Patent Application
20120209548
The present invention relates generally to electrical power systems and more particularly to monitoring electrical transmission and distribution for the occurrence of severe system upsets called grid code events.
Generally, an electric power system is comprised of generation facilities, consumers and one or more transmission and distribution networks that link them together. The transmission networks are typically owned and controlled by a system operator, who establishes generation standards and guidelines to satisfy the needs of the power consumers. This guideline is called a grid code. Very severe deviations from normal operation are called grid code events.
Electrical parameters describing a grid code event are typically in frequency and voltage. For example, loss of large nuclear power plants in Florida and Los Angeles, Calif. have resulted in frequency dips from 60 Hz to less than 57 Hz, and severe voltage dips of 40% or more.
Consider another example in 2003 when the northeastern USA experienced a power outage that resulted in a complete fissure or cleavage in the grid from Cleveland, Ohio to New York City, N.Y. This cleavage of the grid during this power outage resulted in a side with more load than generation. As a result, the side with more load than generation experienced under-frequency and under-voltage. On the other hand, the other side with more generation than load, experienced over-frequency and over-voltage.
In one aspect of the present invention, a grid code meter is provided. The grid code meter comprises a metering component configured to obtain data for a plurality of power-related parameters associated with power consumption needs. A grid code criteria tracking component is configured to track the data related to the plurality of power-related parameters obtained by the metering component for compliance with grid code criteria required by a transmission company to satisfy power consumer needs for power quality and reliability. A grid code event detection component is configured to detect an occurrence of a grid code event in accordance with the tracked data being in compliance with the grid code criteria.
Various embodiments of the present invention are directed to monitoring the transmission side of an electric power system for the occurrence of grid code events by power consumption devices used in industrial, commercial, residential and medical facility applications. In one embodiment, a grid code meter is disclosed that obtains data for a multitude of power-related parameters that are associated with power consumption needs. In one embodiment, the grid code meter tracks the data related to the power-related parameters for compliance with grid code criteria required by a transmission company to satisfy power consumer needs for power quality and reliability. In one embodiment, the grid code meter detects an occurrence of a grid code event if the tracked data for the power-related parameters is not in compliance with the grid code criteria.
Technical effects of the various embodiments of the present invention include improving monitoring and management of the transmission side of an electric power system. Improved monitoring and management of the transmission side of an electric power system result in increased power quality and reliability for power consumers. For example, power consumers would be able to minimize product losses in a factory. Currently, many factory processes are frequency sensitive, but are unable to afford back-to-back DC conversion to be frequency independent of the grid, or large uninterruptible power supplies for voltage stability, and thus suffer product losses. Grid code detection as provided by the various embodiments of the present invention can allow a power consumer to gracefully trip a process that can be damaged until the meter indicates that the system is nominal.
Referring to the drawings,
As shown in
In addition to performing these functions and others described herein, grid code meter 130 may perform other functions associated with protection of motor 110. These functions may include protecting against items that include unbalanced loads, excessively high over-current faults, under-voltage conditions, over-voltage conditions, mechanical jams and load losses.
Grid code meter 130 may be implemented by configuring a commercially available motor protection device such as an electric meter or relay. One example of a commercially available motor protection device that may be used to configure grid code meter 130 is a 469 Motor Management Relay sold by GE Multilin. Those skilled in the art will recognize that there are other commercially available motor protection devices that perform functions and generate information similar to the 469 Motor Management Relay that can be used to configure grid code meter 130 to perform the functions described in the various embodiments of the present invention.
Monitoring system 100 as shown in
Grid code meter 130 further includes a grid code criteria tracking component 205 configured to track the data related to the plurality of power-related parameters obtained by metering component 200. In particular, grid code criteria tracking component 205 determines if the data for each of the power-related parameters is in compliance with grid code criteria required by the transmission company to satisfy the consumption needs of power consumer 105 for power quality and reliability. In one embodiment, grid code criteria tracking component 205 classifies the obtained data into one of a plurality of classifications specific to a respective power-related parameter. For example, for each power-related parameter (e.g., voltage and frequency) there would be various classifications that correspond to a value of ranges for the data that are representative of certain operating conditions of power consumer 105.
In one embodiment, the classifications specific to frequency may comprise a system nominal classification, a severe low frequency classification, a low frequency classification, a severe high frequency classification and a high frequency classification. Data values that can be grouped into one of these classifications can provide an indication of the status of motor 110. As a result, a plant operator, motor engineer, or process engineer can be notified that motor 110 may be at risk if the frequency data generated therefrom has a troublesome value. In one embodiment, the nominal classification may comprise a frequency ranging from about 59.5 Hz to about 60.5 hertz (Hz), the severe low frequency classification may comprise a frequency less than about 57.8 Hz, the low frequency classification may comprise a frequency ranging from about 57.8 Hz to about 59.5 Hz, the severe high frequency classification may comprise a frequency greater than about 62.2 Hz and the high frequency classification may comprise a frequency ranging from about 60.5 Hz to about 62.2 Hz.
In one embodiment, the classifications specific to voltage (V) may comprise a nominal voltage classification, an extreme under-voltage classification, a severe under-voltage classification, a low voltage classification, an extreme over-voltage classification, a severe over-voltage classification and a high voltage classification. Data values that can be grouped into one of these classifications can provide an indication of the status of motor 110. As a result, a plant operator, motor engineer, or process engineer can be notified that motor 110 may be at risk if the data generated therefrom has a troublesome voltage value. In one embodiment, the nominal voltage classification may comprise a voltage ranging from about 95% to about 105% of a nominal system rating, the extreme under-voltage classification may comprise a voltage less than about 80% V, the severe under-voltage classification may comprise a voltage ranging from about 80% V to about 90% V, the low voltage classification may comprise a voltage ranging from about 90% V to about 95% V, the extreme over-voltage classification may comprise a voltage greater than about 120% V, the severe over-voltage classification may comprise a voltage ranging from about 110% V to about 120% V, and the high voltage classification may comprise a voltage ranging from about 105% V to about 110% V.
Those skilled in the art will recognize that any number of classifications can be used for each parameter and that embodiments of the present invention are not limited to any specific classification labels. Furthermore, those skilled in the art will recognize that differing data value ranges can be used for each parameter and that embodiments of the present invention are not limited to any specific data ranges.
As shown in
Grid code event detection component 210 is also configured to make other determinations in addition to grid code event detection. In one embodiment, grid code event detection component 210 determines a ratio of voltage to frequency (V/Hz) in response to detecting the presence of a grid code event. The ratio of voltage to frequency (V/Hz) provides an indication of the severity of over-flux or under-flux of the grid code event. Generally, an over-flux grid code event is characterized by iron core heating of machines on the grid (i.e., motor and generator stators and transformers), while an under-flux grid code event has no deleterious effects.
Grid code meter 130 further includes a grid code event capture component 215 that records the data related to the power-related parameters in response to grid code event detection component 210 determining the occurrence of a grid code event. In one embodiment, grid code event capture component 215 is a digital fault recorder that is configured to automatically capture power-related parameters such as voltage, frequency, and ratio of voltage to frequency (V/Hz) from the instant that a respective low or high level is reached until system 100 determines that power consumer 105 is at a nominal level.
A grid code event plotting component 220 uses the data captured by grid code event capture component 215 to plot a plurality of waveforms describing the grid code event. Waveforms generated by grid code event plotting component 220 may include, for example, off-nominal frequency capability curves, voltage versus time plots that indicate low and high voltage excursions, current, power and var fluctuations. In one embodiment, grid code event plotting component 220 is configured to plot the waveforms describing the grid code event in response to grid code event detection component 210 determining the occurrence of the grid code event. Those skilled in the art will recognize that various time steps can be used to capture appropriately timed-spans of certain grid code events.
Grid code meter 130 further includes an interruption component 225 that is configured to disable production of power to motor 110 in response to grid code event detection component 210 determining the occurrence of the grid code event. In one embodiment, interruption component 225 can be configured to trigger the latching of a relay to hold motor 110 in a closed position during any non-zero level for a frequency and/or voltage value. This anticipates a downing event and assumes that the relay is not on an uninterruptible supply. When power is restored to the relay, it will again access the grid. If conditions are normal, then interruption component 225 will disable the relay. In this embodiment, if the grid is still in distress, then the queuing of the relay by interruption component will continue.
Grid code meter 130 as shown in
Those skilled in the art will recognize that grid code meter 130 can perform more functions than those previously described herein with respect to
In one embodiment, voltage and frequency excursion tracking component 235 tracks the voltage and frequency of motor 110 for excursions from limits specified by National Electrical Manufacturers Association (NEMA). In particular, NEMA allows for +/−10% voltage and +/−5% frequency excursions, where the sum of the two variations may not exceed 10%. Voltage and frequency excursion tracking component 235 simultaneously tracks the voltage and frequency readings obtained from motor 110 for excursions from the above-noted NEMA limits using the following algorithm:
In this embodiment, NEMA=0 is an indication that the power consumed is within NEMA guidelines for safe motor operation, while NEMA=1 is an indication that the motor is exposed to abnormal conditions and may sustain thermal damage, either in the stator, rotor or both. Those skilled in the art will appreciate that the NEMA output variable (i.e., NEMA=0 or NEMA=1) may be of small interest in the grid of the continental USA, but is of greater interest in second and third world countries where grid code issues are common. The NEMA output variable is also of issue for motor applications where generation is islanded. Examples would be gas pipeline compressor stations, offshore drilling platforms, or other locations where applications are vulnerable to a single or few sources of generation.
In various embodiments of the present invention, portions of grid code meter 130 can be implemented in the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment containing both hardware and software elements. In one embodiment, the processing functions performed by grid code meter 130 may be implemented in software, which includes but is not limited to firmware, resident software, microcode, etc.
Furthermore, the processing functions performed by grid code meter 130 can take the form of a computer program product accessible from a computer-usable or computer-readable medium providing program code for use by or in connection with a computer or any instruction execution system (e.g., processing units). For the purposes of this description, a computer-usable or computer readable medium can be any computer readable storage medium that can contain or store the program for use by or in connection with the computer or instruction execution system.
The computer readable medium can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or apparatus or device). Examples of a computer-readable medium include a semiconductor or solid state memory, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk and an optical disk. Current examples of optical disks include a compact disk—read only memory (CD-ROM), a compact disk—read/write (CD-R/W) and a digital video disc (DVD).
As data is obtained, grid code meter 130 tracks the data related to the power-related parameters at 310 to determine if the data for each of the power-related parameters is in compliance with grid code criteria required by the transmission company of power consumer 105. In one embodiment, this step involves classifying the data into one of a variety of classifications specific to a respective power-related parameter.
Grid code meter 130 via grid code event detection component 210 detects an occurrence of a grid code event from the tracked data at 315. As mentioned above, grid code event detection component 210 detects the occurrence of a grid code event as a function of the classification of the data into one of the plurality of classifications for the power-related parameters. If the data is classified into any one of the classifications that are indicative of an abnormal condition, then grid code event detection component 210 will determine that power consumer 105 (e.g., motor 110) is not in compliance with the specified grid code criteria. Grid code event detection component 210 is also configured to determine a ratio of voltage to frequency (V/Hz) in response to detecting the presence of a grid code event.
Flow chart 300 of
Another action that may be taken in response to detecting the occurrence of a grid code event includes using interruption component 225 to disable production of power to motor 110 at 330 in response to grid code event detection component 210 determining the occurrence of the grid code event. Once conditions become normal than interruption component 225 can be used to re-establish connection of power to power consumer including motor 110.
The other action shown in
Flow chart 300 of
The foregoing flow chart of
In the embodiments described heretofore, grid code meter 130 was described with respect to a power consumer that is an industrial consumer. Those skilled in the art will appreciate that embodiments described with respect to grid code meter 130 are also suitable for power consumers that include commercial, medical (e.g., hospital) and residential consumers. Like the grid code meter described for industrial consumers, the grid code meter for residential, commercial and medical consumers provides information that indicates the occurrence of grid code events. Instead of grid code events occurring in industrial motors, the grid code events would occur with power consumption devices used in residences, commercial facilities and medical facilities. These power consumption devices could range anywhere from life sustaining medical equipment to simple motor/compressor sets for air condition units. In this embodiment, residential consumers can use information pertaining to the grid code events to alert them on how well their transmission company is meeting grid code criteria specified in their power agreements for power quality and reliability. For medical facilities that normally own backup diesel generator sets for emergency power, it may provide precious time to start this equipment before transfer is required. Typically backup sets respond simply to a loss of power after it is too late. The ability to measure early frequency problems that typically precede voltage collapse provides precious time for precautionary measures.
As discussed for grid code meter 130, grid code meter 400 performs functions such as tracking grid code criteria for determining if the voltage and frequency (power-related parameters) are in compliance with grid code criteria required by the transmission company to satisfy the consumption needs of the residential consumer for power quality and reliability. In addition, grid code meter 400 determines a ratio of voltage to frequency (V/Hz) in response to detecting the presence of a grid code event. In one embodiment, the determined ratio of voltage to frequency (V/Hz) can be displayed on the faceplate of
With respect to the functionality of tracking grid code criteria, grid code meter 400 would work in a similar manner described above for grid code meter 130, except the criteria would be different. For example, in one embodiment, the classifications specific to frequency may comprise a system nominal classification, a low frequency classification and a high frequency classification. In one embodiment, the nominal classification may comprise a frequency ranging from about 59.5 Hz to about 60.5 Hz, the low frequency classification may comprise a frequency being less than about 59.5 Hz, and the high frequency classification may comprise a frequency being greater than 60.5 Hz. In one embodiment, the classifications specific to voltage may comprise a nominal voltage classification, a low voltage classification, and an over-voltage classification. In one embodiment, the nominal voltage classification may comprise a voltage that is less or equal to 100%+/−5%, the low voltage classification may comprise a voltage being less than or equal to about 95% V, and the over-voltage classification may comprise a voltage greater than about 105% V.
Those skilled in the art will recognize that any number of classifications can be used for each parameter and that embodiments of the present invention are not limited to any specific classification labels. Furthermore, those skilled in the art will recognize that differing data value ranges can be used for each parameter and that embodiments of the present invention are not limited to any specific data ranges.
While the disclosure has been particularly shown and described in conjunction with a preferred embodiment thereof, it will be appreciated that variations and modifications will occur to those skilled in the art. Therefore, it is to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure.
