WO1999030300A1 - System and method for detecting voltage and current imbalance in an electrical energy supply - Google Patents
System and method for detecting voltage and current imbalance in an electrical energy supply Download PDFInfo
- Publication number
- WO1999030300A1 WO1999030300A1 PCT/US1998/024780 US9824780W WO9930300A1 WO 1999030300 A1 WO1999030300 A1 WO 1999030300A1 US 9824780 W US9824780 W US 9824780W WO 9930300 A1 WO9930300 A1 WO 9930300A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- phase value
- phase
- imbalance
- determining
- normalized
- Prior art date
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/26—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents
- H02H3/32—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors
- H02H3/34—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors of a three-phase system
- H02H3/353—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors of a three-phase system involving comparison of phase voltages
Definitions
- the present invention relates in general to the field of electronic energy meters. More particularly, the present invention relates to electronic energy meters with systems for detecting voltage and current imbalances in the electrical energy supply that is provided to the energy meter.
- Imbalance can exist, for example, when two phases are at the top of their current or voltage range, and one is at the bottom of its range.
- phases A and B may be at 110% of their nominal values
- phase C may be at 90% of its nominal value.
- Each phase may be within individual phase limits, but the voltages / currents supplied by each phase are not equal (e.g. , there may be a problem with phase C).
- Imbalance is not desirable, and in many applications, it is desirable to maintain closely balanced phase voltages and phase currents. Thus, in prior art systems, there is no indication of a phase voltage or phase current problem as long as each phase is within its predetermined limits, although imbalance may exist.
- imbalance will affect equipment and processes and can result in misoperation and damage of equipment, disruption of operations, and other such anomalies.
- imbalance is prohibited within some systems (e.g., imbalance determination is mandatory in some countries, such as India).
- a consumer such as a business, may now be able to choose its utility provider, and therefore the customer may now have a need or desire to determine the quality of the power supplied by its present supplier.
- the utilities have a need to monitor the power they supply to customers to ensure that they are providing power that is sufficiently balanced to retain their customers. Therefore, utilities and consumers are now in need of a metering system to detect voltage and current imbalance.
- the present invention is directed to a method for detecting a current imbalance and/or a voltage imbalance in multiphase electrical energy provided to an energy meter via a service type.
- the method comprises the steps of measuring a phase value for each phase of the electrical energy; determining a normalized phase value for each phase; determining a high normalized phase value responsive to the measured phase values; determining a normalized phase value ratio responsive to the normalized phase values; comparing the high normalized phase value to a first threshold; comparing the normalized phase value ratio to a second threshold; and determining that an imbalance exists when the high normalized phase value is greater than the first threshold and the normalized phase value ratio is less than the second threshold.
- an imbalance indicator is activated responsive to the imbalance.
- the step of determining a normalized phase value for each phase comprises the steps of determining a nominal phase value for each phase, and dividing the measured phase value by the nominal value.
- the step of determining the nominal phase value comprises the step of retrieving the nominal phase value for the service type from a memory.
- the invention further comprises the step of determining a low normalized phase value responsive to the measured phase values, and the step of determining the normalized phase value ratio comprises the step of dividing the low normalized phase value by the high normalized phase value.
- Another embodiment within the scope of this invention includes a system for detecting a current imbalance and/or a voltage imbalance in multiphase electrical energy provided to an energy meter via a service type.
- the system comprises means for measuring a phase value for each phase of the electrical energy; means for determining a normalized phase value for each phase; means for determining a high normalized phase value responsive to the measured phase values; means for determining a normalized phase value ratio responsive to the normalized phase values; means for comparing the high normalized phase value to a first threshold; means for comparing the normalized phase value ratio to a second threshold; and means for determining that an imbalance exists when the high normalized phase value is greater than the first threshold and the normalized phase value ratio is less than the second threshold.
- means are provided for activating an imbalance indicator responsive to the imbalance.
- the imbalance indicator preferably comprises at least one of an LCD display, an event log, and a relay output that can be attached to an option connector.
- a memory for storing the nominal phase values for the service type, the first threshold, and the second threshold.
- the means for determining the nominal phase value comprises means for retrieving the nominal phase value for the service type from the memory.
- the memory comprises a non-volatile memory
- the means for determining a normalized phase value for each phase comprises an integrated circuit
- the means for determining that the imbalance exists comprises a microcontroller.
- the integrated circuit preferably comprises at least one analog/digital (A/D) converter and a programmable digital signal processor (DSP).
- Fig. 1 is a block diagram showing the functional components of an exemplary meter and their interfaces in accordance with the present invention.
- Fig. 2 is a flow chart of an exemplary process in accordance with the present invention.
- a meter for metering three-phase electrical energy preferably includes a digital LCD type display 30, a meter integrated circuit (IC) 14 which preferably comprises A/D converters and a programmable DSP, and a microcontroller 16.
- IC meter integrated circuit
- Analog voltage and current signals propagating over power transmission lines between the power generator of the electrical service provider and the users of the electrical energy are sensed by voltage dividers 12A, 12B, 12C and current transformers or shunts 18A, 18B, 18C, respectively.
- the outputs of the resistive dividers 12A-12C and current transformers 18A-18C, or sensed voltage and current signals, are provided as inputs to the meter IC 14.
- the A/D converters in the meter IC 14 convert the sensed voltage and current signals into digital representations of the analog voltage and current signals. In a preferred embodiment, the A/D conversion is carried out as described in U.S. Patent No.
- the meter IC 14 and the microcontroller 16 each preferably interface with one or more memory devices through an IIC bus 36.
- a memory preferably a non- volatile memory such as an EEPROM 35, is provided to store nominal phase voltage and current data and threshold data as well as programs and program data.
- EEPROM 35 Upon power up after installation, a power failure, or a data altering communication, for example, selected data stored in the EEPROM 35 may be downloaded to the program RAM and data RAM associated within the meter IC 14, as shown in Fig. 1.
- the DSP under the control of the microcontroller 16 processes the digital voltage and current signals in accordance with the downloaded programs and data stored in the respective program RAM and data RAM. To perform imbalance measurements, the microcontroller 16 may use both voltage and current measurement information from the DSP.
- the meter IC 14 monitors the digital phase voltage signals and phase current signals over, for example, two line cycles and then computes the near-instantaneous RMS phase values for instrumentation purposes. It should be understood that the number of line cycles is preferably programmable and a different number of line cycles may be used for designated measurements .
- the phase values computed for each phase, A, B, and/or C, are then stored in registers in the data RAM. The microcontroller 16 polls for data in these registers via the IIC bus 36 for instrumentation processing.
- the DSP in the meter IC 14 also drives potential indicators 27, 29, and 31 which are preferably designated sections on the display 30. These indicators may be used alone or in combination to indicate a voltage or current imbalance. Thresholds that are used in the imbalance determination are preferably downloaded from the EEPROM 35 to the data RAM in the IC 14. A comparator performs the desired comparisons and generates an output that is high whenever the measurement exceeds the programmable threshold. Phase A, B, and C potential signals are output from the meter IC 14 to the microcontroller 16, which in turn drives the potential indicators 27, 29, and 31 so that the potential indicator(s) remains lit when the corresponding potential signals are high.
- a service test can be performed to identify and/or check the electrical service.
- the meter may be preprogrammed for use with a designated service or it may determine the service using a service test.
- an initial determination is made of the number of active elements. To this end, each element (i.e. , 1, 2, or 3 elements) is checked for voltage. Once the number of elements is identified, many of the service types can be eliminated from the list of possible service types.
- the voltage phase angle relative to phase A may then be calculated and compared to each phase angle for abc or cba rotations with respect to the remaining possible services, e.g. , within ⁇ 15°.
- the service voltage is preferably determined by comparing the RMS voltage measurements for each phase with nominal phase voltages for the identified service. If the nominal service voltages for the identified service matches measured values within an acceptable tolerance range, a valid service is identified and the phase rotation, service voltage, and service type are preferably displayed.
- the service may be locked, i.e. , the service information is stored in a memory, preferably a non- volatile memory, such as the EEPROM 35, manually or automatically.
- the service test preferably checks to ensure that each element is receiving phase potential and that the phase angles are within a predetermined percentage of the nominal phase angles for the known service.
- the per-phase voltages are also measured and compared to the nominal service voltages to determine whether they are within a predefined tolerance range of the nominal phase voltages. If the voltages and phase angles are within the specified ranges, the phase rotation, the service voltage, and service type are displayed on the meter display. If either a valid service is not found or the service test for a designated service fails, a system error code indicating an invalid service is displayed and locked on the display to ensure that the failure is noted and evaluated to correct the error.
- the meter of Fig. 1 also provides for remote meter reading, remote power quality monitoring, and reprogramming through an optical port 40 and/or an option connector 38.
- optical communications may be used in connection with the optical port 40
- the option connector 38 may be adapted for RF communications or electronic communications via modem, for example.
- the imbalance indicator comprises a relay output that can be attached to an option connector, such as the option connector 38.
- the warnings and alerts may be time and date stamped and logged in an event log and the number of events and cumulative time of the conditions may be separately logged in an occurrence log unique to each type of imbalance test; i.e., occurrence logs are optionally assigned to the imbalance tests.
- the logs are preferably stored in a memory, such as the EEPROM 35 shown in Fig. 1. The information stored in these logs may be accessed through software for further diagnostic processing and evaluation external to the meter itself.
- the systems for performing imbalance tests according to the present invention are preferably implemented in firmware, wherein such operations are enabled by the correct programming of data tables .
- the system of the present invention can be implemented in general purpose computers using software, or exclusively in special purpose hardware, or in a combination of the two.
- Fig. 2 is a flow chart of an exemplary process of detecting imbalance in accordance with the present invention.
- the service type is determined, in accordance with the description above for example, either automatically within the meter, or retrieved from a memory within the meter.
- a phase value such as a phase voltage or phase current, for a particular phase is measured, at step 105.
- the nominal phase value is then determined at step 110.
- the nominal phase value for each phase of each service is preferably stored in a non-volatile memory in the meter, such as the EEPROM 35. It can also be computed from the nominal service value if the ratio of the phase value to the nominal service is known.
- a meter can store the ratios in memory, such as the EEPROM 35, and then use the ratios to generate each phase value.
- a normalized phase value is determined by dividing the measured value by the nominal value. Normalized phase values are used because in some service types, the individual nominal phase values are not equal to each other. For example, a 240 V delta system may have nominal phase voltages of 120 V, 120 V, and 208 V, respectively, for phases A, B, and C. A direct comparison of phase A to phase C would yield a difference so large that smaller deviations between phases A and B would appear insignificant. This problem is solved by dividing each measured phase value by its nominal phase value to produce a normalized phase value for each phase.
- Steps 105 - 115 are repeated for each phase.
- a high normalized phase value and a low normalized phase value are determined for the set of phases that have been measured, at step 120.
- a phase value ratio of the lowest normalized value to the highest normalized value is determined at step 125.
- the highest normalized phase value is compared to a first predetermined threshold. If the highest normalized phase value is not greater than the first threshold, then it is determined at step 135 that no imbalance exists, and the process exits at step 160.
- the ratio determined at step 125 is compared to a second predetermined threshold, at step 140. If the ratio is not less than the second threshold, then it is determined at step 145 that no imbalance exists, and the process exits at step 160. If the ratio is less than the second threshold, then it is determined at step 150 that an imbalance exists, and an indicator, such as a message, is activated and displayed. The process then exits at step 160.
- the threshold numbers for comparison are dimensionless values that are applicable to all service types (e.g., threshold numbers range between 0 and 1 because the measurements are normalized for each service type), and are preferably stored in a memory within the meter, for example, the EEPROM 35.
- an imbalance exists when the absolute value of the ratio of the lowest phase service phase value to the highest service phase value is less than a predetermined ratio threshold. Moreover, the highest service phase value is used as an imbalance qualifier. If the highest service phase value is greater than a predetermined threshold, the ratio is determined and checked. If an imbalance exists, an indicator is activated.
- Fig. 2 can be used to detect phase current imbalance and phase voltage imbalance. It should be noted that a phase current imbalance can exist without a phase voltage imbalance, and vice versa. The phase current imbalance and phase voltage imbalance tests check for different conditions and thus can be performed independently.
Abstract
Description
Claims
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/555,553 US6246332B1 (en) | 1998-11-18 | 1998-11-18 | System and method for detecting voltage and current imbalance in an electrical energy supply |
BR9814259-3A BR9814259A (en) | 1997-12-05 | 1998-11-18 | System and method for detecting voltage and current imbalances in an electricity supply |
AU15943/99A AU1594399A (en) | 1997-12-05 | 1998-11-18 | System and method for detecting voltage and current imbalance in an electrical energy supply |
CA002312723A CA2312723C (en) | 1997-12-05 | 1998-11-18 | System and method for detecting voltage and current imbalance in an electrical energy supply |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US6781697P | 1997-12-05 | 1997-12-05 | |
US6774897P | 1997-12-05 | 1997-12-05 | |
US60/067,816 | 1997-12-05 | ||
US60/067,748 | 1997-12-05 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1999030300A1 true WO1999030300A1 (en) | 1999-06-17 |
Family
ID=26748217
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US1998/024780 WO1999030300A1 (en) | 1997-12-05 | 1998-11-18 | System and method for detecting voltage and current imbalance in an electrical energy supply |
Country Status (5)
Country | Link |
---|---|
AU (1) | AU1594399A (en) |
BR (1) | BR9814259A (en) |
CA (1) | CA2312723C (en) |
RU (1) | RU2202114C2 (en) |
WO (1) | WO1999030300A1 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6946972B2 (en) | 2001-01-25 | 2005-09-20 | Smartsynch, Inc. | Systems and methods for wirelessly transmitting data from a utility meter |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
RU2482588C1 (en) * | 2012-04-06 | 2013-05-20 | Открытое акционерное общество "Федеральная сетевая компания Единой энергетической системы" | Device to generate synchronised data on power unit condition |
GB2606337A (en) | 2021-03-26 | 2022-11-09 | Airbus Sas | apparatus and method for detecting current imbalance |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4319298A (en) * | 1979-08-28 | 1982-03-09 | General Electric Company | Motor protection device |
-
1998
- 1998-11-18 RU RU2000114633A patent/RU2202114C2/en not_active IP Right Cessation
- 1998-11-18 WO PCT/US1998/024780 patent/WO1999030300A1/en active Application Filing
- 1998-11-18 CA CA002312723A patent/CA2312723C/en not_active Expired - Fee Related
- 1998-11-18 BR BR9814259-3A patent/BR9814259A/en not_active Application Discontinuation
- 1998-11-18 AU AU15943/99A patent/AU1594399A/en not_active Abandoned
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4319298A (en) * | 1979-08-28 | 1982-03-09 | General Electric Company | Motor protection device |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6946972B2 (en) | 2001-01-25 | 2005-09-20 | Smartsynch, Inc. | Systems and methods for wirelessly transmitting data from a utility meter |
Also Published As
Publication number | Publication date |
---|---|
CA2312723A1 (en) | 1999-06-17 |
BR9814259A (en) | 2000-10-03 |
RU2202114C2 (en) | 2003-04-10 |
CA2312723C (en) | 2002-06-25 |
AU1594399A (en) | 1999-06-28 |
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