Power quality utility metering system having waveform capture

Details Power quality utility metering system having waveform capture Power quality utility metering system having waveform capture

1999-01-08

2004-01-06

Black, Thomas (Department: 2121)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Electrical power generation or distribution system

C700S294000, C702S062000, C340S661000

Reexamination Certificate

active

06675071

ABSTRACT:

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 t

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