Communications: electrical – Systems – Selsyn type
Reexamination Certificate
2002-02-15
2004-02-24
Lieu, Julie (Department: 2636)
Communications: electrical
Systems
Selsyn type
C340S315000, C340S315000, C361S602000, C361S603000
Reexamination Certificate
active
06696925
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to electrical metering, and in particular to providing a portable apparatus for metering.
BACKGROUND
The manner in which electrical power is generated and distributed is generally of no concern to a consumer who has simply come to expect that electrical power will always be available. The distribution of electrical power, however, is not a simple task. On a basic level, a power system takes electrical power from a generator, such as a steam or hydraulic turbine, and transports the electrical power over a distribution network to the customers' premises. On a more detailed level, the distribution network is a network of lines, often both overhead and underground, and includes transmission, sub-transmission, and distribution lines. The voltages on the lines are stepped up at the generator, and then progressively stepped down or reduced as the electrical power travels from the transmission lines, to the sub-transmission lines, and then to the distribution lines. The distribution lines then carry the electrical power to the customers' premises, where the electrical power is typically stepped down once more before being transported to the customers' wiring.
In addition to the lines and generators, a power distribution network also includes a number of transformers dispersed throughout the network. In general, a transformer is a device that takes electrical power having one voltage and outputs the same electrical power at a different voltage. A transformer has a set of primary windings or coils which are coupled to a set of secondary windings or coils, with the primary and secondary windings often being immersed in oil. Based on a ratio of the number of primary windings to the number of secondary windings, the voltage can be stepped up to a higher voltage or stepped down to a lower voltage as the electrical power passes from the primary windings to the secondary windings. The transformers are used extensively throughout the network and couple generators to the transmission lines, step down the voltages between the transmission lines and sub-transmission lines, step-down voltages between the sub-transmission lines and the distribution lines, and finally step-down voltages between the distribution lines and the customer premises.
For electrical power to be distributed by local utilities or utilized by large industrial customers, transmission voltages, typically, greater than 25 kV, must be stepped down for introduction into a distribution grid. Typically, this voltage reduction is accomplished by a substation transformer. Occasionally, these transformers must be replaced or repaired. During this time, the defective transformer must be disconnected from the power network so that the necessary work can be safely performed. Frequently, an electrical revenue meter and associated instrument transformers are located in close proximity to the transformer so when the defective transformer is disconnected from the network the electrical revenue meter and associated instrument transformers are necessarily also disconnected. As a result, the electrical revenue meter and associated instrument transformers are unable to measure the amount of power that is being provided through a temporary hook-up, such as through a temporary transformer. Because the electrical revenue meter and associated instrument transformers are inoperable during repairs and replacement of a transformer, the amount of power being delivered through the network is often estimated based on historical usages or other such averages. For example, the amount of power used for the same period last year may form the basis for the estimate of power delivered during the work period. The estimates of power usage are subject to a great degree of inaccuracy, especially in light of inevitable weather and load variations. Inaccurate estimates typically translate into over- or under-recovery of revenue from the sale of electric power. This estimate is often an unsatisfactory measure of the power and may be commercially unacceptable to the interested entities.
Electrical power, as with many other utilities, is being deregulated or has been deregulated in many states. The price for power no longer remains relatively constant year-by-year but instead can fluctuate day-by-day or even hour-by-hour. The fluctuations and volatility in electric power pricing is most evident in the electrical power crisis that affected California in 2001 and continues to plague California as a result of deregulation. California experienced escalating prices for electrical power and demand which exceeded the capacity of the power grid. Consumers took drastic measures to reduce their consumption of electrical power and experienced black-outs, rolling black-outs, and brown-outs. The price of electrical power is therefore no longer a routine fixed cost.
Because of deregulation and also other market conditions, more accurate metering of electrical power is being mandated while work is being performed on the network. As mentioned above, the metering associated with a transformer is so closely associated with the transformer that it effectively cannot be used during the work period. However, temporary metering can be accomplished by bypassing the permanent substation meters and substituting a temporary metering station.
Installing the temporary metering station typically involves a labor-intensive, time-consuming, and therefore, expensive process. Installation usually requires a first work crew, using the auger of a digger derrick or similar earth moving equipment, to dig an approximately 10′ deep hole. Using a distribution crane, a second work crew lifts a distribution power pole and “sets” the pole in the hole, which is then backfilled with dirt. Next, an “instrument cluster” is constructed. For each phase, the instrument cluster includes two instrument transformers. Typically, one of the instrument transformers is a current transformer (CT) for reducing the current, and the other is a potential transformer (PT) for further reducing the voltage to levels that are suitable for measurement using meter instruments. Using a hydraulic tool, the distribution power pole is bored such that the instrument cluster can be mounted thereon. For each phase, connections are made between the secondary side of the substation transformer and each CT and PT. A third crew typically uses a bucket truck to mount the instrument cluster and make the connections. Secondary conductors are buried, slack-spanned, or tension-spanned from the substation transformer to the instrument cluster, and from the instrument cluster to the other substation equipment. Metering conductors are connected at one end to the CT and the PT, and the metering conductors are enclosed in a conduit that is attached down the length of the pole. The other ends of the metering conductors are attached to metering instruments. Only after this work is completed can the temporary substation transformer be energized and the power usage measured by the electrical meter. As can be appreciated by those skilled in the art, the entire process is a custom installation that may take dozens of man-hours to complete, requires the coordination between several work crews, and is a costly endeavor that can easily exceed $10,000.
The work involved in placing a meter is a fraction of the work involved in replacing a defective transformer. As mentioned above, when a defective transformer is being repaired or replaced, a temporary transformer can be brought to the premises to fulfill the functions of the defective transformer while the work is being performed. When the defective transformer is a substation transformer, this temporary transformer is transported to the work site with a tractor-trailer, and is commonly referred to as a “mobile substation.” U.S. Pat. No. 4,367,512 to Fujita, U.S. Pat. No. 4,427,898 to Miyake et al., U.S. Pat. No. 4,562,360 to Fujimoto, and U.S. Pat. No. 6,272,733 to Baker, Jr., all of which are incorporated herein by reference, describe tempor
Kilpatrick & Stockton LLP
Lieu Julie
Lynn-Edward Professional Services, Inc.
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