metering circuit and power quality circuit is shown in detail in FIGS. 5A and 5B. In general, the DSP circuit  45  receives the analog line voltage information and analog line current information and performs the preliminary metering calculations as well as preliminary power quality determinations as described herebelow. With respect to metering calculations, the DSP circuit  45  samples and processes the analog line voltage and current signals using high computational speeds and generates interim values such as accumulated watts, VA, and VAR values. By way of example, the DSP circuit  45  samples each line voltage and line current signal 32 times per second. This sampling rate, combined with the use of 20 bit resolution samples, allows the meter  40  to perform revenue accurate metering measurements. 
     The microprocessor  48  periodically retrieves the accumulated interim values and uses them to generate standard meter energy pulses. The microprocessor  48  also accumulates various energy consumption values in compliance with metering standards. The microprocessor  48  further operates to cause display of certain metering values and/or communication of metering values to the consumer or the utility. 
     The DSP circuit  45  further employs the sampled or digitized line voltage signals, and in some cases the digitized line current samples, to determine the presence of undesired variations in the electrical signal representative of power received by a power customer  60  across electrical power lines or the like such as spikes, surges, sags, harmonic distortion, and/or other disturbances. The variation determining means preferably is a variation determiner, or other power quality circuit  200 , as illustrated coupled in electrical communication with the receiver for determining frequency, i.e., time periods or time occurrences, and duration of undesired variations in the received voltage signal during a plurality of predetermined time periods. These undesired signal variations are preferably minimum or maximum threshold variations and/or timing frequency variations of the supplied signal. The operation of the power quality circuit is discussed in further detail in connection with FIG.  6 . 
     Once an undesired signal variation is detected, information is passed to the microprocessor  48  which controls the communication and/or storage of information regarding the variation, including waveform capture in accordance with the present invention, as described below in connection with FIGS. 7A,  7 B and  7 C. 
     As best illustrated in FIGS. 5A and 5B, the DSP circuit  45  receives analog line voltage information VX and analog line current information IX which is representative of the power received by a power customer on one phase of a polyphase system. In a three phase system, the DSP circuit  45  receives the line current information and line voltage information of each phase in sequential manner. To this end, the analog line current and analog line voltage information is multiplexed so that only one line voltage VX and only one line current IX is received at any particular instant. It will be noted that in the alternative, the circuit shown in FIG. 5A may suitably be duplicated for each of the phases of the system. 
     In any event, the sample and digitize circuit  111 , which is preferably an A/D converter, converts IA to a digital line current signal. Likewise, the sample and digitize circuit  101 , which is also preferably an A/D converter, converts VA to a digital line voltage signal. Time compensators  102 ,  112  then compensate for time skew in sampling due to multiplexing a single analog-to-digital converter. The time compensators  102 ,  112  may suitably be short FIR or smoothing filters with nonsymmetrical coefficients to get the proper time skew with a reasonably flat frequency response. 
     Alternatively, time compensators  102 ,  112  may be omitted if simultaneously sampling A/D converters are used. In such a case, measurement alignment is achieved through synchronization of the A/D converters. 
     In any event, the compensated digital signals then are respectively received by low pass filters  103 ,  113 . The digital line current signal passes through a fixed high pass filter  114  and the digital line voltage signal passes through an adjustable high pass filter  104 . A calibration factor  115 ,  135  is then respectively applied to the filtered signals. After calibration, the digital line current signal and the digital line voltage signal is applied to the power quality circuit  200  of the meter  40  according to the present invention. As understood by those skilled in the art, the power quality circuit  200  preferably is in the form of software and/or hardware resident within or in electrical communication with the DSP circuit  45  and the microprocessor  48  of the present invention. FIGS. 6,  7 A,  7 B, and  7 C illustrate the operations of the power quality circuit  200  in further detail. 
     Once the power quality circuit  200  receives the digital line current and digital line voltage information, the meter calculations are then preferably continued by initiating the start customer load detectors  125 ,  145 . As understood by those skilled in the metering art, these detectors  125 ,  145  preferably assure that relatively very small signals, i.e., due to leakage current, register as zero usage. The signal then passes through delay adjustments  126 ,  146  to lower the sampling rate, e.g., through decimation. The delay adjustments preferably allow the normal power measurement process to run at a slower rate and therefore use less of the resources of the microprocessor  48  or DSP circuit  45 . The signal passes to a system configuration block  147  to allow for special meter types such as a 2½ wye meter. 
     As illustrated in FIG. 5B, the signal further passes through a filtering configuration  162  preferably such as illustrated. The current signal preferably is applied to a low pass filter  103 A. This filter  103 A produces a phase shift that approaches 90 degrees lag as the frequency of the amplitude signal increases. This filter  103 A also produces an amplitude response that decreases with frequency, which is compensated by the two FIR filters  103 B and  104 A as illustrated. The output of the voltage FIR filter  104 A is then applied to a low pass filter  104 B. Because the VAR measurement preferably may require a 90 degree lag of voltage relative to current, as understood by those skilled in the art, and the current is lagged by 90 degrees already, an additional lag of 180 degrees is needed in the voltage. A signal inversion by an inverter  104 D preferably supplies this lag. The output of multiplier  129  thus provides VARs with errors due to  103 A only approaching 90 degrees. Multiplier  128  produces an error correction signal of the correct level and phase to correct the errors when summed in summer block  148 . 
     The scalers  103 C,  104 C, and  104 E preferably adjust signal levels so that watts and VARs have the same scale factors in the system  162 . The outputs of multipliers  151 ,  154 ,  161 , and  192  are therefore amperes squared, watts, volts squared, and neutral amps squared as measured by conventional metering. Multipliers  172 ,  175  and  182  preferably have their input 60 Hertz fundamental removed by filters  171  and  181  so that their outputs are the harmonic amperes squared, harmonic watts, and harmonic volts squared. As illustrated by FIG. 5B, multiplier  192  also has as its input the output of a 3-phase current summer  191 . These values or quantities are then integrated in accumulators  152 ,  155 ,  163 ,  165 ,  173 ,  176 ,  183 ,  193 ,  197  and copied into buffers  153 ,  156 ,  164 ,  166 ,  174 ,  177 ,  184 ,  194 ,  198 . In addition, the harmonic amperes for the three phases are summed and multiplied (Blocks  195 ,  196 ) to generate harmonic neutral current squared. The original signal prior to the filter is also checked at block  158 . The zero cross signal from block  158  causes the accumulator copies  153 ,  156 ,  164 ,  166 ,  174 ,  177 ,  184 ,  194 ,  198  to have an integer number of cycles such as for stable short term readings. 
     The microprocessor  48  then periodically retrieves the values from the buffers  153 ,  156 ,  164 ,  166 ,  174 ,  177 ,  184 ,  194  and  198  and generates the metering quantities therefrom. In particular, the microprocessor  48  accumulates watts, VAs, VARs and performs other energy-related calculations known in the art. Once the values have been retrieved from the buffers, the buffers  153 ,  156 ,  164 ,  166 ,  174 ,  177 ,  184 ,  194 , and  198  are cleared. 
     FIG. 6 illustrates a power quality circuit  200  of the invention illustrated in the form of a variation determiner. The power quality circuit  200  at its input receives per phase digital line voltage information (and/or digital line current information) in the form of digital samples. It will be noted that the power quality circuit  200  segregates each phase such that each of the below operations is performed individually for each phase. 
     The digital samples are provided to both the circular buffer  52  and the scaler  210  of the variation determiner. In particular, each digital line voltage sample is provided to the circular buffer  52  prior to further processing within the variation determiner. The circular buffer  52  stores the most recent NN samples, where NN is a predetermined number, typically defined by an operator and programmed into the meter. Further detail regarding the programming of values into the meter  40  is discussed below in connection with FIG.  9 . The circular buffer  52  therefore, at any time, contains digital line voltage information representative of the line voltage waveform for the most recent MM cycles, where MM=NN/(samples per cycle). 
     In an alternative embodiment, a data compression function may be introduced at the input of the circular buffer  52 . The data compression function could be any suitable data compression algorithm and would reduce the amount of samples required to represent the waveform shape. The use of such a data compression function would thereby conserve memory space, albeit at the cost of processing power. 
     In any event, the scaler  210 , which also receives the digital line voltage information, provides the scaled digital line voltage signal to a summation device  111 . The scaler  210  preferably scales the size of the signal to assure against math overflows. The scaler  210  also preferably squares the signal so as to make the meter responsive to root mean square (“RMS”) voltage. The scaled signal is then summed at the summation device  211 . A voltage cycle time determiner  212  is coupled in electrical communication with the scaler and/or squarer  210 , i.e., through the summation device  211 , for determining voltage cycle time. Half-cycle timing  213  and waiting  214  periods are preferably for synchronizing or zeroing the sum  215  of the timing of the system  200 . Accumulation preferably occurs for one-half cycle, passes the result to an FIR filter  216 , then clears the accumulator, i.e., S=0. 
     The multiple tap FIR filter  216 , i.e., preferably includes 1-6 taps, and is coupled in electrical communication with the cycle time determiner  212  for smoothing and/or filtering the voltage squared signal. The number  216   a  and the coefficients  216   b  for the taps are input into the FIR signal smoothing device  216 . It will also be understood that the electrical signals as illustrated in FIGS. 6-7C of the power quality circuit  200  are illustrative for the voltage signals, but under appropriate current signal characterization parameters may also include the current signals. 
     The output of the FIR signal smoothing device  216  is then provided to a voltage handler  230 . The voltage handler  230  is the block that compares the resultant value with expected values to determine if a line voltage variation is present. More importantly, the voltage handler  230  determines whether a detected line voltage variation exceeds one or more variation thresholds and causes waveform capture in accordance with the present invention. In addition, once such a variation is detected, the voltage handler  230  subsequently determines when the variation reduces to a point where it no longer exceeds one or more thresholds and causes further waveform capture in accordance with the present invention. To this end, the voltage handler  230  in the exemplary embodiment described herein operates as described below in connection with FIGS. 7A,  7 B, and  7 C. 
     The flow diagram illustrated in FIGS. 7A,  7 B, and  7 C illustrate the steps of the variation detection and waveform capture operations of the exemplary embodiment of the present invention. It is noted that the most of the operation of the voltage handler  230  as illustrated in FIGS. 7A,  7 B, and  7 C is preferably carried out in the DSP circuit  45 , which is designed to readily handle calculations at the sample rate required for the revenue accurate metering circuit operation. However, because the operations of the voltage handler  230  in the present embodiment require the voltage measure for an entire half cycle, the operations are suitably slow enough to be carried out by the microprocessor  48  if desired. In some cases, it may be preferable to have a combination of the DSP circuit  45  and the microprocessor  48  carry out the operations of the voltage handler  230 . 
     In any event, referring to FIG. 7A, the voltage handler  230  first receives the voltage magnitude information, represented herein as the value VOLT, from the FIR smoothing circuit  216  (step  305 ). The voltage handler  230  then determines whether the variation of VOLT from an expected value exceeds a first variation threshold (step  310 ). If so, then the voltage handler  230  proceeds to step  320 . If not, however, then the voltage handler  230  proceeds to step  315 . 
     In particular, in step  310 , the voltage handler  230  compares VOLT to a set point level, which may be a high set point level or a low set point level. The high set point level represents a voltage magnitude level (in the same units as VOLT) above which a potential waveform capture event is identified. Typically, the high set point level corresponds to a voltage level that, if maintained for several half-cycles, indicates a power quality event. Likewise, a low set point level represents a voltage magnitude level below which a potential waveform capture event (i.e. power quality event) is identified. Thus, for example, if the nominal or expected line voltage level is 120 volts, then a low set point level may be set to correspond to a detected line voltage of 90 volts. Set point levels may either be preset or programmed into the meter  40  by the programming device  600  discussed below in connection with FIG.  9 . 
     In the preferred embodiment discussed herein, the programming device  600  may be used to set multiple points both for high set points and low set points. The second set point may suitably identify a sub-event within a power quality event, such as a further voltage sag, that occurs within a power quality event identified by the first set point. Accordingly, it can be seen that several layers of set points, both below the expected line voltage level and above the expected line voltage level may be employed. 
     In any event, if the variation of VOLT exceeds the first variation threshold (or in other words, VOLT is greater than a first high set point or less than a first low set point), then an index of consecutive variations N is incremented (step  320 ). If, however, the variation of VOLT does not exceed the first variation threshold, then the index N is reset to zero (step  315 ) and the voltage handler  230  returns to step  305  and proceeds accordingly with the next value received from the FIR smoothing filter  216 . 
     Referring again to step  320 , after the index N is incremented, the voltage handler  230  determines whether N exceeds a predetermined variation duration value (step  325 ). The variation duration value represents a minimum number of half-cycles that the variation of VOLT must exceed the first variation threshold to trigger the waveform capture. The predetermined value is set such that a spurious transient that is insignificant from a power quality standpoint will not trigger a waveform capture and other power quality event recording and reporting functions. To this end, the predetermined valve may be 2, 4, or 6 half-cycles. The predetermined value may suitably be set by an operator. 
     It will be noted that other techniques for distinguishing between spurious variations and real power quality events may be used. For example, FIGS. 7A,  7 B, and  7 C of U.S. Pat. No. 5,627,759 illustrate in further detail such a technique that may be incorporated into the meter  40  described herein. 
     In any event, if the voltage handler  230  determines that N does not exceed the predetermined variation duration value, then the voltage handler returns to step  305  to receive the next voltage magnitude value and proceed accordingly. 
     If, however, N exceeds the predetermined variation duration value, then the voltage handler resets N (step  330 ) and records the time and date of the power quality event (step  335 ). In particular, the time and date information provided by the clock circuit  57  is written immediately to a buffer signifying the detection of a waveform capture event. 
     The voltage handler  230  also retrieves the circular buffer contents. The circular buffer contents include the previous MM cycles worth of historical waveform sample data. The voltage handler  230  then forms a power quality event record. The power quality event record may suitably be a time value series data structure that includes the circular buffer contents and the time and date information. 
     The voltage handler  230  then writes the record to a memory and/or communicates the record to the utility customer or the utility generator or supplier (step  345 ). In particular, the voltage handler  230  may cause the record to be stored in either a memory that is inherent to either the DSP circuit  45  or the microprocessor  48 , or an external memory, not shown. Such a memory may suitably be a random access memory or a sequentially accessed memory. However, it is preferable that at least some power quality event records be written to the non-volatile memory in order to preserve the data upon loss of power to the meter. 
     Thus, each time the line voltage magnitude exceeds the first variation threshold for N half-cycles, the buffer contents are recorded, or in other word, the line voltage (or line current) waveform is captured, by generation of the power quality event data record. 
     It is noted that it is also preferable to obtain data representative of several waveform cycles that occur after the power quality event is first detected in step  335 . To this end, the voltage handler  230  may execute a subprocess in which the requisite number of additional line voltage samples are provided to the power quality event data record. The number of line voltage samples to be recorded after detection of a variation that exceeds the first variation threshold also is programmed into the meter  40  by an operator. 
     It will thus be noted that the waveform that is captured after detection of the variation exceeding the first variation threshold may consist of: digital line voltage information corresponding to a predetermined amount of time before and up to the detection; digital line voltage information corresponding to the time of the detection to a predetermined amount of time after the detection; or digital line voltage information corresponding to a predetermined time before to a predetermined time after the detection. In this manner, the waveform information directly surrounding the time a power quality event occurs is captured for subsequent analysis. 
     The use of a precision time standard clock provides a further advantage of allowing several meters having the capability of the meter  40  to record power quality event data having time stamps that are completely synchronized. For example, if a power quality event occurs and is detected by four meters in a several mile radius, then the waveforms captured at those four meters may be analyzed to determined how the power quality e vent affected the power network. Because each of the four meters employs a precision time standard clock, the captured waveform data from each meter can be corresponded exactly to waveforms from the other meters. Such information allows analysis of how a particular problem propagated through the network as well as other valuable power network analysis information. 
     In any event, after step  345 , the voltage handler proceeds to step  350  of FIG.  7 B. The portion of the flow diagram in FIGS. 7B and 7C illustrate an example of how end-of-event and sub-event waveform capture according to the present invention may be carried out. It is noted that when the voltage handler  230  executes step  350 , the meter  40  has already detected and indeed is currently within a power quality event as defined by the first variation threshold. 
     At step  350 , the voltage handler  230  again awaits and receives the voltage magnitude information, VOLT, from the FIR smoothing circuit  216 . The voltage handler  230  then determines whether the variation of VOLT from an expected value is less than the first variation threshold (step  355 ). If so, then the voltage handler  230  proceeds to step  365 . If not, however, then the voltage handler  230  proceeds to step  360 . If the variation is less than the first variation threshold, then it may indicate that the present power quality event is ending and the line voltage is returning to within normal parameters. 
     Specifically, if the variation is less than the first variation threshold, then a second variation duration index L is reset to zero (step  360 ). The second variation duration index L is discussed in further detail below in connection with steps  410  to  420 . The voltage handler  230  then increments the variation reduction duration index M (step  370 ). The voltage handler  230  then determines whether the index M is less than a predetermined variation reduction duration value. In particular, similar to the detection of the first variation in steps  310  to  325 , the voltage handler  230  only records a reduction in the variation of the line voltage from the first variation threshold if there are a predetermined number of half-cycles in which the variation is below the first variation threshold. 
     If M does not exceed the variation reduction duration value, then the voltage handler  230  returns to step  350  to await further line voltage information. If, however, M exceeds the variation reduction duration value, then the voltage handler  230  performs the waveform capture operations described below in connection with steps  380  through  395 . Accordingly, the meter  40  of the present invention performs waveform capture not only at the beginning of a power quality event, such as that detected in the operation of steps  330  through  345 , but also at the end of a power quality event. To this end, the meter  40  performs waveform capture both when a variation of the line voltage exceeds a variation threshold and when the variation of the line voltage is reduced below the variation threshold. 
     In step  380 , the voltage handler  230  resets M. The voltage handler  230  then records the time and date of the power quality event (step  385 ). In particular, the time and date information provided by the clock circuit  57  is written immediately to a buffer signifying the detection of a waveform capture event. 
     The voltage handler  230  also retrieves the circular buffer contents (step  390 ). In particular, as discussed above, the circular buffer contents include the previous MM cycles worth of waveform sample data. The voltage handler  230  generates a power quality event record comprising the circular buffer contents and the time and date information. 
     The voltage handler  230  then writes the record to a memory and/or communicates the record to the utility customer or the utility generator or supplier (step  395 ). As discussed above, it is often preferable to obtain several cycles of waveform sample data after the power quality event is identified in step  335 . To this end, the voltage handler  230  may execute a subprocess in which the requisite number of additional line voltage samples are provided to the power quality event data record. 
     After step  395 , the voltage handler  230  has determined that the line voltage magnitude has returned to within normal parameters. The voltage handler  230  than returns to step  305  of FIG.  7 A and proceeds accordingly. Referring again to step  355 , if it is determined that the variation of the present measure of VOLT is not below the first variation threshold, then the voltage handler  230  executes a sequence of operations that determine whether the variation of VOLT exceeds a second variation threshold, which could indicate a sub-event within the presently detected power quality event. 
     In particular, if in step  355  it is determined that the variation of VOLT is not below the first variation threshold, then the variation reduction duration index M is reset to zero (step  360 ). The voltage handler  230  then determines whether the variation of VOLT from a value representative of the expected line voltage exceeds the second variation threshold (step  405 ). 
     In particular, the second variation threshold corresponds to a second predetermined set point level that is in the same direction as the first set point level. In other words, if the first variation threshold that was exceeded was a variation of the line voltage below the expected voltage level, then the second variation threshold is a variation of the line voltage further below the expected voltage level. Conversely, if the first variation threshold that was exceeded was a variation of the line voltage above the expected voltage level, then the second variation is a variation of the line voltage further above the expected line voltage level. 
     If the variation is not greater than the second variation threshold, then the second variation duration counter L is reset to zero (step  415 ) and the voltage handler  230  returns to await further values of VOLT at step  350 . 
     If, however, the variation is greater than the second variation threshold, then the voltage handler  230  increments the second variation duration index L (step  410 ). After the counter L is incremented, the voltage handler  230  determines whether L exceeds a predetermined second variation duration value (step  420 ). The second variation duration value represents a minimum number of half-cycles that the variation of VOLT must exceed the second variation threshold to trigger the waveform capture, which provides similar protections from spurious voltage anomalies as those discussed above in connection with step  325 . 
     If the voltage handler  230  determines that L does not exceed the predetermined second variation duration value, then the voltage handler returns to step  350  to receive the next voltage magnitude value and proceed accordingly. 
     If, however, L exceeds the second variation duration value, then the voltage handler resets L (step  425 ) and obtains the time and date information corresponding to the detection (step  430 ). The voltage handler  230  also retrieves the circular buffer contents (step  435 ). The voltage handler  230  then generates a power quality event record comprising the circular buffer contents, the time and date information, and a predetermined number of post detection line voltage samples. The voltage handler  230  then writes the record to a memory and/or communicates the record to the utility customer or the utility generator or supplier (step  440 ). 
     Thus, once power quality event has been detected in steps  305  to  325 , the meter  40  of the present invention monitors for a second level of variation of the line voltage (or line current) from an expected value. Such a second level of variation may be preprogrammed as a second set point into the meter  40  by an operator as discussed below in connection with FIG.  9 . As discussed above, the meter  40  then captures the waveform of the line voltage at the time surrounding the detection of the second level of variation. Such information provides further, in depth information relating to a power quality event. Power providers, generators, and consumers may use such information to learn about how and why the event occurred, and what effect it may have had on the power consumer&#39;s equipment. 
     An exemplary use of the captured waveform data for two or more such nested levels of variation within a disturbance event is to plot the data in order to measure customer equipment response to the disturbance as compared to standard power quality tolerance curves. One such power quality disturbance curve is the Computer Business Equipment Manufacturing Association (CBEMA) curve, which is provided in I.E.E.E. standard  446 . 
     Once the second variation power quality event record has been generated and stored and/or communicated in step  440 , the voltage handler  230  then monitors the line voltage to detect when the variation is reduced to less than the second variation threshold (or first variation threshold). To this end, the voltage handler  230  executes the flow diagram illustrated in FIG. 7C, beginning with step  445 . It is noted that in accordance with the flow diagram illustrated in FIG. 7C, the voltage handler  230  will cause waveform capture if the variation of VOLT falls below the second variation threshold and not the first variation threshold for a predetermined number of half-cycles. However, the voltage handler  230  also monitors whether the variation of VOLT from the expected value falls below the first variation threshold. 
     In step  445 , the voltage handler  230  receives a voltage magnitude information value, VOLT, from the FIR smoothing circuit  216 . The voltage handler  230  then determines whether the variation of VOLT from an expected value is less than the second variation threshold (step  450 ). If so, then the voltage handler  230  proceeds to step  455 . If not, however, then the voltage handler  230  proceeds to step  460 . In step  460 , an index J, which represents the number of consecutive values of VOLT that varied from the expected value in an amount less than the second variation threshold, is reset to zero. After step  460 , the voltage handler returns to step  445  to await the next value of VOLT. 
     In step  455 , which is executed when the variation of VOLT does fall below the second variation threshold, the index J is incremented. 
     The voltage handler  230  then determines whether the variation of VOLT from an expected value is less than the first variation threshold (step  465 ). If so, then the voltage handler  230  increments the counter M (step  470 ) and then proceeds to step  480 . If not, however, then the voltage handler  230  resets the value of M (step  475 ) and then proceeds to step  480 . Steps  465  through  475  begin accumulation of the index M in the event that the line voltage returns to a value that is less than the first variation threshold before the value of J reaches the second variation reduction duration value. In other words, before the value of J is sufficient to signify that the sub-event represented by the second variation threshold is over, the line voltage may have returned to within its normal parameters. In such a case, the steps  465  through  475  begin incrementing the counter M for use when the voltage handler  230  returns to the flow diagram in FIG. 7B, as discussed further below. 
     The voltage handler  230  then determines whether J exceeds the second variation reduction duration value (step  480 ). In particular, similar to the detection of the first variation in steps  310  to  325 , the voltage handler  230  only records a reduction in the variation of the line voltage from the second variation threshold if there are a predetermined number of half-cycles in which the variation is below the second variation threshold. 
     If J does not exceed the second variation reduction duration value, then the voltage handler  230  returns to step  445  to await further line voltage information. If, however, M exceeds the second variation reduction duration value, then the voltage handler  230  performs the waveform capture operations described below in connection with steps  485  through  500 . Accordingly, the meter  40  of the present invention performs waveform capture not only at the beginning and end of a power quality event, such as described above in connection with steps  330  through  395 , but also at the beginning and end of a power quality sub-event within a power quality event. To this end, the meter  40  performs waveform capture both when a variation of the line voltage exceeds each of two variation thresholds and when the variation of the line voltage is reduced below one or both of those variation thresholds. 
     In step  485 , the voltage handler  230  resets J. The voltage handler  230  then records the time and date of the power quality event (step  490 ). In particular, the time and date information provided by the clock circuit  57  is written immediately to a buffer signifying the detection of the waveform capture event. 
     The voltage handler  230  also retrieves the circular buffer contents (step  495 ). The voltage handler  230  generates a power quality event record comprising the circular buffer contents, the time and date information, and a predetermined number of post detection line voltage samples. 
     The voltage handler  230  then writes the record to a memory and/or communicates the record to the utility customer or the utility generator or supplier (step  500 ). After step  500 , the voltage handler returns to step  375  of FIG.  7 B and proceeds accordingly to determine whether the value of VOLT has varied from the expected value less than the amount of the first variation threshold for enough cycles to indicate that the entire power quality event is over. 
     It will be appreciated that the use of two nested variation thresholds, as discussed above in connection with FIGS. 7A,  7 B and  7 C, is given by way of example only. Those of ordinary skill in the art may readily modify the embodiment described herein to accommodate three or more nested variation thresholds corresponding to three or more user-defined set points. 
     As discussed above, the power quality event data records generated by the voltage handler  230  are provided to memory within the meter or to data communication ports  41 - 44  as the measuring by the meter  40  continues. This signal variation information provided by the voltage handler  230  of the meter  40  which reflects the quality of power not only provides competitive information for utility companies and customers thereof, but also provides troubleshooting information for utility companies and customers in areas of power distribution such as through a secondary distribution system. 
     The meter  40  of the present invention may further include circuitry for performing energy management functions. FIG. 8A shows a functional block diagram of an energy management controller  90  that may be incorporated into the meter  40  of FIG.  3 . 
     In general, the revenue accuracy meter  40  receives a signal from a temperature controller or HVAC controller from a customer  60  into a transducer  91 . A signal is responsively converted to an electrical signal by the transducer  91  and compared to temperature, or other energy system data, to desired predetermined settings  92 . This data is then analyzed by an energy analyzer  95  preferably to analytical calculate optimum desired settings based on power cost or billing data  94  and/or to perform various load curtailment functions. The analyzer  95  then responsively communicates to a power customer&#39;s energy system to adjust temperature or other energy system settings  93  as illustrated. Blocks  92 ,  94  and  95  may suitably be carried out by the microprocessor  48 . 
     Because the revenue accuracy meter  40  preferably includes a power quality circuit  200 , the energy management controller  90  of the meter  40  can advantageous include real time information to the power customer  60  about the quality of power received and how this affects the customer&#39;s energy usage and control capabilities. Additionally, this information can then be used to adjust billing calculations or projected energy usage costs related to the quantity of power used and/or the quality of the power supplied from the power generator  80 . It will also be understood by those skilled in the art that such a meter  40  according to the invention may also include information related to a third party or same party power generator such as a large industrial company, i.e., cogeneration. 
     The energy management controller  90  also preferably provides centralized data retrieval and management from the energy analyzer  95  responsive to predetermined command signals from a customer  60 . These functional capabilities preferably include spreadsheet interface, basic reporting, record-keeping, overall system control, enhanced user interfaces, and other real-time access to energy utilization data for statistical manipulation and graphic presentation to the customer  60 . These manipulation capabilities preferably are software driven with computer programs resident in a microprocessor or memory in communication therewith, and preferably include kilowatt load curves for day, week, and month, kilowatt duration curves, kVA/kQ load curves, power factor curves, energy worksheets, demand worksheets, excessive reactive worksheets, fuel recovery, contract minimum demand, rate worksheets, billing dates table, demand history table, season demand multiplier table, and predictive monitoring. The communication is preferably through a modem or other data communication interface, i.e., data communication ports  41 - 44 , with the customer  60  as understood by those skilled in the art. 
     Also, according to the present invention as described above and as further illustrated in FIGS. 1-8, methods of measuring the quality of power received by a power customer  60  are provided. The method of the present invention preferably includes determining frequency and duration of undesired variations in an electrical signal representative of power received by a power customer  60  across electrical power lines during a plurality of predetermined time periods and communicating a signal representative of the undesired power variations to a power generator  80 . The method preferably further includes measuring power usage of a power customer  60  responsive to an electrical signal representative of a customer load and communicating a signal representative of the amount of power used responsive to a command signal received from a power generator  80  or other entity. 
     Another method of measuring the quality of power supplied across electrical power lines by a power generator  80  is further provided by the present invention. The method preferably includes receiving an analog signal representative of voltage received across electrical power lines and converting the received analog signal to a digital signal representative of the voltage. The frequency and duration of undesired variations in the digital voltage signal during a plurality of predetermined time periods are then determined. The data representative of these undesired variations are then stored and signals representative of the frequency and duration variations are transmitted to a power generator  80  responsive to a predetermined command signal received from the power generator  80 . The step of determining frequency and duration of undesired variations preferably includes comparing a voltage signal to a predetermined voltage threshold value and determining a time period that the voltage signal is above or below the predetermined voltage threshold value. Further, the methods preferably also includes measuring power usage of a power customer responsive to an electrical signal representative of a customer load, and communicating a signal representative of the amount of power used responsive to a command signal received from a power generator. The power usage also may then be controlled responsive to predetermined command signals received from a power customer. 
     By providing power quality and power usage measurement, as well as other beneficial functions such as energy management control  90 , in a revenue accuracy meter, the meter  40 , and associated methods, of the present invention provides a compact and relatively inexpensive solution to problems associated with prior devices and systems. Additionally, the data communications capabilities of a revenue accuracy meter  40  of the invention enhances a power generator&#39;s capability to monitor power quality situations at specific customer sites, i.e., including problems in the secondary power distribution system  36 , remote from the power generating stations  21  or SCADA control facilities  22 . These problems, for example, may include harmonic distortion, surges, sags, or other disturbances that greatly affect the quality of power received by the power customer  60  at its industrial/commercial facility  41  or residence  42 . 
     FIG. 9 shows a block diagram of a control programmer  600  for use in connection with the meter  40 . In particular, the control programmer  600  is a device that may be used to program control parameters into the meter  40 . The control programmer  600  may be a stand alone, portable programmer or laptop computer that communicates through the optical port in the meter  40 , or may be a remote computer that communicates through one or more of the other communication ports  41 ,  42 ,  43 , or  44 . 
     The control programmer  600  includes a user interface  605  operable to receive control parameters for the meter  40 , including information identifying a first variation threshold and the second variation threshold. To this end, the user interface  605  may suitably include a keypad or keyboard input device and a display for feedback. 
     The control parameters may further include metering calibration values, user defined configurations of reports obtained by the meter  40 , and on/off controls for various meter features. The first and second variation thresholds may suitably be provided as first and second set points above the expected line voltage and first and second set points below the expected line voltage. Other power quality related parameters may include the number of waveform cycles before and after an event which are to be captured (timing parameters), the first and second variation duration values, the first and second variation reduction values, the number of events stored in non-volatile memory as opposed to volatile memory. 
     Still other control parameters may define whether, when, how and where to automatically communicate power quality event records. Such parameters may be used to provide differing quantities of power quality event records to different external locations using different communication methodologies. Accordingly, the meter  40  is preferably configured to provide flexible captured waveform communication capabilities in addition to the above described advantages. 
     Coupled to or integral with the user interface  605  is a programming device  610 . The programming device  610  is a device that is configured to provide information to the electrical meter  40 . In particular, the programming device  610  is operable to communicate the control parameters identified above to the electrical energy meter  40 . To this end, the programming device  610  may suitably convert the control parameters in the form obtained by the user interface  605  to a table of parameter values in a form that is utilized by the meter  40 . 
     The programming device  610  then communicates the control parameters through one of the communication ports  41 ,  42 ,  43 , and  44 . The table of parameter values may suitably be stored in the meter  40  in the non-volatile memory  53 . The microprocessor  48  and/or DSP circuit  45  may then download and/or retrieve the parameters as necessary. 
     In the drawings and specification, there have been disclosed typical preferred embodiments of a revenue accuracy meter  40 , and associated methods, according to the invention and, although specific terms are employed, they are used in a descriptive sense only and not for purposes of limitation. The invention has been described in considerable detail with specific reference to these various illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the invention as described in the foregoing specification and as defined in the appended claims. 
     For example, while the above-described embodiments show a power quality meter in which multiple set points for waveform capture are preprogrammed into the meter  40 , waveform capture may also be, or alternatively be, triggered through receipt of an externally-generated trigger signal, such as one received through one of the communication ports  41 ,  42 ,  43 ,  44 . 
     Moreover, it is noted that the source of externally-generated time standard information could alternatively be a communication receiver that is coupled to a time standard source within another meter. For example, if several meters are located on a local area network, it is possible to have only one meter that includes a GPS, WWV OR IRIG receiver and to have that meter communicate the calendar clock information to the other meters on the LAN periodically to calibrate all the clocks. 
     Finally, while the exemplary embodiment described above focuses primarily on handling detected line voltage variations, it may be advantageous in some circumstances to provide the waveform capture features of the present invention in connection with other line energy variations, such as line current variations.