Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific quantity comparison means
Reexamination Certificate
1999-10-25
2001-10-02
Sherry, Michael J. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific quantity comparison means
C361S015000, C323S211000
Reexamination Certificate
active
06297940
ABSTRACT:
TECHNOLOGY FIELD
The invention relates to a protection system for devices in an electrical distribution network.
BACKGROUND
Devices such as capacitor banks and reactors are often installed into electrical distribution networks to maximize the delivery of power to a load.
SUMMARY
The invention provides a computer-implemented protection system for use in a multi-phase electrical distribution network. To this end, the system includes a sensor operable to measure an impedance of a device connected to a phase of the distribution network, the device used to improve coupling of electrical potential from a source to a load. The system also includes a processor connected to the sensor. The processor is programmed to receive an impedance measurement from the sensor, and to automatically calculate a variation in impedance of the device. The variation is based on a ratio of the impedance measurement and a previous impedance measurement. The processor is further programmed to automatically perform a protection analysis of the device based on the impedance variation.
Implementations may include one or more of the following features. For example, the device may include a capacitor or an inductor, or the sensor may include a relay.
The variation in impedance may be based on a difference between the ratio of the impedance measurements and one.
Performance of the protection analysis may include determining whether the impedance variation exceeds a predetermined threshold. Performance of the protection analysis may also include determining whether an excessive impedance variation has persisted for a predetermined period of time. The predetermined period of time may be based on the design of the distribution network, placement of the device in the distribution network, or a design of the device.
Performance of the protection analysis may include determining whether the impedance variation is caused by ambient temperature fluctuations.
The processor may be programmed to automatically perform a protective action for the device when it determines that the impedance variation exceeds a predetermined threshold for a predetermined period of time, which indicates that the excessive impedance variation is caused by a problem with the device. If the processor determines that the impedance variation is less than or equal to the predetermined threshold before expiration of the predetermined period of time, then the processor may assume that the impedance variation is caused by ambient temperature fluctuations and take no action for the device.
The system may also include a second sensor operable to measure a second impedance of a second device connected to a second phase of the distribution network, the second device being used to improve coupling of electrical potential from the source to the load. The processor may be connected to the second sensor, the processor being programmed to perform the following during a predetermined period of time after the device and the second device are turned on. The processor may receive a second impedance measurement from the second sensor, and may automatically calculate a start up variation in impedance of the device. The start up variation is based on a start tip comparison of the impedance measurement in the device to the second impedance measurement in the second device. The processor may automatically perform a start up protection analysis of the device based on the start up impedance variation. The start up comparison may be based on a difference between a start up ratio of the impedance measurement in the device to the second impedance measurement in the second device, and a ratio of an impedance measurement in the device taken before the device has been turned on to an impedance measurement in the second device taken before the second device has been turned on.
Performance of the start up protection analysis may include determining whether the start up impedance variation exceeds a predetermined threshold. Performance of the start up protection analysis may include determining whether an excessive start up impedance variation has persisted for a start up predetermined period of time. Performance of the start up protection analysis may include determining whether the start up impedance variation is caused by ambient temperature fluctuations.
The processor may be programmed to automatically perform a protective action for the device when it determines that the start up impedance variation exceeds a start up predetermined threshold for a start up predetermined period of time.
Other features and advantages will be apparent from the following description, including the drawings, and from the claims.
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“IEEE Standard Requirements, Terminology, and Test Code for Shunt Reactors Rated Over 500 kVA”, C57.21-1990; by the Inst. Of Electrical and Electronics Engineers, Inc. and approved Aug. 13, 1990 by IEEE Standards Board, pp. 1-15.
“IEEE Standard for Shunt Power capacitors”, IEEE Std 18-1992; by the Inst. Of Electrical and Electronics Engineers, Inc. and approved Sep. 17, 1992 by IEEE Standards Board, pp. 1-5, 10.
“IEEE Guide for the Protection of Shunt Capacitor Banks”, IEEE C37.99-1990; by the Inst. Of Electrical and Electronics Engineers, Inc. and approved Sep. 28, 1990 by IEEE Standards Board, p. 1.
“IEEE Guide for the Protection of Shunt Reactors”, ANSI/IEEE C37.109-1998; by the Inst. Of Electrical and Electronics Engineers, Inc. and approved Oct. 20, 1988 by IEEE Standards Board, pp. 7 and 11.
“IEEE Guide for the Protection of Shunt Capacitor Banks”, IEEE C37.99-1990; by the Inst. Of Electrical and Electronics Engineers, Inc. and approved Sep. 28, 1990 by IEEE Standards Board, pp. 1-59.
Fish & Richardson PC
McGraw -Edison Company
Sherry Michael J.
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