Patent Description:
Electricity meters are devices that measure and/or meter aspects of energy provided to a load. The load may be a residence, business, or even part of a larger electricity distribution system. Commonly available meters include electromechanical meters and electronic meters. Electromechanical meters employ a rotating disk that rotates in response to electric and magnetic fields induced by the electricity passing to the load. As is known in the art, the disk rotation speed is a function of the amount of electricity delivered to the load. Mechanical counters accumulate the number of disk rotations, which is indicative of energy consumed by the load. In some cases, an electromechanical meter can employ processing circuitry to perform additional operations with the consumption information provided by the rotating disk.

Electronic meters typically employ processing circuitry instead of the rotating disk and mechanical counters. In such meters, sensors within the meter detect the voltage and current that is delivered to the load. Circuitry within the meter converts the sensed voltage and current into digital values. Processing circuitry then employs digital signal processing to calculate consumed energy, among other things, from the digital values. Electronic meters provide greater flexibility in the types of energy consumption information that they may calculate, track, and store.

During operation, the electric lines that an electric meter monitors may experience interruptions in providing power due to power outages that occur in a power grid. In many instances, electrical utilities are required to provide aggregate information about an average amount of time that different portions of a power grid experience an interruption to electrical power. This measurement can refer to an average amount of time that the power grid experiences a power loss during a predetermined time span, such as a monthly or annual time span, where of course in many instances only a portion of the power grid experiences an interruption at any one time. One example of such a measurement is the System Average Interruption Duration Index (SAIDI), which is expressed mathematically as: <MAT> where Ni refers to a total number of customers at a particular location i, Ui is the total duration of power interruptions at the location i, and NT is the total number of customer locations. The SAIDI measurement is generally calculated over a one year period to provide an average duration of power interruptions for a power grid that provides power to multiple locations and customers.

In some existing electrical systems, interruptions to electrical power delivery are monitored from a centralized system, but while such monitoring can identify large-scale power outages effectively, the monitoring process may not identify smaller-scale power outages that have shorter durations accurately. Consequently, improvements to systems that monitor the consumption of electrical power to increase the accuracy of measuring periods of power interruption would be beneficial.

<CIT> relates to a power distribution unit (PDU) having at least one power receptacle for enabling attachment of an AC power cord of an external device thereto. A branch receptacle controller (BRC) has at least one bistable relay and is associated with the one power receptacle for supplying AC power thereto from an AC power source. The BRC monitors a parameter of a line voltage and uses it to detect when AC power is lost, and then toggles the bistable relay, if the relay is in a closed position, to an open position. A rack power distribution unit controller (RPDUC) monitors the bistable relay and commands the BRC to close the bistable relay after AC power is restored.

<CIT> describes a power source device and an image processing apparatus. A main power source portion generates a primary DC power from an input AC power, and a first sub power source portion generates a power source control secondary DC power from the primary DC power. Each of a plurality of second sub power source portions, upon input of an activation signal, generates an equipment secondary DC power from the primary DC power. A sub-power-source control portion starts to operate upon receiving the power source control secondary DC power. The sub-power-source control portion outputs the activation signal to a display-related second sub power source portion with higher priority when the detection result of a power state detection portion satisfies a predetermined unfavorable condition, than when the detection result does not satisfy the unfavorable condition, and outputs an alarm signal to cause display-related equipment to output an alarm.

<CIT> refers to an electronic device and a toilet apparatus that can reliably distinguish between energization and noise even in an environment where a power supply with a variable frequency is used, and can accurately resume operation. A power supply circuit that receives power supply from an AC power supply that changes in frequency, detects a zero cross of the AC power supply and outputs a zero cross detection signal, a control unit that outputs a control signal, and a control signal based on the control signal. When the AC power supply fails, the control unit resumes the operation of the controlled unit when the zero cross detection signal has received a predetermined number of times within a predetermined time.

In <CIT> a watt-hour meter is disclosed which includes: a microprocessor coupled to a solid-state Hall-Effect sensor; an electrically alterable ROM coupled to the microprocessor; a power supply; a power outage timing means using the discharge characteristic of a capacitor; apparatus for supplying a <NUM> clock signal to the microprocessor; a readout device coupled to the microprocessor to provide an indication of the power consumed; an output on the microprocessor for controlling a circuit breaker; and a switch for overriding the microprocessor controlled circuit breaker. The microprocessor and the electrically alterable ROM are connected and programmed: to sense the time of day as determined from an initial time of day and setting the <NUM> clock signal; to sense and compute the power used by the consumer; to automatically open the circuit breaker when power demand on the electric power source is high and/or the cost per kilowatt hour is high; to automatically close the circuit breaker when the power demand on the source of electric power is low and/or the cost per kilowatt power is low; and to allow a consumer to override the microprocessor's control of the circuit breaker.

<CIT> relates to a demand electronic electricity meter having load profile recording capabilities. Load profile recording requires memory for storing the recorded information, whereby either on-board memory or external memory is required. Load profile parameters include the number of channels (e.g., <NUM>, <NUM> or more channels), interval size (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM> minutes), quantities to be recorded (e.g., kWh and kvarh, kV Ah, or Qh) and channel scalar/divisor (e.g., for each channel, a <NUM> byte divisor and a <NUM> byte scalar). With two channels, only two quantities are available for recording, kWh and the one other quantity that the meter has been configured to record, (e.g., kvarh, KVAh, or kQh). For each quantity selected, snapshots of the corresponding total accumulator; (i.e. total kWh and total kvarh, kV Ah or kQh) are automatically maintained.

<CIT> describes a utility meter having data logging with power loss recovery. A method for storing information within the utility meter includes storing a data stream comprising a plurality of data values regarding a metered quantity delivered to a load corresponding to a plurality of time periods, wherein the plurality of data values are stored sequentially based on their corresponding time periods. The method also includes responsive to a power outage, inserting into the data stream a time stamp corresponding to a time period in the plurality of time periods in which the power outage occurred.

The invention is defined by a method of identifying power interruptions according to claim <NUM> and by the associated system according to claim <NUM>. Further aspects are defined by the corresponding dependent claims.

The foregoing aspects and other features of system and methods for the measurement of the duration of electrical power interruptions are explained in the following description, taken in connection with the accompanying drawings.

For a general understanding of the environment for the device disclosed herein as well as the details for the device, reference is made to the drawings. In the drawings, like reference numerals designate like elements.

As used herein, the term "metrology circuit" refers to any suitable circuit that detects, measures, and determines one or more electricity and/or electrical energy consumption values based on energy flowing between terminals of an electric meter that are connected in-line with a power line between an electric power source and the load that receives the electric power. In one common configuration, a power grid or other generation source is connected to one set of terminals and the load that receives the electrical power is connected to the other set of terminals. The electric power in the power line flows through the electric meter and the metrology circuit measures various aspects of the electrical signal including, but not necessarily limited to, voltage and current.

As used herein, the terms "power outage" and "power interruption" are used interchangeably and refer to an event in which the normal supply of electric power through one or more power lines that are connected to an electric meter temporarily ceases. Power outage and interruption events are also referred to as "blackouts" in which all electrical power ceases to flow through the power lines or the level of electrical power drops to a level that prevents normal operation of a load and the electric meter.

<FIG> depicts an electric meter <NUM> that is configured to measure the duration of power interruptions in the supply of electricity through one or more power lines that are connected to the electric meter <NUM> and to transmit load profile data to an external monitoring system <NUM> via a network <NUM>. The electric meter <NUM> includes a meter base <NUM> and a metrology circuit <NUM> that are supported by and at least partially contained within a housing of the electric meter.

The meter base <NUM> includes two pairs of terminals 124A/128A and 124B/128B that are electrically connected together by conductors 126A and 126B, respectively. In the meter base <NUM>, each of the terminals 124A, 124B, 128A, and 128B is formed from an electrically conductive member, often referred to as a "blade" or a "stab", which extends from the housing of the electric meter to engage a socket that is connected to a power line (socket and power line not shown). Each of the terminal pairs 124A/128A and 124B/128B is configured to connect in-line with a conductor in a powerline where all of the power that passes through the power line from an energy source to a load passes through the terminal pairs 124A/128A and 124B/128B to a load. The terminal pairs 124A/128A and 124B/128B and the electrical conductors 126A and 126B effectively become part of the power line connected between the generation source and the load when the electric meter <NUM> is connected to the socket. While <FIG> depicts two pairs of terminals with two conductors that are configured to be connected in-line with a power line that includes two conductors (and that often includes a neutral conductor not shown in the drawings), alternative embodiments optionally include only one pair of terminals for a single conductor or additional pairs of terminals with additional conductors to enable monitoring of power lines that include more than two conducting lines, such as three-phase power lines.

The meter base <NUM> includes inductive coils 132A and 132B that are inductively coupled to the electrical conductors 126A and 126B, respectively. As described in further detail below, the inductive coils 132A and 132B are electrically connected to electrical current sensors 154A and 154B in the metrology circuit <NUM>. The alternating current (AC) power signals in the electrical conductors 126A and 126B induce a current in the inductive coils 132A and 132B, respectively, that the metrology circuit <NUM> uses to monitor electrical current levels in the power line. The inductive coils 132A and 132B are also referred to as "coil transformers" since in some embodiments the inductive coils 132A and 132B form one set of coils in a current transformer in which a second set of coils produce a current measurement signal. While <FIG> depicts the coils 132A/132B and current sensors 154A/154B for illustrative purposes, other embodiments may employ different current sensing devices that are otherwise known to the art.

Referring to the metrology circuit <NUM> include current sensors 154A/154B, and voltage sensors <NUM>. The metrology circuit <NUM> further includes an analog-to-digital converter <NUM>, a digital control device <NUM>, network communication device <NUM>, and in-meter control interface <NUM>. The metrology circuit <NUM> receives electrical power for operation from the power line via the terminal pairs 124A/128A and 124B/128B that are connected to a power supply <NUM> (connections omitted for clarity). The power supply <NUM> is, for example, a switched capacitor power supply or other suitable conversion circuit that produces direct current (DC) electrical output power from the AC power received at the terminals to provide electrical the components in the electric meter <NUM>. The power supply <NUM> provides electrical power to the components in the metrology circuit <NUM> and the meter base <NUM> that require electrical power during operation of the electric meter <NUM>. The power supply <NUM> further includes a battery <NUM> that provides electrical power to operate the control device <NUM> during a power interruption to the normal AC voltage and current flow through the power lines that are connected to the electric meter <NUM>. In other embodiments a capacitor or other energy storage device in the electric meter <NUM> supplies electrical power to the control device <NUM> and optionally other components in the electric meter <NUM> during a power interruption.

In the metrology circuit <NUM>, the current sensors 154A/154B are each connected to one of the inductive coils 132A and 132B, respectively, to enable the current sensors to monitor the levels of electrical current in the electrical conductors 126A and 126B, respectively. In one embodiment, the current sensors 154A and 154B each includes a second set of coils that are coupled to the corresponding inductive coils 132A or 132B in a coil transformer arrangement. The coils in the current sensors 154A and 154B generate electrical currents that correspond to the current levels in the electrical conductors 126A and 126B, although at greatly reduced amplitudes to enable measurement of the current in an efficient manner and with the current sensors having galvanic isolation from the much higher current levels of the electrical conductors 126A and 126B. The current sensors 154A and 154B generate analog current measurement signals that are supplied to the ADC <NUM> to be provided as digital current level signals to the control device <NUM>, although in an analog electrical meter an analog control circuit may receive the analog current measurement signals directly.

In the metrology circuit <NUM>, the voltage sensor <NUM> is connected to both of the electrical conductors 126A and 126B. The voltage sensor <NUM> is configured to generate an analog voltage measurement signal having a waveform representative of the voltage provided to the load through the power line. The outputs of the voltage sensor <NUM> is connected to the ADC <NUM> to enable the control device <NUM> to receive digitized representations of the measured voltage levels from the voltage sensors <NUM>. In one embodiment, the voltage sensor <NUM> includes a voltage divider circuit to bring the measured voltage waveform to a magnitude that is suitable for the ADC <NUM>. The voltage sensor <NUM> may alternatively take other known forms.

In the electric meter <NUM>, the control device <NUM> is a digital logic device that includes, for example, one or more microprocessors, microcontrollers, field programmable gate arrays (FPGAs), digital signal processors (DSPs), programmable logic controllers (PLCs), application specific integrated circuits (ASICs), and the like. In the embodiment of <FIG>, the control device <NUM> also includes or is operatively connected to a real time clock (RTC) <NUM> and a memory <NUM>. The RTC <NUM> tracks the time at which the meter <NUM> records samples of input sensor data from the current sensors 154A/154B and voltage sensor <NUM>. As described below, the control device <NUM> also uses the RTC <NUM> to measure the duration of "time on battery" events that correspond to the duration of power interruptions in some embodiments. The memory <NUM> includes one or more memory devices that store programmed software or firmware instructions that the control device <NUM> executes to operate the electric meter <NUM> in conjunction with the other components of the electric meter. The memory <NUM> also stores "load profile" records that the electric meter generates during a predetermined monitoring period, which is typically on the order of one minute to one hour in duration although other embodiments may use longer or shorter monitoring periods. The load profile typically includes multiple data fields in the load profile that are referred to as "channels" that include, for example, measurements of the accumulated energy consumption of loads that are attached to the power line, an accumulation of frequency measurements in the voltage of the AC power signal, an accumulation of zero crossing events in the voltage of the AC power signal, and other information that the electric meter <NUM> records and reports to a centralized monitoring system. In some embodiments, if the electric meter <NUM> experiences a power interruption during a monitoring period then the electric meter <NUM> sets a value in the load profile indicating that monitoring only occurred for a partial monitoring period instead of for the full predetermined monitoring period. The memory <NUM> is implemented using at least one non-volatile memory device such as a NAND or NOR memory device or other suitable solid-state memory, and in some embodiment the memory <NUM> includes a volatile memory device such as random access memory (RAM). In addition to the specific functions described herein, the control circuit <NUM> also performs metrology routines, display routines, communication routines, that are commonly associated with the operation of electric meters. As depicted in <FIG>, the control device <NUM> receives input data from the current sensors 154A and 154B and the voltage sensor <NUM>, either directly or indirectly via the ADC <NUM>.

In the metrology circuit <NUM>, the control device <NUM> is operatively connected to network communication device <NUM> and the in-meter interface <NUM> in addition to being connected to receive input data from the current sensors 154A/154B and the voltage sensors <NUM>. The network communication device <NUM> and the in-meter interface are both examples of output devices. The network communication device <NUM> is, for example, an analog modem or digital subscriber line (DSL) device that couples to a telephone network, an Ethernet transceiver that transmits data over a wired network, a local serial bus output such as RS-<NUM> or Universal Serial Bus (USB), or either or both of a wireless local area network (WLAN) or wide area network (WWAN) transceiver that transmits metrology data to the external monitoring system <NUM>. In the metrology circuit <NUM>, the in-meter interface <NUM> provides a visual and in some instances audible output device that enables manual meter reading and manual inspection of the electric meter to retrieve power consumption and power interruption data. Examples of in-meter interfaces include mechanical gauges, indicator lights, LCD or LED display screens, alarm bells or speakers and the like. The in-meter interface optionally includes control inputs that enable an operator to send commands to the control device <NUM> while physically present at the electric meter. While the metrology circuit <NUM> includes both the network communication device <NUM> and the in-meter interface <NUM>, some embodiments of electric meters that measure the durations of power interruptions only include a network communication device <NUM> or an in-meter interface <NUM>, but not both elements. For example, some electric meters have no need to communicate with a remote system via a data network and only include the in-meter interface <NUM>, while other electric meters rely exclusively on the network communication device <NUM> to transmit the meter data and do not include the in-meter interface <NUM>.

In <FIG>, the external monitoring system <NUM> includes a processor <NUM> that is operatively connected to a memory <NUM> and a network communication device <NUM>. In the external monitoring system <NUM>, the processor <NUM> is a central processing unit (CPU) or other suitable digital logic device that is configured to process load profile information that the external monitoring system <NUM> receives using the network communication device <NUM> to communicate with the corresponding network communication device <NUM> in the electric meter <NUM> via the network <NUM>. The memory <NUM> stores programmed instructions for the processor <NUM>, load profile data that are received from the electric meter <NUM>, and stores records of the accumulate duration of power interruptions that may occur in the electric meter <NUM> over a series of predetermined monitoring periods. While not depicted in further detail in <FIG>, in some configurations the external monitoring system <NUM> receives and processes load profile data from a plurality of electric meters with the same or similar configuration as the electric meter <NUM>.

In various configurations the external monitoring system <NUM> includes, for example, a head end unit that monitors the electric meter <NUM> and in some embodiments other electric meters that are not expressly shown in <FIG>. Electric utilities, site owners, or other entities operate the external monitoring system <NUM> to monitor power interruptions in the electric meter <NUM> to calculate SAIDI and monitor power interruptions. In particular, the external monitoring system <NUM> periodically receives a load profile from the electric meter <NUM> that includes channels for either or both of the accumulated frequency measurement and accumulated zero crossing measurement. The external monitoring system <NUM> determines the duration of one or more power interruptions that may occur during a predetermined monitoring period based on the accumulated frequency measurement and accumulated zero crossing channels. Additionally, in some configurations the external monitoring system <NUM> transmits command messages to the control device <NUM> in the electric meter <NUM> via the network communication device <NUM>.

During operation, the electric meter <NUM> transmits load profile data including the channels that identify either or both of the accumulated frequency counts and accumulated zero crossing counts to the external monitoring system <NUM> via the network <NUM>. As described in more detail below, the external monitoring system <NUM> identifies the duration of power interruptions that the electric meter <NUM> experiences during one or more predetermined monitoring periods to enable fine-grained tracking of the duration of power interruptions to measure SAIDI and to perform other monitoring operations in an electric power distribution system. The control device <NUM> in the electric meter optionally measures the durations of power interruptions and stores records of the total duration of any power interruptions that occur during a predetermined monitoring period (e.g. a <NUM> minute period). The control device <NUM> also generates transmits reports of the total duration of power interruptions that occur over one or more monitoring periods, such as a total duration of power interruptions over the course of an hour, day, week, month, or year, to a monitoring service using the network communication device <NUM>. The operation of the electric meter <NUM> to track the duration of power interruptions is described in further detail below.

<FIG> depicts a process <NUM> for operation of an electric meter to measure, record, and report the durations of power interruptions. In the description below, a reference to the process <NUM> performing a function or action refers to the operation of a digital processing device, such as a control device in a meter, a processor in an external monitoring system, or a combination thereof, to execute stored program instructions to perform the function or action in association with other components in an electric meter. The process <NUM> is described in more detail below in conjunction with the electric meter <NUM> of <FIG> and the graph of <FIG>.

During the process <NUM>, the control device <NUM> monitors the voltage of the AC power signal that is supplied from a power line using the voltage sensors <NUM> to record measurements of the accumulated value of frequency measurements, the accumulated value of a total number of zero crossing events, or both, during the predetermined monitoring period (block <NUM>). In the electric meter <NUM>, the voltage of the AC power signal is supplied from a power line and passes between the terminal pairs 124A/128A and 124B/128B in the electric meter <NUM> during the predetermined monitoring period. In one embodiment, the ADC <NUM> generates digital samples of the voltage values from the voltage sensors <NUM> at a sampling frequency that exceeds the expected frequency (e.g. <NUM> or <NUM>) of the AC sinusoidal signal to enable the control device <NUM> to identify features such as positive and negative peaks and zero crossing events in the voltage waveform of each cycle of the AC sinusoidal signal. In one specific example, the ADC <NUM> generates digital voltage samples at rate in a range of, for example, <NUM> to <NUM> to collect multiple samples in each cycle of the sinusoidal AC power signal. As described above, the predetermined monitoring period is any suitable length of time, such as a <NUM> minute period used in the illustrative embodiment of <FIG>, which enables the electric meter <NUM> to produce an average value of the measured AC signal frequency or total number of zero crossings in the AC power signal.

In one configuration, the control device <NUM> identifies the time difference T between successive positive peaks or negative peaks in the voltage waveform of the AC power signal to measure the frequency of the AC power signal. Each peak occurs when a series of samples of data from the ADC for the voltage of the AC power signal reach a maximum absolute value (positive or negative) and begin to return to zero, and the control device <NUM> optionally interpolates between data samples to identify the time of each peak with greater accuracy. The control device <NUM> identifies the frequency of each cycle as T-<NUM> and the measured frequency of the signal is an averaged value for multiple cycles that are measured over the predetermined monitoring period. The electric meter <NUM> generates records of the accumulated frequency measurements of the AC power signal as part of a load profile during a predetermined monitoring period and reports the frequency measurement information to an external monitoring system at regular intervals as one channel in the load profile that also includes additional data collected by the electric meter <NUM>.

<FIG> depicts a graph <NUM> of the electrical voltage levels of an example AC power signal over time with time periods <NUM>, <NUM>, and <NUM> that correspond to the expected frequency of the sinusoidal AC power signal at a predetermined frequency, such as <NUM> or <NUM>. In another configuration, the meter <NUM> measures the same periods based on the time between troughs (negative peaks) in each cycle of the AC power signal. The frequency of an AC power signal in a large power grid is generally stable and experiences far smaller variations during normal operation than the voltage levels of the AC signal. During operation, the control device <NUM> measures the frequency of the AC power signal at a predetermined rate (e.g. four measurements per second in one embodiment) and stores an accumulation of all the frequency measurements in the frequency channel of the load profile that is stored in the memory <NUM> during each predetermined monitoring period. <FIG> also depicts a power interruption <NUM> in the AC power signal in which there are no additional peaks. The control device <NUM> does not record any frequency measurements during the power interruption <NUM> and in most embodiments is not activated during the power interruption <NUM>. The electric meter <NUM> restarts after the power interruption and the controller <NUM> continues to record additional frequency measurements, although the total accumulated value of all the frequency measurements during the predetermined monitoring period is lower than expected due to the power interruption. While <FIG> depicts a single interruption <NUM>, in some situations the electric meter <NUM> experiences multiple power interruptions during a single monitoring period, and the embodiments described herein can identify the accumulated duration of one or more power interruptions.

In another configuration, the control device <NUM> records a count of the accumulated number of zero crossing events that occur in the AC power signal. As depicted in <FIG>, the zero crossing events occur when the voltage in the AC power signal transitions from a positive to negative or negative to positive voltage, and the control device <NUM> optionally interpolates between data samples to identify the time of each zero crossing with greater accuracy. In this configuration, the electric meter <NUM> generates records of the measured zero crossing events of the AC power signal as part of a load profile during a predetermined monitoring period and reports the accumulated zero crossing event measurement information to the external monitoring system at regular intervals as one channel the load profile that also includes additional data collected by the electric meter <NUM>.

<FIG> depicts the zero crossings 404A/404B, 408A/408B, 412A/412B, and 416A/416B that occur during different cycles of the AC power signal, where each cycle of the AC power signal includes two zero crossings. The control device <NUM> identifies each zero crossing event based on a transition of the measured voltage values from a positive value to a negative value or from a negative value to a positive value in the digital sensor data samples that the control device <NUM> receives from the ADC <NUM>. The control device <NUM> records an accumulated value of the total number of measured zero crossing events that occur during each predetermined monitoring period. As depicted in <FIG>, during the power interruption period <NUM> the AC signal does not produce any zero crossings and the control device <NUM>, which is typically deactivated during the power interruption <NUM>, does not record zero crossing events during the power interruption. During the predetermined monitoring period, the control device <NUM> records a reduced number of zero crossings compared to a predetermined expected value based on the predetermined frequency of the AC power signal when power interruptions occur.

Referring again to <FIG>, the process <NUM> continues as the electric meter <NUM> transmits the recorded load profile that includes either or both of the accumulated frequency and zero crossing count channels to an external monitoring system that identifies the duration of power interruptions, if any, during one or more of the predetermined monitoring periods (block <NUM>). The electric meter <NUM> continues monitoring during a subsequent monitoring period as described above with reference to the processing of block <NUM>. In some embodiments of the process <NUM>, the external monitoring system <NUM> identifies the duration of any power interruptions that the meter <NUM> experiences based on one or both of the accumulated frequency channel and the accumulated zero crossing count channel in the load profile (block <NUM>).

In one configuration, the external monitoring system <NUM> identifies the duration of a power interruption that occurs during at least one of the predetermined monitoring periods based on the accumulated frequency channel in the load profile data that are received from the electric meter <NUM>. For example, if the nominal frequency of an AC power signal is <NUM> and the electric meter <NUM> is configured to record a measurement of the frequency four times per second over a predetermined monitoring period of <NUM> minutes (<NUM> second), then the accumulated frequency channel in the load profile data has an expected predetermined accumulated frequency value of <NUM>,<NUM> ((<NUM>)(<NUM>)(<NUM> sec) = <NUM>,<NUM>). If the recorded accumulated frequency measurement deviates from the predetermined accumulated frequency value, then the processor <NUM> in the external system <NUM> calculates the duration of the power interruption based on the magnitude of the deviation. For example, if the frequency channel in the load profile that is generated in the electric meter <NUM> produces a value of <NUM>,<NUM>, then the external system identifies that the electric meter <NUM> recorded one or more power interruptions with a total duration ID of <NUM> seconds <MAT>. Once again, the total duration of power interruptions ID is based on a ratio of the accumulated frequency measurement divided by the predetermined accumulated frequency value, as well as the length of the predetermined monitoring period. In some configurations, the processor <NUM> in the external monitoring system <NUM> only calculates the duration of a power interruption if the electric meter <NUM> sets the partial monitoring period flag in the load profile, which indicates that the electric meter <NUM> detected at least one power loss event during a predetermined monitoring period. In this configuration, the external monitoring system ignores small deviations in the accumulated frequency count that might occur during normal operation of the electric meter <NUM>.

In another configuration, the external monitoring system <NUM> identifies the duration of a power interruption that occurs during at least one of the predetermined monitoring periods based on the accumulated zero crossing count in the load profile data that are received from the electric meter <NUM>. As described above, the zero crossing channel includes a data parameter for the accumulated number of zero crossing events that the meter <NUM> detects during the predetermined monitoring period. The processor <NUM> in the external monitoring system <NUM> identifies the total duration of one or more power interruptions that occur during a monitoring period based on a deviation between the total number of recorded zero crossing events in the load profile from a predetermined nominal number of expected zero crossing events that are expected to occur during the predetermined monitoring period. For example, given a <NUM> frequency AC power signal and a monitoring period with a duration of <NUM> seconds, the nominal value of the predetermined number of zero crossing events Znom that is expected occur during the predetermined monitoring period is Znom = <NUM>(<NUM>Hz)(<NUM>sec) = <NUM>,<NUM> zc where zc represents "zero crossings". If the processor <NUM> measures Zcounted = <NUM>,<NUM> during a predetermined monitoring period for the zero crossing channel, then the processor <NUM> in the external monitoring system <NUM> identifies that the measured accumulated value of zero crossings corresponds one or more power interruptions with a total duration ID of: <MAT>. Once again, the total duration of power interruptions ID is based on the ratio of the counted zero crossing events divided by the predetermined number of zero crossing events, as well as the length of the predetermined monitoring period. The duration of the power interruption increases as the number of measured zero crossing events in the zero crossing channel of the load profile experiences larger deviations from the predetermined nominal number of zero crossing events that are expected to occur during the predetermined monitoring period. In some configurations, the processor <NUM> in the external monitoring system <NUM> only calculates the duration of a power interruption if the electric meter <NUM> sets the partial monitoring period flag in the load profile, which indicates that the electric meter <NUM> detected at least one power loss event during a predetermined monitoring period. In this configuration, the external monitoring system ignores small deviations in the accumulated zero crossing count that might occur during normal operation of the electric meter <NUM>.

In an alternative configuration, the control device <NUM> in the electric meter <NUM> identifies the total duration of power interruptions during each predetermined monitoring period based on either or both of the accumulated frequency count channel and the zero crossing channel in the load profile (block <NUM>). In this embodiment, the control device <NUM> identifies the total duration of the power interruptions in the same manner that is described above for the external monitoring system <NUM>, and the control device <NUM> stores the total duration of power interruptions in the memory <NUM>. In some embodiments, the control device <NUM> generates the load profile data including a separate channel that indicates the total duration of power interruptions that occur during each predetermined monitoring period and transmits the power interruption data to the external monitoring system <NUM> as part of the load profile. Additionally, the control device <NUM> can store a sum of a total value for all power interruptions that occur over a series of monitoring periods, such as a sum of the total duration of power interruptions that occur during a predetermined monitoring period added to a sum stored in the memory <NUM> for one or more earlier monitoring periods. The external monitoring system <NUM> can request the total duration of power interruptions from the electric meter <NUM> as part of the process for calculating SAIDI or other power interruption monitoring calculations that cover longer periods of time such as hours, days, months, weeks, years, etc., and the control device <NUM> optionally resets the sum of the total duration of power interruptions after reporting the data to the external monitoring system <NUM>. In some configurations, both the external monitoring system <NUM> and the electric meter <NUM> identify the total duration of power interruptions as described above.

<FIG> depicts a process <NUM> for operation of an electric meter to measure, record, and report the durations of power interruptions. In the description below, a reference to the process <NUM> performing a function or action refers to the operation of a control device to execute stored program instructions to perform the function or action in association with other components in an electric meter. The process <NUM> is described in more detail below in conjunction with the electric meter <NUM> of <FIG>.

During the process <NUM>, the processor <NUM> in the external monitoring system <NUM> or the control device <NUM> in the electric meter <NUM> measures the duration of a power interruption based on a duration of a "time on battery" event (block <NUM>). The term "time on battery" refers to a time period of operation in the electric meter <NUM> in which the power supply <NUM> uses the battery <NUM> to provide electrical power to components in the electric meter <NUM>. The time on battery occurs when the power supply <NUM> receives no electrical power or an insufficient level of electrical power for normal operation from the external power line during a power interruption. While <FIG> depicts the battery <NUM> as being integrated with the power supply <NUM> for illustrative purposes, in some embodiments the battery <NUM> is incorporated into the metrology circuit <NUM>, including in embodiments where the battery <NUM> only supplies electrical power to the RTC <NUM> during power interruptions.

In one configuration, the battery <NUM> in the power supply <NUM> provides electrical power to maintain operation of at least the control device <NUM> in the electric meter <NUM> and the power supply <NUM> sends a first signal to the control device <NUM> to indicate that the electric meter <NUM> is operating on battery power at the start of the power interruption. After external electrical power is restored, the power supply <NUM> sends a second signal to the control device <NUM> to indicate that the electric meter <NUM> is again receiving external electricity from the power line and is not operating from electrical power supplied by the battery <NUM> at the end of the power interruption. The control device <NUM> identifies the "time on battery" and the duration of the power interruption based on the difference in time between receiving the first on-battery signal from the power supply <NUM> and the second off-battery signal from the power supply <NUM>.

In another configuration, the battery <NUM> in the power supply <NUM> does not provide power for full operation of the control device <NUM>, which shuts down during a power interruption. Instead, the battery <NUM> supplies enough power to maintain operation of the RTC <NUM> while the other components in the electric meter <NUM> are not operational. In many practical embodiments the battery <NUM> can supply power to operate the RTC <NUM> for prolonged power interruptions that may last for hours, days, or weeks. After the end of the power interruption, the control device <NUM> returns to operation and identifies the time on battery as the time difference between a timestamp associated with a shutdown event that is stored in an event log in a non-volatile portion of the memory <NUM> at the beginning of the power interruption and the present time of the RTC <NUM> that the control device <NUM> reads at the end of the power interruption. The control device <NUM> identifies the duration of the power interruption based on the time on battery even though the control device <NUM> was not fully operational during the power interruption.

The process <NUM> continues as the control device <NUM> records the duration of the power interruption to the memory <NUM> after the electric meter <NUM> returns to normal operation (block <NUM>). In one configuration the control device <NUM> stores the duration of each power interruption in the memory <NUM> in association with a timestamp identifying the start or end of the power interruption. In another configuration, the control device <NUM> stores a single record of a total duration of one or more power interruptions in the memory <NUM> and adds the duration of the most recent power interruption to a value stored in the memory <NUM> that corresponds to a total sum of durations for previously recorded power interruptions.

The process <NUM> continues as described above with reference to the processing of blocks <NUM> - <NUM> until the electric meter <NUM> transmits the load profile data including a channel that indicates the total duration of one or more recorded power interruptions to the external monitoring system <NUM> based on the measured time on battery (block <NUM>). In one configuration, the control device <NUM> uses the network communication device <NUM> to transmit the power interruption duration data stored in the memory <NUM> to the external monitoring system <NUM> via a data network. In another configuration, the control device <NUM> operates the in-meter interface <NUM> to report the power interruption duration data via a display screen or a peripheral connection to a computerized meter reader device. In some embodiments, the electric meter <NUM> transmits the power interruption duration data as part of the load profile at regular intervals (e.g. after each monitoring period, hourly, daily, weekly, monthly, annually), while in other embodiments the electric meter <NUM> transmits the power interruption duration data in response to a request from the external monitoring system <NUM> or meter reader. After reporting the total duration of the power interruptions, the electric meter <NUM> can reset internal power interruption counters in the memory <NUM>, if any, and continue the operations of the process <NUM> as described above to record the durations of additional power interruptions during operation of the electric meter <NUM>.

The embodiments described herein improve the accuracy of monitoring the duration of power interruption events in large power systems because individual electric meters, such as the meter <NUM>, can monitor the duration of even short power interruptions with a high level of accuracy and report the total duration of the power interruptions to a centralized monitoring system. The centralized monitoring system uses the power interruption data from multiple electric meters to monitor the reliability of a power grid and to identify SAIDI for a power grid with greater accuracy than in prior art systems.

Claim 1:
A method of identifying power interruptions comprising:
receiving, with a monitoring system (<NUM>) that is external to an electric meter (<NUM>), a load profile from the electric meter that includes at least one of an accumulated frequency measurement and an accumulated number of zero crossing events that the electric meter records in an AC power signal during one or more predetermined monitoring periods,
wherein the load profile further includes, for one or more of the one or more predetermined monitoring periods, a monitoring period flag set by the electric meter that indicates that the electric meter detected at least one power loss event during the respective predetermined monitoring period; and
identifying, with a processor (<NUM>) in the external monitoring system and for each monitoring period flag detected in the load profile, a total duration of at least one power interruption during a particular predetermined monitoring period associated with the monitoring period flag based on at least one of a deviation of the accumulated frequency measurement in the load profile from a predetermined accumulated frequency value or a deviation of the accumulated number of zero crossing events in the load profile from a predetermined number of zero crossing events during the predetermined monitoring period.